The nerve

*  Nerve

Nerves are organs of the PNS. 

There are three types of nerves in the nervous system :

* Sensory (afferent) nerves convey sensory information to the CNS.

* Motor (efferent) nerves convey motor impulses from the CNS to the muscles and glands.

* Mixed nerves: both sensory and motor Axons terminate as they contact other neurons, muscle cells, or gland cells.

¤ An axon transmits a nerve impulse at a specialized junction with another neuron called synapse.

Structure of peripheral nerve trunk :

* A nerve is a cable-like bundle of parallel axons.

* Three connective tissue wrappings:

1. Endoneurium Delicate layer of loose connective tissue.

2. Perineurium A cellular and fibrous connective tissue layer Wraps groups of axons into fascicles.

3. Epineurium A superficial connective tissue covering It is a thick layer of dense irregular fibrous connective tissue encloses entire nerve Provides support and protection

*  Myelin sheath

Myelin sheath is a fatty tubular covering around the axons It is composed of Cholesterol Fatty acids Phospholipids

 It is formed by:

1- Schwan’s cells in the PNS.

2- Oligodendrocytes in the CNS.

*The myelin sheath is white in color It is interrupted by an interval by the Node of Ranvier and Lanterman's clefts.