MCQs on Human Nerve and Muscle Physiology

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1. Which part of the neuron is responsible for transmitting electrical impulses away from the cell body?

  • a) Dendrite
  • b) Axon
  • c) Soma
  • d) Synapse

Answer: b) Axon
Explanation: The axon is responsible for transmitting electrical impulses away from the cell body of the neuron. It conducts signals to other neurons, muscles, or glands. Axons are often covered by myelin, which speeds up the transmission of impulses.

2. What is the main neurotransmitter involved in muscle contraction at the neuromuscular junction?

  • a) Dopamine
  • b) Acetylcholine
  • c) Serotonin
  • d) Norepinephrine

Answer: b) Acetylcholine
Explanation: Acetylcholine is released at the neuromuscular junction and binds to receptors on the muscle fiber, triggering an action potential that leads to muscle contraction. It plays a critical role in communication between nerves and muscles.

3. What ion is primarily responsible for the depolarization phase of an action potential in a neuron?

  • a) Sodium (Na+)
  • b) Potassium (K+)
  • c) Calcium (Ca2+)
  • d) Chloride (Cl-)

Answer: a) Sodium (Na+)
Explanation: During depolarization, sodium ions rush into the neuron through voltage-gated channels, causing the inside of the neuron to become more positive. This influx of sodium ions generates the action potential that transmits nerve signals.

4. Which type of muscle is under voluntary control?

  • a) Smooth muscle
  • b) Cardiac muscle
  • c) Skeletal muscle
  • d) All of the above

Answer: c) Skeletal muscle
Explanation: Skeletal muscle is the only type of muscle under voluntary control. It is controlled by the somatic nervous system and is responsible for movements such as walking, talking, and other conscious motor activities.

5. What is the resting membrane potential of a typical neuron?

  • a) +40 mV
  • b) -70 mV
  • c) +60 mV
  • d) -55 mV

Answer: b) -70 mV
Explanation: The resting membrane potential of a typical neuron is around -70 mV. This negative potential is maintained by the sodium-potassium pump, which moves sodium ions out and potassium ions into the cell.

6. Which of the following is true about the refractory period in nerve conduction?

  • a) It allows the neuron to generate another action potential immediately.
  • b) It ensures the action potential moves in one direction.
  • c) It occurs only during depolarization.
  • d) It decreases the strength of the action potential.

Answer: b) It ensures the action potential moves in one direction.
Explanation: The refractory period is a phase during which a neuron cannot fire another action potential or can only fire with a stronger stimulus. This prevents backward propagation of the action potential and ensures unidirectional nerve signal transmission.

7. What is the term for the space between two neurons or between a neuron and a muscle?

  • a) Synapse
  • b) Myelin sheath
  • c) Axon terminal
  • d) Node of Ranvier

Answer: a) Synapse
Explanation: The synapse is the gap between two neurons or between a neuron and a muscle. Chemical signals called neurotransmitters are released from the presynaptic neuron and bind to receptors on the postsynaptic neuron or muscle cell.

8. What is the role of calcium ions (Ca2+) in muscle contraction?

  • a) They stimulate the release of acetylcholine.
  • b) They bind to troponin, causing a conformational change that allows actin and myosin to interact.
  • c) They inhibit ATP hydrolysis.
  • d) They initiate the action potential in the muscle fiber.

Answer: b) They bind to troponin, causing a conformational change that allows actin and myosin to interact.
Explanation: Calcium ions bind to troponin in muscle fibers, causing a shift in the position of tropomyosin, allowing myosin heads to bind to actin filaments, which enables muscle contraction.

9. What is the role of myelin in nerve conduction?

  • a) It increases the speed of nerve impulse transmission.
  • b) It generates the action potential.
  • c) It maintains the resting membrane potential.
  • d) It transports neurotransmitters.

Answer: a) It increases the speed of nerve impulse transmission.
Explanation: Myelin is a fatty layer that wraps around the axons of neurons. It acts as an insulator, allowing action potentials to jump between nodes of Ranvier, thereby speeding up the transmission of nerve impulses.

10. What type of muscle is found in the walls of the heart?

  • a) Skeletal muscle
  • b) Smooth muscle
  • c) Cardiac muscle
  • d) Voluntary muscle

Answer: c) Cardiac muscle
Explanation: Cardiac muscle is found only in the walls of the heart. It is an involuntary muscle that contracts to pump blood throughout the body and has unique properties like rhythmic contraction and the ability to generate its own action potential.

11. What is the function of the sodium-potassium pump in neurons?

  • a) It generates an action potential.
  • b) It maintains the resting membrane potential.
  • c) It releases neurotransmitters.
  • d) It helps muscle fibers contract.

Answer: b) It maintains the resting membrane potential.
Explanation: The sodium-potassium pump actively transports sodium ions out of the neuron and potassium ions into the neuron, helping maintain the resting membrane potential of approximately -70 mV, essential for the neuron’s ability to generate action potentials.

12. Which of the following statements is true regarding the sliding filament theory of muscle contraction?

  • a) Myosin filaments slide past actin filaments to shorten the muscle.
  • b) Actin filaments slide past myosin filaments to elongate the muscle.
  • c) Both myosin and actin filaments shorten during contraction.
  • d) The sarcomere remains unchanged during contraction.

Answer: a) Myosin filaments slide past actin filaments to shorten the muscle.
Explanation: According to the sliding filament theory, muscle contraction occurs when myosin heads bind to actin filaments and pull them toward the center of the sarcomere, shortening the muscle fiber.

13. What is the function of the refractory period in muscle contraction?

  • a) It prevents the muscle from contracting too frequently.
  • b) It ensures that muscle fibers remain relaxed.
  • c) It allows calcium to be removed from the muscle fibers.
  • d) It generates ATP for muscle contraction.

Answer: a) It prevents the muscle from contracting too frequently.
Explanation: The refractory period in muscle fibers ensures that after one contraction, the muscle cannot contract again until it has fully relaxed. This prevents tetanus and ensures coordinated muscle movement.

14. What is the role of ATP in muscle contraction?

  • a) It is required for the formation of actin-myosin cross-bridges.
  • b) It initiates the action potential.
  • c) It maintains the resting membrane potential.
  • d) It removes calcium ions from the muscle fiber.

Answer: a) It is required for the formation of actin-myosin cross-bridges.
Explanation: ATP is essential for muscle contraction because it provides energy for myosin heads to attach to actin filaments, pull them together (power stroke), and then release to repeat the cycle.

15. Which type of muscle contraction occurs when the muscle generates force but does not change length?

  • a) Isotonic contraction
  • b) Isometric contraction
  • c) Concentric contraction
  • d) Eccentric contraction

Answer: b) Isometric contraction
Explanation: In an isometric contraction, the muscle generates force without changing its length. This type of contraction is important for maintaining posture or stabilizing joints.

