The peripheral nerves are bundles containing many individual nerve-fibers, and are similar to telephone cables carrying many individual wires. There are two basic types of nerve-fibers–motor and sensory. The motor fibers carry electrical impulses outward from the spinal cord to the muscles, causing them to contract. The sensory fibers carry electrical impulses inward from the skin, joints and other structures to the spinal cord, providing the nervous system with inputs, among others, concerning the senses of touch, pain and temperature.
Peripheral nerves can be pinched or injured in specific locations. When this occurs, the problem is called a “mononeuropathy,” meaning that a single peripheral nerve is affected. Examples of mononeuropathy include carpal tunnel syndrome in which the median nerve is pinched at the wrist, and peroneal neuropathy in which the peroneal nerve is injured near the knee. Because the median and peroneal nerves contain both motor and sensory fibers, people with these conditions can experience both weakness and numbness.
In carpal tunnel syndrome, certain muscles of the thumb can become weak, while numbness affects the...