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Biology 10th Class Biology

Chapter Number 12 Coordination and Control – 10th Class Biology Notes

Chapter Number 12 Coordination and Control – 10th class biology

Question 1: Explain what can happen if there is no coordination in the activities of organisms.

Coordination: the ability to use different parts of the body together smoothly and efficiently is called coordination.

 

Coordination and Control: The ability of an organism to keep the different body parts in an association; so that the functions of these parts are carried out in a control way is called coordination and control.

Coordination occurs in all living bodies, either unicellular or multicellular, plants or animals.

Explanation of Coordination: The tissues and organs in the bodies of multicellular organisms do not work independently of each other. They work together performing their many tasks as the needs of the whole body. This means that these activities are coordinated. Coordination also enables the organism to respond to happenings in the world around it.

 

Animals have both chemical and nervous coordination while plants have only chemical coordination. Coordination also occurs in unicellular organisms through chemicals. Life activities are controlled and coordinated i.e. body works as one unit, in which its different organs and systems cooperate and work in harmony with each other.

 

Examples of coordination:

 

Example 1: Movement of muscles: One familiar example of coordination is the way in which muscles work together during movement. When a boy runs to catch a ball, he uses hundreds of muscles to move his arms, legs and back. His nervous system uses information from his sense organs and coordinates these muscles. Due to this coordination, the muscles contract in the correct sequence, power and length of time.

 

Example2: Letter writing: If you want to write a letter. You first take a pen and a paper. Then think what to write, in which language to write and then start writing. This all occurs by a process called coordination.

 

Example3: Nail in foot: If a nail comes under your bare foot. You at once lift your foot, sit down somewhere and pull out the nail. This occurs by coordination.

 

Example4: Plant movements: A plant shoot moves in direction of light due to coordination.

 

Example 5: Breathing and heartbeat rates are increased blood pressure is adjusted, and extra heat is removed fast from the body.

 

Question 2: Write a note on types of coordination?

Answer:

 

TYPES OF COORDINATION:

There are two types of coordination in organisms:

  1. Nervous coordination.
  2. Chemical coordination.

 

1)Nervous coordination:Nervous coordination is brought about by neurons. Nervous system receives process and integrates nerve impulses, caused by stimuli received from the external and internal environment.

This type of coordination works on the speed of electricity. This type of coordination occurs in animals only. Usually, nervous coordination produces immediate but short-living responses.

 

2)Chemical coordination:Coordination that occurs through certain chemicals or hormones is called chemical coordination or hormonal coordination. In animals this type of coordination occurs through endocrine glands. Plants have no endocrine glands and each and every cell is capable of producing hormones.

Plant hormones regulate cellular processes in targeted cells and when moved to other locations. They perform various functions there. This type of coordination occurs in all living organisms. Chemical coordination produces slow but long-living responses.

 

Question 3: What are different components of coordinated action?

Answer: Components of a Coordinated Action:

A coordinated action has five components.

 

i- Stimuli: Any change in environment (external and internal), which can provoke a response in organism is called stimulus.

 

Examples of stimuli: Heat, cold, pressure, sound waves, presence of chemicals, microbial infections etc.

 

ii- Receptors OR Sense organs: The organs, tissues or cells which are specifically built to detect particular type of stimuli are called receptors. The receptor transmits signals to sensory nerves.

Examples: Eyes, ears, etc.

 

iii- Coordinators

These are the organs that receive information from receptors and send messages to particular organs for proper action. In nervous coordination, brain and spinal cord are coordinators. They receive information and send messages through neurons in the form of nerve impulses.

On the other hand, in chemical coordination, various endocrine glands play the role of coordinators. They receive information in the form of various chemicals and send messages by secreting particular hormones in blood.

 

iv- Effectors

These are the parts of body which receive messages from coordinators and produce particular responses. In nervous coordination, neurons carry messages from coordinators (brain and spinal cord) to muscles and glands, which act as effectors. In chemical coordination, particular hormones carry messages from coordinators (endocrine glands) to particular target tissues, which act as effectors. For some hormones, nephrons act as effectors. Similarly, bones and liver act as effectors for many hormones.

 

v- Response

The action perform by effector on receiving the message from coordinators is called response. For example, pulling our hand away from something very hot and the movement of the flower of sunflower towards light are responses. Usually, nervous coordination produces immediate but short-living responses while chemical coordination produces slow but long-living responses.

 

Question4: Differentiate between nervous coordination and chemical coordination?

Answer: Difference between nervous coordination and chemical coordination:

Nervous CoordinationChemical Coordination
Formed of a collection of neuron cellsFormed of a set of glands
Electrochemical pulses are the mean of signal transmissionChemicals called hormones are the means of signal transmission
Signal transmission is fast but the functions are not prolongedSignal transmission is slow, but the functions are long lasting
The cells are interconnected and the whole system is continuousThe organs of the whole system are not physically connected yet those are discrete
Use the neurons to transmit the signal.Use the circulatory system to transmit the signal.

 

Question 5: What are the main components of human nervous system?

Answer: HUMAN NERVOUS SYSTEM:

The nervous system in man and in other higher animals is composed of two major components.

1) Central nervous system and peripheral nervous system. Central nervous system comprises of coordinators i.e. brain and spinal cord.

2) Peripheral nervous system consists of nerves that arise from central nervous system and spread in different parts of body. All these components are made of neurons. PNS consists of autonomic and somatic nervous system.

 

Question6: Define neuron and describe the structure of a general neuron.

Answer: Nerve cell or Neuron:

Nerve cell or neuron is the structural and functional unit of the nervous system. The human nervous system consists of billions of neurons plus supporting (neuroglial) cells. Neurons are specialized cells that are able to conduct nerve impulses from receptors to coordinators and from coordinators to effectors. In this way they communicate with each other and with other types of body cells.

 

Structure of neuron: A typical neuron has three main parts.

  1. a) Cell body:The cell body consisting of cytoplasm, nucleus, nucleolus and organelles like Golgi bodies, endoplasmic reticulum and ribosomes.
  2. b) Axon:An axon is a long thread like un-branched part of neuron that arise from cell body. It carries impulses away from cell body.

Schwann cells: Schwann cells are special neuroglial cells located at regular intervals along axons.

Myelin sheath: Axon of large neurons are covered by an insulating fatty layer called myelin sheath. The Schwann cells secrete this fatty material or myelin. The myelinated neurons conduct impulses faster than non-myelinated neurons. Myelin sheath is an insulator so the membrane coated with this sheath does not conduct nerve impulse. In Such impulses are called saltatory(‘jumping’) impulses. This increases the speed of nerve impulse.

Nodes: The area in between myelin sheaths is called node of Ranvier.

Synaptic terminal: Axon may be branched and each branch may give rise to hundreds of of specialized endings called Synaptic terminals.

Synapse: The gap at the site of contact between a synaptic terminal and target cell is called synapse.

Dendrites: These are the small cytoplasmic processes or projections of cell body. It carries impulses towards cell body.

 

Figure: Neurons

 

A nerve impulse is a wave of electrochemical changes that travels along the length of neurons.

 

Unlike ordinary cells, mature neurons never divide. But a protein called nerve-growth-factor promotes the regeneration of broken nerve cells. The degenerating brain cells could be repaired, by using embryonic stem cells.

 

Question 7: What are the different types of neuron?

