Palmar Grasp Reflex(Archived)

The palmar grasp reflex is a primitive, prehensile, involuntary response to a mechanical stimulus present in a newborn. This appears around 16 weeks of gestation and can be elicited in preterm infants as young as 25 weeks of postconceptional age (see Image. Palmar Grasp Reflex). To elicit the reflex, the infant is laid in a symmetrical supine and comfortable position while he or she is awake. The examiner strokes the palm of the infant with his or her index finger. The response to this stimulus comprises 2 phases: finger closure and clinging. The infant's fingers undergo flexion to enclose the examiner's finger (finger closure). The pressure applied to the palm produces traction on the fingers' tendons, leading to the clinging action. The thumb is not affected by this reflex. The higher brain centers regulate the palmar grasp, though it is a spinal reflex. The afferent nerve fibers include the ulnar and median sensory nerves that supply the palmar surface. The spinal relay center is in the cervical spinal cord, and the efferent nerve fibers have the motor nerves that supply the hand's flexors and adductors. The premotor cortex, supplementary cortex, and cingulate motor cortex of the brain are implicated in controlling the grasp reflex through the spinal interneurons.