Neurology Syllabus

What are the signs distinguishing an upper motor neuron lesion from a lower motor neuron lesion?

UMN lesion: spastic paralysis, hyperreflexia, positive Babinski sign, no significant atrophy. LMN lesion: flaccid paralysis, hyporeflexia/areflexia, marked muscle atrophy, fasciculations.

What is the function of the cerebellum, and what is the classic triad of cerebellar dysfunction?

The cerebellum coordinates movement, balance, and motor learning. Cerebellar dysfunction causes ataxia, intention tremor, and dysmetria (plus nystagmus, dysdiadochokinesia, and scanning speech).

Outline the direct pathway of the basal ganglia and its net effect on movement.

Cortex $\to$ striatum (inhibits) $\to$ globus pallidus internus/substantia nigra pars reticulata (inhibits) $\to$ thalamus (disinhibited) $\to$ cortex. Net effect: facilitation of movement; dopamine via D1 receptors reinforces this pathway.

Describe the phototransduction cascade in retinal rod cells.

Light isomerizes 11-cis-retinal to all-trans-retinal, activating rhodopsin $\to$ transducin $\to$ phosphodiesterase, which hydrolyzes cGMP; falling cGMP closes $\ce{Na+}$ channels, hyperpolarizing the rod and reducing glutamate release.

Trace the visual pathway from retina to primary visual cortex.

Retinal ganglion cells $\to$ optic nerve $\to$ optic chiasm (nasal fibers decussate) $\to$ optic tract $\to$ lateral geniculate nucleus of the thalamus $\to$ optic radiations $\to$ primary visual cortex (V1) in the occipital lobe.

How does the cochlea encode sound frequency (tonotopy)?

The basilar membrane is tonotopically organized: the stiff, narrow base responds to high frequencies and the flexible, wide apex to low frequencies, so different frequencies maximally displace different regions and stimulate specific hair cells.

Define homeostasis and name the brain region that is its principal integrator.

Homeostasis is the maintenance of a stable internal environment despite external changes. The hypothalamus is the principal integrator, regulating temperature, hunger, thirst, circadian rhythms, and the endocrine system via the pituitary.

What structures comprise the limbic system and what is its primary role?

The limbic system includes the hippocampus, amygdala, cingulate gyrus, fornix, and parts of the hypothalamus; it governs emotion, memory formation (hippocampus), and motivation.

Differentiate the roles of the hippocampus and amygdala in memory.

The hippocampus is essential for forming new declarative (explicit) memories and their consolidation; the amygdala attaches emotional significance to memories, especially fear-related memories.

What are the core clinical and pathological features of Parkinson's disease?

Clinical: resting tremor, rigidity, bradykinesia, and postural instability. Pathology: loss of dopaminergic neurons in the substantia nigra pars compacta and intracytoplasmic Lewy bodies containing alpha-synuclein.

What is the pathological hallmark of Alzheimer's disease?

Extracellular beta-amyloid (senile) plaques and intracellular neurofibrillary tangles of hyperphosphorylated tau protein, with cortical/hippocampal atrophy and a cholinergic deficit.

What is amyotrophic lateral sclerosis (ALS) and which neurons does it affect?

ALS is a progressive neurodegenerative disease affecting both upper and lower motor neurons, producing a combination of spasticity/hyperreflexia and muscle weakness/atrophy/fasciculations, with sensation and cognition typically spared.

What genetic mutation causes Huntington's disease and what is its inheritance pattern?

An autosomal dominant CAG trinucleotide repeat expansion in the huntingtin (HTT) gene on chromosome 4; expansions of $\geq 36$ repeats cause disease, and more repeats correlate with earlier onset (anticipation).

Distinguish ischemic from hemorrhagic stroke and give their approximate relative frequencies.

Ischemic stroke (~85%) results from arterial occlusion (thrombotic or embolic) reducing blood flow; hemorrhagic stroke (~15%) results from vessel rupture causing intracerebral or subarachnoid bleeding.

What is the classic presentation and most common cause of subarachnoid hemorrhage?

A sudden 'thunderclap' worst-headache-of-life, often with neck stiffness and photophobia; the most common cause is rupture of a saccular (berry) aneurysm, typically at circle of Willis branch points.

