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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) 1