Answer: Types of neuron: On the basis of their functions, neurons are of three types.

 Sensory neurons: Sensory neurons conduct sensory information (nerve impulse) from receptors towards the CNS. Sensory neurons have one dendrite and one axon.

  1. Inter neurons Or Associative neurons:form brain and spinal cord. They receive information, interpret them and stimulate motor neurons. They have many dendrites and axons.
  2. Motor neurons:Motor neurons carry information from interneurons to muscle or glands (effectors). They have many dendrites but only one axon.
In certain parts of body, the cell bodies of many neurons form a group enveloped by a membrane. This is called ganglion

 

 

Nerve: A nerve means the union of several axons that are enveloped by a covering made of lipid. Based on the property of axons, the nerves are classified into three types.

  1. Sensory nerves contain the axons of sensory neurons only.
  2. Motor nerves contain the axons of motor neurons only.
  3. Mixed nerves contain the axons of both i.e sensory and motor neurons.

 

Question8: Explain the types of nervous system? What are the different devisions of central nervous system? Explain the location and function of these parts of brain; cerebrum, cerebellum,  Pituitary gland, Thallamus, hypothalamus and medulla oblongata?

 

Answer:  Divisions of the Nervous System: The nervous system of man is divided into two main components, The central and peripheral nervous systems.

Central nervous system:

The central nervous system consists of brain and spinal cord.

A- Brain: The main control center of the body present inside the cranium is called brain.

Location of Brain: Brain is a soft organ present inner to cranium.

Meninges: The tough three layered membrane that surround and protect the brain is called meninges.

Meninges protect brain and also provide nutrients and oxygen to brain tissue through their capillaries.

Ventricles: The cavities present in the brain continuous with central canal of spinal cord are called ventricles.

Cerebrospinal fluid (CSF): The fluid filled in meninges, central canal of spinal cord and ventricles is called Cerebrospinal fluid (CSF). It is similar in composition to blood plasma. It bathes neurons of brain and spinal cord.

Weight of Brain: Human brain weighs approximately 1.5 kg.

Colour of Brain: Colour of brain is whitish.

Volume: 1130 cubic centimeter in women and 1260 cm3 in men.

 

The Divisions of Brain:

There are three major regions in the brain of human and other vertebrates. These are forebrain, midbrain and hindbrain. Important parts of each of these regions are described below:

 

Forebrain:

Forebrain is the largest area of brain. It is most highly developed in humans. Fore brain is divided into following main parts.

 

(i) Thalamus: It is oval shaped part of the forebrain and lies just below cerebrum. It serves as a relay centre between various parts of brain and spinal cord. It also receives and modifies sensory impulses (except from nose) before they travel to cerebrum. Thalamus is also involved in pain perception and consciousness (sleep and awakening).

 

(ii) Hypothalamus: Hypothalamus lies above midbrain and just below thalamus. In humans, it is roughly the size of an almond. One of the most important functions of hypothalamus is to link nervous system and endocrine system and thus control hormone production to regulate thirst, hunger, sexual response, flight and fight response and biorhythms. It controls the secretions of pituitary gland. It also controls feelings such as rage, pain, pleasure and sorrow.

 

(iii) Cerebrum: Cerebrum is the largest part of forebrain and form 2/3 of whole brain by weight. Cerebrum is unique to humans. It controls skeletal muscles, thinking, intelligence and emotions. Speech centre is also present here. It is divided into two cerebral hemispheres.

The anterior parts of cerebral hemispheres are called olfactory bulbs which receive impulses from olfactory nerves and create the sensation of smell. The upper layer of cerebral hemispheres i.e. cerebral cortex consists of grey matter.

The grey matter of nervous system consists of cell bodies and non-myelinated axons. Beneath this layer is present the white matter. The white matter of nervous system consists of myelinated axons. Cerebral cortex has a large surface area and is folded in order to fit in skull. It is divided into four lobes.

 

LobeFunction
FrontalControl motor functions,permits conscious control of Skeleton muscles and coordinates movements invovles in speech
ParietalContains sensory areas that receive impulses from skin.
OccipitalReceive and analyzes visual information
TemporalConcerned with hearing and smell

 

  1. iv) Hippocampus:Hippocampus is a small structure that is deep in the cerebrum. It functions for the formation of new memories. People with a damaged hippocampus cannot remember things that occurred after the damage but can remember things that had occurred before damage.
  2. v) Amygdala (plural amygdalae):These are two almond shaped parts of fore brain. It produces sensations of pleasure, punishment, decision making, etc.

Midbrain: Midbrain lies between hindbrain and forebrain and connects the two. It receives sensory information and sends it to the appropriate part of forebrain. Midbrain also controls some auditory reflexes (hearing), eye movements, muscular activities and posture (position of the body).

Hindbrain: It is the last part of the brain that is attached to spinal cord.

Hindbrain consists of three major parts.

(i) Medulla oblongata: Medulla oblongata lies on the top of spinal cord and is the posterior most part of hind brain. It also controls many reflexes such as breathing, heart rate, blood pressure, digestion, sweating, vomiting, coughing, sneezing etc. Information that passes between spinal cord and the rest of brain pass through medulla.

(ii) Cerebellum: Cerebellum is second largest part of the brain and constitute 10% of the total mass of brain. It lies behind medulla. It coordinates muscle movements, helps in correct movement of the body, maintain balance of the body and also controls behaviours.

(iii) Pons: pons is small structure present on top of medulla. It assists medulla in controlling breathing. It act as a bridge between cerebrum, medulla oblongata and cereblum. It also serves as a connection between cerebellum and spinal cord. It regulate respiration, sleep and wakefulness.

 

For your information:

The medulla oblongata, pons, and midbrain connect the rest of brain to spinal cord. They are collectively referred to as brain stem.

 

 

B- Spinal Cord: The large group of nerves present in the back bone that connects nearly all parts of the body to the brain. Spinal cord is approximately 45 cm long in men and 43 cm long in women. It is a tubular bundle of nerves. It starts from brain stem and extends to lower back. Like brain, spinal cord is also covered by meninges. The vertebral column surrounds and protects spinal cord.

 

 

Structure of spinal cord: The outer region of spinal cord is made of white matter (containing myelinated axons). The central region is butterfly shaped that surrounds the central canal. It is made of grey matter (containing neuron cell bodies).

31 pairs of spinal nerves arise along spinal cord. These are “mixed” nerves because each contains axons of both sensory and motor neurons. At the point where a spinal nerve arises from spinal cord, there are two roots of spinal nerve. Both roots unite and form one mixed spinal nerve.

  • The dorsal root contains sensory axons and a ganglion where cell bodies are located.
  • The ventral root contains axons of motor neurons.

Functions of Spinal cords: Spinal cord performs following main functions:

  1. It serves as a link between body parts and brain. Spinal cord transmits nerve impulses from body parts to brain and from brain to body parts.
  2. Spinal cord also acts as a coordinator, responsible for some simple reflexes below neck region.
  3. It reduces burden on the brain.

 

For your information:

Spinal cord is the continuation of medulla oblongata.

Spinal cord is roughly 40cm long and about as wide as your thumb for most of its length.

 

PERIPHERAL NERVOUS SYSTEM: The peripheral nervous system (PNS) is composed of nerves and ganglia. Ganglia are the clusters of neuron cell bodies outside CNS. Nerves arise or lead to brain and spinal cord. So they are named as cranial and spinal nerves.

