Cellular physiology Flashcards
Describe the differences in action potentials of different tissues. Why?
neuronal (2 msec) and skeletal muscle (5 msec) are much faster than cardiac (200msec)
- functional reason:
- -Muscle: need rapid repetitive activation so no twitch
- -Cardiac has longer for protection! from additional electrical activity
- anomalous rectification (as cell depolarizes K+ permeability decreases)
- have L-type calcium channels: allow calcium to enter cell: outward potassium overall -> long plateau
When is an action potential generated?
When the cell is depolarized to threshold
What is the relationship between space constant and conductivity?
the longer the constant, the faster the conduction
- can transmit the depolarization farther
- larger diameter axon has lower internal resistance than membrane resistance
How does local current flow cause conduction?
an area of membrane is activated by AP (depolarized region) and this causes reversal of polarity
- cuz of potential diff, local current flows
- that activates Na+ channels to depolarize the next segment -> start AP
- propagation!!!
how does myelination help transmit the AP?
They have greater membrane resistance so allows them to have a longer space constant
Describe the phases of the action potential
- resting: m activation gate closed, h inactivation gate open
- upstroke: sub threshold potential reaches threshold and activates Na channels–>depolarization
-opens m! h starts to close slowly. while open: sodium flows down gradient into the cell-> drive up toward ENa (+70) - depolarization: open K+ channel (slower, smaller)- efflux
AND close Na+ channel off (turn itself off) - Repolarization caused by activation of K+ channels along with inactivation of Na channels move toward Ek (-80)
- K+ channel is turned off by repolarization
- K+ channels super slow so cause hyperpolarization
- back to resting: potassium flux equilibrates and cell returns to RMP
Describe sodium channels
depended on time (activate fast) and voltage (respond to depol)- for both activation and deactivation
Regenerative depolarization: Na moves into cell down electrical and concentr gradient to depolarize cell towards E-Na
depolarization increases Na permeability (open more Na channels) which cause more depolarization! positive feedback
inactivate at positive voltages (depol)
inactivation requires repolarization ^o^
Describe potassium channels
time and voltage dependent activation but no inactivation gates :o
- remain open during depolarized membr
- deactivate with repolarization
depolarization of AP upstroke activate opening of K+ channels -> flow out of cell
outward current repolarizes membrane toward Ek ==> all the way to hyperpolarization
deactivate self during repolarization
-@ same time reactivate Na channels (2 x 1)
What affect sodium channel availability?
more positive RMP results in less available Na channels
e.g. channels inactivate at + voltages
What is absolute refractory period?
stimulus can’t elicit AP
no available Na channels!
What is relative refractory period?
stimulus can elicit an AP
membrane repolarizing so some Na channels recovered
How does calcium affect membrane excitability?
alter membrane charge!
hypercalcemia or HYPOVENTILATION (incr free [Ca])
-raises threshold for Na channel activation= decr membrane excitability
hypocalcemia or HYPERVENTILATION
-lowers threshold = incr membr excitability
How does potassium affect membrane excitability?
hyperkalemia: if too much K+ outside then potassium can’t leave the cell, stays inside and makes RMP more positive
- rem that less Na channels are available then…
- less Na comes in -> slower conduction
hypokalemia: so few outside that K wants to leave
- would take too much energy to bring all K back into the cell so in the heart we have anomalous rectification: the K permeability decreases so it won’t leave
* no change in RMP
