AN58.1-4 | Medulla Oblongata — Practice Quiz

Correct! The pyramid contains corticospinal (pyramidal) tract fibres descending from the motor cortex to the spinal cord. 85% decussate at the caudal medulla (pyramidal decussation), forming the lateral corticospinal tract.

Pyramidal tract = corticospinal + corticobulbar. The "pyramids" are the anterior medullary ridges containing corticospinal fibres. Pyramidal decussation = where 85% of fibres cross. Injury above decussation = contralateral UMN weakness. Injury at decussation = cruciate paralysis (rare).

Incorrect. Pyramid = corticospinal fibres. Medial lemniscus lies dorsal to the pyramid. Spinothalamic = lateral. Olivocerebellar = from inferior olivary nucleus to cerebellum.

Correct! CN XII rootlets emerge from the preolivary sulcus (between the pyramid medially and the olive laterally). CN IX, X, XI emerge from the postolivary sulcus (lateral to the olive).

Medulla surface: MEDIAL = pyramid (corticospinal). Between pyramid and olive (preolivary) = CN XII. LATERAL to olive (postolivary) = CN IX, X, XI. "Twelve angry men (XII) sit between the pyramid and olive; Nine, Ten, Eleven leave from behind the olive."

Incorrect. CN XII = preolivary sulcus (between pyramid and olive). CN IX, X, XI = postolivary sulcus (lateral to olive). This distinction is tested in anatomy practicals.

Correct! Internal arcuate fibres = axons of 2nd order neurons from nucleus gracilis (lower limb) and nucleus cuneatus (upper limb). They sweep anteromedially and cross the midline (sensory decussation) to form the medial lemniscus on the opposite side.

Medial lemniscal pathway relay: DRG (1st order) → spinal cord posterior column → nucleus gracilis/cuneatus in medulla → internal arcuate fibres cross → medial lemniscus → VPL thalamus → somatosensory cortex (3rd order). The crossing at the medulla is why posterior column lesions above the medulla cause contralateral loss.

Incorrect. Internal arcuate fibres = from nucleus gracilis and cuneatus (posterior column relay nuclei). After crossing, they form the medial lemniscus. Clarke's column gives rise to the posterior spinocerebellar tract, not the arcuate fibres.

Correct! Nucleus ambiguus = SVE (special visceral efferent / branchiomotor) for pharyngeal and laryngeal muscles via CN IX (stylopharyngeus), CN X (pharynx and larynx), and the cranial root of CN XI (that joins the vagus).

In bulbar palsy, the nucleus ambiguus is damaged → LMN palsy of pharynx and larynx → dysphagia (difficulty swallowing), dysphonia (hoarseness), nasal regurgitation. Gag reflex: afferent = CN IX (sensory), efferent = CN X (via nucleus ambiguus motor). Loss of gag reflex = CN IX or X nucleus/nerve damage.

Incorrect. Nucleus ambiguus → pharynx + larynx → CN IX, X, XI (cranial). CN XII motor nucleus → tongue. CN V motor nucleus → mastication. CN VII motor nucleus → facial expression.

Correct! The dorsal (motor) nucleus of the vagus is the GVE (general visceral efferent) nucleus — preganglionic parasympathetic fibres to thoracic and abdominal viscera (heart, lungs, GI tract down to the left colic flexure).

Vagal nuclei: (1) Dorsal motor nucleus = GVE parasympathetic. (2) Nucleus ambiguus = SVE motor (pharynx/larynx). (3) NTS = GVA + SVA (visceral sensory + taste). (4) Spinal nucleus of CN V = GSA (skin of ear). Pharmacology: Atropine blocks vagal (muscarinic) effects on heart → tachycardia. Used in bradycardia from vagal dominance.

Incorrect. Dorsal nucleus of vagus = preganglionic parasympathetic (GVE) to thoracoabdominal viscera. Motor to pharynx/larynx = nucleus ambiguus. Taste = nucleus tractus solitarius. Tongue = hypoglossal nucleus.

Correct! Descending sympathetic fibres from the hypothalamus travel through the lateral tegmentum of the brainstem and cervical cord to reach T1. Lateral medullary infarct damages these descending sympathetics → ipsilateral Horner's syndrome (ptosis, miosis, anhidrosis).

