Physiology - Muscles, Body Movement, Blood & Cardiovascular
Which of the following changes would produce the greatest change in total peripheral resistance?
10%% change in vessel diameter The main determinant of total peripheral resistance is the diameter of the small arterioles. As blood vessel diameter increases, resistance goes down, and vice versa. Resistance is inversely proportional to the fourth power of the blood vessel radius. Radius is one-half of the vessel diameter. This means any change in vessel diameter will affect resistance by a factor of 1/r4 where r is the radius. For example, a doubling of the vessel diameter will have a 2*2*2*2 or 16-fold reduction in resistance.
Which of the following would reflect the typical net hydrostatic pressure (HP) at the arterial end of the capillary?
34 mm Hg HPc (35 mm Hg) - HPI (1 mm Hg) = 34 mm Hg, which is the net hydrostatic pressure at the arterial end. The hydrostatic pressure of the blood is much higher at the arterial end of the capillary, thus favoring filtration.
Calculate the cardiac output if heart rate (HR) is 90 beats per minute, stroke volume (SV) is 110 ml/beat, end diastolic volume (EDV) is 140 ml, and end systolic volume (ESV) is 30 ml.
9.9 L/min Cardiac output is the product of heart rate times stroke volume. Cardiac output increases to meet increased metabolic demand, often by increasing both heart rate and stroke volume at the same time. This occurs, for example, during maximal exercise, when cardiac output may increase to four or five times the resting level.
Which event causes cross bridge detachment?
ATP binding to the myosin head As ATP binds, the myosin head releases from the active site on actin
After a power stroke, the myosin head must detach from actin before another power stroke can occur. What causes cross bridge detachment?
ATP binds to the myosin head. The binding of ATP to the myosin head weakens the bond between myosin and actin, forcing the myosin head to detach. ATP also provides the energy for the next power stroke.
Which part of the intrinsic conduction system delays the impulse briefly before it moves on to the ventricles?
AV node the AV node slows down the impulse giving the atria time to contract before the ventricles contract.
Which of the following best describes the contraction phase of the excitation-contraction coupling reaction?
Actin and myosin filaments slide past each other to shorten the sarcomere, bringing Z disks closer together.
The following activities and body conditions affect blood pressure by changing one of the two listed factors.
Blood volume: blood donation excessive sweating Total Peripheral Resistance: growth smoking high-altitude living increased sympathetic activity
The following physiological changes either increase or decrease blood pressure.
Decreases blood pressure: Increase blood vessel diameter Increases blood pressure: Increase blood vessel length Increase total peripheral resistance Increase cardiac output Increase blood volume Increase blood viscosity
These activities change heart rate by changing the balance of parasympathetic and sympathetic stimulation of the heart. Sort each of the activities according to whether it decreases or increases heart rate.
Decreases heart rate: Lying down, Digesting a meal Increases heart rate: Fright or anger, Standing up, Exercise The balance between parasympathetic and sympathetic stimulation to the heart controls heart rate. Increased parasympathetic activity decreases heart rate, and sympathetic activity increases heart rate.
Contraction of the atria results from which wave of depolarization on the ECG tracing?
P wave the P wave represents atrial depolarization, which leads to atrial contraction.
Describe the pressures in the atria and ventricles that would cause the opening of the AV valves.
Pressure in the atria would be greater than the pressure in the ventricles. higher pressure in the atria than in the ventricles forces the AV valves to open and blood moves into the ventricles.
Match the terms in the left column to the blanks near their definition on the right.
Total peripheral resistance: the amount of friction blood encounters during flow through blood vessels. Blood viscosity: the friction red blood cells encounter when moving past each other. Blood pressure: the force of the blood against the vessel wall. Cardiac output: the volume of blood pumped out by one ventricle each minute.
When threshold is reached at the SA node (an autorhythmic cell), what channels open causing further depolarization of the membrane?
fast calcium unlike nerve cells or cardiac muscle cells, fast calcium channels are responsible for the depolarization phase of the autorhythmic cell action potential. When the fast calcium channels open, calcium rushes into the cell making it less negative (or more positive).
