Bio

Question 1

Which combination of features allowed Cajal to observe the individuality of neurons more effectively than previous researchers?

A. Adult brains and electron microscopy
B. Golgi stains and infant brains
C. Nerve dissection and silver nitrate solution
D. MRI technology and radioactive tracers

Answer 1

B. Cajal used Golgi’s silver staining method but applied it to infant brains, where neurons are smaller and easier to observe individually.

Question 2

Which of the following best explains why Santiago Ramón y Cajal’s work fundamentally changed our understanding of the nervous system?

A. He discovered neurons could regenerate after injury.
B. He demonstrated that neurons communicate through electrical impulses only.
C. He showed that neurons are individual cells rather than a continuous network.
D. He confirmed that glial cells are responsible for memory storage.

Answer 2

C. Cajal used improved staining methods to show that neurons are individual cells separated by small gaps, refuting the earlier idea that they formed a continuous network.

Question 3

The philosophical appeal of the older belief that neurons formed a continuous network most directly reflects which of the following assumptions?

A. The brain is a purely electrical system with no chemical involvement.
B. Sensory experience is divided into separate cognitive modules.
C. Conscious experience feels unified, suggesting the brain functions as a singular entity.
D. All cells must merge to function effectively in organ systems.

Answer 3

C. The belief that neurons formed a continuous network was appealing because conscious experience feels undivided, as if arising from a unified system rather than many separate cells.

Question 4

What was ironic about the 1906 Nobel Prize shared by Cajal and Golgi?

A. They were father and son with opposing theories.
B. Golgi’s methods discredited Cajal’s findings shortly after the award.
C. Despite sharing the prize, they argued for opposite theories in their acceptance speeches.
D. Both scientists ultimately agreed that glia outnumber neurons.

Answer 4

C. Cajal and Golgi both received the Nobel Prize but defended contradictory theories—Cajal supporting the neuron doctrine, Golgi still supporting the reticular theory.

Question 5

Mitochondria within neurons are particularly important because they:

A. Synthesize new proteins essential for communication between neurons.
B. Generate energy necessary for neural activity and may influence mental health.
C. Serve as the storage site for neurotransmitters.
D. Regulate the expression of DNA within the nucleus.

Answer 5

B.Mitochondria perform metabolic activities and supply energy. Their functionality is linked to mood, energy levels, and possibly conditions like autism.

Question 6

Which of the following accurately distinguishes neurons from glial cells based on the provided information?

A. Neurons are found only in the brain; glia are found throughout the body.
B. Neurons transmit information; glia perform supportive roles that are multifaceted and less defined.
C. Glia transmit faster signals; neurons support glia metabolically.
D. Glia contain DNA; neurons do not.

Answer 6

B.Neurons transmit signals, while glial functions are supportive and varied, not easily summarized in a single definition.

Question 7

Which structure would be most directly affected by a genetic mutation causing inefficient energy use in neurons?

A. Nucleus
B. Ribosome
C. Endoplasmic Reticulum
D. Mitochondrion

Answer 7

D.Mitochondria are responsible for energy production; mutations in mitochondrial DNA can impair this function and affect overall neuronal activity.

Question 8

Which of the following statements about mitochondria is most accurate?

A. They are found only in neurons with axons.
B. They synthesize proteins for metabolic processes.
C. They contain their own unique genetic material and differ genetically across cells.
D. They are exclusively found in the soma of a neuron.

Answer 8

Answer: C
Explanation: Mitochondria have their own DNA separate from the nucleus and differ genetically from one another. They provide energy for cellular functions, but they are not involved in protein synthesis (that’s the job of ribosomes), and they’re not exclusive to the soma or neurons with axons.

Question 9

Which of the following best differentiates ribosomes from mitochondria in a neuron?

A. Ribosomes store energy; mitochondria produce proteins.
B. Ribosomes conduct impulses; mitochondria modulate dendritic activity.
C. Ribosomes synthesize proteins; mitochondria perform metabolic activities.
D. Ribosomes produce myelin; mitochondria generate neurotransmitters.

Answer 9

Answer: C
Explanation: Ribosomes synthesize proteins, while mitochondria handle metabolic processes that produce energy.

Question 10

What would most likely occur if a neuron’s dendritic spines were significantly reduced?

