Final answer:
The specialized connection that allows communication between a motor neuron and a skeletal muscle fiber at the neuromuscular junction includes the axon terminal, motor end plate, and synaptic cleft. Answer 4) All of the above is correct and encompasses all these components, which work together to trigger muscle contraction.
Step-by-step explanation:
The specialized intercellular connection that enables a motor neuron to communicate with a skeletal muscle fiber at the neuromuscular junction (NMJ) includes several components. Specifically, the correct answer is 4) All of the above, which comprises the axon terminal, the motor end plate, and the synaptic cleft. The axon terminal (presynaptic element) contains synaptic vesicles filled with the neurotransmitter acetylcholine. When an action potential reaches the axon terminal, acetylcholine is released into the synaptic cleft. This neurotransmitter then binds to nicotinic acetylcholine receptors located on the sarcolemma at the motor end plate (postsynaptic element), triggering muscle fiber contraction. The synaptic cleft is the gap that separates the axon terminal from the motor end plate through which the neurotransmitter diffuses.