What causes the aortic semilunar valve to close?
greater pressure in the aorta than in the left ventricle backflow of blood in the aorta (towards the left ventricle) closes the aortic semilunar valve.
If blood pressure is increased at the arterial baroreceptors, what would happen with the activity level of the parasympathetic nervous system (PNS) and sympathetic nervous system (SNS)?
increased PNS activity and decreased SNS activity Yes, the PNS activity would increase and the SNS activity would decrease in an attempt to lower blood pressure.
By what mechanism would an increase in venous return increase stroke volume?
increased end diastolic volume an increase in venous return increases the end diastolic volume. The fibers are stretched more, resulting in an increase in the force of contraction (preload, or the Frank-Starling Mechanism).
Which of the following would increase cardiac output to the greatest extent?
increased heart rate and increased stroke volume cardiac output = heart rate x stroke volume
Which heart chamber receives blood from the pulmonary veins?
left atrium the left atrium receives oxygenated blood from the pulmonary veins
Which chamber pumps oxygenated blood out the aorta to the systemic circuit?
left ventricle the left ventricle pumps oxygenated blood out the aorta to the entire body (systemic circuit).
Which net pressure draws fluid into the capillary?
net osmotic pressure the proteins exert colloid osmotic pressure, which draws fluid into the capillary.
A decrease in blood pressure at the arterial baroreceptors would result in which of the following?
an increase in heart contractility sympathetic nervous system activity would be increased because of the low blood pressure. Sympathetic fibers go to the ventricles of the heart and increase their contractility. An increase in contractility would increase stroke volume which would lead to an increase in cardiac output and blood pressure.
Stimulation of the adrenal medulla would result in which of the following?
an increase in heart rate and contractility epinephrine and norepinephrine are released from the adrenal medulla and act as part of the sympathetic nervous system, increasing heart rate and contractility. Epinephrine and norepinephrine have other effects that would also increase blood pressure.
Which of the following events is NOT represented on an ECG?
atrial repolarization
What causes the myosin head to disconnect from actin?
binding of ATP the binding of ATP causes the myosin head to disconnect from actin.
In the capillaries, hydrostatic pressure (HP) is exerted by __________.
blood pressure blood pressure is the driving force for filtration.
Blood pressure would INCREASE as a result of a DECREASE in __________.
blood vessel diameter Decreases in blood vessel diameter increase blood pressure because blood has more difficulty flowing through small vessels than large vessels. In other words, a decrease in blood vessel diameter increases total peripheral resistance. Assuming cardiac output remains constant, the increased total peripheral resistance would increase blood pressure. Or perhaps more intuitively, if cardiac output is to remain constant, blood pressure must increase.
The net hydrostatic pressure (HP) is the hydrostatic pressure in the __________ minus hydrostatic pressure in the __________.
capillary; interstitial fluid the capillary hydrostatic pressure (HPC; caused by blood pressure) is much higher than the interstitial hydrostatic pressure (HPI). The interstitial fluid is forced out of the capillaries.
Where are the sensors for the arterial baroreceptor reflex located?
carotid sinus and aortic arch Yes, the sensors are the arterial baroreceptors themselves, located at the carotid sinus and aortic arch. They detect changes in blood pressure by the degree of stretch on the blood vessel.
Waves and Flat Lines
current flow vector is toward the positive electrode current flow vector toward the negative electrode a vector that is perpendicular to the axis of the electrode
Would you call this QRS early, on time, or late compared to when other QRS complexes are formed?
early
What does the ECG wave tracing represent?
electrical activity in the heart the ECG waves show the depolarization and repolarization in various areas of the heart.
Which of the following statements best describes the neuromuscular junction?
the point of synapse between a motor neuron and the muscle fiber that it innervates
Which of the following statements best describes the electrical events recorded by an ECG?
the sum of the electrical activity of all cells in the heart
The binding of calcium to which molecule causes the myosin binding sites to be exposed?
troponin Yes, when calcium binds to troponin, troponin releases tropomyosin, exposing the myosin binding sites.
The heart is actually (one, two, or three) pumps?
two pumps the right side of the heart pumps to/from the lungs (pulmonary circuit) and the left side of the heart pumps to/from the rest of the body (the systemic circuit).