A. The neuron would no longer be able to generate action potentials.
B. Protein synthesis in the soma would be halted.
C. The surface area available for synaptic input would decrease.
D. Mitochondrial energy output would drastically increase.

Answer 10

Answer: C
Explanation: Dendritic spines increase the dendrite’s surface area, allowing for more synaptic connections. Fewer spines mean less input from other neurons.

Question 11

A researcher stimulates a neuron’s axon and observes chemical release from boutons. What structure is directly responsible for this action?

A. Endoplasmic reticulum
B. Presynaptic terminal
C. Dendritic spine
D. Ribosome

Answer 11

Answer: B
Explanation: The presynaptic terminal (or bouton) is the site where chemicals (neurotransmitters) are released into the synaptic cleft.

Question 12

Which of the following is the correct classification of a neuron with its axon and dendrites entirely within the hippocampus?

A. Efferent neuron
B. Sensory neuron
C. Interneuron (intrinsic neuron)
D. Afferent neuron

Answer 12

Answer: C
Explanation: When both the axon and dendrites are within the same structure, it’s an intrinsic or interneuron of that structure.

Question 13

A neuron that transmits signals from the skin to the spinal cord would best be described as:

A. An efferent interneuron
B. An afferent sensory neuron
C. A myelinated motor neuron
D. A presynaptic terminal

Answer 13

Answer: B
Explanation: Sensory neurons are afferent, bringing information into the nervous system. In this case, it’s transmitting touch signals from the skin.

Question 14

The ability of Purkinje cells to integrate input from up to 200,000 neurons is primarily due to which structural feature?
A. Myelinated axon hillock
B. Extensive axonal branching
C. Numerous voltage-gated ion channels
D. Broad, highly branched dendritic tree

Answer 14

Answer: D
Explanation: Purkinje cells have an elaborate dendritic arborization, allowing them to receive input from a vast number of neurons.

Question 15

Which of the following best distinguishes astrocytes from other glial cells in terms of their role in neural signaling?
A. They produce the fastest myelin sheath
B. They synchronize neuronal activity by recycling neurotransmitters
C. They guide embryonic neuron migration
D. They destroy damaged neurons through phagocytosis

Answer 15

Answer: B
Explanation: Astrocytes regulate neurotransmitter levels and ion balance at synapses, helping coordinate neuron firing in waves.

Question 16

Which statement about glial distribution in the brain is most accurate?
A. Glial cells outnumber neurons in all brain regions
B. Neurons outnumber glial cells in the cerebral cortex
C. Glial cells outnumber neurons in the cerebellum
D. The ratio of glia to neurons varies by brain region

Answer 16

Answer: D
Explanation: Glia outnumber neurons in the cortex, but neurons outnumber glia in the cerebellum—showing regional variation.

Question 17

A deficiency in oligodendrocyte function would most likely result in which of the following symptoms?
A. Impaired immune response in the brain
B. Disrupted neuronal migration during development
C. Slower transmission speed along CNS axons
D. Reduced ability to regulate breathing rhythm

Answer 17

Answer: C
Explanation: Oligodendrocytes form myelin in the CNS; without them, signal conduction slows significantly.

Question 18

The tripartite synapse hypothesis suggests that astrocytes may enhance learning and memory by:
A. Forming myelin sheaths around axons
B. Directly triggering action potentials in adjacent neurons
C. Releasing their own transmitters in response to axonal activity
D. Blocking synaptic transmission to reduce noise

Answer 18

Answer: C
Explanation: In the tripartite synapse, astrocytes respond to neurotransmitters by releasing their own chemicals, modulating the signal

Question 19

Which glial cell type acts most directly as the brain’s immune defense and helps sculpt neural circuits through synaptic pruning?
A. Astrocyte
B. Schwann cell
C. Oligodendrocyte
D. Microglia

Answer 19

Answer: D
Explanation: Microglia act like macrophages, removing debris and pruning unused synapses to aid learning and neural refinement.

Question 20

Which of the following correctly pairs the glial cell with its unique embryonic role?
A. Schwann cell – forms synaptic junctions in the retina
B. Radial glia – guides migration of neurons and axons
C. Microglia – produces cerebrospinal fluid during gestation
D. Astrocytes – form myelin to support fetal brain activity

Answer 20

Answer: B
Explanation: Radial glia serve as scaffolding during development, guiding neurons and axonal/dendritic growth.

