Please enable JavaScript.
Coggle requires JavaScript to display documents.
Electrical communication - conduction of action potentials (10) - Coggle…
Electrical communication - conduction of action potentials (10)
Non-invasive monitoring of neurone function in humans
you cannot measure the action potential in a single neurone
you can record activity from populations of axons in peripheral nerves and determine sensory or motor neurone dysfunction
peripheral nerves are bundles of single neurone axons
Compound action potential
can be recorded from peripheral nerve
extracellular recording
a nerve contains many axons of different diameters and myelination, when stimulated they dont all conduct at the same speed, recorded signal is the combined electrical activity
multiple peaks - each peak represents a group of axons firing together, large, myelinated axons, fast conduction, early peak, small or unmyelinated axons, slower conduction, later peaks
not all or nothing, more stimulus, more axons firing, larger overall signal, amplitude represents number of axons activated, not size of single action potential
conduction velocity increases with increase in axon diameter and increase in axon myelination
bigger length constant = higher conduction velocity
depolarisation declines with distance from stimulus due to spreading of local ion flow in axon
Axon classes
A-alpha - motorneurone muscle spindle afferent
A-beta - touch, pressure
A-gamma - motor to muscle spindle
A-delta - pain, touch
B - preganglion autonomic
C - pain, temperature
Determinants of conduction velocity
Fibre diameter
small diameter, high resistance of cytoplasm, harder for ions to flow along axon, depolarisation decays more rapidly, slow conduction
large diameter, low resistance of cytoplasm, easier for ions to flow along axon, depolarisation maintained for longer, fast conduction
Membrane resistance
low resistance of membrane, easier ions to flow out of axon, depolarisation decays more rapidly, slow conduction
high resistance of membrane, easier for ions to flow along axon, depolarisation maintained for longer, fast conduction
myelin sheath increases the effective membrane resistance, increases length constant
myelination results in saltatory conduction, action potential appears to jump from node to node and action potential regenerated at each node of Ranvier
demyelination results in slowed nerve conduction, leak of current slows conduction, can be detected using knee jerk reflex or measurement of compound action potential and conduction velocity