Campbell Biology Chapter 49 Review: Nervous Systems

49.1 From nerve nets to brains and spinal cords

pp. 1062–1067

On the AP exam? Background

Nervous system anatomy, glia and the divisions of the nervous system aren't in the current course. What carries over: neurotransmitters as local signals (Topic 4.1), opposing controls that keep the body steady (Topic 4.4), fight-or-flight as a response to the environment (Topic 8.1), nervous systems shaped by lifestyle (Topic 7.2) and the blood-brain barrier as a permeability question (Topic 2.4).

In the course: Topic 4.1 Cell Communication, Topic 4.4 Feedback, Topic 8.1 Responses to the Environment, Topic 7.2 Natural Selection, Topic 2.4 Membrane Permeability (notes, videos and more questions)

Key points

Detecting and reacting to the surroundings is far older than animals; single-celled organisms do it too. Animals added neurons, cells built to carry fast signals over long distances.
Cnidarians such as jellies and sea anemones have a nerve net, a mesh of neurons with no control center. Other animals bundle axons into nerves and gather neurons into ganglia. Animals that move head-first show cephalization: a brain and sense organs at the front end, linked to one or more nerve cords.
Nervous systems tend to match lifestyle. Fast, active hunters usually have more neurons and sharper senses than relatives that stay put or move slowly.
In vertebrates, the brain and spinal cord form the central nervous system (CNS), which processes information. Everything outside them, the nerves and ganglia, makes up the peripheral nervous system (PNS), linking the CNS to muscles, glands and sense organs.
A reflex is a fast, automatic response that runs through a short circuit in the spinal cord: a sensory neuron, often an interneuron, then a motor neuron. The muscle can act before the brain even registers what happened.
Gray matter is mostly cell bodies and dendrites; white matter is bundles of myelinated axons. Cerebrospinal fluid fills the brain's ventricles and the spinal cord's central canal, cushioning the CNS and moving nutrients and wastes. Glia, about as common as neurons in the human brain, support them: astrocytes tend synapses and help form the blood-brain barrier, oligodendrocytes (CNS) and Schwann cells (PNS) make myelin, and microglia fight infection.
Afferent neurons carry signals in to the CNS; efferent neurons carry commands out. Efferent output has two branches: the motor system, which drives skeletal muscles, and the autonomic nervous system, which runs smooth muscle, heart muscle and glands. Its sympathetic division drives fight-or-flight, its parasympathetic division drives rest-and-digest, and its enteric division runs the gut.

Key terms (15)

nerve net: A web of connected neurons spread through the body with no brain or control center. Cnidarians like jellies have one.
cephalization: The gathering of sense organs and neurons at the front end of an animal, forming a head and brain.
ganglion: A cluster of neuron cell bodies. Insects have a chain of them along a nerve cord; in vertebrates they sit outside the brain and spinal cord.
central nervous system (CNS): The brain and spinal cord in vertebrates, where incoming information is processed and responses are decided.
peripheral nervous system (PNS): All the nerves and ganglia outside the brain and spinal cord. It carries signals in from sensors and out to muscles and glands.
reflex: A quick, automatic response to a stimulus, handled by a short circuit of neurons that often skips the brain.
white matter: CNS tissue made mostly of myelinated axons, which look pale. Gray matter, by contrast, is mostly cell bodies and dendrites.
cerebrospinal fluid: The clear fluid that fills the brain's ventricles and surrounds the CNS. It cushions the brain and carries nutrients and wastes.
glia: Cells of the nervous system that support neurons instead of sending long-distance signals: they make myelin, feed and protect neurons, and tidy up synapses.
astrocyte: A star-shaped glial cell with many jobs: it helps seal brain capillaries into the blood-brain barrier, mops up spare neurotransmitter and ions near synapses, and widens nearby blood vessels when neurons are working hard.
blood-brain barrier: Capillary walls in the brain and spinal cord whose cells are joined by tight junctions, so only selected molecules can pass from the blood into nerve tissue.
afferent neuron: A neuron that carries information toward the CNS, such as a sensory neuron from the skin.
efferent neuron: A neuron that carries commands away from the CNS to muscles, glands or other effectors.
sympathetic division: The part of the autonomic nervous system behind fight-or-flight: faster heart, slower digestion and more glucose in the blood.
parasympathetic division: The part of the autonomic nervous system behind rest-and-digest: slower heart, more digestion and storing fuel. It mostly opposes the sympathetic division.

