Lectures 1.4-1.5 Flashcards
How does ion diffusion across a semi-permeable cell membrane lead to a membrane potential?
ion channels facilitate diffusion of ions across the lipid bilayer. A diffusion potential arises when diffusion of ions leads to an unequal number of charges on the inside versus the outside of the cell.
equilibrium potential
the membrane potential where the net flow through any open channels is 0
Goldman-Hodgkin-Katz equation
describes the membrane potential for biological membranes
properties of action potentials
rapid, transient, self-propagating electrical excitation in the plasma membrane of an excitable cell.
- All-or-none
what ion currents contribute to depolariation and repolarization phases of an action potential ?
Na+ flows through voltage-gated channels causing an inward positive current (depolarization) and K+ flows through voltage-gated channels causing an outward positive current (repolarization)
what is the function of voltage gated ion channels during an action potential?
an inward current depolarizes membrane potential to threshold. this depolarization triggers voltage-gated Na+ channels to open, as Na+ floods into the cell, it is further depolarized and causes more voltage-sensitive Na+ channels to open.
how do axon diameter and myelination affect action potential conduction velocity?
- increased axon diameter increases conduction velocity by decreasing internal resistance
- myelination increases conduction velocity
how do refractory periods contribute to action potential conductance?
they limit the rate of action potential firing and help to ensure unidirectional propagation
how do refractory periods arise?
inactivation gates of the Na+ channels are closed and no action potential can occur until the channel is in the resting closed conformation with the inactivation gates open
local potential
small change in the resting membrane potential of a neuron at one point in the cell
depolarization
an instance where the membrane potential becomes more positive than the resting potential
diffusion potential
the potential difference generated across a membrane because of a concentration difference of an ion. It can be generated only if the membranes is permeable to the ion. The size of the diffusion potential depends on the size of the concentration gradient
membrane repolarization
the period where the membrane potential returns back to resting potential
threshold potential
- the membrane potential at which the action potential is inevitable.
- when a local potential leads to depolarization above the threshold potential, an action potential arises
axon hilock
the section of axon adjacent to the cell body that has a high density of voltage-gated Na+ channels
voltage-gated K+ channels
depolarization causes K+ channels to open slowly and increases K+ conductance
- repolarization is caused by outward K+ current
internode
flattened plasma membrane that is wrapped around the axon to form a segment of biochemically specialized sheath
nodes of ranier
regions of axon between internodes of myelin (location of most membrane channels)
saltatory conduction
when the action potential jumps from node to node
- action potentials travel faster as it is not passing through the entire axon
- metabolic energy is conserved
Multiple Sclerosis
demyelinating disease that affects the central nervous system