16. What is the primary function of the axon hillock in a neuron?

  • a) Transmit electrical impulses.
  • b) Generate action potentials.
  • c) Maintain the resting membrane potential.
  • d) Release neurotransmitters.

Answer: b) Generate action potentials.
Explanation: The axon hillock is the region of the neuron where action potentials are generated. It integrates the electrical signals from the dendrites and, if the threshold is reached, initiates the action potential that travels down the axon.

17. What is a motor unit in muscle physiology?

  • a) A single muscle fiber and its associated motor neuron.
  • b) A group of muscle fibers controlled by different motor neurons.
  • c) A muscle fiber and its associated blood vessel.
  • d) A single motor neuron and all the muscle fibers it innervates.

Answer: d) A single motor neuron and all the muscle fibers it innervates.
Explanation: A motor unit consists of a single motor neuron and all the muscle fibers it controls. When the motor neuron fires an action potential, all the muscle fibers in the unit contract.

18. What is the term used to describe the process of muscle fibers receiving electrical signals that lead to contraction?

  • a) Synaptic transmission
  • b) Excitation-contraction coupling
  • c) Action potential propagation
  • d) Depolarization

Answer: b) Excitation-contraction coupling
Explanation: Excitation-contraction coupling is the process by which an electrical signal (action potential) leads to muscle contraction. This involves the transmission of an action potential across the muscle fiber membrane and its subsequent conversion into mechanical movement via calcium ion release.

19. Which of the following best describes a dendrite's role in a neuron?

  • a) Transmits electrical impulses away from the cell body.
  • b) Receives electrical signals from other neurons.
  • c) Synthesizes neurotransmitters.
  • d) Insulates the axon for faster transmission.

Answer: b) Receives electrical signals from other neurons.
Explanation: Dendrites are the branching extensions of a neuron that receive signals from other neurons. They transmit the received electrical impulses to the cell body, where the information is processed.

20. The contraction of muscle fibers is initiated by the release of which ion from the sarcoplasmic reticulum?

  • a) Sodium (Na+)
  • b) Potassium (K+)
  • c) Calcium (Ca2+)
  • d) Magnesium (Mg2+)

Answer: c) Calcium (Ca2+)
Explanation: The release of calcium ions from the sarcoplasmic reticulum triggers muscle contraction. Calcium binds to troponin on actin filaments, allowing myosin to interact with actin, resulting in contraction.

21. What is the all-or-nothing principle in nerve conduction?

  • a) Nerve impulses can vary in strength depending on the stimulus.
  • b) Nerve impulses are always of the same strength once initiated.
  • c) The neuron can choose not to propagate the impulse if the stimulus is weak.
  • d) The strength of the nerve impulse depends on the size of the axon.

Answer: b) Nerve impulses are always of the same strength once initiated.
Explanation: The all-or-nothing principle states that once a nerve impulse reaches the threshold level, the action potential is generated and propagated with the same strength. It does not vary based on the stimulus intensity once initiated.

22. What is the primary purpose of the synaptic cleft in neural transmission?

  • a) To store neurotransmitters for later use.
  • b) To prevent neurotransmitter overflow.
  • c) To allow the transmission of action potentials between neurons.
  • d) To provide a space for neurotransmitter diffusion between neurons.

Answer: d) To provide a space for neurotransmitter diffusion between neurons.
Explanation: The synaptic cleft is the small gap between the axon terminal of one neuron and the dendrite of the next. Neurotransmitters are released into this gap, where they diffuse across to bind with receptors on the next neuron.

23. What is the function of the sarcoplasmic reticulum in muscle cells?

  • a) To store and release calcium ions for muscle contraction.
  • b) To synthesize ATP for muscle contraction.
  • c) To transport oxygen to muscle fibers.
  • d) To remove waste products from muscle fibers.

Answer: a) To store and release calcium ions for muscle contraction.
Explanation: The sarcoplasmic reticulum (SR) is an organelle in muscle cells that stores calcium ions. Upon stimulation, it releases calcium, which binds to troponin and triggers muscle contraction by allowing actin and myosin to interact.

24. Which structure in a muscle fiber is responsible for storing energy in the form of ATP?

  • a) Mitochondria
  • b) Sarcomere
  • c) Myofibrils
  • d) Golgi apparatus

Answer: a) Mitochondria
Explanation: Mitochondria are the energy-producing organelles in muscle fibers. They generate ATP through aerobic respiration, which is used during muscle contraction and other cellular processes that require energy.

25. Which part of the brain is primarily responsible for voluntary muscle movement?

  • a) Cerebellum
  • b) Medulla oblongata
  • c) Cerebrum
  • d) Spinal cord

Answer: c) Cerebrum
Explanation: The cerebrum, specifically the motor cortex, is responsible for voluntary muscle movement. It sends signals to muscles via the spinal cord and motor neurons, allowing for controlled actions such as walking and speaking.

26. What is the primary neurotransmitter used by motor neurons at the neuromuscular junction?

  • a) Dopamine
  • b) Serotonin
  • c) Acetylcholine
  • d) Glutamate

Answer: c) Acetylcholine
Explanation: Acetylcholine is the neurotransmitter released by motor neurons at the neuromuscular junction. It binds to receptors on the muscle cell membrane, triggering the release of calcium ions and initiating muscle contraction.

27. What does the term "muscle tone" refer to?

  • a) The force generated during a single muscle contraction.
  • b) The continuous and passive partial contraction of muscles.
  • c) The muscle's ability to generate a rapid contraction.
  • d) The level of oxygen available in muscle fibers.

Answer: b) The continuous and passive partial contraction of muscles.
Explanation: Muscle tone refers to the constant low-level contraction of muscles, which is essential for maintaining posture and readiness for movement. It is controlled by the brain and spinal cord and is maintained even at rest.

28. Which of the following is the correct order of events during skeletal muscle contraction?

  • a) Calcium binds to troponin, myosin heads bind to actin, ATP is used to move myosin.
  • b) ATP binds to troponin, calcium binds to actin, myosin pulls actin.
  • c) Myosin binds to calcium, ATP binds to actin, troponin pulls myosin.
  • d) Troponin binds to myosin, calcium binds to ATP, actin is pulled.

Answer: a) Calcium binds to troponin, myosin heads bind to actin, ATP is used to move myosin.
Explanation: During muscle contraction, calcium binds to troponin, causing a conformational change that allows myosin heads to bind to actin. ATP then provides energy for the myosin heads to perform the power stroke, pulling actin filaments.

