Final answer:
Inside a nerve cell, proteins and neurotransmitters are generally transported in the form of vesicles, which are moved by motor proteins such as kinesin and dynein along the axon, eventually leading to their release at the synaptic cleft.
Step-by-step explanation:
In what form are proteins and neurotransmitters usually transported down the axon of a nerve cell? Proteins and neurotransmitters are primarily transported in the form of vesicles along the axon of a nerve cell. This vesicular transport is facilitated by motor proteins such as kinesin and dynein, which use ATP to move the vesicles along the axonal microtubules.
Neurons communicate with other cells at junctions known as synapses. When an electrical signal, or action potential, arrives at the axon terminal, it triggers the release of neurotransmitters from synaptic vesicles into the synaptic cleft. Neurotransmitters then bind to receptors on a postsynaptic neuron, which can result in the generation of a new action potential in that neuron or a response in another type of cell, such as a muscle cell.
Carrier proteins also play a role in transporting molecules across cell membranes by binding to the molecules and facilitating their movement across the membrane by changing the protein's shape. However, in the context of axonal transport of neurotransmitters, it is the vesicular transport system that is the primary mode of moving these molecules down the axon.