Neurones and Synapses

To communicate between receptors and effectors the body uses two main methods.

These are:

•  nerves
•  hormones.

A neurone is a specialised cell that is adapted to pass electrical impulses. 

Each neurone has a small diameter so many can fit into one nerve. There are 3 types of neurones

1. Sensory – carry signals from sense organs (receptors) to the brain (CNS: Central Nervous System)

2. Relay – they pass messages between neurones in the CNS.

3. Motor – carry signals from CNS to muscles (effectors)

Image

Although all neurones have different shapes, they all have certain features in common:

• One or more long projections from the cell body to carry the impulse a long distance.
• A fatty covering (myelin sheath) around the projection for insulation.
• Many fine endings (dendrites) so that the impulse can be passed on to many cells.

KEY POINT: Exam questions often ask how neurones are adapted for their job.

The Structure of a Neurone

Image

Sensory Neurone 

Image

Motor Neurone 

Image

Synapse

Each neurone does not directly end on another neurone. There is a small gap between the two neurones called a synapse. In order for an impulse to be generated in the next neurone, a chemical transmitter is released. This then diffuses across the small gap.

Many drugs work by interfering with synapses. They may block or copy the  action of neurotransmitters in certain neurones.