29. Which of the following best describes a synapse in the nervous system?

  • a) The space between a neuron and its target organ.
  • b) The electrical connection between two neurons.
  • c) The gap where neurotransmitters are released to transmit nerve impulses.
  • d) The chemical signal that transmits nerve impulses.

Answer: c) The gap where neurotransmitters are released to transmit nerve impulses.
Explanation: A synapse is the junction between two neurons or between a neuron and a muscle or gland. Neurotransmitters are released from one neuron and bind to receptors on the next, transmitting the signal across the gap.

30. What is the function of the myelin sheath in a neuron?

  • a) To store neurotransmitters.
  • b) To protect the axon and increase the speed of impulse transmission.
  • c) To generate electrical signals.
  • d) To connect the neuron to other cells.

Answer: b) To protect the axon and increase the speed of impulse transmission.
Explanation: The myelin sheath is a fatty layer that insulates the axon of neurons, speeding up the transmission of electrical signals by allowing them to jump between gaps in the sheath called nodes of Ranvier.

31. Which part of the nervous system controls involuntary actions like heart rate and digestion?

  • a) Somatic nervous system
  • b) Autonomic nervous system
  • c) Central nervous system
  • d) Peripheral nervous system

Answer: b) Autonomic nervous system
Explanation: The autonomic nervous system controls involuntary actions such as heart rate, blood pressure, digestion, and breathing. It includes two divisions: the sympathetic and parasympathetic systems, which regulate these functions to maintain homeostasis.

32. Which of the following best describes the function of a motor unit in muscle contraction?

  • a) It contains a single muscle fiber and its associated motor neuron.
  • b) It involves the coordination of multiple muscle fibers for fine motor control.
  • c) It contains both the muscle fibers and the sensory neurons.
  • d) It generates electrical signals to initiate muscle movement.

Answer: a) It contains a single muscle fiber and its associated motor neuron.
Explanation: A motor unit consists of a motor neuron and all the muscle fibers it innervates. The contraction of these fibers results from the activation of the motor neuron, which stimulates the muscle fibers to contract simultaneously.

33. Which of the following is an effect of acetylcholine release at the neuromuscular junction?

  • a) It triggers the contraction of smooth muscle.
  • b) It inhibits action potentials in skeletal muscles.
  • c) It activates the enzyme acetylcholinesterase.
  • d) It stimulates muscle contraction by increasing calcium release.

Answer: d) It stimulates muscle contraction by increasing calcium release.
Explanation: When acetylcholine is released at the neuromuscular junction, it binds to receptors on the muscle fiber membrane (sarcolemma), leading to an action potential that stimulates the release of calcium ions from the sarcoplasmic reticulum, triggering muscle contraction.

34. What is the term for the resting membrane potential of a neuron?

  • a) Depolarization
  • b) Hyperpolarization
  • c) Resting potential
  • d) Action potential

Answer: c) Resting potential
Explanation: The resting membrane potential is the electrical charge difference across the membrane of a neuron when it is not actively sending a signal. It is typically around -70mV and results from the unequal distribution of ions inside and outside the cell.

35. Which of the following is true regarding muscle fiber types?

  • a) Type I fibers are suited for short bursts of power and strength.
  • b) Type II fibers are slow-twitch fibers, ideal for endurance activities.
  • c) Type I fibers are fast-twitch fibers used for explosive movements.
  • d) Type II fibers are fast-twitch fibers, ideal for short, powerful movements.

Answer: d) Type II fibers are fast-twitch fibers, ideal for short, powerful movements.
Explanation: Type II fibers are fast-twitch fibers designed for quick, powerful movements but fatigue rapidly. Type I fibers are slow-twitch fibers, suitable for endurance activities due to their resistance to fatigue and efficient use of oxygen.

36. Which of the following processes is responsible for the generation of an action potential in neurons?

  • a) Na+/K+ pump action
  • b) Passive diffusion of chloride ions
  • c) Depolarization caused by sodium influx
  • d) Potassium efflux during repolarization

Answer: c) Depolarization caused by sodium influx
Explanation: The generation of an action potential occurs when sodium channels open, allowing sodium ions to flow into the neuron, causing depolarization. This rapid change in membrane potential is the foundation of nerve signal transmission.

37. Which of the following is the most important role of calcium ions during muscle contraction?

  • a) Stimulate the release of acetylcholine at the neuromuscular junction.
  • b) Initiate the formation of the cross-bridge between actin and myosin.
  • c) Regulate ATP production in muscle fibers.
  • d) Trigger the release of neurotransmitters at the synapse.

Answer: b) Initiate the formation of the cross-bridge between actin and myosin.
Explanation: Calcium ions bind to troponin, a regulatory protein on the actin filament, causing a conformational change that exposes binding sites for myosin. This allows the myosin heads to form cross-bridges with actin, resulting in muscle contraction.

38. What is the role of the sodium-potassium pump in maintaining the resting membrane potential of neurons?

  • a) It maintains a higher concentration of sodium inside the cell than outside.
  • b) It moves potassium and sodium ions equally in and out of the cell.
  • c) It pumps sodium out of the cell and potassium into the cell.
  • d) It generates action potentials in response to stimuli.

Answer: c) It pumps sodium out of the cell and potassium into the cell.
Explanation: The sodium-potassium pump actively transports three sodium ions out of the neuron and two potassium ions into the neuron, helping to maintain the resting membrane potential and establish the conditions necessary for generating action potentials.

39. What is the primary role of the neuromuscular junction in muscle contraction?

  • a) To provide ATP for muscle contraction.
  • b) To transmit electrical impulses to the muscle fibers.
  • c) To release calcium ions into the muscle fibers.
  • d) To transmit the action potential from the muscle to the neuron.

Answer: b) To transmit electrical impulses to the muscle fibers.
Explanation: The neuromuscular junction is the site where motor neurons communicate with muscle fibers. The action potential travels down the motor neuron, leading to the release of acetylcholine, which stimulates the muscle fibers to contract.

40. During which phase of the action potential do potassium ions exit the neuron?

  • a) Resting phase
  • b) Depolarization
  • c) Repolarization
  • d) Hyperpolarization

Answer: c) Repolarization
Explanation: During repolarization, potassium channels open, allowing potassium ions to exit the neuron. This restores the negative charge inside the neuron, returning the membrane potential to its resting state after depolarization.

41. What is the primary function of the axon in a neuron?

  • a) To receive electrical signals from other neurons.
  • b) To transmit electrical impulses away from the cell body.
  • c) To store neurotransmitters.
  • d) To support the structure of the neuron.

Answer: b) To transmit electrical impulses away from the cell body.
Explanation: The axon is the long, threadlike part of the neuron that carries electrical impulses away from the cell body toward other neurons or muscles. It is essential for transmitting signals throughout the nervous system.

