PHYS335: Lab 4

1. Difference in ion concentration between ECF/ICF (controlled by the Na+/K+ pump)

2. Difference in membrane permeability to different ions (i.e. channels)

What does the magnitude of the resting potential depend on?

Voltage gated ion channels

ion channels that are gated by electrical events

Ligand gated

ion channels that are gated by chemical events

Stretch sensitive

ion channels that are gated by mechanical events

Leak channels

ion channels that are UNGATED and mainly exist at open channel conformation at rest

determines resting membrane potential

K+

At rest there is more (Na+/K+) permeability.

 0mV

When 0 ion channels are open, the membrane potential is __.

More toward the K+ equilibrium potential of -90mV

When only K+ channels are open, the membrane potential is ___.

More toward the Na+ equilibrium potential of +60mV

When only the Na+ channels are open, the membrane potential is __.

Type 1 neuronal cell

intracellular concentration of Cl- set at 7mM

equilibrium potential for Cl- = -70 (same as RMP)

Type 2 neuronal cell

has a Cl- pump (out), which lowers intracellular concentration of Cl- to 5mM

equilibrium potential for Cl- = -79mV

Depolarizing

membrane potential moving toward 0

excitatory stimulus, action potential more likely

Overshoot

membrane potential > 0 (positive)

Repolarization

membrane potential returning to -70 RMP (from negative OR positive)

Hyperpolarization

membrane potential more negative than -70mV

inhibitory stimulus, action potential less likely

Graded potential

short distance signals relying only on local flow of ionic currents

proportional to size of stimulus

generated by ligand gated ion channels

decrease with distance from stimulus site (bc charge leaks back out)

can be depolarizing or hyperpolarizing

can summate with each other

Synaptic potential

graded potential change produced in post synaptic neuron in response to neurotransmitter

Receptor potential

graded potential produced at peripheral endings of afferent neurons in response to stimulus

Pacemaker potential

in muscle, spontaneously occurring graded potential change

Action potential

large, rapid depolarization and repolarization of plasma membrane that can occur at increased frequencies and travel long distances

begins at threshold potential

generated by voltage gated ion channels

are not graded by stimulus size

cannot summate

Same

The action potential amplitude is (the same/different) when stimulus size is taken into account.

-55mV

threshold potential at axon hillock

Inactivated confirmation

of voltage gated SODIUM channels, pore open, but part protein (ball and chain) plugging pore

allows for rapid off switch

rapidly; slowly

Voltage gated Na+ channels change confirmation ____, whereas voltage gated K+ channels change confirmation _____.

Depolarization, repolarization

____ opens both voltage gated  Na+ and K+channels, whereas ____ closes both.

Positive

Voltage gated Na+ channels operate under a ___ feedback loop.

The ball and chain inactivation protein

What is the terminating event of a voltage gated Na+ channel’s feedback loop?

Negative

Voltage gated K+ channels operate under a ___ feedback loop.

All or none

the principle that either the action potential occurs at the threshold or not

Absolute refractory period

no matter the length of a stimulus, you will get no further response of a membrane because all Na+ channels are inactivated

Relative refractory period

can have another action potential only if stimulus of greater strength/amplitude than original occurs because only some Na+ channels are inactivated and K+ channels closing so slowly

1. Dendrite/cell body receives graded potential; if sum to -55mV, action potential occurs

2. Action potential initiated at axon hillock because increased density of voltage gated Na+ channels there

3. Action potential moves in one direction down axon (absolute refractory period replaces action potential as it moves down axon, so no option to go backwards)

How does the propagation of a signal occur in an UNMYELINATED NEURON?

Action potential propagates by jumping between nodes of ranvier (saltatory conduction), which is much faster than in unmyelinated axons

How does the propagation of a signal occur in a MYELINATED AXON?

Nodes of ranvier

bare regions of axon (i.e. without myelination) which are the only location of voltage gated Na+ channels and where action potentials occur

frequent action potentials during refractory periods allow us to continuously perceive strong sensations (i.e. hot coffee)

How is the relative refractory period relevant to macro physiology?

• time

• negative membrane potential

What two elements are necessary for the Na+ channel to go back to closed confirmation after being activated?

• Na+/K+ ATPase - establishes/maintains gradient

• K+ leak channel

• Na+ leak channel

What 3 things are required for resting membrane potential?

axon diameter; myelination

Conduction velocity is determined by ___ and ____.

Decreases; increases

As the diameter of an axon increases, the resistance ___, and conduction velocity ____.