Final answer:
The D) neuromuscular junction is the connective area where neurotransmitters like acetylcholine are sent from nerve impulses to muscle cells to stimulate contraction.
Step-by-step explanation:
The connective area where nerve impulses send neurotransmitters across a synapse to a muscle cell to stimulate muscle contraction is known as the neuromuscular junction. This specialized structure allows motor neuron axons to connect to muscle fibers by synapsing with the muscle fiber sarcolemma. Neurotransmitter molecules, specifically acetylcholine (ACh), are released from synaptic vesicles within the synaptic end bulbs of the motor neurons and bind to the receptors on the sarcolemma, triggering depolarization and initiating muscle contraction. A nerve impulse arriving at the neuromuscular junction ensures that a muscle fiber will contract each time it is received, although the strength and the number of contracting fibers can vary based on the impulse frequency.