Nerves arise from the brain are called cranial nerves while nerves arise from the spinal cord are called spinal nerves. Humans have 12 pairs of cranial nerves and 31 pairs of spinal nerves. Some cranial nerves are sensory, some are motor and some are mixed. On the other hand, all spinal nerves are mixed nerves.

The cranial and spinal nerves make two pathways i.e. sensory pathway (conducting impulses from receptors to CNS) and motor pathway (conducting impulses from CNS to effectors). Motor pathway makes two systems.

 

Somatic Nervous System

It is responsible for the conscious and voluntary actions. It includes all of the motor neurons that conduct impulses from CNS to skeletal muscles.

 

Autonomic Nervous System

It is responsible for the activities, which are not under conscious control. It consists of motor neurons that send impulses to cardiac muscles, smooth muscle and glands. Autonomic nervous system comprises of sympathetic system and parasympathetic system. Sympathetic nervous system prepares body to deal with emergency situations.

This is often called the “fight or flight” response. During an emergency situation, this system takes necessary actions. For example; it dilates pupils, accelerates heartbeat, increases breathing rate and inhibits digestion. When stress ends, the parasympathetic nervous system takes action and normalizes all the functions. It causes pupils to contract, promotes digestion, and slows the rate of heartbeat and breathing rate.

Figure : Divisions of the nervous system

Question9: Define reflex action and reflex arc? Trace the pathway of a reflex action or reflex arc?

Answer: Reflex Action: Reflex action is an automatic, quick and involuntary response to stimuli. Involuntary actions are those that are not under conscious control.

The pathway followed by the nerve impulses for producing a reflex action, is called reflex arc.

 

Example: The most common example of reflex action is the withdrawal of hand after touching a hot object. In this reflex action, spinal cord acts as coordinator. Heat stimulates temperature and pain receptors in skin.

A nerve impulse is generated which is carried by sensory neurons to the interneurons of spinal cord. From interneurons, the impulse is passed to motor neurons, which carry it to the muscles of arm. As a result, the muscles contract to withdraw hand. During it, other interneurons transmit nerve impulses up to brain so that the person becomes aware of pain and what happened.

For your information:It doesn’t matter how clever we are we will always pull our hand away from a flame without thinking about it

 

Question10: Define receptor? Write a note on structure and function of human eye?

answer: Receptors in humans: Organs or parts which are specifically built to detect particular type of stimuli are called sense organs or receptors. Main receptors in man are eyes, ears, nose, taste buds, receptors of touch, heat and cold etc.

 

Eyes OR Photoreceptors OR visual receptors: Photoreceptors in man is a pair of eye.

Location: Our eyes are located in small portions of skull known as the orbits or eye sockets.Eyelids: Eyelids wipe eyes and prevent dehydration. They spread tears on eyes, which contains substances for fighting bacterial infections.

Eyelashes: Eyelashes prevent fine particles from entering eye.

Shape of eye: Eyes are oval in shape.

Size: Eye is 1-2 inches in diameter.

Weight: Human eye has average weight of 7-8 gram.

 

Structure of eye: The structure of eye can be divided into three main layers.

1) Sclerotic: It is the whitish outer coat of the eye. At the inner side it appears brown. It consists of dense and flexible connective tissues so that the eye can move easily. It also protects the inner components of eye and maintains its shape. Other parts present in sclera are as follows.

  1. a) Cornea:In the front, sclera forms the transparent dome shaped cornea. Cornea admits light to the interior of eye and bends light rays so that they can be brought to a focus. It also protects the eye from elements that can cause damage.

Figure: Structure of human eye.

2) Choroid: The middle vascular layer is called choroid. It is made of connective tissues, contains blood vessels and gives the inner eye a dark colour. The dark colour prevents disruptive reflections within eye. It provide oxygen and nourishment to the outer layer of retina.

Iris: Behind cornea, choroid bends to form a muscular ring, called iris. It contains the pigments which gives the eye its colour. It regulates the amount of light entering the eye. During extensive light the iris closed the pupil to let in less light, and when there is low light, the iris opens up the pupil to let in more light.

Pupil: The dark hole in the middle of iris is called pupil. It controls the amount of light entering the eye.

Figure: Contraction and dilation of pupil

 

Lense: Behind iris, there is a convex lens, which focuses light on retina. Lens is attached to ciliary muscles of eye via a ring of suspensory ligament. To clearly see an object far away, ciliary muscles are relaxed and lens becomes less convex. When ciliary muscles contract, lens becomes more convex and round.

 

3) Retina OR Screen of eye: The inner layer is sensory and is called as retina. It contains the photosensitive cells called rods and cones and associated neurons. Rods are sensitive to dim light while cones are sensitive to bright light and so distinguish different colours. Retina has two points i.e. fovea and optic disc.

Fovea is a rod-free dip in retina, directly opposite to lens and is densely packed with cone cells. It is largely responsible for colour vision and sharpness. Optic disc is a point on retina where the optic nerve enters retina. There are no rods and cones at this point, that is why it is also referred to as the blind spot.

Aqueous humour and Vitreous humour: The iris divides the cavity of eye into two chambers. The anterior chamber is in front of iris i.e. between cornea and iris; whereas the posterior chamber is between iris and retina. The anterior chamber contains a clear fluid known as aqueous humour while the posterior chamber contains a jelly-like fluid known as vitreous humour. It helps maintain the shape of eye and suspends the delicate lens.

 

How Eye works OR working of the eye: Light from objects enters eye and is refracted when it passes through cornea, aqueous humour, lens and vitreous humour. Lens also focuses light on retina. As a result, the image falls on retina. Rods and cones generate nerve impulses in the optic nerve. These impulses are carried to the bain, which makes the sensation of vision.

 

Rods contain a pigment called rhodopsin. When light falls on rhodopsin, it breaks for generating a nerve impulse. In the absence of light, the breakdown products are again converted into rhodopsin. Body synthesizes rhodopsin from vitamin A and that is why the deficiency of vitamin A causes poor night vision. This problem is called night blindness.

 

Cones also contain a pigment, known as iodopsin. There are three main types of cones and each type has a specific iodopsin. Each type of cones recognizes one of the three primary colours i.e. blue, green and red. If any type of cones is not working well, it becomes difficult to recognize that colour. Such person is also not able to distinguish different colours. This disease is called colour blindness and it is a genetic problem.

 

For your information:

Too much light being let in could damage the retina; too little light makes sight difficult.

 

For your information:

In a human eye there are about 125 lakhs rods and 7 lakhs cones.

 

For your information:

 

Have you seen the eyes of cat and dog shining in the night? The reason for this is the presence of tapetum behind the eye which is a layer capable of reflecting light.

Question11: What are short sight and long sight problems and how these can be treated?

Answer:  Disorders of the Eye

The working of eye is affected by the changes in the shape of eyeball.

 

Myopia (Short sight): The elongation of eyeball results in myopia. Such persons are not able to see distant objects clearly. The image of a distant object is formed in front of retina. This problem can be rectified by using concave lens.

 

Hypermetropia (Long sight): It happens when eyeball shortens. Such persons are not able to see near objects clearly. The image is formed behind retina. Convex lens is used to rectify this problem.

