Electrophysiology Flashcards
What causes currents and the flow of charge in cells?
- ions
- cation = (+) charge
- anion = (-) charge
Test utilized to measure ion levels:
- complete metabolic panel (CMP)
Cell and tissue function is controlled by:
- ionic flux
Nomenclature of current in a cell:
- I(ion abbreviation)
- e.g. INa+
Ionic gradients confer distribution of charge across plasma membranes. This distribution of charge allows for:
- electrogenecity
- the ability to generate electrical current
Electrogenic tissues can create:
- action potentials via the use of anions and cations in the tissue
Major electrogenic tissues in the body:
- heart
- skeletal muscle
- neurons
- GI smooth muscle
- vascular smooth muscle
Distribution of charge across the membrane of a motor neuron in the resting state:
- Inside cell (cytoplasm)
- little sodium
- little calcium
- a lot potassium
- Outside cell (interstitium):
- a lot sodium
- a lot calcium
- little potassium
SODIUM AND CALCIUM WANT TO MOVE INTO CELL.
POTASSIUM WANTS TO MOVE OUT OF CELL.
Electromotive force is:
- the desire/potential for something to move
What is the electromotive force present across the membranes of motor neurons?
- Interstitium is more positive than the cytoplasm.
- Interstitium contains more sodium and calcium.
- Sodium and calcium want to move down their gradient into the cell.
At rest, there is passive flux of K+ and Na+ through the plasma membrane of motor neurons. How is the electrochemical gradient across motor neuron membranes maintained at rest?
- Na+/K+ ATP-dependent pump.
- Moves 3 Na+ out of cell and 2 K+ into cell.
State of a motor neuron at rest:
- Hyperpolarized (-80mV).
- Na+/K+ ATP-dependent pump active.
- Voltage-gated K+ channel inactive.
- Voltage-gated Na+ channel inactive.
Potential stimuli that can cause an action potential:
- electrical
- chemical
- mechanical
Process of motor neuron depolarization:
- Stimuli causes activation of some voltage-gated Na+ channels
- Slight influx of Na+.
- Threshold value reached, majority of voltage-gated Na+ channels open.
- Na+ rushes in and depolarizes cell.
Motor neuron depolarization is _______ dependent.
- Sodium dependent.
- Positive charge rushes into cell.
Motor neuron repolarization is _______ dependent.
- Potassium dependent.
- Positive charge rushes out of cell.
The two fail-safe mechanisms of voltage-gated ion channels:
- voltage-dependent (only open at certain voltages)
- time dependent (close after some time open)
The three phases of a motor neuron action potential:
- Depolarization (Na+ rushes in)
- Repolarization (K+ rushes out)
- Refraction (inactive; recovery stage)
Timing and types of refractory phases:
- Follows repolarization.
- absolute and relative
Absolute refraction:
- Na+ channels inactive.
- No stimulus will elicit a second action potential regardless of stimulus strength.
Relative refraction:
- some Na+ channels resting.
- second AP can be elicited if a stronger than normal stimulus is applied.
Steps in motor neuron action potential:
- Refraction period ends.
- Stimulus activates some voltage-gated Na+ channels.
- Threshold reached.
- Voltage-gated Na+ channels open; sodium rushes in.
- Depolarization (more positive).
- Voltage-gated Na+ channels close.
- Voltage-gated K+ channels open; potassium rushes out.
- Repolarization (more negative).
- Hyperpolarization/Refraction.
The excitability of neuromuscular tissue is dependent on:
- difference between the resting potential and the threshold potential.
The resting potential of electrogenic cells is set by:
- ratio of intercellular K+ to extracellular K+
- an important component of this is the passive flux of K+ through the plasma membrane at rest.
Effect of increased extracellular K+ levels on action potentials?
- Passive flux of K+ impeded.
- More K+ (positive charge) retained intercellularly.
- Cells begin to depolarize due to increased intercellular positive charge.
- Action potentials fired at wrong times, cells become refractory, irregular electrical transmission occurs.
Altering a neurons resting membrane potential by varying the levels of potassium (too high or too low) in the body will result in:
- impeding the neuron’s ability to fire an AP
The two types of action potentials in the heart:
- Pacemaker potentials (SA node)
- Plateau potentials (myocardium)
Where do pacemaker potentials occur in the heart?
- SA node
Where do plateau potentials occur in the heart?
