[PHYSIO] Nerve & Muscle (2024)

Question 1

1. More than 95% of all energy used by muscles for sustained, long-term contraction is derived from which source?
   A. Phosphocreatine
   B. Glycogen
   C. Oxidative metabolism
   D. Adenosine diphosphate

Answer 1

C. Oxidative metabolism
Rationale: For long-term, sustained muscle contraction, the primary source of energy is oxidative metabolism. This process generates ATP through the oxidation of nutrients (like glucose and fatty acids) in the presence of oxygen, which is highly efficient and can support prolonged activity.

Question 2

2. Repeated stimulation of a skeletal muscle fiber causes sustained contraction. Accumulation of which solute in intracellular fluid is responsible for tetanus?
   A. Troponin
   B. Magnesium
   C. Calmodulin
   D. Calcium

Answer 2

D. Calcium
Rationale: Tetanus in muscle fibers occurs due to the accumulation of calcium ions (Ca2+) in the intracellular fluid. Continuous stimulation prevents the reuptake of Ca2+ into the sarcoplasmic reticulum, leading to sustained muscle contraction.

Question 3

3. The amount of calcium released from the sarcoplasmic reticulum depends on which of the following?
   A. The amount of ATP released by the cell
   B. The amount of calcium previously stored
   C. The amount of potassium that enters the cell
   D. The degree of adhesion between myocytes

Answer 3

B. The amount of calcium previously stored
Rationale: The amount of calcium released from the sarcoplasmic reticulum (SR) is directly dependent on the amount of calcium that has been previously stored in the SR. This stored calcium is released into the cytoplasm to facilitate muscle contraction.

Question 4

4. What occurs during the upstroke of the action potential?
   A. Net outward current and the cell interior becomes less negative
   B. Net inward current and the cell interior becomes positive
   C. Net inward current and the cell becomes less negative
   D. Net outward current and the cell interior becomes negative

Answer 4

B. Net inward current and the cell interior becomes positive
Rationale: During the upstroke of the action potential, there is a net inward current primarily due to the influx of sodium ions (Na+), causing the interior of the cell to become more positive.

Question 5

5. What makes up the thin filament of cardiac muscle cells?
   A. Troponin
   B. Tropomyosin
   C. Myofilament
   D. Actin

Answer 5

D. Actin
Rationale: The thin filament in cardiac muscle cells is composed of actin, along with other regulatory proteins like troponin and tropomyosin, but the primary structural component is actin.

Question 6

6. Which is not part of the general mechanism of muscle contraction?
   A. The action potential depolarizes the muscle fiber membrane and also travels deeply within the muscle fiber where it causes the sarcoplasmic reticulum to release large quantities of calcium ions
   B. An action potential travels along a motor nerve to its endings on muscle fibers where the nerve secretes small amounts of acetylcholine.
   C. Acetylcholine channel allows large quantities of calcium ions to flow to the interior of the muscle fiber membrane at the point of the nerve terminal which initiates an action potential in the muscle fiber
   D. Calcium ions initiate attractive forces between actin and myosin filaments causing them to slide together

Answer 6

C. Acetylcholine channel allows large quantities of calcium ions to flow to the interior of the muscle fiber membrane at the point of the nerve terminal which initiates an action potential in the muscle fiber
Rationale: In the general mechanism of muscle contraction, acetylcholine (ACh) released at the neuromuscular junction binds to receptors on the muscle fiber membrane, causing an influx of sodium ions, not calcium ions, which then initiates an action potential. Calcium release occurs subsequently from the sarcoplasmic reticulum, not directly through acetylcholine channels.

Question 7

7. Which of the ions’ equilibrium potential exerts the greatest effect on determining the cell’s overall resting membrane potential?
   A. Na
   B. Cl
   C. K
   D. Ca
   E. HCO3-

Answer 7

C. K
Rationale: Potassium (K+) has the greatest influence on the resting membrane potential because the cell membrane is most permeable to K+ ions. The equilibrium potential of K+ is closest to the cell’s resting membrane potential.
Lecture Rationale:
C. K - cell has highest permeability for K+. Thus, RMP is closest to its equilibrium potential

Question 8

9. In skeletal muscle, which of the following events occurs before depolarization of the T tubules in the mechanism of excitation-contraction coupling?
   A. Depolarization of the sarcolemmal membrane
   B. Opening of Ca2+ release channels on the sarcoplasmic reticulum (SR)
   C. Uptake of Ca2+ into the SR by Ca2+-adenosine triphosphatase (ATPase)
   D. Binding of Ca2+ to troponin C
   E. Binding of actin and myosin

Answer 8

A. Depolarization of the sarcolemmal membrane
Rationale: In the excitation-contraction coupling mechanism, the depolarization of the sarcolemmal membrane (muscle cell membrane) occurs first, which then triggers the depolarization of the T tubules, leading to the release of calcium from the sarcoplasmic reticulum.

Question 9

10. A cell is most excitable at this phase of action potential:
    A. Resting Membrane Potential
    B. Overshoot
    C. Repolarization
    D. Hyperpolarization
    E. All phases the same

Answer 9

A. Resting Membrane Potential
Rationale: A cell is most excitable when it is at the resting membrane potential because it is ready to respond to a stimulus. At this phase, the cell is in a state where it can easily depolarize and generate an action potential.