Figure: Myopia and hypermetropia

 

For your information:

 

For a pilot, colour vision is essential so that he/she can recognize aircraft position lights, light-gun signals,airport beacon, approach-slope indicators, and chart symbols, especially at night. A pilot must have the ability to perceive these colours necessary for the safe performance of his/her duties.

Question12: Relate the contribution of Ibn-al-Haitham and Al-Ibn-Isa with knowledge about the structure of eye and treatment of various ophthalmic diseases.

Answer: Contributions of Muslim Scientists:

Ali ibn Isa (950 – 1012) was a famous Arab scientist. He wrote three books on ophthalmology (study of the diseases and surgery of eyes). He described 130 eye diseases and prescribed 143 drugs to treat these diseases.

 

Ibn al-Haytham (965 – 1039), an Arab scientist, made significant contributions to the principles of eye and vision. He is regarded as the father of optics (study of the behaviour of light). His “Book of Optics” correctly explained and proved the modern theory of vision.

He discussed the topics of medicine and eye surgery in his book. He made several improvements to eye surgery and accurately described the process of sight, the structure of eye, image formation in eye and visual system. Ibn al-Haytham also described the principles of pinhole camera.

 

Ibn al-Haytham’s “Book of Optics” has been ranked alongside a book of Isaac Newton. It is one of the most influential books ever written in the history of physics.

 

 

For your information:

 

Owl is not able to see during day time. The reason for this is the deficiency of cones which receive and sense the bright light. But the presence of more rods gives it greater power of vision during night. All animals that search for prey during night have this characteristic.

Question13: How would you describe the structure of the external, middle and inner ear of man?

Answer:  Ear OR Sono-receptor OR sense of hearing:

Hearing is very important. Our ear detect sound and helps us in hearing and also to maintain the balance or equilibrium of our body. Ear has three main parts i.e. external ear, middle ear, and internal ear.

 

A- External Ear: External ear consists of pinna, auditory canal and ear drum (tympanum).

 

i) Pinna:Pinna is the broad external part, made of cartilage and covered with skin. It helps to direct sound waves into auditory canal.

 

ii) Auditory canal:Auditory canal is a tube running from the outer ear to the middle ear. There are special glands in the walls of auditory canal, which produce wax. The wax and the hairs in auditory canal protect ear from small insects, germs and dust.

In additions to this, they help to maintain the temperature and dampness of auditory canal. Auditory canal ends in ear drum. This thin membrane separates external ear from middle ear.

 

iii) Ear drum: The ear drum or tympanic membrane is a thin cone shaped membrane that separates the central ear from middle ear completely. It produces vibrations and transmit sound from the external ear to ossicles.

 

           Figure: Structure of human ear

 

For Your Information:

Stapes is the smallest bone of the human body.

 

Hold the fingers of your palm close to each other and place it behind the pinna. Then concentrate on a particular sound continuously having the same frequency. Remove the palm and concentrate on the same sound again.

 

B- Middle Ear: Middle ear is a chamber or air filled cavity after external ear. It consists of following parts.

i) Auditory ossicles:Ossicle means tiny bone. Ossicles are three small moveable bones in middle ear. These are mallus or hammer bone, incus or anvil bone and stapes or stirrup bone. Malleus is attached with ear drum, then comes incus and finally stapes that is connected with a membrane called oval window.

Oval window separates middle ear from inner ear. The ossicles receives vibration from ear drum and transmits it sound to cochlea.

ii) Eustachian tube:It is a long tube that connects the middle ear into nasal cavity (nasopharynx). This tube regulates the air pressure on both sides of ear drum.

C- Inner Ear OR Membranous labyrinth:

Inner ear consists of three parts i.e. vestibule, semicircular canals and cochlea. Vestibule is present in the centre of inner ear. Three canals called semicircular canals are posterior to the vestibule. The cochlea is made of three ducts and wraps itself into a coiled tube. Sound receptor cells are present within the middle duct of cochlea. It is the real organ of hearing.

For your information:

A thunderstorm is characterized by the presence of lightning and a thunder. The lightning is caused by an electrical charge due to the movement of water droplets or crystals carried by the wind.

The sudden increase in pressure and temperature from lightning produces rapid expansion of the air. This expansion of air produces a sound of thunder. The flash of lightening is followed after some seconds by a roar of thunder. This time difference is due to the fact that sound travels slower than light.

 

Question 14: Write a note on the process of hearing and soundless world?

Answer: Process of Hearing: The pinna of the external ear focuses and directs sound waves into auditory canal. The sound waves strike ear drum and produce vibrations in it. From ear drum, the vibrations strike middle ear and produce further vibrations in malleus, incus and then stapes.

From stapes, the vibrations strike the oval window and then reach the fluid-filled middle duct of cochlea. The fluid of cochlea is moved and receptor cells are stimulated. The receptor cells generate a nerve impulse, which travels to brain and is interpreted as sound.

Soundless world: Deafness is a state in which hearing is not possible. The defect of ear drum, cochlea, middle ear ossicles, or auditory nerve may cause deafness. Infection in Eustachian tube may spread to middle ear too. Ear drum may be damaged by an infection in auditory canal. Excessive noise, strong blows on cheek, pointed objects entering auditory canal and attack from insects may also affect hearing.

 

Question15: Explain the role of ear in the maintenance of balance?

Answer: Ears maintain the Balance of Body: Semicircular canals and vestibule help to maintain the balance of body. Semicircular canals contain sensory nerves which can detect any movement of head. Vestibule can detect any changes in the posture of body. The neurons coming from these two receptors reach cerebellum through the auditory nerve.

 

Question 16: Write a short note on exocrine and endocrine glands? What are the main types of endocrine glands?

Answer: Exocrine Glands: – These are glands with ducts that produce fluid secretions that are delivered by tubes or ducts to the body surface

E.g. pancreas delivers pancreatic juice to intestine for digestion.

ENDOCRINE SYSTEM: The endocrine system refers to the collection of glands of an organism that secrete hormones directly into the circulatory systemto be carried towards distant target organs.

Endocrine glands: Endocrine glands that secrete various chemicals or hormones which reach to various parts in living body and perform dedicated functions.

Hormone: A hormone is a specific organic messenger molecule synthesized and secreted by an endocrine gland. They are produced in ductless glands, poured into the blood and are transported to respective target tissues, where they affect the target cells. Hormones cannot initiate a reaction but can regulate the already present enzymatic and other chemical reactions. They either stimulate or inhibit a function.

Chemical nature of hormones: Most hormones are proteins but some are fatty acids.

Human important endocrine glands: Important endocrine glands in human body are as follows.

1) Pituitary gland.

2) Thyroid gland.

3) Parathyroid gland.

4) Adrenal glands.

5) Pancreas.

6) Gonads.

 

For your information:

Many glands in our body are exocrine. Such glands have ducts for releasing their secretions e.g. digestive glands, skin glands etc.

 

Question17: Outline the major glands of the endocrine system (pituitary, thyroid, pancreas, adrenal, gonads), with name of their hormones and their functions.

Explain how adrenaline may be involved in exercise and emergency conditions.

Answer:    1. Pituitary Gland: Pituitary gland or hypophysis is a very small gland. It is also called master gland, as it controls the functions of other endocrine glands.

Location: It is attached to the hypothalamus of brain.

Shape: It is a pea-shaped or oval gland.

Size: It is about the size of a pea grain.

