Lecture 5 -- The Chemistry of Behaviour Flashcards
(18 cards)
What are the steps when one neuron releases a chemical signal to affect another.
- The action potential arrives at the presynaptic axon terminal.
- Voltage-gated calcium channels in the membrane of the axon terminal open, allowing calcium ions (Ca2+) to enter.
- Ca2+ causes exocytosis. Synaptic vesicles filled with neurotransmitter fuse with the presynaptic membrane and rupture, releasing the transmitter molecules into the synaptic cleft.
- Transmitter molecules bind to special receptor molecules in the postsynaptic membrane, leading to the opening of ion channels in the postsynaptic membrane. The resulting flow of ions creates a local EPSP or IPSP in the postsynaptic neuron.
- The IPSPs and EPSPs in the postsynaptic cell spread toward the axon hillock. (If the sum of all the EPSPs and IPSPs ultimately depolarizes the axon hillock enough to reach threshold, an action potential will arise.)
- Synaptic transmission is rapidly stopped, so the message is brief and accurately reflects the activity of the presynaptic cell. Enzymes in extracellular space break down excess transmitter or reuptake occurs.
- Transmitters may also activate presynaptic autoreceptors, as a way of monitoring the levels of transmitter.
What is an IPSP?
INHIBITORY POSTSYNAPTIC POTENTIAL (IPSP)
a kind of synaptic potential that makes a postsynaptic neuron less likely to generate an action potential
What is an EPSP
EXCITATORY POSTSYNAPTIC POTENTIAL
a synaptic potential that makes a postsynaptic neuron more likely to generate an action potential.
What is synaptic delay and why is it needed?
The brief delay between the arrival of an action potential at the axon terminal and the creation of a postsynaptic potential.
This time is needed for Ca2+ to enter the axon terminal via voltage-gated channels, vesicle exocytosis, and transmitters diffusing across the synaptic cleft and binding to receptors.
How do receptor molecules recognize transmitters using the lock & key analogy?
- A ligand (key) binds to receptor proteins (lock) to activate or block it.
- Neurotransmitter Acetylcholine fits into ligand-binding sites in neurotransmitter receptor molecules in the postsynaptic membrane.
- However various chemicals (other keys) can fit onto receptor proteins and block the entrance of the key
When is ACh a master key, submaster key, and what is an example of a single-key?
ACh is a master key for the entire cholinergic system (both nicotinic and muscarinic receptors).
It is a submaster key when acting on just one receptor family, like only nicotinic or only muscarinic subtypes.
Nicotine is a single-key mimic of ACh that only fits nicotinic receptors
How can ACh be excitatory and inhibitory?
– At excitatory synapses, binding of ACh to one type of receptor opens channels for Na+ and K+ ions. Facilitating depolarization
– At inhibitory synapses, ACh may act on another type of receptor to open channels that allow Cl– ions to enter, thereby hyperpolarizing the membrane
What is an agonist and one example?
A substance that mimics or boosts the actions of a transmitter or other signaling molecule.
- Nicotine mimics ACh increasing alertness and heart rate.
What are antagonists in the neurochemical context?
- A substance that blocks or attenuates the actions of a transmitter or other signaling molecule.
– Curate blocks ACh receptors in muscles causing paralysis.
Why is the coordination of neurotransmitter receptor systems in the brain considered complex?
Each receptor subtype has a unique brain distribution, becomes active at different developmental stages, and remains plastic in adulthood
How does the degradation process bring transmitter effects to a prompt halt?
DEGRADATION: Enzymes chemically breakdown a neurotransmitter into inactive metabolites.
- Enzyme Acetylcholinesterase (AChE) breaks ACh into products that are recycled to make more ACh in the axon terminal.
How does the reuptake process bring transmitter effects to a prompt halt?
REUPTAKE: The reabsorption of neurotransmitter by the neurons that released them.
- Norepinephrine, dopamine, and serotonin are terminated by reuptake. Special receptors for the transmitter, (transporters), are located on the presynaptic axon terminal and bring the transmitter back inside to be repackaged into newly formed synaptic vesicles.
What are axo-axonic synapses?
A synapse at which a presynaptic axon terminal synapses onto the axon terminal of another neuron.
This allows the presynaptic neuron to facilitate or inhibit the activity of the postsynaptic axon terminal
What is an IONOTROPIC neurotransmitter receptor?
A Ligand-gated ion channel.
A receptor protein containing an ion channel that changes shape in response to a neurotransmitter, allowing ions to flow and change the membrane potential.
What is a METABOTROPIC neurotransmitter receptor?
A receptor protein that activates secondary messengers (G Proteins) that open other ion channels and cause changes in the cell.
What are the qualifications of a transmitter?
It can be synthesized by presynaptic neurons and stored in axon terminals.
It is released when action potentials reach the terminals.
It is recognized by specific receptors located on the postsynaptic membrane.
It causes changes in the postsynaptic cell.
Blocking its release interferes with the ability of the presynaptic cell to affect the postsynaptic cell.
What are some amino acid neurotransmitters and examples? And peptide neurotransmitters?
An amino acid neurotransmitter is itself an amino acid.
EX: GABA, glycine, and glutamate.
A peptide neurotransmitter consists of a short chain of amino acids.
What are the amine neurotransmitters?
What are quaternary amines and monoamine neurotransmitters?
What monoamines are catecholamines and indoleamines?
A neurotransmitter based on modifications of a single amino acid nucleus.
QUATERNARY: A neurotransmitter with a nitrogen atom bonded to four groups.
- ACh
MONOAMINE: One amine group.
- INDOLEAMINES: derived from tryptophan. Serotonin, Melatonin.
- CATECHOLAMINE: derived from tyrosine. Hormones too. Norepinephrine, epinephrine, dopamine
