OSMT (Ontario Society of Medical Technologists) Practice Exam

Which statement is NOT true of the neuromuscular junction?

1. The axon terminal is the end of the motor neuron

2. The sarcolemma contains cholinesterase to inactivate acetylcholine

3. The synapse is the small space between the axon terminal and the sarcolemma

4. Acetylcholine makes the sarcolemma very permeable to potassium ions

The correct answer is: The sarcolemma contains cholinesterase to inactivate acetylcholine

The statement regarding the sarcolemma containing cholinesterase to inactivate acetylcholine is indeed not true. While it is accurate that cholinesterase is important for breaking down acetylcholine in the synaptic cleft to terminate the signal for muscle contraction, this enzyme is not found in the sarcolemma itself. Instead, it is primarily located in the synaptic cleft, which is the space between the axon terminal and the muscle fiber. This ensures that once acetylcholine is released from the axon terminal and binds to receptors on the sarcolemma, it is quickly inactivated to prevent continuous stimulation of the muscle. The other statements regarding the neuromuscular junction are accurate. The axon terminal is the end of the motor neuron where neurotransmitter release occurs, and the synapse is indeed the small space between the axon terminal and the sarcolemma, facilitating communication between the motor neuron and the muscle fiber. Acetylcholine does not increase permeability specifically to potassium ions; rather, it primarily causes an influx of sodium ions which depolarizes the muscle cell membrane, leading to muscle contraction.