Weight: It weighs about 0.5 gram (500-600mg).

Structure: Many hormones (trophic hormones) of pituitary gland influence the secretions of other endocrine glands. However some hormones of this gland act directly on various tissues of body. There are two lobes of pituitary gland in mammales i.e. anterior lobe and posterior lobe.

 

Anterior Lobe:It produces many hormones.

i) Somatotrophin (STH):It increase cell division and promotes the growth of body. If the production of this hormone is diminished during growing age, the rate of growth decreases. This condition is called dwarfism. If this hormone is excessively produced during growing age, it leads to gigantism (very tall and overweight). If somatotrophin is excessively produced after growing age, internal organs and body extremities alone grow large. This condition is known as acromegaly. Such persons will have large hands, feet and jawbones.

 

  1. ii) Thyroid stimulating hormone (TSH):It stimulates thyroid gland to secrete its hormones (Thyroxine).

 

iii) Adrenocorticotrophic hormone (ACTH): It controls cortex part of adrenal gland to release adrenal hormone.

  1. iv) Gonadotrophic hormone:These hormones act on the gonads and help in their function and development.

 

  1. Posterior Lobe:The posterior lobe of pituitary gland stores and secretes two hormones i.e. oxytocin and vasopressin (antidiuretic hormone: ADH). These hormones are produced by hypothalamus (a part of brain).

 

Vasopressin OR antidiuretic hormone: This hormone act on renal tubule to reabsorb large amount of water from glomerular filtrate. When we have low amount of water in body fluids, pituitary gland secretes vasopressin and so more reabsorption of water occurs from nephrons into blood. In this way, body retains water and less amount of urine is produced. On the other hand, when body fluids have more than normal water, there is a decline in the secretion of this hormone. If pituitary gland does not secrete this hormone in the required amount, less water is reabsorbed from nephrons and there is excessive loss of water through urine. This condition is known as diabetes insipidus.

 

Oxytocin: The hormone, oxytocin stimulates the contraction of uterus walls in mothers for child birth. Moreover, this hormone is necessary for the ejection of milk from breast. In man its function is unknown.

 

  1. Thyroid gland:

This is the largest endocrine gland in human body. It is present in neck region, below larynx. It consists of two lobes one on each side of the larynx. It produces an iodine containing hormone thyroxin. Iodine is required for the production of this hormone.

Calcitonin: The thyroid gland produces another hormone called calcitonin. It decreases the level of calcium ions in blood and promotes the absorption of calcium from blood into bones.

Functions of thyroxin: Thyroxin increases the breakdown of food (oxidation) and release energy in body. It is also responsible for the growth of body, so secreted more in young age.

Effects of under secretion of thyroxin: Hypothyroidism is caused by the under-production of thyroxin. It is characterized by low energy production in body and slowing down of heart-beat. Under secretion of thyroxin leads to following disorders.

  1. a) Cretinism:In childhood reduce production of thyroxin cause dwarfism or cretinism. The patient has yellowish scaly skin, retarded physical, mental and sexual development.
  2. b) Myxedema:Deficiency of thyroxin in adults cause myxedema. It is characterized by lower metabolic rate, thickness of the skin, brittleness of hairs, nails and mental retardation.
  3. c) Goiter:It is an enlarged form of the thyroid gland. It is caused by deficiency of iodine in human body. Due to deficiency of iodine the thyroid gland is not able to produce thyroxin. The gland when tries to produce the hormone, swells up and the condition is called goiter. This disease is common in women and in hilly areas.

Hyperthyroidism: Hyperthyroidism is caused by over-production of thyroxin. Its symptoms are increase in energy production, increased heart-beat, frequent sweating and shivering of hands. Over production of thyroxin also leads to grave’s disease. It is an immune system disorder. This disorder affects a number of body systems. It affect overall life but rarely life threatening. It is more common in women and before the age of 40.

 

For your information: 1.The stepwise process of metamorphosis in many animals is controlled by hormones. Life activities such as cell division in invertebrates are also regulated by hormones. Hormones also control activities like migration in birds. Hormones have been identified even in unicellular organism.

2. Have you noticed that during summer, the urine output is low? Due to increased sweating, the water level of blood is lowered. As a result, pituitary gland releases more ADH into blood.

 

3. Our government encourages salt refiners to add iodine to salt. It also encourages people to choose this iodized salt.

 

4. Calcitonin and parathormone complemen each other and regulate the level of calcium ions in the blood.

 

5. Tetany is marked by sharp flexion of the wrist and ankle joints, muscle twitching, cramps and convulsions. It is due to decreased blood calcium level which makes the nerves and muscles more excitable.

 

6. When a person experiences fear, anger or anxiety, the rate and intensity of heartbeat increases, blood pressure increases, blood flow to the limbs increases, blood flow to the alimentary canal and skin is reduced. Such changes prepare the body to face any emergency situation.

 

  1. Parathyroid glands:

 

These are four tiny glands situated on the posterior side of thyroid gland in the neck region. Each gland is about the size of a grain of rice (weighs approximately 30 milligrams and is 3-4 millimeters in diameter). They produce a hormone known as parathormone or parathyroid hormone (PTH). It increases the level of calcium ions in blood by:

breaking down the bone (where most of the body’s calcium is stored) and causing calcium release

increasing the body’s ability to absorb calcium from food

increasing the kidney’s ability to hold on to calcium that would otherwise be lost in the urine. When there is increased production of parathormone, more than normal calcium salts are absorbed from the bones and added to blood. Consequently the bones become brittle. If there is deficiency in the production of parathormone, blood calcium level falls. It leads to tetany, which affects the functioning of muscles. (a state marked by severe muscular pain due to abnormal calcium metabolism. In general, tetany involves overly stimulated neuromuscular activity. These overly stimulated nerves cause involuntary muscle cramps and contractions, most often in the hands and feet. But these spasms can extend throughout the body, and even into the larynx, causing breathing problems)

 

  1. Adrenal glands:Glands that are present at the top of kidneys are called adrenal glands.

Numbers and location: Two, each on each kidney.

Weight: Each gland is approximately 12 gram in weight.

Structure: consists of two parts. The adrenal cortex and adrenal cortex.

  1. a) Adrenal cortex:It is the outer reddish part of adrenal gland.
  2. b) Adrenal medulla:It is inner greyish part of adrenal gland.

 

  1. a) Hormones of adrenal cortex:The adrenal cortex secretes many hormones called corticosteroids which maintain the balance of salts and water in blood.

 

b)Hormones of Adrenal medulla: Adrenal medulla secretes two important hormones.

  1. a) Epinephrine or adrenaline:It dilate blood vessels, increase blood flow and heartbeat. It produces in anger and emotions, so the face becomes red due to more blood flow.
  2. b) Nor-adrenaline or non-epinephrine:It constricts blood vessels in certain parts of the body such as gut and face. That is why in fear the face becomes pale or white and a person feel hollow in gut.

 

Adrenal gland hormones are also called emergency, fright, fight or flight hormone because these are produces during stress or emergency.

 

For your information: Adrenal cortex works under the action of ACTH from anterior pituitary. It secretes many steroid hormones. All are collectively called Corticosteroids or corticoids.These hormone are further classified on the basis of their function.

a) Glucocorticoids: Effect carbohydrates, lipids and proteins metabolism.

b) Mineral Corticoids: Keep balance of water and salts in the body. E.g. aldosterone promotes absorption of ion from glomerular filtrate. (Cl, K+, Na+ ions.

c) Sex hormones: It also secrete some amount of testerone (Androgen).

