Grand Synthesis of Excitable Tissues

Question 1

At any given moment, the membrane potential is determined by the _____________.

Answer 1

equilibrium potential of the ion with greatest permeability

Question 2

What drives transport, establishes membrane potentials, and powers ATP production?

Answer 2

Asymmetrical ion distribution

Question 3

What is the critical data for the Nernst equation?

Answer 3

The RATIO of the ion outside and inside

Question 4

Which ion primarily determines resting potential?

Answer 4

Potassium permeability establishes resting potential

Question 5

Describe the use of sulfonylureas.

Answer 5

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

Question 6

During depolarization/action potential, what drives the depolarization?

Answer 6

Transient increase in sodium PERMEABILITY (VG Na channel)

Question 7

Why can the action potential not ‘backfire’/why is there unidirectionality

Answer 7

Because of inactivation gates

Question 8

Describe a cardiac action potential

Answer 8

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

Question 9

In cardiac muscle, sustained calcium influx maintains ______ AND contributes to
_______.

Answer 9

depolarization; Calcium Induced Calcium Release, augmenting myocardial contractility

Question 10

What are receptors for ligand gated ion channels?

Answer 10

ionotropic receptors

Question 11

What is another name for second messenger receptors that are mostly G-protein
receptors?

Answer 11

Metabotropic

Question 12

What type of receptors do NTs have? What does the action of the NT depend on?

Answer 12

Both ionotropic and metabotropic. Action at a given location depends on which NT and
receptor type or types at that location

Question 13

Describe the possible effects of ionotropic post-synaptic receptors and give examples

Answer 13

Excitatory – induce depolarization by increasing permeability to Na (i.e. ACh,
glutamate). Inhibitory – induce hyperpolarization by increasing permeability to Cl (i.e.
GABA, glycine)

Question 14

Generally describe ionotropic post-synaptic receptors

Answer 14

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.

Question 15

Describe a graded response. Include where graded potentials occur

Answer 15

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.

Question 16

Describe metabotropic post-synaptic receptors.

Answer 16

(i.e. GPCRs). Slow, complex multiple effects, common structural motif of 7 TM
spanning regions (TM7) – usually one TM7 protein forms receptor

Question 17

What is the major means of inaction of NTs? What’s the exception?

Answer 17

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

Question 18

What type of receptors does ACh have?

Answer 18

(1) Nicotinic are ionotropic (2) Muscarinic are metabotropic

Question 19

What does AChE do?

Answer 19

Degrades ACh into acetate and choline. Choline is then reuptaken into presynaptic
neuron via a Na+/Choline symporte

Question 20

What is sarin and what does it do?

Answer 20

Sarin = organophosphate “nerve agent” = cholinesterase inhibitors. Irreversible
inhibitor of AChE

Question 21

What are the energy hogs that use aerobic metabolism? How does this relate to
mitochondrial myopathies

Answer 21

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.

Question 22

What has low energy use that primarily uses anaerobic metabolism?

Answer 22

Erythryocytes: bags of hemoglobin but must maintain membrane potential: glycolysis
only