Synaptic Transmission Flashcards
What are the two parts of a synapse?
Axon terminal of presynaptic cell and the membrane of the post synaptic cell, which is either neuronal or non neuronal.
What is the difference between an electrical synapse and a chemical synapse in terms of function, location, and directionality?
Electrical: Rapidly pass an electrical signal/current via movement of ions directly from the cytoplasm of one cell to another via gap junction (delay = 0.2ms). It is present in some neurons, but common in cardiac and smooth mucsle, and either unidirectional or bidirectional.
Chemical: conversion of electric signal to ligand (neurocrine molecule) that is exocytosed to bind to receptor on target cell. Makes up vast majority of synapses in nervous system and are unidirectional.
What are the classic neurotransmitters?
Acetylcholine, amines (norepinephrine, dopamine, histamine, serotonin), Amino acids (glutamate, GABA)
What are novel neutrotransmitters?
Peptides (oxytocin, melanocortin), and Purines (ATP)
What is the difference between ionotropic and metabotropic receptors?
Ionotropic: Receptor channel specific for a single ion that alter ion flow to mediate rapid responses.
Metabotropic: GPCR triggers a cascade that mediates slower responses.
What is the general mechanism of chemical synaptic transmission?
- AP depolarization opens voltage gated Ca++ channels at end of axon, allowing Ca++ to enter presynaptic terminals
- Ca++ entry causes some synaptic vesicles to fuse with presynaptic membrane and release neurotransmitter contents into the cleft
- Neurotransmitter binds to postsynaptic receptors (ionotropic, metabotropic) taking a minimum synaptic delay of 2ms.
- Neurotransmitter is removed from the cleft via enzymatic degradation, active transport back to terminal, diffusion away from synapse, endocytosis into post synaptic cell.
What is the difference between EPSP and IPSP?
Excitatory Post Synaptic Potential: synaptic potential depolarizes and makes the cell more likely to fire an action potential.
Inhibitory Post Synaptic Potential: synaptic potential is hyperpolarizing and makes the cell less likely to fire an action potential.
What is Acetylcholine? Where is it used in?
Neurotransmitter at a cholinergic synapse used by motorneurons (excitation of skeletal muscle), every pathway of the autonomic nervous system, and diffusely through CNS
What are the two types of cholinergic receptors?
Nicotinic: IONOTROPIC. Monovalent cation channels where Na+ and K+ can pass. Na+ entry > K+ exit, therefore Na+ entry depolarizes post synaptic cell.
Muscarinic: METABOTROPIC. GPCR linked to second messenger systems that occur in CNS and targets of autonomic parasympathetic division of PNS.
What is the difference between the binding of ACh to a nicotinic and muscarinic receptor?
Nicotinic: ACh binding opens channel, allows entry of Na+ and exit of small amount of K+, which causes excitatory depolarization within miliseconds (Fast EPSP)
Muscarinic: Binding of ACh to GPCR causes generation of second messengers, activation of kinases, phosphorylation of proteins which COULD include closing Na+ or K+ leakage or opening Ca++ channels, which cause depolarization within seconds (Slow EPSP)
What is norepinephrine?
AKA noradrenaline. Major neurotransmitter of PNS autonomic sympathetic division that are secreted by and bind to (nor)adrenergic neurons.
What are adrenergic receptors?
GPCR receptors that come in alpha and beta classes and bind to noradrenaline. Classes differ based on second messenger pathways.
What is glutamate?
Primary excitatory neurotransmitter of the many neurons of the CNS that bind to ionotropic (NMDA, AMPA) and metabotropic glutamate receptors.
What is the difference between NMDA and AMPA?
NMDA: normally blocked with Mg++ but ejects it upon depolarization to open it. Now open, when glutamate binds, it allows Na+ AND Ca++ to enter which depolarizes the cell.
AMPA: Allows monovalent cations to pass, depolarizing the cell via Na+ influx.
What is gamma-aminobutyric acid?
Main inhibitory neurotransmitter in the brain that hyperpolarize target cells by opening Cl- channels, allowing it to enter the cell. It binds to GABA(a) receptor and GABA(b) receptor.