Question 10

11. These are characteristics of facilitated transporters EXCEPT?
    A. It is stereospecific for either the L or D isomer
    B. It is saturable
    C. It is an active transport
    D. Monosaccharide transport inside a cell is an example
    E. Competitive inhibition may occur

Answer 10

C. It is an active transport
Rationale: Facilitated transport (or facilitated diffusion) involves the passive movement of molecules across the cell membrane via specific carrier proteins. This process is stereospecific, saturable, can exhibit competitive inhibition, and examples include monosaccharide transport inside a cell. However, it does not require energy input, distinguishing it from active transport, which does.
Lecture Rationale:
Facilitated diffusion is a type of passive transport.
It is carrier-mediated.
It has three important characteristics:
Saturation
Stereospecificity
Affected by competitive inhibition

Question 11

12. What is the major mechanism directly contributing to the resting membrane potential?
    A. Na K ATPase pump
    B. Potassium leak channel
    C. Sodium leak channel
    D. Na Ca exchanger

Answer 11

B. Potassium leak channel
Rationale: The resting membrane potential is primarily determined by the high permeability of the cell membrane to potassium ions through potassium leak channels. These channels allow K+ to move out of the cell, creating a negative charge inside the cell. The Na+/K+ ATPase pump helps maintain this gradient, but the direct contributor is the potassium leak channels.

Question 12

13. This is characteristic of type II muscle fiber?
    A. Oxidative
    B. Larger in size
    C. Low myosin ATPase
    D. Prolonged contraction duration
    E. Red fiber

Answer 12

B. Larger in size
Rationale: Type II muscle fibers (fast-twitch) are larger in size, have higher myosin ATPase activity, and are capable of generating more force but fatigue faster compared to Type I (slow-twitch) fibers, which are oxidative, smaller, and red in color due to higher myoglobin content.
Lecture Rationale:
A. Oxidative (glycolytic)
C. Slow myosin ATPase (fast)
D. Prolonged contraction duration (fast)
E. Red fiber (white)

Question 13

15. Which of the following is NOT true of a sympathetic nervous system response?
    A. Capable of mass discharge
    B. Decreased rate of formation of thrombin
    C. Increased muscle strength
    D. Decreased renal blood flow
    E. Increased glycolysis

Answer 13

B. Decreased rate of formation of thrombin
Rationale: The sympathetic nervous system is involved in the “fight or flight” response, which includes mass discharge, increased muscle strength, decreased renal blood flow, and increased glycolysis. However, it typically increases the rate of thrombin formation as part of the body’s preparation for potential injury and blood loss, not decreasing it.

Question 14

16. During repolarization of the nerve action potential, opening of the potassium gates causes:
    A. Sodium influx
    B. Sodium efflux
    C. Calcium influx
    D. Potassium efflux
    E. Potassium influx

Answer 14

D. Potassium efflux
Rationale: During repolarization, voltage-gated potassium channels open, allowing K+ to flow out of the cell (efflux), which restores the negative membrane potential following depolarization.

Question 15

17. In the excitation-contraction of skeletal muscle, the following events take place except:
    A. Depolarization of T tubules
    B. Activation of Dihydropyridine receptor
    C. Decrease in intracellular calcium concentration
    D. Calcium binds troponin C
    E. Tropomyosin moves and allows interaction of actin and myosin

Answer 15

C. Decrease in intracellular calcium concentration
Rationale: During excitation-contraction coupling in skeletal muscle, intracellular calcium concentration increases as calcium is released from the sarcoplasmic reticulum, leading to muscle contraction. A decrease in calcium concentration would occur during relaxation, not during contraction.

Question 16

18. Which of the following characteristics is shared by simple and facilitated diffusion?
    A. Inhibition of Na+-K+ pump
    B. Stereospecificity
    C. Carrier-mediated
    D. Does not require metabolic energy
    E. Saturation

Answer 16

D. Does not require metabolic energy
Rationale: Both simple and facilitated diffusion are passive processes that do not require metabolic energy (ATP). They rely on the concentration gradient to move molecules across the membrane.

Question 17

19. Which of the following responses is NOT mediated by sympathetic receptors?
    A. Erection
    B. Skeletal muscle vasodilation
    C. Dilation of bronchiolar smooth muscle
    D. Mydriasis
    E. GI Sphincter contraction

Answer 17

A. Erection
Rationale: Erection is primarily mediated by the parasympathetic nervous system, which induces vasodilation and increases blood flow to the penile tissue. The other responses listed are mediated by the sympathetic nervous system.
Lecture Rationale:
Erection – Parasympathetic
Ejaculation- Sympathetic

Question 18

21. Which of the following inhibits the interaction of myosin and actin in smooth muscle?
    A. Myosin light chain kinase
    B. Caldesmon, calponin
    C. Calmodulin
    D. Troponin I

Answer 18

B. Caldesmon, calponin
Rationale: Caldesmon and calponin are proteins in smooth muscle that inhibit the interaction of actin and myosin, thus regulating muscle contraction.

Question 19

22. Which among the following is a characteristic of a fast twitch muscle as compared to a slow twitch muscle?
    A. They are smaller in size
    B. More dependent on oxidative metabolism
    C. They are usually the red muscles
    D. They have less mitochondria and myoglobin
    E. Example of which are anti-gravity muscles

Answer 19

D. They have less mitochondria and myoglobin
Rationale: Fast-twitch muscles (Type II fibers) are designed for short bursts of power and speed. They have fewer mitochondria and less myoglobin compared to slow-twitch (Type I) fibers, which are more reliant on oxidative metabolism and have higher endurance.

Question 20

23. In a motor neuron, which of the following will enter the presynaptic neuron after the action potential has reached its terminal?
    A. K
    B. Ca
    C. Na
    D. Acetylcholine
    E. Cl

Answer 20

B. Ca
Rationale: When an action potential reaches the terminal of a motor neuron, voltage-gated calcium channels open, allowing calcium ions (Ca2+) to enter the presynaptic neuron. This influx of calcium triggers the release of neurotransmitters into the synaptic cleft.

