Nerve Innervation and Muscle Function Quiz

Sensory Innervation

• The radial nerve is responsible for extending all the joints in the arm and proximal fingers
• The median nerve controls the thumb side of the hand and wrist
• The ulnar nerve controls the pinky side of the hand and wrist

Muscle Flexion & Extension

• The flexor digitorum profundus is responsible for flexion at the distal interphalangeal joint
• The flexor digitorum superficialis and the flexor digiti minimi muscles contribute to flexion of the proximal interphalangeal joint
• Muscles contributing to extension of the distal interphalangeal joint are the extensor digitorum, extensor indicis, and extensor digiti minimi

Thumb Muscles

• Muscles contributing to movement of the thumb are innervated by the following nerves: radial, ulnar, median
• The nerves are easily remembered by the mnemonic RUM, which means radial, ulnar, median
• The superficial peroneal nerve controls eversion of the foot
• The deep peroneal nerve controls dorsiflexion of the foot and toe extension
• The tibial nerve controls plantar flexion, inversion, and toe flexion

Common Plexus and Nerve Syndromes

• The brachial plexus is located in the neck and shoulder and is often affected by trauma
• Brachial plexus injuries can cause upper trunk injury (Erb-Duchenne palsy)
• The symptoms of Erb-Duchenne palsy are weakness of external rotation, abduction and elbow flexion of the arm, as well as decreased tone and absent biceps reflex
• The ulnar nerve can be compressed in the cubital canal at the elbow, which can be treated by surgically translocating the nerve to the flexor side
• Ulnar nerve entrapment in the hand can occur when it passes over the hamate bone, resulting in weakness in finger adduction and abduction
• Chronic median and ulnar nerve lesions result in thenar and hypothenar atrophy
• The femoral nerve can be injured by pelvic surgery, retroperitoneal hematoma, or pelvic mass
• Sciatic neuropathy can be caused by posterior hip dislocation, acetabular fracture, or intramuscular injection in the buttocks

Common Plexus and Nerve Syndromes (Continued)

• Femoral neuropathy can be caused by compression of the femoral nerve by a retroperitoneal hematoma or pelvic mass
  • weakness of thigh flexion and knee extension, loss of the patellar reflex, and sensory loss in the anterior thigh
• Sciatic neuropathy can be caused by posterior hip dislocation, acetabular fracture, or intramuscular injection in the buttocks
  • weakness of all foot and ankle muscles and of knee flexion, loss of the Achilles tendon reflex, and sensory loss in the foot and lateral leg below the knee

Clinical Cases

• Case 9.1: A patient presents with weakness in left arm external rotation, abduction, and elbow flexion, with decreased tone and absent biceps reflex
  • The patient was diagnosed with Erb-Duchenne palsy, affecting C5 and C6 innervated muscles, caused by left shoulder traction at birth
• Case 9.2: A patient presents with right apical lung cancer extending into the region of the brachial plexus
  • T1-weighted coronal MRI scan of the chest reveals a tumor, causing compression of the brachial plexus
  • Symptomology in such a case may include Horner’s syndrome, sensory changes in the T1 dermatome of the upper medial arm or involvement of hand muscles innervated by the median nerve
• Case 9.3: A patient presents with hand weakness and numbness following a blow to the medial arm
  • The patient had decreased pinprick and light touch sense along the lateral surface of the hand, and their thumb opposition, second and third finger flexors, and wrist flexion and abduction were weakened
  • The patient experienced compression of the median nerve and ulnar nerve resulting from damage to the brachial plexus due to the blow to the medial arm