Download Fundamentals on Peripheral Nerves

Fundamentals on Peripheral Nerves
Types of Nerve Fibers in Peripheral Nerves
Although there are many different ways of classifying nerve fibers, in this course we will use only
a very simple method based primarily on the direction of impulse transmission. Fundamentally, nerve
fibers can be divided into AFFERENT FIBERS which conduct impulses toward the central nervous
system and EFFERENT FIBERS which conduct impulses away form the central nervous system. The
efferent fibers can be further subdivided into three types: 1) EFFERENT FIBERS TO SKELETAL
MUSCLE, 2) EFFERENT FIBERS TO AUTONOMIC GANGLIA, and 3) EFFERENT FIBERS
TO SMOOTH MUSCLE, GLANDS, or CARDIAC MUSCLE. The latter two types of efferent fibers
are more commonly referred to as PREGANGLIONIC EFFERENT FIBERS and
POSTGANGLIONIC EFFERENT FIBERS.
Afferent
Afferent
Efferent
Efferent to skeletal muscle
Efferent to Autonomic Ganglia (preganglionic
efferent)
Efferent to smooth muscle, cardiac muscle, or
glands (postganglionic efferent)
Only rarely are all four of these types of nerve fibers found in a single nerve. Most nerves have only two
or three of these fiber types.
Fiber Composition of the Roots and Rami of Spinal Nerves
Dorsal Roots1. Afferent fibers only.
Ventral Roots1. Efferent Fibers to skeletal muscle (all ventral roots)
2. Preganglionic efferent fibers (T1-L2 and S2-S4 only
Branches to Skeletal Muscles- all branches to skeletal muscles and all nerves that supply such
branches (e.g., anterior primary rami, posterior primary rami, etc.) have three types of fibers:
1. Efferent fibers to skeletal muscle
2. Afferent fibers
3. Postganglionic efferent fibers (to smooth muscle in the walls of the blood vessels that
supply the muscle)
Gray Rami
1. Postganglionic Efferent Fibers
White Rami
1. Preganglionic Efferent Fibers
2. Afferent Fibers (from viscera, i.e., visceral afferents)
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