Check yourself: 49.1 From nerve nets to brains and spinal cords

4 questions on 49.1 From nerve nets to brains and spinal cords. Pick an answer to see if you got it, and why.

Question 1 of 4

Touching one tentacle of a sea anemone makes its whole body pull in. Its neurons form an interconnected mesh spread through the body wall, with no cluster of neurons acting as a control center. Which kind of nervous system does this describe?

Question 2 of 4

Two closely related species of marine bristle worms live in the same bay. One stays in a burrow and swallows mud for the bits of food in it. The other crawls and swims across the seafloor hunting small animals. Which difference between them is most likely?

Question 3 of 4

In a classic physiology demonstration, the spinal cord of a frog is cut just below the brain. When a small drop of dilute acid is placed on the skin of the frog's thigh, the leg on that side still makes wiping movements toward the spot. Which conclusion is best supported?

Question 4 of 4

An autoimmune disease destroys oligodendrocytes but leaves Schwann cells unharmed. Which effect is most likely?

0 of 4 answered

49.2 Main regions of the vertebrate brain

pp. 1067–1072

On the AP exam? Background

You won't be asked to name brain regions or their jobs. What carries over: daily rhythms (nocturnal and diurnal activity) and fight-or-flight as responses to the environment (Topic 8.1), the hypothalamus running negative feedback (Topic 4.4), melatonin as a long-distance signal (Topic 4.1) and clock genes switched on and off in a daily loop (Topic 6.5).

In the course: Topic 8.1 Responses to the Environment, Topic 4.4 Feedback, Topic 4.1 Cell Communication, Topic 6.5 Regulation of Gene Expression (notes, videos and more questions)

Key points

In the embryo, the front of the neural tube swells into the forebrain, midbrain and hindbrain, which become the adult brain. In humans the forebrain's cerebrum grows so much that it folds over most of the rest.
The brainstem (midbrain, pons and medulla oblongata) relays signals between the body and higher brain areas. The medulla runs automatic functions like breathing, heart rate, blood vessel tone and swallowing. Many of the long motor pathways switch sides at this level, which is why damage to one side of the brain weakens the other side of the body.
The cerebellum compares planned movements with what the body is actually doing and fixes errors, so it's key for coordination, balance and learning motor skills.
The thalamus is the gateway for almost all sensory signals bound for the cerebrum, steering each kind to its own cortex area. The hypothalamus controls body temperature, hunger, thirst and the pituitary gland. The pineal gland releases melatonin, mostly at night.
The cerebrum has two hemispheres joined by the corpus callosum, a broad cable of axons. Its outer cortex handles perception, voluntary movement and thinking, and the basal nuclei buried inside help pick, start and smooth out movements and turn practiced actions into habits.
The reticular formation in the brainstem filters sensory input and helps set how alert you are. Your brain stays busy while you sleep, cycling through stages that show up as different wave patterns on an EEG, and sleep appears to help lock in what you learned. Sleeping and waking follow a circadian rhythm. In mammals the suprachiasmatic nucleus (SCN) in the hypothalamus is the master clock, reset each day by light signals from the eyes. Inside cells, clock proteins switch off their own genes in a roughly 24-hour loop.
Emotion depends on a set of linked structures called the limbic system, including the amygdala (central to fear and emotional memories) and the hippocampus. Functional imaging such as PET and fMRI shows which areas become more active during a task.

Key terms (15)

brainstem: The stalk connecting the rest of the brain to the spinal cord, made of the midbrain, pons and medulla oblongata. It relays signals and runs many automatic functions.
medulla oblongata: The lowest part of the brainstem. It controls breathing, heart rate, blood pressure, swallowing and vomiting without you thinking about them.
pons: The part of the brainstem above the medulla. It relays signals between the cerebrum and cerebellum and helps regulate breathing.
cerebellum: The brain region behind the brainstem that keeps movements smooth and balanced and helps you learn physical skills.
thalamus: A pair of egg-shaped structures deep in the forebrain that act as the gateway for sensory signals, steering each kind to its own area of the cerebral cortex.
hypothalamus: A small region below the thalamus that runs homeostasis: body temperature, hunger, thirst and the pituitary gland. It also holds the master daily clock.
cerebrum: The largest part of the human brain, with left and right hemispheres. It handles perception, voluntary movement, memory, language and thought.
corpus callosum: The wide bridge of nerve fibers that joins the two halves of the cerebrum so they can trade information.
basal nuclei: Clusters of neurons buried in the cerebrum that help select, start and smooth out movements and turn practiced actions into habits. They are also called basal ganglia.
reticular formation: A web of neurons in the brainstem that filters incoming sensory input and helps control alertness and sleep.
circadian rhythm: A cycle in body activity that repeats about every 24 hours, like sleeping and waking. It keeps running even without day-night cues.
suprachiasmatic nucleus (SCN): A cluster of neurons in the hypothalamus that acts as the body's master clock, kept in step with the day by light signals from the eyes.
limbic system: A ring of linked structures, including the amygdala and hippocampus, best known for emotion and also tied to memory, drive and the sense of smell.
amygdala: An almond-shaped cluster of neurons deep in each temporal lobe, central to fear and to storing emotional memories.
fMRI: Functional magnetic resonance imaging: a brain scan that detects changes in blood oxygen to show which areas are more active during a task.

