Living organisms respond to various stimuli like heat, light, cold, touch, pressure etc.

Example: Withdrawal of hand on touching a hot object.

Control and Coordination in Animals

It is brought about in all animals with the help of two main systems

(a) Nervous System

(b) Endocrine System

Nervous System: Consists of Brain, Spinal network and a huge network of nerves.


  • To receive the information from the environment through the sense organ.
  • Transportation of information to the brain through the spinal cord and nerves.
  • After analyzing the information, to act accordingly through muscles and glands.

Stimulus: Any change in the environment to which the organisms respond is called stimulus. E.g., touching a hot plate.

Response: The reaction of our body to a stimulus. E.g. withdrawal of our hand on touching a hot plate.

Coordination: The working together of various organs of the body of an organism in a proper manner to produce an appropriate reaction to a stimulus is called coordination.

Receptors: Are specialized tips of some nerve cells that detect the information from the environment.

Receptors are sense Organs

Neuron: Neurons are specialized cells combined to form nerves of the nervous system. As nerves are emerged from brain and spinal cord and branch out to almost all parts of the body so neuron is also called the unit of the nervous system.

A typical neuron consists of cell body, axon, and dendrites. The cell body contains the nucleus. Dendrites detect the information from the environment. This information is picked up by the dendritic tips and sets off the electrical impulse which travels from dendrite to the cell body and then to the axon.

Structure of the Neuron

Parts of neuron

The primary components of the neuron are the cell body,

the axon – a long slender projection that conducts electrical impulses away from the cell body, dendrites – tree-like structures that receive messages from other neurons, and

synapses – specialized junctions between neurons.

Working of neuron

When a receptors sense anything a chemical reaction is triggered. This chemical reaction produces electrical impulses in dendrites.  This impulse travels through the body of the neuron to the axon endings. A tiny amount of chemical is released at the synapse by the axon ending when impulse reaches there. These chemical crosses the synapse and reaches the dendrites of next neuron where it again produces an electrical impulse. And in this way signal travels along the neuron.

Reflex Action

A quick, automatic response to some environmental stimulus without the involvement of the brain is known as a reflex action. For example, we sudden take off our hand from the flame without thinking.

Reflex Arch  The pathway taken by nerve impulses in a reflex action is called reflex arc.

Types of reflexes

Cerebral reflex: A cerebral reflex / cranial reflex is one that is controlled by the one of the cranial nerves and tends to take place in the facial or head area. For example: change of size of pupil in bright light.

Spinal reflex: The spinal reflex is the reflex that involves only spinal nerves and spinal cord and is not processed by the brain. For example: Taking off hand from the hot object.

How muscles cause movement?    

Muscles are made up of muscle cell which have proteins. These proteins can change their arrangement on receiving the message from the brain. When they do shape of muscle changes. They can contract or expand. This contraction and expansion causes movement in the body.

HUMAN NERVOUS SYSTEM: The nervous system of vertebrates (including humans) is divided into the central nervous system (CNS) and the peripheral nervous system (PNS). The (CNS) is the major division, and consists of the brain and the spinal cord.

Human Brain:

It is enclosed in cranium (brain box) and is protected by cerebrospinal fluid which acts as a shock absorber.

  • Brain: The human brain is the command centre for the human nervous system. It receives input from the sensory organs and sends output to the muscles.
  • Brain is protected by a fluid called cerebrospinal fluid which acts as shock absorber. It has 3 layers of tissue called MENINGES.
  • Spinal Cord: Spinal Cord is enclosed in Vertebral column.

Human brain has three major parts or region: (a) Fore-brain (b) Mid Brain (c) Hind Brain.

(a) Fore-brain (CEREBRUM)

Most complex/specialized part of the brain is Cerebrum or the forebrain.


  1. Thinking part of the brain
    2. Control the voluntary actions.
    3. Store information (Memory)
    4. Centre associated with HUNGER
    5. Receives sensory impulses from various body parts and integrates it.

There are 4 lobes in cerebrum:

Occipital lobe: For visual perception

Temporal lobe: For auditory perception

Frontal lobe: For muscular activities

Parietal lobe: For touch smell, temperature and consciousness

(b) Mid Brain

It connects the fore-brain with the hind-brain. It is the portion of the central nervous system associated with vision, hearing, motor control, sleep/wake, arousal (alertness), and temperature regulation.

(c) Hind-Brain

Spinal cord: spinal cord is started at medulla and extends towards downward. It is enclosed by a bony structure called vertebral column at back centre of body.

It carries message between brain and nerves.

It controls spinal reflexes.


Endocrine system is a system of endocrine glands in our body which secretes chemical substance called hormones to different parts of body. This system controls various activities of the body.

Hormones: The chemical substances secreted by endocrine glands are called hormones. Hormones are like messengers that are responsible for telling some part of the body to do something or to stop doing something.

Glands are specialized groups of cells or organs that secrete chemical substances. These are of two types:  Endocrine glands and Exocrine glands

Endocrine glands: These are glands that secrete chemical substances into the bloodstream or tissues of the body. Endocrine glands are characterized by being ductless.

Exocrine glands: These are glands that secrete chemical substances onto surface through ducts. Examples of exocrine glands are: sebaceous and sweat glands (in the skin), salivary glands (oral).

Endocrine gland Location Hormones Function
Hypothalamus  Centre of the brain Releasing hormone Control hormone secretion from pituitary gland.
Pituitary gland Centre of the brain, beneath hypothalamus. Growth hormone


Tropic hormone




Prolactin hormone



Oxytocin hormone

Overall growth of the body and development of muscle.

Regulates secretion from thyroid glands, adrenal gland and regulates reproductive organs.

Growth and development of mammary glands, milk production in females.

Regulates contraction and expansion of uterus muscle during pregnancy.

Thyroid gland At base of larynx Thyroxin





Cellular oxidation, carbohydrate, fats and protein metabolism.

Regulates calcium and phosphorus in blood

Adrenal gland Top of kidneys Adrenaline It prepares the body for emergency situation, excitement and anger. Secreted all time in small amount.
Pancreas Below stomach Insulin Regulate sugar level in blood.
Testes Pelvic cavity of abdomen in females Estrogen


Development of female genital organs.

Development of secondary sexual characters in woman.

Ovary Present in the scrotum in males Testosterone Development of male genital organs.

Development of secondary sexual characters in man.



HORMONES are chemical compounds which help to coordinate growth, development and responses to the environment.

Plant Hormones:

(a) AuxinAuxin is a plant hormone produced in the stem tip that promotes cell elongation. It controls the growth of stem, fruits and root.
(b) Gibberellin: it controls growth of stem,  breaking dormancy of buds and seeds and growth of fruit.

(c) Cytokinins: it controls the growth of plant by cell division, functioning of stomata, breaking dormancy of seeds. It is mostly present in seeds and fruits.

 (d) Abscisic acid: it controls inhibit of growth, control shedding of leaves, functioning of stomata, promote dormancy of seeds.


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