A living being does not live in isolation. It has to constantly interact with its external environment and has to respond properly for its survival. The responses which a living being makes in relation to external stimuli are controlled and coordinated by a system; especially in complex animals.

The working together of the various organs in a systematic manner so as to produce a proper response to the STIMULUS, is called coordination.

Stimulus- The changes in the environment to which the organism respond and react is called stimulus. Lion responds to the bite given by

his cub

A system made up of nerve cells is called NERVOUS SYSTEM. It consists brain, spinal cord, nerves and sense organs.

Receptor- A receptor is cell in a sense organ which is sensitive to a particular type of stimulus.

Effector- an effector is a part of the body which can respond to a stimulus according to the instructions sent from the nervous system(brain & spinal cord).

Neuron is the structural and functional unit of nervous system. They carry electrical messages called IMPULSES throughout the body.

There are 3 types of neurons-

Sensory NeuronMotor NeuronRelay Neuron(Inter

Neuron)

Synapse

Synapse

Synapse

Sensory

Neuron

Relay neuron

Motor Neuron

Muscle Contract

s

Reflex Action & Reflex ArcReflex action is an

automatic involuntary response to stimulus. It is the simplest form of response in the nervous system. Example- Yawning, Sneezing

Reflex arc is the pathway taken by nerve impulse in a reflex action.

BRAIN Cerebrum Voluntary or conscious

activities of the body-learning, judgment

Cerebellum Coordinates and balances the

actions of the muscles

Medulla Oblongata (Brain Stem)

Controls involuntary actions like blood pressure, heart rate, breathing, and swallowing

Spinal Cord The main communications link

between the brain and the rest of the body

ENDOCRINE SYSTEMA group of

endocrine glands which produces various hormones is called ENDOCRINE SYSTEM.

The HORMONES produced by endocrine glands act as messengers between the nervous system and the organs of our body.

Control and coordination are the functions of the nervous system and hormones in our body.

The responses of the nervous system can be classified as reflex action, voluntary action & involuntary action.

The nervous system uses electrical impulses to transmit messages.

The nervous system gets information from our sense organs and acts through our muscles.

A “FEEDBACK MECHANISM” regulates the action of hormones.