Nervous System in Humans

A nerve cell or neuron is the basic structural unit of the nervous system. It has three parts — cell body, axon and dendrites.

1. The cell body called cyton contains the nucleus.
2. Many short fibres called dendrons arise from the cell. They further divide to form dendrites. Dendrites receive messages from other neurons.
3. A single, long fibre called axon extends from the other side of the cell body. It is covered by a sheath called myelin sheath.

Below diagram shows the structure of a neuron:

The central nervous system consists of the brain and the spinal cord. It is the control centre for all body functions. It is the site for all information processing in the body. It is responsible for processing every sensation and thought a human being experiences. It has two parts — Brain and Spinal Cord.

1. Brain — The Brain is the main control centre of the nervous system situated in the cranium of the skull. It controls our thinking, feelings, movement and senses. It has three parts — Cerebrum, Cerebellum and Medulla oblongata.
   1. Cerebrum — The cerebrum is the uppermost, largest and the most prominent part of the brain. It is responsible for the sensation of pain, temperature, touch, sight, sound, taste and smell. It also controls mental activities such as memory, intelligence, thinking and reasoning.
   2. Cerebellum — The cerebellum is a small, egg-shaped lobe located at the base under the cerebrum. It helps in the muscle coordination and balance of the body.
   3. Medulla oblongata — The Medulla oblongata is the lowermost part of the brain located at the base of the skull. It controls breathing, heartbeat, coughing, sneezing and other involuntary functions.
2. Spinal cord — The spinal cord is the continuation of the medulla oblongata of the brain. It is like a cord that emerges from a hole at the base of the skull and runs through the vertebral column. The spinal cord conducts reflexes below the neck. It conducts sensory impulses from the skin and muscles to the brain. It conducts motor responses from the brain to the muscles of the trunk and limbs.

The peripheral nervous system transmits messages to and from the sense organs and is responsible for voluntary actions such as cycling, swimming and so on. Messages enter the spinal cord from all parts of the body and reach the brain, which sends back the messages to various body parts through the spinal cord.

Any sudden change in the environment of an organism that causes a reaction in that organism is called a stimulus.

The three important parts of the brain are:

1. Cerebrum
2. Cerebellum
3. Medulla oblongata

The functions of the cerebrospinal fluid are:

1. Nourishes the brain.
2. Protects it by absorbing shocks.

Reflex action is a quick, automatic response to a stimulus, without the involvement of the brain.

The reaction of an organism to a stimulus is called a response.

The basic structural unit of the nervous system is called a neuron.

Cerebrospinal fluid nourishes the brain and absorbs shocks.

Cerebrum is the largest part of the brain.

Cerebellum maintains the balance of the body.

Neuron is the basic structural unit of the nervous system.

A single long fibre extending from the cell body of a neuron is called axon.

The central nervous system comprises brain and spinal cord.

The peripheral nervous system comprises the nerves arising from the brain and spinal cord.

The brain is enveloped by three membranes called meninges.

cerebrum

Reason — Cerebrum is the part of brain while others are part of nerve cell or neuron.

body balance

Reason — Body balance is the function of cerebellum while thinking, reasoning and memory are functions of cerebrum

This picture shows 'Synapse between neurons'. The labelled parts are shown below:

Spinal cord is responsible for this action. Immediately withdrawing our foot after stepping on a needle is a reflex action which happens without thinking i.e., the brain is not involved. Reflex actions are controlled by spinal cord.

dendrons

Reason — Short fibres extending from the cell body of a nerve cell are called dendrons which further divide to form dendrites.

impulse

Reason — Messages along the neuron travel in the form of a wave of chemical disturbance. This chemical disturbance is called an impulse.

medulla oblongata

Reason — Medulla oblongata controls involuntary movements like breathing and heartbeat.

cerebrum

Reason — Centre for intelligence and memory is cerebrum.

cerebellum

Reason — Cerebellum maintains the balance of the body.

False

Corrected statement — Each nerve cell consists of a cell body, many short fibres which further divide into dendrites and a long fibre.

False

Corrected statement — Mixed nerves contain both sensory and motor fibres hence they perform the function of both sensory nerves and motor nerves.

False

Corrected statement — The cerebrum is the largest part of the brain.

False

Corrected statement — Thinking, reasoning and memory are controlled by the cerebrum.

False

Corrected statement — The cerebellum controls the balance of the body.