 

  1. Pancreas:The large leaf like gland behind the stomach which secretes digestive enzymes into the duodenum.

Size: Approximately 6 inches long.

Shape: Leaf like long tube.

Exocrine activities of pancreas: Exocrine portion of pancreas is located near the liver. It secretes pancreatic or digestive juices.

Endocrine activities: The endocrine function is performed by islets of Langerhans. Alpha (α) islets of Langerhans (small cells) produce glucagon while Beta (β) islets of Langerhans produce insulin.

Functions of insulin: Insulin influences the liver to take excess glucose from blood and so the blood glucose concentration falls.

Functions of glucagon: Glucagon influences the liver to release glucose in blood and so the blood glucose concentration rises.

Hypo-secretion or lower secretion of insulin: If a person’s pancreas produce less than normal quantity of insulin, the blood glucose concentration rises and we say that the person has diabetes mellitus. Persons with diabetes have loss of body weight, weakening of muscles and tiredness. The disease can be controlled by insulin administration. Formerly, insulin extracted from animals was used for this purpose. But now human insulin produced from bacteria through genetic engineering is available.

Hyper-secretion or over secretion of insulin: Over secretion of insulin lower blood glucose level and lead to a disease called hypoglycemia. It affects the neurons.

 

For your information: The blood glucose concentration is maintained at the rate of 80 to 120 mg per 100 ml of blood.

 

 

Blood Glucose Concentration (BGC) Test:

The amount of glucose in blood is measured by this test. It is used to diagnose diabetes. Blood glucose may be measured on a fasting basis (collected after an 8 to 10 hour fast),randomly (anytime) and after a meal.The results of some BGC tests are given here.

Blood Glucose

After 8-10 hours Fast

BGCDiagnosis
From 70 to 90 mg/100mlNormal
From 100 to 125 mg/100mlPre-diabetic
126mg/100ml and aboveDiabetic
Blood Glucose

2 hours After a 75gram Glucose Drink

BGCDiagnosis
Less than 150mg/100mlNormal
From 140 to 200mg/100mlPre-diabetic
Over 200mg/100mlDiabetic

 

 

  1. Gonads:The reproductive organs of organisms are called gonads.

Testes (Singular: testis) and ovaries are the male and female reproductive organs i.e. gonads. In addition to producing gametes, gonads also secrete hormones, called sex hormones.

Testicular hormones: Cells of the testes produce testosterone.

Functions of testosterone: i) Before puberty this hormone act to slowly grow the male genitalia.

  1. ii) At puberty it brings about development of secondary sexual characters like growth of hairs on face and other places, thickening of voice, etc.

 

Ovarian hormones: Ovaries secrete estrogen and progesterone.

Functions of estrogen: i) it brings about secondary sexual characters in females like mammary glands enlargement or development of breast, hair growth in specific places, high pitch of voice, etc.

  1. ii) Thickening of the uterine wall.

iii) Responsible for ovulation or release of ova.

  1. iv) Onset of menstrual cycle.
  2. v) In case of fertilization maintains pregnancy.

 

Functions of progesterone: i) It prepare the female body for the state of pregnancy.

  1. ii) Further thickening of the uterine wall.

iii) Suppresses ovulation.

 

Question18: What is feed back mechanism? Describe negative feedback with reference to insulin and glucagon?

 

Feedback Mechanisms: Feedback mechanism means the regulation of a process by the output of the same process. “OR” The response within a system that influences the continued activity or productivity of that reaction. “OR” A type of interaction in which a controlling mechanism is itself controlled by the products of the reaction.

Endocrine glands do not secrete their hormones at a constant rate. The rate varies with the needs of the body. Like many other functions in body, the secretion of hormones is also regulated by feedback mechanisms.

 

Types of feedback mechanism: Feedback mechanisms are of two types.

  1. I) Negative feed backs.
  2. II) Positive feed backs.

 

  1. I) Negative feedback mechanism:Negative feedback mechanism happens when a system needs to slow down or completely stop a process that is happening.

In negative feedback, the output of a process decreases or inhibits the process. This mechanism works to return a condition towards its normal value.

 

Example 1: when the blood glucose concentration rises, pancreas secretes insulin. It decreases the blood glucose concentration. Decline in the blood glucose concentration to a normal set-point inhibits the secretion of insulin. Similarly, when blood glucose concentration drops below normal, pancreas secretes glucagon. It raises the blood glucose concentration. In this case, rise in the blood glucose concentration to a normal set-point inhibits the secretion of glucagon. In other words, the blood glucose concentration (output) controls the process i.e. the secretion of insulin and glucagon.

“OR”

When glucose level in the blood increases β islets of Langerhans secrete insulin that change glucose to glycogen, so reduce the level of glucose.

Example 2: When temperature of the body rises, sweating occurs that reduce the body temperature.

 

 

  1. II) Positive feedback mechanism:A positive feedback mechanism happens when a system needs to stimulate a process that is happening. In positive feedback, the changes resulting from a process increase the rate of process. Positive feedback is a cyclic process that can continue to amplify your body’s response to a stimulus until a negative feedback response takes over.

Example 1: suckling action of an infant stimulates the production of a hormone in mother. This hormone works for the production of milk. More suckling leads to more hormones, which in turn leads to more milk production.

Example 2: During childbirth pressure of the fetus on the uterine walls stimulates production and secretion of the hormone oxytocin. Oxytocin causes muscles in the walls to contract, which increases pressure on the fetus and the baby expels from the mother out.

Example 3: Stomach secretes a compound called pepsinogen. It is an inactive enzyme. As body convert some of pepsinogen to pepsin. It stimulates to convert other pepsinogen to pepsin. Due to this large amount of pepsin is formed in the stomach.

Figure : Endocrine glands in human body

 

Question19: Enlist the important symptoms and treatments of paralysis and epilepsy?

Answer: Disorders of nervous system: nervous system disorders are certain disturbances or diseases in nervous system.

Types of nervous disorders: Nervous disorders are broadly categorized into two main types.

1) Vascular disorders: Vascular disorders are those disorders that occurs due to any disturbance in the blood supply to nervous system e.g. paralysis.

2) Functional disorders: Functional disorders are those that occur due to disturbance in nerve impulse generation and transmission. e.g. epilepsy.

 

Paralysis: (From Latin paraluesis. Para means beside and luesis means loosen).

Paralysis is the complete loss of function by one or more muscle groups due to abnormal function of a part of brain. It is vascular disease of the brain in which blood supply to a part of brain reduce or stop.

 

Causes: It is most often caused by damage to the central nervous system (brain or spinal cord). The damage may be due to stroke (rupture in a blood vessel of brain or spinal cord), blood clotting in these blood vessels, or poison produced by polio viruses.

 

Affects: The part of body controlled by affected part of brain do not function properly or stops functioning.

 

Treatment: During temporary paralysis treatment is possible. And doctors give medicines that dissolves the clot. The normal functioning may be restored by physiotherapy. Physiotheraphy is the treatment of any disease by physical means. By exercise, etc.

 

Epilepsy (Fits or Margi):

Epilepsy is a nervous disorder in which there is abnormal and excessive discharge of nerve impulses from grey matter of brain.