Check yourself: 49.2 Main regions of the vertebrate brain

4 questions on 49.2 Main regions of the vertebrate brain. Pick an answer to see if you got it, and why.

Question 1 of 4

A gymnast practices a new beam routine for several weeks. At first her movements are jerky and she makes many small corrections partway through each move; later the moves become smooth and automatic. Which brain structure most directly compares intended movements with actual ones and helps learn motor skills like this?

Question 2 of 4

Signals from the eyes, ears and skin each stop at one paired structure deep in the forebrain, which steers each type on to its own area of the cerebral cortex. Which structure is this?

Question 3 of 4

Fruit flies with different versions of one gene, called period, were kept in constant darkness and their daily activity cycles were recorded (classic results first reported by Konopka and Benzer in 1971, rounded). Genotype | Length of activity cycle in constant darkness Wild type | about 24 hours Mutant 1 | about 19 hours Mutant 2 | about 28 hours Mutant 3 | no regular cycle Which conclusion is best supported?

Question 4 of 4

After hours of hiking without water, a person's blood becomes more concentrated. Sensors in one brain region detect this and trigger thirst and the release of a hormone that makes the kidneys save water. Once the person drinks, these responses shut off. Which region is this, and what kind of control does it show?

0 of 4 answered

49.3 The cerebral cortex: lobes, language and thinking

pp. 1072–1076

On the AP exam? Not tested

Cortex lobes, language areas and differences between the hemispheres aren't part of AP Biology (AP Psychology covers them). The only links are the brain turning sensory input into behavior (Topic 8.1) and comparing bird and mammal brains as evidence of common ancestry (Topics 7.6 and 7.7).

In the course: Topic 8.1 Responses to the Environment, Topic 7.6 Evidence of Evolution, Topic 7.7 Common Ancestry (notes, videos and more questions)

Key points

The cerebral cortex is the thin, folded outer layer of the cerebrum. Folding fits a large surface area inside the skull. Each hemisphere has four lobes: frontal, parietal, temporal and occipital.
Cortex areas do three broad kinds of work. Primary sensory areas take in one kind of input (vision in the occipital lobe, hearing in the temporal lobe, touch in the parietal lobe). Association areas pull the inputs together and work out what they mean. Motor areas send out commands.
Typical flow: sense organs → thalamus → primary sensory area → association areas → prefrontal cortex for planning → primary motor cortex at the back of the frontal lobe → brainstem and spinal cord → motor neurons → muscles.
The motor cortex and the somatosensory cortex are maps of the body. A body part gets cortex in proportion to how finely it's controlled or how many touch receptors it has, not its size, so the lips, tongue and fingers take up a lot of space.
Language depends on a network mostly in the left hemisphere. Broca's area in the frontal lobe is needed to produce speech; Wernicke's area in the temporal lobe is needed to understand it. Imaging shows other areas join in for reading and finding word meanings.
Lateralization means the hemispheres specialize. In most people the left leads for language, and the right leads for recognizing faces and judging spatial relationships. The hemispheres constantly share information through the corpus callosum, and the popular idea of 'left-brained' and 'right-brained' personalities isn't supported by evidence.
The prefrontal cortex supports executive functions such as planning, judgment and controlling impulses. In mammals, the outer cortex (neocortex) is arranged in six layers. Birds organize their equivalent region, the pallium, mostly as clusters of neurons, yet some birds show problem-solving that rivals apes. Both arrangements trace back to a pallium in a shared ancestor.