Question 21

24. When a nerve action potential reaches a muscle membrane, which of the following events take place in chronological order?
    A. Opening of sodium channels → Depolarization → Power stroke → Calcium release from SR
    B. Depolarization → Opening of sodium channels → Calcium release from SR → Power stroke
    C. Opening of sodium channels → Depolarization → Calcium release from SR → Power stroke
    D. Depolarization → Opening of sodium channels → Power stroke → Calcium release from SR
    E. None of the above

Answer 21

C. Opening of sodium channels → Depolarization → Calcium release from SR → Power stroke
Rationale: The sequence begins with the opening of sodium channels leading to depolarization. This is followed by the release of calcium from the sarcoplasmic reticulum (SR), which then triggers the power stroke of muscle contraction.

Question 22

25. The latch mechanism of smooth muscles serves to:
    A. Increase the number of cross-bridges between actin and myosin
    B. Increase the power of muscle contraction
    C. Allow a prolonged relaxed state
    D. Avoid muscle fatigue
    E. Maintain prolonged tonic contraction

Answer 22

E. Maintain prolonged tonic contraction
Rationale: The latch mechanism in smooth muscle allows it to maintain prolonged tonic contraction with minimal energy expenditure, which is important for functions like maintaining blood vessel tone and gastrointestinal motility.

Question 23

26. Which is a correct statement regarding acetylcholine?
    A. It binds both to nicotinic and adrenergic receptors.
    B. It is usually the hormone released by postsynaptic parasympathetic neurons.
    C. It is rapidly degraded by pseudocholinesterases.
    D. It functions only in the parasympathetic system

Answer 23

B. It is usually the hormone released by postsynaptic parasympathetic neurons.
Rationale: Acetylcholine (ACh) is the neurotransmitter released by postsynaptic parasympathetic neurons. It binds to muscarinic receptors on the target organs.

Question 24

27. Cross-section of the sarcomere through the H zone will reveal what structures?
    A. Actin and myosin
    B. Myosin only
    C. Actin only
    D. Actin, myosin, and troponin
    E. None of the above

Answer 24

B. Myosin only
Rationale: The H zone is the region within the A band of the sarcomere that contains only thick filaments (myosin) and no thin filaments (actin).

Question 25

28. Which of the following is true regarding the sympathetic nervous system?
    A. It is responsible for accommodation of vision to near objects
    B. It is responsible for relaxation of urinary and gastrointestinal sphincters
    C. It has short preganglionic fibers and long postganglionic fibers
    D. It only utilizes norepinephrine as a neurotransmitter
    E. The autonomic ganglia are usually embedded inside the effector organs

Answer 25

C. It has short preganglionic fibers and long postganglionic fibers
Rationale: The sympathetic nervous system is characterized by short preganglionic fibers that synapse in the sympathetic ganglia, and long postganglionic fibers that extend to the target organs.

Question 26

29. Which of the following is false of skeletal muscle contraction?
    A. Action potential travels down, depolarizing the terminal axonal bouton promoting release of acetylcholine
    B. During membrane depolarization, the inside of the cell becomes positively charged
    C. Acetylcholine diffuses across the synaptic cleft stimulating muscarinic acetylcholine receptors
    D. Acetylcholinesterase leads to the breakdown of acetylcholine terminating the synaptic transmission
    E. The acetylcholine receptor at the postsynaptic membrane is a ligand-gated ion channel

Answer 26

C. Acetylcholine diffuses across the synaptic cleft stimulating muscarinic acetylcholine receptors
Rationale: In skeletal muscle, acetylcholine binds to nicotinic receptors, not muscarinic receptors. Muscarinic receptors are found in the parasympathetic nervous system affecting organs like the heart and glands.

Question 27

30. Absence of T-tubules in skeletal muscle cells will result in:
    A. Asynchronous waveforms and failure of calcium release
    B. Absence of action potential generation
    C. Absence of calcium uptake by the sarcoplasmic reticulum
    D. Inability of acetylcholine to bind and activate receptors at the neuromuscular junction
    E. All of the above

Answer 27

A. Asynchronous waveforms and failure of calcium release
Rationale: T-tubules help transmit the action potential deep into the muscle fiber, ensuring coordinated contraction and efficient calcium release from the sarcoplasmic reticulum. Without T-tubules, there would be asynchronous contraction and failure in the proper release of calcium, disrupting muscle contraction.

Question 28

31. The resting membrane potential of an isolated cell is found to be -70 mV. Which of the following solutes is most likely responsible for this?
    A. Sodium
    B. Potassium
    C. Calcium
    D. Sodium and Calcium
    E. Sodium and Chloride

Answer 28

B. Potassium
Rationale: The resting membrane potential is primarily influenced by the potassium ion (K+) concentration gradient across the cell membrane. Potassium ions have the highest permeability at rest, making them the main determinant of the resting membrane potential, which is typically close to the equilibrium potential of potassium.
Lecture Rationale:
B. Potassium - equilibrium potential of K+ is approximately -85 to -95 mV

Question 29

33. At resting membrane potential, the sodium channel must have this configuration where m is the activation gate and h is the inactivation gate:
    A. m gate open and h gate closed
    B. m gate open and h gate open
    C. m gate closed and h gate open
    D. m gate closed and h gate closed

Answer 29

C. m gate closed and h gate open
Rationale: At resting membrane potential, the sodium (Na+) channel has the m (activation) gate closed and the h (inactivation) gate open. This configuration prevents sodium ions from entering the cell until depolarization occurs, which opens the m gate.

Question 30

34. In smooth muscle contraction, calcium initially binds with:
    A. Troponin C
    B. Ryanodine receptor
    C. Calmodulin
    D. Dihydropyridine receptor

Answer 30

C. Calmodulin
Rationale: In smooth muscle, calcium ions (Ca2+) bind to calmodulin initially. This calcium-calmodulin complex then activates myosin light chain kinase (MLCK), which phosphorylates myosin and initiates contraction.

