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George E. Carvell, PhD, PT   University of Pittsburgh
BC&P fig 12.1  p 398
BC&P fig 13.6  p 442
Dorsal root afferents innervate somatosensory receptors located in the skin and deep tissues (fig 12.1). Touch, pressure, temperature, pain, and position sense are modalities associated with these afferents. Clinical sensory exam tests the integrity of these modalities. However, somatosensory deficits may result from lesions anywhere along the sensory pathway from periphery to brain. Clinical sensory nerve conduction studies may be used to rule-in or rule-out peripheral nerve involvement. Other sensory conduction tests may rule-out central pathway disorders (somatosensory evoked potential or SSEP Studies: stim peripheral nerve & record over scalp).
Alpha motor axons in the ventral roots originate from alpha motor neurons in the ventral horn of the spinal cord. Skeletal muscle fibers are innervated by these motor axons via functional patterns. The smallest functional unit is the motor unit (fig 13.6a). Muscles are innervated by Motoneuronal pools (fig 13.6b). Muscles can be tested by a manual muscle test (MMT) to reveal specific weakness. However, weakness may be caused by lesions in the CNS or PNS and the MMT may not be appropriate with certain forms of paresis. Clinical Needle Electromyographic (EMG) exam may be used to rule-in or rule-out certain forms of peripheral motor disorders (nerve or muscle). In addition, motor nerve conduction tests may be performed to assess the viability of alpha motor axonal conduction. Special test may be performed to rule-out neuromuscular junction disease.
Motor Unit