42. What is the role of troponin in muscle contraction?

  • a) It binds to myosin and allows contraction to occur.
  • b) It binds to actin and exposes myosin-binding sites.
  • c) It releases calcium ions for contraction.
  • d) It prevents the interaction between actin and myosin.

Answer: b) It binds to actin and exposes myosin-binding sites.
Explanation: Troponin is a protein located on the actin filament. When calcium ions bind to troponin, it undergoes a conformational change, which exposes the binding sites on actin for myosin, allowing the cross-bridge cycle to occur and muscle contraction to take place.

43. Which type of muscle tissue is involuntary and found in the walls of internal organs?

  • a) Skeletal muscle
  • b) Cardiac muscle
  • c) Smooth muscle
  • d) Voluntary muscle

Answer: c) Smooth muscle
Explanation: Smooth muscle tissue is involuntary and is found in the walls of internal organs such as the stomach, intestines, and blood vessels. It contracts slowly and is controlled by the autonomic nervous system.

44. In which part of the neuron does the action potential begin?

  • a) Axon terminal
  • b) Dendrite
  • c) Cell body
  • d) Axon hillock

Answer: d) Axon hillock
Explanation: The action potential begins at the axon hillock, which is the junction between the cell body and the axon. The axon hillock has a high density of voltage-gated ion channels that initiate the action potential when the threshold is reached.

45. Which of the following statements best describes the function of the sarcomere in muscle fibers?

  • a) It stores calcium for muscle contraction.
  • b) It is the contractile unit of a muscle fiber.
  • c) It produces ATP for muscle contraction.
  • d) It generates the electrical impulses for muscle contraction.

Answer: b) It is the contractile unit of a muscle fiber.
Explanation: The sarcomere is the basic contractile unit of a muscle fiber, composed of actin and myosin filaments. The interaction between these filaments leads to muscle contraction, which is the fundamental process of muscle function.

46. What is the effect of a myelin sheath on the conduction of nerve impulses?

  • a) It decreases the speed of impulse conduction.
  • b) It increases the speed of impulse conduction.
  • c) It blocks the conduction of impulses.
  • d) It has no effect on impulse conduction.

Answer: b) It increases the speed of impulse conduction.
Explanation: The myelin sheath is an insulating layer around the axon of neurons. It increases the speed of electrical signal conduction by allowing impulses to jump from one node of Ranvier to the next, a process known as saltatory conduction.

47. Which of the following is the primary neurotransmitter involved in muscle contraction at the neuromuscular junction?

  • a) Dopamine
  • b) Acetylcholine
  • c) Serotonin
  • d) Glutamate

Answer: b) Acetylcholine
Explanation: Acetylcholine is the primary neurotransmitter released from motor neurons at the neuromuscular junction. It binds to receptors on the muscle fiber membrane, triggering an action potential that leads to muscle contraction.

48. What is the role of the sodium-potassium pump in maintaining the resting membrane potential of neurons?

  • a) It helps restore the ion balance after an action potential.
  • b) It generates the action potential in neurons.
  • c) It maintains the electrical gradient for depolarization.
  • d) It promotes neurotransmitter release at synapses.

Answer: a) It helps restore the ion balance after an action potential.
Explanation: The sodium-potassium pump actively transports three sodium ions out of the neuron and two potassium ions into the neuron, helping to restore the ion concentration gradient after an action potential and maintain the resting membrane potential.

49. What is the main purpose of myosin heads during muscle contraction?

  • a) To bind with actin filaments and generate force.
  • b) To release calcium ions from the sarcoplasmic reticulum.
  • c) To transport ATP into the muscle fibers.
  • d) To initiate action potentials in muscle fibers.

Answer: a) To bind with actin filaments and generate force.
Explanation: The myosin heads attach to actin filaments, forming cross-bridges, and use energy from ATP hydrolysis to pull the actin filaments toward the center of the sarcomere, generating the force required for muscle contraction.

50. Which of the following ion channels is responsible for depolarization during an action potential in a neuron?

  • a) Potassium channels
  • b) Sodium channels
  • c) Calcium channels
  • d) Chloride channels

Answer: b) Sodium channels
Explanation: Depolarization during an action potential occurs when sodium channels open, allowing sodium ions to rush into the neuron. This influx of positive ions causes the membrane potential to become less negative and ultimately trigger the action potential.

51. What is the role of acetylcholinesterase at the neuromuscular junction?

  • a) To degrade acetylcholine and stop muscle contraction.
  • b) To enhance the release of acetylcholine.
  • c) To stimulate calcium release in the muscle fibers.
  • d) To regenerate acetylcholine for continuous contraction.

Answer: a) To degrade acetylcholine and stop muscle contraction.
Explanation: Acetylcholinesterase is an enzyme that breaks down acetylcholine in the synaptic cleft. This degradation stops the signal, preventing continuous muscle contraction, and allows the muscle to relax.

52. Which of the following is a characteristic of fast-twitch muscle fibers?

  • a) High endurance, low power output.
  • b) Low fatigue resistance, high power output.
  • c) Primarily aerobic metabolism.
  • d) Slow contraction time and high endurance.

Answer: b) Low fatigue resistance, high power output.
Explanation: Fast-twitch muscle fibers are designed for rapid, powerful contractions but fatigue quickly. They rely more on anaerobic metabolism and are involved in activities requiring short bursts of power, such as sprinting.

53. Which of the following best describes the function of the T-tubules in muscle fibers?

  • a) They store calcium for muscle contraction.
  • b) They conduct action potentials deep into the muscle fiber.
  • c) They synthesize proteins for muscle growth.
  • d) They release acetylcholine at the neuromuscular junction.

Answer: b) They conduct action potentials deep into the muscle fiber.
Explanation: T-tubules (transverse tubules) are extensions of the muscle fiber membrane that carry the action potential deep into the muscle, ensuring that the signal reaches all parts of the fiber to trigger calcium release and contraction.

54. What is the function of the sarcoplasmic reticulum in muscle cells?

  • a) To generate ATP for muscle contraction.
  • b) To store and release calcium ions for muscle contraction.
  • c) To facilitate the exchange of ions between the cell and blood.
  • d) To produce proteins involved in muscle structure.

Answer: b) To store and release calcium ions for muscle contraction.
Explanation: The sarcoplasmic reticulum is an organelle in muscle cells that stores calcium ions. Upon receiving an action potential, it releases calcium ions, which bind to troponin, triggering muscle contraction.

55. Which of the following describes the resting membrane potential of a neuron?

  • a) The membrane potential is positive due to high potassium ion concentration.
  • b) The membrane potential is negative due to high sodium ion concentration.
  • c) The membrane potential is negative due to high potassium ion concentration inside the cell.
  • d) The membrane potential is neutral with equal ion concentrations inside and outside.