Isovolumetric relaxation and ventricular filling (two phases of the cardiac cycle) take place during __________.
ventricular diastole both occur during ventricular diastole when the ventricles are not actively contracting and ejecting blood.
The anatomy of the intrinsic conduction system causes contraction of the ventricles to begin at the apex and move superiorly. Why is this important?
so blood is forced upward, toward the semilunar valves Beginning contraction at the apex causes blood to be forced upward, through the semilunar valves, and into the aorta and pulmonary trunk. This makes ventricular ejection more efficient, much like squeezing a tube of toothpaste up from the bottom is more efficient at dispensing the toothpaste than is squeezing from the top.
What change in peripheral resistance would help raise blood pressure?
increase
What would you predict must happen to cardiac output to increase arterial pressure?
It must increase.
A myosin head binds to which molecule to form a cross bridge?
actin the myosin head binds to actin, the major component of thin filaments.
Which of the following processes produces 36 ATP?
Krebs cycle and oxidative phosphorylation 36 ATPs are produced for each glucose molecule. This process, which takes place in the mitochondria, is considered aerobic respiration because oxygen is required.
Which chamber receives blood from the superior and inferior vena cavae?
right atrium the right atrium receives unoxygenated blood from the systemic circuit.
Which heart chamber pumps unoxygenated blood out the pulmonary trunk?
right ventricle the right ventricle pumps unoxygenated blood out the pulmonary trunk to the lungs.
What structure is the functional unit of contraction in a skeletal muscle fiber?
The sarcomere A sarcomere is a regular arrangement of thin and thick myofilaments that extends from one Z disc to the next. A myofibril consists of a series of sarcomeres.
When does cross bridge cycling end?
Cross bridge cycling ends when sufficient calcium has been actively transported back into the sarcoplasmic reticulum to allow calcium to unbind from troponin. The sarcoplasmic reticulum contains Ca2+-ATPases that actively transport Ca2+ into the SR. Without Ca2+, troponin returns to its resting shape, and tropomyosin glides over and covers the myosin binding sites on actin.
Which of the following best summarizes the events of excitation-contraction coupling?
Muscle action potentials initiate calcium signals that activate a contraction-relaxation cycle.
Which of the following is correct about the filling of the ventricles?
Most blood flows passively into the ventricles through open AV valves. most of the ventricular filling is passive; atrial contraction adds just a little more blood.
Which loss of function would occur if you introduced a chemical that functioned as an inhibitor of the ryanodine receptor channel?
Myosin would not be able to bind to actin in order to cause shortening of the sarcomere
Based on the typical shapes of ECG waves, which wave does this 11th cardiac cycle most resemble?
QRS complex
Calcium entry into the axon terminal triggers which of the following events?
Synaptic vesicles fuse to the plasma membrane of the axon terminal and release acetylcholine. When synaptic vesicles fuse to the plasma membrane, acetylcholine is released via exocytosis.
What role does tropomyosin play in the cross bridge cycle?
The displacement of tropomyosin exposes the active sites of actin, allowing cross bridges to form. Tropomyosin covers active sites in relaxed muscle. When tropomyosin is displaced, the active sites are exposed for cross bridge formation.
During exercise, cardiac output may increase by more than 170%% to meet the body's increased O2O2 demands. This increase in cardiac output increases blood pressure. But the accompanying increase in arterial pressure is relatively small—only about 40%%. What limits this increase in blood pressure so that it doesn't reach dangerously high levels during exercise?
Vasodilation causes arterial diameter to increase in the exercising skeletal muscle. During exercise, total peripheral resistance decreases. This is primarily due to an increase in the diameters of arterioles supplying the exercising muscles. Vasodilation of the blood vessels increases blood flow, providing the oxygen and nutrients necessary to support increased muscle metabolism. In addition, vasodilation of the arterioles in the skin also allows for greater blood flow to the skin for evaporative cooling.
