Physiology Exam 3

increase permeability of Na+

Causes a depolarization. Increases the transport of Na+ into the cell. Causes more positive charge on inner membrane.

decrease permeability of Na+

Causes hyperpolarization. Decreases the transport of Na+ into the cell. Causes less positive charge on inner membrane.

increase permeability of K+

Causes a hyperpolarization. Increases the transport of K+ out of the cell. Causes more positive charge on outer membrane.

decrease permeability of K+

Causes a depolarization. Decreases the transport of K+ out of the cell. Causes less positive charge on outer membrane.

Increase permeability of Cl-

Causes a hypoerpolarization. Increases the transport of Cl- into the cell. Causes more negative charge on inner membrane.

decrease the permeability of Cl-

Causes a depolarization. Decreases the transport of Cl- into the cell. Causes less negative charge on inner membrane.

Membrane potential

Voltage generated due to the distribution of negative and positive charges lining the inner membrane and lining the outer membrane of cells. Measured value based on inner membrane charges relative to outer membrane charges.

millivolts

units of measurement of membrane potential is _______.

resting membrane potential

Membrane potential of a cell when it is not being stimulated or inhibited. Distribution of potassium plays the biggest role. Distribution of other ions play a small role. Proteins lining inner membrane play a small role.

Potassium

intracellular concentration~ 135mEq/L

extracellular concentration~ 5mEq/L

permeability~ 1.0

plays largest role in determining resting membrane potential.

Sodium

intracellular concentration~ 15mEq/L

extracellular concentration~ 140mEq/L

permeability~ 0.05

Chloride

intracellular concentration~ 10mEq/L

extracellular concentration~ 100mEq/L

permeability~ 0.45

Sodium Potassium pump

Na+ and K+ concentration gradient is maintained by the ______.

resting membrane potential

Na+/K+ pump is not responsible for _________.

Membrane potential

______ is dictated by 2 factors:

• size of concentration gradients of ions

• size of the permeabilities of the membrane to ions

passive transport

___________ of ions via ion channels primarily establishes resting membrane potential.

out

K+ is transported _____ of the cell during resting conditions.

• at resting Vm, permeability of K+ is the largest

• very large amount of positive charge on outer membrane

• therefore, K+ has the greatest influence on resting Vm

into

Na+ is transported _____ the cell during resting conditions.

• at resting Vm, permeability of Na+ is small

• small amount of positive charge on inner membrane

into

Cl- is transported ______ the cell during resting conditions.

• at resting Vm, permeability of Cl- is large

• Large amount of negative charge on inner membrane

depolarize

• Vm becomes more positive

• inner membrane becomes either more positive or less negative

• outer membrane becomes either less positive or more negative

hyperpolarize

• Vm becomes more negative

• inner membrane becomes either more negative or less positive

• outer membrane becomes either more positive or less negative

repolarize

Vm returns towards resting Vm after a change in Vm

increase extracellular Na+

• causes a depolarization

• predicted by GHK equation

• increases the Na+ gradient

  • more Na+ into cell (causes more positive charge on inner membrane)

increase extracellular K+

• causes a depolarization

• predicted by GHK equation

• decreases the K+ gradient

  • less K+ out of cell (causes less positive charge on outer membrane)

increase extracellular Cl-

• causes a hyerpolarization

• predicted by GHK equation

• increases Cl- gradient

  • more Cl- into cell (causes more negative charge on inner membrane)

decrease extracellular Na+

• causes hyperpolarization

• predicted by GHK equation

• decreases Na+ gradient

  • less Na+ into cell (causes less positive charge on inner membrane)

decrease extracellular K+

• causes a hyperpolarization

• predicted by GHK equation

• increases K+ gradient

  • more K+ out of cell (causes more positive charge on outer membrane)

decrease extracellular Cl-

• causes a depolarization

• predicted by GHK equation

• decreases the Cl- gradient

  • less Cl- into cell (causes less negative charge on inner membrane)

increase intracellular Na+

• causes a hyperpolarization

• predicted by GHK equation

• decrease the Na+ gradient

  • less Na+ into cell (causes less positive charge on inner membrane)

Increase intracellular K+

• causes a hyperpolarization

• predicted by GHK equation

• increases the K+ gradient

  • more K+ out of cell (causes more positive charge on outer membrane)

increase intracellular Cl-

• causes a depolarization

• predicted by GHK equation

• decrease the Cl- gradient

  • less Cl- into cell (causes less negative charge on inner membrane)

decrease intracellular Na+

• causes a depolarization

• predicted by GHK equation

• increases the Na+ gradient

  • more Na+ into cell (causes more positive charge on inner membrane)

decrease intracellular K+

• causes a depolarization

• predicted by GHK equation

• decrease the K+ gradient

  • less K+ out of cell (causes less positive charge on outer membrane)

decrease intracellular Cl-

• causes a hyperpolarization

• predicted by GHK equation

• increases the Cl- gradient

  • more Cl- into cell (causes more negative charge on inner membrane)

action potential

local, very large and very rapid depolarization followed by repolarization. Only a handful of cells can generate action potentials. (e.g. neurons and muscle cells)

threshold

depolarized V, that must be reached to generate an action potential

All or None

response of an action potential

• If threshold is met an action potential will be generated

• if threshold is not met an action potential will not be generated

neuron

Generation and dynamics of an action potential in a _______.