Answer: c) The membrane potential is negative due to high potassium ion concentration inside the cell.
Explanation: The resting membrane potential is negative, primarily due to the higher concentration of potassium ions inside the cell and sodium ions outside the cell. The sodium-potassium pump maintains this gradient.

56. During muscle contraction, which of the following occurs first?

  • a) Calcium ions bind to troponin.
  • b) Myosin heads bind to actin.
  • c) ATP is hydrolyzed to release energy.
  • d) Actin filaments slide over myosin filaments.

Answer: a) Calcium ions bind to troponin.
Explanation: When a muscle is stimulated, calcium ions are released from the sarcoplasmic reticulum and bind to troponin. This causes a conformational change, allowing myosin to bind to actin and initiate the cross-bridge cycle.

57. What is the term for the period in muscle contraction when the muscle is relaxing and not producing force?

  • a) Contraction period
  • b) Latent period
  • c) Relaxation period
  • d) Refractory period

Answer: c) Relaxation period
Explanation: The relaxation period follows contraction, during which calcium ions are pumped back into the sarcoplasmic reticulum, the actin and myosin filaments detach, and the muscle returns to its resting state.

58. What causes the depolarization of a neuron during an action potential?

  • a) Influx of sodium ions into the neuron.
  • b) Efflux of potassium ions from the neuron.
  • c) Influx of potassium ions into the neuron.
  • d) Efflux of sodium ions from the neuron.

Answer: a) Influx of sodium ions into the neuron.
Explanation: Depolarization occurs when sodium channels open, allowing sodium ions to rush into the neuron. This influx of positively charged ions causes the inside of the neuron to become more positive, triggering the action potential.

59. Which of the following structures stores neurotransmitters in a neuron?

  • a) Nucleus
  • b) Dendrites
  • c) Axon terminals
  • d) Soma

Answer: c) Axon terminals
Explanation: Axon terminals are the distal ends of the axon where neurotransmitters are stored in vesicles. When an action potential reaches the axon terminal, the neurotransmitters are released into the synaptic cleft to transmit signals to other neurons or muscles.

60. What is the primary function of the neuromuscular junction?

  • a) To facilitate ATP production in muscle cells.
  • b) To transmit the action potential from the neuron to the muscle fiber.
  • c) To secrete acetylcholinesterase for muscle relaxation.
  • d) To convert chemical energy into mechanical energy.

Answer: b) To transmit the action potential from the neuron to the muscle fiber.
Explanation: The neuromuscular junction is the site where motor neurons communicate with muscle fibers. When an action potential reaches the terminal, acetylcholine is released, stimulating the muscle fiber to contract.

61. What is the role of the synaptic cleft in nerve transmission?

  • a) To amplify the electrical signal between neurons.
  • b) To allow neurotransmitters to cross from one neuron to another.
  • c) To store neurotransmitters for later release.
  • d) To conduct electrical impulses directly between neurons.

Answer: b) To allow neurotransmitters to cross from one neuron to another.
Explanation: The synaptic cleft is the small gap between two neurons at a synapse. Neurotransmitters are released into the synaptic cleft from the presynaptic neuron, allowing them to bind to receptors on the postsynaptic neuron, transmitting the signal.

62. Which ion is primarily responsible for the repolarization phase of an action potential?

  • a) Calcium ions
  • b) Sodium ions
  • c) Potassium ions
  • d) Chloride ions

Answer: c) Potassium ions
Explanation: Repolarization occurs when potassium channels open, allowing potassium ions to flow out of the neuron. This movement of positively charged ions helps restore the negative charge inside the neuron, returning the membrane potential to its resting state.

63. What happens during the latent period of a muscle contraction?

  • a) The muscle generates force and shortens.
  • b) Calcium ions are released and bind to troponin.
  • c) The muscle relaxes after contraction.
  • d) ATP is hydrolyzed for muscle contraction.

Answer: b) Calcium ions are released and bind to troponin.
Explanation: The latent period is the brief time between the application of the stimulus and the beginning of muscle contraction. During this time, calcium ions are released from the sarcoplasmic reticulum, bind to troponin, and prepare the muscle fibers for contraction.

64. What is the primary function of the action potential in a neuron?

  • a) To transmit information across synapses.
  • b) To generate ATP for cellular processes.
  • c) To carry an electrical signal along the axon.
  • d) To store neurotransmitters for future use.

Answer: c) To carry an electrical signal along the axon.
Explanation: The action potential is an electrical impulse that travels along the axon of a neuron. It is crucial for transmitting information over long distances within the nervous system, enabling communication between neurons and other cells.

65. Which of the following describes the "all-or-nothing" principle in nerve impulse conduction?

  • a) A neuron either conducts an action potential at full strength or not at all.
  • b) The strength of an action potential can vary depending on the stimulus.
  • c) Neurons can transmit partial action potentials.
  • d) Action potentials decrease in strength as they travel.

Answer: a) A neuron either conducts an action potential at full strength or not at all.
Explanation: The "all-or-nothing" principle states that once a neuron reaches the threshold level of stimulation, it generates an action potential at full amplitude. If the stimulus is below threshold, no action potential is generated.

66. What type of muscle fibers are used for long-duration, endurance activities like marathon running?

  • a) Fast-twitch fibers
  • b) Slow-twitch fibers
  • c) Type IIb fibers
  • d) Type IIB fibers

Answer: b) Slow-twitch fibers
Explanation: Slow-twitch muscle fibers (also known as Type I fibers) are designed for endurance activities. They have a high resistance to fatigue, rely on aerobic metabolism, and are rich in mitochondria and capillaries to support sustained, long-duration activities.

67. Which of the following best describes the role of the neurotransmitter dopamine in the nervous system?

  • a) It inhibits the release of acetylcholine.
  • b) It acts as a pain-relieving neurotransmitter.
  • c) It regulates mood, attention, and motor control.
  • d) It causes muscle contraction directly.

Answer: c) It regulates mood, attention, and motor control.
Explanation: Dopamine is a neurotransmitter that plays a critical role in regulating mood, attention, and voluntary movement. Its deficiency is associated with disorders like Parkinson's disease and depression, while excess levels are linked to conditions like schizophrenia.

68. Which structure in the muscle fiber stores calcium ions required for muscle contraction?

  • a) Mitochondria
  • b) Sarcoplasmic reticulum
  • c) Golgi apparatus
  • d) Nucleus

Answer: b) Sarcoplasmic reticulum
Explanation: The sarcoplasmic reticulum is an organelle within muscle cells that stores calcium ions. When a muscle fiber is stimulated, calcium ions are released from the sarcoplasmic reticulum, triggering the contraction process.

