Bio 2 Flashcards
(46 cards)
What was the primary evidence that led Sherrington to infer the existence of a synapse?
A. The speed of conduction through a reflex arc matched that of a single axon.
B. Reflex responses ceased when the spinal cord was disconnected from the brain.
C. Reflex arcs exhibited a delay inconsistent with the known speed of action potentials along axons.
D. Pinching a dog’s foot caused immediate leg flexion regardless of spinal integrity.
Correct Answer: C
Explanation: Sherrington noticed that reflex responses were significantly slower than conduction along a single axon, implying an additional process—synaptic transmission—was involved.
Which statement best explains why reflex movements were more consistent after Sherrington severed the spinal cord from the brain?
A. Synaptic communication became more efficient.
B. Brain signals normally inhibit reflexes.
C. Reflex arcs require only brain input.
D. The absence of descending brain input removed variable modulation.
Correct Answer: D
Explanation: The spinal cord alone controlled the reflexes, and without descending input from the brain, the reflexes were more stable due to the lack of modulation.
What fundamental conclusion about neurons did Cajal’s anatomical work support?
A. That neurotransmitters were responsible for electrical transmission.
B. That electrical conduction happens across one continuous fiber.
C. That neurons are structurally continuous with one another.
D. That neurons are discrete cells separated by a small gap.
Correct Answer: D
Explanation: Cajal demonstrated that neurons are separate from one another, divided by a small anatomical gap — a foundational idea in neuroscience.
In Sherrington’s view, which property of reflexes most strongly suggested communication between neurons involves a special process?
A. Reflex speed matched motor neuron conduction speed.
B. Reflexes persisted even when the spinal cord was damaged.
C. The combined effect of multiple weak stimuli was stronger than one alone.
D. Motor responses only occurred in response to direct brain commands.
Correct Answer: C
Explanation: This summation effect (temporal or spatial) indicated synaptic integration—an emergent property not present in single-neuron conduction
- Why are Cajal and Sherrington considered complementary pioneers in neuroscience?
A. Both independently discovered the function of glial cells.
B. Cajal proved that synaptic gaps exist physiologically, while Sherrington proved it anatomically.
C. Cajal’s anatomical findings supported Sherrington’s physiological inference of synaptic function.
D. Both measured axonal speeds and deduced the chemical nature of neurotransmission.
Correct Answer: C
Explanation: Cajal showed anatomical separation between neurons; Sherrington demonstrated the physiological significance of this gap, supporting the idea of synapses.
Which of the following best explains why a series of rapid pinches at the same location can produce a reflex when a single pinch cannot?
A. The threshold for the presynaptic neuron increases with repetition.
B. Temporal summation allows subthreshold EPSPs to accumulate, triggering an action potential.
C. Repeated stimulation causes inhibitory postsynaptic potentials (IPSPs) to reverse.
D. Refractory periods shorten with repeated input, enabling continuous firing.
Correct Answer: B
Explanation: Temporal summation refers to the additive effect of multiple subthreshold stimuli over time, leading to a postsynaptic neuron reaching threshold.
What did Eccles demonstrate when he recorded two EPSPs in quick succession that together triggered an action potential?
A. Synaptic transmission requires multiple neurons firing in unison.
B. Hyperpolarization events can be reversed with spatial summation.
C. Graded potentials decay slowly, allowing inhibitory signals to dominate.
D. Temporal summation occurs when subsequent EPSPs build on residual depolarization.
Correct Answer: D
Explanation: Eccles showed that a second EPSP occurring shortly after the first adds to the remaining depolarization, potentially reaching threshold.
Why is spatial summation critical to brain function?
A. It allows subthreshold signals from a single axon to trigger multiple EPSPs in parallel.
B. It enhances inhibitory transmission by separating EPSPs and IPSPs spatially.
C. It enables a neuron to integrate inputs from multiple locations to reach threshold.
D. It allows temporal inputs to bypass refractory periods and build spatial overlap.
Correct Answer: C
Explanation: Spatial summation involves multiple presynaptic neurons providing simultaneous input that combines to surpass the postsynaptic threshold
A researcher stimulates two sensory neurons at the same time, neither of which evokes a reflex alone, but together they do. This is best explained by:
A. Decreased synaptic resistance during paired stimuli
B. Spatial summation from converging excitatory inputs
C. Increased frequency of action potentials at the axon hillock
D. Activation of inhibitory interneurons blocking competing reflexes
Correct Answer: B
Explanation: Sherrington observed that inputs from separate locations converging on a single postsynaptic neuron can summate and produce a response.
