Ability of living organisms to react to the change in environment. It is highly developed in higher animals. Plant also posses sensitivity but not as much developed as higher animals.

Any factor which cause protoplasm to react.

Regulation of various activities of the body in organized manner is called coordination.

Coordination in multicellular organisms is brought by following system.

1. Nervous system.
2. Endocrine system.

Coordination is brought about by following steps.

1. Passage of the information in the form of stimuli to coordinator.
2. Interpreting the information in coordinator and coveying the orders to effectors.
3. Responding of effector in accordance with the message received from coordinator.

In all multicellular animals main types of structures related to stimuli and responses are present. These are receptors, neurons and effectors.

Central nervous system of man consist of brain and spinal cord which contain million of special cells called neurons.

Neuron consist of following parts.

It is rounded structure contain nucleus and other organelles.

Many fine branches are arised from cell body called dendrites.

At the other end long fiber is arised from the cell body called axon.

Neurons are specialized for transmission of stimuli in the form of nerve impulse.

Following are important types of neurons.

Neurons which carry impulses from receptors to CNS.

Neurons which carry impulses from CNS to effectors. The peripheral effectors are muslces and glands. Muscles respond by contracting and glands by producing hormones.

Inter Neuron found in CNS, connect sensory with motor neurons.

It is an automatic involuntary response mediated through the central nervous system.

Withdrawal of hand immediately when touched to hot object.

Blinking of eyes on exposure to strong light.

It is circuit of neurons through which reflex action takes place. Most of the reflex arc involve only three neurons. One of them is sensory which takes stimuli to spinal cord. Second is in CNS called inter neuron and third is motor neuron which bring message to effector.

Action which is under the control of our will is caled voluntary action. E.g., movement of limbs.

Action which is not under the control of our will is called involuntary action. E.g., contraction of cardiac muscles.

Human brain consist of following parts.

1. Fore brain
2. Mid brain
3. Hind brain

Fore brain consist of cerebrum and aienciphalon. Cerebrum consist of two cerebral hemispheres.

It is high control center of brain. Information is stored here. This part control all parts of nervous system.

It is located under the cerebral hemispheres.

It is associated with sense of sight and hearing.

Hind brain consist of cerebellum, pons and medulla oblongata.

It controls the body balance and movement.

It controls heart beat, respiration and circulation.

Transform impulses from medulla to cerebellum.

Spinal cord is with vertebral column and continuous with medulla oblongata of brain. Spinal concerned with:

1. Reflex functions of parts below head level.
2. Conduction of sensation received from trunk and limbs to the brain.
3. Receiving messages command from the brain.

Morphine, aspirin, sleeping pills and alcohol are used in medicine to help people in getting control over pain or to feel relaxed. Frequent use (abuse) of these drugs result in certain disorders of nervous system.

Heroin, cocaine and marijuana are drugs of addiction which are being used by people to get pleasure. Many disorder of nervous system results from the use of these drugs.

There are five types of senses in man.

1. Sense of touch
2. Sense of smell
3. Sense of taste
4. Sense of sight
5. Sense of hearing

Receptors for touch are simple nerve endings which are present in through out the skin. They are specialized to detect temperature, texture, pressure etc.

Many olfactory cells are found in nasal mincora of olfactory chamber. They are specified to receive smell stimuli.

Receptors for taste are groups of hair cells situated inside the flask shaped taste buds on the tongue. Their base is in contact with nerve fibers.

Human eye consist of following three layers.

1. Fibrous coat
2. Choroid
3. Retina

It is outermost coat. It consist of

Posterior 2/3 opaque portion called sclera.

It is exterior 1/3 of fibrous coat. It is transparent portion.

It is vescular pigmented coat. It contains many blood vessels which provide nutrition to the cells of the eye.

It is the innermost layer of the eye. This is nervous coat of the eye. This layer contain rods and cones which are photoreceptors. Rods are for night vision and cones are responsible for colour vision. Rods contain rhodopsia and cones contain pigment called liopsin.

It is transparent fluid in front of lens.

It is transparent biconvex lens which converge the rays of light at retina.

It is viscous jelly like substance present behind the lens.

It project from retina.

It is an opening in the center of radial fibers of iris.

Rays of light pass from cornea to lens. Here these rays are converged and focussed at fovea centralis (point on retina where sharp image is obtained). Light stimulus is received by photoreceptors and its message is send to brain by optic nerve.

Human ear consist of three portions

1. Outer ear
2. Middle ear
3. Inner ear

It consist of pinna, auditory canal. The outer and middle ear are separated by tympanic membrane or ear drum.

It consist of bony ossicles mellius, incus and stapes. These ossicles connected with tympanic membrane (ear drum) at the one end and at another end with inner ear.

It consist of semicircular canals and cochlea. Receptors for hearing are located in cochlea and receptors of balance are located in semicircular canal.

When sound waves strike the pinna they are transferred to tympanic membrane through auditory canal. From tympanic membrane these waves are brought to inner ear through bony ossicles. When these waves are reached to cochlea receptors for hearing convert this stimulus into nerve impulse and send to the brain.

These are ductless glands which pour their secretion into the blood. Hormones are specific secretions of the endocrine glands. Following are important endocrine glands of man.

1. Pituitary gland
2. Thyroid gland
3. Parathyroid gland
4. Adrenal gland
5. Ovaries and testes
6. Pancreas

It is the master of all endocrine glands. It is located in head. It consist of two lobes. Anterior lobe of pituitary secretes seven hormones and posterior lobe secretes two hormones.

It is located in neck. It consist of right and left lobes connected by isthamus. It produces a hormone called thyroxin which control general metabolism of the body.

There are two pairs of pea grain size parathyroid glands embedded in thyroid. Hormone of parathyroid gland control calcium and phosphate metabolism.

It measure about 7 inches in length. Pancreas produces 2 hormones.

It decrease blood sugar level by facilitating entry of glucose into the cell.

It increases the blood sugar level by inducing glycogenolysis.

There is a pair of adrenal gland, each located above the kidney. There are two regions of adrenal gland.

It produces cortisones and aldosterone.

It produces adrenaline and non adrenaline.

It produces androgens. In this group important is testosterone which maintain male reproductive characters.

Two important hormones are produced by ovary.

1. Oestrogen
2. Progestron

Increase in secretion of thyroxin result in hyperactivity of person. Deficiency of iodine result in abnormal development of thyroid called goiter.

Insulin and glucogen maintain blood sugar level. Abnormalities of pancreas result in hyperglycemia or hypoglycemia.

Abnormalities in testes and ovary hormone result in abnormal reproductive and sexual characters.

Top