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Anatomy Quiz

Lecture 5

How long are cardiac muscles? shorter than skeletal muscles.
What is the shape of cardiac muscles? they are shorter than skeletal muscles and less cicular in transverse section. They have a stair-step appearance.
Why are cardiac muscles said to have a stair-step appearance? The muscles exhibit branching.
What size are caridac muscle fibers? They are about 50-100 micometers long and have a diameter of 12 micrometers.
Figure 20.9 (page 731) - Identify desmosomes, mitochondrion, sarcolemma, nucleus, cardiac muscle fiber, intercalated discs, opening of transverse tubule, gap junctions
Figure 20.9 (page 731) - Identify nucleus, sarcolemma, transverse tubule, mitochondrion, sarcoplasmic reticulum, thin filament, thick filament, z disc, m line, i band, a band, i band, sarcomere, h zone.
How many nuclei does a muscle fiber have? Usually one but sometimes two.
How are the ends of cardiac muscle fibers connected to neighboring fibers? By irregular transverse thickenings of the sarcolemma called intercalated discs.
What are intercalated discs? irregular transverse thickenings of the sarcolemma that connect the ends of cardiac muscle fibers to neighboring fibers.
What do intercalated discs contain? desmosomes
What do desmosomes do? hold the fibers together.
What do gap junctions do? Allow muscle action potentials to conduct from one muscle fiber to its neighbors. Allow the entire myocardium of the atria or the ventricles to contract as a single, coordinated unit.
How does the mitochondira of skeletal and muscle fibers compare? Larger and more numerous in cardiac muscle fibers. In Cardiac muscle fiber take up 25% of the cytosolic space but only 2% of the cytosolic space in skeletal muscle fiber
How do the arrangements of skeletal and cardiac compare? They have the same arrangement of actin and myosin, and the same bands, zones, and z discs.
How do the transverse tubules of skeletal and cardiac compare? They are wider but less abundant than those of skeletal muscle.
How does the sarcoplasmic reticulum compare? Smaller than skeletal muscle fibers and results in a smaller intracellular reserve of CA2+.
What is the reason fo the heart's lifelong beat? An inherent and rhythmical electrical activity.
What is the source of the rhythmical activity? autorhythmic fibers
What are autorhythmic fibers? The source of electrical activity . Network of specialized cardiac muscle fibers. Self excitable. Repeatedly generate action potentials that trigger heart contractions.
What percent of cardiac muscle fibers become autorhythmic fibers? 1%
What do authorhythmic fibers function as? pacemaker and form the conduction system
What is a pacemaker? sets the rhythm of electrical excitation that causes contraction of the heart.
What is the conduction system? A network of specialized cardiac muscle fibers that provide a path for each cycle of cardiac excitation to progress through the heart.
What is the conduction system? pt 2 Ensures that cardiac chambers become stimulated to contract in a coordinated manner, which makes the heart an effective pump.
Where does cardiac excitation begin? In the sinoatrial node.
What is the sinoatrial node? Located in the right atrial wall just inferior and lateral to the opening of the superior vena cava. That do not have a stable resting potential and repeatedly depolarize to threshold spontaneously. It triggers an action potential.
What is a pacemaker potential? spontaneous depolarization.
What does the action potential do? From the SA node it propagates throughout both atria via gap junctions in the intercalated disc of atrial muscle fibers. Following the action potential the atria contract.
Where does the action potential go? reaches the atrioventricular node.
where is the atrioventricular node? interatrial septum just anterior to the opening of the coronary sinus.
After the atrioventricular node where does it go? enters the atrioventricular bundle or the bundle of His.
Where is the only site that action potentials can conduct from the atria to the ventricles? Atrioventicular bundle.
After the AV bundle where does the action potential go? Right and left bundle branches.
Where are the right and left bundle branches. They extend through the interventricular septum toward the apex of the heart.
What is the final step of the action potential? Purkinje fibers rapidly conduct the action potential from the apex of the heart upward to the remainder of the ventricular myocardium. Then the ventricles contract, pushing the blood upward toward the semilunar valves.
What acts as the natural pacemaker of the heart? SA node
What modifies the timing and strength of each heart beat? nerve impulses from the autonomic nervous system and blood-borne hormones
What are contractile fibers? atrial and ventricular muscle fibers.
What is the stable resting membrane of contractile fibers? -90mv
When do voltage-gated fast Na+ channels open? When a contractile fiber is brought to threshold by an action potential from neighboring fibers.
What happens when these channels open? Allow Na+ in flow because the cytosol of contractile fibers is electrically more negative than interstitial fluid and Na+ concentration is higher in interstitial fluid.
What stage comes after depolarization? Plateau
What is the plateau? A period of maintained depolarization. through add
What occurs during a plateau? Voltage-gated slow Ca2+ channels in the sarcolemma open and calcium ions move from the interstitial fluid into the cytosol.This causes more Ca2+ to pour out of the sarcoplasmic reticulum into the cytosol . The high calcium causes contraction.
What also occurs during the plateau phase? potassium channels open and release from the contractile fiber.
How long does the plateau phase last? 0.25 sec
What occurs after the plateau phase? Repolarization
What is the repolarization phase? recovery of the restin membrane potential.
What occurs in the repolatization phase? After a delay additional voltagegated potassium channels open. Outflow of potassium restore the negative resting membrane potential. The calcium channel in the sarcolemma and the sarcoplasmic reticulum are closing which also contributes to repolarization.
Created by: aamanda_88