The Nerves

A nerve is a cable-like collection of peripheral axons (the long slender, projections of the neurons) that are enclosed within a dense casing of connective tissue (this tissue is known as epineurium).

Some facts about nerves, they:

• Are only ever located in the peripheral nervous system
• Provide a route for electrochemical nerve impulses to travel along
• Convey information in the form of electrochemical impulses (commonly referred to as nerve impulses). These impulses originate from the individual neurons that constitute the nerve.
• Relay information through their impulses at an extremely rapid rate, often up to speeds of 120 m/s 
• Can be damaged by physical injury, autoimmune diseases, infection, swelling or failure of surrounding blood vessels
• Cause discomfort, pain, numbness, weakness and even paralysis when they are damaged

Classification of Nerves

Functional categorisation;

• Motor Nerves – These conduct information from the central nervous system to the muscles to advise the muscles how to behave and react.
• Sensory Nerves – Information is received from the sensory neurons (receptors) and passed onto the central nervous system. 

There are three common types of nerves;

• Afferent Nerves – these types of nerves conduct and transport signals from the sensory neurons to the central nervous system. 
• Efferent Nerves – there nerves conduct and transport signals in the opposite way to the afferent nerves, from the central nervous system to the muscles or glands. Their signals are conducted through motor neurons.
• Mixed Nerves – Some nerves are capable of conducting and transporting both information received from sensory neurons and commands to muscles and glands from the motor neurons. This is because they contain both afferent and efferent axons. 

Regardless the type of nerve, it can be classified into one of two categories; 

• Spinal Nerves – innervate much of the body, and connect through the spinal column to the spinal cord.
• Cranial Nerves – innervate regions of the head and connect directly to the brainstem.

Complete Process

When the sensory neurons detect stimuli they pass this information onto the afferent nerves who convey the information back to the central nervous system. The brain then assesses and analyses the information and distributes its orders for response to the muscles and glands through the efferent nerves.