Neurology and Neurophysiology of Communication
This domain tests neural organization, excitation and transmission, motor control, cranial nerve function, and the localization of communication disorders. Expect questions that link a lesion site to aphasia, dysarthria, apraxia, or auditory processing signs.
Core neurophysiology
- Neurons transmit via action potentials; myelin increases conduction velocity. Synaptic transmission is chemical, usually excitatory or inhibitory.
- The pyramidal (corticospinal/corticobulbar) tract supports voluntary movement. Extrapyramidal circuits, basal ganglia, and cerebellum regulate tone, scaling, and coordination.
- Left perisylvian cortex is dominant for language in most right-handed people. Auditory cortex lies in the superior temporal plane; Wernicke and Broca areas connect through the arcuate fasciculus.
- CN VII supplies facial muscles; CN IX and X supply velar and laryngeal structures; CN XII supplies tongue. Upper motor neuron lesions spare the forehead in facial palsy; lower motor neuron lesions affect the whole side.
Worked example
An adult presents with fluent, empty speech, poor auditory comprehension, and poor repetition after a left posterior superior temporal gyrus stroke. Reasoning: the lesion involves Wernicke area, producing receptive aphasia; repetition is impaired because the posterior temporal–arcuate loop is affected. If repetition were preserved, consider transcortical sensory aphasia. If speech were nonfluent with preserved comprehension and impaired repetition, consider Broca aphasia.
Traps
Dysarthria is a motor execution disorder; aphasia is a language disorder; apraxia of speech is a planning/programming disorder. Do not localize all fluent aphasias to Wernicke area. Do not confuse CN VII with CN V in jaw movement. Do not treat Bell palsy as an upper motor neuron sign.