Major Neuron Types And Structure Of The Central Nervous System
Don’t Shoot the Messenger
Much of the CNS is made up of neurons. Each neuron has a cell body, which includes a soma with a nucleus, a nucleolus, a cytoplasm called the perikaryon, and wide branching extensions called dendrites. Dendrites are like antennae which receive signals from other neurons or body cells. Their plasma membranes and cell bodies contain many receptor sites for binding chemical messengers, or neurotransmitters. Such structures are often short, tapering, and highly branched. They forming a tree-like variety of processes extending from its soma. …show more content…
These 20 billion cells are usually multipolar, and most are located in the brain and spinal. They coordinate motor activity and distribute sensory information. The more complex a reaction is, the more interneurons are involved in it.
Major Neuron Types by Structure
Anaxonic neurons are small without any clues to distinguish axons from dendrites. They are located in the brain and special sense organs and because all of their functions look alike, their processes are not yet well understood.
Bipolar neurons consist of one dendrite which branches extensively at the distal tip, one axon, and a soma between them. They are rare and found in special sense organs like the brain’s olfactory area. The largest bipolar neuron is 30 mm long, proving that they are quite small.
Unipolar neurons have continuous dendrites and one axon with the cell body lying to one side. Dendrites converge at the initial segment, and this neuron type is found in the PNS but connects to CNS’ synapses. They begin as bipolar neurons in embryo which fuse together during development. The trigger zone is between the dendrites and the axon, and impulses then propagate toward synaptic end bulbs. These neurons are usually found in spinal and cranial nerves’