Question 31

35. What allows calcium to be stored at high concentrations inside the sarcoplasmic reticulum?
    A. DHPR
    B. Calsequestrin
    C. RYR
    D. Troponin C
    E. None of the above

Answer 31

B. Calsequestrin
Rationale: Calsequestrin is a calcium-binding protein within the sarcoplasmic reticulum (SR) that allows the SR to store high concentrations of calcium ions. It binds calcium ions with low affinity but high capacity, helping maintain a reservoir of calcium in the SR.
Lecture Rationale:
A. DHPR - voltage sensor
B. Calsequestrin - low-affinity Ca++ binding protein
C. RYR - releases Ca++ release from SR
D. Troponin C – binds Ca++ to allow conformational change of tropomyosin to expose actin

Question 32

37. The transport of calcium ions back to the sarcoplasmic reticulum during muscle relaxation is achieved through which of the following mechanisms?
    A. Simple diffusion
    B. Facilitated diffusion
    C. Primary active transport
    D. Secondary active transport via symport
    E. Secondary active transport via antiport

Answer 32

C. Primary active transport
Rationale: The transport of calcium ions back into the sarcoplasmic reticulum (SR) during muscle relaxation is accomplished by primary active transport. This process involves the use of the SERCA (sarcoplasmic/endoplasmic reticulum calcium ATPase) pump, which actively transports calcium ions into the SR against their concentration gradient using ATP.
Lecture Rationale:
C. Primary active transport - via SERCA or Ca++-ATPase pumps in the SR

Question 33

41. A 24-year-old woman was diagnosed with myasthenia gravis. She was prescribed with Pyridostigmine and she noted increased muscle strength when she took the prescribed medicine. The basis for this improvement is an increase in the:
    A. Amount of acetylcholine destroyed in the motor end plates
    B. Levels of acetylcholine at the motor end plates
    C. Number of acetylcholine receptors in the motor end plate
    D. Amount of norepinephrine released from the motor nerves
    E. Amount of norepinephrine receptors in the motor end plates

Answer 33

B. Levels of acetylcholine at the motor end plates
Rationale: Pyridostigmine is an acetylcholinesterase inhibitor, which prevents the breakdown of acetylcholine (ACh) in the synaptic cleft. This leads to increased levels of acetylcholine at the motor end plates, enhancing neuromuscular transmission and improving muscle strength in patients with myasthenia gravis.
Lecture Rationale:
Pyridostigmine is an indirect-acting cholinomimetic.
It inhibits acetylcholinesterase, which increases levels of acetylcholine at the motor end plates.
This results in increased muscle strength.

Question 34

42. Tetrodotoxin block or inhibit:
    A. Sodium channel
    B. Potassium channel
    C. Sodium-potassium pump
    D. Na-K leak channel
    E. Calcium channel

Answer 34

A. Sodium channel
Rationale: Tetrodotoxin is a potent neurotoxin that specifically blocks voltage-gated sodium (Na+) channels. By inhibiting these channels, tetrodotoxin prevents the generation and propagation of action potentials in nerves and muscles.
Lecture Rationale:
Tetrodotoxin is a potent neurotoxin from a pufferfish.
It inhibits the firing of action potentials in nerves.
It achieves this by binding to the voltage-gated sodium channels in nerve cell membranes.
This binding blocks the passage of sodium ions.

Question 35

43. What is the function of Troponin I?
    A. Attaches troponin complex to tropomyosin
    B. Inhibits actin-myosin binding
    C. Inhibits calcium binding protein
    D. All of the above
    E. None of the above

Answer 35

B. Inhibits actin-myosin binding
Rationale: Troponin I is a part of the troponin complex in muscle fibers and its primary function is to inhibit the interaction between actin and myosin, thereby preventing muscle contraction until calcium ions are present.
Lecture Rationale:
A. Attaches troponin complex to tropomyosin – troponin T
C. Inhibits calcium binding protein – troponin C is Ca++-binding protein

ACTIN
G-actin
Forms F-actin.
Contains the myosin binding sites.
Tropomyosin
During the resting state (low Ca++ levels), it covers the myosin binding sites.
Troponin (3 subunits):
Troponin C: Binds 4 Ca++.
Troponin T: Binds tropomyosin.
Troponin I: Facilitates inhibition of myosin binding to actin by tropomyosin.

Question 36

45. This is true of action potentials:
    A. Depolarization makes the membrane potential more negative
    B. Hyperpolarization makes the membrane potential less negative
    C. The RMP of skeletal muscles is approximately -70 mV
    D. Repolarization closes the activation gates of the sodium channel
    E. All of the above

Answer 36

C. The RMP of skeletal muscles is approximately -70 mV
Rationale: The resting membrane potential (RMP) of skeletal muscle cells is around -70 mV. Depolarization makes the membrane potential less negative (not more negative), and repolarization involves the closing of inactivation gates of sodium channels, not the activation gates.

Question 37

46. A young college student had nausea, vomiting, visual disorders, and muscular paralysis after eating canned tuna fish. The probable diagnosis is botulism, caused by ingestion of the Clostridium botulinum toxin. The physiological effect of this toxin is to
    A. Bind to and thus inactivate acetylcholine receptors at myoneural junctions
    B. Prevent release of calcium ions from the sarcoplasmic reticulum, thus inhibiting muscle contraction
    C. Inhibit release of acetylcholine from presynaptic membranes
    D. Inhibit hydrolysis of adenosine triphosphate during the contraction cycle

Answer 37

C. Inhibit release of acetylcholine from presynaptic membranes
Rationale: Botulinum toxin inhibits the release of acetylcholine (ACh) from presynaptic membranes at the neuromuscular junction, leading to muscular paralysis.
Lecture Rationale:
The toxin from Clostridium botulinum inhibits the release of acetylcholine, the neurotransmitter at myoneural junctions.
As a result, motor nerve impulses cannot be transmitted across the junction.
Consequently, muscle cells are not stimulated to contract.

