Lecture 4 Flashcards
sensory stimulus
activation of cutaneous receptors associate with intense deformations
neural code
action potential
post synaptic potential
frequency and discharge pattern
interpretation/action
flexor withdrawal reflex
action potentials
transfers information over long distances
synonyms
spike, nervous impulse, nervous influx, discharge
phases of action potentials
- rising phase (depolarisation)
- overshoot
- falling phase (repolarisation)
- hyperpolarisation (absolute refractory period, relative refractory period)
generation of action potential
-caused by a depolarization of the membrane beyond of a threshold
-electrical, chemical or mechanical stimulation
-«all or nothing»
-chain reaction (feedforward loop, opening of channels permeable to Na+)
stimulation too weak
does not reach action potential threshold
just above the threshold
a few action potentials
stronger stimulation
increase of the frequency of discharge
experiment of Hodgkin + Huxley
-studied the giant axon of the squid (inserted a metal filament the length of the axon)
-determined the importance of the permeabilities of Na+ and K+
-made a mathematical model
simple model of an action potential
-rest: a few K+ channels open
-depolarisation crossing the threshold: rapid opening of Na+ channels
-repolarization: rapid closing of Na+ channels and slow opening of K+ channels
-return to rest: some K+ channels open
cellular electrophysiology
-techniques to observe the electrical activity of a neuron
current-clamp
-useful to observe the behaviour of a neuron by Vm
-measure Vm by injecting currents through an electrode
voltage-clamp
-useful to observe the properties of ion channel by monitoring their conductances
-to measure Im at a desired Vm, we use an electronic circuit that can fix (or “clamp”) Vm at a value (Vclamp), and then measure the current that the circuit must inject to maintain Vm at Vclamp
patch-clamping
-pipette apposed to the membrane
-extract a portion of the membrane
-impose a voltage
-allows you to record from a single ion channel at a time
sodium channels
-four domains similar to the four sub-units of K+ channels
-selective pore for Na+ ions
-S4 segment charged + (sensitive to Vm)
tetrodotoxin (TTX)
blocks the pore of channels to Na+
saxitoxin (dinoflagellate)
toxin that targets Na+ channel
lidocaine
anesthetic
batrachotoxin (frog)
blocks inactivation –> channel stays open
veratridine (lilies)
lowers the activation threshold
aconitine (buttercups)
lowers activation threshold
K+ vs Na+ dependence to voltage
-the 2: open in response to depolarisation
-K+channels open mroe slowly than Na+ channels
-only Na+ channels inactivate
K+ vs Na+ delayed rectifier
-K+ conductance serves to rectify or reset Vm
-necessary to free Na+ channels from their inactivations
how many subunits do K+ channels have
4
how many domains do Na+ channels have
4
orthodromic
action potential travels towards the nerve terminals
antidromic
frim nerve terminals towards the dendrites
what is the duration of an action potential
2 minutes
what is the typical conduction velocity
10 m/s
nodes of ranvier
-uninsulated
-high density of Na+ channels
-allows passage of ions
initiation zone of action potentials
-in sensory neurons (nerve terminals –> dendritic extremities)
-other neurons (axon hillock)