69. What happens to the muscle fibers during the contraction phase of muscle contraction?

  • a) The muscle fibers lengthen and relax.
  • b) The actin and myosin filaments slide past each other, shortening the muscle.
  • c) The muscle fibers extend and elongate.
  • d) The myosin heads detach from actin filaments.

Answer: b) The actin and myosin filaments slide past each other, shortening the muscle.
Explanation: During muscle contraction, the myosin heads form cross-bridges with actin filaments. These cross-bridges pull the actin filaments toward the center of the sarcomere, shortening the muscle fiber and generating force.

70. In which part of the neuron does synaptic transmission occur?

  • a) Axon
  • b) Dendrites
  • c) Axon terminals
  • d) Soma

Answer: c) Axon terminals
Explanation: Synaptic transmission occurs at the axon terminals. When an action potential reaches the axon terminals, neurotransmitters are released into the synaptic cleft, where they bind to receptors on the postsynaptic neuron, transmitting the signal.

71. What is the main function of the myelin sheath in neurons?

  • a) To conduct action potentials faster.
  • b) To store neurotransmitters.
  • c) To produce ATP for the neuron.
  • d) To support the structural integrity of the neuron.

Answer: a) To conduct action potentials faster.
Explanation: The myelin sheath is a fatty layer that insulates the axon, allowing action potentials to travel faster by jumping from node to node in a process called saltatory conduction. This enhances the speed and efficiency of nerve signal transmission.

72. Which of the following events occurs during the depolarization phase of an action potential?

  • a) Potassium ions leave the cell.
  • b) Sodium ions enter the cell.
  • c) Calcium ions enter the cell.
  • d) Chloride ions leave the cell.

Answer: b) Sodium ions enter the cell.
Explanation: During depolarization, sodium channels open, allowing sodium ions to flow into the neuron. This influx of positive ions makes the inside of the neuron more positive, leading to the generation of an action potential.

73. What is the function of troponin in muscle contraction?

  • a) To bind ATP and provide energy for muscle contraction.
  • b) To bind calcium and move tropomyosin to expose the actin binding sites.
  • c) To synthesize new proteins during muscle repair.
  • d) To contract and generate force.

Answer: b) To bind calcium and move tropomyosin to expose the actin binding sites.
Explanation: Troponin is a protein that binds to calcium ions during muscle contraction. This binding causes a conformational change in the troponin-tropomyosin complex, exposing the binding sites on actin for myosin to form cross-bridges and initiate contraction.

74. Which part of the brain is primarily responsible for the initiation of voluntary muscle movements?

  • a) Cerebellum
  • b) Medulla oblongata
  • c) Basal ganglia
  • d) Motor cortex

Answer: d) Motor cortex
Explanation: The motor cortex, located in the frontal lobe, is responsible for the voluntary control of skeletal muscles. It sends motor signals via the corticospinal tract to initiate voluntary movements.

75. What type of muscle contraction occurs when a muscle produces tension without changing its length?

  • a) Isotonic contraction
  • b) Isometric contraction
  • c) Concentric contraction
  • d) Eccentric contraction

Answer: b) Isometric contraction
Explanation: An isometric contraction occurs when a muscle generates tension but does not shorten or lengthen. This type of contraction is commonly seen in activities like holding a weight steady without moving it.

76. What is the primary function of the sodium-potassium pump in neurons?

  • a) To move sodium and potassium ions to generate action potentials.
  • b) To maintain the resting membrane potential by actively pumping sodium out and potassium in.
  • c) To release neurotransmitters from the neuron.
  • d) To repair the neuron after an injury.

Answer: b) To maintain the resting membrane potential by actively pumping sodium out and potassium in.
Explanation: The sodium-potassium pump actively transports sodium ions out of the neuron and potassium ions into the neuron, maintaining the proper ion gradients and the resting membrane potential, essential for proper nerve function.

77. Which of the following statements is true about smooth muscle?

  • a) It is striated and controlled voluntarily.
  • b) It is non-striated and controlled involuntarily.
  • c) It has multiple nuclei per cell.
  • d) It contracts more rapidly than skeletal muscle.

Answer: b) It is non-striated and controlled involuntarily.
Explanation: Smooth muscle is non-striated and is under involuntary control, regulated by autonomic nerves. It is found in the walls of internal organs such as the intestines and blood vessels and contracts more slowly compared to skeletal muscle.

78. What is the primary neurotransmitter involved in neuromuscular transmission?

  • a) Serotonin
  • b) Norepinephrine
  • c) Acetylcholine
  • d) Glutamate

Answer: c) Acetylcholine
Explanation: Acetylcholine is the neurotransmitter released from motor neurons at the neuromuscular junction. It binds to receptors on muscle fibers, triggering muscle contraction.

79. Which of the following is responsible for the "refractory period" in nerve conduction?

  • a) The closing of sodium channels.
  • b) The inactivation of sodium channels.
  • c) The opening of potassium channels.
  • d) The release of neurotransmitters.

Answer: b) The inactivation of sodium channels.
Explanation: The refractory period occurs after an action potential when sodium channels become inactivated, preventing another action potential from being generated immediately. This ensures that the action potential travels in one direction along the neuron.

80. Which of the following structures in the brain is primarily responsible for maintaining balance and coordination?

  • a) Cerebellum
  • b) Thalamus
  • c) Hypothalamus
  • d) Medulla oblongata

Answer: a) Cerebellum
Explanation: The cerebellum is responsible for the coordination of voluntary movements, balance, and motor control. It processes sensory input and fine-tunes motor commands to ensure smooth and coordinated movement.

81. Which of the following is the main source of ATP during muscle contraction?

  • a) Glucose
  • b) Oxygen
  • c) Creatine phosphate
  • d) Glycogen

Answer: c) Creatine phosphate
Explanation: Creatine phosphate is the primary source of ATP for muscle contraction during short bursts of intense activity. It donates a phosphate group to ADP, regenerating ATP quickly for energy.

82. What is the role of acetylcholinesterase at the neuromuscular junction?

  • a) To produce acetylcholine.
  • b) To degrade acetylcholine and stop nerve transmission.
  • c) To stimulate muscle contraction.
  • d) To store calcium ions.

Answer: b) To degrade acetylcholine and stop nerve transmission.
Explanation: Acetylcholinesterase is an enzyme that breaks down acetylcholine in the synaptic cleft, ending the signal transmission and allowing the muscle to relax after contraction.

83. Which ion primarily causes muscle contraction in skeletal muscle?

  • a) Sodium
  • b) Potassium
  • c) Calcium
  • d) Magnesium

Answer: c) Calcium
Explanation: Calcium ions play a central role in muscle contraction. They bind to troponin on the actin filaments, causing a conformational change that moves tropomyosin and exposes binding sites for myosin, allowing muscle contraction.