Question 21

Schwann cells are functionally analogous to oligodendrocytes, but differ primarily in that they:
A. Are involved in pruning weak synapses
B. Myelinate axons in the peripheral nervous system
C. Guide early neuron migration
D. Store calcium for synaptic release

Answer 21

Answer: B
Explanation: Schwann cells form myelin in the PNS, while oligodendrocytes do so in the CNS.

Question 22

Which of the following best explains why the brain requires a blood–brain barrier, unlike most other tissues?
A. To regulate the passage of hormones into the bloodstream
B. Because the brain consumes more oxygen than other organs
C. Because neurons are rarely replaced if damaged
D. To promote rapid immune cell entry into the CNS

Answer 22

Answer: C
Explanation: Neurons in the vertebrate brain are generally irreplaceable. The BBB protects them from damage caused by infections or immune responses

Question 23

Which of the following characteristics allows a molecule to passively cross the blood–brain barrier without special transport?
A. It is large and charged
B. It is hydrophilic and acidic
C. It dissolves in lipids and is uncharged
D. It is bound to a plasma protein

Answer 23

Answer: C
Explanation: Small, uncharged, and lipid-soluble molecules (like oxygen, CO₂, and fat-soluble vitamins) can diffuse freely across the BBB.

Question 24

Why don’t all organs in the body have a barrier like the blood–brain barrier?
A. Because only the brain needs selective nutrient intake
B. Because the barrier would trap red blood cells
C. Because the barrier also blocks essential nutrients
D. Because other tissues are already protected by skull and meninges

Answer 24

Answer: C
Explanation: While protective, the BBB blocks both harmful and useful substances. Most other tissues require continuous, easy access to nutrients and drugs.

Question 25

Which of the following molecules would most likely require active transport to cross the blood–brain barrier? A. Carbon dioxide B. Glucose C. Heroin D. Vitamin D

Answer 25

Answer: B Explanation: Glucose is essential for brain function and is transported into the brain via active, energy-dependent protein transporters.

Question 26

In what way does the structure of brain capillaries differ from those in the rest of the body? A. Brain capillaries lack endothelial cells B. The endothelial cells in brain capillaries have tight junctions C. Brain capillaries are surrounded by Schwann cells D. Brain capillaries are fenestrated and loosely connected

Answer 26

Answer: B Explanation: In the brain, endothelial cells are joined by tight junctions, forming the physical basis of the blood–brain barrier.

Question 27

Which of the following is TRUE about viruses and the blood–brain barrier? A. All viruses are completely blocked by the blood–brain barrier B. Viruses are actively transported across the barrier for immune detection C. Some viruses can cross the barrier and remain dormant in neurons D. The barrier becomes stronger when viruses are present in the blood

Answer 27

Answer: C Explanation: Certain viruses like chickenpox and herpes can cross the BBB, hide in neurons, and later reactivate.

Question 28

A patient is diagnosed with a brain tumor. Which of the following presents the greatest challenge in treating it with chemotherapy? A. Chemotherapy is too toxic for neurons B. The drugs stimulate an immune response in brain tissue C. Most chemotherapy drugs cannot cross the blood–brain barrier D. Tumor cells disable the immune system

Answer 28

Answer: C Explanation: The BBB blocks nearly all chemotherapy drugs, making it extremely difficult to treat brain cancers pharmacologically.

Question 29

The microglia’s unique immune response within the CNS is important because: A. They eliminate infected neurons rapidly to halt viral spread B. They engulf invading viruses without triggering inflammation C. They trigger apoptosis in astrocytes D. They fight viruses while sparing neurons from destruction

Answer 29

Answer: D Explanation: Unlike other immune cells, microglia can suppress infections while trying to preserve delicate, irreplaceable neurons

Question 30

A person with Alzheimer’s disease is likely to have a compromised blood–brain barrier due to: A. Increased tight junction strength B. Overactive glucose transporters C. Shrinking of endothelial cells D. Excessive immune cell activity

Answer 30

Answer: C Explanation: In Alzheimer’s, endothelial cells lining the blood vessels shrink, allowing harmful substances to breach the BBB.

