Lab 2: Excitable Cell Membrane

triggers voltage

Depolarization at axon terminal ________ gated Ca2+ channels (Ca2+ messenger)

Resting membrane potential difference (resting potential)

voltage difference across the cell membrane at rest

Graded potential

depolarization of soma and dendrites via influx of Na+

Membrane receptors

gated Na+ channels lining the soma and dendrites that respond to stimulus (ACh, other chemical ligand, mechanical force on cell membrane, etc.)

Summation

accumulation of Na+ from multiple graded potentials

Temporal summation

from multiple graded potentials over short period of time from the same origin (separated by time)

Spatial summation

from multiple graded potentials arriving at about the same time from different origins (separated by space)

Action potential

depolarization along length of axon

Threshold

voltage required to initate action potential

Axon hillock

connection between soma and axon

Absolute refractory period

time during which another action potential cannot be initiated

Relative refractory period

time during which it is more difficult than normal to initiate an action potential

Frequency coding

frequency or number of action potentials codes for strength of signal or strength of stimules

Axon diameter

walls cause resistance to flow, more distance from walls = faster rate; threfore larger axons allow for faster transduction (less efficient but faster)

Myelination

prevents ion leakage, if Na+ leaks back out along axon → [Na+] inside axon decreases → diffusion rate decreases → transduction rate decreases

Compound action potential

nerve segment is bundle of axons, generally not possible to separate a single one to be tested (except for squid giant axon); the sum of action potentials travelling on parallel axons at the same time, will vary in strength as number of axons depolarizing at one time changes

What is resting membrane potential difference (or resting potential)?

voltage difference across the cell membrane at rest

Is there a higher or lower concentration of K+ in ECF or ICF at rest?

higher [K+] in ICF

Is there a higher or lower concentration of Na+ in ECF or ICF at rest?

higher [Na+] ECF

What is the normal range of resting potential?

-40 to -80 mV

Stimulus --> ___ potential --> ___ potential --> exocytosis of ACh from axon terminal

graded; action

What is graded potential?

depolarization of soma and dendrites via influx of Na+

What lines the soma and dendrites that respond to a stimulus?

membrane receptors (gated Na+ channels)

What determines the strength of graded potential?

strength of stimulus

Number of membrane receptors opened, length of time membrane receptors stay open, and amount of Na+ allowed to influx affect ___.

strength of potential

What is summation?

accumulation of Na+ from multiple graded potentials

True or False: There can be multiple action potentials from a single graded potential and/or summation.

True

What is temporal summation?

multiple graded potentials over short period of time from the same origin (separated by time)

What is spatial summation?

multiple graded potentials arriving about the same time from different origins (separated by space)

What is action potential?

depolarization along length of axon

What is threshold?

voltage required to initate action potential

What is axon hillock?

connection between soma and axon

When does the activation gate of voltage gated Na+ channels open?

threshold

What does the opening of the activation gate of voltage gated Na+ channels do?

allows influx of Na+ from ECF causing depolarization

When does the inactivation gate of voltage gated Na+ channels close?

at overshoot (tip of graph)

True or False: Once the inactivation gates of voltaged gated Na+ channels close, it is ready to respond to another stimulus.

False - does not respond to voltage again after closing, takes time to reset

Voltage gated K+ channels open at ?

threshold

What does the opening of voltage gated K+ channels cause?

efflux of K+ from ICF causing repolarization and hyperpolarization

True or False: Voltage gated K+ channels have an activation and inactivation gate.

False - Only has one gate (Na+ has two gates)

Is voltage gated Na+ or K+ channels slower to open?

K+

Voltage gated K+ channels open fully when?

at overshoot (tip of graph)

What is absolute refractory period?

time during which another action potential cannot be initiated

When does the absolute refractory period occur?

between activation of the voltage gated Na+ channel and when it resets to resting state

What is relative refractory period?

time during which it is more difficult than normal to initiate an action potential

When does the relative refractory period occur?

during hyperpolarization (takes greater amound of Na+ to reach threshold)

What is frequency coding?

frequency or number of action potentials codes for strength of signal or strength of stimulus

Strength of stimulus --> strength of ___ potential --> number or frequency of ___ potentials --> amount of ___ exocytosed at axon terminal

graded; action; ACh

Smaller axon diameter cause what to occur?

resistance to flow

Larger axon diameter --> ___ transduction

faster

Myelination prevents what from occuring?

ion leakage

Why is ion leakage not good for cells?

[Na+] inside axon decreases --> diffusion rate decreases --> transduction rate decreases

Myelination is benefical because?

fewer gated channels involved, less Na+ required to be moved therefore more efficient

Fast pain is associated with myelinated or non-myelinated axon?

myelinated

Slow pain is associated with myelinated or non-myelinated axon?

non-myelinated

What is compound action potential?

the sum of action potentials travelling on parallel axons at the same time

True or False: It is possible to test a single axon.

False - nerve segment is a bundle of axons therefore not normally possible (except in squid giant axon)

What is exocytosis?

depolarization at axon terminal triggers voltage gated Ca2+ channels

Influx of Ca2+ triggers release of what?

synaptic vesicles from the cytoskeleton