Control and Coordination

1. What is Control and Coordination?

Control and coordination are the processes that help living organisms control their body activities and respond to changes around them. These processes are crucial for survival, growth, and maintaining balance in their internal environment.
The two major systems responsible for control and coordination in humans are:
1. Nervous system — works mainly through electrical impulses.
2. Endocrine system — works through chemical messengers called hormones.
Plants do not have a nervous system or muscles, but they coordinate their responses through chemical signals (hormones ) and growth-related movements.

2. Why do organisms need control and coordination?

To detect changes in the environment.
To respond appropriately to different stimuli.
To protect themselves from danger.
To coordinate the activities of different organs.
To maintain proper growth and functioning.

3. Stimuli

The changes in the environment to which the organisms respond is called stimuli such as light, heat, cold, sound, smell, touch etc.
Plants and animals both respond to stimuli but in different manner.

4. Control and Coordination in Animals

4.1 Receptors

Receptors are specialised nerve cells which initiate waves of impulses towards the central nervous system on receiving a stimulus.

These are classified as follows :

Phono-receptors: These are present in inner ear.
Functions: The main functions are hearing and balance of the body.
Photo-receptors: These are present in the eye.
Function: These are responsible for visual stimulus.
Thermo-receptors: These are present in skin.
Functions: These receptors are responsible for pain, touch and heat stimuli.
These receptors are also known as thermoreceptors.
Olfactory-receptors: These are present in nose.
Functions: These receptors receive smell.
Gustatory-receptors: These are present in the tongue.
Functions: These helps in taste detection.

Example: When we smell an incense stick, olfactory receptors in the nose detect the smell and send signals through sensory nerves towards the brain.

4.2 Nervous System

Basic unit: Neuron

Neuron: A neuron is the structural and functional unit of the nervous system.

A neuron is a specialised nerve cell that receives and transmits information through electrical impulses.

Its main parts are:

Dendrites: These are branched structures that receive nerve impulses from receptors or other neurons and carry them towards the cell body.
Cyton or cell body: The cell body or cyton is somewhat star-shaped, with many hair like structures protruding out of the margin.It contains the nucleus and cytoplasm. It controls the activities of the neuron and maintains the cell.
Axon: This is the tail of the neuron.It is a long, fibre-like structure that carries nerve impulses away from the cell body to another neuron, muscle or gland.
Nerve endings: These are the branched ends of the axon that transmit the nerve impulse to another neuron, muscle or gland through a synapse.

Transmission of a nerve impulse

The sequence is:

A stimulus is detected by a receptor.
A chemical reaction generates an electrical impulse at the receiving end of the neuron.
The impulse travels from the dendrite towards the cell body and along the axon.
At the axon ending, chemicals are released.
These chemicals cross the synapse and initiate an impulse in the next neuron, or communicate with an effector cell.

Types of neuron

Neurons are classified into three types on the basis of their functions:

1. Sensory Neurons: These neurons carry nerve impulses from receptors or sense organs to the central nervous system (brain and spinal cord).

2. Motor Neurons: These neurons carry nerve impulses from the central nervous system to effectors, such as muscles or glands, to produce a response.

3. Association Neurons (Relay Neurons): These neurons are present in the central nervous system and transmit nerve impulses between sensory neurons and motor neurons.

Remember:

Sensory neuron — carries impulses towards the CNS.
Motor neuron — carries impulses away from the CNS.
Relay neuron — connects neurons within the CNS.

Structure of the Human Nervous System

The human nervous system controls and coordinates the activities of the body by receiving information, processing it and transmitting instructions to different body parts.

It consists of the following parts:

1. Central Nervous System (CNS): It consists of the brain and spinal cord. It receives and processes information and coordinates the responses of the body.

2. Peripheral Nervous System (PNS): It consists of nerves that connect the central nervous system to different parts of the body. It carries messages to and from the CNS.

3. Autonomic Nervous System (ANS): It regulates involuntary activities of the body, such as heartbeat, digestion and glandular secretion.

