sensory and reflex examination
Strength is only half of how the nervous system shows itself in the body. The other half is what a person can feel — the warmth of a cup, the pinprick of a needle, the position of a limb in the dark — and how the body's automatic loops respond when tapped. The sensory and reflex examination tests these quieter channels, mapping where feeling is dulled and how brisk the reflexes are.
The sensory part checks several distinct senses, because they travel through the spinal cord by different routes. The examiner tests light touch (a wisp of cotton), pinprick (sharp versus dull), temperature, vibration (a buzzing tuning fork on a bony bump), and joint position sense (moving a toe up or down with the eyes closed). Because the skin is supplied in bands by the spinal nerves, the pattern of numbness can point to exactly where the problem sits. The reflex part taps a tendon — at the knee, ankle, elbow — to trigger a quick muscle jerk; the examiner grades how strong this response is. Crucially, the direction of abnormality tells different stories: reflexes that are too brisk, sometimes with a fanning of the big toe known as a Babinski sign, point to a problem in the brain or spinal cord (an upper motor neuron lesion), while reflexes that are absent point to a problem in the peripheral nerve itself (a lower motor neuron lesion).
These tests matter because they help localize where in the long wiring of the nervous system something has gone wrong, and because lost sensation is dangerous in its own right — a person who cannot feel a pressure sore, a too-hot bath, or an ill-fitting brace can be injured without knowing. In rehabilitation, the sensory map shapes everything from how an amputee's socket is fitted to how often someone with a spinal cord injury must shift their weight to protect the skin.
A man complains his hand feels 'asleep'. Pinprick is dulled over the thumb, index and middle fingers but normal over the little finger, and the reflexes are normal. That sensory map — three and a half digits, sparing the little finger — fits compression of one specific nerve at the wrist far better than a problem in the brain.
The shape of numbness, not just its presence, points to where the wiring is damaged.
The key distinction is direction: overly brisk reflexes (with signs like Babinski) suggest an upper motor neuron lesion in the brain or cord, while absent reflexes suggest a lower motor neuron or peripheral nerve problem — they are not the same disease, and the examination is how you tell them apart.