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What are the main structural parts of a neuron?
Answer: Dendrites, cell body (soma), axon hillock, axon, myelin sheath, nodes of Ranvier, axon terminals (synaptic boutons).
Dendrites receive signals; soma integrates them; axon hillock initiates the action potential; axon conducts it to terminals, which release neurotransmitter.
How are neurons classified structurally?
Answer: Unipolar (one process from soma, e.g. sensory neurons), bipolar (two processes, e.g. retina/olfactory), multipolar (many dendrites + one axon, most common, e.g. motor neurons).
How are neurons classified functionally?
Answer: Sensory (afferent) neurons carry signals to the CNS; motor (efferent) neurons carry signals away from the CNS to effectors; interneurons connect neurons within the CNS.
Name the four types of CNS glial cells and their main functions.
Answer: Astrocytes (support, blood-brain barrier, nutrient exchange), oligodendrocytes (myelinate CNS axons), microglia (immune defense/phagocytosis), ependymal cells (line ventricles, produce/circulate CSF).
Name the two types of PNS glial cells and their functions.
Answer: Schwann cells myelinate PNS axons; satellite cells support neuron cell bodies in PNS ganglia.
How does myelination differ between CNS and PNS?
Answer: One oligodendrocyte myelinates segments of multiple axons in the CNS, whereas one Schwann cell myelinates only one segment of one axon in the PNS.
This difference also affects regeneration: PNS axons can regenerate (Schwann cells guide regrowth), CNS axons generally cannot.
What is the typical resting membrane potential of a neuron?
Answer: Approximately -70 mV (inside negative relative to outside).
What maintains the resting membrane potential?
Answer: The Na+/K+-ATPase pump (3 Na+ out, 2 K+ in per cycle) plus higher resting permeability to K+ through leak channels, and large intracellular anions (proteins) that cannot cross the membrane.
K+ permeability dominates at rest, pulling the membrane potential close to the K+ equilibrium potential.
State the Nernst equation and what it calculates.
Answer: E_ion = (61.5 mV / z) × log10([ion]_outside / [ion]_inside), at body temperature (37°C).
E_ion = equilibrium potential for that ion; z = ion's charge. Example for K+ (z=+1, out=5 mM, in=140 mM): E_K = 61.5 × log10(5/140) ≈ -89 mV, close to the actual resting potential.
What is the threshold potential for triggering an action potential?
Answer: Approximately -55 mV.
If depolarization reaches threshold, voltage-gated Na+ channels open explosively, triggering an all-or-none action potential.
Describe the phases of an action potential.
Answer: 1) Depolarization: voltage-gated Na+ channels open, Na+ rushes in, potential rises toward +30 mV. 2) Repolarization: Na+ channels inactivate, voltage-gated K+ channels open, K+ exits. 3) Hyperpolarization (undershoot): K+ channels close slowly, potential dips below resting. 4) Return to resting potential via Na+/K+ pump and leak channels.
Sketch/identify the phases of a neuronal action potential over time.
Answer: A sharp depolarizing spike from -70 mV to about +30 mV, followed by rapid repolarization, a brief hyperpolarizing undershoot, then return to resting potential.
Depolarization is driven by Na+ influx; repolarization and the undershoot by delayed K+ efflux.
What is the 'all-or-none' principle of action potentials?
Answer: If depolarization reaches threshold, a full-amplitude action potential fires; if threshold is not reached, no action potential occurs. The size of the action potential does not vary with stimulus strength.
Stimulus intensity is instead encoded by frequency of action potentials (rate coding).
Distinguish the absolute and relative refractory periods.
Answer: Absolute refractory period: no new action potential can be generated regardless of stimulus strength (Na+ channels inactivated). Relative refractory period: a stronger-than-normal stimulus can trigger another action potential (K+ channels still open, membrane hyperpolarized).
These periods limit maximum firing frequency and ensure one-way propagation.
What is saltatory conduction?
Answer: Action potentials 'jump' from one node of Ranvier to the next along a myelinated axon, greatly speeding conduction.
Myelin insulates internodal segments so depolarization only needs to regenerate at the exposed nodes.
What two factors increase action potential conduction velocity?
Answer: Increased myelination and increased axon diameter.
Both reduce internal resistance/current leak, so the signal travels faster.
Outline the steps of chemical synaptic transmission.
Answer: 1) Action potential arrives at axon terminal. 2) Voltage-gated Ca2+ channels open, Ca2+ enters. 3) Ca2+ triggers synaptic vesicles to fuse with presynaptic membrane. 4) Neurotransmitter is released into synaptic cleft by exocytosis. 5) Neurotransmitter binds receptors on postsynaptic membrane. 6) Postsynaptic ion channels open, producing EPSP or IPSP. 7) Neurotransmitter is removed (reuptake, enzymatic breakdown, or diffusion).
