Action potentials Flashcards
role of graded potentials?
integrate incoming inputs at a local area. info comes from diff parts of nervous system
role of action potential?
used for communication. all or nothing
T/F if threshold is reached communication does not occur?
False, communication does not occur if threshold is not reached in graded potential
Local synaptic potentials occur at synapse. caused by what?
chemical agent that opens chemically gated channels
what is the response of synaptic potential if both potassium and sodium channels open?
excitatory
What type of potentials are generator potentials?
mechanically gated
what happens at an electronic potential
opens electric voltage gated channels in response to current change
how is size related to strength of local potential?
larger size larger stimulus strength
where are local potentials generated?
axon hillock
what is spatial summation?
same time different location on dendrite
what is temporal summation?
same location different times
where is an action potential initiated?
axon hillock then propagated down axon
what is the RMP?
-65
what is the voltage in order to reach threshold?
-55
what occurs during depolarization phase?
sodium channels open membrane potential becomes more positive
what happens after the peak of an action potential?
sodium channels close, potassium channels open
why does hyperpolarization occur??
gated potassium channels are open as well as already high permeability of potassium so it will polarize below RMP
what is an absolute refractory period?
start of an action potential when the sodium channels are open, a second AP cannot be stimulated
what is a relative refractory period?
hyperpolarization phase when potential is lower than resting so it takes an even bigger AP to trigger a reaction
during an action potential why is homeostasis not affected?
astrocytes buffer away extra potassium leaving the cell, sodium potassium pump removes sodium from inside the cell
where are the most sodium channels located?
at axon hillock and nodes of ranvier
where are the most potassium channels located?
along unmyelinated neurons, under the myelin
where are the most calcium channels?
dendrites, soma, terminal site of an axon
where are the more chloride channels?
dendrites and soma
does strength of action potential decrease along the axon?
no, the strength stays the same
calculate the conduction velocity given diameter of unmyelinated? myelinated?
Velocity = diameter (.5)
diameter (5.5)
T/F myelinated axons do not have an after hyperpolarization
True
if the membrane potential remains depolarized above threshold, another action potential can not be stimulated. T/F
true
Explain why someone suffering from MS can sometimes recover? (CNS)
with demyelination more potassium will leave the cell than normal, in order to create an action potential there needs to be more sodium channels to balance. over time there is a migration of electrically gated sodium channels. neuron will take on the appearance of unmyelinated nerve
how is recovery possible for people with Guillian Barre syndrome (PNS)?
In PNS schwann cells can replace the myelin
what is the time course difference between Guillian Barre syndrome and MS?
MS gets worse over time with periods of remission. Barre is an acute one time event
what is the incidence rate of MS?
60 to 100 / 100,000 people
typical age onset of MS?
20-40
if a neuron dies can it be replaced?
No, mature neurons withdraw from division cycle
what occurs in a neuron after a neuronal trauma?
the axon is severed, distal segment degenerates. Glial cells come in and remove degenerated parts, astrocytes remove incoming inputs
what happens in PNS neuron if trauma occurs?
schwann cells will increase and form a pathway. neurons will regenerate and send branches to replace the damaged segment. the neuron will return to normal with smalled diameter
what kind of transport is used in PNS neuronal damage reparation?
slow anterograde transport. 3mm/day
