ENS 304 Exam 2

Which of the following statements about cardiac muscle contraction is TRUE?

Depolarization of the membrane allows extracellular Ca²⁺ influx, triggering calcium-induced calcium release

During rhythmic exercise, the increase in systolic arterial pressure results from:

Sympathetic activation of the myocardium

At power outputs eliciting more than 50% VO₂max, the stroke volume can either increase, plateau, or slightly decrease. However, cardiac output will always change proportionally to VO₂ because:

Heart rate changes proportionally to O₂

The decrease in peripheral resistance during rhythmic exercise is directly due to:

Vasodilation of arterioles due to local metabolic factors

right atrium and ventricle

receive blood from systemic circulation and pump to pulmonary circulation

left atrium and ventricle

receive blood from pulmonary circulation and pump to systemic circulation

atrioventricular valves (between atria and ventricles) and semilunar valves (between ventricles and arteries)

prevent backflow of blood

“lub-dub” sound the heart makes during contractions

due to closure of valves

myocardium

muscle of heart; composed by cardiomyocytes (cardiac muscle cells)

cardiomyocytes

single nucleated cells connected by intercalated disks

intercalated disks

allow electrical signals to flow between cells

cardiomyocytes vs. skeletal muscle

cardiomyocytes do not have different “types”

myocardium contracts as if:

it is a single unit

calcium activation of myofilaments is similar (not equal) to:

skeletal muscle - myosin, actin, troponins, SERCA

myocardium does not contract by:

stimulation of motor neurons

location of skeletal muscle

throughout body attached to the skeleton and fascia to allow movement

appearance of skeletal muscle

long, cylindrical, unbranched fibers; muscle is striated with fibers arranged in parallel bundles; cells have multiple nuclei

activity type of skeletal muscle

contracts as needed to produce movement or resist gravity through excitation-contraction coupling

fiber types of skeletal muscle

several: type I, type IIa, type IIx

stimulation of skeletal muscle

contraction is stimulated through voluntary or reflex action of nervous system

location of cardiac muscle

heart and adjacent portions of large blood vessels (aorta, vena cava)

appearance of cardiac muscle

branching shorter fibers connected end to end by dark-staining regions called intercalated disks; striated fibers; cells have single, central nucleus

activity type of cardiac muscle

continuous, rhythmic contraction through calcium-induced calcium release

fiber types of cardiac muscle

contains only one fiber type, similar to type I fibers in skeletal muscle

stimulation of cardiac muscle

contraction is involuntary; spontaneous rhythmicity allows muscle to contract without any external stimulation

without neural or hormonal stimulation:

heart rate is 100 bpm, which can be observed in transplanted heart patients

specialized cardiac muscle cells serve as:

pacemakers of the heart

P wave

atrial depolarization; electrical impulse traveling from SA node to AV node

QRS complex

ventricular depolarization; electrical impulse spreads from AV node to Purkinje Fibers

T wave

ventricular repolarization

extrinsic control of heart rate

autonomic and hormonal control of depolarization