Signalling Flashcards
what is electrical signalling?
ion movement, i.e. movement of electrical charge
what is the axon of a neutron?
can be very long, where the nerve impulse travels along
what is a nerve impulse?
a wave of altered charge across tercel cell membranes that sweeps along axon. also known as depolarisation, action potential
what is a membrane potential?
voltage difference between the inside and the outside of the cell. it is maintained by ion pumps in plasma membrane.
what is the electrical potential difference across neutron plasma membrane?
approx -79mV. K+ ions higher inside the cell, Na+ and Cl- higher outside the cell.
what happens when a nerve impulse is stimulated?
Na+ ion channels open and they flow into cell, increasing membrane potential. this causes the opening of voltage gated K+ to flow out of the cell
what ensures the signal only travels in one direction?
the refractory period. the time immediately following AP when new AP cannot be initiated in the same area of membrane
what are the multiple inputs from the multiple different dendrites?
(EPSP’s) - excitatory Pre-synaptic potentials
(IPSP’s) inhibitory pre- synaptic potentials
(graded) very in magnitude
what is the summation of changes in membrane potential?
EPSP increases chance of AP initiation ; IPSP decreases chances
what is the threshold voltage in most human nerve cells and what happens If this is reached?
-55mV, if overall membrane potential reaches this then the Na+ channels open and AP is initiated
what is spatial summation?
summation of inputs from different areas of cell, eg from different dendrites
what is temporal summation?
-input occurs multiple times from the same area/ dendrite
-repeated inputs in short Time period - summation
-summation -> AP’s generated more or less frequently
how is the AP frequency increased?
the greater the stimulus then the greater the frequency, the magnitude always stays the same
what happens when the AP reaches the end of the neuron?
it must cross the synapse and then the AP can be set up in the next neutron
what are excitatory chemical signals?
promote formation of AP in receiving neutron
what are inhibitory chemical signals?
inhibit formation of AP in receiving neuron
amino acid and derivatives NT examples?
glutamine - main excitatory neurotransmitters in CNS
GABA - main inhibitory neurotransmitters in CNS
catecholamines (monoamines)?
derived from Tyr
eg dopamine, serotonin
acetylcholine?
derived drom choline
neuromuscular junction
peptides?
substance P, endorphins
How does GABA-A (ion channel receptor) work ?
binding of the ligand GABA to receptor causes conformational change that opens the ion channel (ligand- gated). Cl- move into cell and hyper polarisation makes it harder to reach the threshold voltage for AP formation in post synaptic cell.
how does the acetylcholine channel work?
-nAChR is a sodium ion channel receptor
-ACh binding allows Na+ entry
-Na+ influx - depolarisation of muscle cell membrane
-depolarisation initiates contraction
-acetylcholinesterase in cleft removes EACh
what are gap junctions?
small pores in adjacent cells which are formed by connexions. pre is very small and ions can diffuse between cells according to concentration gradients.
what are some examples of electrical signalling between gap junctions?
electrical synapses between neurons (most are chemical) and cardiac myocytes
