Nerves 3 Flashcards
what is the “magic treshold”?
-55mV
what makes a cell depolarise to -55mV? (become more positive from RMP)
external stimuli acting on specific ion channels to create a graded potential where size of potential is related to size of stimulus
where do graded potentials occur in neruones?
in terminals of the sensory neurones (in response to stimuli)
when does the graded potential become an action potential?
when GP becomes big enough and reaches treshold
where does AP release neurotransmitter molecules which activate pharmacological receptors on the second cell?
at the synapse (junction between two neurones)
what is an endplate potential?
- Graded potential; occurs at neuromuscular junction as the motor neurone depolarises the muscle to treshold by evoking a GP.
- on post-synaptic cell, occurs in skeletal muscle
what is the main job of a GP?
get the cell up to treshold (decides if AP should be fired and when)
what is signal transduction?
when a physical stimulus is turned into an electrical impulse
where are generator potentials made? (example of a GP)
in SENSORY receptors
when is the electrical impulse passed from cell to the next cell?
when it reaches treshold (if action potential that is fired, depolarises the cell and makes it reach minimum treshold)
what are 4 examples of graded potentials? (GPEP)
- generator potentials (at sensory receptors)
- Postsynaptic potentials (at synapses)
- endplate potentials (at neuromuscular junction)
- pacemaker potential (in pacemaker tissues)
what are the 4 properties of graded potentials? (ENDL)
- electrotonic potentials
- decremental potentials
- non-propagated potential
- local potential
If Na/K pump is poisoned, what will happen to the cell membrane potential?
little immediate effect
what does decremental mean?
gradual decrease in GP
what distances does GP travel in?
short distances
why can GPs only work on short distances?
most of the current will leak out along the axon (like a leaky hose) so smaller depolarisation will occur at the end due to current leaking out.
-potentials decay quickly
what effect does a big stimulus have on the GP?
-stronger stimulus
-more receptors activated
- more channels open
- bigger current flows
-bigger potential generated
and vice versa
can GPs excite and inhibit a cell?
Yes (hyperpolarisation and depolarisation can occur)
What is EPSP?
depolarising of post-synaptic membrane (making cell more positive, excitatory)
what is IPSP?
hyperpolarising of post-synaptic membrane (inhibitory as cells are taken AWAY from treshold) making cell more negative, inhibitory
how to depolarise a cell?
- open Na channels ( +ve flowing in)
how to hyperpolarise a cell? (2)
- Open Cl channels ( -ve flowing in)
- Open K channels ( +ve flowing out
what are 2 main inhibitory neurotransmitters?
- glycine
- GABA
what is an example of a fast IPSP?
when Cl enters cell (neurotransmitter DIRECTLY binds to ion channels)
what is an example of a fast IPSP?
when K leaves cell (neurotransmitter INDIRECTLY activates G protein which opens ion channels)
how to depolarise a cell? (2)
- Open Na channels (+ve flowing in)
- Close K channels (+ve stays in)
what is an example of a fast EPSP?
Na enters the cell (neurotransmitter directly open channels)
what is an example of a slow EPSP?
K channels close ( neurotransmitter indirectly binds to receptor closing ionic gates)
what are ligand gated channels?
post-synaptic potentials are produced by a neurotransmitter opening/closing ion channels
what are voltage gated channels?
action potentials are produced by depolarisation of the membrane potential, opening/closing ion channels
GPs can summate, what does that mean?
they can gradually add to each other (increase)
what type of summations do GPs have? (2)
- temporal summation
- spatial summation
what is a temporal summation example?
A+A (same impulse) can reach treshold
what is a spatial summation example?
A+B (different impulses stimulated at once), can reach treshold
what is synaptic integration?
the process of summing all those inputs in space and time to determine whether or not the initial segment reaches treshold (temporal +spatial)
what are 4 main properties of GPs?
- decremental
- graded
- depolarising or hyperpolarising
- can summate
What do IPSPs do in terms of treshold?
prevent cells from reaching treshold (inhibits all inputs)
