Dr Gawad Physiology Course Online Exam - Excitable – Course Lecture 5 – Neuromuscular Junction

The correct answer is acetyl choline because it is the primary neurotransmitter responsible for transmitting signals from motor neurons to muscle fibers at the neuromuscular junction. Acetylcholine binds to receptors on the motor endplate, causing muscle contraction. Adrenaline and noradrenaline are not directly involved in muscle contraction, while calcium ions play a role in muscle contraction but are not neurotransmitters. Atropine is a medication that blocks the effects of acetylcholine and is not the neurotransmitter itself.

The correct answer is EPP is a localized state of depolarization at the motor end plate. This is because EPP refers to the depolarization of the motor end plate, which is the specialized region of the muscle fiber where the nerve terminal makes contact. It is a localized event that occurs specifically at the motor end plate and is crucial for initiating muscle contraction. The other statements mentioned in the question are incorrect or unrelated to the concept of EPP.

The motor end plate contains a high concentration of acetylcholine receptors that are specific to skeletal muscle, not smooth muscle. Smooth muscle has different types of receptors. Therefore, the statement that the acetylcholine receptors in the motor end plate are similar to those in smooth muscle is false.

The correct answer explains that neuromuscular transmission shows a permeability change to Na+ at the receptor side of the neuro-muscular junction. This means that when a nerve impulse reaches the neuromuscular junction, the receptor site on the muscle cell membrane becomes permeable to Na+ ions, allowing them to enter the cell. This influx of Na+ ions triggers a series of events that ultimately leads to muscle contraction. This explanation highlights the key mechanism involved in neuromuscular transmission and how it is related to the permeability change to Na+ ions.

The firing level is reached after about +40 mV of depolarization.

During neuromuscular transmission, the impulse is transmitted in one direction. This is because the release of Ach (acetylcholine) from the synaptic cleft triggers an action potential in the muscle fiber, causing muscle contraction. The impulse can only travel from the presynaptic neuron to the postsynaptic neuron, ensuring that the muscle contracts in response to the signal and preventing any backward transmission of the impulse. This unidirectional transmission is crucial for proper muscle function and coordination.