Question 31

Which of the following is LEAST likely to be transported into the brain by active transport? A. Iron B. Choline C. Heroin D. Amino acids

Answer 31

Answer: C Explanation: Heroin crosses the BBB passively by dissolving in membrane fats; it does not require active transport

Question 32

Which of the following best explains why glucose is the primary fuel source for vertebrate neurons? A. Glucose is the only nutrient neurons can metabolize without oxygen. B. Glucose is the only nutrient synthesized in the brain. C. Glucose is the only nutrient that crosses the blood–brain barrier in large quantities. D. Neurons store large quantities of glucose for emergencies.

Answer 32

Answer: C Explanation: The passage notes that although neurons can use ketones and lactate, glucose is the only nutrient that crosses the blood–brain barrier in significant amounts.

Question 33

What consequence is most directly linked to a prolonged deficiency in vitamin B1 (thiamine)? A. The accumulation of ketones in the brain. B. An increase in glucose availability to neurons. C. The inability of neurons to store oxygen. D. Neuronal death leading to Korsakoff’s syndrome.

Answer 33

Answer: D Explanation: Thiamine is necessary for glucose metabolism. Its prolonged deficiency results in neuronal death and Korsakoff’s syndrome, particularly common in chronic alcoholism

Question 34

Why is glucose shortage rare in most individuals despite the brain’s high demand? A. The brain can switch to protein as a primary fuel. B. The pancreas stores glucose and releases it as needed. C. The liver produces glucose from various substrates. D. Neurons can store glucose in large amounts.

Answer 34

Answer: C Explanation: The liver synthesizes glucose from carbohydrates, amino acids, and glycerol, which helps maintain a steady supply.

Question 35

In which scenario would neurons most likely struggle to obtain sufficient fuel, despite normal glucose levels in the blood? A. When oxygen supply is slightly reduced. B. During short-term fasting. C. When thiamine is deficient. D. When lactate levels rise in the bloodstream

Answer 35

Answer: C Explanation: The liver synthesizes glucose from carbohydrates, amino acids, and glycerol, which helps maintain a steady supply.

Question 36

Which of the following is NOT true about glucose and neuronal function? A. Neurons require oxygen to metabolize glucose. B. Glucose crosses the blood–brain barrier via active transport. C. The brain consumes over 20% of the body’s glucose. D. Neurons frequently use ketones under normal, well-fed conditions.

Answer 36

Answer: D Explanation: Neurons can use ketones, but they rely almost entirely on glucose under normal conditions.

Question 37

Which of the following best explains why the inside of a resting neuron is negatively charged relative to the outside? A. The sodium–potassium pump transports more potassium out than sodium in. B. Negatively charged proteins remain trapped inside the cell, and potassium leaks out. C. The membrane is impermeable to sodium and potassium, resulting in charge separation. D. Chloride ions flow inward, creating a net negative potential inside the neuron.

Answer 37

Answer: B Explanation: The resting potential is mainly due to large negatively charged proteins trapped inside the cell and the slow leakage of potassium out of the cell, which carries positive charge out.

Question 38

At rest, which of the following correctly describes the forces acting on sodium ions? A. Both the electrical and concentration gradients drive sodium out of the cell. B. The electrical gradient pulls sodium in, while the concentration gradient pushes it out. C. Both the electrical and concentration gradients drive sodium into the cell. D. Sodium is unaffected by the resting membrane potential due to closed channels.

Answer 38

Answer: C Explanation: Sodium is more concentrated outside and is attracted to the negatively charged interior, so both gradients would drive sodium inward—if the channels were open.

Question 39

What would most likely occur if the membrane suddenly became highly permeable to sodium while the sodium–potassium pump was inhibited? A. Sodium would remain stationary due to lack of energy-dependent transport. B. Sodium would rush into the cell, depolarizing the membrane. C. Sodium would exit the cell rapidly, repolarizing the membrane. D. The membrane potential would remain unchanged because potassium channels are still closed.

Answer 39

Answer: B Explanation: If sodium channels open and the pump is off, sodium will enter down both its electrical and concentration gradients, leading to depolarization.

Question 40

Why is the sodium–potassium pump necessary despite the selective permeability of the neuronal membrane? A. The pump balances the osmotic pressure across the membrane. B. Without it, chloride ions would enter the cell and eliminate the resting potential. C. It maintains the unequal concentration of sodium and potassium necessary for future signaling. D. It helps positively charge the neuron’s interior to prepare for an action potential

Answer 40

Answer: C Explanation: The pump maintains ion gradients (high extracellular sodium, high intracellular potassium), which are critical for action potentials.

