3. Membrane and Action Potentials

What is the normal membrane potential of a cell?

-70 mV

What is the equilibrium potential for Potassium ion?

-90 mV

What is the equilibrium potential for Sodium ion?

60 mV

What are the types of Graded potentials?

EPSP and IPSP

What type of signal is generated in a chlorine graded potential?

Hyperpolarizing

What ion is high in the intracellular environment?

Potassium

What ion has the greatest membrane permeability in the body?

Potassium ions

What is the resting membrane potential due to mainly?

Potassium ions

What ion is high in the extracellular environment?

Sodium

What is an action potential?

a transient, regenerative electrical impulse in which the membrane potential rapidly rises to a peak

What initiates the signal of an action potential?

above threshold graded potential at the trigger zone opens ion channels

What happens if a strong enough graded potential reaches the trigger zone?

action potential occurs

What is saltatory conduction?

action potentials jumping from node to node

What is the strength of signal of a graded potential measured by?

addition of the strengths

What is the strength of the action potential signaled by?

all-or-one, can't be added

Why doesn't an action potential diminish as it moves down the axon?

because of the continuous entry of sodium as more sodium channels open

What is the refractory period?

can't activate a second action potential

Where do action potentials occur?

cells that are electrically excitable

What does an action potential result from?

changes in membrane permeability

What determines the voltage difference?

concentration gradient

What factors influence membrane potential?

concentration gradients across membranes and, membrane permeability

What happens to graded potentials as they spread out from the point of origin?

decrease in strength

What does the presence of myeline do?

decreases the capacitance

What leads to the symptoms of MS?

demylination of nerves

Where do graded potentials occur?

dendrites and cell body

What type of signal is generated by an action potential?

depolarizing

What type of signal is generated in a sodium graded potential?

depolarizing

What is the movement of cations inward to make the interior more positive called?

depolization

What is overshoot?

development of a charge reversal

What is hyperpolarization?

development of even more negative charge inside the cell

What initiates the signal of a graded potential?

entry of ions through gated channels

What does a shorter time constant cause?

faster conduction velocity

What is required to cause an action potential?

graded potential reaches a certain threshold

What are the two types of voltage changes across a membrane?

graded potentials and action potentials

How do action potentials change between tissues?

have different excitability

What is polarized?

having positive and negative portions

What is the movement of cations outward to make the interior more negative called?

hyperpolarization

What happens as you increase the size of the nerve?

increase the conduction velocity

What determines the shape and duration of the action potential?

ion channel composition and tissue type

Why do graded potentials decrease in strength as the spread out from the origin?

leaky channels and cytoplasmic resistance

What is the purpose of myelin sheaths?

limits amount of membrane contact with extracellular fluid

What types of gated ion channels are involved in graded potentials?

mechanically, chemically or voltage-gated channels

What do voltage-gated channels open and close due to?

membrane potential

What is the equilibrium potential?

membrane potential at which an ion's chemical and electrical gradients are equal in magnitude but opposite in direction

What is repolarization?

movement back toward resting potential

What surrounds axons?

myelin

What type of axon has the smaller time constant and therefore the fast action potential?

myelinated axon

What is released and diffuses across the synaptic cleft?

neurotransmitters

What leads to hyperpolarization?

potassium channels stay open longer than the sodium channel

What leads to the difference in the Potassium membrane permeability and the resting membrane potential?

potassium moving into the cell through an ATPase

What is diffusion potential?

potential difference generated across a membrane when a charged solute diffuses down its concentration gradient

Where do graded potentials travel to?

presynaptic axon terminal

What is the function of the cell membrane?

prevents free movement of ions between intracellular and extracellular environment

What is the function of myelin sheaths?

prevents ion flow out of the cytoplasm

What are voltage-gated ion channels?

require a voltage change in order to open them

What are ligand gated channels?

require binding of ligand to the channel in order to open them

What ions are involved in action potentials?

sodium and potassium

What ions are involved in graded potential?

sodium, chlorine, and calcium

What helps to equilibrate the voltage difference?

specific ion channels

What is conduction velocity?

speed at which action potentials are conducted along a nerve or muscle fiber

What blocks the inward movement of sodium?

tetradotoxin and lidocain

What blocks the outward movement of potassium?

tetraethylammonium

Which portion of the cell is more negative?

the interior portion

What does the Nernst Equation tell us?

the membrane potential that would result if the membrane were permeable to only one ion

What ions equilibrium potential will the resting membrane potential be closest to?

the one with greatest permeability

What does the conduction velocity determine?

the speed at which information can be transmitted in the nervous system

What are the cable properties?

time and length constant

What happens to the time constant and length constant of a normal person?

time constant decreases and the length constant increases

What happens to the time constant and length constant of a person with MS?

time constant increases and the length constant decreases

What are the types of ion channels?

voltage and ligand gated

What is membrane potential?

voltage difference that exists across a plasma membrane

What types of gated ion channels are involved in action potentials?

voltage-gated channels

When does a voltage difference occur?

when an ion is membrane permeable

When does depolarization occur?

when ion movement reduces the charge imbalance