Nervous and behavioural: USMLE Step 1 video lessons
Neuroscience, special senses, behavioural science and psychiatry.
Localise the lesion: upper vs lower motor neuron signs, the ascending and descending tracts, spinal cord syndromes, the brainstem cranial-nerve map and crossed findings, medullary syndromes, stroke territories and lacunes, visual field defects, the basal ganglia, the cerebellum, herniation, CSF flow and the hypothalamus.
5:08Upper vs lower motor neuron lesions: signs and localisation
Weak is weak, but the muscle tells you which neuron broke. Learn the signs of upper and lower motor neuron lesions and use them to place the damage.
5:01Dorsal column vs spinothalamic tract: where each pathway crosses
Both sensory pathways start in the same ganglion and end in the same cortex, but one crosses in the medulla and the other in the cord. That one fact predicts the pattern of sensory loss.
5:06Spinal cord syndromes compared: rebuild each from three tracts
Every spinal cord syndrome is the same cross-section with a different shape of damage. Three tracts and the cord's blood supply are enough to predict each pattern.
5:10Cranial nerve nuclei: a brainstem map by level and position
Ten pairs of cranial nerves have nuclei in the brainstem, and they look like a list to memorise. Two rules sort them, level and position from the midline, with one exception: the trigeminal nuclei run the whole length.
4:50Brainstem crossed findings: the localisation rule
A cranial nerve sign on one side with weakness on the other points to the brainstem. Learn which side each tract carries and how the cranial nerve names the level.
5:30Medial vs lateral medullary syndrome: artery, structures and signs
Split the medulla at the olive level into a medial strip and a lateral part. Each has its own artery, its own structures and its own signs, and the two syndromes mirror each other.
4:59Facial nerve palsy: why the forehead tells you the lesion
Two droops can look alike. The forehead separates an upper motor neuron lesion from a lower motor neuron one, and the nerve's branches show where along the nerve the lesion sits.
4:41Stroke syndromes by artery: ACA, MCA and PCA
Each cerebral artery supplies a patch of cortex, and the deficits of a stroke follow from that patch and from the body map inside it. Place the territory, then read the syndrome.
4:54Lacunar stroke syndromes: pure motor, pure sensory and more
A small deep infarct can cause a dense deficit with no cortical signs. Learn the five classic lacunar stroke syndromes and match each one to its small vessel and site.
4:42Visual pathway lesions and field defects
Predict the visual field defect from the site of the lesion. Before the chiasm, one eye; at the chiasm, both outer fields; after the chiasm, the same side in both eyes, opposite the lesion.
5:19Basal ganglia direct and indirect pathways: D1, D2 and movement
The basal ganglia act as a brake held on the thalamus. The direct and indirect pathways and dopamine set that brake, and Parkinson and Huntington disease are what happens when it is too strong or too weak.
4:42Cerebellar lesion localisation: vermis vs hemisphere
Name the site of a cerebellar lesion from the pattern of ataxia. The midline steadies the trunk, the hemispheres steady the limbs, and hemisphere signs stay on the same side.
4:56Brain herniation syndromes: what is squeezed, and where
Brain herniation syndromes are told apart by the structure compressed and the signs it produces: subfalcine, uncal, central, tonsillar and upward, plus the Kernohan notch and Cushing triad.
5:12CSF flow and hydrocephalus: where the flow fails
Trace cerebrospinal fluid from the choroid plexus to the dural venous sinuses, then use the point of failure to separate communicating, non-communicating and normal pressure hydrocephalus.
4:59Corticospinal tract: from cortex to anterior horn
The corticospinal tract carries voluntary motor commands from the cortex to the spinal cord. Knowing its course lets you predict the deficit from a lesion at each level.
5:24Hypothalamic nuclei and their functions
One small structure runs water, food, heat and the body clock. Match each hypothalamic nucleus to its job and a lesion becomes a single missing function you can predict.