| Neuron | Structural and functional unit of nervous system; consists of soma, dendrites, axon | Basic neural unit |
| Axon | Single long process that transmits impulses AWAY from cell body | Outgoing signal |
| Dendrite | Short, branched processes that RECEIVE signals | Incoming signal |
| Cyton/Soma | Cell body of neuron; contains nucleus and Nissl granules | Neural "factory" |
| Nissl granules | Rough ER in neuron soma; protein synthesis | Only in soma and dendrites |
| Myelin sheath | Lipid insulation around axon; increases conduction speed | Speed upgrade |
| Schwann cell | PNS myelinating cell; one cell per axon segment | PNS insulator |
| Oligodendrocyte | CNS myelinating cell; one cell myelinates multiple axons | CNS insulator |
| Node of Ranvier | Unmyelinated gap between Schwann cells; site of AP regeneration | Jump point |
| Resting membrane potential | -70 mV; inside negative; maintained by Na+/K+ pump + K+ leak channels | Baseline state |
| Depolarization | Na+ influx → inside becomes positive (up to +30 mV) | Rising phase of AP |
| Repolarization | K+ efflux → inside becomes negative again | Falling phase of AP |
| Hyperpolarization | Brief overshoot below -70 mV after repolarization | After the AP |
| All-or-none principle | AP fires at full magnitude at threshold or not at all | Binary firing |
| Saltatory conduction | AP jumps node to node in myelinated neurons | Fast conduction |
| Synapse | Junction between two neurons (or neuron and effector) | Signal transfer point |
| Synaptic knob | Axon terminal; contains synaptic vesicles | Presynaptic structure |
| Synaptic cleft | 20 nm gap between pre- and postsynaptic membranes | Chemical crossing |
| Action potential (AP) | Rapid reversal and restoration of membrane potential; nerve impulse | Signal |
| Neurotransmitter (NT) | Chemical messenger released at synapse (ACh, NE, DA, 5-HT, GABA, Glutamate) | Chemical signal |
| Acetylcholine (ACh) | NT at NMJ, all ANS preganglionic, parasympathetic postganglionic | Most widespread NT |
| Norepinephrine | Sympathetic postganglionic NT; increases HR, alertness | Fight/flight NT |
| Refractory period | Post-AP period when neuron cannot (absolute) or barely can (relative) fire | Prevents backward conduction |
| Cerebrum | Largest forebrain structure; higher cognition, INITIATES voluntary movement | Cognition centre |
| Cerebellum | Hindbrain structure; COORDINATES movement, balance, posture | Coordination centre |
| Thalamus | Sensory relay centre in forebrain; relays all senses EXCEPT smell to cortex | Sensory gateway |
| Hypothalamus | Homeostasis control; links nervous and endocrine systems; controls pituitary | Homeostasis hub |
| Medulla oblongata | Vital involuntary centres (cardiovascular, respiratory) | Life centre |
| Pons | Relay between cerebrum and cerebellum; pneumotaxic centre | Respiratory modulator |
| Sympathetic NS | "Fight or flight": ↑HR, dilates pupils, inhibits digestion | Stress response |
| Parasympathetic NS | "Rest and digest": ↓HR, constricts pupils, stimulates digestion | Peace response |
| Rhodopsin | Photopigment in rods; opsin + retinal (from Vitamin A) | Dim-light pigment |
| Iodopsin | Photopigment in cones (3 types: R, G, B) | Colour pigment |
| Fovea | Region of highest visual acuity; densely packed cones | Sharpest vision point |
| Accommodation | Lens shape change for near/far focusing via ciliary muscles | Focus adjustment |
| Myopia | Near-sightedness; image in front of retina; concave lens | Short eyeball defect |
| Hypermetropia | Far-sightedness; image behind retina; convex lens | Long eyeball defect |
| Presbyopia | Age-related loss of lens elasticity; reduced accommodation | Old-age near vision loss |
| Stapes | 3rd ear ossicle; smallest bone in human body; connects to oval window | Smallest bone |
| Organ of Corti | Hearing receptor in cochlea; contains hair cells | Hearing transducer |
| Vestibular apparatus | Semicircular canals + utricle + saccule; maintains balance | Balance organ |
| Reflex arc | Neural pathway for involuntary reflexes: receptor→afferent→interneuron→efferent→effector | Rapid response pathway |