The purpose of the motor examination is to localize neurologic pathology by looking for characteristic distributions of muscle weakness.

Examination of muscle strength is an essential part of all neurologic examinations and is particularly important in the examination of patients who present with a complaint of weakness. The choice and extent of muscles to be tested should be dictated by the clinical scenario; for example, the muscles that should be examined in a patient in a screening neurologic examination would differ from that of a patient who complains of weakness in an extremity. The assessment for drift of the outstretched arms (see Chapter 25, Examination of Upper Extremity Muscle Strength) should also be performed routinely. Muscle tone, a component of the motor examination that does not need to be assessed in all patients but is helpful in many situations, is described in Chapter 27, Examination of Tone.

The pathway for muscle movement begins in nerve cells—the upper motor neurons—located on the precentral gyrus of each frontal lobe. The axons from these nerve cells become the corticospinal tracts, which travel through the internal capsule and into the brainstem; each corticospinal tract then crosses in the low medulla to the opposite side and continues downward through the spinal cord. Within the spinal cord, the corticospinal tracts on each side synapse with nerve cells in the anterior horns of the ipsilateral spinal cord gray matter. Axons from these second-order neurons—the lower motor neurons—leave the spinal cord as the cervical, thoracic, or lumbosacral nerve roots. The nerve roots in the extremities become the brachial or lumbosacral plexus and then the peripheral nerves, which innervate muscles through the neuromuscular junction.

None.