Neuroanatomy and Neurophysiology
Domain 1 - Neuroanatomy and Neurophysiology
The exam tests whether you can connect structure to the recordings you make: which cortical cells generate EEG, where each evoked potential is born, and how a lesion explains a pattern. Expect localization questions, not pure anatomy recall.
Core rules
- Cortical generators. The scalp EEG comes mainly from synchronized excitatory and inhibitory postsynaptic potentials in pyramidal cells of layers III and V, whose apical dendrites run perpendicular to the cortex. Action potentials contribute little because they are brief and asynchronous.
- Lobar function. Frontal: primary motor cortex, premotor planning, Broca area (dominant inferior frontal). Parietal: primary somatosensory cortex on the postcentral gyrus. Temporal: primary auditory cortex, Wernicke area, hippocampus. Occipital: primary visual cortex.
- Arousal. The ascending reticular activating system in the midbrain and upper pons, relayed by the intralaminar thalamus, keeps the cortex awake; its failure produces diffuse slowing or coma patterns.
- Brainstem auditory pathways. Wave I = distal VIII nerve, II = proximal VIII nerve, III = cochlear nucleus, IV = superior olivary complex, V = inferior colliculus.
- Somatosensory pathways. Dorsal columns carry vibration and proprioception; median nerve SSEP N20 reflects primary somatosensory cortex; posterior tibial P37 is its lower-limb counterpart.
- Motor pathway. Corticospinal fibers cross in the medullary pyramids, so a right hemispheric lesion causes left weakness.
Worked example
A 62-year-old has sudden right face and arm weakness plus nonfluent speech. Localization: left inferior frontal and motor cortex, left middle cerebral artery territory. Expected EEG: polymorphic delta and theta over the left frontotemporal region, with preserved alpha posteriorly if the occipital lobe is spared. The reasoning: the deficit is contralateral because of pyramidal decussation; aphasia places the lesion in the dominant hemisphere.
Traps
Assuming EEG directly records action potentials; reversing left and right in localization; forgetting that deep midline lesions may produce little scalp change; mixing up BAEP wave generators.