Key terms (14)

cerebral cortex: The thin, folded outer layer of the cerebrum. It handles perception, voluntary movement, language and thinking.
frontal lobe: The front lobe of each hemisphere. It holds the motor cortex, Broca's area and the prefrontal cortex.
parietal lobe: The lobe behind the frontal lobe. It holds the somatosensory cortex and helps combine sensory input, such as where things are in space.
temporal lobe: The lobe on the side of each hemisphere. It holds the auditory cortex and Wernicke's area.
occipital lobe: The lobe at the back of the brain that receives and processes visual information.
association area: A region of cortex that combines and interprets information from primary sensory areas, for example turning shapes into a recognized face.
prefrontal cortex: The front part of the frontal lobe, used for planning, decisions, judgment and controlling impulses.
primary motor cortex: A strip at the back of the frontal lobe whose neurons send commands for voluntary movement, with each body part mapped to its own zone.
somatosensory cortex: A strip at the front of the parietal lobe that receives touch, pain, temperature and body-position signals, arranged as a map of the body.
Broca's area: A region in the frontal lobe, usually on the left, needed to produce speech.
Wernicke's area: A region in the temporal lobe, usually on the left, needed to understand spoken and written language.
lateralization: The way the two hemispheres specialize, such as the left usually leading for language and the right for faces and spatial skills.
neocortex: The six-layered sheet of neurons that makes up most of the mammalian cerebral cortex.
pallium: The roof of the forebrain. In mammals it forms the layered cerebral cortex; in birds its neurons are grouped mainly in clusters.

Check yourself: 49.3 The cerebral cortex: lobes, language and thinking

4 questions on 49.3 The cerebral cortex: lobes, language and thinking. Pick an answer to see if you got it, and why.

Question 1 of 4

During awake brain surgery, a surgeon applies weak electrical current to small spots on the cortex to map areas that must be protected. While a patient counts aloud, stimulating one spot in the left frontal lobe stops her from producing words, although between stimulations she understands questions normally. This spot is most likely part of which area?

Question 2 of 4

Volunteers in a brain scanner look at a flashing black-and-white checkerboard, with no sound or touch. Which region shows the largest increase in activity?

Question 3 of 4

On the somatosensory cortex, the strip devoted to the fingertips is much larger than the strip devoted to the middle of the back, even though the back has more skin. In a test where two points touch the skin at once, which result does this predict?

Question 4 of 4

A ball is thrown toward you and you reach out to catch it. Which sequence best describes how the information flows?

0 of 4 answered

49.4 How experience rewires synapses

pp. 1076–1079

On the AP exam? Background

LTP, NMDA and AMPA receptors and memory systems aren't in the current course. What carries over: ligand-gated ion channels that open when a ligand binds (Topic 4.2), signals that trigger enzymes or programmed cell death (Topic 4.3), stem cells becoming specialized cells (Topic 6.6) and learned behavior (Topic 8.1).

In the course: Topic 4.2 Introduction to Signal Transduction, Topic 4.3 Signal Transduction Pathways, Topic 6.6 Gene Expression and Cell Specialization, Topic 8.1 Responses to the Environment (notes, videos and more questions)

Key points

Development overbuilds, then trims. Neurons compete for limited survival signals from the tissues they reach, and those that miss out undergo apoptosis; about half the neurons made in an embryo die this way. Developing neurons also form extra synapses, and many are later removed.
Neural plasticity is the nervous system's ability to rewire itself after birth, mostly at synapses. Connections whose activity lines up with the cell's other inputs tend to be reinforced or joined by new ones ("cells that fire together wire together"), while connections that fire out of step tend to fade.
Early experience matters: the visual cortex, for example, needs normal input from the eyes early in life to wire up properly. Changes in how synapses are remodeled are thought to play a part in autism, which has a strong genetic component. Large studies have ruled out vaccines as a cause.
Short-term memory holds information briefly. New long-term memories first depend on the hippocampus, which links pieces of information stored across the cortex. Over time, partly during sleep, lasting connections form within the cortex, so older memories no longer need the hippocampus.
Linking new information to what you already know makes it easier to store. Motor skills learned by repetition seem to involve growing new connections, while facts may rely more on strengthening existing ones.
In long-term potentiation (LTP), a synapse's signal strength rises and stays high. At glutamate synapses, NMDA receptors are plugged by Mg²⁺ at rest. When glutamate binds while the postsynaptic cell is already depolarized, the plug comes out and Ca²⁺ flows in. Ca²⁺ activates enzymes such as protein kinases, which add more AMPA receptors to the membrane, so the same glutamate now gives a bigger response.
Adult mice and many other mammals make new neurons from neural stem cells, especially in the hippocampus, and these neurons help with learning. How much this happens in adult humans is still debated. The CNS repairs itself poorly compared with the PNS, so researchers are exploring stem cells to replace lost neurons.