Question 41

Which of the following best describes potassium’s behavior at the resting membrane potential? A. Both gradients drive potassium into the cell, but the sodium–potassium pump removes it. B. Potassium remains completely stationary because its channels are closed. C. The electrical gradient pulls it in, but the concentration gradient pushes it out, resulting in a small net outward flow. D. Potassium flows freely in and out of the cell in equal amounts.

Answer 41

Answer: C Explanation: At rest, the electrical gradient pulls potassium in, while its higher concentration inside drives it out—causing a small net outward flow

Question 42

Opening chloride channels at the resting membrane potential would result in: A. A strong influx of chloride ions, neutralizing the negative interior. B. Little to no net movement of chloride ions due to balanced gradients. C. Outward movement of chloride to balance potassium leakage. D. Immediate depolarization of the membrane.

Answer 42

Answer: B Explanation: At rest, chloride's concentration and electrical gradients are balanced, so opening its channels does little unless the membrane is already depolarized

Question 43

Which of the following is essential for maintaining the effect of the sodium–potassium pump? A. Constant depolarization of the membrane B. High permeability of the membrane to sodium C. Selective permeability that prevents sodium from diffusing back in D. Large amounts of intracellular chloride to neutralize sodium ions

Answer 43

Answer: C Explanation: If sodium could easily diffuse back in, the pump’s efforts would be undone. Selective permeability preserves the sodium gradient created by the pump.

Question 44

Why does the neuron maintain a resting potential despite the high energy cost? A. To keep sodium and potassium ions balanced at all times B. To maintain structural stability in the membrane C. To prepare the neuron for rapid activation upon stimulation D. To allow chloride ions to remain inside the cell

Answer 44

Correct Answer: C Explanation: The neuron maintains a resting potential to prepare for rapid activation. Like a pulled bowstring, the stored energy (via ionic gradients) enables a swift response once a stimulus triggers an action potential

Question 45

What would most likely happen if the sodium–potassium pump ceased functioning? A. Chloride ions would rush into the neuron uncontrollably B. The neuron would hyperpolarize and fire repeatedly C. The resting potential would gradually diminish, reducing excitability D. The action potential peak would increase due to excess sodium entry

Answer 45

Correct Answer: C Explanation: Without the pump, sodium would accumulate inside the cell and potassium would leak out, diminishing the resting potential and reducing the neuron’s ability to generate action potentials.

Question 46

Which of the following best illustrates the concept of hyperpolarization? A. A neuron’s membrane potential becoming more negative than −70 mV B. Sodium rushing into the neuron, increasing membrane potential C. A slight reduction in membrane polarity that does not trigger an action potential D. The neuron releasing neurotransmitters across a synapse

Answer 46

Correct Answer: A Explanation: Hyperpolarization refers to an increase in membrane polarization, making the inside more negative (e.g., more negative than −70 mV).

Question 47

Which of the following describes an all-or-none response in neurons? A. Sodium channels gradually open in proportion to the stimulus B. Any depolarization causes a graded response based on intensity C. Once the threshold is passed, the neuron fires a full action potential regardless of stimulus strength D. The magnitude of the action potential increases with stronger stimuli

Answer 47

Answer: C Explanation: Neurons exhibit all-or-none firing: once the threshold is reached, the action potential always occurs fully and does not vary in strength.

Question 48

Suppose a stimulus depolarizes a neuron just below the threshold. What is the most accurate description of the resulting electrical activity? A. Sodium channels will open, but only partially B. An action potential will still occur but at a slower rate C. A small, decaying voltage change will occur, but no action potential will fire D. The neuron will fire continuously until the stimulus stops

Answer 48

Correct Answer: C Explanation: Subthreshold depolarizations result in small voltage changes that fade away and do not trigger an action potential.

Question 49

During an action potential, which of the following ion movements is primarily responsible for the rapid depolarization phase? A. Potassium exits the neuron rapidly B. Sodium enters the neuron rapidly C. Chloride ions move into the neuron D. Calcium ions rush into the dendrites

Answer 49

Correct Answer: B Explanation: During the action potential, sodium channels open, allowing Na⁺ ions to flood into the cell, causing rapid depolarization.

