Synapse & Receptors
What ion enters the presynaptic terminal when voltage-gated calcium channels open, triggering neurotransmitter release?
Calcium (Ca²⁺).
What is the primary excitatory neurotransmitter in the central nervous system?
Glutamate.
Which method records electrical activity produced by large groups of neurons, primarily reflecting cortical activity?
EEG (electroencephalography).
Which brain structure is especially important for balance, coordination, and fine-tuning movement?
Cerebellum.
A patient has difficulty producing fluent speech after a stroke affecting Broca’s area. What deficit would you expect?
Impaired speech production, potentially slow, effortful, nonfluent speech.
What is one major difference between ionotropic and metabotropic receptors in how they produce postsynaptic effects?
Ionotropic receptors directly open or control ion channels and generally act faster. Metabotropic receptors activate G proteins and intracellular signaling, generally acting more slowly.
What are the three broad size-based categories of neurotransmitters? Give one example of each.
Small-molecule neurotransmitters, such as acetylcholine; neuropeptides, such as beta-endorphin; and gaseous neurotransmitters, such as nitric oxide.
Which method uses magnetic fields to produce detailed images of brain structure: CT, MRI, EEG, or fMRI?
MRI.
Name the five major subdivisions of the brain.
Telencephalon, diencephalon, mesencephalon, metencephalon, and myelencephalon.
A toxin blocks the release of acetylcholine at the neuromuscular junction. What happens to muscle contraction?
Less acetylcholine reaches the muscle, reducing contraction and potentially causing weakness or paralysis.
A drug blocks voltage-gated calcium channels in the presynaptic terminal. Predict what happens to neurotransmitter release and the postsynaptic response.
Calcium entry decreases or stops, reducing vesicle fusion and neurotransmitter release. EPSPs and IPSPs would be reduced or absent.
Describe how acetylcholine is synthesized in the presynaptic terminal and how it is removed from the synaptic cleft.
Choline and acetyl-CoA are combined by choline acetyltransferase (ChAT) to synthesize acetylcholine. Acetylcholinesterase (AChE) breaks it down into choline and acetate.
Explain the difference between fMRI and PET scans in how they help researchers investigate brain function.
fMRI tracks changes in blood oxygenation and blood flow associated with neural activity. PET uses radioactive tracers to investigate metabolic activity or chemical uptake.
What information does the dorsal column-medial lemniscus pathway carry, and in which direction does that information travel?
Fine touch, vibration, and conscious proprioception. Information travels from the body toward the CNS and brain; fibers cross the midline in the medulla before relaying through the thalamus to the somatosensory cortex.
A mutation reduces acetylcholinesterase activity. How would this affect acetylcholine signaling at the neuromuscular junction?
Acetylcholine remains active longer, prolonging receptor stimulation and potentially causing sustained muscle contraction or twitching.
Explain how an excitatory postsynaptic potential (EPSP) differs from an inhibitory postsynaptic potential (IPSP), including the changes in membrane potential that can produce each.
EPSPs generally depolarize the membrane, often through positive-ion influx such as Na⁺. IPSPs make action potentials less likely, often through Cl⁻ influx or K⁺ efflux, which can hyperpolarize the membrane.
How is glutamate converted into GABA, and what enzyme is responsible for this conversion?
Glutamate is converted into GABA by glutamic acid decarboxylase (GAD).
What was the purpose of lobotomies, and what contributed to their decline in use?
Lobotomies were intended to make some severely mentally ill patients more manageable by disrupting frontal-lobe connections. Their serious side effects and the availability of antipsychotic medication, including chlorpromazine, contributed to their decline.
Identify the primary function of each structure:
Thalamus
Hypothalamus
Superior colliculi
Inferior colliculi
Thalamus: major relay for sensory and motor information to and from the cortex.
Hypothalamus: homeostasis, autonomic regulation, and hormone regulation.
Superior colliculi: visual information and visual orienting.
Inferior colliculi: auditory information and auditory orienting.
A toxin destroys astrocytes. Explain how this could affect the blood-brain barrier and overall brain function.
Astrocytes support the environment around brain capillaries and help maintain blood-brain barrier function. Their destruction can compromise barrier integrity, allowing harmful substances to enter brain tissue and impairing normal brain function.
A postsynaptic neuron receives several EPSPs that are individually too small to reach threshold. Explain how spatial summation and temporal summation could help the neuron reach threshold.
Spatial summation combines postsynaptic potentials from different synapses arriving around the same time. Temporal summation combines potentials arriving close together in time, often from repeated activity at the same synapse. Either can help the membrane reach threshold if the combined effect is sufficient.
Explain how degeneration of dopamine-producing neurons in the substantia nigra disrupts movement and is associated with Parkinson’s disease.
Dopamine-producing neurons in the substantia nigra project to the striatum, part of the basal ganglia motor circuitry. Their degeneration reduces dopamine signaling and disrupts movement control, contributing to Parkinson’s symptoms.
A researcher wants to measure rapid changes in cortical electrical activity while a participant performs a task. Which method would be most appropriate, and why would an MRI scan not directly answer the same question?
EEG is appropriate because it records rapid changes in electrical activity. MRI primarily provides structural images rather than a direct, moment-to-moment recording of electrical activity.
A patient has impaired sensation after damage to the dorsal root ganglion, but the ventral root remains intact. Explain why sensory function is affected and why motor output may remain relatively intact.
The dorsal root ganglion contains sensory neuron cell bodies, so damage can disrupt sensory information. The ventral root carries motor axons; if it remains intact, motor output is not directly disrupted by an isolated dorsal root ganglion injury.
Excess glutamate causes prolonged activation of glutamate receptors, including NMDA receptors. Explain how excessive activation can damage neurons and identify the ion whose influx is especially important in this process.
Excessive glutamate receptor activation can cause excitotoxicity. Excessive Ca²⁺ entry, particularly through NMDA receptors, can trigger damaging intracellular processes that injure or kill neurons.