NEUROSCIENCE: PRACTICE EXAMINATION ANSWERS

SENSORY FUNCTION and SOMATIC SENSATION

1. D. Note that opening of nonselective channels leads to entry of Na ions because of the electrochemical gradient for Na

2. B. Lateral inhibition also increases contrast

3. C. Pacinian corpuscles are innervated by A-beta fibers

Note: There are two questions numbered "4"

4. B. Due to adaptation of the thermosensitive endings

4. C. One of the functions of the ascending reticular system is cortical arousal

5. D; I'd also accept E

6. B. Note that the larger fibers form the medial aspect of the dorsal root and the smaller fibers form the lateral aspect. Note also that a dorsal column lesion would cause loss of sensation on T5-T6-T7 and all more caudal dermatomes. Destruction of the T5-T6-T7 dorsal root ganglia would loss of all somatic sensation from the corresponding dermatomes, not just loss of touch-pressure

7. B. Cuneatus transmits information from the upper part of the body

8. C. The spinothalamic tracts is composed of second order neurons whose cell bodies are in the dorsal horn

9. C.

10. B.

11. E. This is the exception to the general rule that CNS nuclei contain synpatic connections; the mesencephalic nucleus contains cell bodies (but not synapses) from orofacial proprioceptors

12. D.

13. A. A sensory cortex column is a group of several hundred to several thousand cells arranged perpendicular to the sensory cortex which function as a unit; the column consists of six layers of cells, with each layer having a specific function. A column represents the location and modality or a property (such as line orientation) of the stimulus.

13. B. The primary somatosensory map is a representation of the body surface according to the area to which the surface projects on the postcentral gyrus. The map of the body is distorted; densely innervated areas with high acuity, such as the fingers and lips, occupy a relatively large area on the cortex while more sparsely innervated areas have a relatively small cortical representation.

13. C. A dermatome is the cutaneous area innervated fibers in a single dorsal root.