Question

A disease deactivates the acetylcholine receptors at myoneural junctions. Would this prevent muscle contraction or muscle relaxation, and why?

Answer 1

Deactivation of acetylcholine receptors at myoneural junctions by a disease would prevent muscle contraction, not relaxation, because the receptors are necessary for muscles to receive the signal to contract.

Step-by-step explanation:

If a disease deactivates the acetylcholine receptors at myoneural junctions, it would prevent muscle contraction. This is because acetylcholine (ACh) is a neurotransmitter that is essential for muscle fibers to receive the signal to contract. When ACh is released from the motor neuron, it binds to ACh receptors on the muscle cell, triggering a series of events that lead to muscle contraction. Diseases like myasthenia gravis result in a reduction of ACh receptors due to the immune system creating antibodies against them, which either block or destroy the receptors. Without functioning receptors, the muscle cannot receive the signal to contract, leading to severe muscle weakness and potentially life-threatening complications when respiratory muscles are affected.

Inhibitors like d-tubocurarine also work by blocking ACh receptors at the neuromuscular junction, causing muscle relaxation and paralysis. This is a principle mechanism utilized by many toxins and drugs to impair muscle function.

Answer 2

Prevent contraction, bc ACh must bind receptors, leading to Na+ rushing in --> Ca2+ release --> actin-myosin binding --> contraction