Which of the following statements accurately distinguishes an EPSP from an action potential?
A. EPSPs are self-propagating and all-or-none, while action potentials are not.
B. EPSPs are graded and decay with distance, while action potentials maintain constant amplitude.
C. EPSPs only occur at the axon hillock, while action potentials occur at the dendrites.
D. EPSPs are inhibitory and result from potassium influx, unlike excitatory action potentials.
Correct Answer: B
Explanation: EPSPs are local, graded depolarizations that diminish over time and space, unlike the all-or-none nature of action potentials
If a postsynaptic neuron fails to fire despite receiving rapid input from one axon and simultaneous input from another axon, the most likely explanation is:
A. The neuron lacks sufficient myelination for summation.
B. The EPSPs did not reach the axon terminal.
C. The inputs were asynchronous and failed to summate effectively.
D. The refractory period prevented IPSPs from converting to EPSPs
Correct Answer: C
Explanation: Both temporal and spatial summation depend on the timing and coordination of inputs. Asynchronous signals may not summate to reach threshold.
During Sherrington’s experiment, when one of a dog’s legs was raised due to a pinch, the extensor muscles of the stimulated leg were inhibited. Which of the following best explains the neural mechanism responsible for this inhibition?
A. Direct synaptic activation of the extensor muscle motor neurons
B. Hyperpolarization of interneurons in the stimulated leg
C. Inhibitory input from an interneuron to the extensor motor neurons
D. Simultaneous excitation of all muscle groups by the sensory neuron
Correct Answer: C
Explanation: Sherrington inferred that interneurons in the spinal cord inhibit specific motor neurons—such as those controlling the extensor muscles of the pinched leg—by sending inhibitory signals to reduce their activity.
What ionic movement primarily causes an inhibitory postsynaptic potential (IPSP) in a neuron?
A. Sodium ions enter the cell, depolarizing it
B. Potassium ions enter the cell, hyperpolarizing it
C. Chloride ions exit the cell, increasing internal negativity
D. Potassium ions leave or chloride ions enter, hyperpolarizing the cell
Correct Answer: D
Explanation: IPSPs occur when potassium leaves the neuron (taking positive charge out) or when chloride enters (bringing negative charge in), both of which make the interior more negative and move it away from the action potential threshold.
Which of the following best describes why inhibition was a controversial concept during Sherrington’s time?
A. Electrical stimulation could only excite neurons, not inhibit them
B. There was no anatomical evidence of inhibitory neurotransmitters
C. Scientists did not yet understand how action potentials were generated
D. No physiological mechanism had yet been discovered to explain inhibition
Correct Answer: D
Explanation: At the time, inhibition was a theoretical idea—no one had discovered the physiological process (like hyperpolarization via IPSPs) to support it. Sherrington’s work provided the first inferred evidence for it.
In a neural circuit where neuron 1 excites both neuron 2 and neuron 3, and neuron 2 inhibits neuron 3, what would be the likely outcome for neuron 3?
A. Continuous excitation due to reinforcement from both neurons
B. A delayed IPSP followed by an EPSP
C. A brief EPSP followed by inhibition from neuron 2
D. No change in membrane potential due to cancellation
Correct Answer: C
Explanation: The excitatory signal from neuron 1 reaches neuron 3 quickly, causing an initial EPSP. However, the pathway to neuron 2 takes longer (an extra synapse), so the inhibition from neuron 2 slightly lags and suppresses further excitation in neuron 3.
A neuron has a spontaneous firing rate of 10 action potentials per second. If it receives a stream of strong IPSPs, what is the most likely outcome?
A. The neuron will fire more frequently, reaching 15 spikes/sec
B. The neuron will cease firing action potentials altogether
C. The neuron’s firing rate will decrease below 10 spikes/sec
D. The neuron will maintain its spontaneous firing rate unchanged
Correct Answer: C
Explanation: IPSPs hyperpolarize the neuron, making it less likely to reach the threshold. This reduces the frequency of its spontaneous action potentials, but doesn’t necessarily stop firing completely unless inhibition is extremely strong.
