LENGTH

• The part, where axon is attached to the cell body of the nerve cell, is known as axon hillock. This segment comprises of specialized protein complexes which help in initiating the electrical impulse. Thus, the main function of this part is to generate the impulse and is 25μm in length usually.
• The remainder of axon lacks these complexes but contains special proteins in the membrane which help transmitting the signal.
• The membrane of axon is known as axolemma.
• An axon can be myelinated or unmyelinated. That means axon may have a myelin sheath around its length. Myelin sheath is actually a fatty substance that forms a protective coating around axon and acts as insulator not dissipating the electric impulse around. It also speeds up the conduction which is known as saltatory conduction. The mechanism underlying is that, the points where myelin sheath is absent are called Nodes of Ranvier, the impulses jump over these nodes hence speeding up the conduction.

TYPES OF AXONS

On the basis of presence and absence of myelin sheath and the diameter of axon, it can be divided into several types:

•     Type Aα: Diameter 13-20μm and is myelinated having conduction velocity 80 to 120m/sec.
•     Type Aβ: Diameter 6-12μm and is myelinated having conduction velocity 33 to 75m/sec.
•     Type Αγ: Diameter 5-8μm and is myelinated having conduction velocity 4 to 24m/sec.
•     Type Aδ: Diameter 1-5μm and is thin myelinated having conduction velocity 3 to 30m/sec.
•     Type B: Diameter 1-5μm and is myelinated having conduction velocity 3 to 15m/sec.
•     Type C: Diameter 0.2-1.5μm and is unmyelinated having conduction velocity 0.52m/sec.

FUNCTIONS OF AXON

Axon conduct electrical impulses to

•     Muscle fibers
•     Golgi tendon organs
•     Cutaneous mechanoreceptors in skin
•     Free nerve endings of touch, pressure and temperature
•     Preganglionic and postganglionic fibres of autonomic nervous system