Neurological Exams: Sensory Nerves and Deep Tendon Reflexes
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|
|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|
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|
|Abdominal||T8, T9, T10, T11, T12 (Thoracic)|
|Quadriceps/Patellar (thigh, knee)||L3, L4 (Lumbar)|