Question
What is the anatomical origin of the mammillary body, a structure located beneath the brain’s surface, and what is its relationship to the limbic system? Additionally, which neural pathway provides afferent fibers to the mammillary body?
| A. |
Corpus callosum
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| B. |
Thalamus
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| C. |
Pituitary gland
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| D. |
Fornix
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Show Answer
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Correct Answer » D
Explanation
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Clinical Reasoning for the Correct Answer:
– The mammillary bodies are paired structures on the undersurface of the brain, part of the hypothalamus.
– They are integral to the limbic system, acting as relay nuclei within the Papez circuit (limbic pathway for memory and emotion).
– The fornix is the principal pathway delivering afferent fibers from the hippocampus to the mammillary bodies.
Why Option A (Corpus callosum) is Incorrect:
– The corpus callosum is a large white matter tract connecting the two cerebral hemispheres.
– It does not provide fibers to the mammillary bodies and is not directly involved in the limbic memory circuit.
– Typical corpus callosum lesions cause disconnection syndromes, not memory impairment related to mammillary function.
Why Option B (Thalamus) is Incorrect:
– The thalamus relays sensory information and has roles in consciousness and alertness.
– It receives efferent projections from the mammillary bodies (via the mammillothalamic tract), not afferent input to them.
– Thalamic connections complete the Papez circuit downstream, but do not provide primary afferents to mammillary bodies.
Why Option C (Pituitary gland) is Incorrect:
– The pituitary gland is an endocrine organ below the hypothalamus.
– It has no direct neural connection with the mammillary bodies; it receives hypothalamic releasing/inhibiting hormones via the hypothalamo-hypophyseal portal system.
– Pituitary lesions do not affect mammillary bodies or limbic memory circuits.
Why Option D (Fornix) is Correct:
– The fornix originates from the hippocampus and projects to the mammillary bodies.
– This hippocampal→fornix→mammillary body pathway is vital for memory consolidation.
– Lesions in the fornix or mammillary bodies are associated with amnestic syndromes (e.g., in Wernicke–Korsakoff syndrome).
