Chemicals released from the terminal buttons that excite the next neuron into firing.

Chemicals released from the terminal buttons that excite the next neuron into firing.

• A. Inhibitory Neurotransmitters
• B. Excitatory Neurotransmitters
• C. Neuromodulators
• D. Hormones

Answer: (B)

Excitatory neurotransmitters are the chemicals released from the presynaptic terminal that increase the chance the postsynaptic neuron will fire. They are packed in vesicles in the terminal buttons and released into the synaptic cleft in response to an action potential. When they bind to receptors on the next neuron, they typically open ligand-gated cation channels, allowing positive ions like Na+ (and sometimes Ca2+) to flow in. This depolarizes the postsynaptic membrane, creating an excitatory postsynaptic potential that brings the neuron closer to threshold and increases the likelihood of firing an action potential. Examples include glutamate in the brain and acetylcholine at many neuromuscular junctions. Inhibitory neurotransmitters, by contrast, tend to hyperpolarize the postsynaptic neuron or stabilize it, making firing less likely. Neuromodulators modify how strongly or how often neurons release neurotransmitters or respond to them over longer timescales, rather than directly triggering firing at a single synapse. Hormones are endocrine signals that travel through the bloodstream and affect distant targets, not the rapid, localized chemical signaling of a synapse.

Excitatory neurotransmitters are the chemicals released from the presynaptic terminal that increase the chance the postsynaptic neuron will fire. They are packed in vesicles in the terminal buttons and released into the synaptic cleft in response to an action potential. When they bind to receptors on the next neuron, they typically open ligand-gated cation channels, allowing positive ions like Na+ (and sometimes Ca2+) to flow in. This depolarizes the postsynaptic membrane, creating an excitatory postsynaptic potential that brings the neuron closer to threshold and increases the likelihood of firing an action potential. Examples include glutamate in the brain and acetylcholine at many neuromuscular junctions.

Inhibitory neurotransmitters, by contrast, tend to hyperpolarize the postsynaptic neuron or stabilize it, making firing less likely. Neuromodulators modify how strongly or how often neurons release neurotransmitters or respond to them over longer timescales, rather than directly triggering firing at a single synapse. Hormones are endocrine signals that travel through the bloodstream and affect distant targets, not the rapid, localized chemical signaling of a synapse.