The human nervous system consist of Central Nervous System (CNS) and Peripheral Nervous System (PNS). It allows us to make sense of our surrounding and respond to them, and to coordinate and regulate body functions.

Central Nervous System

The brain and the spinal cord.

Peripheral Nervous System

All of the bundle of neurones; nerves in the body.

Informations is sent through the nervous system as nerve impulses — electrical signals that pass along nerve cells known as neurones.

Structure of Neurones

Neurones have a long fibre — axon.

Means that less time is wasted transferring the impulse from one cell to another.

Axon is insulated by myelin sheath with small uninsulated sections along it — nodes.

Thus electrical impulse does not travel down whole axon; jump from one node to next

The cell body itself contains many extensions — dendrites.

They can connect to many other neurones and receive impulses from them, forming a network for easy communication.

Synapses

Where two neurones meet or join, they do so at a junction — a synapse.

They don’t touch with each other.

• Electrical impulse travels along the axon of the first neurone.
• This impulse triggers vesicles in the nerve ending to release neurotransmitters molecules.
• Neurotransmitters transport across the synaptic gap (cleft) by diffusion.
• They bind to receptor molecules on the membrane of the second neurone.

• This stimulates a new electrical impulse in the second neurone.

• Neurotransmitters are then broken down or removed to stop continuous stimulation.

• Synapses ensure one-way transmission of impulses.

• How does Drug X affects the transmission of electrical impulse / function of relay neurone?

There are three main types of neurones: Sensory. Relay. Motor.

• Sensory Neurone: Carry impuleses from sense organs to CNS.
• Relay Neurone: Found inside the CNS connect sensory and motor neurones.
• Motor Neurone: Carry impulses from CNS to effector. (e.g., Muscles or Glands)