Q 1.28. Peripheral Nervous System (PNS) Syndromes of Damage

The peripheral nervous system (PNS) connects your brain and spinal cord to the rest of your body. It’s like the network of secondary roads branching out from the main highway (the central nervous system). Let’s explore it:

1. Peripheral Nerves:

• • These are the workhorses of the PNS. Each nerve consists of bundles of nerve fibers (axons) and their connective tissue coverings.
  • Afferent neurons transmit information toward the CNS (sensory neurons), carrying sensations like touch, pain, temperature, and proprioception (position in space).
  • Efferent neurons transmit impulses from the CNS (motor neurons), controlling skeletal muscles.
  • Some afferent neurons also handle special senses like smell, vision, hearing, and balance.

2. Functional Components:

• • Autonomic Nervous System (ANS):
    • Involuntary control over cardiac, smooth, and glandular cells.
    • Divided into sympathetic (fight-or-flight) and parasympathetic (rest-and-digest) arms.
  • Somatic Nervous System (SNS):
    • Voluntary control over skeletal muscles and somatic sensations.

In other words the PNS consists of nerves outside the brain and spinal cord, including sensory, motor, and autonomic nerves. It plays a crucial role in transmitting signals between the central nervous system (CNS) and the rest of the body. Damage to the PNS can result in various syndromes, each presenting distinct clinical features.

Syndromes of Peripheral Nervous System Damage:

1. Peripheral Neuropathy:

• • Symptoms: Numbness, tingling, burning sensations, muscle weakness, and pain, typically in the hands and feet (glove-and-stocking distribution).
  • Causes: Diabetes, infections, autoimmune diseases, toxins, and certain medications.

2. Carpal Tunnel Syndrome:

• • • Symptoms: Numbness, tingling, and weakness in the hand and fingers, particularly the thumb, index, and middle fingers.
    • Causes: Compression of the median nerve as it travels through the carpal tunnel in the wrist.

3. Guillain-Barré Syndrome (GBS):

• • Symptoms: Rapid-onset muscle weakness, starting in the legs and progressing upward, potentially leading to paralysis.
  • Causes: Often triggered by infections; it is an autoimmune response where the body attacks the peripheral nerves.

4. Bell’s Palsy:

• • Symptoms: Sudden, temporary weakness or paralysis of the facial muscles on one side, leading to drooping of the mouth and eyelid.
  • Causes: Inflammation or viral infection affecting the facial nerve (cranial nerve VII).

5. Radiculopathy:

• • Symptoms: Pain, weakness, numbness, or difficulty controlling specific muscles, depending on the affected nerve root.
  • Causes: Compression or irritation of nerve roots, often due to herniated discs or spinal stenosis.

6. Charcot-Marie-Tooth Disease:

• • Symptoms: Progressive muscle weakness, atrophy, and sensory loss, starting in the feet and legs and eventually affecting the hands.
  • Causes: Genetic mutations affecting peripheral nerve function.

Diagnosis and Management: Diagnosis typically involves clinical evaluation, electromyography (EMG), nerve conduction studies, blood tests, and imaging. Treatment varies based on the underlying cause and may include medications, physical therapy, surgery, or addressing the specific cause, such as controlling blood sugar in diabetes.

References:

1 catalog.ninds.nih.gov

2 merckmanuals.com

3 mayoclinic.org

4 link.springer.com