3-neuron sympathetic pathway to the eye: (1) Hypothalamus → lateral tegmentum of brainstem → ciliospinal centre (T1 lateral horn) [CENTRAL]. (2) T1 → over lung apex → superior cervical ganglion [PREGANGLIONIC]. (3) Along ICA/ECA → dilator pupillae + Müller's muscle + sudomotor [POSTGANGLIONIC]. Horner's in Wallenberg = 1st order lesion. Horner's from Pancoast = 2nd order. Horner's from carotid dissection = 3rd order.

Incorrect. Horner's in Wallenberg = damage to descending sympathetic fibres in the LATERAL MEDULLARY TEGMENTUM (not the peripheral sympathetic chain). These are the central fibres (1st order of the 3-neuron sympathetic pathway to the eye).

Correct! Medial medullary syndrome (Dejerine): contralateral hemiplegia (right) + contralateral loss of touch/vibration/proprioception (right) from medial lemniscus damage + IPSILATERAL LMN tongue palsy (left tongue deviation = left CN XII lesion = LEFT side lesion). Left medial medullary infarct.

Key distinction: LATERAL medullary = no limb weakness (pyramids spared), ipsilateral Horner + ataxia + facial pain/temp loss, contralateral body pain/temp. MEDIAL medullary = contralateral hemiplegia + sensory loss, ipsilateral LMN tongue palsy. Tongue always deviates TOWARD the side of LMN lesion (the good side pushes the tongue over).

Incorrect. Tongue in LMN palsy deviates TOWARD the lesion. Left tongue deviation = LEFT CN XII damage = LEFT medial medullary infarct. Right hemiplegia = left pyramid lesion. Confirms left medial medulla.

Correct! ~85% of corticospinal fibres decussate at the pyramidal decussation in the caudal medulla → form the lateral corticospinal tract (contralateral). The remaining ~15% continue ipsilaterally in the anterior corticospinal tract (crosses near the level of the target).

Cruciate paralysis (rare): Injury precisely at the pyramidal decussation can cause ipsilateral arm paralysis (fibres for arm decussate higher) + contralateral leg paralysis (fibres for leg decussate lower) — forming a cross pattern. More commonly occurs with central cervical cord injuries from hyperextension neck injuries.

Incorrect. 85% cross at pyramidal decussation → lateral corticospinal tract. 15% remain uncrossed → anterior corticospinal tract (crosses near target, mainly for trunk).

Correct! NTS = the main sensory nucleus for visceral sensation (GVA: from CN IX — carotid body, CN X — thoracoabdominal viscera) and taste (SVA: CN VII — anterior 2/3 tongue; CN IX — posterior 1/3; CN X — epiglottis).

Clinical relevance of NTS: (1) Carotid sinus reflex (baroreceptor reflex) — afferent: CN IX → NTS → nucleus ambiguus + dorsal motor nucleus → vagus → bradycardia/hypotension. (2) Vomiting reflex: chemoreceptor trigger zone (area postrema) → NTS → vomiting centre → CN XII/X/phrenic for coordinated vomiting.

Incorrect. NTS = GVA (visceral sensory) + SVA (taste) from CN VII, IX, X. Pain from face = spinal nucleus of CN V. Motor for swallowing = nucleus ambiguus. Tongue proprioception → CN XII.

Correct! The severe hypertension (from medullary vasomotor centre ischaemia and catecholamine surge) activates baroreceptors → reflex vagal (parasympathetic) bradycardia via the cardiovascular centre in the medulla. The bradycardia is a REFLEX response to the hypertension.

Cushing's triad (Cushing's reflex): (1) Hypertension (widened pulse pressure) — medullary ischaemia → sympathetic activation → vasoconstriction. (2) Bradycardia — baroreceptor reflex response to hypertension. (3) Irregular breathing — compression of respiratory centres. Triad = impending herniation/coning. Immediate action: reduce ICP (mannitol, head elevation, hyperventilation).

Incorrect. Bradycardia in Cushing's triad = baroreceptor-mediated REFLEX vagal response to severe hypertension. Not direct CN XII or ambiguus compression. The cardiovascular (vasomotor + cardiac) centres are in the medullary reticular formation.