Structure and Functions of Nervous Tissue

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.

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:

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:

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:

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.

For more details see the diagram and description of a Motor Neuron - recall that the neurone (nerve cell) transmits electrical impulses, in comparison with the neuroglia cell (Schwann Cell), which does not transmit nerve impulses but is, nevertleless, a specialised cell of the nervous system.