The Nervous System

Nervous System Neuron Diagram

The nervous system is a collection of organs in the human body that include the brain, spinal cord, nerves and neural support cells, and sensory organs such as the eye, and the ear. The nervous system is a network that provides the human body with a means of communication between nearly every organ. The neuron is the functional unit of the nervous system, which is capable of sending chemical and electric signals from one cell to another.

The Structure and Function of the Neuron

All neurons have a basic cell structure which includes dendrites, an axon, and a cell body. The dendrites in a neuron are the part of the cell that receive any signal to be transmitted by the cell. The stimulus is transmitted from the dendrite to the axon hillock to generate an action potential down the axon. The stimulus ultimately reaches the synapse, which in turn is responsible for transmitting the stimulus to another cell.

Neurons use glucose as the primary source of energy. The cells use facilitated transport to move glucose from the blood to the interior of the cell. Insulin is used by most cells to facilitate the transport of glucose across the cell membrane, however, neurons do not.

Other Nervous System Cells

Although the functional unit of the nervous system is the neuron, the nervous system is also composed of glial cells (also know as neuroglia). Glial cells, unlike neurons, are capable of multiplying. There are six different types of glial cells.

  1. Astrocytes.
  2. Ependymal Cells.
  3. Microglia.
  4. Neurolemmocytes (Schwann Cells). Schwann cells are helper cells that enable the propagation of an action potential (an electrical or chemical signal) across the axon of a neuron. These cells wrap around the axon and act as a kind of insulator – just like an electrical wire. Schwann cells are primarily located in the peripheral nervous system. These cells are the primary component of the myelin sheath (see below).
  5. Oligodendrocytes. Oligodendrocytes are the “Schwann cells of the central nervous system.” Unlike other glial cells, oligodendrocytes are unable to replicate or repair.
  6. Satellite Cells.

Myelin sheaths are an electrically insulating material produced by glial cells. Myelin sheaths are wrapped around the axons of the neurons and increase the speed of transmission of action potential down the axon.

There are small gaps between myelin sheaths called the Nodes of Ranvier. Action potential moves across the gaps through a process known as saltatory conduction.

Nervous System Communication

Cells in the nervous system communicate with one another using chemical or electrical means through a synapse. The transmission of impulses across the synapse are the slowest step in nervous system communication. There are two different synapses.

  1. Electrical Synapses.
  2. Chemical Synapses.

The most common synapse is a chemical synapse. The chemical synapse facilitates the unidirectional transmission of chemical signals, called neurotransmitters, from the presynaptic neuron to the postsynaptic neuron through gaps know as the synaptic cleft.

A blank diagram of the brain

Nervous System Structure

The nervous system is composed of two parts: the central nervous system and the peripheral nervous system. The central nervous system includes the brain and the spinal cord. The peripheral nervous system is simply every other part of the nervous system that is not part of the CNS.

The peripheral nervous system, or PNS, is responsible for the execution of sensory and motor functions of the nervous system. The PNS can be further divided into two parts: the somatic nervous system and the autonomic nervous system.

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