Question 38

47. What is the main difference between voltage-gated and ligand-gated ion channels?
    A. Voltage-gated channels are located in cardiac cells whereas ligand-gated are in neuronal cells
    B. Voltage-gated are activated by membrane potential changes whereas ligand-gated channels are by chemical messenger binding
    C. Ligand-gated are found in resting conformational state
    D. Ligand-gated channels contain an alpha-subunit protein

Answer 38

B. Voltage-gated are activated by membrane potential changes whereas ligand-gated channels are by chemical messenger binding
Rationale: Voltage-gated ion channels open in response to changes in membrane potential, while ligand-gated ion channels open in response to the binding of a chemical messenger (ligand) such as a neurotransmitter.

Question 39

48. All of the following are correct about Type I muscle fibers except:
    A. Also called slow fibers
    B. Have a more extensive blood vessel system and more capillaries to supply extra amounts of oxygen
    C. Have a greatly increased number of mitochondria
    D. Have an extensive SR for rapid release of calcium ions to initiate contraction

Answer 39

D. Have an extensive SR for rapid release of calcium ions to initiate contraction
Rationale: Type I muscle fibers, also known as slow-twitch fibers, have more mitochondria, extensive blood supply, and are designed for endurance and continuous activity. They do not have an extensive sarcoplasmic reticulum (SR) like Type II fibers (fast-twitch) do.

Question 40

49. In contrast to a chemical synapse, an electrical synapse:
    A. Speed of communication is slower
    B. Pre- and postsynaptic cells are separated by a synaptic cleft
    C. Neurotransmitter involved is aspartate
    D. Impulses are conveyed via gap junctions

Answer 40

D. Impulses are conveyed via gap junctions
Rationale: In an electrical synapse, impulses are transmitted directly between cells through gap junctions, allowing for faster communication compared to chemical synapses.

Question 41

50. This is observed in the length-tension relationship of both skeletal and cardiac muscles:
    A. Bell-shaped active tension curve
    B. Length and tension are inversely related
    C. Active and passive tension are inversely related at all lengths
    D. Constant passive tension curve

Answer 41

A. Bell-shaped active tension curve
Rationale: Both skeletal and cardiac muscles exhibit a bell-shaped curve for active tension, indicating that there is an optimal muscle length (sarcomere length) at which maximal active tension can be generated.

Question 42

52. In smooth muscle, calcium is released from the sarcoplasmic reticulum by:
    A. DAG
    B. Phospholipase C
    C. IP3
    D. Ryanodine receptor

Answer 42

C. IP3
Rationale: In smooth muscle, the release of calcium from the sarcoplasmic reticulum (SR) is often mediated by inositol triphosphate (IP3). IP3 binds to its receptor on the SR membrane, leading to the release of stored calcium ions into the cytoplasm.

Question 43

53. Extracellular calcium plays a direct role in the excitation-contraction coupling of this type of muscle/s:
    A. Cardiac
    B. Skeletal
    C. Smooth
    D. Cardiac and smooth

Answer 43

D. Cardiac and smooth
Rationale: In both cardiac and smooth muscle, extracellular calcium plays a critical role in excitation-contraction coupling. In cardiac muscle, calcium enters through voltage-gated calcium channels and triggers further calcium release from the SR (calcium-induced calcium release). In smooth muscle, extracellular calcium can enter the cell through various channels and contribute to muscle contraction.

Question 44

54. One of the following is important for skeletal muscle but not for smooth muscle contraction:
    A. Actin
    B. Myosin
    C. Troponin
    D. Phospholipase C

Answer 44

C. Troponin
Rationale: Troponin is a regulatory protein complex that is crucial for the contraction of skeletal (and cardiac) muscle by mediating the interaction between actin and myosin. Smooth muscle contraction, however, is regulated by calmodulin and myosin light chain kinase (MLCK) rather than troponin.

Question 45

55. Depolarization of the T-tubule is a prerequisite in this type of muscle contraction:
    A. Skeletal
    B. Cardiac
    C. Smooth
    D. Skeletal and cardiac

Answer 45

D. Skeletal and cardiac
Rationale: In both skeletal and cardiac muscle, the depolarization of the T-tubules is essential for initiating muscle contraction. This depolarization leads to the activation of voltage-sensitive proteins, which in turn trigger calcium release from the sarcoplasmic reticulum, initiating contraction. Smooth muscle does not rely on T-tubules for excitation-contraction coupling.

Question 46

What is a synapse?

A) A junction between two neurons where electrical impulses are transmitted.

B) A point where blood vessels connect to neurons.

C) A structure that stores neurotransmitters within a neuron.

D) A junction between a neuron and a bone cell.

Answer 46

A) A junction between two neurons where electrical impulses are transmitted.

Rationale:
A synapse is a neuronal junction that serves as the site of transmission of electrical impulses between two neurons or between a neuron and a muscle cell. This transmission can be chemical or electrical, facilitating communication within the nervous system. The synapse is crucial for the propagation of neural signals, enabling various physiological responses and functions.

Question 47

Which of the following statements is true about electrical synapses?

A) They are important for the transmission of action potentials in the central nervous system and in cardiac muscles.

B) They involve the release of neurotransmitters into the synaptic cleft.

C) They transmit signals unidirectionally with a synaptic delay.

D) They primarily involve chemical signaling through synaptic vesicles.

Answer 47

A) They are important for the transmission of action potentials in the central nervous system and in cardiac muscles.

