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===CNS Neurons===

===CNS Neurons===

Neural tissue found in the CNS is composed of '''gray''' and '''white''' matter. The gray matter includes nerve cell bodies and some short branches from these cell bodies. The white matter is composed of the long extensions of the nerve, the nerve fibres. Within the central nervous system there are two major cell types; '''[[#Neurons|neurons]]''' which are the "functional" cells of the central nervous system and '''glial cells''' which play a supporting role within the CNS. Within the CNS there are also a number of other cells that play a supportive role to the neurone and these include [[#Astrocytes|astrocytes]], [[#Oligodendrocytes|oligodendrocytes]], [[#Microglial Cells|microglial cells]], [[#Ependymal Cells|ependymal cells]] and [[#Choroid Plexus Epithelial Cells|horoid plexus epithelial cells]].

Neural tissue found in the CNS is composed of [[Central Nervous System - Anatomy & Physiology#Grey Matter|'''gray''']] and [[Central Nervous System - Anatomy & Physiology#White Matter|'''white''' matter]]. The gray matter includes nerve cell bodies and some short branches from these cell bodies. The white matter is composed of the long extensions of the nerve, the nerve fibres.  

 

Within the central nervous system there are two major cell types; '''neurons''' which are the "functional" cells of the central nervous system and '''glial cells''' which play a supporting role within the CNS. Within the CNS there are also a number of other cells that play a supportive role to the neurone and these include [[#Astrocytes|astrocytes]], [[#Oligodendrocytes|oligodendrocytes]], [[#Microglial Cells|microglial cells]], [[#Ependymal Cells|ependymal cells]] and [[#Choroid Plexus Epithelial Cells|choroid plexus epithelial cells]].

 

===PNS Neurons===

===PNS Neurons===

The PNS contains a series of paired nerves that extend from the spinal nerves originating from the spinal cord and [[Cranial_Nerves_-_Anatomy_%26_Physiology|cranial nerves]] that originate from the brain stem. Neurones found in the PNS are similar to those found in the CNS aside from a few subtle differences. Supportive cells that surround the nerves in the PNS are called Schwann cells (rather than Glial cells). The main neurotransmitter found in the PNS is [[Neurotransmitters_-_Anatomy_%26_Physiology#Other_SMTs|acetylcholine]].

The PNS contains a series of paired nerves that extend from the spinal nerves originating from the spinal cord and [[Cranial Nerves - Anatomy & Physiology|cranial nerves]] that originate from the brain stem. Neurones found in the PNS are similar to those found in the CNS aside from a few subtle differences. Supportive cells that surround the nerves in the PNS are called [[Schwann Cell|Schwann cells]] (rather than Glial cells). The main neurotransmitter found in the PNS is [[Neurotransmitters - Anatomy & Physiology#Other SMTs|acetylcholine]].

==Neurons==

==Neurons==

A typical neuron can be exmplified by a motor neuron in which the cell body of the nerve is located within the gray matter of the spinal cord and the nerve fibre, or axon, extends to the muscle. Nerve '''axons''' can be very long permitting electrical impulses to be sent over long distances throughout the body. The information below specifically regarding neurons is inter-changable between the CNS and PNS and therefore links have been provided where appropriate on this page to the [[PNS_Structure_-_Anatomy_%26_Physiology|'''PNS Structure''']], where information specific to the PNS can be found.  

A typical neuron can be exemplified by a motor neuron in which the cell body of the nerve is located within the gray matter of the [[Spinal Cord - Anatomy & Physiology|spinal cord]] and the nerve fibre, or axon, extends to the [[Muscles - Anatomy & Physiology|muscle]]. Nerve '''axons can be very long''' permitting electrical impulses to be sent over long distances throughout the body. The information below specifically regarding neurons is interchangeable between the CNS and PNS and therefore links have been provided where appropriate on this page to the [[PNS Structure - Anatomy & Physiology|'''PNS Structure''']].  

===Basic Nerve Structure===

===Basic Nerve Structure===

The basic structure of a nerve is that of a cell body, or soma, which has a single long nerve fibre, or axon, attached at one end to the cell body and at the other end to another nerve cell body or to a structure requiring nerve impulses such as skeletal muscle. The interface between two nerves or a nerve and another structure is called the nerve synapse. The cell body of the nerve itself also contains numerous dendrites which increase it's surface area enabling other nerve axons to connect with the cell body. The cell body usually has connections with many other axons from other nerve cells with many synapses on the cell body. The axon of the nerve cell is usually surrounded by some form of insulating protection, or myelination. This protective layer is called the myelin sheath.  

The basic structure of a nerve is that of a '''cell body (soma)''', which has a '''single long nerve fibre (axon)''', attached at one end to the cell body and at the other end to another nerve cell body or to a structure requiring nerve impulses such as skeletal muscle. The interface between two nerves or a nerve and another structure is called the '''nerve synapse'''. The cell body of the nerve itself also contains numerous '''dendrites''' which increase its surface area enabling other nerve axons to connect with the cell body. The cell body usually has connections with many other axons from other nerve cells with many synapses on the cell body. The axon of the nerve cell is usually surrounded by some form of insulating protection, or '''myelination'''. This protective layer is called the myelin sheath.  

