Resting potential

−70 mV; membrane polarised (Na⁺ outside, K⁺ inside)

Threshold

−55 mV; all-or-nothing law

Action potential peak

+30 to +40 mV (depolarisation), then repolarisation

Main neurotransmitters

Acetylcholine (cholinergic) and Noradrenaline (adrenergic)

CNS

Brain + spinal cord

PNS

Cranial nerves (12 pairs) + spinal nerves (31 pairs)

Sympathetic NS

Fight-or-flight; noradrenaline

Parasympathetic NS

Rest-and-digest; acetylcholine

Reflex arc route

Receptor → sensory → (relay) → motor → effector

Rods / Cones

Rods = dim light, no colour; Cones = bright light, colour, high acuity

Myopia / Hypermetropia

Corrected with concave / convex lens respectively