An action potential is a very brief shift or spike in a neuron's electrical charge that sends a message down the axon. An action potential is the can be described as a neuron "firing.” Action potentials occur after the resting potential and before a refractory period.

The synaptic cleft is the microscopic gap between neurons. The refractory period is a very brief period of time after an action potential in which another action potential cannot begin. One can think of the refractory period like a very brief rest period.

Neurons—also called nerve cells—are the basic links that allow communication within the nervous system. Neurotransmitters are chemical messengers that activate neighboring neurons, but they are not cells. Dendrites are part of a neuron—they are the branchy parts of the neuron that are specialized to receive incoming information. Hormones are also a type of chemical messenger; however, they are transmitted by the circulatory system and not the nervous system. 

The axon terminal of a neuron contains synaptic vesicles containing neurotransmitters. After an action potential, neurotransmitters are released and diffuse across the synaptic cleft, where they bind to receptors on the dendrites of another neuron. This can cause an action potential in the second neuron. Neurons are not directly connected to each other. Synaptic vesicles do not exist outside of the cell body.

Nerve cells, or neurons, have a basic tree-like structure, which allows them to communicate with other nerve cells. Branch-like dendrites extend from the cell body (i.e. soma) and receive electrochemical signals from other cells. The long, thin axon endings—terminal buttons—extend from the other end of the soma. If the positively-charged signals received into the cell from the dendrites exceed the cell’s normally negative charge, then the axon allows the excess positive ions to travel down it to the terminal buttons, which in turn send neurotransmitters into the gap (i.e. synapse) between them and other cell’s dendrites. The myelin sheath does not itself relay signals, but rather is a natural lipid insulation on the axons of some cells. 

Sodium and potassium are vital components associated with neural electrical transmissions. When it is at rest, a neuron is surrounded by a positive charge due to sodium and maintains an internally negative charge with potassium. When the neuron depolarizes, there is an influx of sodium into the cell. Upon repolarization, there is a potassium efflux where the neuron is restored to its original resting charges.

The correct answer is antagonist. An antagonist is any chemical that prevents a neurotransmitter from binding to its receptor site. Recall that a neurotransmitter is simply any chemical in the brain that enables the transmission of signals between neurons via synapses. Contrastingly, an agonist is any chemical that mimics the shape of a neurotransmitter well enough that it can bind to that neurotransmitter's receptor and stimulate the receptor just as if the neurotransmitter itself was binding to it. A so-called reuptake agent is not a real chemical classification, but the reuptake mechanism is an important aspect of neurotransmission. Reuptake refers to the process by which the presynaptic neuron reabsorbs its released neurotransmitter after the neurotransmitter has done its job by binding to the postsynaptic neuron.

Information enters the neuron through dendrites, the branch-like extensions which carry signals to the cell body (soma). When an action potential occurs, its signal will propagate down the axon of the cell, culminating in the release of neurotransmitters into the synapse from the terminal buttons. These neurotransmitters will cross the synaptic cleft in mere milliseconds, and bind to the receptor sites on the adjacent neuron's dendrites. This process leads to communication between neurons.

An action potential occurs when a neuron transmits an electrical charge down its axon, which terminates in the release of chemical signals in the form of neurotransmitters. These neurotransmitters communicate with other neurons, allowing for the flow of information between the cells of the nervous system. The chemical compounds emitted by neurons as a result of action potential are known as neurotransmitters. Though the release and binding of neurotransmitters to receptor sites on dendrites may result in either inhibitory or excitatory responses, they themselves are referred to as action potentials. Although an action potential is able to occur by way of a maintained electrical gradient within the neuron, it is not correctly described as 'the latent energy of a system'. Likewise, an action potential is not a behavioral predisposition.

Neurons transmit electrical signals between one another, which allows for the communication of incoming stimuli from sensory receptors with the brain, communication of internal states of the body, communication between the brain and muscles to coordinate movement, and communication between the many cells of the brain to allow for the complex array of processes that form the basis for our everyday lives. Although neurons in the visual centers of the brain will indeed play a role in processing color information, at the level of the retina this information is derived from the the cones in photoreceptor cells, and subsequently communicated to the brain via the optic nerves. Neurons will communicate messages between the brain and glands of the body, but they themselves are not responsible for the production of enzymes. Neurons do not serve as energy stores for the body.

Action potentials created by neural impulses are described as being "all or nothing" because the cell either gains sufficient stimulation to release an action potential, or it does not. Once the minimum threshold for excitation is reached, an action potential will be triggered regardless of further stimulation, and no signal will be weaker or stronger than any other. That being said, continued stimulation of a neuron may lead to continued firing of action potentials, which may trigger a stronger or enduring response over time. At the scale of the individual action potential; however, the activity of the neuron may be considered as either a value of 0 (i.e. no action potential), or 1 (i.e. action potential). No decimals are used in this measure.