Stimulus is the change in the environment or environmental factors to to which the organism can respond or react. Theresponse shown by organisms towards or awaya stimulus is called reaction.

The nervous system is a network oforgans and tissues that controlsand co-ordinates all the activitiesof the body with the help of nerves.

Nerves are the communication lines for transmittingimpulses from one part of the body to another.
The difference between afferent and efferentnervesare:

Afferent	Efferent
It transmits impulses from different part of the body to brain or spinal cord.	It transmits impulses from brain or spinal cord to different parts of body.
They are also called sensory nerves.	They are also called motor nerves.

A neuron or nerve cell is a highly specialized cell whichacts as the structural and functional unit of nervous system.
A neuron basically consists of three parts, viz. cell body,axon and dendrites. The cellbody contains large centralnucleus surroundedby cytoplasm. The cytoplasm contains granules and neurofibrilsalong with mitochondria,endoplasmicreticulum, golgi complex, etc. Numerous short,thread like structure arises from the cell body (dendrites)which carries the impulses to nerve cell. One...

a. Cerebrum:
- It governs the mental abilities (thinking, learning).
- It enables sense organs to observe things.
b. Corpus callosum:
-It transmit info from one to other hemisphere ofcerebrum.
c. Cerebellum:
-It maintain equilibrium andmaintains posture.
-It regulates and coordinatesthe contraction of voluntary muscles.
d. Pons varolii:
-It transmit signal to and from cerebrum from and tocerebellum.
-It regulates respiration.
e. Medulla oblongate:
- It controls breathing, blood...

The main part of hind brain are:
a.Cerebellum:
-It maintain equibiriumand controls posture.
-It makes body movt.smooth, steady andcoordinated.
-It regulates and coordinates voluntary muscles.
b.Pons varolii:
-It serves asrelay station carryingsignal fromthe cerebrum to cerebellum.
-It regulatesrespiration.
c.Medulla Oblongata:
-It controls breathing, blood pressure and heart beat.
-It controls contraction and relaxation of blood vessels.

Spinal cord is a long, cylindrical structure thatarises from the medulla oblongata of the brain andpasses through the neural cannelof thevertebralcolumn.
Spinalcord a found inside the boney cage of thevertebral column. It is protected by the spinal meningsand cerebro spinal fluid, which cushions, the chord byacting as a shock absorber. Each vertebra has anopening on its left and right side to let spinal nevepass through. These nerves are extended to the bodyforming the peripheralnervous...

A spontaneous, mechanical and automatic response to a stimulus controlled by the spinal cord without the involvement of the brain is called reflex action.
For eg. Watering of mouth while seeing tasty food.

A reflex arc isa pathwayfollowed by the sensory andmotor nerves in a reflex action.

The function of sensory neurons is tocarry messagefrom receptor organ to the spinal cord.
The function of motor neuron is tocarry messagefrom the spinal cord to the effectororgans.

The system formed by a group of endocrine gland iscalled theendocrinesystem.
The differences are:

Endocrine glands	Exocrine glands
They don't have duct and pour their secretion directly into the bloodstream.	They have duct and secretes their product into duct.
They secrete hormones.	They secrete enzymes.
They are present away from the action.	They are located near the site of action.

Hormone are the chemical messengers which control,co-ordinate and integratethe function of various organs ofthe body.
Its properties are:
-It is produced by endocrineglands.
- They arerequired in small amount and their effect arelong lasting.
-They arechemicallyproteins, steriod and amino acid.
-They act as chemical messengers.
Its functions are:
-It stimulate and control various psychologicaland metabolic.
-They regulate growth and reproduction.
-They synthesize, store and utilize...

Pituitary gland :
Location: Below the mid brain attachedto the lower surface of the brain.
Hormone: (262)
Thyroid gland:
Location: In front of trachea just belowthe larynx.
Hormone: Thyroxine
Pancreas:
Location:Attached to duodenum in theabdominal region.
Hormone: Insulin
Adrenal:
Location: On the top of each kidney.
Hormone: Adrenalin
Testes:
Location: Small muscular pouch calledstratum.
Hormone:Testosterone

The name of hormones produced by the ovaries are:
Oestrogen:
-It controls the devt. of female sex organ.
-It controls the secondary sex characteristicsof female.
Progesterone:
-It plays a role in ovulation.
-It helps in the maintenanceofpregnancy.

Hyposecretion of the thyroxine hormone cause simplegoiters, the thyroid glandenlargesand become visible as a swelling of neck.
Hypersecretion of thyroxine hormone cause roughness onpuffiness of the skin, falling of hairs, obesity, imbalance,digestivedisorders, loss of weight and so on.

We all know, hormones are the chemicals carried to allparts of the body through blood circulation to bringabout the hormonious working of the body. So, hormonesare called chemical messengers.

We all know, the pituitary gland controls and stimulates many activities of the body and the secretion of other endocrine glands too. So, it is called master gland.

We all know, adrenal gland secretes adrenalin hormone at the time of emergency which prepares the body to face an emergency situation. So, it is called emergency gland.

We all know, animals have well developed nervous systemthat coordinateswith the stimulus but plants don't have such system. So, animals can respond quickly to astimulus but plants cannot.

Thegroups of small nerves tissues that is located near the spinal cord made up of grey matter is ganglia.
It is located near the spinal cord. They establish connection between the spinal cord and the brain.

Thenervous system consists of nervous tissuesthatcommunicate between the brain and different parts of thebody is peripheral nervous system.
Its functions are:
-It communicate between brain anddifferent body parts.
-It hold reflex action within it.

The nervoussystem that controls certain muscles andglands while sleeping or waking up is called the autonomicnervous system.
Its types are:
-Sympathetic nervous system.
-Para sympatheticnervous system.

The function of sympathetic nervous system is itincrease the activities of the heart, stomach lungs,intestine, etc.
The function of parasympatheticnervous system is tobring activities of the heart, stomach, Intestine, etc. tonormal condition.

When the adrenal cortex increases in male, enlargement ofthe breasts can be seen.

Masculine characters like horse sound, development ofbeard, etc. are seen when the adrenal cortexincreases inthe adult females.

The function of testosteroneare:
-It controls secondary sex characters of male.
-It controls the growth of facial and pubic hair.
The function of progesterone are:
-It plays an important role in ovulation.
-It helps in the maintenanceof pregnancy.

a. Axon and dentrite.

Axon	Dentrite
The dentrite that grows larger than others are axion.	The thread like structure that arise from the cell body of neuron is called dentrite.
It carries impulses away from the cell body.	It carries impulses to the nerve cell.

b. Cerebrum and cerebellum.

Cerebrum	Cerebellum
It occupies 80% total weight of brain.	It occupies 10% total weight of brain.
It is situated in front of mid brain and corpus callosum.	It is situated below the...

The human heart lies near the middle of the thoriccavity betweentwo lungs. It is the hollow, conical organmade up of cardiacmuscles. It is about the size of afist of the owner.It measures about 12cm in lengthand 9 cm in breadth. The average weight of the heartisabout 300 gm in adults.
The human heart contains four complete chambers. ItE is dividedinto two halves (right and left) by septum.Each half consists of two chamber the upper, smallsized atrium or auricle and lower larger sizedventricle....