A neuron receives, integrates, and transmits information. Dendrites receive incoming signals (dendrites detect); the soma (cell body) integrates them; the axon sends the signal to the terminal buttons, which release chemical messengers. Many axons are wrapped in a fatty myelin sheath that speeds transmission.
A resting neuron sits at about −70 mV (the resting potential). When incoming signals push it past its threshold, positive ions rush in and an action potential — the neural impulse — sweeps down the axon, followed by a brief refractory period during which it cannot fire again. The action potential is all-or-none: a neuron fires at full strength or not at all. Stimulus intensity is coded by how often neurons fire and how many fire — never by a bigger spike.
Neurons don't touch; a tiny gap called the synapse separates them. The action potential triggers release of neurotransmitters, which cross the gap and bind to receptor sites on the next neuron, nudging it toward or away from firing. Leftover neurotransmitter is often reabsorbed through reuptake. Know each transmitter by its job:
| Neurotransmitter | Primary function | Notable link |
|---|---|---|
| Acetylcholine (ACh) | Muscle movement, learning, memory | Loss linked to Alzheimer's |
| Dopamine | Reward, motivation, motor control | Too little → Parkinson's; excess linked to schizophrenia |
| Serotonin | Mood, sleep, appetite | Undersupply linked to depression |
| GABA | Main inhibitory ("calm") messenger | Undersupply linked to anxiety, seizures |
| Endorphins | Natural painkillers, pleasure | Released during exercise/pain ("runner's high") |
The cerebral cortex is the wrinkled outer layer, split into two hemispheres and four lobes:
| Lobe | Location | Primary function |
|---|---|---|
| Frontal | Behind the forehead | Planning, judgment, voluntary movement; contains the motor cortex |
| Parietal | Top rear | Touch and body position; contains the somatosensory cortex |
| Occipital | Very back | Vision |
| Temporal | Sides (temples) | Hearing |
The motor cortex (rear of the frontal lobe) triggers voluntary movement; the somatosensory cortex (front of the parietal lobe) registers touch. Association areas integrate information for thinking, learning, and language.
The corpus callosum connects the hemispheres. For most people the left hemisphere specializes in language. In Roger Sperry's split-brain studies, a word flashed to the left visual field (processed by the right hemisphere) could not be named aloud, yet the left hand could pick out the matching object — showing the right hemisphere can process information but usually cannot produce speech. Neuroplasticity is the brain's ability to reorganize and form new connections, especially after damage or new learning.
The endocrine system is a set of glands that secrete hormones into the bloodstream — slower to act than neurons but longer-lasting. The pituitary gland (at the base of the brain) is the "master gland," secreting hormones that regulate other glands; it takes orders from the hypothalamus. The adrenal glands release adrenaline (epinephrine) during fight-or-flight, and their effects linger because hormones clear slowly.
Heritability is the proportion of variation in a trait within a population that is attributable to genetic differences. It is a population statistic, not a statement about one person, and it depends on the environment — a heritable trait can still change.
1. (C) Dendrite. Dendrites are the receiving branches that detect incoming signals. (A) the axon sends signals; (B) terminal buttons release neurotransmitters at the sending end; (D) myelin insulates the axon; (E) the soma integrates signals but is not the receiving structure. Fix: Dendrites detect (both start with d); trace the path receive → integrate → send → release.
2. (A). All-or-none means a neuron fires at full strength or not at all. (B) is the classic misconception — intensity is coded by frequency and number of neurons, not spike size; (C) the resting potential is the charged waiting state, not firing; (D) firing depends on reaching threshold, not on every dendrite; (E) neurons fire repeatedly after the refractory period. Fix: Every spike is identical; the brain reads intensity from rate and number, never size.
3. (B) GABA. GABA is the brain's main inhibitory transmitter; undersupply is linked to anxiety and seizures. (A) dopamine governs reward and motor control; (C) acetylcholine governs movement and memory; (D) serotonin governs mood and sleep; (E) endorphins are natural painkillers. Fix: GABA = the brake (inhibitory); it calms the brain down.
