NBME Histology 3

Question 1

Which feature distinguishes cardiac muscle from both skeletal and smooth muscle on light microscopy?

Accepted Answer

Intercalated discs

Answer

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?

Accepted Answer

Rough endoplasmic reticulum with ribosomes

Answer

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?

Accepted Answer

Schwann cell

Answer

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?

Accepted Answer

Allow saltatory conduction to increase impulse speed

Answer

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?

Accepted Answer

Astrocytes

Answer

Satellite cells in peripheral ganglia support and regulate the microenvironment of neuronal somas, analogous to astrocyte function in the CNS.

NBME Practice Test