how nerves work 3 Flashcards
how does a graded potential form?
1- receptors are stimulated by changes in a variable (e.g. heat, pressure..)
2- this causes ion channels to open which establishes an electrical gradient
3-If generator potentials reach threshold they cause an action potential to be generated.
different types of graded potential
1- post-synaptic potential
2-pacemaker potential
3-endplate potential-at neuromuscular junction. neurotransmitter is released onto muscle cell and depolarises it
4-generator potential
properties of a graded potential
decremental: charge leaks out as it travels along the axon
graded: the stronger the stimulus, the greater the number of ion channels which open, the greater the current which flows
hyperpolarising: causes the axon membrane to become more negative
depolarising: causes the axon membrane to become more positive.
how is the membrane depolarised
by opening Na+ channels and Ca2+ channels.
fast EPSP: neurotransmitter released onto receptor of post-synaptic membrane which causes non-specific ion channel (+1 charge) Na+ to flow in/ K+ to flow out. more Na+ flows in than K+ out
slow EPSP: neurotransmitter released which binds to receptor, this causes G-protein to close K+ channel so no more K+ can flow out
how is the membrane hyper polarised??
by opening K+ or Cl- channels.
Fast IPSP: neurotransmitter causes cl- channels to open s cl- flows in
slow IPSP: neurotransmitter binds to receptor which causes G-protein to open potassium channels.
summation and synaptic integration
temporal summation: when more than one stimuluses is released in short period of time.these are added together to reach threshold.
spatial summation: when stimuluses released into same synapse are added together to allow axon to reach threshold.
synaptic integration: process by which inputs are added together to see whether stimulus reaches threshold.
what Does the strength of the stimulus depend on?
how close it is to the hillock. the longer the distance it must travel the weaker the stimulus will be.
