Introduction to Neurons

 

The information on this page will familiarize you with the structure and function of our nerve cells (neurons). There are millions of these cells throughout our body that serve to transfer information about our external world (think temperature, pressure, pain, hot or cold) to our brain.

NeuronDefinitions
Dendrite
Treelike protrusion from the soma of a neuron; along with the soma, constitutes the receiving zone for messages from other cells. The dendrites, which constitute all the fibers extending out from the neuron except the axon, are best thought of as extensions of the cell body. The dendrites serve to extend the receptive surface of the neuron, as they are literally covered with synapses... both the dendrites and the cell body receive information through synaptic connections from other neurons.
Cell Body
The cell body contains all the same organelles as other cells in the body, including the mitochondria, smooth and rough endoplasmic reticulum, nucleus,and microtubules
Nucleus
The nerve cell; the basic unit of a synaptic nervous system. Specialized for the transmission of information.
Axon
The fiberlike extension of a neuron through which the cell sends information to target cells. The axon has two essential functions in the neuron. One function is to conduct information in the form of the action potential from the neuron cell body to the synaptic terminals in order to trigger synaptic transmission. The other major function is to transport chemical substances from the cell body to the synaptic terminals and backward from the synaptic terminals to the cell body.
Synaptic Vesicle
The tiny storage organelles (“bladders”) with an axon where a neuron’s neurotransmitter is stored; each vesicle contains thousands of copies of the transmitter molecules.
Synapse
The area of contact between the axon of a presynaptic neuron and the dendrite or soma of a postsynaptic neuron; site of information transfer between nerve cells.
Receptor Field
A receptor cell’s region of sensitivity.
Schwann Cell
Specialized glial cell found in the peripheral nervous system; responsible for the production of myelin.
Myelin
Compact wrapping material that surrounds and insulates axons of some neurons; produced by oligodendrocytes in the central nervous system and Schwann cells in the peripheral nervous system.

Axon

Image above adapted from Bloom, Nelson, & Lazerson’s “Brain, Mind, and Behavior” Lower Image courtesy of U of Miami http://fig.cox.miami.edu/~cmallery/150/neuro/c7.48.8.node.ranvier.jpg

All definitions taken from:
Bloom, F.E., Lazerson, A., & Nelson, C.A. (2001). Brain, Mind, and Behavior (3rd ed.). U.S.A.: Worth Publishers. 

How do Neurons Communicate?
(1) Neurons communicate using synaptic neurotransmitters as the basic conveyors of information
-neurotransmitter: chemical released by nerve cells at a synapse for the purpose
of relaying information
(2) The neuron sending the message across the synapse is known as the presynaptic neuron
(3) The neuron receiving the message across the synapse is known as the postsynaptic neuron
(4) the presynaptic neuron releases its neurotransmitter into the synapse when the action potential has moved down to the end of the axon
(5) Synaptic vesicles at the end of the axon receive the message from the action potential to migrate to the outer membrane of the axon terminal. Once migrate, these vesicles fuse temporarily to the membrane and open to release their neurotransmitters into the synapse
(6) The released neurotransmitters diffuse in the synaptic gap and bind to the membrane of the postsynaptic neurons
(7) If more neurotransmitters are released into the synapse than can bind to the postsynaptic neuron, there are a few mechanisms that clear them from the area:
-Sometimes, the excess neurotransmitters are destroyed by an enzyme released into the synapse from the membrane of the postsynaptic neuron
-Other times, the presynaptic neuron uses a process known a reuptake, recollecting the excess neurotransmitters and repackaging them into synaptic vesicles

Image adapted from Bloom, Nelson, & Lazerson’s “Brain, Mind, and Behavior”

Types of Synaptic Messages

  1. Excitatory, (depolarizing): the presynaptic neuron commands the postsynaptic to fire
  2. -In this situation, the receiving cell may or may not fire in response to the neurotransmitter; signals coming in must reach a designated threshold before it will fire

  3. Inhibitory: the presynaptic neuron commands the postsynaptic neuron NOT to fire