Neurological Exams: Sensory Nerves and Deep Tendon Reflexes

Sensory
Numbness, tingling, burning, and pain are abnormal feelings that may be felt in the back and/or extremities. Sometimes these symptoms radiate from one area into another. Sciatica is a good example of pain that can radiate into an extremity (leg).

Nerves originate from the spinal cord and divide into sensory and motor nerves. The sensory nerve gives sensation to the skin (dermatomes). The dermatomal patterns appear similar to a map on the body. For example, dermatomes on the trunk of the body correspond to the thoracic spinal nerve roots, those on the arms to the cervical spine nerve roots, and legs to the lumbar spinal nerve roots.

Dermatome Location	Corresponding Spinal Level
Shoulders	C4, C5
Inner and outer forearms	C6 and T1
Thumbs and little fingers	C6, C7, C8
Front of both thighs	L2
Middle and side of both calves	L4, L5
Little toes	S1

The physician may use a piece of cotton, a swab, pin or paperclip to test symmetrical feeling in the arms and legs. Abnormal responses may be indicative of a nerve root problem.

Deep Tendon Reflexes
Most people have experienced their physician tapping their knees with a rubber hammer. The normal response is a ‘knee jerk’. This is an example of a reflex, which is an involuntary muscular response elicited by the rubber hammer tapping the associated tendon.

When reflex responses are absent this could be a clue that the spinal cord, nerve root, peripheral nerve, or muscle has been damaged. When reflex response is abnormal, it may be due to the disruption of the sensory (feeling) or motor (movement) nerves or both. To determine where the neural problem may be, the physician tests reflexes in different parts of the body. See the following examples in the chart below.

Area Tested for Reflex	Corresponding Spinal Level
Biceps (upper arm)	C5-C6 (Cervical)
Distal Radius (forearm)	C6-C7
Triceps (elbow)	C7
Abdominal	T8, T9, T10, T11, T12 (Thoracic)
Quadriceps/Patellar (thigh, knee)	L3, L4 (Lumbar)
Ankle	S1 (Sacral)