Caudal Medulla

Question 1

Nucleus Gracilis

Answer 1

Second-order somatosensory neurons whose axons cross at this level to form the leg portion of the medial lemniscus. These neurons relay proprioception, vibration, and 2-point discrimination.

Question 2

Fasciculus cuneatus

Answer 2

Uncrossed branches of primary afferents, carrying tactile and proprioceptive information from the arm. Does NOT exist below T6.

Question 3

Nucleus cuneatus

Answer 3

Second-order somatosensory neurons whose axons cross at this level to form the arm portion of the medial lemniscus.

Question 4

Nucleus of the solitary tract, surrounding the solitary tract

Answer 4

This is much like a posterior column system for information from viscera. (X) Central branches of afferents from cranial nerves VII, IX, and X travel through the tract to convey taste to the upper or gustatory part of the nucleus. Only information from viscera reaches this caudal level. Taste = SVA; Visceral Portion = GVA.

Question 5

Dorsal motor nucleus of the vagus

Answer 5

Preganglionic parasympathetic neurons for thoracic and abdominal viscera. (GVE)

Question 6

Central canal

Answer 6

No description.

Question 7

Spinal trigeminal tract

Answer 7

Primary afferents from the ipsilateral side of the face, at this caudal level conveying information about pain and temperature, (like the STT).

Question 8

Spinal trigeminal nucleus

Answer 8

At this caudal level second order pain and temperature neurons whose axons cross the midline join the spinothalamic tract. Trigeminal pain and temperature afferents from the ipsilateral face reach the nucleus via the spinal trigeminal tract.

Question 9

Hypoglossal nucleus

Answer 9

Lower motor neurons for ipsilateral tongue muscles. (GSE) Tongue points toward lesion.

Question 10

Spinothalamic pathway

Answer 10

Mostly crossed fibers of second-order spinal neurons conveying pain and temperature information to the thalamus, reticular formation, and midbrain. Remember sensory fibers come in the lateral division of the dorsal root and synapse on nucleus proprius. Second order neurons cross the midline and then head north in the tract to the VPL.

Question 11

Nucleus ambiguous

Answer 11

Lower motor neurons for laryngeal and pharyngeal muscles (also contains preganglionic parasympathetic neurons for the heart). Mostly SVE for 9, 10, 11.

Question 12

Reticular formation

Answer 12

No description.

Question 13

Medial longitudinal fasciculus (MLF)

Answer 13

At this level, the fibers of the medial vestibulospinal tract (part of the descending MLF).

Question 14

Medial lemniscus

Answer 14

The principal ascending pathway for tactile and proprioceptive information. Originates in the contralateral posterior column nuclei and terminates in the thalamus (VPL). Fibers seen crossing from the nuclei cuneatus and gracilis are termed internal arcuate. Lemniscus means, “ribbon”.

Question 15

Raphe nuclei

Answer 15

Widely projecting serotonergic neurons that collectively blanket the CNS. Those in caudal brainstem levels like this project mainly to the spinal cord.

Question 16

Pyramid

Answer 16

Corticospinal fibers from the ipsilateral precentral gyrus (area 4) and adjacent areas of cerebral cortex. These are upper motor neurons that synapse on the anterior horn cells (lower motor neurons).