NBME Histology 3 — Questions and Answers
Question 1: Which feature distinguishes cardiac muscle from both skeletal and smooth muscle on light microscopy?
- Striations
- Peripheral nuclei
- Intercalated discs (Correct answer)
- Involuntary control
Correct answer: Intercalated discs
Intercalated discs are unique to cardiac muscle and contain gap junctions and desmosomes that electrically and mechanically couple cardiomyocytes.
Question 2: Nissl bodies, seen in the neuronal soma, represent which ultrastructural organelle?
- Smooth endoplasmic reticulum
- Golgi apparatus
- Rough endoplasmic reticulum with ribosomes (Correct answer)
- Mitochondria clusters
Correct answer: Rough endoplasmic reticulum with ribosomes
Nissl bodies are stacks of rough ER studded with ribosomes, reflecting the neuron's high protein synthesis demands.
Question 3: In the peripheral nervous system, which glial cell forms the myelin sheath around a single axon segment?
- Oligodendrocyte
- Schwann cell (Correct answer)
- Astrocyte
- Microglia
Correct answer: Schwann cell
Each Schwann cell myelinates one segment of a single PNS axon, whereas one oligodendrocyte myelinates multiple CNS axons.
Question 4: Nodes of Ranvier are gaps in the myelin sheath where the axonal membrane is exposed. What is their primary functional significance?
- Provide structural support to the axon
- Allow saltatory conduction to increase impulse speed (Correct answer)
- Serve as sites of synapse formation
- Anchor the axon to connective tissue
Correct answer: Allow saltatory conduction to increase impulse speed
Action potentials jump between nodes (saltatory conduction), dramatically accelerating nerve impulse propagation in myelinated fibers.
Question 5: Satellite cells surrounding neuronal cell bodies in dorsal root ganglia are analogous to which CNS glial cell type?
- Microglia
- Oligodendrocytes
- Astrocytes (Correct answer)
- Ependymal cells
Correct answer: Astrocytes
Satellite cells in peripheral ganglia support and regulate the microenvironment of neuronal somas, analogous to astrocyte function in the CNS.
Question 6: A biopsy of skeletal muscle shows central nuclei in many fibers. This finding is most consistent with which condition?
- Normal mature skeletal muscle
- Muscle regeneration after injury (Correct answer)
- Denervation atrophy
- Myasthenia gravis
Correct answer: Muscle regeneration after injury
Centrally located nuclei in skeletal muscle fibers indicate regenerating myofibers, as mature fibers have peripherally located nuclei.
Question 7: Which structural feature of smooth muscle cells allows for coordinated contraction of the bladder wall?
- Sarcomeres with Z-discs
- T-tubule system
- Gap junctions between cells (Correct answer)
- Intercalated discs
Correct answer: Gap junctions between cells
Gap junctions electrically couple smooth muscle cells in visceral (unitary) smooth muscle, enabling coordinated wave-like contractions.
NBME Histology 3
Which feature distinguishes cardiac muscle from both skeletal and smooth muscle on light microscopy?