Neuron and Impulse: Resting potential = -70 mV (Na+/K+ pump: 3 Na+ out, 2 K+ in). AP: Na+ IN = depolarization (+30 mV) → K+ OUT = repolarization. All-or-none. Saltatory conduction in myelinated neurons (15-120 m/s); 20 nm synaptic cleft; Ca2+ triggers NT release.

Brain: Cerebrum INITIATES voluntary movement; cerebellum COORDINATES (NOT initiate — damage = ataxia NOT paralysis); medulla = vital functions (CV + respiratory); hypothalamus = homeostasis + pituitary; thalamus = relay (not smell).

ANS: Sympathetic $\frac{fight}{flight}$: ↑HR, dilate pupils, NE postgang. Parasympathetic $\frac{rest}{digest}$: ↓HR, constrict pupils, ACh postgang. All preganglionic = ACh.

Eye: Rods = 120M, rhodopsin, dim light, peripheral. Cones = 6-7M, iodopsin, colour, fovea. Myopia → concave lens. Hypermetropia → convex. Accommodation: ciliary muscles contract → lens rounds up (near vision).

Ear: MIS order: Malleus → Incus → Stapes (smallest bone) → oval window; 20x amplification. Cochlea = hearing (organ of Corti, hair cells). Vestibular = balance (3 semicircular canals + utricle + saccule). 31 spinal nerve pairs: 8C+12T+5L+5S+1Cx.