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The structure of the nervous system

Nervous system structure

The nervous system is responsible for all internal communication, with its primary role to maintain a constant balance of the internal environment, known as homeostasis. It achieves this with the help of the brain and a complex network of electrical nerves and chemical messages that run throughout the body.

There are two primary divisions of the nervous system, the central nervous system (CNS) consisting of the brain & spinal cord which is the control centre, and the peripheral nervous system (PNS) consisting of all the branches of nerves that lie outside the spinal cord which feed signals into and out of the CNS. The PNS subdivides into the  somatic PNS which controls voluntary (conscious) movement of the skeletal muscles and the autonomic PNS which controls involuntary functions, such as heart rate and digestion.

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Neuron structure

A neuron is the term giving to a nerve cell which transmits the electrical messages via a one way circuit within the nervous system. There are two different types of neurons including sensory and motor. Sensory neurons relay messages from the different sensory receptors of the peripheral nervous system to the central nervous system, all sensory neurons run into the posterior aspect of the spinal cord. The second type of neurons are motor neurons which relay messages from the central nervous system to different muscles and glands of the peripheral nervous system., they do this from the anterior aspect of the spinal cord.

Both sensory and motor neurons are responsible for transmitting electrical messages, essentially behaving like a one way cable or wire. The distance travelled by the signal might be short, such as from one part of the CNS to another, or it may be relatively long, such as the PNS from the bottom of the feet to the lumbar region for example. Nevertheless, all neurons possess the same fundamental anatomical features including dendrites: These small, branch-like projections which make the connections to other cells allowing the neuron to communicate with that cells, it is dendrites that actually ‘sense’ the stimulus (e.g. heat, cold, pain, pressure or touch). Cell body or (soma) which regulates the neurons cell activity & contains all the necessary components of the cell, including the nucleus (which contains DNA), endoplasmic reticulum & ribosomes (for building proteins) & mitochondria (for making energy). The neuron axon this long cable-like projection transmits the signal known as action potentials by carrying electrochemical messages along the length of the neuron. The axon is surrounded by myelin sheath which is a thin insulating layer which helps to speed up the action potential as it travels along the axon to the axon terminal. The axon terminal is the interface between the neuron and other cells it connects with and contains the synaptic end bulbs which are embedded right at the end of axon terminals, these are where the neurotransmitter which is the substance that transmits the action potential to the next structure is released continuing the communication to the connected structure.

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