Neurotransmission Flashcards
how is RMP maintained
1) NaK pump
2) membrane more permeable to K than Na due to K leak channels
3) gibbs-donnan effect: macromolecules like proteins are built in the cell and are too large to leave the cell, ionise to become anions, H+ released are small enough to leave
passive electrical properties of membranes
local potential
influx of Na: depolarisation
efflux of K: hyperpolarisation
local potentials diminish over long distances, not transmittable
action potential concept
all or none response, transmit a message through the neuron’s membrane, positive feedback after threshold value is exceeded
3 channels involved in action potentials
ligand gated Na channels –> only opens when there is a ligand at the receptor
voltage gated Na channels –> open when exceed threshhold voltage of -55mV, close a few ms later, inactivated for a few ms afterwards
voltage gated K channels –>
start to open when exceed threshold voltage of -55mV, much slower to open than Na channels, close a few ms later
sub-threshold stimulus
ligand gated Na channels open, allowing Na to diffuse into cell
some depolarisation occurs, membrane potential increases to -55mV
depolarisation
threshold membrane potential is exceeded, all voltage gated Na channels open
Na floods into cell down electrochemical gradient, membrane potential rises rapidly, membrane has been depolarised
repolarisation
at peak cell MP, Na channels close and are inactivated
K channels open, K floods out of cell down electrochemical gradient, membrane potential rapidly decreases, membrane is repolarised
hyperpolarisation
K+ channels are slower to close, some K+ leaks back out of the cell, causing membrane potential to temporarily be lower than -70mV
refractory period
Na channels are inactivated for a few ms before opening
Absolute: neuron cannot have an action potential, all Na channels are inactivated
Relative: neuron can generate AP, but requires a greater stimulus as some Na channels are reactivated
impulse travels in 1 direction only
propagation of APs
APs spread from 1 membrane microdomain to the next membrane microdomain to transmit nerve impulse
AP starts in the trigger zone (area with highest Na channel density) after the neuron soma
how to increase rate of transmission
increase nerve diameter
saltatory conduction - impulse jumps from 1 node of ranvier to the next for myelinated neurons
Define synapse
Gap between the axon of 1 neuron and the dendrites of the adjacent neuron
EPSP and IPSP
opening a channel either depolarises (Na, Ca) or hyperpolarises (K, Cl0 the membrane
increasing or decreasing probability of action potential
summation of PSPs
PSPs are graded instead of all-or-nothing
summed spatially (different dendrites) or temporally (different times)
sum of all IPSP and EPSP cause either depolarisation or hyperpolarisation, if threshold exceeded at trigger zone, action potential occurs
when is there graded and all-or-none
graded: at synapse and cell bodies
all-or-none: axons
where does synaptic electrical transmission occur
cardiac muscle at gap junction between pre and postsynaptic neuron, allows all cells to contract at the same time so heart can beat
smooth muscle eg in the gastrointestinal tract for peristalsis
structure of neurotransmitters
derivatives of amino acids, produced by enzymes
eg tryptophan –> seretonin
tyrosine –> dopamine/noradrenaline
neurotransmitter storage
stored in vescicles for secondary active transport
vescicles docked at cell membrane
vSNARE and tSNARE only partially assemble, blocked by complexin, preventing vescicle from fusing with membrane and releasing neurotransmitter
neurotransmittor release
REGULATED exocytosis
action potential depolarises presynaptic terminus
voltage gated Ca channels open, Ca floods into cell
Ca binds synaptotagmin
synaptotagmin displaces complexin, vescicle fusion completed, exocytosis
ionotropic vs metabotropic receptors
ligand gated ion channels
ligand binding outside cell activates enzyme inside cell
the same neurotransmitter can be exitatory and inhibitory because it can open different receptors
CNS neutrotransmitters
Glutamate : excitatory
AMPA receptor (ion)
NMDA receptor (ion)
GABA : inhibitory
both ion and meta
PNS neurotransmitters
Acetylcholine : both
nicotinic receptor (ion)
muscarinic (meta)
Noradrenaline :
only metabotropic
neurotransmitter re-uptake
uptake by presynaptic neuron or glial cells
acetylcholine degredation
acetyl-CoA + choline
choline acetyltransferase (CAT)
acetylcholine
acetylcholinesterase (AChE)
acetate + choline