- myocardium (ventricles and atria)
The first step of a pacemaker potential is:
- slow depolarization
- dependent on:
- T-type calcium channels (slow influx)
- HCN+ sodium channels (slow influx)
- Outflux of potassium
- dependent on:
The slow depolarization of a pacemaker potential is dependent on:
- T-type calcium channels (slow influx)
- HCN+ sodium channels (slow influx)
- Outflux of potassium
Above are antagonistic, which leads to a slow depolarization.
Threshold.
Depolarization of pacemaker cells in the SA node (pacemaker potentials) is _____ dependent.
Calcium-dependent.
Repolarization of pacemaker cells in the SA node (pacemaker potentials) is _____ dependent.
Potassium-dependent.
Steps in pacemaker potential in SA node:
-
Slow depolarization.
- T-type Ca2+; HCN+ Na+; outflux K+
-
Rapid depolarization at -50mV.
- T-type Ca2+
-
Repolarization.
- voltage-gated K+; K+ outflux
The trigger of pacemaker potentials in the SA node is:
- spontaneous.
- no stimulus required.
The four phases of plateau potentials:
- Phase 0: depolarization
- Phase 1: transient repolarization
- Phase 2: transient repolarization
- Phase 3: transient repolarization
- Phase 4: refraction
What channels are responsible for the repolarization of myocardium cells following a plateau potential?
- Calcium channels.
- Three isoforms of potassium channels.
- Each isoform opens at a different voltage.
Depolarization of myocardium cells in the heart (plateau potentials) is _____ dependent.
sodium
Steps in plateau potential in myocardium cells:
-
Phase 0:
- voltage-gated sodium channels open
- depolarization
-
Phase 1:
- isoform (1) potassium channel opens
- transient repolarization
-
Phase 2:
- isoform (2) potassium channel opens
- voltage-gated calcium channels open
- transient repolarization
-
Phase 3:
- isoform (3) potassium channel opens
- transient repolarization
-
Phase 4:
- refraction
In general, what results in depolarization of an electrogenic cell?
inward positive charge
In general, what results in repolarization/hyperpolarization of an electrogenic cell?
outward positive charge
OR
inward negative charge
Arrhythmias are due to:
- disruptions in voltage-gated channels functions in the heart.
- affects depolarization and repolarization.
- can be treated with drugs that target specific ion channels in the heart in specific regions.
Pathway of pain transmission:
- Pain-evoking stimulus
- Nociceptors (pain receptors)
- AP in afferent pain nerves
- Relay of AP to dorsal horn
- Relay of AP to thalamus
Mechanism of lidocaine:
- lidocaine blocks voltage-gated sodium channels from the interior
- threshold cannot be achieved
- AP does not occur in response to pain
alpha toxins are:
ACh receptor antagonists
Beta bungarotoxins are:
Cholinesterase inhibitors
Botulinus toxins and tetanus block:
ACh release
Tetrodotoxin blocks:
neuronal and cardiac voltage-gated Na+ channels
Dendrotoxin blocks:
motor neuron voltage-gated K+ channels
Steps in release of synaptic vesicles from an axon terminal:
- AP reaches axon terminal
- Voltage-gated calcium channels open
- Calcium rushes in
- Synaptic vesicles are mobilized and released into the synaptic cleft where they release neurotransmitters
- Neurotransmitters bind to receptors on post-synaptic dendrite
Which is faster at a nerve terminal, ionotrophic or metabotrophic transmission?
ionotrophic
Ionotrophic transmission:
- Very fast.
- No ligand-receptor binding or intracellular signaling required to activate ion channels.
Metabotropic transmission:
- Fast, but slower than ionotrophic.
- Ligand-receptor binding or intracellular signaling REQUIRED to activate ion channels.
GABA function:
- inhibitory neurotransmitter
- activates chlorine(-) channels in neurons.
- negative charge rushes in, neuron becomes more hyperpolarized and further from the threshold value for depolarization.
Glutamate function:
- excitatory neurotransmitter
- activates membrane sodium(+) and calcium(+) channels.
- positive charge rushes in, cells become closer to threshold value for depolarization.
How does the parasympathetic nervous system slow the heart rate?
- metabotrophic transmission causes outflux of K+.
- cells become more hyperpolarized, further from depolarization threshold.
- heart rate slows due to slower AP rate.
