lecture 8 conduction Flashcards
what does an oscilloscope do
shows voltage vs time
what is conductance
ability of ions to flow through channels
what is conduction
movement of action potential from one part to another (axon hillock to presynaptic terminal)
what is capacitance
the ability of a system to store an electric charge.
difference between distance and time flipped action potential graph
distance is flipped graph (where undershoot is drawn first because that’s the way the direction of propagation of action potential is)
how long does an action potential take
2 ms
how is an action potential conducted
na enters through VGna and causes charge reversal through depolarization
positive charge displaces negative charge both locally at the site of charge entry and in both directions along the axon cylinder
within a few ms the na channels activate at the site of na entry and that region of axon membrane becomes refractory to further depolarization
cable properties of an axon
an axon is like a leaky hose
water pressure is like the voltage
bulgability is like the capacitance
hose leaks like leak ion conductance in axon
what is axial resistance inversely related to
caliber (diameter) so bigger axon means bigger flow of charge
what is membrane resistance inversely related to
the number of open leak channels
what is membrane capacitance inversely related to
distance between intra and extracellular sites that store charge
what does the flow of na in during the rising phase do
causes a nearly instantaneous change in membrane
voltage is largest at site of na entry and gradually weakens over distance due to
axial resistance (thinner axon more resistance), passive leak channels, membrane capacitance
when would smaller axons be needed even if they have a larger axial resistance and slower conduction
optic nerve
how can axonal membrane resistance and capacitance be altered by
myelin
what is myelin made by
oligodendrocytes in cns and schwann cells in
what does myelin do
creates low membrane capacitance and creates high membrane resistance
essentially plugs leaks and makes conduction faster
what are nodes of ranvier
myelin is broken up into nodes of ranvier where sodium can flow in again to ensure action potential can reach full amplitude
what is saltatory conduction
action potential recharges at nodes (goes fast slow fast)
na chemicals concentrates by nodes, k channels along internodes
what is a demyelinating disease
multiple schlerosis (ms) nerve impulses slow or slop, sodium cant come in
how does na enter membrane
This spread of charge occurs in the backward direction (toward the
soma) where Na+ channels have already opened and inactivated (the membrane is refractory),
and the forward direction where Na+ channels are simply closed (not inactivated). Within a few
milliseconds (ms), the Na+ channels inactivate at the site of Na+ entry and that region of the
axon membrane becomes refractory to further depolarization (temporarily). But in the forward
direction the positive charges change the membrane potential causing an increase in gNa+
(additional channels opening) to allow local Na+ entry and action potential propagation
Attenuation
reduction in current magnitude due to distance and/or time
Membrane resistance (Rm) -
the opposition of ionic flow across the membrane. The more
channels in the membrane, the lower the membrane resistance. The lower the membrane
resistance, the more the signal will attenuate over distance
Axial resistance (Ra)
the opposition of ionic flow down the axon or neurite. The greater
the diameter of the neurite, the lower the axial resistance. The greater the axial resistance,
the more the signal will attenuate over distance
Membrane capacitance (Cm)
property of the membrane that allows for the storage of
charge. Determines how quickly a neuron’s membrane potential can respond to changes in
current. The membrane capacitance is proportional to the surface area. The greater the
capacitance, the more the signal will attenuate over distance.
How does an action potential alter the membrane potential along an axon (voltage vs
distance)?
Explain the ways in which an axon’s passive properties: membrane resistance, membrane
capacitance, and internal resistance alter the voltage change with distance from the site
where an action potential is peaking.
How and why does axon caliber affect conduction velocity?
Describe multiple sclerosis, including biologic and physiologic symptoms
Examples of typical MS relapses include blurring of vision in one eye (optic neuritis), persistent numbness or tingling of a body part (sensory system relapse), weakness of a body part (motor system relapse), or loss of coordination (cerebellar system relapse).