Which of the following structures is/are necessary to initiate the muscle action potential? Select all that apply.
acetylcholine motor neuron muscle fiber ACh receptor-channels motor end plate
As part of a blood drive on campus for the American Red Cross, you and your friends have just donated 500 ml of blood. You are now relaxing at the student lounge, waiting for A&P lab to begin. Unfortunately, even though you are thirsty, you haven't bothered to buy yourself a drink. Other than a little soreness of the skin and tissue around your median cubital vein, you feel fine. How has your 500 ml decrease in blood volume most likely affected your cardiac output, heart rate, and stroke volume?
no change in cardiac output, increased heart rate, decreased stroke volume Donating blood does not alter resting cardiac output. However, the decreased blood volume does decrease venous return and end diastolic volume. This decreases preload, thereby lowering stroke volume. By itself, decreased stroke volume would decrease cardiac output. But remember, the body still requires a resting blood flow of around 5 L/min. To meet this demand, homeostatic mechanisms quickly restore cardiac output to resting levels. For example, heart rate is increased as parasympathetic influence is removed and sympathetic activity is increased. Even though your blood volume is a bit low, your body has no problem compensating to meet your resting metabolic needs. Running away from a tiger? Now that might be a different story.
Which hormone works directly in the intestine to increase plasma calcium levels?
parathyroid hormone (PTH) activates Vitamin D into calcitriol in the kidney. Calcitriol then increases absorption of calcium in the intestine.
One of the changes that occurs in the pacemaker potential (unstable resting membrane potential) in the SA node (an autorhythmic cell) is a decreased efflux of what ion?
potassium if there is a decreased efflux of potassium while there is a normal influx of sodium, the inside of the cell would become less negative. Thus, threshold would be reached. The ability of these autorhythmic cells to spontaneously depolarize is what results in the pacemaker potential.
The colloid osmotic pressure in the capillary is caused by __________.
proteins in the blood the non-diffusible proteins in the plasma exert the colloid osmotic pressure, which pulls fluid into the capillary.
Match the cardiac components in the left column to the blanks near their functions on the right.
1. AV bundle : Electrical link(s) between atria and ventricles 2. AV node: Delay(s) occurs here while atria contract 3. Purkinje fibers: Convey(s) the impulse throughout the ventricular walls 4. Bundle branches: Convey(s) the impulse down the interventricular septum 5. SA node: Set(s) the pace for the entire heart 6. Internodal pathways: Link(s) between the SA node and AV node
When observing an ECG, you will see many different deflections from baseline known as waves. These deflections represent various electrical events taking place in the heart that give rise to the mechanical events that help move blood. In addition to the waves that can be observed, there are flat lines between waves and successive cardiac cycles called segments that also represent particular electrical events that take place in the heart. Finally, certain combinations of waves and segments, known as intervals, also identify important events recorded by the ECG. Match each of the following events with the correct phase of an ECG.
1. Einthoven's triangle is an electrode placement technique that uses three leads in order to record an electrocardiogram. 2. An intracellular recording of electrical activity in either a contractile cell or autorhythmic cell is known as a(n) Action potential. 3. A two electrode pair constitutes a Lead, which records the electrical activity of the heart. 4. An extracellular recording of electrical activity of both autorhythmic and contractile cells of the heart is known as a(n) Electrocardiogram.
Match the term in the left column to the blanks near their definition on the right.
1. Heart rate (HR): the number of heart beats per minute 2. Venous return (VR): the volume of blood per minute flowing into one atrium 3. End diastolic volume (EDV): the volume of blood in one ventricle before contraction 4. Stroke volume (SV): the volume of blood per heart beat pumped out by one ventricle 5. Cardiac output (CO): the volume of blood per minute pumped out by one ventricle 6. End systolic volume (ESV): the volume of blood in one ventricle after contraction
When observing an ECG, you will see many different deflections from baseline known as waves. These deflections represent various electrical events taking place in the heart that give rise to the mechanical events that help move blood. In addition to the waves that can be observed, there are flat lines between waves and successive cardiac cycles called segments that also represent particular electrical events that take place in the heart. Finally, certain combinations of waves and segments, known as intervals, also identify important events recorded by the ECG. Match each of the following events with the correct phase of an ECG.