Key terms (13)

neural plasticity: The nervous system's ability to change its connections in response to activity and experience.
synapse elimination: The removal of unused or weak synapses during development, leaving the connections that are actually used.
apoptosis: Programmed cell death, an orderly self-destruct. In the developing nervous system it removes neurons that don't get enough survival signals.
short-term memory: Memory that holds information briefly, like a code you need for a minute, before it's dropped or stored for the long term.
long-term memory: Memory that lasts days to a lifetime, stored as lasting connections in the cerebral cortex.
hippocampus: A curved structure deep in each temporal lobe that's essential for forming new long-term memories of facts and events.
memory consolidation: The gradual process of making a new memory stable, shifting it from depending on the hippocampus to lasting connections in the cortex.
long-term potentiation (LTP): A long-lasting increase in how strongly a synapse transmits signals after intense, well-timed activity. It's thought to underlie much learning and memory.
glutamate: The main excitatory neurotransmitter in the vertebrate brain. Binding to its receptors usually depolarizes the next neuron.
NMDA receptor: A glutamate-gated ion channel that's plugged by Mg²⁺ at rest. It only lets Ca²⁺ in when glutamate binds and the cell is already depolarized.
AMPA receptor: A glutamate-gated ion channel that lets Na⁺ in and carries most ordinary signaling at glutamate synapses. LTP adds more of them.
neural stem cell: An unspecialized cell in the nervous system that can divide and give rise to new neurons or glia.
autism: A developmental condition affecting social communication, often with repetitive behaviors. It has a strong genetic contribution and isn't caused by vaccines.

Check yourself: 49.4 How experience rewires synapses

4 questions on 49.4 How experience rewires synapses. Pick an answer to see if you got it, and why.

Question 1 of 4

After long-term potentiation (LTP) has been set up at a glutamate synapse, the same amount of glutamate released by the presynaptic neuron produces a larger response in the postsynaptic cell. Which change in the postsynaptic cell best explains this?

Question 2 of 4

Slices of rat hippocampus were given a burst of high-frequency stimulation. The size of the postsynaptic response was measured before and 1 hour after (invented data). Treatment during the burst | Response before (% of baseline) | Response 1 hour after (% of baseline) No drug | 100 | 180 NMDA receptor blocker | 100 | 102 Calcium-binding chemical injected into the postsynaptic cell | 100 | 98 Which conclusion is best supported?

Question 3 of 4

The AMPA receptor is a glutamate receptor that is itself an ion channel. Which description of how it works is correct?

Question 4 of 4

Rats learned the location of a hidden platform in a pool. Researchers then briefly switched off the hippocampus with a drug and tested whether the rats still remembered where the platform was (invented data). Time between learning and test | Rats remembering the location, hippocampus working (%) | Rats remembering the location, hippocampus switched off (%) 1 day | 90 | 25 30 days | 85 | 80 Which explanation best fits the data?

0 of 4 answered

49.5 Brain disorders at the molecular level

pp. 1079–1082

On the AP exam? Background

Specific disorders and drugs aren't in the current course. They're good practice for tested ideas: neurotransmitters as local signals (Topic 4.1), drugs that block or boost one step of a signaling pathway (Topic 4.3), misfolded proteins that clump (Topic 1.7), enzymes that cut proteins (Topic 3.1) and traits shaped by both genes and environment (Topic 5.5).

In the course: Topic 4.1 Cell Communication, Topic 4.3 Signal Transduction Pathways, Topic 1.7 Proteins, Topic 3.1 Enzymes, Topic 5.5 Environmental Effects on Phenotype (notes, videos and more questions)