Human Brain

The human brain is the main coordinating centre of the nervous system. It receives information from different parts of the body, processes it and sends instructions to bring about appropriate responses.

Main Parts of the Human Brain

The human brain is divided into three main regions:

1. Forebrain

The forebrain is the main thinking part of the brain. It performs the following functions:

Cerebrum: The cerebrum is the largest part in the human brains. It is divided into two hemispheres called cerebral hemispheres.
Function : It controls thinking, memory, intelligence, learning and voluntary actions. Its sensory areas receive and interpret information from sense organs.
Hypothalamus: The hypothalamus lies at the base of the cerebrum.
Regulates hunger, thirst, body temperature and certain emotional responses.It controls sleep and wake cycle of the body.

2. Midbrain

The midbrain sits in the middle of our head, connecting the top and bottom parts of the brain.
Controls certain reflex movements in response to visual and auditory stimuli.
Helps coordinate responses to sensory information.

3. Hindbrain

The hindbrain consists of the cerebellum, pons and medulla.

Cerebellum: It is located below the cerebrum, at the back of the brain.It has numerous folds and furrows.
Maintains posture and balance and coordinates muscular movements to ensure precision.
Medulla: It is a part of the hindbrain, located at the base of the brain and continuous with the spinal cord.
Controls involuntary activities such as heartbeat, breathing, blood pressure and vomiting.
Pons: The pons is a rounded bulge on the brainstem, located above the medulla and below the midbrain.
Helps regulate breathing and connects different parts of the brain.

Spinal Cord

The spinal cord is a long, cylindrical bundle of nervous tissue that extends from the medulla oblongata of the brain. It is protected by the vertebral column (backbone).

Functions of the Spinal Cord:

It conducts nerve impulses between the brain and different parts of the body.
It acts as the reflex centre and controls reflex actions, enabling quick responses to stimuli without waiting for instructions from the brain.

Example: When we touch a hot object, the spinal cord coordinates a quick response that causes us to withdraw our hand.

Protection of the brain and spinal cord

Brain: Protected by the skull, or cranium. It is also surrounded by protective membranes and cerebrospinal fluid, which helps absorb shocks.
Spinal cord: Protected by the vertebral column, or backbone.

4.3 Synapse

A synapse is the tiny gap between the nerve ending of one neuron and the dendrite or cell body of another neuron. It helps in the transmission of nerve impulses from one neuron to another through chemical messengers called neurotransmitters.

Neuromuscular Junction (NMJ)

A neuromuscular junction is the junction between the nerve ending of a motor neuron and a muscle fibre. When a nerve impulse reaches this junction, chemical messengers are released that stimulate the muscle fibre to contract.

Transmission of Nerve Impulses

Nerve impulses travel through a neuron in the following sequence:

Dendrites → Cell body → Axon → Nerve endings → Synapse → Next neuron

5. Reflex Action and Reflex Arc

5.1 Reflex Action

A reflex action is a quick, automatic and involuntary response to a stimulus that occurs without conscious thinking. It helps protect the body from injury.

Examples:

Pulling the hand away from a hot object.
Blinking when an object suddenly approaches the eye.
Withdrawing the foot after stepping on a sharp object.

5.2 Reflex Arc

A reflex arc is the pathway followed by nerve impulses during a reflex action.

The pathway of a reflex arc is:

Stimulus → Receptor → Sensory neuron → Spinal cord (relay neuron) → Motor neuron → Effector → Response

Example: When we touch a hot pan, receptors in the skin detect the heat and generate nerve impulses. The sensory neuron carries the impulses to the spinal cord, where a relay neuron passes them to a motor neuron. The motor neuron carries the impulses to the arm muscles, causing the hand to withdraw quickly.

5.3 Why is the Spinal Cord Involved in Reflex Actions?

The spinal cord acts as the reflex centre and coordinates many reflex actions without waiting for conscious processing by the brain. This allows the body to respond quickly and reduces the risk of injury.