 

Affects: It causes unprovoked seizures in patient. A seizure of epilepsy is a temporary abnormal state of brain marked by convulsions.

 

Causes:

  • In younger people, epilepsy may be due to genetic or developmental causes.
  • In people over age 40 years, brain tumors are more likely to cause epilepsy.
  • Head trauma (injury) and central nervous system infections may cause epilepsy at any age.
  • Low oxygen during birth.
  • Use of alcohols.

Symptoms: Epilepsy patient first cries and falls down unconscious. His body becomes rigid and stiff. Patients hands are clenched and throws legs and arms and frequently bites his tongue. It is usually started before the age of 30.

Treatment: There is no known cure of epilepsy but medicines can control seizures. Patients of epilepsy have to take medicines daily for the treatment as well as prevention of seizures. These are termed “anticonvulsant” or “antiepileptic” drugs. For example: Dilantin.

During a seizure attack, objects should never be placed in a patient’s mouth as it can result in serious injury. It is possible that the patient will bite his/her own tongue.

 

For your information: The knowledge of the composition and functioning of nervous system has helped man in the diagnosis and treatment of nervous disorders including paralysis and epilepsy. Man has discovered the areas of brain that receive information from different sense organs and the areas that send messages to different effectors. Such knowledge helps a lot in identifying the malfunctioning areas of brain.

UNDERSTANDING THE CONCEPT

  1. Explain what can happen if there is no coordination in the activities of organisms.

Answer: Please see answer of question no.1

 

  1. Explain the location and function of these parts of brain; cerebrum, cerebellum, pituitary gland, Thallamus, hypothalamus and medulla oblongata.

Answer: Cerebrum, cerebellum, pituitary gland, thalamus, hypothalamus and medulla oblongata related to question no.8 while Pituitary gland related to question no.17.

 

  1. Define neuron and describe the structure of a general neuron.

Answer: Please see answer of question no.6.

 

  1. Describe the structure of human eye.

Answer: Please see answer of question no.10.

 

  1. How would you describe the structure of the external, middle and inner ear of man?

Answer: Please see answer of question no.13.

 

  1. What are short sight and long sight problems and how these can be treated?

Answer: Please see answer of question no.11.

 

  1. Explain the role of ear in the maintenance of balance.

Answer: Please see answer of question no.15.

 

  1. Relate the contribution of Ibn-al-Haitham and Al-Ibn-Isa with knowledge about the structure of eye and treatment of various ophthalmic diseases.

Answer: Please see answer of question no.12.

 

  1. Outline the major glands of the endocrine system (pituitary, thyroid, pancreas, adrenal, gonads), with name of their hormones and their functions.

Answer: Related to question no.17.

 

  1. Describe negative feedback with reference to insulin and glucagon.

Answer: Please see answer of question no.18.

 

  1. Explain how adrenaline may be involved in exercise and emergency conditions.

Answer: Related to question no.17.

 

  1. Enlist the important symptoms and treatments of paralysis and epilepsy.

Answer: Please see answer of question no.19.

 

SHORT QUESTIONS

  1. Identify the two types of coordination in living organisms.

Answer: TYPES OF COORDINATION:

There are two types of coordination in organisms:

  1. Nervous coordination:Nervous coordination is brought about by neurons.
  2. Chemical coordination:Coordination that occurs through certain chemicals or hormones is called chemical coordination or hormonal coordination.

 

  1. Differentiate between the modes of nervous and chemical coordinations.

Answer:

1) Nervous coordination is brought about by neurons while chemical coordination is brought about by hormones.

2) Nervous coordination works on the speed of electricity while chemical coordination works on the speed of blood.

3) Nervous coordination produces immediate but short-living responses while chemical coordination produces slow but long living response.

 

  1. What are the main components of coordination?

Answer:

Components of a Coordinated Action:

A coordinated action has five components.

Chapter Number 12 Coordination and Control

 

  1. Define reflex action and reflex arc.

Answer: Reflex Action: Reflex action is an automatic, quick and involuntary response to stimuli. Involuntary actions are those that are not under conscious control.

The pathway followed by the nerve impulses for producing a reflex action, is called reflex arc.

 

Example: The most common example of reflex action is the withdrawal of hand after touching a hot object. In this reflex action, spinal cord acts as coordinator. Heat stimulates temperature and pain receptors in skin. A nerve impulse is generated which is carried by sensory neurons to the interneurons of spinal cord. From interneurons, the impulse is passed to motor neurons, which carry it to the muscles of arm. As a result, the muscles contract to withdraw hand. During it, other interneurons transmit nerve impulses up to brain so that the person becomes aware of pain and what happened.

 

  1. Trace the path of a nerve impulse in case of a reflex action.

Answer:  Reflex Action: Reflex action is an automatic, quick and involuntary response to stimuli. Involuntary actions are those that are not under conscious control.

The pathway followed by the nerve impulses for producing a reflex action, is called reflex arc.

 

Example:The most common example of reflex action is the withdrawal of hand after touching a hot object. In this reflex action, spinal cord acts as coordinator. Heat stimulates temperature and pain receptors in skin. A nerve impulse is generated which is carried by sensory neurons to the interneurons of spinal cord. From interneurons, the impulse is passed to motor neurons, which carry it to the muscles of arm. As a result, the muscles contract to withdraw hand. During it, other interneurons transmit nerve impulses up to brain so that the person becomes aware of pain and what happened.

 

  1. Describe the pupil reflex in dim and bright light.

Answer: A small round hole in the centre of iris is called pupil. It controls the amount of light entering the eye. After striking the cornea, light passes through the pupil. The muscles of iris adjust the size of pupil. During extensive light the iris closed the pupil to let in less light, and when there is low light, the iris opens up the pupil to let in more light.

  1. How would you associate the role of vitamin A with vision and effects of its deficiency on retina?

Answer: Rods contain a pigment called rhodopsin. When light falls on rhodopsin, it breaks for generating a nerve impulse. In the absence of light, the breakdown products are again converted into rhodopsin. Body synthesizes rhodopsin from vitamin A and that is why the deficiency of vitamin A causes poor night vision. This problem is called night blindness.

  1. Define the terms; hormone and endocrine system.

Answer: ENDOCRINE SYSTEM: The endocrine system refers to the collection of glands of an organism that secrete hormones directly into the circulatory system to be carried towards distant target organs.

Hormone: A hormone is a specific organic messenger molecule synthesized and secreted by an endocrine gland. They are produced in ductless glands, poured into the blood and are transported to respective target tissues, where they affect the target cells. Hormones cannot initiate a reaction but can regulate the already present enzymatic and other chemical reactions. They either stimulate or inhibit a function.

The terms to know:

 

Acromegaly: Abnormal growth due to excessive production of growth hormone after growing age; the internal organs and body extremities alone grow large and affected persons have large hands, feet and jawbones.

Antidiuretic hormone: The hormone of the posterior pituitary; promotes the reabsorption of water in renal tubules.

Aqueous humour: The fluid present in the anterior chamber of the eye i.e. between the cornea and the iris.

Axon: A long, thin fibre that carries nerve impulse away from the cell body of a neuron.

Calcitonin: A thyroid gland hormone that decreases the level of calcium ion in blood and promotes the absorption of calcium from blood into bones.

