Medical Lecture Notes

A BLOG FOR all medical students contains a lot of knowledge in beautiful perfect notes.

Saturday, 22 July 2017

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.

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