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