1. Ventricular depolarization −−QRS complex 2. Total time it takes for the ventricular muscle to depolarize and repolarize −−QT interval 3. Atrial depolarization −−P wave 4. Conduction through the atrioventricular (AV) node −−PR segment 5. Ventricular repolarization −−T wave 6. The ventricles are in their depolarized state −−ST segment 7. Conduction through the atrioventricular (AV) bundle −−Q wave
Another useful purpose for the ECG is the determination of heart rate and whether or not there are any irregularities in the heart rate. In order to calculate heart rate, you must know the scale on which the ECG is recorded. Each square on the ECG grid represents 1 mm, and the ECG taken for Part I was taken at 25 mm/sec. In order for you to calculate the heart rate of the individual from the ECG trace, you need to keep in mind that heart rate is represented as beats per minute and you want to count full cardiac cycles as beats. Use the normal ECG trace below to determine how many seconds the trace represents as well as the heart rate.
4 seconds; 75 beats/minute
Drag and drop each of the following words with its appropriate function with regard to the neuromuscular junction. Drag the terms on the left to the appropriate blanks on the right to complete the sentences.
A change in membrane voltage that travels down the T-tubule to cause opening of Ca2+ channels Action potential A structure that when bound to a ligand opens a divalent channel for the movement of both Na+ and K+ ACh receptor-channel An area of muscle fiber membrane that is in close association with the axon terminal of the motor neuron, contain receptors for acetylcholine Motor end plate An area that contains many synaptic vesicles filled with acetylcholine Axon terminal of motor neuron
The cross bridge cycle is a series of molecular events that occur after excitation of the sarcolemma. What is a cross bridge?
A myosin head bound to actin As soon as the activated myosin head forms a cross bridge with actin, the power stroke begins.
A triad is composed of a T-tubule and two adjacent terminal cisternae of the sarcoplasmic reticulum. How are these components connected?
A series of proteins that control calcium release. When action potentials propagate along T-tubules, a voltage-sensitive protein changes shape and triggers a different protein to open it's channels, resulting in the release of calcium from the terminal cisternae.
Which of these structures conduct(s) action potentials the slowest?
AV node Action potentials slow down as they pass through the AV node. This gives the atria time to finish contracting before the ventricles are depolarized.
Increased pressure in the ventricles would close what valve(s)?
AV valves only increased pressure in the ventricles would close the AV valves.
Action potential propagation in a skeletal muscle fiber ceases when acetylcholine is removed from the synaptic cleft. Which of the following mechanisms ensures a rapid and efficient removal of acetylcholine?
Acetylcholine is degraded by acetylcholinesterase. Acetylcholinesterase is an enzyme that degrades acetylcholine. This degradation results in a rapid cessation of the acetylcholine signal and a swift removal from the cleft.
The neuromuscular junction is a well-studied example of a chemical synapse. Which of the following statements describes a critical event that occurs at the neuromuscular junction?
Acetylcholine is released by axon terminals of the motor neuron. Acetylcholine is released into the synaptic cleft via exocytosis.
Putting It All Together
Acetylcholine is released from motor neuron Action potential travels down the T-tubule Ca2+ is released from the sarcoplasmic reticulum Myosin generates the power stroke Ca2+-ATPase channels actively pump Ca2+ back into the sarcoplasmic reticulum Ca2+ unbinds from troponin Actin filament slip back to rest position
How/when does the myosin head cock back to store energy for the next cycle?
After the myosin head detaches, energy from ATP hydrolysis is used to re-cock the myosin head. In addition to breaking the cross bridge, ATP provides energy to cock the heads back after the previous power stroke.
Events of Contraction in Order
An action potential that travels down the T-tubule changes the structural confirmation of the DHP L-type Ca2+ channel Ryanodine receptor channels open Ca2+ leaves the sarcoplasmic reticulum Acting and myosin bind to one another Myosin heads utilize energy from ATP hydrolysis to produce the power stroke Actin filaments slide toward the M line, shortening the sarcomere
The binding of the neurotransmitter to receptors on the motor end plate causes which of the following to occur?
Binding of the neurotransmitter causes chemically gated sodium channels to open in the motor end plate (junctional folds of the sarcolemma) and sodium enters the cell. sodium enters the cell and causes depolarization. A small amount of potassium also leaves the motor end plate (junctional folds of the sarcolemma).