Rationale:
Electrical synapses are crucial for the rapid transmission of action potentials, especially in visceral smooth muscles, cardiac muscles, and the central nervous system. These synapses involve gap junctions that allow the direct movement of ions between cells, facilitating bidirectional signal transmission without synaptic delay. Unlike chemical synapses, electrical synapses do not rely on the release of neurotransmitters and synaptic vesicles, allowing for faster and more direct communication between neurons.

Question 48

Which of the following statements is true about chemical synapses?

A) They allow direct communication between two cells without a synaptic cleft.

B) They involve the release of neurotransmitters from the presynaptic terminal.

C) They transmit signals bidirectionally without any synaptic delay.

D) They primarily involve gap junctions for the movement of ions between cells.

Answer 48

B) They involve the release of neurotransmitters from the presynaptic terminal.

Rationale:
Chemical synapses are the most common type of synapse used for signal transmission in the central nervous system. They do not allow direct communication between two cells; instead, there is a synaptic cleft between the pre- and post-synaptic elements. The presynaptic terminal releases neurotransmitters, which then bind to receptors on the postsynaptic cell, leading to the opening or closing of ion channels and the generation of excitatory or inhibitory postsynaptic potentials (EPSPs or IPSPs). Unlike electrical synapses, chemical synapses transmit signals unidirectionally and involve a slight synaptic delay.

Question 49

Which of the following statements best describes an Excitatory Post-Synaptic Potential (EPSP)?

A) It increases the negativity of the membrane potential, leading to hyperpolarization.

B) It represents a small, localized depolarization of the postsynaptic cell.

C) It decreases the chances of reaching the action potential threshold.

D) It is always hyperpolarizing in nature.

Answer 49

B) It represents a small, localized depolarization of the postsynaptic cell.

Rationale:
An Excitatory Post-Synaptic Potential (EPSP) is a decrease in membrane potential (decrease in negativity) in a postsynaptic cell in the nervous system, leading to a small, localized depolarization. EPSPs can summate with other EPSPs to decrease the resting potential to a less negative value, increasing the chances of reaching the action potential threshold and generating an action potential. EPSPs are always depolarizing, not hyperpolarizing.

Question 50

Which of the following statements accurately describes an Inhibitory Post-Synaptic Potential (IPSP)?

A) It decreases the negativity of the membrane potential, leading to depolarization.

B) It is a local graded potential that is usually hyperpolarizing.

C) It is always generated by the influx of sodium ions.

D) It increases the chances of reaching the action potential threshold.

Answer 50

B) It is a local graded potential that is usually hyperpolarizing.

Rationale:
An Inhibitory Post-Synaptic Potential (IPSP) is characterized by an increase in the negativity of the membrane potential, leading to hyperpolarization. This local graded potential is triggered by the binding of neurotransmitters to postsynaptic receptors and typically involves chloride or potassium ions. The hyperpolarization decreases the likelihood of reaching the action potential threshold, thus inhibiting neuronal firing. In contrast, depolarization and the influx of sodium ions are associated with Excitatory Post-Synaptic Potentials (EPSPs), not IPSPs.

Question 51

Which of the following correctly describes the events during the depolarization phase of an action potential?

A) Voltage-gated potassium channels open, and potassium ions exit the cell.

B) Voltage-gated sodium channels open, and sodium ions enter the cell.

C) The membrane potential becomes more negative as chloride ions enter the cell.

D) The sodium-potassium pump actively transports sodium ions out of the cell and potassium ions into the cell.

Answer 51

B) Voltage-gated sodium channels open, and sodium ions enter the cell.

Rationale:
During the depolarization phase of an action potential, voltage-gated sodium channels open, allowing sodium ions to enter the cell. This influx of positive ions causes the membrane potential to become less negative and move towards a positive value. In contrast, voltage-gated potassium channels opening and potassium ions exiting the cell occur during repolarization. The sodium-potassium pump operates throughout the action potential to maintain ion gradients but is not the primary driver of depolarization.

Question 52

At which phase of the action potential is sodium conductance greatest?

A) Resting phase

B) Depolarization phase

C) Repolarization phase

D) Hyperpolarization phase

Answer 52

B) Depolarization phase

Rationale:
Sodium conductance is greatest during the depolarization phase of the action potential. This is when voltage-gated sodium channels open, allowing a rapid influx of sodium ions into the cell, leading to a sharp rise in the membrane potential. Potassium conductance increases later, during the repolarization and hyperpolarization phases.

Question 53

At which phase of the action potential is the cell the least excitable?

A) Resting phase

B) Depolarization phase

C) Repolarization phase

D) Hyperpolarization phase

Answer 53

D) Hyperpolarization phase

Rationale:
The cell is least excitable during the hyperpolarization phase of the action potential. During this phase, the membrane potential is more negative than the resting potential, making it more difficult for the cell to reach the threshold for another action potential. This phase is also known as the refractory period, where the cell’s excitability is at its lowest.

Question 54

What is the major mechanism directly contributing to the resting membrane potential?

A) Active transport of chloride ions into the cell

B) Passive diffusion of sodium ions out of the cell

C) Active transport of sodium ions out of the cell and potassium ions into the cell by the sodium-potassium pump

D) Active transport of potassium ions out of the cell and sodium ions into the cell by the sodium-potassium pump

Answer 54

C) Active transport of sodium ions out of the cell and potassium ions into the cell by the sodium-potassium pump

Rationale:
The major mechanism contributing to the resting membrane potential is the active transport of sodium ions out of the cell and potassium ions into the cell by the sodium-potassium pump (Na+/K+ ATPase). This pump helps maintain the concentration gradients of these ions across the cell membrane, which is essential for the resting membrane potential, typically around -70mV.

