Excitable cell Flashcards
What is an action potential?
a fixed size, all-or-nothing response that travels along an axon
What is a graded response?
variable size,local signal, that is not propagated over long distances
What ways do graded and action potentials pass in axon?
Graded potentials can go either way, action potentials tend to travel in one direction(away from cell body).
How are action and graded potentials coded?
APs coded by frequency (unit of size)
GPs coded by size (according to stimulus strength)
Why do neurons have a resting potential?
selectively permeable membrane, unequal distribution of ions on either side of membrane, physical forces
What physical forces determine resting potential?
diffusion, electircal potential
what is Vm of nervous systen?
negative (-65mV)
What is Eion?
the membrane potential that would be achieved in a neuron if membrane was selectively permeable to that one ion ONLY
What does nernst equation calculate?
calculate Eion for an ion
What is nernst equation at 37 degrees?
Eion = 61.54mV log [ion]outside/[ion]inside
What does increase in extracellular K+ cause?
membrane depolarizes (more positive )
Why is resting membrane potential close to Eion for K?
At rest membrane is very permeable to K+ but slughtly permeable to other ions.
What does goldman equation calculate?
membrane potential but multiple ions are taken into account
What happens to membrane ppotential during an action potential
it increase - from negative to positive due to sodium permeability increase
What happens in overshoot phase?
Membrane potential rises to near Eion sodium
What factors effect conduction velocities?
axon diameter
Myelination
How does axon diameter affect conduction velocity?
The wider the axon the greater the velocity
As resistance to current flow is inversely proportion to cross sectional area of axon. so resistance is lower the wider the axon
Why are there so many unmyelinated small axons?
space constant is proportional to rm/ri so benefit of high membrane resistnace is reduced by high internal resistance
How big was sqid giant axon?
1000 micro meters 25m/s
What does TEA do?
block K+ channels
What blocks Na channels?
Lidocaine, TTX, STX
Where is action potential initiated?
Spike initiation zone in the axon hillock
What is temporal and spatial summation?
Temproal- more frequent APs
Spatial - multiple inputs add up to same neuron.
How can EPSPs be shunted?
By inhibitory input (excitatory post synaptic potential)
where are electrical synapses?
They are rare in human. but in smooth muscle, cardiac muscle and retinal neuronal cells.
How can electrical synapses work?
can work 2 ways and are gap junctions.
