- Nerve cells
- The nervous system is composed of nerve cells or neurones. A neurone has a cell body with extensions leading off it.
- Several dendrons carry nerve impulses towards the cell body while a single long akon carries the nerve impulse away from the cell body.
- Nerve impulses are passed from the axon of one neurone to the dendron of another at a synapse. Numerous dendrites provide a large surface area for connecting with other neurones.
- Most neurones also have many companion cells called shwann cells which are wrapped around the axon many times in a spiral to form a thick lipid layer called the myelin sheath.
- This provides physical protection and electrical insulation for the axon. There are gaps in the sheath called Nodes of Ranvier
- Sensory neurone -they have long dendrons and transmit nerve impulses from sensory receptors to the central nervous system.
- Effector/ motor neurone - they have long axons and transmit nerve impulses from the central nervous system to effectors all over the body
- Interneurones /relay neurones - these are much smaller with many connections. They comprise the central nervous system, 99.9% of all neurones are relay neurones.