Question 50

How does the analogy of a “bow and arrow” help explain the function of the resting potential? A. It shows how neurons must relax completely before firing B. It illustrates the need to accumulate neurotransmitters before action C. It demonstrates how prior energy investment enables a rapid response D. It emphasizes that only strong neurons can fire action potentials

Answer 50

Correct Answer: C Explanation: The analogy highlights how the neuron “pulls back” its membrane potential like a bowstring, storing energy that enables a quick and forceful action potential when stimulated.

Question 51

Which of the following best explains why a neuron cannot generate a stronger action potential in response to a more intense stimulus? A. The sodium-potassium pump limits depolarization. B. The number of sodium channels is fixed. C. The action potential obeys the all-or-none law. D. Stronger stimuli open calcium channels instead.

Answer 51

Answer: C Explanation: According to the all-or-none law, once threshold is reached, the action potential is always the same size and speed.

Question 52

What would be the most likely consequence of a mutation that caused sodium channels to remain open longer than usual during an action potential? A. The neuron would be hyperpolarized more quickly. B. The action potential would fail to reach threshold. C. The action potential peak would be broader or prolonged. D. The potassium channels would open more slowly.

Answer 52

Answer: C Explanation: Prolonged sodium influx would delay repolarization, extending the peak of the AP.

Question 53

A neuron is exposed to a toxin that selectively blocks potassium channels. Which of the following would most likely occur? A. Sodium influx would be inhibited. B. The neuron would fail to reach threshold. C. The neuron would depolarize and remain depolarized longer. D. The sodium-potassium pump would immediately reverse the effects.

Answer 53

Answer: C Explanation: Without potassium outflow, the membrane cannot repolarize properly, causing prolonged depolarization.

Question 54

Which statement is false about voltage-gated ion channels during an action potential? A. Potassium channels contribute to repolarization and hyperpolarization. B. Sodium channels open in response to depolarization and later inactivate. C. Voltage-gated channels allow free and continuous ion flow regardless of membrane potential. D. Sodium influx occurs because both the electrical and concentration gradients favor it.

Answer 54

Answer: C Explanation: Voltage-gated channels open or close depending on the membrane potential; ion flow is not continuous or free.

Question 55

What determines the frequency of action potentials fired by a neuron in response to a stimulus? A. The amplitude of the action potential B. The width of the axon membrane C. The intensity of the stimulus above threshold D. The number of potassium ions leaving the neuron

Answer 55

Answer: C Explanation: Although AP amplitude doesn't change, more intense stimuli above threshold can increase firing frequency

Question 56

Why do local anesthetics like Novocain prevent pain transmission? A. They permanently inactivate the sodium-potassium pump. B. They hyperpolarize the neuron beyond threshold. C. They prevent sodium ions from entering through voltage-gated channels. D. They stimulate potassium efflux, blocking depolarization.

Answer 56

Answer: C Explanation: By blocking sodium channels, anesthetics prevent the initiation of action potentials.

Question 57

Which of the following best describes what happens at the peak of an action potential? A. Sodium channels are maximally open and potassium channels are still closed. B. Sodium influx reverses membrane polarity and sodium channels close. C. Potassium efflux is at its maximum and sodium influx continues. D. Both sodium and potassium channels close simultaneously.

Answer 57

Answer: B Explanation: At the peak, membrane polarity reverses, and sodium channels inactivate.

Question 58

Which of the following is not a factor that influences conduction velocity in axons? A. Axon diameter B. Frequency of action potentials C. Myelination (not mentioned directly but implied) D. Temperature (in some contexts, not in this passage)

Answer 58

Answer: B Explanation: Frequency affects stimulus encoding, not conduction velocity. Axon diameter and myelination do.

Question 59

Which of the following best explains why action potentials do not lose strength as they travel along an axon? A. Sodium ions continuously diffuse down the axon, sustaining depolarization. B. Voltage-gated sodium channels regenerate the action potential at each point along the axon. C. Potassium ions reinforce the depolarization across the membrane. D. The dendrites continuously back-propagate action potentials to the axon hillock.

Answer 59

Correct Answer: B Explanation: The action potential is regenerated at each segment of the axon by voltage-gated sodium channels, ensuring the signal remains strong throughout.

Question 60

What feature of myelinated axons allows for faster conduction of action potentials compared to unmyelinated axons? A. Increased density of sodium channels throughout the membrane B. Decreased diameter allowing more rapid ion flow C. Action potential jumps between nodes of Ranvier, reducing ion exchange D. Higher concentration of potassium channels in the dendrites

Answer 60

Correct Answer: C Explanation: In myelinated axons, action potentials "jump" from one node of Ranvier to the next—a process called saltatory conduction—which increases conduction speed and efficiency.

