Physiology Quiz 2 (2/2) Flashcards
In depolarization, does the membrane charge change in a positive or negative direction?
Positive-due to large increase in sodium conductance g=3 or 4
Resting potential (mV)
65 mV
During depolarization with increase in Na conductance, which direction will Na flow?
Concentration and electrical gradient favor inward flow
-passively diffuses
Does membrane charge change in a positive or negative direction during repolarization?
Negative
Repolarization is due to
Sudden large increase in K conductance (overall outward flux)
Sodium-potassium pump
What will happen to K when its conductance suddenly increases dramatically?
Overall outward flux due to concentration and electrical gradient
-passive diffusion
Wy does sodium-potassium pump only have influence during repolarization?
It is always running but it is simply overwhelmed during depolarization because of the large amount of Na rushing in
Excitability/irritability
Possessing the ability to produce an action potential
Stimulus
Event or process which elicits a depolarization
Threshold stimulus
A stimulus strong enough to elicit a depolarization that is an action potential.
Subthreshold stimulus
A stimulus that causes a depolarization, but not an action potential
All-or-none phenomenon
Once a threshold stimulus occurs and if there are no abnormalities in the nerve cell, the action potential will always look the same for that single nerve cell (resting charge and peak will always be the same)
Temporal summation
Two or more stimuli occur close in time so that they are able to add their effects
Spatial summation
Two or more stimuli that occur close in proximity so that they are able to add their effects
Electronic or decremental conduction
An impulse travels through a nerve membrane without self propagation and gradually dies out over distance due to the resistance of the membrane to electrical current; applies to subthreashold stimuli only
Absolute refractory period
The time during an action potential when it is impossible to cause another action potential, no matter how strong the stimulus is
Relative refractory period
The time during an action potential when it is possible to cause another action potential, however you need a stimulus stronger than usual
Voltage dependent
Membrane depends of voltage becoming more negative to reset
Time dependent
Takes time for membrane to repolarize
Accommodation
Situation where several subthreashold stimuli arrive at a nerve fiber but are separated enough by time or distance that they cannot sum enough to reach threshold; results in cell or fiber becoming less ale to fire due to Na channels being in refractory periods and not all reset and available to fire
Tetrodotoxin (TTX)
Toxin found in puffer fish which blocks Na channels of nerves; dos not allow nerves to fire (usually respiratory nerves are blocked and victim stops breathing)
Tetraethylammonium (TEA)
Blocks K channels; no/super slow repolarization because K channels will not allow K to flow back out; only sodium-potassium channel will be at work
Myelin
Fatty sheath that covers nerve cell to insulate it
How I myelinated action potentials travel
Self propagation; velocity of impulse is proportional to the diameter of the cell (^diameter, ^velocity)
Types of stimuli
Chemical
Electrical
Mechanical
How myelinated fibers transmit
Saltatory conduction
Saltatory conduction
Skipping from node to node
Alpha motor neurons
Largest, fastest, myelinated fibers. Usually found in skeletal muscle and reflex loops
How myelin affects size of cells
Allows nerve trunks to be smaller and still conduct quickly
How myelin influences energy conservation
Don’t lose as much energy while nerve conducts
-less Na needed for depolarization–> less Na to expell using sodium-potassium pump–> less ATP needed for pump
How Myles influences rapid repetitive firing
Less Na to remove from cell= quicker repolarization= quicker ability to fire again
How myelin insulates
Lipid material= strong insulating properties; prevents cross reactions
How MS relates to myelin
Motor control issues due to loss of myelination causing neurons to cross-react
