Neurons (Leaving Cert Biology): Revision Notes

Neurons

• A neuron is a nerve cell.
• There are three types of neurons:
  1. Sensory neurons
  2. Motor neurons
  3. Interneurons

Type of Neuron	Information
Sensory Neurons	• Carry electrical impulses from sense organs to the CNS. • The cell body is located outside the CNS.
Motor Neurons	• Carry electrical impulses away from the CNS to muscles and glands (effectors). • Effectors are organs or tissues that carry out the action of the CNS. • The cell body is located inside the CNS.
Interneurons	• Carry information between sensory and motor neurons. • Found only in the CNS. • Do not contain a myelin sheath.

Neuron Structure

Sensory neurons

Sensory neurons have very long dendrites and axons with a cell body in between.

Motor neurons

Motor neurons have very short dendrites and very long axons.

Neuron Components

Component	Description
Dendrites	• Receive impulses from other neurons. • Transmit impulses towards the cell body.
Cell Body	• Located between dendrites and axons. • Helps with cell upkeep and produces neurotransmitters.
Axon	• Carries electrical impulses away from the cell body.
Myelin Sheath	• Made from lipids. • Surrounds axons and dendrites. • Comprised of Schwann cells. The Schwann cell wraps its cell membrane around the axon/dendrite a few times to form the myelin sheath. • Protects axon and dendrites, speeds up electrical impulses.
Axon Terminals	• Contain synaptic vesicles which contain neurotransmitter chemicals.
Synaptic Vesicles	• Contain neurotransmitter chemicals.
Nodes of Ranvier	• Gaps in the myelin sheath that speed up electrical impulses by allowing them to jump from node to node.