Bio260 Unit 2 Resource 9b. Cardiac Muscles

times on slide 38 not important, just know general process

Cardiac Muscle

• Striated/Have intercalated discs

• Centrally located nuclei

• Y shape allows muscle fibers to interweave producing efficient contraction mechanism

• Myofibrils are less dense/organized

• Alternate with abundant mitochondria

• t tubules are larger/more numerous

• reduced sarcoplasmic reticulum

• diads instead of triads

• makes up myocardium of heart

• capable of generating endogenous action potentials

What is rest membrane potential at?

-55

Pacemaker potential process

1) slow depolarization/pacemaker potential

2) rapid depolarization

3) action potential

4) rapid repolarization

Phase 1: Pacemaker potential

• opening of voltage gated Na+ channels (funny channels) and voltage gated transient Ca2+ channels

• closure of voltage gated K+ channels

Phase 2: Rising Phase/Depolarization

• Opening of long-lasting voltage gated Ca2+ channels

• large influx of Ca2+

Phase 3: Falling Phase/Repolarization

• opening of voltage gated K+ channels

• closing of long lasting voltage gated Ca2+ channels

• Potassium Efflux

Sinoatrial/SA Node

• located in right atrial wall just inferior/above to superior vena cava

• generates 75 action potentials

• pacemaker (has sinus rhythm)

• no contractile elements, but connected directly to atrial fibers which makes it spread faster

Internodal Pathway

• SA to AV node

• Atria/Ventricles separate by non conductive fibrous tissue

• AV is only electrical connection

Interartial pathway

• right → left atrium

• thru gap junctions

• really fast

Atrioventricular/AV node

• located in upper part of interarterial septum

• uses internodal pathway to spread depolarization

Bundle of His

• AV bundle

• only electrical connection btwn atria/ventricles

• left and right branch

Purkinje fibers

• modified muscle fibers with few myofibrils

• controls ventricles and papillary muscles

  • tighten chordae tenineae

  • open tricuspid/mitral valve

Control of heart rhythm

1) pacemaker (SA node) generates wave of signals to contract

2) signals delayed getting to AV node

3) signals pass to heart apex

4) signals spread thru-out ventricles

P-wave

depolarization of SA node → atria

QRS wave

ventricular depolarization/covers atrial repolarization

T-waves

ventricular repolarization

Cardiac Muscle Refractory Period

• long

• period which heart cant make AP

• cannot go into tetany/summation

Regulation of Stroke Volume

Regulated by: Preload, contractility, and afterload

Explain the process happening in this image

1. fluids flow from the SA node into the right and left atrium

   • it flows faster into the left atrium and slower into the right

2. the fluids then make contact with the AV node, travels quickly into the left and right ventricles, and spreads out