BIOLOGY Volume 1 - A Guide to General Biology - 2004

6. HISTOLOGY

6.6. Nervous Tissue

6.6.2. Nerves

Nerves consist of bundles of nerve fibers surrounded by a Connective Tissue sheath called the epineurium. Inward extensions of the epineurium, known as the perineurium, divide the bundle of nerve fibers into smaller fascicles, while each individual fiber is covered by its own connective tissue sheath known as the endoneurium (Fig. 6.31). Nerves are classified into two types based on the direction in which they transmit impulses. Sensory or afferent nerves, such as the olfactory, optic, and vestibulocochlear nerves, transmit impulses to the Central Nervous system, whereas efferent or motor nerves, such as the oculomotor, abducens, or trochlear nerves, transmit them away from the central nervous system. Mixed nerves transmit impulses in both directions (for example, all Spinal Nerves).

The conduction of nerve impulses is discussed in Chapter 17.

Class="center">

Fig. 6.31. Diagrammatic representations of a myelinated nerve fiber in cross-section (A) and a segment of such a fiber (B).