HUBS 191 Lecture 19 Flashcards
(15 cards)
during rapid depolarisation, a flood of ____ enters the axon hillock
Na+
what is a refractory period
a period of rest after a stimulus during which another stimulus won’t have an effect or it will need to be a much larger stimulus in order to have an effect
neurons use _________ to keep unidirectional movement of a signal down a neuron
refractory periods
what is the absolute refractory period
the period during which a second action potential cannot be generated
when do absolute refractory periods occur
during rapid depolarising or the start of repolarising - when voltage gated Na+ channels are already open or become inactive
what is a relative refractory period
a period during which a second action potential can be generated only if the stimulus is much larger than normal
when do relative refractory periods occur
when some of the voltage gated Na+ channels begin to shift from an inactive to closed state
can VG channels open when inactive
no - they can only open from a closed state
when thinking of the neuron as segmented how does the action potential propagate down in a unmyelinated axon
the action potential diffuses in segments, where the first segments depolarisation triggers the VG Na+ channels to open in the second segment which triggers depolarisation of the third segment etc. the segments repolarise (VG Na+ channels close and VG K+ channels open)
how fast do action potentials propagate down an unmyelinated axons
around 1-5m/s
what is saltatory conduction
when in a myelinated axon the ion movement is restricted to the areas without myelin (nodes) so conduction appears to jump from one node to the next
what is the first step in synaptic transmission
when the action potential arrives at the axon terminal, the change in voltage causes VG Ca+ channels to open. Ca+ moves down its electrochemical gradients into the axon terminal causing it to become depolarised
what is the second step in synaptic transmission
Ca2+ interacts with vesicles causing them to fuse with the membrane and release neurotransmitter into the synaptic cleft (exocytosis). neurotransmitter diffuses across the synaptic cleft
what is the third step in synaptic transmission
neurotransnitter binds to chemically-gated ion channels on the post-synaptic cell
- excitatory neurotransmitter opens Na+ channels to cause EPSPs
- inhibitory neurotransmitter opens Cl- or K+ channels to causes IPSPs
how do we terminate synaptic transmission
neurotransmitter unbinds from chemical gated channels
enzymes in teh synaptic cleft degrade neurotransmitter
portions of the degraded neurotransmitter are recycled back into the axon terminal
