F4 Neurotransmission Flashcards
what is meant by ‘excitability’?
- the ability to dynamically alter the voltage across the plasma membrane (i.e. the electrochemical gradient)
what is the range for resting membrane potential?
-50 to -90 mV
during resting potential, is the inside or outside of the cell more negative?
inside is more negative
describe the distributions of sodium, chloride, calcium and potassium ions in resting potential
- more sodium and chloride ions outside the cell rather than inside
- more potassium ions inside cells rather than outside
- minimal calcium ions inside and outside
what happens when an ion channel is activated?
- membrane becomes porous to charged molecules
- causes rapid movement along electrochemical gradient
the concentration of what ion is strictly regulated and how do they typically move?
- calcium ions
- they typically flow into the cell from the exterior after calcium ion channels are activated to open
what happens to the charge of the inside of the cell during depolarisation?
becomes more positive
what does membrane depolarisation cause in regards to the ion channel protein and what does this lead to?
- structural rearrangements
- leads to channel opening and allowing ions to flow into cell
in terms of charges, explain how voltage-gated channels open and close
- paddle of channel protein has positive residues
- when inside of cell is negative, the positive paddle is attracted to the inside of the cell so the channel stays closed
- inside of cell becoming positive causes paddle to repel and channel to open
describe membrane DEpolarisation
- depolarisation open sodium ion channels fast
- sodium ions flood into cell causing further depolarisation
describe membrane REpolarisation
(after sodium floods into cell)
- potassium ion channels open (slower than sodium channels)
- potassium ions flood out of cell
- sodium ion channels inactivate
- membrane is repolarised (due to lots of positive ions moving back out of cell)
describe the process of establishing resting potential after depolarisation and repolarisation
- potassium channels inactivate but too many will have left so the inside of the cell is too negatively charged
- ion pumps and transporters use energy from ATP or counter-transport to reestablish membrane conditions (3 sodium ions out, 2 potassium ions in)
what does saltatory conduction help to do?
increase speed and reliability of conduction
what types of cells coat axons in insulating myelin sheaths?
glial cells / oligodendrocytes
describe saltatory conduction
- action potentials ‘jump’ between nodes of ranvier where ion channels are clustered
- sodium ion channels open, sodium ions move into the cell, cell becomes more positive and current flows through the axon to the next node
- current gets to next node and pushes the next node to threshold potential to open the sodium ion channels here too
- action potential is generated here too and the cycle repeats
why can action potential not back flow during saltatory conduction?
- sodium channels inactivate for a short period of time after opening
what is a synapse?
neuron to neuron junction in the ganglion
how is neurotransmitter made?
- synthetic enzymes make transmitter from inactive precursors
- they convert precursor into neurotransmitter
- vesicles will store the neurotransmitter in the active zone until their release is triggered
where is transmitter transported into vesicles and how?
- in the presynaptic nerve terminal
- vesicular transporters use active transport to concentrate transmitter into vesicles
describe how vesicles are released from the presynaptic membrane
- action potential depolarises the terminal
- voltage-gated calcium channels open and calcium flows into presynaptic knob
- calcium triggers vesicle fusion with presynaptic membrane are NT is released into synaptic cleft
describe how action potential is initiated in postsynaptic knob after NT is released to synaptic cleft
- NT binds to nicotinic receptors on postsynaptic cell and they’re activated
- ligand-gated sodium ion channels open and action potential is initiated when sodium ions influx into postsynaptic knob
what needs to bind to the receptor for a ligand-gated ion channel to open?
an agonist
what are varicosities?
- swellings formed by nerve terminals of autonomic projections in almost all tissues
- often the sites of synapses
- lie close to target cells and receptors
describe the release of NT at autonomic terminals
- boutons release onto smooth muscle, endocrine cells etc.
- activate GPCRs
- causes activation or inhibition of second messenger pathways
what does noradrenaline act on?
alpha and beta adrenoceptors
what does acetylcholine act on?
muscarinic receptors
what are the 3 types of muscarinic receptors and what are their effects when ACh binds?
- M1, M2, M3
- M1 and M3 lead to smooth muscle contraction when ACh binds
- M2 leads to cardiac muscle relaxation when ACh binds