84. What is the function of the axon hillock in a neuron?

  • a) To produce neurotransmitters.
  • b) To receive electrical signals from other neurons.
  • c) To initiate the action potential.
  • d) To maintain the cell's resting membrane potential.

Answer: c) To initiate the action potential.
Explanation: The axon hillock is the region where the action potential is initiated. If the depolarization from the dendrites reaches the threshold, an action potential is generated and travels down the axon.

85. What is the result of a "muscle twitch"?

  • a) A sustained contraction of the muscle.
  • b) A rapid cycle of contraction and relaxation.
  • c) The muscle becomes paralyzed.
  • d) The muscle generates force for movement.

Answer: b) A rapid cycle of contraction and relaxation.
Explanation: A muscle twitch is a brief, involuntary contraction and relaxation of a muscle in response to a single action potential. It is not strong enough to produce movement but is important for understanding muscle function.

86. What is the primary characteristic of slow-twitch muscle fibers?

  • a) They are fast to contract and fatigue quickly.
  • b) They are resistant to fatigue and suited for endurance activities.
  • c) They rely on anaerobic metabolism.
  • d) They are found primarily in the arms.

Answer: b) They are resistant to fatigue and suited for endurance activities.
Explanation: Slow-twitch fibers (Type I fibers) are designed for endurance activities. They have high mitochondrial content and rely on aerobic metabolism, making them resistant to fatigue and ideal for prolonged exercise.

87. Which part of the neuron receives signals from other neurons?

  • a) Axon
  • b) Axon terminal
  • c) Dendrites
  • d) Soma

Answer: c) Dendrites
Explanation: Dendrites are the branched extensions of a neuron that receive signals from other neurons. These signals are then transmitted to the cell body and processed.

88. What is the role of the T-tubules in muscle contraction?

  • a) To store calcium ions for muscle contraction.
  • b) To transmit the action potential deep into the muscle fibers.
  • c) To produce ATP.
  • d) To release neurotransmitters at the neuromuscular junction.

Answer: b) To transmit the action potential deep into the muscle fibers.
Explanation: T-tubules (transverse tubules) are extensions of the cell membrane that conduct the action potential deep into the muscle fiber, ensuring that the entire muscle contracts simultaneously by signaling the release of calcium ions from the sarcoplasmic reticulum.

89. Which of the following is responsible for the strength of muscle contraction?

  • a) The frequency of action potentials.
  • b) The amount of neurotransmitter released.
  • c) The number of motor units recruited.
  • d) The type of muscle fiber.

Answer: c) The number of motor units recruited.
Explanation: The strength of a muscle contraction is determined by the number of motor units recruited. A motor unit consists of a motor neuron and the muscle fibers it controls. More motor units recruited leads to a stronger contraction.

90. What is the main function of the sodium-potassium pump during nerve conduction?

  • a) To generate the action potential.
  • b) To establish and maintain the resting membrane potential.
  • c) To propagate the action potential along the axon.
  • d) To transport neurotransmitters to the synaptic cleft.

Answer: b) To establish and maintain the resting membrane potential.
Explanation: The sodium-potassium pump actively transports sodium ions out of the neuron and potassium ions into the neuron, maintaining the resting membrane potential. This is essential for the proper conduction of nerve impulses.

91. What is the role of tropomyosin in muscle contraction?

  • a) To generate ATP for muscle contraction.
  • b) To bind to calcium and expose actin binding sites.
  • c) To block the myosin binding sites on actin at rest.
  • d) To store calcium ions.

Answer: c) To block the myosin binding sites on actin at rest.
Explanation: Tropomyosin is a regulatory protein that covers the myosin binding sites on actin in relaxed muscle fibers. When calcium binds to troponin, tropomyosin shifts, exposing these binding sites and allowing myosin to form cross-bridges for contraction.

92. What is the function of the resting membrane potential in neurons?

  • a) To generate ATP for nerve transmission.
  • b) To maintain an electrical gradient across the membrane, ready for an action potential.
  • c) To allow neurotransmitter release.
  • d) To transmit the action potential down the axon.

Answer: b) To maintain an electrical gradient across the membrane, ready for an action potential.
Explanation: The resting membrane potential is the electrical charge difference across the neuron’s membrane when it is not transmitting an impulse. This gradient is essential for the neuron to respond to stimuli and generate an action potential.

93. What happens during the refractory period of a neuron?

  • a) The neuron is incapable of generating another action potential.
  • b) The neuron produces a stronger action potential.
  • c) The neuron releases neurotransmitters.
  • d) The neuron generates ATP for further transmission.

Answer: a) The neuron is incapable of generating another action potential.
Explanation: During the refractory period, the sodium channels are inactivated, preventing the neuron from generating another action potential immediately. This ensures that action potentials move in one direction and are not re-triggered prematurely.

94. Which of the following best describes the role of the sarcoplasmic reticulum in muscle contraction?

  • a) To provide energy for muscle contraction.
  • b) To store and release calcium ions.
  • c) To facilitate the exchange of sodium and potassium ions.
  • d) To generate action potentials in muscle fibers.

Answer: b) To store and release calcium ions.
Explanation: The sarcoplasmic reticulum is a specialized organelle in muscle cells that stores calcium ions. During muscle contraction, calcium is released from the sarcoplasmic reticulum, initiating the process of muscle contraction by allowing actin and myosin to interact.

95. What is the main difference between smooth muscle and skeletal muscle?

  • a) Smooth muscle is under voluntary control, while skeletal muscle is involuntary.
  • b) Smooth muscle is striated, while skeletal muscle is non-striated.
  • c) Smooth muscle is non-striated and involuntary, while skeletal muscle is striated and voluntary.
  • d) Smooth muscle contracts more rapidly than skeletal muscle.

Answer: c) Smooth muscle is non-striated and involuntary, while skeletal muscle is striated and voluntary.
Explanation: Smooth muscle is non-striated, and its contraction is involuntary, regulated by the autonomic nervous system. Skeletal muscle, in contrast, is striated and under voluntary control, allowing conscious movement.

96. Which of the following best describes the term "action potential"?

  • a) A brief electrical signal that travels along the axon of a neuron.
  • b) A chemical signal that crosses the synaptic cleft to activate muscle contraction.
  • c) A type of neurotransmitter released by neurons.
  • d) The process by which a neuron is repaired after injury.

Answer: a) A brief electrical signal that travels along the axon of a neuron.
Explanation: An action potential is a rapid, transient electrical signal that travels down a neuron’s axon to transmit information. It is the primary mechanism of communication in the nervous system.

