Chapter 4: The Action Potential Flashcards
the info that the brain deals with
neural code
the neural code can be obtained from the () of the action potentials fired in the nervous system
frequency and pattern
other names for the action potential (3)
- spike
- nerve impulse
- discharge
used to study APs
oscilloscope
properties of the action potential
- rising phase
- overshoot
- falling phase
- undershoot
2 ways to measure membrane potential
- intracellular recording (more sensitive)
- extracellular recording (collective action of 100s of neurons together)
the generation of an AP is caused by (1) of the membrane beyond (2)
- depolarization
- threshold
AP is generated if and only if membrane potential goes beyond threshold = () response
all-or-none
when generating multiple action potentials, the firing frequency reflects the () of the depolarizing current
magnitude
max AP firing frequency
1000 Hz (1000 impulses per second)
() delas the next firing of AP
absolute and relative refractory periods
in theory, depolarization of membrane potential is due to ()
influx of Na+
in theory, repolarization of membrane potential is due to ()
efflux of K+
current across membrane is largely due to movement of (1) across membrane (aka 2)
- K+ ions
- Ik
the K+ channel number is proportional to ()
electrical conductance
ideally, resting membrane potential is due to ()
equilibrium of K+
Hodgkin and Huxley’s experiment found that there was a transient increase in () during the rising phase
Na+ conductance -> influx of Na+
similarly, Hodgkin and Huxley’s experiment found that there was a transient increase in () during the falling phase
K+ conductance -> efflux of K+ ions
Na+ gates in the axonal membrane are activated by (1) and deactivated when the membrane acquires a (2)
- depolarization beyond threshold
- positive membrane potential
structure of the voltage-gated Na+ channel
transmembrane domains and an ion-selective (to Na+) pore
the voltage-gated Na+ channel has (1) distinct domains, each consisting of () transmembrane alpha helices
- 4
- 6
voltage sensor in voltage-gated Na+ channels
S4
how does depolarization affect the S4 domain of voltage-gated Na+ channels
depolarization causes S4 to twist and results in S4 moving upwards and outwards to open the channel
() method allows one to record ionic currents through single channels
patch-clamp
the absolute refractory period is due to the () of the channel
inactivation
genetic diseases that cause mutations in the voltage-gated Na+ channels
channelopathies
toxin that clogs Na+ permeable pore and blocks all Na+ dependent APs
tetrodotoxin (TTX)
Na+ channel-blocking toxin
(red tide) saxitoxin
toxin that blocks inactivation so channels remain open
batrachotoxin (frog)
toxins with similar effects as batrachotoxin
veratridine (lilies), and aconitine (buttercups)
because (some) K+ channels open later than Na+ channels, the K+ channels serve as ()
delayed rectifiers -> rectify or reset membrane potential
the threshold of the membrane is mainly determined by open ()
Na+ channels
undershoot is described as (1) due to (2)
- hyperpolarization
- high K+ conductance
greater stimuli (depolarization) is required to initiate another AP during the relative refractory period due to ()
open K+ channels (rectifiers) -> K+ efflux
spike initiation zones in neurons
- sensory nerve endings
- axon hillock
what characterizes spike initiation zones
higher expression (number) of voltage-gated Na+ channels
2 types of AP propagation
- orthodromic
- antidromic
action potential travels in one direction (towards axon terminal) due to inactivation of sodium channels
orthodromic
experimental AP propagation wherein AP propagates backwards
antidromic
factors influencing conduction velocity
- axon structure
- path of positive charge
- axonal excitability
synthetic anesthetic that prevents APs by binding to voltage-gated Na+ channels; affect smaller axons before larger axons
lidocaine
lidocaine binds to the () alpha helix to inhibit APs
S6
insulate axons to facilitate current flow
myelin
keep axons myelinated in peripheral NS
Schwann cells
keep axons myelinated in central NS
oligodendroglia
propagation of APs along myelinated axons
saltatory conduction
like spike initiation zones, nodes of Ranvier have () to facilitate AP generation
increased number of ion channels
types of AP firing patterns
- fast spiking
- burst spiking
- regular spiking
