Cardiovascular System Weekly Quiz 2

Cardiac Muscle Characteristics

-Involuntary

-Striated

-Uninucleated

-Short, highly branched fibers

Involuntary

automatically done (autonomic nervous system)

Cause of striation

sarcomeres (contractile unit)

Sarcomeres composed of:

Actin and myosin

How are the short, branched fibers of the heart connected?

intercalated discs

Intercalated disc junction types:

-desmosomes

-gap junctions

Desmosomes in intercalated discs function:

creates a physical connection

Gap junctions in intercalated discs function:

allow AP to pass through

What causes the heart to involuntarily beat?

Autorhythmic fibers

Characteristics of autorhythmic fibers

-self excitable (do not need outside stimulus)

-generate AP’s automatically

Autorhythmic fibers function:

-pacemaker

-form the conduction system

Conduction system:

pathway for movement of electrical impulses that stimulate the contraction of the atria and ventricles

1st step in conduction system pathway

the SA node spontaneously depolarizes to threshold and propagates to each atrium simultaneously

SA node is composed of

a collection of autorhythmic fibers

2nd step in conduction system pathway

AP reaches the AV node which delays the AP so that the ventricles can fill with blood

3rd step in conduction system pathway

AP enters the Bundle of His (in the ventricle)

4th step in conduction system pathway

AP enters through the left and right bundle branches

5th step in conduction system pathway

the AP reaches the Purkinje fibers

Purkinje fibers function

conduct the AP from the apex up to the ventricle myocardium for contraction

Factors affecting the conduction pathway

-SA node

-Nervous system slows down AP timing

-Hormones

SA node as an affecting factor:

generates an AP every .6 seconds

Nervous system slows down the conduction pathway through:

the parasympathetic nervous system (Acytacholine)

How do hormones modify the timing of the conduction pathway?

epinephrine releases during certain activities

Cardiomyocyte AP’s

1. depolarization

2. plateau

3. repolarization

Plateau of a cardiomyocyte AP

because Ca2+ channels open up, allowing it into the cell combatting the K+ leaving the cell causing a plateau

Ca2+ significance

needed for contraction

Differences in a cardiomyocyte AP

-takes longer

-RMP -90mV

-Ca2+ needed to contract

-threshold is -75mV

-no undershoot

Which way do AP’s get sent in the heart?

in both directions of the cardiac muscle

How is ATP produced?

through aerobic cellular respiration

Oxygen for aerobic cellular respiration is generated through:

-coronary circulation

-myoglobin

What do cardiac muscle cells possess a lot of?

mitochondria