Question 55

What is likely to happen if the resting membrane potential becomes more negative (e.g., from -70mV to -90mV)?

A) The cell becomes more excitable and action potentials are more easily generated.

B) The cell becomes less excitable and action potentials are less easily generated.

C) The resting membrane potential has no effect on cell excitability.

D) The cell becomes unable to generate action potentials.

Answer 55

B) The cell becomes less excitable and action potentials are less easily generated.

Rationale:
If the resting membrane potential becomes more negative (hyperpolarized), the cell becomes less excitable because it is further from the threshold needed to generate an action potential. This makes it harder for the cell to reach the threshold and initiate an action potential.

Question 56

What is likely to happen if the resting membrane potential becomes less negative (e.g., from -70mV to -60mV)?

A) The cell becomes more excitable and action potentials are more easily generated.

B) The cell becomes less excitable and action potentials are less easily generated.

C) The resting membrane potential has no effect on cell excitability.

D) The cell becomes unable to generate action potentials.

Answer 56

A) The cell becomes more excitable and action potentials are more easily generated.

Rationale:
If the resting membrane potential becomes less negative (depolarized), the cell becomes more excitable because it is closer to the threshold needed to generate an action potential. This makes it easier for the cell to reach the threshold and initiate an action potential.

Question 57

What happens to the motor end plate upon the release of acetylcholine (Ach) at the neuromuscular junction?

A) Ach binds to muscarinic receptors, causing hyperpolarization of the motor end plate.

B) Ach is rapidly degraded by acetylcholinesterase, preventing any change in the motor end plate.

C) Ach binds to nicotinic receptors, causing depolarization of the motor end plate.

D) Ach binds to adrenergic receptors, leading to an increase in intracellular calcium levels.

Answer 57

C) Ach binds to nicotinic receptors, causing depolarization of the motor end plate.

Rationale:
Upon release at the neuromuscular junction, acetylcholine (Ach) binds to nicotinic receptors on the motor end plate. This binding causes an influx of sodium ions, leading to depolarization of the motor end plate. This depolarization is known as the end plate potential, which can initiate an action potential in the muscle fiber, leading to muscle contraction. Ach is indeed rapidly degraded by acetylcholinesterase, but this degradation happens after the initial depolarization.

Question 58

Which of the following best describes the process of excitation-contraction coupling in skeletal muscle?

A) Calcium ions are released from the sarcoplasmic reticulum and bind to tropomyosin, initiating contraction.

B) An action potential travels along the T-tubules, triggering calcium release from the sarcoplasmic reticulum.

C) Acetylcholine binds to receptors on the muscle cell membrane, directly causing muscle contraction.

D) Myosin heads bind to actin filaments in the absence of calcium, resulting in muscle contraction.

Answer 58

B) An action potential travels along the T-tubules, triggering calcium release from the sarcoplasmic reticulum.

Rationale:
Excitation-contraction coupling in skeletal muscle involves the propagation of an action potential along the T-tubules, which triggers the release of calcium ions from the sarcoplasmic reticulum. These calcium ions then bind to troponin, causing a conformational change that moves tropomyosin away from the actin binding sites, allowing myosin heads to bind to actin and initiate contraction.

Question 59

How does excitation-contraction coupling in cardiac muscle differ from that in skeletal muscle?

A) Cardiac muscle relies on calcium-induced calcium release from the sarcoplasmic reticulum.

B) Cardiac muscle does not require calcium for muscle contraction.

C) Cardiac muscle utilizes sodium ions instead of calcium ions for contraction.

D) Cardiac muscle contraction is initiated by acetylcholine release at the neuromuscular junction.

Answer 59

A) Cardiac muscle relies on calcium-induced calcium release from the sarcoplasmic reticulum.

Rationale:
In cardiac muscle, excitation-contraction coupling involves calcium-induced calcium release (CICR). When an action potential reaches the T-tubules, calcium enters the cell through L-type calcium channels, which then triggers further release of calcium from the sarcoplasmic reticulum. This additional calcium is essential for contraction. This mechanism is different from skeletal muscle, where the action potential directly triggers calcium release from the sarcoplasmic reticulum without the initial influx of extracellular calcium.

Question 60

What is the cause of the slower action potential observed in cardiac muscle compared to skeletal muscle?

A) The presence of fewer sodium channels in cardiac muscle.

B) The prolonged opening of calcium channels during the plateau phase.

C) The absence of potassium channels in cardiac muscle.

D) The faster inactivation of sodium channels in cardiac muscle.

Answer 60

B) The prolonged opening of calcium channels during the plateau phase.

Rationale:
The slower action potential observed in cardiac muscle is primarily due to the prolonged opening of L-type calcium channels during the plateau phase of the action potential. This influx of calcium ions maintains the depolarization for an extended period, leading to a longer action potential duration compared to skeletal muscle. This plateau phase is crucial for the proper timing of contraction and relaxation in the cardiac cycle.

Question 61

Which of the following are primary sources of energy for muscle contraction?

A) ATP, creatine phosphate, and glycogen

B) Glucose, fatty acids, and lactic acid

C) ADP, nucleotides, and proteins

D) Oxygen, carbon dioxide, and nitrogen

Answer 61

A) ATP, creatine phosphate, and glycogen

Rationale:
The primary sources of energy for muscle contraction are ATP, creatine phosphate, and glycogen. ATP provides immediate energy for muscle contraction, creatine phosphate serves as a quick reserve to regenerate ATP, and glycogen is broken down to glucose, which is further metabolized to produce ATP.

Question 62

What is the role of calcium in skeletal muscle contraction?

A) Calcium binds to troponin, allowing actin-myosin interaction.

B) Calcium binds to tropomyosin, causing it to inhibit actin-myosin interaction.

C) Calcium activates the sodium-potassium pump.