4. (B) Occipital lobe. The occipital lobe at the back of the head processes vision, so damage there impairs sight even with healthy eyes. (A) frontal handles planning and movement; (C) temporal handles hearing; (D) parietal handles touch; (E) the prefrontal cortex handles judgment and impulse control. Fix: Vision lives at the back of the brain — occipital lobe.
5. (E) Endorphins. Endorphins are the body's natural painkillers and pleasure boosters, released during sustained exertion — the "runner's high." (A) GABA inhibits neurons; (B) dopamine drives reward/motor control; (C) serotonin affects mood/sleep; (D) acetylcholine drives muscle movement and memory. Fix: Reduced pain + mild euphoria from exertion = endorphins (endogenous morphine).
6. (E) Sympathetic nervous system. Pounding heart, sweating palms, and halted digestion are the fight-or-flight signature of the sympathetic system. (A) parasympathetic does the opposite (calming); (B) somatic controls voluntary movement; (C) "central nervous system" is too broad and isn't the division driving these autonomic changes; (D) the cerebellum coordinates movement. Fix: The S in Sympathetic = Stress; the body ramps up for action.
7. (D) Parasympathetic nervous system. Slowing heart, returning salivation, and restored appetite are "rest-and-digest," the parasympathetic system's job. (A) sympathetic is the activating opposite; (B) somatic governs voluntary movement; (C) a reflex arc is a rapid spinal loop, not gradual calming; (E) the adrenal medulla releases hormones and would prolong, not end, arousal. Fix: "Heart slowed, digestion resumed" = parasympathetic, every time.
8. (D) Processing fear and emotional responses. Amygdala damage blunts fear even when the person intellectually knows a threat is dangerous, pinpointing its role in fear and emotion. (A) is the hippocampus's job; (B) is the cerebellum's; (C) is the hypothalamus's; (E) is the thalamus's. Fix: Amygdala = alarm; "knows danger but feels no fear" points straight to it.
9. (A) Pituitary gland. The pituitary, at the base of the brain, is the "master gland" whose hormones regulate other endocrine glands, so damage there disrupts the whole system. (B) the thyroid regulates metabolism; (C) the adrenal glands sit atop the kidneys and release stress hormones; (D) the pancreas regulates blood sugar; (E) the parathyroid regulates calcium. Fix: Master gland at the base of the brain = pituitary.
10. (D). The right hemisphere processed the image (so the left hand could respond) but could not produce speech (the verbal left hemisphere never received it). (A) is backward — each hemisphere controls the opposite side of the body; (B) is false — patients still see; (C) is false — the callosum normally links the hemispheres; (E) is false — speech is usually left-lateralized. Fix: Split-brain = the right hemisphere knows but can't talk; the left is the verbal one.
11. (C) Neuroplasticity. Recovery through other regions taking over a lost function is neuroplasticity, the brain's capacity to reorganize. (A) lateralization is specialization, not recovery; (B) a reflex arc is a spinal protective loop; (D) the all-or-none principle concerns single-neuron firing; (E) sensory adaptation is reduced response to constant stimulation. Fix: Brain rewires/reorganizes after damage = neuroplasticity.
12. (C). Heritability is the proportion of variation across a population attributable to genetic differences — here about 60%. (A) wrongly applies a population statistic to one person; (B) is the common misconception — heritable traits can still change with environment; (D) confuses heritability with prevalence; (E) confuses it with genetic relatedness. Fix: Heritability = population variation due to genes, setting-dependent — never "% genetic for one person."
1. (C) Dendrite. Dendrites are the receiving branches that detect incoming signals. (A) the axon sends signals; (B) terminal buttons release neurotransmitters at the sending end; (D) myelin insulates the axon; (E) the soma integrates signals but is not the receiving structure. Fix: Dendrites detect (both start with d); trace the path receive → integrate → send → release.
