Chapter 14: Electrolyte Physiology/Pathology Flashcards
when cell becomes more positive than baseline
depolarization
when cell becomes more positive than threshhold
overshoot
when cell becomes more negative than baseline
hyperpolarization
When cell becomes negative from a positive potential
repolarization
What is the electrical charge of all cells (except neurons and Purkinje cells) at rest?
-90mv
What is the electrical charge of neurons and Purkinje cells at rest?
-70mv
What electrolyte always wants to move out of the cell and can move freely at rest?
K (potassium)
What is important about the Nerst number (electrolyte electrical charge) - (cell electrical charge at rest) usually electrolyte electrical charge - (-90)
The higher the number, the faster the conduction speed, but also have to consider concentration gradient and size of electrolyte. i.e. Mg and Ca have higher Nerst numbers but they cannot fit through Na channels that are opened.
What is used to depolarize every cell in your body (except atrium and thalamus)?
Na
What depolarizes atrium and thalamus?
Ca
How does Na enter a cell?
first slow leaking Na channels open and by concentration gradient Na comes inside slowly; by making cell more positive, it reaches threshhold and opens fast Na channels (voltage gated) Na rushes in until it reaches equilibrium with its driving force; then voltage gates close.
What repolarizes a cell?
K leaks out and makes cell more negative and Na/K/ATPase will put 3 Na out and pump 2 K back in to re-establish concentration gradient but not the membrane potential
What other pump is used to re-establish membrane potential?
Na/Ca exchange (3 Na in/1 Ca out)
Every membrane’s action potential has phase 0,3,4: what happens during these stages?
Phase 0–depolarization–Na moves in
Phase 3–repolarization–K moves out
Phase 4–resetting–Na (in)/Ca out
What is the period during which no signal, no matter how large or strong, can depolarize the membrane?
absolute refractory period
What is the period after ARP in which some channels are reset; if the signal is strong enough, the membrane could depolarize but amplitude of depolarization will be lower:
relative refractory period
What is (TENS) transcutaneous electrical nerve stimulation unit
It is a pain relief therapy that uses the gate theory and keeps all nerve cells in the ARP, blocking all pain fibers of Spinothalamic tract
If there is increase in the depolarization of the brain, what will happen and how can we stop it?
seizures, use Na to stop it, use Na blockers like Phenytoin or Carbamazepine
If there is increase in depolarization of atrium, what will happen and how can we stop it?
atrial fibrillation or tachycardia; use Ca to stop it, need Ca blockers like Diltiazem or Verapamil
If there is increase in depolarization of the thalamus, what will happen and how can we stop it?
absence seizure, block Ca with Ethosuximide
Which agents can cause local anesthesia by blocking Na channels and stopping depolarization?
Lidocaine /Procainamide
Which drug is used for temporal lobe seizures?
carbamazepine
Which drug is used for mixed/myotonic seizures?
valproic acid
Which drug is used for febrile seizure?
acetaminophen (bring down fever)
Which drug is used for infantile spasm?
ACTH injections
Which drug is used for status epilepticus?
diazepam, lorazepam
What are the phases of AV node depolarization and what happens in each phase?
Phase 0–slurred curve due to slow Ca channels
Phase 1–Cl- in/ K out because of concentration gradient
Phase 2 plateau Ca (in)/K out because of concentration gradient (heart needs to “pause” for atrial contraction to fill up ventricles
Phase 3 K out (ARP)
Phase 4 automacity is less steep Na (in)/Ca (out)
What has the slowest conduction rate: SA, AV, or Purkinje?
AV
What controls the overall ventricular rate?
AV node
What has the fastest depolarization rate (atrium or ventricles) and why?
ventricles because they have Purkinje fibers
What are the phases of ventricular depolarization and what happens in each phase?
Phase 0: straight up due to fast Na channels
Phase 1 Cl (in)/K (out)
Phase 2 plateau Ca (in)/K (out)
Phase 3 K out
Phase 4 automacity is flat (Na in/Ca out)
If SA node depolarization is lost, what “takes over”?
AV node
If AV node depolarization is lost, what “takes over”?
Purkinje
What happens if ectopic sites take over?
arrhythmias
If pt is symptomatic and decompensating from arrhythmias, what do you do?
defibrillate! shock the heart will pause all cells so SA can reprogram
What does P wave indicate?
atrial depolarization, Ca in , Phase 0
What does PR segment indicate?
AV node pause or atrial contraction
What does PR interval indicate?
total conduction time from SA to AV to ventricle
What does QRS indicate?
ventricular depolarization, Na in , ventricular phase 0, Q is septum, R anterior and S posterior wall
What does ST segment indicate?
Ca in, ventricular contraction
What does T wave indicate?
ventricular repolarization, K out, ventricular phase 3
What does U wave indicate?
ventricular automacity, Na in/Ca out
What does QT interval indicate?
one complete ventricular cycle
On EKG what do width and height indicate?
width is duration (time); height is voltage