ABEM ABEM Anatomy & Neurophysiology 2 — Questions and Answers
Question 1: Which muscle is the primary abductor of the thumb and is commonly tested in thenar EMG?
- Flexor pollicis brevis
- Opponens pollicis
- Abductor pollicis brevis (Correct answer)
- Adductor pollicis
Correct answer: Abductor pollicis brevis
The abductor pollicis brevis is the most superficial thenar muscle and is the primary target for median nerve EMG assessment.
Question 2: The sural nerve is formed by contributions from which two nerves?
- Tibial and common peroneal nerves (Correct answer)
- Femoral and obturator nerves
- Sciatic and femoral nerves
- Saphenous and tibial nerves
Correct answer: Tibial and common peroneal nerves
The sural nerve is formed by the medial sural cutaneous nerve (from tibial) and the peroneal communicating branch (from common peroneal nerve).
Question 3: Which segment of the spinal cord is responsible for the Achilles tendon reflex?
- L2-L3
- L3-L4
- L4-L5
- S1-S2 (Correct answer)
Correct answer: S1-S2
The Achilles tendon reflex is mediated primarily by the S1 nerve root, with S2 contribution in some individuals.
Question 4: The lateral femoral cutaneous nerve exits the pelvis near which anatomical landmark?
- Greater sciatic notch
- Inguinal ligament near ASIS (Correct answer)
- Obturator foramen
- Femoral triangle
Correct answer: Inguinal ligament near ASIS
The lateral femoral cutaneous nerve passes under or through the inguinal ligament near the anterior superior iliac spine, where it can be compressed.
Question 5: What is the functional consequence of demyelination on nerve conduction velocity?
- Conduction velocity increases
- Conduction velocity is unchanged
- Conduction velocity decreases (Correct answer)
- Action potential amplitude increases
Correct answer: Conduction velocity decreases
Demyelination disrupts saltatory conduction, forcing the action potential to travel continuously along the axon, markedly slowing conduction velocity.
Question 6: Which nerve supplies sensation to the medial aspect of the forearm?
- Medial cutaneous nerve of the forearm (Correct answer)
- Lateral cutaneous nerve of the forearm
- Medial brachial cutaneous nerve
- Radial sensory nerve
Correct answer: Medial cutaneous nerve of the forearm
The medial cutaneous nerve of the forearm (medial antebrachial cutaneous nerve) provides sensory innervation to the medial forearm.
ABEM ABEM Anatomy & Neurophysiology 2
Which muscle is the primary abductor of the thumb and is commonly tested in thenar EMG?