Components of Nervous System

 

1-Neuron:

 

Neuron is unit of nervous system. It has two main parts:

 

Cell body:

 

It is thicker region containing nucleus and cytoplasm. Many wire like dendrites are also present here.

 

Axon or Nerve Fibre:

 

It is long projection carrying nerve impulses. Usually a single neuron has a single axon. A fatty substance called myeIin sheath cover the axon.

 

Types of neurons:

 

There are three types of neurons:

 

Sensory neurons:

 

These neurons carrying impulses from sensory organs to CNS.

 

Associated Neurons:

 

These neurons are link between sensory and motor neurons. They form the CNS. They are very intelligent. They are responsible for input messages and issuing orders.

 

Motor neurons:

 

They carry impulses from CNS to effectors.

 

Synapse:

 

It is microscopic gap between two consecutive neurons which connect the neurons.

 

2-Brain:

 

The brain is well protected in bony shell called cranium. Three layers called meninges also protect the brain. The brain has three parts:-

 

The Hind Brain:

 

1. i) Medulla Oblongata is present on the tip of spinal cord. It controls breathing, blood pressure, heartbeat, vomiting etc.

 

1. ii) Pons is present on the top of the medulla. They control balance and muscle coordination.

iii) Cerebellum is present behind the medulla. It controls balance and muscle coordination. It also helps in accurate movement.

 

The Mid Brain:

 

It is present between the hind and forebrain and connects the two. It controls the visual and auditory reflex of eyes and ears.

 

The Fore Brain:

 

1. i) Hypothalamus is present above the midbrain. It controls heart rate, blood pressure, body temperature, hunger, thirst, sex, anger etc.

 

1. ii) Thalamus is connection between many parts of brain and cerebrum. It controls moods, feelings sleep and ability to keep alert.

 

iii) Cerebrum is present on the top. It consists of 15 billion nerve cells. It controls the memory track.

 

3-Spinal cord:-

 

1. i) It is a thick dorsal neural track.

 

1. ii) It is present from the brainstem to the lower back.

 

iii) It serves as reflex center possibly involving a variable numbers of inter neurons.

 

1. iv) There are 31 pairs of spinal nerves arising from the spinal cord.

 

1. v) Its main function is concerned with spinal reflex actions and also pathway of information form and to the brain.

 

Spinal nerve:

 

Spinal nerve arises from spinal cord by two roots:

 

1. i) A dorsal root consisting of sensory neurons

 

1. ii) A ventral root consisting of motor neurons.

 

These two roots combine to form a spinal nerve. This nerve is a mixed nerve.

 

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