Describe differences between skeletal muscle and cardiac muscle.
Triad ofSR and T tubule (skeletal), died of SR and T-tubule (cardiac), branching cardiac cells, syncitium (cardiac)
Describe cardiac A.P. shape & ion conductance.
Phase 4: slow Na+ leak Phase 0: threshold reached and voltage gated Na open, causing rapid upstroke Phase 1: beginning of depolarization, but arrested by phase 2 Phase 2: voltage gated Ca2+ open, causing cardiac AP "plateau" Phase 3: K+ effluent prompting depolarization
Location of fast cardiac action potentials
Conductive tissues of the atria and ventricles (NOT Purkinje fibers)
Slow action potentials found in what tissues?
SA and AV nodes, Purkinje fibers,
What type of tissues have slow, automatically depolarizing cells?
Slow SA/AV nodal tissues (automaticity)
Fast APs are caused by _________.
Na+, K+, and Ca2+ ion conductance
Slow AP tissues lack _____ channels and have ____ channels, resulting in slow conduction.
Large diameter, rapidly conductive of APs, high amplitude APs
Fast contractile myocytes
Cardiac tissue with rapid upstroke and large diameter
Fast, non-contractile myocytes
Type of cardiac tissue with slow depolarization, small diameter, and low amplitude
Slow, non-contractile fibers
Two sources of Ca2+ in cardiac contraction:
1)Ca2+ from phase 2 (plateau) of AP diffuses through DHP-R into sarcoplasm 2) Ca2+ released from SR during AP transmission to T-tubule
Why is diffusion of the Ca2+ from the plateau phase of the AP so important?
Without the calcium from the T tubules, the strength of cardiac muscle contraction would be reduced considerably because the sarcoplasmic reticulum of cardiac muscle is less well developed than that of skeletal muscle and does not store enough calcium to provide full contraction.
Describe the similarities between skeletal & cardiac muscle.
Banded appearance due to sarcomeres, mononucleate
Slow action potential conducting tissues are found in ______. Why?
SA and AV nodal tissues. These act to slowly depolarize, causing the production of the cells "pacemaker" ability.
Fast action potentials serve to ______.
"Conduct and contract"
Slow action potentials serve to ______.
Set the pace
Slow action potential tissues (SA and AV nodal tissues) resting membrane potential:
Past action potentials RMP is:
Appx. -90 mV
Cardiac electromechanical coupling Ca2+ comes from?
1) Diffusion thought the DHP-R (from plateau phase) 2) Released from the SR through Ry-R
There is a _____ delay from the SA node to the Bundle of His
Ion conductance at A-F
A) Na in
B) K out
C) Some K out
D) Some Ca in
E) Ca close, K out
F) Na leak in
What channel is responsible for the less negative RMP in fast action potential cardiac fibers?
Leaky Na+ channels
What is the RMP of slow action potential cardiac fibers?
- 60 mV
_____ ESV (or pre-load) will increase stroke volume
_____ ESV (after load) will increase stroke volume