Talbot - The Action Potential Flashcards
what is a resting potential and what is it for a typical cell
a potential maintained across a membrane of excitable cells = -60/-70mV
what is hyperpolarization
membrane potential is more negative than the rest - due to an influx of anions or efflux cations
what is depolarization
membrane potential is less negative or positive than the rest - due to influx of cations or efflux of anions
what is the threshold potential
level of depolarization that triggers an action potential
what is a graded potential
variable strength signals that travel short distances and lose strength as they travel - may initiate an action potential
what are the 2 membrane domains in the neuron
somatodendritic domain and axonal domain
where is the somatodendritic domain located
membrane of cell body/soma and dendrites (all cells everywhere)
where is the axonal domain located
starts at axon hillock and includes axon and nerve terminals (only neuron cells)
what are the 2 types of openings located on the somatodendritic domain
ligand-gated channels and GPCR (G-protein coupled receptors)
how do ligand-gated channels work
they directly link incoming signals to opening of channel
how do GPCR (G-protein coupled receptors) work
they indirectly link the receptor to ion channel - activation of G-protein = open channel
what type of response do ligand-gated channels and GPCR have to changes in membrane potential
can only respond passively to changes in membrane potential = graded potentials
what is the amplitude of the voltage deflection across the membrane proportional to
the amplitude of the stimulus pulse (current) - assuming constant resistance (V=IR)
what type of channels are located on the axon
Voltage-gated Na and K channels
what type of channels are located at the nerve termini
Voltage-gated Na, K, and Ca channels
what type of response does the axonal domain have
all or nothing response
what happens if the magnitude of the graded potential reaches and goes above threshold
an action potential is developed - maximum all or none voltage
what happens if the depolarizing stimulus is less than threshold
no action potential is generated
does the depolarizing stimulus intensity change the type of response given
no - same as long as it is above threshold
what is the path of an action potential
from resting state - depolarization phase - repolarization phase - hyperpolarizing phase
what is happening to the ion channels in the resting phase
all voltage-gated Na+ and K+ channels are closed (K+ have some leaking) - permeability to K+ is greater than Na+
what is happening to the ion channels in the depolarizing phase (rising phase)
Na+ channels open/activate and Na+ goes into the cell (K+ are slower to open) becomes more positive and approaches the equilibrium potential of Na (ENa) - Na+ permeability is higher than K+
what is happening to the ion channels in the repolarizing phase (falling phase)
the Na+ channels become inactive (NOT closed) and K+ channels are open - K+ leaving the cell making the cell more negative and membrane potential move towards the equilibrium potential K+ (Ek)
what is happening to the ion channels in the hyperpolarizing phase
K+ channels slowly close and Na+ are still inactive and start to close (K+ stay open longer than Na+ allowing membrane potential to fall below resting)
what type of glial cells make myelin in the PNS
Schwann cells
what is electronic spread
passive process (doesn’t require proteins) spread of depolarization, happens in all membranes and decays with distance
why doesn’t an action potential decay with distance
they are regenerated at each node
what is an orthodromic action potential
it moves down axon away from cell body towards terminus
what is an antidromic action potential
moves up an axon towards cell body
what 3 things govern the passive spread of charge
shape of cell, resistance to ion flow across membrane and in cytoplasm, and capacitance of membrane
what 2 things determine the conduction velocity
axonal diameter (larger = faster) and if it is myelinated or not
what is the actual current/conductance that develops
the sum of all individual openings and closings of ion channels
what is a Na+ channel made up of
1 large alpha subunit and 1 or more beta subunit that is specific to type of Na+ channel
what is the large alpha subunit of the Na+ channel made of
4 transmembrane domains (forms ion conduction pore) - each domain has 6 membrane spanning regions
what does the 4th membrane spanning helix in each domain of Na+ do
contains voltage sensors for the channel
what is the absolute refractory period
no action potential of any type may be generated - no matter how large the stimulus intensity (excitability = 0)
what is the relative refractory period
smaller than normal height action potential may be generated in response to a larger than normal stimulus (excitability = increases)
what is excitability
likelihood that a neuron will fire an action potential at its normal threshold (lower excitability - the greater the stimulus intensity must be)
what is the Hodgkin cycle
positive feedback in voltage-gated Na+ channels: as Na+ channels are opened the membrane is further depolarized (inducing more Na+ channels to open) and the cycle continues - need an outside mechanism to stop cycle
when would a Ca2+ channels open
located in the nerve terminus - opens in response to depolarization and Ca2+ flows into the cell acting as a “second” messenger to trigger the release of vesicles containing neurotransmitters
