The neurotransmitter that causes an action potential to occur in a muscle cell membrane is called:

Correct Answer: D

Rationale: Acetylcholine, released by somatic motor neurons, crosses the neuromuscular junction, binding sarcolemma receptors to depolarize the membrane, triggering an action potential. Inorganic phosphate and ADP relate to ATP cycling, calcium regulates contraction internally not membrane depolarization. Acetylcholine's neurotransmitter role initiates muscle activation, distinguishing it from intracellular or energy-related molecules, key to voluntary movement.

Correct Answer: C

Rationale: Gluteus maximus is avoided for injections due to sciatic nerve proximity; gluteus medius, deltoid (shoulder), and vastus lateralis (thigh) are safer, with ample muscle mass. This safety distinction marks gluteus maximus as non-standard, critical for clinical practice.

Correct Answer: C

Rationale: Parallel fascicles run along a muscle's long axis, straight from origin to insertion, as in the sartorius, optimizing range of motion over force. Circular fascicles form rings (e.g., orbicularis oculi), not linear. Pennate fibers angle into a tendon (e.g., rectus femoris), not parallel. 'Rectus' means straight but isn't a fascicle type it's a naming convention (e.g., rectus abdominis, which is parallel). Parallel arrangement's alignment with the muscle's length, enhancing lengthening/shortening, makes 'c' the correct description.

Correct Answer: A

Rationale: The anterior abdominal wall includes rectus abdominis , internal oblique (c, likely 'interior' typo), and external oblique , forming the front's muscular sheath for flexion and compression. Quadratus lumborum , in the posterior abdominal wall, attaches to the lumbar vertebrae and iliac crest, aiding lateral flexion and posture, not anteriorly. Its deep, posterior location excludes it from the anterior group, making 'a' the correct non-member.

Correct Answer: B

Rationale: The vastus intermedius, part of the quadriceps, lies deep to the rectus femoris, which overlays it, both inserting into the patella via the quadriceps tendon for knee extension. Biceps femoris , a hamstring, is posterior, not overlying. Vastus medialis and lateralis , also quadriceps, are lateral and medial to intermedius, not superficial. Rectus femoris's anterior position over intermedius, per thigh anatomy, makes 'b' the correct answer.