Neurologic System – Concise Exam Notes

CNS: brain + spinal cord; PNS: cranial & spinal nerves, ganglia
Functional split: somatic (voluntary) vs. autonomic (sympathetic & parasympathetic)
Afferent pathways ascend with sensory input; efferent pathways descend with motor output

Neuron = soma + dendrites (to soma) + axon (from soma via axon hillock)
Myelin (oligodendrocytes in CNS, Schwann in PNS) ➔ saltatory conduction → ↑velocity
Neuroglia: astrocytes (BBB, support), oligodendrocytes (myelin), microglia (phagocyte), ependymal (CSF); Schwann + satellite in PNS
Neuron types: unipolar / pseudounipolar (sensory), bipolar, multipolar (motor, interneuron)
Wallerian degeneration after injury; regeneration efficient only in PNS if neurilemma intact

Resting potential → threshold → action potential (all-or-none)
Chemical synapse: transmitter exocytosis → bind receptors → EPSP or IPSP
Summation (temporal/spatial) + convergence/divergence integrate input; neuroplasticity = lifelong synaptic remodeling
Major transmitters: acetylcholine, norepinephrine, dopamine, serotonin, GABA, glutamate, etc.

Forebrain: Telencephalon (cortex, basal ganglia, limbic) & Diencephalon (thalamus, hypothalamus, epithalamus, subthalamus)
Midbrain: tectum (superior/inferior colliculi), tegmentum (red nucleus, substantia nigra), cerebral peduncles
Hindbrain: Metencephalon (cerebellum, pons) & Myelencephalon (medulla)
Brainstem = midbrain + pons + medulla; reticular activating system (wakefulness, vital reflexes)

Frontal: prefrontal (cognition), premotor, primary motor (precentral gyrus), Broca (speech motor)
Parietal: primary somatosensory (postcentral gyrus), association
Temporal: auditory cortex, Wernicke (speech comprehension), memory, smell
Occipital: visual cortex
Corpus callosum links hemispheres; basal ganglia modulate movement; limbic system mediates emotion/memory

Extends medulla to $L1! -! L2$ → conus medullaris → cauda equina
Gray horns: posterior (sensory), lateral (ANS), anterior (motor); white columns carry tracts
Ascending: posterior columns (fine touch, proprioception), anterior/lateral spinothalamic (crude touch, pain, temperature)
Descending: corticospinal (voluntary), rubro/reticulo/vestibulospinal (posture, tone)
Reflex arc: receptor → afferent → interneuron → efferent → effector; upper vs. lower motor neuron lesions differ

Skull + galea; meninges: dura, arachnoid, pia
Spaces: epidural (potential), subdural, subarachnoid (contains CSF)
Ventricular flow: lateral → Monro → third → aqueduct → fourth → Luschka/Magendie → subarachnoid; CSF ~ $150\,\text{mL}$ , produced $\approx 600\,\text{mL/day}$ by choroid plexus; reabsorbed via arachnoid villi
BBB: tight endothelial junctions + astrocyte feet regulate entry

Internal carotids → anterior & middle cerebral; vertebrals → basilar → posterior cerebral; joined by circle of Willis for collateral flow
Venous drainage → dural sinuses → internal jugular
Spinal cord: anterior spinal artery, paired posterior spinal arteries + radicular branches

$31$ spinal nerve pairs (8C,12T,5L,5S,1Co); mixed fibers; dermatomes map cutaneous supply
Plexuses: cervical, brachial (C5–T1), lumbar, sacral
$12$ cranial nerves (I–XII) supply head/neck + vagus to thoraco-abdominal organs

Two-neuron chain: preganglionic (ACh, myelinated) → ganglion → postganglionic (unmyelinated)
Sympathetic (thoracolumbar $T1! -! L2$ ): paravertebral & collateral ganglia; adrenal medulla releases epinephrine/norepinephrine; mediates “fight-or-flight” (↑HR/BP/glucose, bronchodilation, vasoconstriction)
Parasympathetic (craniosacral CN III, VII, IX, X + $S2! -! S4$ ): long preganglionic, terminal ganglia; “rest-and-digest” (↓HR, ↑GI activity, pupil constriction)
Receptors: nicotinic & muscarinic (cholinergic); $\alpha<em>1,\alpha</em>2,\beta<em>1,\beta</em>2$ (adrenergic) determine organ responses

CNS ↔ PNS via specific ascending & descending tracts; myelin & node spacing govern conduction speed
Synaptic balance (EPSP vs. IPSP) + plasticity underlies learning & adaptation
Circle of Willis ensures cerebral perfusion; BBB protects neural milieu
ANS dual innervation enables fine control; sympathetic chiefly sets vascular tone