Question 61

In what way does saltatory conduction contribute to energy efficiency in neurons? A. It uses fewer neurotransmitters for signaling. B. It prevents depolarization from spreading beyond the axon hillock. C. It limits the use of sodium-potassium pumps to nodes of Ranvier only. D. It increases the rate of potassium influx to sustain membrane potential.

Answer 61

Correct Answer: C Explanation: Because sodium only enters the axon at nodes of Ranvier, fewer ions need to be pumped out, reducing the energy cost of maintaining ion gradients.

Question 62

Why do action potentials only travel in one direction along the axon despite electrical current flowing both ways? A. The axon hillock prevents retrograde flow of ions. B. Myelin blocks electrical current in the opposite direction. C. The regions behind the action potential are still in the refractory period. D. Potassium gates open only in the direction of forward propagation.

Answer 62

Correct Answer: C Explanation: The refractory period prevents the membrane region that just fired an action potential from immediately firing again, ensuring unidirectional movement.

Question 63

Which of the following events marks the transition between the absolute and relative refractory periods? A. Full closing of sodium channels and opening of potassium channels B. Return of membrane potential to resting level C. Partial repolarization with sodium channels inactive and potassium still exiting D. Closure of potassium channels with complete sodium channel reactivation

Answer 63

Correct Answer: C Explanation: During the relative refractory period, the membrane is partially repolarized, sodium channels begin to recover, but potassium is still flowing out.

Question 64

What is the primary functional consequence of back-propagation of the action potential into dendrites? A. It triggers another action potential in the axon. B. It enhances the speed of signal conduction. C. It facilitates synaptic vesicle release at the terminal. D. It increases dendritic plasticity and learning potential.

Answer 64

Correct Answer: D Explanation: Back-propagation can make dendrites more susceptible to structural changes, which are associated with learning and synaptic plasticity.

Question 65

Why are action potentials unable to regenerate along myelinated segments of axons? A. The membrane is too tightly packed with potassium channels. B. Sodium channels are absent between nodes of Ranvier. C. Myelin blocks voltage changes in the membrane. D. The resting membrane potential is too high to reach threshold

Answer 65

Correct Answer: B Explanation: Regeneration cannot occur along the internodal regions because voltage-gated sodium channels are concentrated only at the nodes of Ranvier.

Question 66

Which of the following best explains why local neurons do not follow the all-or-none law? A. They lack synaptic vesicles and neurotransmitter release mechanisms. B. They operate below the action potential threshold due to their reduced membrane surface area. C. They lack an axon and thus rely on graded potentials rather than action potentials. D. Their dendrites inhibit action potential generation through constant hyperpolarization

Answer 66

Correct answer: C Explanation: Local neurons lack an axon, so they do not generate action potentials and instead use graded potentials, which vary in strength.

Question 67

The belief that “we only use 10 percent of our brain” may have originated in part due to: A. Early functional imaging studies showing low metabolic activity in certain brain regions. B. Misinterpretations of local neurons’ small size and presumed underdevelopment. C. Observations that only a small percentage of neurons are structurally connected. D. Misconceptions about the role of glial cells in synaptic transmission.

Answer 67

Correct answer: B Explanation: Early researchers assumed that small, local neurons were undeveloped or unused, possibly leading to the 10% brain use myth.

Question 68

What happens to the graded potential in a local neuron as it spreads across the cell? A. It strengthens at synaptic junctions but disappears in nonsynaptic regions. B. It maintains constant amplitude but becomes more rapid. C. It travels in one direction with increasing intensity. D. It travels in all directions and decays in strength as it moves.

Answer 68

Correct answer: D Explanation: Graded potentials in local neurons spread in all directions and decrease in magnitude over distance.

Question 69

Why is it difficult to study local neurons using traditional electrophysiological techniques? A. They do not generate electrical signals that can be detected externally. B. Their lack of synaptic output makes them functionally irrelevant in networks. C. Their size makes them too fragile to probe without causing damage. D. They are found only in deep brain regions that are inaccessible to electrodes.

Answer 69

Correct answer: C Explanation: Local neurons are very small, and inserting electrodes into them often causes damage, making study difficult.