The Superficial (Cutaneous) Reflexes

Superficial reflexes are responses to stimulation of either the skin or mucous membrane. Cutaneous reflexes are elicited by a superficial skin stimulus, such as a light touch or scratch. The response occurs in the same general area where the stimulus is applied. Too painful a stimulus may call forth a defensive reaction rather than the desired reflex. Superficial reflexes are polysynaptic, in contrast to the stretch reflexes, which are monosynaptic. The superficial reflexes respond more slowly to the stimulus than do the stretch reflexes, their latency is longer, they fatigue more easily, and they are not as consistently present as tendon reflexes. The primary utility of superficial reflexes is that they are abolished by pyramidal tract lesions, which characteristically produce the combination of increased deep tendon reflexes and decreased or absent superficial reflexes. The superficial reflexes obtained most often are the abdominal and cremasteric. Unilateral absence of the superficial abdominal reflexes may be an early and sensitive indicator of a corticospinal tract lesion.

THE SUPERFICIAL ABDOMINAL REFLEXES

The superficial abdominal reflexes consist of contraction of the abdominal muscles, elicited by a light stroke or scratch of the anterior abdominal wall, pulling the linea alba and umbilicus in the direction of the stimulus (Figure 29.1). The response can be divided into the upper abdominal and lower abdominal reflexes. The anterior abdominal wall can be divided into four quadrants by vertical and horizontal lines through the umbilicus. Light stroking or scratching in each quadrant elicits the response, pulling the umbilicus in the direction of the stimulus. The stimulus may be directed toward, away, or parallel to the umbilicus; stimuli directed toward the umbilicus seem more effective. The response is a quick, flicking contraction followed by immediate relaxation. The responses are typically brisk and active in young individuals with good anterior abdominal tone. They may be sluggish or absent in normal individuals with lax abdominal tone, in those who are obese, or in women who have borne children.

THE SUPERFICIAL REFLEXES OF THE LOWER EXTREMITIES

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