2. (A). All-or-none means a neuron fires at full strength or not at all. (B) is the classic misconception — intensity is coded by frequency and number of neurons, not spike size; (C) the resting potential is the charged waiting state, not firing; (D) firing depends on reaching threshold, not on every dendrite; (E) neurons fire repeatedly after the refractory period. Fix: Every spike is identical; the brain reads intensity from rate and number, never size.
3. (B) GABA. GABA is the brain's main inhibitory transmitter; undersupply is linked to anxiety and seizures. (A) dopamine governs reward and motor control; (C) acetylcholine governs movement and memory; (D) serotonin governs mood and sleep; (E) endorphins are natural painkillers. Fix: GABA = the brake (inhibitory); it calms the brain down.
4. (B) Occipital lobe. The occipital lobe at the back of the head processes vision, so damage there impairs sight even with healthy eyes. (A) frontal handles planning and movement; (C) temporal handles hearing; (D) parietal handles touch; (E) the prefrontal cortex handles judgment and impulse control. Fix: Vision lives at the back of the brain — occipital lobe.
5. (E) Endorphins. Endorphins are the body's natural painkillers and pleasure boosters, released during sustained exertion — the "runner's high." (A) GABA inhibits neurons; (B) dopamine drives reward/motor control; (C) serotonin affects mood/sleep; (D) acetylcholine drives muscle movement and memory. Fix: Reduced pain + mild euphoria from exertion = endorphins (endogenous morphine).
6. (E) Sympathetic nervous system. Pounding heart, sweating palms, and halted digestion are the fight-or-flight signature of the sympathetic system. (A) parasympathetic does the opposite (calming); (B) somatic controls voluntary movement; (C) "central nervous system" is too broad and isn't the division driving these autonomic changes; (D) the cerebellum coordinates movement. Fix: The S in Sympathetic = Stress; the body ramps up for action.
7. (D) Parasympathetic nervous system. Slowing heart, returning salivation, and restored appetite are "rest-and-digest," the parasympathetic system's job. (A) sympathetic is the activating opposite; (B) somatic governs voluntary movement; (C) a reflex arc is a rapid spinal loop, not gradual calming; (E) the adrenal medulla releases hormones and would prolong, not end, arousal. Fix: "Heart slowed, digestion resumed" = parasympathetic, every time.
8. (D) Processing fear and emotional responses. Amygdala damage blunts fear even when the person intellectually knows a threat is dangerous, pinpointing its role in fear and emotion. (A) is the hippocampus's job; (B) is the cerebellum's; (C) is the hypothalamus's; (E) is the thalamus's. Fix: Amygdala = alarm; "knows danger but feels no fear" points straight to it.
9. (A) Pituitary gland. The pituitary, at the base of the brain, is the "master gland" whose hormones regulate other endocrine glands, so damage there disrupts the whole system. (B) the thyroid regulates metabolism; (C) the adrenal glands sit atop the kidneys and release stress hormones; (D) the pancreas regulates blood sugar; (E) the parathyroid regulates calcium. Fix: Master gland at the base of the brain = pituitary.
10. (D). The right hemisphere processed the image (so the left hand could respond) but could not produce speech (the verbal left hemisphere never received it). (A) is backward — each hemisphere controls the opposite side of the body; (B) is false — patients still see; (C) is false — the callosum normally links the hemispheres; (E) is false — speech is usually left-lateralized. Fix: Split-brain = the right hemisphere knows but can't talk; the left is the verbal one.
11. (C) Neuroplasticity. Recovery through other regions taking over a lost function is neuroplasticity, the brain's capacity to reorganize. (A) lateralization is specialization, not recovery; (B) a reflex arc is a spinal protective loop; (D) the all-or-none principle concerns single-neuron firing; (E) sensory adaptation is reduced response to constant stimulation. Fix: Brain rewires/reorganizes after damage = neuroplasticity.
12. (C). Heritability is the proportion of variation across a population attributable to genetic differences — here about 60%. (A) wrongly applies a population statistic to one person; (B) is the common misconception — heritable traits can still change with environment; (D) confuses heritability with prevalence; (E) confuses it with genetic relatedness. Fix: Heritability = population variation due to genes, setting-dependent — never "% genetic for one person."