Wk 7 Flashcards
Excitable Membranes
What is membrane potential?
Site of communication between cells (all eukaryotic cells).
What are the two types of cells?
Non-excitable cells - power cell processes.
Excitable cells - nerve and muscle cells signal via changes in membrane potential.
- signals sent long distances fast
What are ionic concentrations in extracellular fluid?
K+ = 4mM
Na+ = 145mM (higher outside)
Cl- = 115mM (higher outside)
Protein = 0.2mM
What are ionic concentrations in intracellular fluid?
K+ = 140mM (higher inside)
Na+ = 15mM
Cl- = 4mM
Protein = 4mM
What direction to ions move?
From high to low concentration.
How do large proteins exit the cell?
Na+/K+ pump
What are the types of membrane ion channels?
- passive
- chemically-gated
- voltage-gated
- mechanically-gated
What are passive channels?
- leakage/non gated
- always open
- greater outflow of K+ produces -ve resting membrane potential (-70)
What are chemically gated channels?
- ligand-gated
- opened by binding of specific neurotransmitter
What are voltage gated channels?
- open/close in response to changes in membrane potential (depolarisation)
What are mechanically gated channels?
- open/close in response to physical deformation of receptors
- response to pressure e.g. ears
What is the role of the Na+/K+ pump?
- pumps 3 Na+ out and 2 K+ in
- ATP as energy
- confirmational change
- establishes and maintains Na/K concentration gradients
What is resting membrane potential?
All cells are negatively charged compared to extracellular fluid (difference in Na+ and K+ conc.).
- Outside = 0mV
- Inside neuron = -70mV
- Maintained by Na/K pump but not main driver
What is the Nernst equation?
Calculates the equilibrium potential based on valence and intracellular/extracellular concentrations.
What are the Nernst Equation conc. of ions at equilibrium for K, Na, Cl?
Veq K = -90mV
Veq Na = +60mV
Veq Cl = -70mV
Which ions are impermeable through the cell membrane at rest?
K+ (more permeable - passive), Na+
What is equilibrium potential?
Electrical force is equal to opposite chemical driving force.
What effects the ion flow and thus the membrane potential?
- conc. of ions across membrane change
- membrane permeability to ion changes
What is the rule for membrane potential (MP)?
An ion will move in the direction that brings the MP closer to the equilibrium potential for that ion.
What are the two types of signals produced from a change in membrane potential?
- Graded potentials
- Action potentials
What are graded potentials?
- incoming signals over short distances (short lived)
- ‘start things off’
- triggered by stimulus that opens gated ion channels
- either depolarisation (-ve –> +ve) or hyperpolarisation (+ve –> -ve)
What are action potentials?
- long distance signals of axons
- ‘movement’
- Na+ flows in, K+ flows out (open/close of voltage gated channel)
- propagating transient change in membrane potential (temporary change spreading down the cell from -70mV to +30mV)
What do the action potential changes lead to?
- depolarisation (-ve –> +ve)
- repolarisation (+ve –> -ve)
- hyperpolarisation (-ve –> -ve)
What does ‘all or nothing’ refer to with action potentials?
Must reach a certain threshold potential to open voltage gated channels, once reached (-50mV) Na+ channel must open.