5.4Voluntary and involuntary actions

Voluntary actions are actions performed under conscious control.

Examples: writing, speaking and deliberately moving a chair.

Involuntary actions are actions that occur without conscious control.

Examples: heartbeat, digestion and regulation of blood pressure.

The medulla in the hindbrain controls several involuntary activities.

5.5 Difference between reflex action and voluntary action

Reflex action

Voluntary action

Rapid and automatic.

Performed by conscious decision.

Does not require deliberate thinking before the response.

Involves decision-making by the brain.

Often coordinated through the spinal cord.

Generally planned and controlled by the brain.

Example: withdrawing a hand from a flame.

6. Endocrine System and Hormones

1. Endocrine System

The endocrine system consists of a group of ductless glands that secrete chemical substances called hormones directly into the bloodstream.

These hormones regulate various activities of the body and work along with the nervous system to bring about control and coordination.

Hormones

Hormones are chemical messengers secreted in small amounts by endocrine glands that regulate and coordinate various activities of the body.

Hormones are released into the blood and carried to their target organs or tissues.

Functions of Hormones

They regulate growth and development.
They control metabolism and blood sugar levels.
They regulate changes during puberty and reproduction.
They help the body respond to stressful situations.
They coordinate activities that require slower and longer-lasting responses than many nervous responses.

Difference between nervous and hormonal control

Nervous control	Hormonal control
Uses electrical impulses along neurons and chemical transmission at synapses.	Uses chemical messengers called hormones.
Generally produces rapid responses.	Generally produces slower responses.
Effects are often short-lived and localised.	Effects may last longer and act on distant target organs.

2. Important Endocrine Glands and Their Functions

1. Pituitary Gland

It is located at the base of the brain.
It secretes growth hormone, which regulates body growth.
Deficiency of growth hormone during childhood may cause dwarfism, while excessive secretion may cause gigantism.
It also secretes hormones that regulate the activities of other endocrine glands.

The pituitary is often called the master gland because it controls several other endocrine glands.

2. Thyroid Gland

It is located in the neck, in front of the windpipe.
It secretes thyroxine, which regulates metabolism, including the metabolism of carbohydrates, proteins and fats.
Iodine is essential for the production of thyroxine.
A deficiency of iodine in the diet may cause goitre, characterised by enlargement of the thyroid gland.

3. Adrenal Glands

A pair of adrenal glands is located above the kidneys.
They secrete adrenaline, which prepares the body to deal with emergency situations.
Adrenaline increases the heartbeat, breathing rate and blood supply to skeletal muscles, helping the body respond to danger. This is known as the fight-or-flight response.

4. Pancreas

The pancreas is located in the abdomen, near the stomach.
It acts as both an endocrine and an exocrine gland.
It secretes insulin, which helps regulate blood glucose levels.
Insufficient insulin production or ineffective insulin action can lead to diabetes mellitus.

5. Testes (Male Gonads)

The testes are a pair of male reproductive organs located in the scrotum.
They secrete testosterone.
Testosterone brings about changes in boys during puberty, such as facial hair growth, deepening of the voice and development of reproductive organs.

6. Ovaries (Female Gonads)

The ovaries are a pair of female reproductive organs located in the pelvic cavity.
They secrete oestrogen and progesterone.
Oestrogen helps bring about female secondary sexual characteristics during puberty.
Progesterone helps regulate the menstrual cycle and supports pregnancy.

3. Summary Table: Endocrine Glands, Hormones and Functions

Endocrine gland	Hormone	Main function
Pituitary	Growth hormone	Regulates body growth
Thyroid	Thyroxine	Regulates metabolism
Adrenal	Adrenaline	Prepares the body for emergencies
Pancreas	Insulin	Regulates blood glucose
Testes	Testosterone	Develops male secondary sexual characteristics
Ovaries	Oestrogen	Develops female secondary sexual characteristics
Ovaries	Progesterone	Supports the menstrual cycle and pregnancy

Example: writing an answer or picking up a book.

DM CLASS

Science

Friday, October 30, 2026