brain, spinal cord, and nerve disorders
Neurologic Examination
Sensory Nerves
Sensory nerves carry information from the body to the brain about such things as touch, pain, heat and cold (temperature), vibration, the position of body parts, and the shape of objects. Each of these senses can be tested. Abnormal sensations or reduced perception of sensations may indicate damage to a sensory nerve, the spinal cord, or certain parts of the brain. Information from specific areas on the body’s surface, called Dermatomes , is carried to a specific location (level) in the spinal cord, then to the brain. Thus, doctors may be able to pinpoint the specific level of damage to the spinal cord by identifying the areas where sensation is abnormal or lost. The surface of the skin is divided into specific areas, called dermatomes. A dermatome is an area of skin whose sensory nerves all come from a single spinal nerve root. Sensory nerves carry information about such things as touch, pain, temperature, and vibration from the skin to the spinal cord. Spinal roots come in pairs—one of each pair on each side of the body. There are 31 pairs: There are 8 pairs of sensory nerve roots for the 7 cervical vertebrae. Each of the 12 thoracic, 5 lumbar, and 5 sacral vertebrae has one pair of spinal nerve roots. In addition, at the end of the spinal cord, there is a pair of coccygeal nerve roots, which supply a small area of the skin around the tailbone (coccyx). There are dermatomes for each of these nerve roots. Sensory information from a specific dermatome is carried by sensory nerve fibers to the spinal nerve root of a specific vertebra. For example, sensory information from a strip of skin along the back of the thigh, is carried by sensory nerve fibers to the 2nd sacral vertebra (S2) nerve root. Sensationin the skin is tested. Usually, doctors concentrate on the area where the person feels numbness, tingling, or pain. The best screening test for loss of sensation involves touching the skin of the face, body, and all four limbs with a pin and a blunt object (such as the head of a safety pin) to see if the person can feel them and tell the difference between sharp and dull. Doctors test both sides of the body. If doctors detect loss of sensation in a specific area, they test nearby areas to estimate the extent of the loss. This approach enables them to determine the abnormality's location in the brain, spinal cord, or peripheral nervous system. Gentle (light) touchis tested with a cotton wisp. Temperature sense(the ability to feel hot and cold) is tested with a tuning fork. Both prongs are cold, so the examiner warms one of them slightly by rubbing it. Then each of the prongs is touched to the person's skin. Vibration senseis also tested with a tuning fork. The fork is lightly tapped to make it vibrate. It is then placed on the joint of a finger to determine whether and how long the person feels the vibration. To testposition sense,doctors move the person’s finger or toe up or down and ask the person to describe its position without looking. Theability to identify the shape of an objectis tested by placing a familiar object, such as a key or safety pin, in a person's hand and asking the person to identify it without looking. Or doctors may trace letters or numbers on the palm of the person's hand and ask the person to identify them. If a person cannot identify them, the cortex of the brain (the outer layer of the cerebrum, the largest part of the brain) may be damaged. This part of the brain integrates and interprets sensory information from different sources. 