NS 2 - Action potentials Flashcards
name two types of chemical signalling in the body
short distance - synapse
Long distance - hormones
Name two types of electrical signalling in the body
graded potentials - short distance
action potentials - long distance
how fast are action potentials?
120m/s
name 2 excellent conductors
copper and plastic
what makes the conductors good?
signal does not decay
explain why nerves are a poor conductor
membrane is a poor conductor in an aqueous environment so the signal decays over 2-3 mm but nerves can be longer than 1m , need a propagating signal - action potential
what is the resting membrane potential?
separation of opposite charges across a membrane
what three factors set the resting membrane potential?
Permeability to key ions
conc. gradients for key ions
gradients maintained by active transporters
how can excitable cells change the membrane potential?
cells such as nerve and muscle can produce rapid changes in membrane potential
what is the normal extracellular and intracellular concentration for sodium (mMol)
extracellular - 150 mMol
intracellular - 15 mMol
what is the normal extracellular and intracellular concentration for potassium?
extracellular - 5 mMol
intracellular - 150 mMol
features of Sodium-potassium pump
- uses ATP
- Transport Na out of cell and K in
- helps maintains concentration gradients
The membrane is more permeable to what ion?
K+
in a chemical gradient, which direction does K+ flow?
out of cell
in an electrical gradient, which direction does K+ flow?
into cell as protein anions cannot flow out so K is attracted in
what value does K+ have for the equilibrium potential
-90mv
the membrane is much less permeable to Na+
true
equilibrium potential for Na+ is
+60mv
the ion with the greater membrane permeability will drive the membrane potential, so what will the RMP be closest to?
K+ equilibrium potential
describe briefly the stages of an action potential
- membrane is permeable to potassium
- depolarisation to threshold
- voltage gated Na channels open
- rapid depolarization overshoot
- Na flows into axon
- Action potential
- repolarisation
define absolute refractory period
an action potential cannot occur
Na channels not in their resting configuration
define relative refractory period
an action potential can occur but it requires a larger stimulus
(K+ gates are open)
name the factors affecting nerve conduction velocity
- width of axon
- myelination
