This is a diagram illustrating the anatomy of a neuron. Review this section's solutions to find out more about the role of each part of a neuron.
The CNS is composed of two broad classes of cells: neurons and glia.
Neuron circuits are the functional basis of how we think, feel, remember, perceive and know. They are comprised of thousands of neurons sending and receiving signals. These neurons are not connected randomly. They selectively communicate with other neurons to form these circuits or networks.
There are two types of synapses that occur between two neurons in a neuron circuit:¹
- Excitatory Synapses are activated when a terminal button releases a transmitter substance that excites a post synaptic neuron on the other side of the synapse. This excitation makes it more likely the synaptic neuron will fire.
- Inhibitory Synapses lower the likelihood that the axons of the postsynaptic neurons will fire when they are activated. This leads to an inhibitory action potential.
Neurons can be classified by function into three distinct groups:¹
- Sensory neurons aka afferent neurons detect information from the physical world and pass that information to the brain.
- Motor neurons aka efferent neurons direct muscles to relax or contract, producing movement. These are impulses carried away from the brain to the body.
- Interneurons are any neurons that are not sensory or motor. They link sensory and motor neurons and work to integrate and communicate information, rather than transmitting information from body to brain or vice versa.
Neurons are assisted in their tasks by the other type of cell found in the CNS: the glial cells. Glial cells provide support for neurons and supply them with some essential chemicals. This support includes helping guide developing neurons, manufacturing chemicals, absorbing negative chemicals and forming protective sheaths. They also serve as the brain’s immune system as protection for invading micro organisms.
Astrocytes are the most abundant and versatile neuroglia.