Synaptic Transmission and Neurotransmitters - Anatomy and Physiology
- What are three ways a neurotransmitter's action in the synaptic cleft is ended?
- Reuptake into the presynaptic terminal or glia, enzymatic degradation, and diffusion away from the synapse.
- Which proteins mediate fusion of synaptic vesicles with the presynaptic membrane?
- SNARE proteins, which pull the vesicle and plasma membranes together when Ca2+ binds its sensor.
- To which class of neurotransmitters do dopamine, norepinephrine and epinephrine belong?
- Catecholamines, which are made from the amino acid tyrosine.
- What is the main inhibitory neurotransmitter of the brain, and which one dominates inhibition in the spinal cord?
- GABA in the brain; glycine in the spinal cord.
- A drug blocks serotonin reuptake transporters. How does this affect serotonin in the synaptic cleft?
- Serotonin remains in the cleft longer and at higher concentration, prolonging its effect on postsynaptic receptors.
- How do electrical synapses differ from chemical synapses?
- They pass current directly through gap junctions, so transmission is nearly instant and can be bidirectional.
- A neurotransmitter opens Cl- channels on a mature neuron, and Cl- flows in. What type of postsynaptic potential results?
- An IPSP. Cl- influx makes the inside more negative (hyperpolarization), moving the membrane away from threshold.
- What is temporal summation?
- Several postsynaptic potentials from one presynaptic neuron arrive in rapid succession and add together.
- What is the difference between an EPSP and an IPSP?
- An EPSP depolarizes the postsynaptic membrane toward threshold; an IPSP hyperpolarizes or stabilizes it away from threshold.
- What is the main excitatory neurotransmitter of the CNS?
- Glutamate.
- What directly triggers neurotransmitter release at a chemical synapse?
- Ca2+ influx through voltage-gated Ca2+ channels in the axon terminal when an action potential arrives.
- How do ionotropic and metabotropic receptors differ?
- Ionotropic receptors are ligand-gated ion channels with fast effects; metabotropic receptors act through G proteins and second messengers, more slowly.