Review of Nervous System Function
The nervous system is composed of neurons and neuroglial cells ( also known simply as glial cells ). Neurons are linked together by synaptic connections , and are named for their positions relative to the synapse located between them : the pre-synaptic neuron is located before the synapse ; the post-synaptic neuron is located after it ( the post-synaptic neuron would then be a pre-synaptic neuron relative to the next synapse along the pathway of neurons ). At a synaptic connection , the regions of the membranes where neurotransmitters are released by the pre-synaptic neuron and picked up by the post-synaptic neuron are called active zones . Glial cells are oligodendrocytes , astrocytes , microglial , and ependymal cells in the central nervous system , and Schwann cells in the peripheral nervous system . Neurons comprise 15 % of the cells of the brain ; glial cells comprise the other 85 %.
When a neuron is sufficiently stimulated to reach action potential , an electrical impulse occurs within the neuron . This impulse travels in one direction , from the dendrites / cell body end of the ( pre-synaptic ) neuron to the ends of the terminal branches of the neuronal axon located at the synapse with the next ( post-synaptic ) neuron . Because the electrical impulse cannot cross the synaptic connection , the pre-synaptic neuron releases chemical neurotransmitter molecules that cross the synapse to the post-synaptic neuron . These neurotransmitters can have a facilitory or inhibitory effect ; in other words , they can facilitate or inhibit the creation of an action potential and therefore nerve impulse in the post-synaptic neuron . Because many ( thousands of ) pre-synaptic neurons converge on a post-synaptic neuron , whether the post-synaptic neuron is sufficiently facilitated / stimulated to action potential is dependent upon the summation of all facilitory and inhibitory pre-synaptic neuron ’ s neurotransmitters . If the post-synaptic neuron is sufficiently stimulated , a nerve impulse will be initiated that can then travel to the axonal end of that neuron and synapse with the next post-synaptic neuron . In this manner , impulses travel throughout the neuronal network . In effect , the presence or absence of impulses translates into binary-code information , just as a computer carries 1s and 0s .
This understanding of nervous system function is called the neuron doctrine because it holds that neurons are principally important for nervous system functioning . Although current research does not contradict our knowledge of neuronal functioning , it is beginning to show us that neurons are not the only important actors on the stage when it comes to impulse transmission . We are finding out that glial cells are far more important than previously thought . Glial cells were once thought to provide support functions and be little more than putty that held the neurons together ; in fact , the term glia literally means glue . They are now becoming understood to be integral to the functional ability of neurons to carry their electrical impulses and transmit their chemical synaptic messages .
Creating Memory Patterns
The creation of a memory pattern occurs by encoding the activation / firing of specific pathways of neurons in a specific timed sequence . A simple memory pattern might involve only a few neuronal pathways . A more involved pattern might involve many , many neuronal pathways , with a precise interplay of timing .
For example , the motor skill memory pattern to play a simple song on the piano would involve learning to successively flex the metacarpophalangeal and proximal interphalangeal joints of the fingers in a certain sequence , with a specific timing . If it is a simple song such as Mary Had a Little Lamb , the sequence of fingers would be 3-2-1-2-3-3-3 , 2-2-2 ,
3-5-5 , 3-2-1-2-3-3-3 , 2-2-3-2-1 ( 3 , middle finger ; 2 , index finger ; 1 , thumb ; and each comma represents a pause ). At the same time , the nervous system would have to simultaneously isometrically contract extensor muscles of the wrist joint and flexor muscles of the elbow joint so that the hand and forearm would be positioned such that the fingers can strike the keys , as well as core muscles to hold the trunk and neck in position , while seated to play . If expression is added to the song , then cognitive and / or emotive ( limbic system ) pathways would be involved , as well as possible other upper extremity joint motions to allow the pianist to strike the keys harder or softer as desired . A memory pattern for this song would involve all these neuronal pathways to engage musculature spatially throughout the body , as well as temporally in sequence and timing to hit the proper order of notes to play the song . And this is a simple song . Imagine if the piece being played is a Beethoven Sonata !
A similar process occurs with a more complicated motor skill , such as hitting a forehand stoke in tennis . Neuronal pathways that encode for hip , knee , and ankle joint motions to place the feet in the right position ; elbow , shoulder , shoulder girdle , and spinal joint motions to bring the racquet back ; and then swinging the racquet forward with a concerted coordination of all the upper extremity ; and spinal , and lower
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