Membrane Potential W2 Flashcards
Why are membrane dynamic (3)
Growth
Movement
Proteins have a finite lifetime
Why are membranes excitable (4)
Communication
Movement
Contraction
Respond to stimulus
What causes membrane potential
Regulation of ion movement which causes a difference in charge
The ….. of membrane in positive
Outside
The …. of the membrane is negative
Inside
What is the resting membrane potential
Charge difference across a cell at rest (unstimulated)
Muscle resting membrane potential …. mV
-85
Nerve testing membrane potential ….mV
70
Membrane is said to be …… at rest
Polarised
Inside cell: Lots of.... Not much.... Compared to outside AT REST
K+
Na+
To cross lipid rich membrane
Ions need
Transport proteins
Proteins responsible for maintaining membrane potential (2)
Ion channels
Membrane bound enzymes
Example of ion channel
Sodium channels
What do sodium channels do
Allow sodium ions to flow down concentration gradients
Example of membrane bound enzymes
Sodium - potassium ATPase
What does Sodium - potassium ATPase pump do
Uses atp to pump ions through membrane against concentration gradient
….. …… form the basis of cell communication
Ion channels
Two types of ion channels
Non gated
Gated
When do gated ion channels open
Randomly
When do ligand gated ion channels open
Open in response to chemical stimuli
When to voltage gated ion channels open
In response to chemical stimuli
Two types of gated ion channels
Ligand gated
Voltage gated
Ion channel structure
5 integral proteins joined together
Which region of ion channels line inside of the protein
Hydrophilic
Which region of ion channels line outside of the protein
Hydrophobic
Ion Channels- what determines which ions may pass
The charge of the hydrophilic region of proteins that join together to make ion channel
How to ligand gated ion channels open - what do they have and process
Exposed receptor site for binding specific ligand molecules
Molecule binds - changing shape of protein and allowing ions to flow through
Example of ligand gated ion channel opening
Muscle contraction -Acetylcholine bonds to Ligan gated sodium channel on surface of muscle fibre
Sodium flows into cell causing depolarisation
Example of voltage gated ion channels opening closing process (Na+/K+)
Na+ flows into nerve cell causing depolarisation
Voltage gated K+channels open causing repolarisation
K+/Na+ ATPase - how many molecules of ….. does it pump out of the cell
3 Na+ molecules
K+/Na+ ATPase - how many molecules of ….. does it pump into the cell
2K+
What two factors maintain the resting membrane potential
Leakage ion channels
K+/Na+ ATPase pump
Passive ion diffusion is up/down the chemical gradient
Down
When ions move to a region of opposite charge they move ….. their electrical gradient
Along
How does membrane potential change
Via ……… or ……… - ……. ion channels
Voltage or ligand gated
Phases of ACTION potential
Initial stimulus - ligand gated ion channels open
Voltage - gated Na+ channels open
Voltage gated K+channels open
1*Phases of ACTION potential -initial stimulus
Describe
Result
Ligand gated channels open allowing Na+ to flow into the cell down its concentration gradient
Depolarises local area of cell to threshold (about -50mV)
2Phases of ACTION potential: Voltage - gated Na+ channels open
Describe
Result
Very brief Na+ rushes in down concentration gradient
Initiates propagated action potential
3Phases of ACTION potential: Voltage - gated K+ channels open
Describe
Result
K+ rushes out of cell (slower rate than that of Na+rushing in before)
Voltage gated Na+ channels begin to close
Repolarisation
Describe the process of action potential
Rest–>depolarisation–>repolarisation–>rest
RESTING MEMBRANE POT atlases pump maintaining rest Most ion movement via leakage channels DEPOLARISATION stimuli(eg the opening of ligand gated Na+ ion channel) opens a voltage gated Na+ channel, depolarising the membrane potential REPOLARISATION voltage gated Na+ channels inactivated Voltage gated K+ channels activated RESTORING MEMBRANE POTENTIAL Na+/K+ ATPase works to restore Reston membrane potential (more Na+ outside that's inside and more K+ inside rather than outside)
Action potentials and skeletal muscle contraction process
Describe
An action potential arrives at neuromuscular junction
Causing aCh to be released
aCh binds to ligand gated sodium ion channels which initiates action potential in that cell
This travels along t tubules
And prompts the release of calcium ions
Calcium ions bind to troponin –> moving tropomyosin away
Action potential and nerve conduction
Describe
In response to signal soma end of axon becomes depolarised
Depolarisation spreads down the axon, meanwhile whilst the soma depolarises
Action potential continues to travel down the axon
What determines how quickly action potentials can be repeated
Refractory period
Two types of refractory periods
Absolute
Relative
What does absolute refractory period mean
Why is this so
Additional depolarising stimuli do not relish in new action potential
Because Na+ channels are inactivated during this time
What does relative refractory period mean
Why is this so
Only strong enough stimuli will result in action potential
Because Na+ channels begin to recover but K+ channels have not closed yet
So and efflux of Na+ ions will be balanced out but he efflux of K+ions unless it’s big enough