Compare electrical and chemical synapses.
Answer: Electrical synapses: gap junctions, direct ion flow, very fast, bidirectional, no neurotransmitter. Chemical synapses: synaptic cleft, neurotransmitter-mediated, slight delay, unidirectional, allow signal amplification/modulation.
Differentiate EPSP and IPSP.
Answer: EPSP (excitatory postsynaptic potential): depolarizes the postsynaptic membrane (e.g., Na+ influx), bringing it closer to threshold. IPSP (inhibitory postsynaptic potential): hyperpolarizes or stabilizes the membrane (e.g., Cl- influx or K+ efflux), moving it away from threshold.
Distinguish spatial and temporal summation.
Answer: Spatial summation: multiple simultaneous inputs from different synapses combine to reach threshold. Temporal summation: repeated inputs from the same synapse in quick succession add together to reach threshold.
How is neurotransmitter signaling terminated?
Answer: Reuptake into the presynaptic neuron (e.g., serotonin, dopamine, norepinephrine transporters), enzymatic degradation (e.g., acetylcholinesterase breaks down ACh), or simple diffusion away from the synapse.
List major neurotransmitters and their general roles.
Answer: Acetylcholine: neuromuscular junction, parasympathetic effects, memory. Dopamine: reward, movement (basal ganglia). Serotonin: mood, sleep. Norepinephrine: arousal, 'fight-or-flight'. GABA: main inhibitory neurotransmitter (CNS). Glutamate: main excitatory neurotransmitter (CNS).
What are the two main divisions of the nervous system?
Answer: Central nervous system (CNS): brain and spinal cord. Peripheral nervous system (PNS): cranial nerves, spinal nerves, and ganglia outside the CNS.
How is the PNS subdivided functionally?
Answer: Somatic nervous system (voluntary control of skeletal muscle) and autonomic nervous system (involuntary control of smooth muscle, cardiac muscle, and glands), the latter split into sympathetic and parasympathetic divisions.
Name the four cerebral lobes and their primary functions.
Answer: Frontal: voluntary movement, executive function, personality, Broca's area (speech production). Parietal: somatosensory processing, spatial awareness. Temporal: auditory processing, memory, Wernicke's area (language comprehension). Occipital: visual processing.
What are the components of the brainstem and their functions?
Answer: Midbrain: visual/auditory reflexes, relay station. Pons: relays signals between cerebrum and cerebellum, regulates breathing rhythm. Medulla oblongata: controls vital autonomic functions (heart rate, breathing, blood pressure, reflexes like coughing/vomiting).
What is the main function of the cerebellum?
Answer: Coordinates voluntary movement, balance, posture, and motor learning.
What are the functions of the thalamus and hypothalamus?
Answer: Thalamus: relay station for almost all sensory information (except smell) to the cerebral cortex. Hypothalamus: regulates homeostasis—temperature, hunger, thirst, circadian rhythms, and controls the pituitary gland/endocrine system.
What structures make up the limbic system and what is its role?
Answer: Includes the hippocampus, amygdala, cingulate gyrus, and hypothalamus; involved in emotion, memory formation, and motivation.
Hippocampus: memory consolidation. Amygdala: fear/emotional processing.
Name the three meningeal layers from outermost to innermost.
Answer: Dura mater (tough outer layer), arachnoid mater (middle, web-like), pia mater (thin, adheres directly to brain/spinal cord surface).
The subarachnoid space, between arachnoid and pia, contains cerebrospinal fluid (CSF).
Where is CSF produced and what are its functions?
Answer: Produced by the choroid plexus in the brain's ventricles; circulates through ventricles and subarachnoid space, then is reabsorbed into venous blood via arachnoid granulations. Functions: cushions the brain/spinal cord, removes waste, provides buoyancy, and maintains stable chemical environment.
Distinguish ascending and descending spinal cord tracts, with examples.
Answer: Ascending (sensory) tracts carry information toward the brain, e.g. dorsal columns (fine touch, proprioception) and the spinothalamic tract (pain, temperature). Descending (motor) tracts carry information from the brain to the spinal cord, e.g. the corticospinal tract (voluntary movement).
List the 12 cranial nerves by number and name with a key function for each.
