Lecture 6 - Cardiac Muscle Tissue

Question 1

Describe differences between skeletal muscle and cardiac muscle.

Answer 1

Triad ofSR and T tubule (skeletal), died of SR and T-tubule (cardiac), branching cardiac cells, syncitium (cardiac)

Question 2

Describe cardiac A.P. shape & ion conductance.

Answer 2

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

Question 3

Location of fast cardiac action potentials

Answer 3

Conductive tissues of the atria and ventricles (NOT Purkinje fibers)

Question 4

Slow action potentials found in what tissues?

Answer 4

SA and AV nodes, Purkinje fibers,

Question 5

What type of tissues have slow, automatically depolarizing cells?

Answer 5

Slow SA/AV nodal tissues (automaticity)

Question 6

Fast APs are caused by _________.

Answer 6

Na+, K+, and Ca2+ ion conductance

Question 7

Slow AP tissues lack _____ channels and have ____ channels, resulting in slow conduction.

Answer 7

Na+; Ca2+

Question 8

Large diameter, rapidly conductive of APs, high amplitude APs

Answer 8

Fast contractile myocytes

Question 9

Cardiac tissue with rapid upstroke and large diameter

Answer 9

Fast, non-contractile myocytes

Question 10

Type of cardiac tissue with slow depolarization, small diameter, and low amplitude

Answer 10

Slow, non-contractile fibers

Question 11

Two sources of Ca2+ in cardiac contraction:

Answer 11

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

Question 12

Why is diffusion of the Ca2+ from the plateau phase of the AP so important?

Answer 12

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.

Question 13

Describe the similarities between skeletal & cardiac muscle.

Answer 13

Banded appearance due to sarcomeres, mononucleate

Question 14

Slow action potential conducting tissues are found in ______. Why?

Answer 14

SA and AV nodal tissues. These act to slowly depolarize, causing the production of the cells “pacemaker” ability.

Question 15

Fast action potentials serve to ______.

Answer 15

“Conduct and contract”

Question 16

Slow action potentials serve to ______.

Answer 16

Set the pace

Question 17

Slow action potential tissues (SA and AV nodal tissues) resting membrane potential:

Answer 17

-60 mV

Question 18

Past action potentials RMP is:

Answer 18

Appx. -90 mV

Question 19

Cardiac electromechanical coupling Ca2+ comes from?

Answer 19

1) Diffusion thought the DHP-R (from plateau phase) 2) Released from the SR through Ry-R

Question 20

There is a _____ delay from the SA node to the Bundle of His

Answer 20

0.16 sec

Question 21

Ion conductance at A-F

Answer 21

A) Na in

B) K out

C) Some K out

D) Some Ca in

E) Ca close, K out

F) Na leak in

Question 22

What channel is responsible for the less negative RMP in fast action potential cardiac fibers?

Answer 22

Leaky Na+ channels

Question 23

What is the RMP of slow action potential cardiac fibers?

Answer 23

• 60 mV

Question 24

_____ ESV (or pre-load) will increase stroke volume

Answer 24

Increase

Question 25

_____ ESV (after load) will increase stroke volume

Answer 25

Decreasing