BMS1052 Lecture Notes - Lecture 3: Resting Potential, Nernst Equation, Goldman Equation
5 May 2018
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Lecture 3
Learning objectives
Identify the factors that lead to movement of ions across a membrane
Describe the factors affecting an ionic equilibrium potential
Desrie the fators affetig a ell’s restig erae potetial
Apply the Nernst equation and Goldman equation
Describe the function of the Na/K-ATPase (Na-K pump)
Describe how selectivity and gating occur in Na+ and K+ channels
Identify the factors that lead to movement of ions across a membrane
Common properties
• Insulation is important!! Poor insulation between
intra- and extracellular space
• Fatter wires/axons conduct faster
• Warmer wires/axons conduct faster
Neurons need to communicate rapidly and reliably Reaction time – well under a second.
Visual processing – information comes in the eye; processed by the visual cortex; passed to
the motor cortex; sent down spinal cord to muscles in leg and foot.
Need to send signals long distances, rapidly, reliably.
Changes in the membrane potential are what propogate down the axon.
red loop is a seletivity filter will ot allow K to go through
Each amino acid comprises H, amino group (NH3+), carboxyl (COO-) and a residue (R).
Amino acids can be linked by peptide bonds between a carbon and nitrogen atom.
The chain coils into an alpha helix, which then forms a globular shape.
Multiple polypetide chains can be associated together, each forming a subunit of a
functional unit.
The subunits have hydrophobic and hydrophilic regions, allowing them to sit stably within
the membrane.
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Membrane-bound ion channels act like gatekeepers
There are many types of channel, e.g.
- Chloride channels
- Potassium channels
- Non-selective cation channels
Some channels can be gated – they are either open or closed depending on:
- The membrane potential
- The binding of a ligand to the channel
Channels are selective because of their physical and chemical (amino acid residues)
structure.
Water crosses the membrane through specialised channels – aquaporins this is because
water diffusion through membrane is a slow process
How do intracellular and extracellular ionic concentrations affect ion movement across a
membrane
Ions cannot move freely across the membrane:
1 ios diffuse dow their oetratio gradiet
(2) ions move towards opposite charges
Ion movement across a membrane depends on
• the concentration gradient across the membrane
• the electrical field across the membrane
At equilibrium, there is no net ion flow (ions movement still occurs due to Brownian
motion)
The equilibrium potential that results from an imbalance in concentration of a single ion
(the Nernst equation)
What happens if K+ channels are opened?
What ions move?
Does the inside of the cell end up at a positive or negative potential?
Answer: K+ ions flow down their concentration gradient (i.e. from inside to outside).
This sets up a net electrical field – the A- anions are left behind, so the inside of the cell
becomes negative, outside becomes positive.
Ionic equilibrium potentials - the Nernst equation
If the membrane is permeable to a single ion, the Nernst equation predicts the membrane
potential at equilibrium
[ ]
[ ]
[ ]
[ ]
in
out
in
out
ion
ion
ion
z
ion
ion
zF
RT
E
10
10
log
5.61
log303.2
=
=
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Identify the factors that lead to movement of ions across a membrane. Describe the factors affecting an ionic equilibrium potential. Des(cid:272)ri(cid:271)e the fa(cid:272)tors affe(cid:272)ti(cid:374)g a (cid:272)ell"s resti(cid:374)g (cid:373)e(cid:373)(cid:271)ra(cid:374)e pote(cid:374)tial. Apply the nernst equation and goldman equation. Describe the function of the na/k-atpase (na-k pump) Describe how selectivity and gating occur in na+ and k+ channels. Poor insulation between intra- and extracellular space: fatter wires/axons conduct faster, warmer wires/axons conduct faster. Neurons need to communicate rapidly and reliably reaction time well under a second. Visual processing information comes in the eye; processed by the visual cortex; passed to the motor cortex; sent down spinal cord to muscles in leg and foot. Need to send signals long distances, rapidly, reliably. Changes in the membrane potential are what propogate down the axon. red loop is a sele(cid:272)tivity filter will (cid:374)ot allow k to go through. Each amino acid comprises h, amino group (nh3+), carboxyl (coo-) and a residue (r).
