What does a neurotransmitter primarily do at the synapse?

Neurotransmitters are crucial chemicals in the nervous system that facilitate communication between neurons at the synapse. When an electrical signal reaches the end of a neuron, neurotransmitters are released into the synaptic cleft, which is the small gap between the sending (presynaptic) neuron and the receiving (postsynaptic) neuron.

Their primary role as messengers allows them to bind to specific receptors on the postsynaptic neuron, leading to changes in that neuron's state, such as initiating a new electrical impulse or inhibiting a response. This messenger function is fundamental for the transmission of signals throughout the nervous system, impacting everything from muscle movement to mood and cognitive processes.

The other options do not accurately represent the primary function of neurotransmitters at the synapse. While muscle contraction can be influenced by neurotransmitters like acetylcholine, that is just one aspect of their broader role. Transporting nutrients is unrelated to neurotransmitter function, as that responsibility typically falls to other cellular mechanisms. Lastly, while some neurotransmitters are involved in the endocrine system, facilitating hormone production is not their primary role at the synapse.