Membranes, Ions and Action potentials Flashcards
is intracellular K+ or extra. conc higher?
intracellular= higher
is intracellular A- or extra. conc higher?
intracellular= higher
what is A-?
fixed negative charges on macromolecules
is intracellular Cl- or extra. conc higher?
extracellular= higher
is intracellular Na+ extra. conc higher?
extracellular= higher
is intracellular pH or extracellular higher?
extracellular = higher (7.4 compared with 7.0)
what is resting memb potential?
between -20 to -95mV depending on cell type
what causes ion gradients ro exist?
ie explain primary active transport
K+ accumulates where the impermeable anion A- locates. A- are fixed -ve charges on macromolecules
O there is a high conc of A- in inside the cell
O intracellular K+ conc is high
Na+ leaks into cell slowly and is pumped out against conc grad by Na pump
(req ATP)
how is the low Na+ conc inside the cell used for glucose transport.
what is the transporter?
Na+ can diffuse into the cell through GLUT transporter WITH GLUCOSE
Na+ pumped out with ATP
the GLUT transporter is a SECONDARY ACTIVE TRANSPORTER
what happens if extracellular K+ conc increases?
makes the membrane potential less negative than the resting membrane potential
- the membrane will be DEPOLARISED
what is an action potential?
a transient depolarisation of the cell
what are cells that generate aps called?
excitable cells
where to aps transfer information to and from?
- from SENSORY CELL to CNS
eg brain to muscle
what can aps initiate?
cellular events, eg muscular contraction
what is all or nothing law?
once an ap has been initiated, varying the stimulus strength doesn’t change the configuration of the ap.
what causes depolarisation?
transient inc of membrane Na+ permeability O Na+ rapidly diffuses in
what causes repolarisation?
greater than normal inc of K+ permeability
O K+ leaves
how do voltage gated channels work?
activated by change to membrane potential (eg electrical stimulus)
how do ligand gated channels work?
what happens when a ligand binds to ligand gated channels?
extracellular chemical binds to receptor on membrane. The receptor is an ion channel
- when a lignd binds, the ion channel opens
give an example of a voltage gated ion channel
eg Na+ channel
what are the general functions of voltage gated channels?
support aps, eg in nerves and muscle
where are ligand gated ion channels found?
muscle and nerve cells
secretory cells
what are the two types of ligand gated channels?
what do each type cause to the cell?
1) cation selective (eg Na+ flows in)
causes DEPOLARISATION- cell becomes MORE EXCITABLE
2) anion selective (eg Cl- flows in)
causes HYPERPOLARISATION-cell becomes LESS EXCITABLE
what is threshold potential?
-60mV
what is resting memb potential?
-80mV
give and explain the 4 ways an ap can be initiated?
1) artificial application of electrical current
2) synapses- NT bind to ligand gated channels on target cell
3) spontaneously in “pacemaker” cells eg in heart
4) sensory cells- convert a stimulus to change of memb pot of the associated nerve.
if stimulus= large enough then THRESHOLD IS REACHED
what are local circuits?
- a local current PRECEDES the ap in cytoplasm of axon
- the ap is +vely charged, but regions around it are -vely charged (still under resting pot)
- Na+ ions at the point of ap are attracted to the -VE CHARGE
- O local circuit is set up and O Na+ channels in the local circuit open
- O ap continues and moves along axon
what factors affect ap conduction velocity?
1) cell diameter (velocity inc as diameter inc)
2) temp (inc temp inc velocity)
3) myelination (myelin allows for saltatory conduction (jump from nodes of Ranvier))