Cell body:  The part of the nerve cell that contains nucleus and other important organelles.

Cerebellum: The part of the hindbrain that controls muscle movements is called cerebellum.

Cerebral hemisphere: The divisions of the cerebrum of the brain.

Cerebrospinal fluid: The fluid in the ventricles of the brain and in the central canal of the spinal cord.

Cerebrum: The largest part of the forebrain; controls many sensory and motor functions.

Choroid: The middle vascular layer is called choroid. It is made of connective tissues, contains blood vessels and gives the inner eye a dark colour. The dark colour prevents disruptive reflections within eye. It provide oxygen and nourishment to the outer layer of retina.

Cochlea: The part of the inner ear; consists of three ducts wrapped in the form of a coiled tube; contains sound receptors and is the real organ of hearing.

Colour blindness: Genetic disorders in which person fails to recognize the basic colors.

 

Cones: The photosensitive cells in the retina of the eye; sensitive to bright light and so distinguish different colours.

Cornea: The transparent part of sclera that forms in the front of the eye through which light enters.

Cranial nerve: Nerves that arise from or lead to the brain.

Dendrite: Short, branched projections of neuron’s cell body; transmits nerve impulse towards cell body.

Diabetes mellitus: More than normal level of glucose in blood; a condition caused by insufficient concentration of insulin in blood.

Dwarfism: Less than normal body growth; a condition caused when growth hormone is insufficient during the growing age.

Ear drum: Tympanic membrane; A membrane stretched across the inner end of the auditory canal of the ear.

Effector: The parts of the coordination system that respond when stimulated by nerve impulses or hormones

Endocrine gland: A ductless gland; produces and secretes hormones.

Epilepsy: A nervous disorder characterized by recurrent unprovoked seizures (convulsions).

Epinephrine or adrenaline: An adrenal gland hormone that dilate blood vessels, increase blood flow and heartbeat. It produces in anger and emotions, so the face becomes red due to more blood flow.

Estrogen: A hormone secreted by the ovaries; promotes development of female secondary sex characteristics and regulates the reproductive cycle.

Eustachian tube: The tube between middle ear and the nasal cavity that equalizes the pressure on both sides of the ear drum.

Exocrine gland: A gland that discharges its secretion into a duct.

Ganglion: The aggregation of the cell bodies of neurons.

Grey matter: The nervous tissue containing cell bodies and non-myelinated processes of the neurons.

Hormone: A hormone is a specific organic messenger molecule synthesized and secreted by an endocrine gland. They are produced in ductless glands, poured into the blood and are transported to respective target tissues, where they affect the target cells. Hormones cannot initiate a reaction but can regulate the already present enzymatic and other chemical reactions. They either stimulate or inhibit a function.

Hypermetropia: The condition in which a person is not able to see near objects clearly; happens when the eyeball shortens and image is formed behind the retina.

Hypothalamus: The part of the forebrain below the thalamus; controls body temperature, blood pressure and emotion.

Insulin: The hormone produced by the Islets of Langerhans; lowers the blood glucose level.

Interneuron: The neurons present in the brain and spinal cord.

Iodopsin: A pigment present in the cones of the retina.

Iris: A muscular ring formed by the bending of the choroid behind the cornea of the eye.

Islets of langerhans: Groups of endocrine cells present in pancreas;secrete hormones insulin and glucagon.

Medulla ablongata: Part of the hindbrain; on the top of the spinal cord; controls breathing, heart rate, blood pressure and many reflexes.

Meninges: The tough three layered membrane that surround and protect the brain is called meninges.

Meninges protect brain and also provide nutrients and oxygen to brain tissue through their capillaries.

Mixed nerve: The nerves containing axons of both the sensory and motor neurons.

Motor nerve: The nerves that contains the axons of motor neurons only.

Myelin sheath: The insulating sheath around the axons of some neurons.

Myopia: The elongation of eyeball results in myopia. Such persons are not able to see distant objects clearly. The image of a distant object is formed in front of retina. This problem can be rectified by using concave lens.

Nerve: The union of several axons that are enveloped by a covering made of lipid.

Nerve impulse: A nerve impulse is a wave of electrochemical changes that travels along the length of neurons.

Neuron or Nerve cell; the unit of the nervous system; able to conduct nerve impulses.

Nodes of Ranvier: The non-myelinated points between the areas of myelin on the axons of neurons.

Optic disc or Blind spot: A point on the retina of the eye where the optic nerve enters the retina; no photosensitive cells exist at this point.

Oxytocin: The hormone secreted by the posterior pituitary; stimulates the contraction of uterus walls in females for child birth; necessary for ejection of milk from the breasts.

 

Paralysis: Complete loss of function by one or more muscle groups due to damage in the nervous system.

Parathormone: Hormone of the parathyroid glands; increases the level of calcium ions in the blood.

Parathyroid gland: These are four tiny glands situated on the posterior side of thyroid gland in the neck region.

Pituitary: A very small endocrine gland attached to the hypothalamus of the brain. Also called hypophysis or master gland.

Pons: Part of the hindbrain; present on top of the medulla; assists the medulla in controlling breathing and serves as a connection between the cerebellum and the spinal cord.

 

Progesterone: A hormone secreted by the ovaries that maintains the uterus during pregnancy.

Pupil: A small round hole in the centre of iris is called pupil. It controls the amount of light entering the eye.

Receptor: The organs, tissues or cells which detect particular type of stimuli.

Reflex arc: The nerve pathway over which the nerve impulses travel in a reflex action.

Retina: The innermost and the light sensitive layer in the eye is called retina.

Retinine: A derivative of the vitamin A formed by the action of light on rhodopsin.

Rhodopsin: A pigment present in the rods of the retina.

Rods: The photosensitive cells present in the retina of the eye; sensitive to dim light.

Schwann cells: The supporting cells around neurons; form the myelin sheath.

Sclera: The tough, white outer layer of the eye.

Semicircular canals: The three bony canals present posterior to the vestibule in the inner ear.

Sensory nerve: The nerves which contain only the axons of sensory neurons.

Somatotrophin: Growth hormone: A hormone of the anterior pituitary;promotes the growth of the body.

Spinal nerve: The nerves which arise from the spinal cord.

Suspensory ligament: The ring that attaches the lens of the eye to the ciliary muscles.

 

Testosterone: The male sex hormone secreted by testis; stimulates the development of male reproductive system and the male secondary sex characteristics.

Thalamus: The part of the forebrain; serves as a relay centre between various parts of the brain and spinal cord.

Thyroid gland: The endocrine gland located in front of the trachea; secretes hormones thyroxin and calcitonin.

Thyroid-stimulating hormone: A hormone of the anterior lobe of the pituitary gland that stimulates thyroid gland to secrete its hormones (Thyroxine).

Thyroxin: Iodine containing hormone secretes by thyroid gland is called thyroxine.

Tympanum or Ear drum: The ear drum or tympanic membrane is a thin cone shaped membrane that separates the central ear from middle ear completely. It produces vibrations and transmits sound from the external ear to ossicles.

Vasopressin OR Antidiuretic hormone: The hormones secreted by the posterior pituitary; responsible for the reabsorption of water from renal tubules of the nephron.

Vestiblue: Part of the inner ear; helps to maintain balance of the body.

Vitreous humour: The fluid present in the posterior chamber of the eye i.e. between the iris and retina.

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