Question

7) Describe a dermatome and trace the complete route of sensory information from a dermatome into to the spinal cord. Also, describe the disorders of peripheral neurophathy and shingles and their connections to dermatomes. 8) Describe the specific steps of the patellar reflex. Explain how the CONTROL of the plantar reflex in adults is different.

Answer 1

Solutions

7.
A dermatome refers to area or region of skin that is served by a single spinal nerve. Usually, knowledge of dermatomes is required to locate and analyze lesions in the nerve root or spinal cord. In the body, there are 8 cervical nerves, 12 thoracic nerves, 5 lumbar nerves and 5 sacral nerves that are responsible for the relaying of sensory information from the particular area of the skin to the brain. Each dermatome has a nerve root, which is the contact point of information to the spine. Whenever a particular region of the skin experiences a sensation (pain, pressure, temperature, etc.), the sensation travels first through the dermatome, and then into the central nervous system, via the nerve root. The CNS then transmits this information to the brain.

Peripheral neuropathy refers to a condition in which the nerves in the peripheral nervous system become damaged. It can be caused due to drugs, shingles, kidney disorders, or even vitamin deficiencies. Neuropathies are diagnosed by sensory exams, blood tests, or biopsies. Treatment focuses on the underlying root cause leading to the disorder.

Shingles is caused by the Varicella zoster virus (also the causative agent of chicken pox). The virus majorly affects neurons, and can be dormant for years before becoming active. When it reactivates, it affects the entire dermatome in which the affected neuron belonged to in the first place. The outcome is seen in the form of rashes on the body. When traversing through a dermatome, the rashes do not occur cross the midline of the body either in the front or back.

8.
The Patellar reflex, also called the knee-jerk reflex, refers to the sudden kicking movement observed in the lower leg as a response to a sharp tap on the patellar tendon. The tendon is situated below the kneecap. The information passes from the sensory neuron into the CNS, and the brain, which sends the response signal via the motor neuron. The response dictates the slight stretching of the quadriceps, and contraction of the muscles. This results in a kicking motion.

The plantar reflex is the response elicited when the sole of the foot is lightly struck with a blunt instrument. In normal adults, this stimulus would cause a downward response of the hallux (flexion). If there are any disorders of the spinal cord or brain, the stimulus would cause an upward response (extension) of the hallux. The response is also known as the Babinski response or Babinski sign.