Flashcards in Cell & Membrane Physiology Deck (42):
What are the 4 characteristics of cardiac muscle?
1. automaticity (electrical activity)
What connections exist between cardiac myocytes?
gap junctions for electrical conductivity and desmosomes for adhesion.
Where is the sinoatrial node (SA node) found?
posterior wall of the right atrium at the area of the crista terminalis
What does the SA node do?
Area which generates electrical impulses and sends them through the gap junctions and desmosomes of atria where they meet the atrioventricular node (AV node).
Where does the electrical impulse travel after the AV node?
Down the bundle of his to the purkinje fibers, which go around the ventricles causing them to contract.
How often do the atria and ventricles contract?
about 80 times/minute (+/- 20)
What occurs across these cardiac membranes as the heart contracts?
Is cardiac muscle different from skeletal and smooth muscle?
What is ischemia?
low blood flow
What happens when cardiac muscle becomes ischemic?
it is not getting adequate blood flow, and therefore not enough O2.
From where does the energy come for cardiac muscle?
mitochondria, which produce ATP
What does the histology look like?
striated, muscle with intercalated discs and nuclei
What is cardiac output (CO)?
Heart rate x stroke volume: (CO= HR x SV)
What makes up a cardiac cell membrane?
A phospholipid bilayer with various membrane proteins. On the surface you will find peripheral proteins and carbohydrate moieties. Thus, the patient must have an intake of cholesterol, fats, lipids, and proteins to maintain these membranes.
What is the purpose of the cell membrane and its channels?
To provide a barrier between the inside and outside of the cell. The channels may be uni-directional or bi-directional.
What is an example of a situation where membrane channels can't open leading to decreased glucose uptake?
Diabetes or pancreatic damage, decreasing insulin function or availability, and leading to increased glucose in the extracellular fluid (blood) = hyperglycemia!
At physiologic pH, is the charge on the intracellular side of the cell membrane slightly positive or slightly negative, with respect to the extracellular side?
slightly negative, due to negatively charged proteins. These will also prevent K+ from leaving, increasing the concentration of K+ on the inside of the cell relative to the outside.
What happens when membrane channels open?
Na+ rushes in due to its electrochemical gradient, changing the charge of the inside relative to the outside, and K+ will begin to flow out at faster rate than the Na+ is entering, to reestablish the electrochemical gradient.
What is the ionic basis for how cardiac contraction occurs?
excitation/contraction = ionic events produce electrical events, which produce mechanical events.
What do cardiac electrical events ultimately produce?
the cardiac action potential
Does the cardiac action potential differ at the SA node, AV node, bundle of his, purkinje fibers, and ventricles?
What modifies the protein membrane channels?
glycolipid and carbohydrate moieties.
How can channels be affected?
chemically and electrically (voltage gated), affecting the permeability of some of the myocyte channels
What is an example of altering voltage gated channels due to dysrhythmias?
using a defibrillator to shock a patient back into sinus rhythm.
How long is a normal cardiac action potential (AP)?
300ms and looks like a fireman's hat.
What phase is the upstroke of the cardiac AP?
phase 0. This is depolarization as Na+ enters taking the membrane potential from -96 mV to +52 mV.
What occurs at phase 1 of the cardiac AP?
potassium channels open slowly to allow K+ to efflux in an attempt to repolarize. Cl- also leaves too.
What occurs at phase 2 of the cardiac AP?
Plateau (maintained depolarization). Na+ is trying to come in, K+ is trying to go out (closing of some K+ channels) and Ca++ is entering into the myocytes as a result of the potential change (voltage-gated slow Ca++ channels opening), which induces Ca++ release from the SR, and binds to troponin C, moving troponin/tropomyosin complex around the actin filament, exposing the myosin binding sites for myosin interaction. ATP will be cleaved allowing for the sarcomeres to get smaller = SYSTOLE.
What occurs at phase 3 of the cardiac AP?
Na+ and Ca++ channels close and more K+ exits (more voltage-gated K+ channels open), repolarizing the cell.
What occurs at phase 4 of the cardiac AP?
this is the resting membrane potential (-96 mV).
What happens when the calcium enters the myocytes?
Ca++ induced Ca++ release for the calcium stores of the SR.
When does the absolute refractory period occur?
during the plateau phase (phase 2).
When does the relative refractory period occur?
during repolarization (phase 3).
What maintains the electrical-chemical gradients?
the sodium potassium ATPase.
What happens to the excess calcium as the cell repolarizes?
it is resequestered into the SR.
What does the P wave of the EKG represent?
What does the QRS wave of the EKG represent?
What does the T wave represent?
Do cardiac APs produce EKGs?
What does the EKG show us collectively?
What is going on with all of the APs going on together in the heart. This is ELECTRICAL only!
Do atrial and ventricular APs look a little different?