What is a transient ischemic attack (TIA) and why is it clinically important?

A TIA is a transient episode of neurological dysfunction from focal ischemia without acute infarction, resolving completely (traditionally within 24 hours); it is a warning sign of high short-term stroke risk.

State the cerebral perfusion pressure formula and its normal target range.

$$\text{CPP} = \text{MAP} - \text{ICP}$$ where MAP is mean arterial pressure and ICP is intracranial pressure; CPP is normally maintained around $60\text{–}80\ \text{mmHg}$.

State the Monro–Kellie doctrine.

The cranial vault is a fixed volume containing brain, blood, and CSF; an increase in one compartment must be offset by a decrease in another, or intracranial pressure rises. It explains compensation and decompensation in mass lesions.

How are bacterial and viral meningitis distinguished by CSF analysis?

Bacterial: high neutrophils, low glucose, high protein, elevated opening pressure, turbid appearance. Viral: lymphocytic predominance, normal glucose, mildly elevated protein, usually clear fluid.

What virus most commonly causes sporadic encephalitis, and which brain region does it favor?

Herpes simplex virus type 1 (HSV-1) is the most common cause of sporadic viral encephalitis, characteristically causing hemorrhagic necrosis of the temporal lobes.

What is multiple sclerosis and what is its underlying pathology?

MS is a chronic autoimmune demyelinating disease of the CNS characterized by inflammatory plaques of demyelination disseminated in space and time; oligodendrocytes and myelin are targeted, slowing or blocking conduction.

Contrast Guillain-Barré syndrome with multiple sclerosis in terms of location and course.

Guillain-Barré is an acute, usually monophasic autoimmune demyelination of the PNS (ascending weakness, areflexia, often post-infectious); MS is a chronic, relapsing–remitting demyelination of the CNS.

What CSF finding supports a diagnosis of multiple sclerosis?

The presence of oligoclonal IgG bands in the CSF that are absent from serum, indicating intrathecal immunoglobulin synthesis; also an elevated IgG index.

What does the Glasgow Coma Scale assess, and what is its score range?

The GCS assesses level of consciousness via best eye opening (1–4), verbal response (1–5), and motor response (1–6); total scores range from 3 (deep coma) to 15 (fully alert).

List the five components of a complete neurological examination.

Mental status, cranial nerves, motor system (tone, power, bulk), sensory system, reflexes, and coordination/gait — assessing the nervous system systematically from cortex to periphery.

How is muscle power graded on the Medical Research Council (MRC) scale?

$0$ = no contraction; $1$ = flicker/trace; $2$ = movement with gravity eliminated; $3$ = movement against gravity only; $4$ = movement against some resistance; $5$ = normal power against full resistance.

Compare the strengths of CT versus MRI in neuroimaging.

CT is fast and superior for acute hemorrhage, bone, and calcification (first-line in trauma/acute stroke). MRI offers superior soft-tissue contrast for tumors, demyelination, posterior fossa, and early ischemia (DWI detects infarcts within minutes).

What is the mechanism of action of levodopa, and why is it combined with carbidopa?

Levodopa is a dopamine precursor that crosses the blood–brain barrier (dopamine cannot) and is converted to dopamine in the CNS. Carbidopa is a peripheral DOPA-decarboxylase inhibitor that prevents peripheral conversion, increasing CNS availability and reducing side effects.

Name three major classes of antiepileptic drug mechanisms with an example of each.

$\ce{Na+}$ channel blockers (phenytoin, carbamazepine); GABA enhancers (benzodiazepines, valproate, phenobarbital); and $\ce{Ca^2+}$ channel modulators / synaptic vesicle binders (ethosuximide for T-type channels, levetiracetam via SV2A).

What is Cushing's triad and what does it indicate?

Hypertension (widened pulse pressure), bradycardia, and irregular respirations — a late sign of dangerously raised intracranial pressure and impending brain herniation, requiring emergency intervention.

Contrast the anatomy and typical cause of epidural versus subdural hematoma.

Epidural hematoma: between skull and dura, usually arterial (middle meningeal artery), biconvex/lens-shaped on CT, often with a lucid interval. Subdural hematoma: between dura and arachnoid, usually venous (bridging veins), crescent-shaped, common in elderly/alcoholics.