REAL week 6 lec quiz

Power stroke

The power stroke is when the myosin head pivots

The action potential traveling down the t-tubule causes depolarization of the

Sarcoplasmic reticulum (SR)

The binding of acetylcholine to its receptor on the muscle cell causes the opening of

Ligand-gated sodium channels

Cross bridge formation occurs when calcium

Binds to troponin

When a new molecule of ATP binds to myosin head during the sliding filament theory, myosin head immediately

Detaches from actin

The hydrolysis of ATP causes myosin to immediately

Return to its cocked (high-energy) position

For contraction to occur, a rise in ________ is needed which is released from the sarcoplasmic reticulum (SR).

Intracellular calcium

Once Ca binds calmodulin, this complex then activates ___.

Myosin light chain kinase (MLCK)

What does “Calcium induce calcium release” mean?

It refers to the process where calcium entry into a cell triggers further release of calcium from the sarcoplasmic reticulum

After death rigor mortis sets in where body is stiff. Why? Then what happens?

ATP is no longer available to detach myosin heads from actin; later, muscle proteins degrade and the body softens

The target in a reflex is the

Effector (muscle or gland)

A polysynaptic reflex has at least ___ in the reflex pathway

One interneuron

What reflex is controlled by the brain stem?

The postural reflexes (e.g. vestibulo-ocular reflex)

The sensory fibers of the muscle spindles synapse onto

Alpha motor neurons and interneurons

The reflex that prevents damage from overstretching is the

Stretch reflex (myotatic reflex)

The flexion reflex

Is a withdrawal reflex in response to pain

What are extrafusal fibers?

Skeletal muscle fibers that generate force

What are intrafusal fibers?

Muscle spindle fibers that detect stretch

What are muscle spindle fibers?

Sensory receptors within the muscle that detect changes in muscle length

The reflex that complements a withdrawal reflex by making compensatory adjustments on the opposite side of the body receiving the stimulus is the

Crossed extensor reflex

Spinal interneurons prevent muscle antagonists from interfering with an intended movement by

Reciprocal inhibition

Motor neurons are sometimes inhibited by

Interneurons (inhibitory, like Renshaw cells)

Most reflex movements are integrated by

The spinal cord

Many reflexes are regulated by

The brain stem

Interneurons of the corticospinal tract synapse onto

Alpha motor neurons

The structure whose abnormal function is associated with Parkinson's disease is the

Basal ganglia

After stretching an intrafusal fiber, the next event is

Increased firing of sensory (afferent) neurons.

When there is a resistance to stretch produced by a given limb muscle

It activates the stretch reflex to contract the muscle and oppose the stretch

"If channels" in SA node action potential allow ___ to enter the cell

Sodium (Na⁺)

The pacemaker potential in SA node action potential occurs due to

Opening of If channels allowing Na⁺ in and K⁺ out

The second phase in a SA node action potential occurs due to

Calcium (Ca²⁺) influx through voltage-gated channels

The third phase in a SA node action potential occurs due to

Potassium (K⁺) efflux

Repolarization in a SA node action potential occurs due to

K⁺ leaving the cell

Depolarization in a SA node action potential occurs due to

Ca²⁺ influx

Depolarization in myocardial action potential occurs due to

Sodium (Na⁺) influx

The depolarization phase of the action potentials of myocardial contractile cells is due to

Na⁺ influx

What is cardiac output

The volume of blood pumped by one ventricle per minute (CO = HR × SV)

What is heart rate

The number of heartbeats per minute

What is end-diastolic volume

The volume of blood in the ventricle at the end of diastole

What is end-systolic volume

The volume of blood remaining in the ventricle after systole

What is stroke volume

The amount of blood ejected by one ventricle in one contraction (SV = EDV - ESV)

During the plateau phase of the action potentials of myocardial contractile cells, which ion(s) is/are crossing the membrane?

Ca²⁺ enters while K⁺ exits.

The flattening of the action potentials of myocardial contractile cells, due to movement of calcium and potassium at the same time is called ___

Plateau

The importance of the plateau phase of the action potential of myocardial cells is in

Preventing tetanus and allowing time for the heart to fill and contract properly

The AV node is important because it

Delays the impulse, allowing atria to contract before ventricles

The SA node is important because it

Acts as the heart's natural pacemaker

The P wave of an ECG corresponds to

Atrial depolarization

The QRS complex of an ECG represents

Ventricular depolarization (and atrial repolarization)

The LUB heart sound occurs due to

Closure of the AV valves

The DUB heart sound occurs due to

Closure of the semilunar valves

During the isovolumic phase of ventricular systole

All valves are closed; pressure rises but volume stays the same.

During early part of ventricular systole,

The ventricles begin to contract but blood hasn’t yet been ejected.

During ventricular ejection / end portion of ventricular systole

Semilunar valves open; blood is ejected from the ventricles.

What would increase peripheral resistance?

Vasoconstriction

What would increase peripheral resistance?

Vasoconstriction

What would decrease peripheral resistance?

Vasodilation, increased blood viscosity, or longer vessel length.

Phase “0” in myocardial cell is called

Depolarization

What is preload? Afterload?

Preload is the stretch of the heart before contraction (related to EDV); afterload is the resistance the heart must pump against.

Progression of the impulse through the AV node can be seen on the ECG as

The PR interval

What is atrial and ventricular diastole?

The relaxation phase of the heart where chambers fill with blood