At the conclusion of this chapter, the reader will be able to:
Understand the varying etiological factors associated with peripheral nerve injury.
Understand the structural and cellular anatomy of the peripheral nervous system.
Appreciate the varying signs and symptoms associated with injury to the peripheral nervous system.
Understand the classification of peripheral nerve injuries.
Develop a systematic algorithm for the clinical assessment of peripheral nerve injuries.
Develop and modify physical therapy intervention strategies for peripheral nerve injuries.
STRUCTURAL AND FUNCTIONAL ANATOMY OF THE PERIPHERAL NERVOUS SYSTEM
Overview of Peripheral Nerve Anatomy
The peripheral nerve is a component of an intricate conduction system that serves as a mediator for bidirectional transport between the central nervous system (CNS) and other tissues. This conduction system is involved in regulation, homeostasis, repair, function, learning, posture, reproduction, mobility, and protection. For descriptive purposes, peripheral nerves are classified according to their function and site of CNS origin. Cranial nerves emerge from the base of the brain, spinal nerves originate in the spinal cord, and the autonomic system is intimately associated with the cranial and spinal nerves but differs in function, structure, and distribution (Figs. 19–1, 19–2).
Divisions of the peripheral nervous system.
Peripheral nerves. A. The entire body with plexus derivation. B. Upper extremity. C. Lower extremity.
The bidirectional movement of action potentials along the peripheral nerve enables afferent pathways, efferent pathways, and autonomic pathways. Afferent pathways are primarily sensory. The variability of sensory modalities are impressive, ranging from vision, hearing, smell, and taste to touch, pressure, and warmth, among others.1 Neurologic symptoms related to impairment are typically described as sensations additive to normal perception such as burning, tingling, hyperalgesia, or pain. Neurologic signs may consist of numbness, ataxia, orthostasis, loss of visual acuity, and dyskinesia. Fortunately, in humans there is a redundancy of sensory modalities that maintains function in the presence of sensory loss. Adequate balance, for example, requires the composite function of the visual, vestibular, and proprioceptive systems.
Efferent pathways are primarily motoric in function. This complex system requires a variety of both afferent and efferent neural tissues as well as contractile and noncontractile connective tissues. These structures work in harmony to provide coordinated movement patterns and locomotion (Table 19–1).
Table 19–1Peripheral Nervous System Pathways ||Download (.pdf) Table 19–1 Peripheral Nervous System Pathways
|PN PATHWAY ||CELL BODY LOCATION ||DIRECTION ||CLASS ||PRIMARY FUNCTIONS ||DYSFUNCTION |
|Afferent ||Dorsal root ganglion (DRG) ||Toward CNS synapsing in the dorsal horn ||Sensory ||Vision, hearing, smell, taste, rotational acceleration, linear acceleration, verticality, ...|