Chapter 4- Neurochemistry Flashcards
What is a synapse?
The “connection” between an axon terminal of one cell (pre-syanptic cell) and the dendrite or soma of another cell (post-synaptic cell)
synaptic cleft
- The small space in between neurons (neurons are not in physical contact)
Neurons are functionally coupled how?
- When one neuron (presynaptic) generates AP, neuron (postsynaptic) with which it’s coupled will exhibit IPSP or EPSP
Summation of EPSPs=action potential
What happens as the result of an action potential?
- The voltage-gated Ca2+ channels at the axon terminal open and Ca2+ enters the cell
- Ca2+ causes synaptic vesicles to fuse w the presynaptic membrane and release nt into the synaptic cleft (process called exocytosis)
What are neurotransmitters?
- the chemical released from the pre-synaptic axon terminal that serves as the basis of communication between neurons
- Each neurotransmitter can trigger a different effect on the post-synaptic cell
Each neurotransmitter can trigger a different effect on the post-synaptic cell
How many neurotransmitters does each neuron release?
- One (or maybe two or three)
- Different neurons release different neurotransmitters (they specialize)
- Each neurotransmitter cab trigger different effects on postsynaptic cell depending on binding to certain receptor
Where are neurotransmitters made?
- Some NT are made in the soma of neurons and then transported to the axon terminals by motor-proteins
- Some neurotransmitters are made in the soma as well as in the axon terminal
How are neurotransmitters produced?
- Neurons must synthesize their NT and move it into vesicles
- A specific enzyme (protein) is involved in producing each NT
- Often, that enzyme converts an amino acid we derive from our diet into a NT
From release to inactivation on the presynaptic side (steps)
- the action potential is propagated over the presynaptic membrane
- Depolarization of the prezynaptic terminal leads to influx of Ca2+
- Ca2+ preomotes exocytosis (the fusion of vesicles with the presynaptic membrane), which releases transmitter into the cleft
- The binding of NT to receptor molecules in the post-synaptic membrane opens channels (so they are no longer active). This permits ion flow and initiating an EPSP or IPSP
- EPSP or IPSP potentials spread over dendrites and cell body to the axon hillock
- Enzyme present in the extracellular space breaks down excess NT/ Reupatake of NT slows synaptic action and recycles NT for subsequent transmission (NT is “prepackaged” and ready for re-release)
- Transmitter binds to the autoreceptors in the presynaptic membrane
enzymes and precursors for synthesis of NT or NT and vesicle wall are continuously transported to axon terminals
What do autoreceptors do?
- regulate release of NT
- Causes release of NT to decrase if there is too much
What does the Reuptake of NT do?
slows synaptic action and recylces NT for subsequent transmission… NT is prepackaged and ready for re-release
What protein will a NT use to go through and back into a cell?
- A transporter
- Never receptors- they only bind to receptors
What is an ionotropic receptor?
- An ionotropic receptor allows ions to flow through when activated
- faster
What is a metabotropic receptor?
- They are couple to a g-protein whihc then activates ion channels
How do ionotropic receptors work?
- Same as ligand-gated ion channels- are chemically triggered
- Form cation (Na+, K+, Ca2+) or anion (Cl-) channels
- NT binding to the channel results in opening of the channel
- Thus, activation of the receptor can result in change in flow of electrically charge ions across the membrane
- Fast responsive
