Graded Potentials And Action Potentials Flashcards
Signal transmission types
. Graded potentials
. Action potentials
Depolarization
. Membrane potential becomes less negative (inside of cell more positive)
Hyperpolarization
. Membrane potential becomes more negative (inside of cell more negative)
Repolarization
. Membrane potential returns toward resting membrane potential after a depolarization of hyperpolarization
Overshoot
. Reversal of polarity of membrane potential (inside of cell becomes positive compared to outside)
Voltage-gated channels
. Voltage sensor that causes channel to undergo conformational change when membrane potential is changed over specific range
. Opening of these initiates action potential (NOT graded)
Ligand-gated channels
. Chemically-gated
. Respond to binding of extracellular neurotransmitters to their receptors (receptor-operated channels) OR respond to intracellular second messengers
. Opening these generates graded potentials
Mechanosensitive channels
. Stretch-activated (respond to membrane deformation)
. Mediate pressure of touch and sensory inputs
. Stimulates graded potentials
Background channels
. Spontaneously open and close in absence of external stimulus
. Generate resting membrane potential
Postsynaptic potentials
. Occur at postsynaptic membrane of neuron-neuron synapse
. Stimulus is neurotransmitter released from presynaptic neuron
. Either excitatory or inhibitory
Excitatory postsynaptic potentials (EPSPs)
. Postsynaptic response to excitatory neurotransmitter opens mixed cation channels that carry Na and K
. Results in depolarization
. Brings membrane closer to hers hold for firing action potentials
Inhibitory postsynaptic potentials (IPSPs)
. Postsynaptic response to inhibitory neurotransmitter
. Opens K (or Cl) channels
. Causes hyperpolarization
. Takes cell further away from threshold for firing action potential
T/F Opening of K or Cl channels stabilize the cell at resting membrane potential without changing the resting membrane potential
T
End-plate potentials (EPPs)
. graded potentials
. Occur at motor end plate of neuromuscular junction
. Stimulus is neurotransmitter (Ach) released from motor nerve
. Caused by opening of mixed cation channel that allows Na and K to pass through
Receptor Potentials
. Graded potentials
. Occur at receptor of afferent (sensory) nerve
. Stimulus is physical (stretch, pressure)
The changes from resting membrane potential that don’t cause AP, the repolarization after removal of stimulus depends on _____
Changes in driving force that were set up by stimulus
When cell is hyperpolarized from resting potential, the driving force for K is ____
Reduced (membrane potential becomes nearer to Ek, driving force for Na influx inc.)
After removal of a stimulus, the return to resting potential is ____
Passive, based solely on driving forces and permeability for specific ions
In response to a depolarization from resting potential, the driving force for K ____ and driving force for Na ______
. K efflux increases
. Na influx decreases
Graded potentials can be depolarizing or ____
. Hyperpolarizing
. Depends on currents involved
Graded amplitude
. Magnitude of response (mV) varies w/ magnitude of stimulus
Decrement also conduction
. Magnitude of potential change declines the further away from the stimulus site you get
Action potentials
. Rapid, large changes in membrane potential
Graded potentials have what relationship to action potentials?
Graded potentials have stimulus (trigger) for generation (firing) of AP
Threshold potential
. Point when stimulus is just adequate to initiate AP 50% of the time
. Due to voltage-dependence of activation (opening) of Na channels responsible for initiating AP
T/F Graded potentials and action potentials have a threshold potential
F, only AP has it
AP relationship to distance
. AP does not decrease in amplitude over distance
. Propagated
Absolute refractory period
. Period where AP can’t be elicited no matter how strong the stimulus
Relative refractory period
. Period where another AP can be elicited only by greater than normal stimulus
How is the shape of an AP determined?
. time-dependent changes in Na and K currents
Voltage clamp technique
. Voltage can be set and help by investigator
. Clamping membrane potential above threshold for AP causes current to flow w/o change in membrane potential
. Allows investigation of current flowing at any membrane potential
. Looked at current in Na-containing, Na free, K-containing, and K free to see contributions of each ion
Upstroke (depolarizing phase) of AP is caused by what kind of mechanism?
Positive feedback
. Opening of some Na channels causes depolarization which causes more Na channels to open
Na vs K channel behavior during voltage clamp pulse
. Na does not remain high, but spontaneously decays (inactivated)
. K turns on more slowly but maintains during voltage pulse, do not exhibit inactivation
Na channels exert what kind of feedback onto voltage-gated channels?
Positive feedback
K channels exert what kind of feedback on voltage-gated ion channels?
Negative feedback
Why doesn’t membrane potential ever reach Ena?
. Driving force for Na dec. as membrane potential approaches Ena
. Na decreases due to inactivation of Na channels
. K slowly starting to build
What causes repolarization?
. Inactivation of Na (dec. inward positive current)
. Activation of K (inc. outward positive current)
Afterhyperpolarization
. Mechanisms responsible for repolarization cause transient hyperpolarization
. Na channels don’t immediately recover from inactivation and K channels are slow to close upon repolarization
.
Role of Na-K-ATPase
. Maintains resting membrane potential by maintaining concentration gradients needed for resorting membrane potential and AP
Conduction of AP by local current flow
. Depolarization causes inside of cell to be positive in that region of axon
. In areas adjacent, the cell is still at rest w/ negative inside
. Current flow locally since opposite charges attract
Saltatory conduction
. Axon covered w/ myelin sheath
. Gaps btw myelin (nodes of Ranvier) have fast Na channels and are the only areas that can generate AP
. AP in one node depolarizers the next node to threshold
. Areas in between don’t generate APs
Saltatory conduction is a good mechanism because of what reasons?
. Faster conduction: process of depolarizing a node further away is faster than depolarizing adjacent areas (less intermediate steps)
. Energy efficient: process fo cintuinally generating APs require less energy in myelinated nn.
What determines speed of conduction?
. Diameter of the fiber (larger fiber conducts faster)
. Presence of myelin (myelinated faster than unmyelinated
Tubocurarine
. Neuromuscular blocking agent found in arrow poison
. Dec. EPP amplitude so it is insufficient to reach threshold for skeletal muscle APs
. Assists w/ intubation, setting fractures and dislocation
. Used to diagnose Myasthenia Gravis
tetrodotoxin (TTX)
. found in puffer fish
. Voltage-gated Na channel inhibitor to inhibit upstroke of AP
. Causes loss of sensory and motor function
Multiple sclerosis
. Attacks myelin of myelinated axons
. As myelin sheath degrades, scarring occurs giving symptoms
. AP conduction is adversely affected by demyelination