97. What happens during the repolarization phase of an action potential?

  • a) Sodium ions move out of the neuron.
  • b) Potassium ions move into the neuron.
  • c) Sodium ions enter the neuron.
  • d) The membrane potential becomes more positive.

Answer: a) Sodium ions move out of the neuron.
Explanation: During repolarization, potassium ions move out of the neuron, and sodium channels close, restoring the membrane to its resting potential. This phase ensures that the neuron is ready for the next action potential.

98. What is the effect of a neurotransmitter binding to a postsynaptic receptor?

  • a) It generates an action potential in the postsynaptic cell.
  • b) It causes an influx of sodium into the postsynaptic cell.
  • c) It triggers the release of calcium ions into the synaptic cleft.
  • d) It prevents the release of neurotransmitters from the presynaptic neuron.

Answer: b) It causes an influx of sodium into the postsynaptic cell.
Explanation: When a neurotransmitter binds to a postsynaptic receptor, it opens ion channels, allowing the influx of sodium ions. This depolarizes the postsynaptic cell, potentially leading to an action potential.

99. Which of the following is a characteristic of cardiac muscle?

  • a) It is voluntary and striated.
  • b) It has multiple nuclei per cell.
  • c) It is involuntary and striated.
  • d) It lacks a defined structure.

Answer: c) It is involuntary and striated.
Explanation: Cardiac muscle is involuntary and striated, with cells joined by intercalated discs. It is found in the heart and is responsible for pumping blood through the circulatory system.

100. What is the role of the neuromuscular junction in muscle contraction?

  • a) To release calcium ions into the muscle fibers.
  • b) To convert electrical signals into chemical signals.
  • c) To generate ATP for muscle contraction.
  • d) To release neurotransmitters that stimulate muscle contraction.

Answer: d) To release neurotransmitters that stimulate muscle contraction.
Explanation: The neuromuscular junction is the synapse between a motor neuron and a muscle fiber. When an action potential reaches the neuron terminal, acetylcholine is released, which stimulates the muscle fiber to contract.

101. Which type of muscle fiber is primarily used for endurance activities like long-distance running?

  • a) Type I (slow-twitch) fibers.
  • b) Type IIa (fast-twitch oxidative) fibers.
  • c) Type IIb (fast-twitch glycolytic) fibers.
  • d) All muscle fibers are used equally.

Answer: a) Type I (slow-twitch) fibers.
Explanation: Type I fibers are designed for endurance activities due to their ability to resist fatigue. They rely on aerobic metabolism and are rich in mitochondria to sustain long-term activity.

102. What does the term "synaptic vesicle" refer to?

  • a) A structure that stores neurotransmitters in the axon.
  • b) A protein that binds neurotransmitters in the synaptic cleft.
  • c) A fluid-filled space that separates two neurons.
  • d) A part of the neuron that generates electrical impulses.

Answer: a) A structure that stores neurotransmitters in the axon.
Explanation: Synaptic vesicles are small, membrane-bound sacs in the presynaptic terminal that store neurotransmitters. Upon an action potential, these vesicles release neurotransmitters into the synaptic cleft, allowing communication between neurons.

103. What is the primary function of the sarcomere in skeletal muscle?

  • a) To store calcium ions for muscle contraction.
  • b) To produce ATP for muscle contraction.
  • c) To contract and generate force.
  • d) To regulate the speed of muscle contractions.

Answer: c) To contract and generate force.
Explanation: The sarcomere is the functional unit of muscle contraction. It consists of actin and myosin filaments, which slide past each other during contraction, generating force and shortening the muscle.

104. What is the role of calcium ions in muscle contraction?

  • a) To bind to troponin and initiate the sliding filament mechanism.
  • b) To store energy for muscle contraction.
  • c) To break down acetylcholine at the neuromuscular junction.
  • d) To produce ATP for muscle movement.

Answer: a) To bind to troponin and initiate the sliding filament mechanism.
Explanation: Calcium ions bind to troponin, a regulatory protein on the actin filaments. This allows tropomyosin to move, exposing binding sites for myosin and enabling the sliding filament mechanism to occur, which leads to muscle contraction.

105. Which type of ion channel is responsible for the depolarization phase of an action potential?

  • a) Potassium channels.
  • b) Sodium channels.
  • c) Calcium channels.
  • d) Chloride channels.

Answer: b) Sodium channels.
Explanation: During depolarization, sodium channels open, allowing sodium ions to flow into the neuron. This influx of positively charged ions causes the inside of the neuron to become more positive, initiating an action potential.

106. What is the function of the myelin sheath in neurons?

  • a) To support the neuron structurally.
  • b) To speed up the transmission of electrical signals.
  • c) To regulate ion concentrations inside the neuron.
  • d) To produce neurotransmitters.

Answer: b) To speed up the transmission of electrical signals.
Explanation: The myelin sheath is a fatty layer that wraps around the axon of neurons, insulating the axon and increasing the speed at which electrical signals (action potentials) travel along the neuron.

107. What is the primary function of the motor unit in muscle contraction?

  • a) To store calcium ions.
  • b) To receive signals from the brain.
  • c) To generate force for muscle movement.
  • d) To break down neurotransmitters.

Answer: c) To generate force for muscle movement.
Explanation: A motor unit consists of a motor neuron and the muscle fibers it controls. The activation of a motor unit generates force for muscle movement, with more motor units recruited for stronger contractions.

108. Which ion is primarily responsible for repolarization of the neuron after an action potential?

  • a) Sodium (Na+)
  • b) Potassium (K+)
  • c) Calcium (Ca2+)
  • d) Chloride (Cl-)

Answer: b) Potassium (K+)
Explanation: During repolarization, potassium ions move out of the neuron, restoring the negative resting membrane potential after the depolarization phase, which is caused by the influx of sodium ions.


109. What is the threshold potential in a neuron?

  • a) The maximum voltage the neuron can reach.
  • b) The membrane potential at which an action potential is triggered.
  • c) The voltage at rest in the neuron.
  • d) The difference in ion concentration across the membrane.

Answer: b) The membrane potential at which an action potential is triggered.
Explanation: The threshold potential is the level of depolarization required to trigger an action potential. Once the membrane potential reaches this threshold, an action potential is initiated and propagated along the axon.

110. What happens when the neuromuscular junction is activated?

  • a) Calcium ions are released from the sarcoplasmic reticulum.
  • b) Acetylcholine is released from the motor neuron into the synaptic cleft.
  • c) Sodium ions enter the muscle fibers, causing contraction.
  • d) ATP is consumed for energy production.

Answer: b) Acetylcholine is released from the motor neuron into the synaptic cleft.
Explanation: When a nerve impulse reaches the neuromuscular junction, acetylcholine is released from the motor neuron. It binds to receptors on the muscle cell membrane, triggering an action potential in the muscle fiber.

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