• _____ is stimulated to cause the Vm to depolarize

Na+ channels

Threshold is reached. Voltage-gated _______ activate rapidly.

• rapid transport of Na+ into the cell

• causes a very large and very fast depolarization Vm

• Action potential passes through zero and towards Ena

• large depolarization causes voltage-gated _______ to inactivate

• Na+ transport into cell stops

• Action potential reaches its peak

K+ channels

Voltage-gated _______ open but less rapidly. 

• rapid transport of K+ out of the cell

• causes a very large and very fast repolarization towards resting Vm starting at the peak of the action potential

• Vm continues towards Ek

after-hyperpolarization

Vm is actually more negative (hyperpolarized) than resting Vm.

• resting Vm re-established by channels responsible for establishing resting Vm.

action potential frequency

• maximum frequency dictated by the refractory period

  • shorter refractory period=greater number of action potentials

• directly proportional to the stimulus strength

  • if the stimulus decreases, action potential frequency decreases

  • if the stimulus increases, action potential frequency increases

Sub-threshold stimulus

Very small stimulus that does not cause a cell to reach threshold

• no action potential generated

threshold stimulus

stimulus that causes a cell to just reach threshold

• one action potential generated

submaximal stimulus

Greater than threshold stimulus but less than maximal stimulus

• greater than one action potential but less than the number of action potentials generated with a maximal stimulus

maximal stimulus

stimulus that causes the maximum action potential frequency

supra-maximal stimulus

(greater than maximal stimulus) Action potential frequency does not increase despite larger stimulus

• cannot go beyond a maximum action potential frequency

action potential conduction

Spread of action potentials along a membrane

• does not move across a membrane

• causes the generation of another in an adjacent region

  • analogous to dominos toppling, one after another

diameter, myelin

velocity of conduction in axons depends on axon _____ and ______.

• larger axons conduct action potentials faster

  • greater surface area with more voltage-gated ion channels

• ______ axons conduct action potentials faster

  • more _____= faster conduction

continuous conduction

• Occurs in unmyelinated axons and membranes of excitable cells

• action potential in one region stimulates another in an adjacent region

• conduction velocity is less than 2 meters. sec

• Dynamics:

  • sodium ions from action potential diffuses to adjacent region

  • causes depolarization of membrane

  • when threshold is reached, another action potential is generated

  • conduction of action potentials continues in one direction

    • ensured by the refractory period

saltatory conduction

• occurs soley in myelinated acons

• action potentials generated at the nodes of Ranvier

  • high concentration of voltage-gated Na+ and K+ channels at nodes

• conduction velocity is anywhere from 3-120 meters/sec

• dynamics:

  • sodium ions from action potential diffuses to adjacent node

  • causes depolarization of membrane

  • myelin sheath allows diffusion of sodium to be rapid

  • when threshold is reached, another action potential is generated

  • conduction of action potential continues in one direction

    • ensured by the refractory period

synapse

junction between two cells that allows communication between those two cells

electrical synapse

• communication between two cells

• molecules flow freely through gap junctions when open

• allows for rapid passage of information between adjoining cells

• allows for coordination between electricity coupled cells

gap junction

forms communication between two cells

connexons

gap junction formed between two ________ (one from each adjoining cell)

connexin

connexon formed proteins called ______.

chemical synapse

communication between two cells via release of neurotransmitters

presynaptic membrane

membrane at the synapse that is carrying the information

postsynaptic membrane

membrane at the synapse that is receiving the information

synaptic cleft

small space between presynaptic and postsynaptic membranes

neurotransmitters

• chemicals released from presynaptic cell to postsynaptic cell

• produced by presynaptic cell and most stored in synaptic vesicles

• gaseous __________ produced and released when needed

synaptic transmission

• action potential conducts to synaptic terminal of presynaptic membrane

• causes voltage-gated calcium channels to open

• intracellular calcium concentration increases

• causes synaptic vesicles to fuse with presynaptic membrane

• neurotransmitter is released into synaptic cleft via exocytosis

• diffuses across synaptic cleft

• binds to specific receptors of the postsynaptic membrane

• modulates ion channels in the postsynaptic membrane

synaptic transmission

• causes production of gaseous neurotransmitter

• neurotransmitter released from presynaptic cell via diffusion

• diffuses across synaptic cleft and into postsynaptic cell

• modulates ion channels in the postsynaptic membrane

fate of neurotransmitter

• reuptake of chemical neurotransmitter by presynaptic membrane

• gaseous neurotransmitters are metabolized by postsynaptic cell

reuptake inhibitor

• drug that inhibits the ruptake of neurotransmitters

• neurotransmitter remains in synaptic cleft longer

• effect of neurotransmitter is enhanced

• administered when natural neurotransmitter level is low

postsynaptic potential

• transient Vm change of postsynaptic membrane

• due to neurotransmitter release on postsynaptic membrane

excitatory postsynaptic potential

• depolarization followed by repolarization

• influx of cations

inhibitory postsynaptic potential

• hyperpolarization followed by repolarization

• influx of anions or efflux of cations

summation

integrated sum of EPSPs and IPSPs. Determines Vm change

Spatial summation

When multiple postsynaptic potentials from different synapses occur at about the same time

temporal summation

When multiple postsynaptic potentials from the same synapse occur at about the same time

synaptic plasticity

• ability of some structure of a synapse to change

• formation of new synapses or loss of synapses

• large “event” must take place to cause plasticity