Key points

Many nervous system disorders trace back to specific molecules: a neurotransmitter, its receptor or transporter, or a protein that clumps. Most are shaped by both genes and environment, and twin and adoption studies help separate the two.
Schizophrenia involves hallucinations and delusions, not multiple personalities. It's strongly heritable. Drugs that boost dopamine signaling can cause similar symptoms, most antipsychotic medicines block dopamine receptors, and glutamate signaling through NMDA receptors is involved too.
Major depressive disorder brings long stretches of low mood and lost interest; bipolar disorder swings between depression and mania. Many antidepressants raise serotonin or norepinephrine at synapses, often by blocking reuptake. How they actually relieve depression is more complex than simply fixing 'low serotonin.'
Addictive drugs, from nicotine and alcohol to opioids and stimulants, all boost the brain's reward pathway: dopamine-releasing neurons in the ventral tegmental area (VTA) that signal to the nucleus accumbens and other forebrain areas. Different drugs act at different steps. Repeated use causes lasting changes that drive craving even when the drug no longer brings much pleasure.
In Alzheimer's disease, a form of dementia, neurons die widely, especially in the hippocampus and cortex. Its hallmarks are amyloid plaques (clumps of β-amyloid peptide outside neurons) and neurofibrillary tangles (clumped tau protein inside them). Rare early-onset forms come from mutations in the gene for the amyloid precursor protein or for the enzymes that cut it. Antibody drugs that clear amyloid can modestly slow decline but don't cure it.
Parkinson's disease is a movement disorder. Its symptoms appear as dopamine-making neurons in the midbrain, whose axons reach the basal nuclei, gradually die. Clumps of a protein called α-synuclein build up in affected neurons, and some inherited forms involve genes needed to keep mitochondria healthy.
There's no cure for Parkinson's yet. L-dopa helps because it crosses the blood-brain barrier and is converted to dopamine inside the brain; dopamine itself can't get across. Deep-brain stimulation and surgery are other options, and replacing lost dopamine neurons with stem-cell-derived ones is being tested.

Key terms (13)

schizophrenia: A serious mental illness with hallucinations, delusions and disordered thinking. It involves altered dopamine and glutamate signaling and is strongly heritable.
dopamine: A neurotransmitter used in pathways for movement, motivation and reward. Too little in the basal nuclei causes Parkinson's symptoms.
major depressive disorder: A mood disorder with long periods of low mood and loss of interest or pleasure, often with poor sleep, appetite shifts and tiredness.
bipolar disorder: A mood disorder that swings between depression and mania: stretches of unusually high or irritable mood, little need for sleep and impulsive choices.
reuptake: The pumping of a neurotransmitter back into the neuron that released it, which ends its signal. Many drugs work by blocking it.
reward system: Brain circuits, centered on dopamine neurons in the VTA, that make you want things that help survival and reproduction. Addictive drugs hijack them.
nucleus accumbens: A forebrain region that receives dopamine from the VTA and is central to motivation and reward.
addiction: A condition in which a person keeps seeking and using a drug despite harm and can't easily cut back, driven by lasting changes in the brain's reward circuits.
Alzheimer's disease: A progressive dementia with memory loss and confusion, caused by widespread death of neurons along with amyloid plaques and tau tangles.
amyloid plaque: A clump of β-amyloid peptide that builds up outside neurons in Alzheimer's disease.
neurofibrillary tangle: A knot of abnormal tau protein inside a neuron. Tau normally helps keep microtubules in axons stable.
Parkinson's disease: A progressive movement disorder with tremor, stiffness and slow movement, caused by the loss of dopamine-releasing neurons in the midbrain.
L-dopa: A drug for Parkinson's disease. It crosses the blood-brain barrier and is turned into dopamine inside the brain.

Check yourself: 49.5 Brain disorders at the molecular level

4 questions on 49.5 Brain disorders at the molecular level. Pick an answer to see if you got it, and why.

Question 1 of 4

Researchers studied people who had been adopted as infants and tracked whether they developed a particular mood disorder by age 40 (invented data). Group | Developed the disorder (%) Biological parent had the disorder; adoptive parents did not | 14 Adoptive parent had the disorder; biological parents did not | 4 No parent of either kind had the disorder | 3 Which conclusion is best supported?

Question 2 of 4

A drug blocks the transporter protein that pumps serotonin from the synaptic cleft back into the presynaptic neuron. What is the most direct effect of the drug at these synapses?

Question 3 of 4

A brain scan uses a tracer that binds to dopamine transporters, which sit on the axon terminals of dopamine-releasing neurons. In people with early Parkinson's disease, the scan shows much less tracer in the basal nuclei than in healthy people. Which explanation best fits?

Question 4 of 4

In neurons, a large membrane protein can be snipped by two enzymes, called secretases, that release a short piece, β-amyloid. In Alzheimer's disease, β-amyloid clumps into plaques outside neurons. Mice that normally develop plaques are given a drug that blocks one of these two secretases. What is the most likely effect?

0 of 4 answered