Anatomy Week Four

We also talked about the diversity of structures of neurons in our bodies.  Neurons vary in sizes and shape.  They also range in different diameters.  The dendritic part of the neurons may also vary in branching styles depending on where they are in relation to where they are in the nervous tissue.  Some lack an axon, and others may have very short axons.  There are some axons that are incredibly long!  They can be as long as a person is tall, extending from a persons toe all the way to the lower part of the brain.  There are three main types neurons that may be classified.  These are multipolar neurons, bipolar neurons, and unipolar neurons.  

Multipolar neurons are the most common type of neuron found in the brain and spinal cord.  They have several dendrites and one axon.  

Bipolar neurons are typically found in the retina of the eye, the inner ear, and the olfactory part of the brain.  These have one main dendrite and one axon.

Unipolar neurons, however, are a little more complicated.  These are sensory neurons that begin in the embryo as bipolar neurons.  The axon and the dendrite fuse into one process that divides into two branches a short distance from the cell body during development.  The two branches that divided have the characteristic structures and functions of an axon.  They are also long and cylindrical processes that propagate action potentials.  The axon branches of these, however, that extend into the periphery has dendrites at its distal tip, whereas the axon branch that extends into the CNS end at synaptic bulbs.  The dendrites of the unipolar neurons monitor a sensory stimulus such as a touch or stretching.  The impulses from this point then propagate toward the synaptic end bulbs.

These structures of the neurons are important in the body, and there are many chemical and electrical factors that get these messages and stimuli sent along through the Central and Peripheral nervous system.  Without being able to send these electrical or chemical messages from the receiving dendrites to the terminal axon, down the axon, to the terminal bulbs, and across the synaptic cleft to the next neuron or effector cell, we wouldn't be able to do something as simple as blinking or lifting a finger.  It is a highly complex process and there are many outside factors that effect or determine how these messages get sent.