 

===Soma (Cell Body)===

===Soma (Cell Body)===

The soma, or cell body is the central part of the neuron and contains the nucleus of the cell, the rough and smooth endoplasmic reticulum, ribosomes and golgi apparatus. Similar processes that would be undertaken by any cell occur within the soma and due to the organelles it contains, the soma is where most protein synthesis occurs.

The soma, or cell body, is the central part of the neuron and contains the nucleus of the cell, the rough and smooth endoplasmic reticulum, ribosomes and golgi apparatus. Similar processes that would be undertaken by any cell occur within the soma and due to the organelles it contains, the soma is where most protein synthesis occurs.

===Dendrites===

===Dendrites===

The neuron's dendrites are effectively branching extensions of the cell body. Collectively, these branching structures of the dendrites is known as the "dendritic tree". The dendritic tree is the site where input to the neuron occurs via synapses with axons from other nerve cells. In most cases nerve impulses travel from other nerve cells to the cell body and are then conducted along the nerve cell's own axon to other cell bodies. However, dendrites themselves are unable to propagate nerve impulses in the manner of axons as dendrites are unable to secrete [[Neurotransmitters_-_Anatomy_%26_Physiology|neurotransmitters]]. Similarly axons do not possess the chemoreceptors that are found within the dendrites and are therefore unable to receive nerve impulses. Nerve impulses are therefore conducted in one direction only.

The neuron's dendrites are effectively branching extensions of the cell body. Collectively, these branching structures of the dendrites are known as the "dendritic tree". The dendritic tree is the site where '''input to the neuron''' occurs via synapses with axons from other nerve cells. In most cases nerve impulses travel from other nerve cells to the cell body and are then conducted along the nerve cell's own axon to other cell bodies. However, dendrites themselves are unable to propagate nerve impulses in the manner of axons as dendrites are unable to secrete [[Neurotransmitters - Anatomy & Physiology|neurotransmitters]]. Similarly axons do not possess the chemoreceptors that are found within the dendrites and are therefore unable to receive nerve impulses. Nerve impulses are therefore conducted in one direction only.

 

===Axon (Nerve Fibre)===

===Axon (Nerve Fibre)===

The axon is a very fine projection that can measure up to thousands of times the diameter of the soma in length. The axon carries nerve signals away from the soma. The structure and function of the axon is very similar between the CNS and the PNS.

The axon is a very fine projection that can measure up to thousands of times the diameter of the soma in length. The axon carries nerve signals away from the soma. The structure and function of the axon is very similar between the CNS and the PNS.  

 

Axon has been covered in detail within the [[PNS Structure - Anatomy & Physiology#Structure|PNS Structure and Anatomy]] page.

This has been covered in detail within the PNS Structure and Anatomy page so for further information please click [[PNS_Structure_-_Anatomy_%26_Physiology#Structure|here]].

 

Glial cells make up approximately 50% of the volume of the nervous system and the number of glial cells out-numbers the nerve cells by a factor of ten to one. The primary function of glial cell is to provide '''support to the neuronal cells'''. There are several different types of glial-style cell; in the PNS these are referred to as '''[[Schwann Cell|Schwann cells]]''' and whilst in the CNS they are referred to as '''Oligodendrocytes'''.  

Glial cells form a protective networked layer around the neuron within the CNS and also help to maintain the fluid content of the tissue surrounding the nerve. This protective layer is referred to as the '''myelin sheath''' and axons that are wrapped within this myelin sheath are able to conduct nerve impulses at higher speeds than those that are not wrapped. During foetal development the glial cells wrap around axons numerous times and as the glial cell matures it looses the majority of its cytoplasm. The remaining cellular structure consists of many layers of tightly packed lipid membranes around the axon.

Glial cells form a protective networked layer around the neuron within the CNS and also help to maintain the fluid content of the tissue surrounding the nerve. This protective layer is referred to as the '''myelin sheath''' and axons that are wrapped within this myelin sheath are able to conduct nerve impulses at higher speeds than those that are not wrapped. During foetal development the glial cells wrap around axons numerous times and as the glial cell matures it looses the majority of it's cytoplasm. The remaining cellular structure consists of many layers of tightly packed lipid membranes around the axon.

Periodically along the surface of the wrapped glial cell there are gaps approximately every 1-2mm. Each gap allows the environment external to the myelin sheath to be exposed to the axon for approximately 1-2υm. These gaps in the sheath are called the '''Nodes of Ranvier''' and are important in the conduction of impulses along the axon.

Periodically along the surface of the wrapped glial cell there are gaps approximately every 1-2mm. Each gap allows the environment external to the myelin sheath to be exposed to the axon for approximately 1-2υm. These gaps in the sheath are called the '''Nodes of Ranvier''' and are important in the conduction of impulses along the axon.

====Schwann Cell====

 

Details regarding the Schwann cell have been covered within the PNS Structure and Anatomy page so for further information regarding Schwann cells please click [[PNS_Structure_-_Anatomy_%26_Physiology#Schwann Cell|here]].

===Schwann Cell===

Details regarding the Schwann cell have been covered within the [PNS Structure - Anatomy & Physiology#Schwann Cell|PNS Structure and Anatomy]].

 

====Oligodendrocytes====

====Oligodendrocytes====

[[Image:oligodendrocyte.jpg|thumb|right|100px|Oligodendrocyte]]

[[Image:oligodendrocyte.jpg|thumb|right|100px|Oligodendrocyte]]