Grand Synthesis of Excitable Tissues Flashcards
At any given moment, the membrane potential is determined by the _____________.
equilibrium potential of the ion with greatest permeability
What drives transport, establishes membrane potentials, and powers ATP production?
Asymmetrical ion distribution
What is the critical data for the Nernst equation?
The RATIO of the ion outside and inside
Which ion primarily determines resting potential?
Potassium permeability establishes resting potential
Describe the use of sulfonylureas.
if you had sulfonlyurea, which blocked potassium channel, then you will see membrane
depolarization because the open Na and Ca channels will be more likely to depolarize cell
- if islet cell in pancreas, more likely to release insulin. Therefore sulfonylurea !
insulin release
During depolarization/action potential, what drives the depolarization?
Transient increase in sodium PERMEABILITY (VG Na channel)
Why can the action potential not ‘backfire’/why is there unidirectionality
Because of inactivation gates
Describe a cardiac action potential
Initial depolarization is dependent on Na channels. Na channels start closing & K channels open to start repolarization. Sustained depolarization (plateau) depends on Calcium channels (Long-lasting L-channels). Repolarization occurs when L-channels begin to close and more K channels open. Resting potential depends on K conductance
In cardiac muscle, sustained calcium influx maintains ______ AND contributes to
_______.
depolarization; Calcium Induced Calcium Release, augmenting myocardial contractility
What are receptors for ligand gated ion channels?
ionotropic receptors
What is another name for second messenger receptors that are mostly G-protein
receptors?
Metabotropic
What type of receptors do NTs have? What does the action of the NT depend on?
Both ionotropic and metabotropic. Action at a given location depends on which NT and
receptor type or types at that location
Describe the possible effects of ionotropic post-synaptic receptors and give examples
Excitatory – induce depolarization by increasing permeability to Na (i.e. ACh,
glutamate). Inhibitory – induce hyperpolarization by increasing permeability to Cl (i.e.
GABA, glycine)
Generally describe ionotropic post-synaptic receptors
Fast, graded response NOT an action potential. Structural motif: 4 transmembrane
spanning regions (TM4) – often multiple TM4 subunits form receptor. Can have excitatory
or inhibitory effects.
Describe a graded response. Include where graded potentials occur
Spatial and temporal summation of local depolarization (excitatory post-synaptic
potential, EPSP) and hyperpolarization (inhibitory post-synaptic potential, IPSP). Neuron
integrates the EPSPs and IPSPs occurring on its dendrite and soma to determine if an
action potential is generated at the axon hillock. It is NOT self-sustaining.
Describe metabotropic post-synaptic receptors.
(i.e. GPCRs). Slow, complex multiple effects, common structural motif of 7 TM spanning regions (TM7) – usually one TM7 protein forms receptor
What is the major means of inaction of NTs? What’s the exception?
The major means of inactivation is re-uptake usually by the pre-synaptic neuron.
EXCEPTION: ACh is inactivated primarily by enzymatic degradation (cholinesterase). Enzymatic degradation and diffusion are minor inactivation mechanisms for all the other
classical neurotransmitters
What type of receptors does ACh have?
(1) Nicotinic are ionotropic (2) Muscarinic are metabotropic
What does AChE do?
Degrades ACh into acetate and choline. Choline is then reuptaken into presynaptic
neuron via a Na+/Choline symporte
What is sarin and what does it do?
Sarin = organophosphate “nerve agent” = cholinesterase inhibitors. Irreversible
inhibitor of AChE
What are the energy hogs that use aerobic metabolism? How does this relate to
mitochondrial myopathies
Brain (membrane potentials and NTs), muscle (mechanical work, membrane potentials,
Ca2+ pumping), liver (metabolic work), kidney (metabolic work). In mitochondrial
myopathies, these organs will be the ones primarily/heavily affected due to inhibited
aerobic metabolism.
What has low energy use that primarily uses anaerobic metabolism?
Erythryocytes: bags of hemoglobin but must maintain membrane potential: glycolysis
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