Why did most scientists initially dismiss T.R. Elliott’s suggestion that sympathetic nerves stimulate muscles by releasing adrenaline?
A. His experiments failed to show consistent physiological effects
B. The technology to measure chemical release was unavailable
C. The idea contradicted Sherrington’s widely accepted electrical theory of synapses
D. Adrenaline was not known to affect human organs at the time
Correct Answer: C
Explanation: Sherrington’s electrical model of synaptic transmission was so dominant that scientists largely ignored Elliott’s chemical hypothesis, even though adrenaline mimicked sympathetic effects.
Otto Loewi’s experiment involving two frog hearts demonstrated chemical transmission by:
A. Directly stimulating the second heart with electricity
B. Using adrenaline injections to mimic neural stimulation
C. Showing that fluid from a stimulated heart could alter another heart’s rate
D. Measuring the electrical activity in both hearts simultaneously
Correct Answer: C
Explanation: Loewi transferred fluid from one frog’s heart (after stimulating its vagus or accelerator nerve) to another, showing that the fluid carried a chemical that influenced heart rate.
What was the key factor that made Loewi’s experiment conclusive evidence for chemical synaptic transmission?
A. It demonstrated that nerve signals could bypass the synapse entirely
B. It isolated and identified adrenaline as the primary neurotransmitter
C. It showed that a chemical, not electricity, mediated effects between hearts
D. It used two different species of frogs for increased generalizability
Correct Answer: C
Explanation: The experiment proved that a chemical substance, not electrical impulses alone, was responsible for transmitting signals between neurons and organs.
Which sequence best describes the chemical events at a synapse?
A. Action potential → neurotransmitter release → calcium influx → postsynaptic activation
B. Neurotransmitter synthesis → calcium entry → neurotransmitter release → receptor binding
C. Receptor binding → neurotransmitter release → postsynaptic action potential → synthesis
D. Calcium entry → neurotransmitter degradation → action potential → receptor stimulation
Correct Answer: B
Explanation: Neurotransmitters are synthesized first; then action potentials trigger calcium influx, leading to neurotransmitter release and binding to postsynaptic receptors
Which of the following statements is true regarding neurotransmitter recycling?
A. All neurotransmitters are destroyed after receptor binding
B. Reuptake into the presynaptic neuron is one possible fate of neurotransmitters
C. Neurotransmitters bind permanently to receptors
D. Postsynaptic cells release neurotransmitters to control the presynaptic cell’s activity
Correct Answer: B
Explanation: After binding, neurotransmitters can be taken back into the presynaptic terminal for recycling, diffuse away, or be degraded.
Nitric oxide (NO) is a unique neurotransmitter because:
A. It functions only in the peripheral nervous system
B. It is stored in vesicles like other neurotransmitters
C. It is a gas that diffuses directly and also affects blood vessels
D. It causes sedation and euphoria similar to nitrous oxide
Correct Answer: C
Explanation: Nitric oxide is a gaseous neurotransmitter that diffuses freely and dilates blood vessels, unlike typical neurotransmitters which are stored in vesicles.
Which discovery finally shifted scientific consensus toward chemical rather than electrical synapses?
A. Elliott’s experiments with adrenaline
B. Loewi’s demonstration of fluid-based signal transmission
C. 1950s research showing widespread chemical transmission in the nervous system
D. The isolation of nitric oxide as a neurotransmitter
Correct Answer: C
Explanation: Although Elliott and Loewi laid the groundwork, it wasn’t until research in the 1950s confirmed that chemical transmission predominated in the nervous system that scientific consensus shifted
Which of the following would most effectively increase serotonin levels in the brain?
A. Eating large amounts of phenylalanine-rich foods
B. Taking L-dopa supplements
C. Eating high-carbohydrate meals while limiting phenylalanine intake
D. Taking MAO to break down serotonin
Correct Answer: C. Eating high-carbohydrate meals while limiting phenylalanine intake
Explanation:
Tryptophan, the precursor to serotonin, competes with other amino acids like phenylalanine to cross the blood–brain barrier. High-carb meals trigger insulin, which reduces competing amino acids in the blood, giving tryptophan better access to the brain. Reducing phenylalanine intake also lowers competition. L-dopa is a dopamine precursor, not serotonin-related. MAO breaks down monoamines, so taking MAO (instead of an inhibitor) would decrease serotonin levels.
