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What is the path of a nerve impulse ?

Structure and Functions of Nervous Tissue

Nervous tissue consists of two main types of cells: neurons and neuroglia.

Nerve cells, or neurones (also written "neurons") transmit nerve impulses that move information around the body.
Neuroglia are also known simply as "glia" and have various functions in support of nerve cells but do not transmit nerve impulses themselves. More information about both of these types of cells follows below:

 

Neurons

Neurons (nerve cells) are sensitive to various types of stimuli such as heat/cold, light/dark, pressure.
They transmit electrical nerve impulses thereby moving information around the body.


There are several types of neurons, including motor neurones, sensory neurones and relay neurones.

Each neurone consists of an enlarged part called the cell body (or "perikaryon") which contains of nucleus of the cell and many "processes" called dendrites that extend away from the cell body and are important because they receive the (electrical signals called) nerve impulses.

For more detailed information parts of neurones and their structures and functions see the page about neurones.

Structure of neurones

Neuroglia / Glia

Neuroglia are sometimes known as simply "Glia".
They are not sensitive to stimuli and so do not generate or conduct nerve impulses. "Glia" or "Neuroglia" are therefore sometimes referred to as the "non-nervous cells of the nervous system".
Their functions within the nervous system depend on the specific type of neuroglia:

Types of Neuroglial Cell:

  • Astroglial Cell Astrocyte

Astroglial cells, also known as "astrocytes" are found throughout the Central Nervous System (CNS), that is in the tissues of the Brain and Spinal Cord.

Structure:

Astrocyte, located in the Central Nervous System (CNS)

An astrocyte is a star-shaped cell that has many processes extending from its cell body into the surrounding network of nerve fibres.

Function(s):

  • Supply of nutrients to neurons.
  • Removes excess neurotransmitters
  • Maintains appropriate balance of Ca2+ and K+ ions (which are important in passing nerve impulses at synapses).
  • Helps migration of neurons during brain development.
  • Aids formation of the blood-brain barrier.
  • (Possibly participating in information storage processes)
  • Ependymal Cell

Ependymal cells are found in the Central Nervous System (CNS),
that is in the tissues of the Brain and Spinal Cord.

Structure:

Ependymal cells, found in the central nervous system (CNS)

Function(s):

  • Protection: Forms lining of the ventricles of the brain and central canal of the spinal cord.
  • Forms cerebrospinal fluid (CSF).
  • Aids circulation of cerebrospinal fluid (CSF).

Ependymal cells form the extremely thin membrane called the ependyma that lines the ventricles of the brain and choroid plexuses.

  • Microglial Cell

Microglial cells are sometimes known simply as "microglia" and are found in the Central Nervous System (CNS), that is in the tissues of the Brain and Spinal Cord.

Structure:

Microglial cells, found in the central nervous system (CNS)
Microglia are small glial cells.

Function(s):

  • Protects CNS neurons from disease -
    e.g. by clearing away debris and dead cells. Therefore some texts describe microglia has having a "mainly scavenging" function.

Microglia may be compared with macrophages (which are large scavenger cells, not specific to the nervous system).

  • Oligodendrocyte

Oligodendrocyte cells are found in the Central Nervous System (CNS), that is in the tissues of the Brain and Spinal Cord.

Structure:

Oligodendrocytes differ from astrocytes (listed higher-up this page) by having fewer and thinner processes and no gap junctions.

Function(s):

  • Forms supporting network around CNS neurons.
  • Some texts describe oligodendrocytes as the CNS "equivalent" of Schwann Cells in the PNS because they produce myelin sheath around several adjacent axons of CNS neurons.
  • Schwann Cell

Schwann cells are found in the Peripheral Nervous System (PNS), that is around the nerves of the extremeties of the body, e.g. located in the skin.

Structure:

Function(s):

  • Forms part of the Myelin sheath (protective covering) around a PNS neuron.
    That is, Schwann cells wrap around the axon of the neurone, forming areas in which myelin forms - resulting in the formation of a "myelin sheath" around the axon - between the axon and the Schwann cell(s). This is important because myelinated nerves conduct impulses more quickly than non-myelinated nerves.
  • Also helps with regeneration of PNS axons.

Compare Oligodendrocytes and Schwann Cells:

Both Oligodendrocytes and Schwann Cells facilitate the formation of myelin around the axons of nerve cells. However, Schwann Cells are found in the Peripheral Nervous System (PNS), and form myelin around a portion of a single axon only. Oligodendrocytes are found in the Central Nervous System (CNS), and each oligodendrocyte can form myelin around several axons.

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