Answer: I Olfactory (smell); II Optic (vision); III Oculomotor (eye movement, pupil constriction); IV Trochlear (eye movement); V Trigeminal (facial sensation, chewing); VI Abducens (eye movement); VII Facial (facial expression, taste anterior 2/3 tongue); VIII Vestibulocochlear (hearing, balance); IX Glossopharyngeal (taste posterior 1/3 tongue, swallowing); X Vagus (parasympathetic to thoracic/abdominal organs, swallowing, speech); XI Accessory (shoulder/neck muscles); XII Hypoglossal (tongue movement).
Mnemonic for names: 'Oh Oh Oh To Touch And Feel Very Good Velvet Ah Heaven.' Mnemonic for sensory/motor/both: 'Some Say Marry Money But My Brother Says Big Brains Matter More.'
Why is the vagus nerve (CN X) especially important?
Answer: It is the primary parasympathetic nerve to the heart, lungs, and most abdominal viscera, slowing heart rate and promoting digestion; it also carries sensory and motor fibers for swallowing and speech.
What are the five components of a basic reflex arc?
Answer: 1) Receptor (detects stimulus), 2) sensory (afferent) neuron, 3) integration center (usually in spinal cord/brainstem), 4) motor (efferent) neuron, 5) effector (muscle or gland that responds).
Differentiate monosynaptic and polysynaptic reflexes.
Answer: Monosynaptic reflex: sensory neuron synapses directly onto motor neuron with one synapse (e.g., patellar/knee-jerk reflex). Polysynaptic reflex: involves one or more interneurons between sensory and motor neurons (e.g., withdrawal/flexor reflex from a painful stimulus).
Compare sympathetic and parasympathetic effects on major organs.
Answer: Heart rate: sympathetic increases, parasympathetic decreases. Pupils: sympathetic dilates, parasympathetic constricts. Digestion: sympathetic inhibits, parasympathetic stimulates. Bronchioles: sympathetic dilates, parasympathetic constricts. Bladder: sympathetic relaxes (retains urine), parasympathetic contracts (promotes urination).
Sympathetic = 'fight or flight'; parasympathetic = 'rest and digest'.
What neurotransmitters are used at each stage of autonomic pathways?
Answer: Preganglionic neurons (both sympathetic and parasympathetic) release acetylcholine onto nicotinic receptors. Postganglionic parasympathetic neurons release acetylcholine (muscarinic receptors) onto target organs; postganglionic sympathetic neurons release norepinephrine (adrenergic receptors), except those innervating sweat glands, which release acetylcholine.
Trace the pathway of light through the eye to the retina.
Answer: Light passes through the cornea → aqueous humor → pupil (size set by iris) → lens (focuses image) → vitreous humor → retina (photoreceptors).
The cornea provides most of the eye's refractive power; the lens fine-tunes focus via accommodation.
Compare rods and cones in the retina.
Answer: Rods: highly sensitive to low light, used for night/peripheral vision, no color discrimination, more numerous. Cones: require brighter light, provide color vision and high visual acuity, concentrated in the fovea centralis.
Trace the visual pathway from retina to brain.
Answer: Retina → optic nerve (CN II) → optic chiasm (partial decussation) → optic tract → lateral geniculate nucleus of the thalamus → optic radiations → primary visual cortex (occipital lobe).
At the optic chiasm, fibers from the nasal half of each retina cross, so each hemisphere processes the opposite visual field.
Trace the pathway of sound through the ear.
Answer: Sound waves enter the external auditory canal → vibrate the tympanic membrane (eardrum) → vibrations amplified across the ossicles (malleus, incus, stapes) → transmitted to the oval window → fluid waves in the cochlea → stimulate hair cells on the basilar membrane → generate signals in the cochlear nerve (CN VIII).
Which inner ear structures are responsible for balance, and what do they detect?
Answer: Semicircular canals detect rotational/angular acceleration (head turning); the utricle and saccule detect linear acceleration and head position relative to gravity.
Both rely on hair cells and are part of the vestibular apparatus, signaling via CN VIII.
What are the five basic taste qualities and which cranial nerves carry taste signals?
Answer: Sweet, sour, salty, bitter, umami. Taste from the anterior 2/3 of the tongue is carried by the facial nerve (CN VII); taste from the posterior 1/3 by the glossopharyngeal nerve (CN IX); taste from the epiglottis/pharynx region by the vagus nerve (CN X).
Taste buds contain gustatory receptor cells that detect dissolved chemicals.
Describe the pathway of smell (olfaction).
Answer: Odor molecules bind olfactory receptor neurons in the nasal epithelium → axons form the olfactory nerve (CN I) → synapse in the olfactory bulb → olfactory tract → limbic system and olfactory cortex.
Olfaction is unique among senses in that it bypasses the thalamus before reaching higher cortical areas, giving smell strong links to emotion and memory.
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