Neuroanatomy Overview

Overview

This lecture reviews high-yield neuroanatomy concepts for NBME/USMLE Step 1, focusing on key clinical presentations, major brain regions, vascular territories, brainstem syndromes, spinal cord tracts, cranial nerves, and important pathologies.

Cerebral Vascular Syndromes

• MCA stroke: contralateral face/arm weakness, aphasia if left side affected.
• ACA stroke: contralateral leg weakness, often from atrial fibrillation embolus.
• PCA stroke: prosopagnosia and visual agnosia, affects occipital lobe.
• Stroke locations determined by side (contralateral symptoms), medial/lateral (homunculus mapping), anterior/posterior to central sulcus (motor vs sensory).

Brain Regions & Functionality

• Broca area (inferior frontal gyrus): non-fluent aphasia, impaired repetition, comprehension intact.
• Wernicke area (superior temporal gyrus): fluent aphasia, impaired repetition, poor comprehension.
• Angular gyrus: Gerstmann syndrome (agraphia, acalculia, finger/left-right agnosia).
• Frontal lobe: personality change, apathy; damaged in frontotemporal dementia.

Brainstem Syndromes

• Medial medullary syndrome: ipsilateral tongue deviation, caused by ASA infarct.
• Lateral medullary (Wallenberg) syndrome: hoarseness, dysphagia, ± Horner syndrome, PICA infarct.
• Lateral pontine syndrome: ipsilateral Bell's palsy, AICA infarct.
• Weber syndrome (midbrain): oculomotor palsy, contralateral hemiparesis.

Cranial Nerves & Lesions

• CN III (oculomotor): down-and-out pupil, mydriasis from PCoM aneurysm.
• CN VI (abducens): most susceptible in cavernous sinus thrombosis.
• Bell’s palsy: CN VII, facial paralysis, hyperacusis from stapedius dysfunction.
• Uvula deviation: contralateral to vagus (CN X) lesion; tongue deviation: ipsilateral to hypoglossal (CN XII) lesion.

Spinal Cord Tracts & Syndromes

• Dorsal columns: vibration/proprioception; fasciculus gracilis (legs), cuneatus (arms).
• Spinothalamic tract: pain/temperature, crosses contralaterally.
• Lateral corticospinal tract: motor function.
• ALS: mixed UMN/LMN dysfunction, no sensory loss.
• Brown-Séquard syndrome: ipsilateral loss of motor/function, contralateral pain/temp.
• Central cord syndrome: upper limb > lower limb weakness.
• Anterior cord syndrome: loss of motor, pain/temp; preserved vibration/proprioception.

Neurocutaneous & Genetic Syndromes

• Acoustic schwannoma: vestibulocochlear nerve, neural crest origin, often NF2 in young.
• Wilson disease: parkinsonism in young adults, copper deposition in basal ganglia (putamen).
• Huntington's: caudate nucleus atrophy.

Key Pathologies & Imaging Findings

• AVM: "Swiss cheese" brain appearance, seizure history.
• Subdural hematoma: crescent shape, bridging veins, slow in elderly.
• Epidural hematoma: lens-shaped, middle meningeal artery, lucid interval.
• Subarachnoid hemorrhage: "worst headache," berry aneurysm, ACoM > PCoM.
• Glioblastoma multiforme: "butterfly glioma," crosses midline.
• Chiari malformations: Type I (cerebellar tonsil herniation, syringomyelia), Type II (myelomeningocele).
• Dandy-Walker: absent cerebellar vermis + cystic dilated 4th ventricle.

Developmental & Structural Concepts

• Neural tube defects: ↑AFP/AChE, prevent with folic acid, risk with antiepileptics.
• Foramen of Monro: connects lateral to third ventricle; aqueduct of Sylvius: third to fourth.
• Brain herniations: subfalcine, uncal, tonsillar, central, transcalvarial.

Sensory & Motor Clinical Correlates

• Visual field defects: parietal lobe (inferior quadrantanopsia), occipital lobe (hemianopia).
• Internuclear ophthalmoplegia (INO): MLF lesion, unable to adduct ipsilateral eye (MS).

Key Terms & Definitions

• Broca aphasia — non-fluent speech, intact comprehension, impaired repetition.
• Wernicke aphasia — fluent, nonsensical speech, poor comprehension, impaired repetition.
• Hemineglect syndrome — neglect of one visual field, usually left (right parietal damage).
• ALS (Amyotrophic Lateral Sclerosis) — progressive degeneration of UMN and LMN, purely motor.
• Tabes dorsalis — loss of dorsal columns from neurosyphilis, impaired vibration/proprioception.
• Locked-in syndrome — basilar artery stroke; can only move eyes vertically.

Action Items / Next Steps

• Review neuroimaging for classic vascular syndromes and pathologies.
• Memorize cranial nerve exit points, spinal cord tracts, and main brainstem syndromes.
• Study the homunculus mapping for localizing cortical strokes.
• Understand visual field defects and pathways for Step 1.