Dr Gawad Physiology Course Online Exam - Excitable - Course Lecture 5
7 MCQs (Only one correct answer)
Each MCQ: 1 mark, Total mark: 7 (you will get the results immediately with correction by the web)
Allowed time: 10 min
Good Luck
dr Mohammed Abel Gawad
- 1.
In the motor end plate, all the following are TRUE EXCEPT:
- A.
The acetylcholine receptors are similar to those in smooth muscle.
- B.
The nerve ending contains many vesicles and mitochondria.
- C.
Lack of Ca diminishes the release of acetylcholine.
- D.
There is a high concentration of the cholinesterase enzyme.
- E.
There is a delay of neuromuscular transmission of 0.5 millisecond
Correct Answer
A. The acetylcholine receptors are similar to those in smooth muscle.Explanation
The motor end plate contains acetylcholine receptors that are similar to those in skeletal muscle, not smooth muscle. The other statements are all true: the nerve ending contains many vesicles and mitochondria, lack of Ca diminishes the release of acetylcholine, there is a high concentration of the cholinesterase enzyme, and there is a delay of neuromuscular transmission of 0.5 milliseconds.Rate this question:
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- 2.
About neuromuscular transmission and end plate potential (EPP):
- A.
Neuromuscular transmission occurs only from the muscle to the nerve.
- B.
EPP is always maximal and rapidly conducted along the surface of the muscle.
- C.
EPP is a localized state of depolarization at the motor end plate.
- D.
EPP is augmented by increased Mg concentration in ECF.
- E.
EPP is associated with decreased excitability of the motor end plate.
Correct Answer
C. EPP is a localized state of depolarization at the motor end plate.Explanation
The correct answer is EPP is a localized state of depolarization at the motor end plate. This is because the end plate potential (EPP) refers to the depolarization of the motor end plate, which is the specialized region of the muscle fiber where the nerve terminal synapses. The EPP is a localized event that occurs specifically at the motor end plate, and it is responsible for triggering the contraction of the muscle fiber.Rate this question:
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- 3.
About activation of skeletal muscles, all the following is true except:
- A.
The resting membrane potential is about -90 mV.
- B.
The magnitude of the action potential is more than that in nerves.
- C.
The firing level is reached after about +40 mV of depolarization.
- D.
The spike is propagated along the muscle surface at a speed of 5 m /second.
Correct Answer
C. The firing level is reached after about +40 mV of depolarization.Explanation
The firing level is reached after about +40 mV of depolarization. This statement is not true because the firing level is actually reached when the membrane potential reaches a threshold level of around -55 mV to -50 mV. At this threshold, an action potential is triggered and the muscle cell contracts. Therefore, the statement is incorrect.Rate this question:
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- 4.
The action potential of skeletal muscles:
- A.
Has a prolonged plateau phase.
- B.
Has a smaller magnitude than that of smooth muscles.
- C.
Causes uptake of Ca into the lateral sacs of the sarcoplasmic reticulum.
- D.
Spreads inwards to all parts of the muscle fibre via the T-tubules.
- E.
Is not essential for contraction.
Correct Answer
D. Spreads inwards to all parts of the muscle fibre via the T-tubules.Explanation
The action potential of skeletal muscles spreads inwards to all parts of the muscle fiber via the T-tubules. The T-tubules are invaginations of the muscle cell membrane that penetrate deep into the muscle fiber. They allow the action potential to rapidly reach the interior of the fiber, ensuring synchronous contraction of all sarcomeres within the muscle. This is crucial for efficient muscle contraction and coordination.Rate this question:
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- 5.
Neuromuscular transmission:
- A.
Is caused by release of acetylcholine from the muscle side.
- B.
Shows a permeability change to Na+ at the receptor side of the neuro-muscular junction
- C.
Can be facilitated by curare.
- D.
Is blocked by curare because it competes with Na+ influx at the M.E.P.
Correct Answer
B. Shows a permeability change to Na+ at the receptor side of the neuro-muscular junctionExplanation
Neuromuscular transmission involves the transmission of signals from the nerve to the muscle. One important step in this process is the permeability change to Na+ at the receptor side of the neuro-muscular junction. This means that when the nerve signal reaches the muscle, the receptors on the muscle membrane become permeable to Na+ ions, allowing them to enter the muscle cell. This influx of Na+ ions triggers a series of events that ultimately leads to muscle contraction. This step is crucial for the successful transmission of the nerve signal to the muscle.Rate this question:
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- 6.
The neurotransmitter at the motor endplate is:
- A.
Adrenaline.
- B.
Noradrenaline.
- C.
Acetyl choline.
- D.
Calcium ions.
- E.
Atropine.
Correct Answer
C. Acetyl choline.Explanation
The correct answer is acetyl choline because it is the neurotransmitter responsible for transmitting signals from motor neurons to muscle fibers at the neuromuscular junction. It binds to receptors on the muscle fibers, causing depolarization and ultimately leading to muscle contraction. Adrenaline and noradrenaline are not neurotransmitters at the motor endplate, but rather hormones involved in the fight-or-flight response. Calcium ions play a crucial role in muscle contraction, but they are not the neurotransmitter at the motor endplate. Atropine is a medication that blocks the effects of acetyl choline, but it is not the neurotransmitter itself.Rate this question:
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- 7.
During neuromuscular transmission:
- A.
Ca++ enters through synaptic cleft.
- B.
Ach is released from synaptic cleft.
- C.
There is a delay of about 5 milliseconds.
- D.
The impulse is transmitted in one direction.
Correct Answer
D. The impulse is transmitted in one direction.Explanation
During neuromuscular transmission, the impulse is transmitted in one direction. This is because the release of Ach (acetylcholine) from the synaptic cleft triggers a cascade of events that ultimately lead to muscle contraction. Once Ach binds to its receptors on the muscle cell, it initiates an electrical impulse that travels along the muscle fiber, resulting in contraction. However, the impulse cannot travel back in the opposite direction due to the presence of a refractory period, which prevents the muscle from immediately responding to another impulse. This ensures that the muscle contraction occurs in a coordinated and controlled manner.Rate this question:
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