D) Calcium is not involved in skeletal muscle contraction.

Answer 62

A) Calcium binds to troponin, allowing actin-myosin interaction.

Rationale:
In skeletal muscle contraction, calcium ions released from the sarcoplasmic reticulum bind to troponin. This binding causes a conformational change in troponin, which moves tropomyosin away from the actin binding sites, allowing myosin heads to interact with actin and initiate contraction.

Question 63

What is the role of calcium in smooth muscle contraction?

A) Calcium binds to troponin, allowing actin-myosin interaction.

B) Calcium binds to calmodulin, activating myosin light chain kinase.

C) Calcium is stored in the nucleus and released during contraction.

D) Calcium directly binds to actin, initiating contraction.

Answer 63

B) Calcium binds to calmodulin, activating myosin light chain kinase.

Rationale:
In smooth muscle contraction, calcium binds to calmodulin, which activates myosin light chain kinase (MLCK). MLCK then phosphorylates myosin light chains, allowing myosin to interact with actin and initiate contraction. This mechanism is different from skeletal muscle, where calcium directly binds to troponin.

Question 64

How does sympathetic stimulation cause an increase in heart rate and force of myocardial contraction?

A) By increasing the release of acetylcholine from parasympathetic nerves

B) By increasing the release of norepinephrine and stimulating beta-adrenergic receptors

C) By decreasing the release of epinephrine from the adrenal medulla

D) By inhibiting the action of calcium in cardiac muscle cells

Answer 64

B) By increasing the release of norepinephrine and stimulating beta-adrenergic receptors

Rationale:
Sympathetic stimulation causes an increase in heart rate and force of myocardial contraction by increasing the release of norepinephrine, which stimulates beta-adrenergic receptors on the heart. This leads to increased calcium influx into cardiac cells, enhancing the rate of depolarization and the force of contraction.

Question 65

Which of the following best describes the length-tension relationship in skeletal muscle?

A) The tension generated by a muscle fiber is independent of its initial length.

B) Maximum tension is generated when the muscle is either fully stretched or fully contracted.

C) Maximum tension is generated when the muscle fiber is at an optimal length, neither too stretched nor too contracted.

D) Muscle tension decreases as the muscle fiber length increases beyond its optimal length.

Answer 65

C) Maximum tension is generated when the muscle fiber is at an optimal length, neither too stretched nor too contracted.

Rationale:
The length-tension relationship in skeletal muscle states that the tension a muscle fiber can generate depends on its initial length. Maximum tension is generated when the muscle fiber is at an optimal length, where the actin and myosin filaments have the greatest degree of overlap, allowing for the most cross-bridge interactions. If the muscle is too stretched or too contracted, fewer cross-bridges can form, resulting in decreased tension.

Question 66

What is the force-velocity relationship in skeletal muscle?

A) The force a muscle generates decreases as the speed of contraction increases.

B) The force a muscle generates is independent of the speed of contraction.

C) The force a muscle generates increases as the speed of contraction increases.

D) The force a muscle generates is maximal at both low and high speeds of contraction.

Answer 66

A) The force a muscle generates decreases as the speed of contraction increases.

Rationale:
The force-velocity relationship in skeletal muscle states that the force a muscle generates is inversely related to the speed of contraction. As the speed of contraction increases, the force the muscle can generate decreases. This is because faster contractions allow less time for cross-bridge formation between actin and myosin filaments, resulting in lower force production.

Question 67

What is length adaptation in smooth muscle?

A) The ability of smooth muscle to maintain constant tension over a range of lengths.

B) The inability of smooth muscle to contract when stretched.

C) The ability of smooth muscle to generate maximum force only at a specific length.

D) The inability of smooth muscle to relax after contraction.

Answer 67

A) The ability of smooth muscle to maintain constant tension over a range of lengths.

Rationale:
Length adaptation in smooth muscle refers to the ability of smooth muscle to adjust its tension to maintain force generation over a wide range of lengths. This property allows smooth muscle to function efficiently in various states of stretch and contraction, which is particularly important in organs that undergo significant changes in volume, such as the bladder and stomach.

Question 68

Why does rigor mortis set in after the death of an individual?

A) Because of an excess of ATP in the muscle cells.

B) Because of the release of acetylcholine from the nerve endings.

C) Because of the lack of ATP, preventing the detachment of myosin heads from actin filaments.

D) Because of increased calcium influx into the muscle cells.

Answer 68

C) Because of the lack of ATP, preventing the detachment of myosin heads from actin filaments.

Rationale:
Rigor mortis sets in after death because the production of ATP ceases. ATP is required for the detachment of myosin heads from actin filaments after a contraction cycle. Without ATP, myosin heads remain bound to actin, causing the muscles to become stiff and rigid. This state of prolonged contraction is known as rigor mortis.

Question 69

Which of the following is an important difference between skeletal and cardiac muscle?

A) Skeletal muscle cells are branched, whereas cardiac muscle cells are not.

B) Cardiac muscle cells have intercalated discs, which are not present in skeletal muscle cells.

C) Skeletal muscle cells contract involuntarily, whereas cardiac muscle cells contract voluntarily.

D) Cardiac muscle cells are multinucleated, whereas skeletal muscle cells are not.

Answer 69

B) Cardiac muscle cells have intercalated discs, which are not present in skeletal muscle cells.

Rationale:
An important difference between skeletal and cardiac muscle is the presence of intercalated discs in cardiac muscle cells. These discs contain gap junctions and desmosomes, which facilitate electrical and mechanical coupling between cells, allowing the heart to contract as a coordinated unit. Skeletal muscle cells, on the other hand, do not have intercalated discs and are controlled voluntarily. Additionally, skeletal muscle cells are typically multinucleated, while cardiac muscle cells generally have a single nucleus.