Which of the following is the most direct cause of muscle relaxation?
Ca2+ unbinds from troponin, which results in tropomyosin re-covering myosin binding sites.
Which of the following best describes the role of calcium (Ca2+ ) in the excitation-contraction coupling reaction? Choose the best answer.
Ca2+ will bind to troponin, which leads to a conformational shift in tropomyosin, allowing for actin and myosin to attach.
What is the role of calcium in the cross bridge cycle?
Calcium binds to troponin, altering its shape. Calcium binding to troponin causes tropomyosin to move away from the active sites on actin
Calcium ions couple excitation of a skeletal muscle fiber to contraction of the fiber. Where are calcium ions stored within the fiber?
Calcium ions are stored in the sarcoplasmic reticulum Sarcoplasmic reticulum is the specific name given to the smooth endoplasmic reticulum in muscle fibers. The sarcoplasmic reticulum is very elaborate in skeletal muscle fibers, allowing for significant storage of calcium ions.
What specific event triggers the uncovering of the myosin binding site on actin?
Calcium ions bind to troponin and change its shape. The shape change caused by the binding of calcium to troponin shifts tropomyosin away from the myosin binding sites on actin.
Which of the following is most directly responsible for the coupling of excitation to contraction of skeletal muscle fibers?
Calcium ions. Action potentials propagating down the T-tubule cause a voltage-sensitive protein to change shape. This shape change opens calcium release channels in the sarcoplasmic reticulum, allowing calcium ions to flood the sarcoplasm. This flood of calcium ions is directly responsible for the coupling of excitation to contraction in skeletal muscle fibers.
Excitation of the sarcolemma is coupled or linked to the contraction of a skeletal muscle fiber. What specific event initiates the contraction?
Calcium release from the sarcoplasmic reticulum initiates the contraction. Sarcoplasmic reticulum is the specific name given to the smooth endoplasmic reticulum in muscle cells. It is especially abundant and convoluted in skeletal muscle cells. It functions in the storage, release, and reuptake of calcium ions.
Excitation-contraction coupling is a series of events that occur after the events of the neuromuscular junction have transpired. The term excitation refers to which step in the process?
Excitation, in this case, refers to the propagation of action potentials along the sarcolemma. These action potentials set off a series of events that lead to a contraction.
Predict the changes in heart rate, stroke volume, and cardiac output for each of the following conditions by filling out the table below.
Increased sympathetic activity: HR increase Stroke volume increase Cardiac output increase Increased preload: HR (no change) Stroke volume increase Cardiac output increase Increased exercise: HR increase Stroke volume increase Cardiac output increase Increased contractility: HR (no change) Stroke volume increase Cardiac output increase
BMD (2,3-butanedione 2-monoximime) inhibits myosin, such that ATP can bind to myosin but myosin is unable to hydrolyze the bound ATP. What effect would BMD have on the cross bridge cycle?
Myosin heads would remain detached, unable to cock. The hydrolysis of ATP is required for the cocking of the myosin head. ATP would still bind to myosin, causing cross bridge detachment, but myosin would be stuck in this step of the cross bridge cycle.
The electrical events of the cardiac cycle give important insight into the mechanical events. Recall that in order for a muscle to contract, it must receive an electrical stimulus. This is especially important in the heart, since we rely on the contraction of the atria and ventricles to move blood. Rank these events in the order in which they occur in the heart, beginning with the P wave.
P wave Atrial contraction (systole) QRS complex Ventricular contraction (systole) T wave Ventricular relaxation (diastole)
A person notices his or her heart beat because he or she senses blood being pumped by the heart. Excessive caffeine intake can lead to irregular heart rhythms (arrhythmias) that patients perceive as "skipped beats." Given that caffeine is a stimulant, which of the following mechanisms best explains the reason for the feeling that the heart skipped a beat?
Purkinje fibers initiate spontaneous action potentials, which cause the ventricles to contract early. Action potentials normally originate in the SA node because the pacemaker cells there depolarize faster than pacemaker cells located elsewhere in the heart. However, certain drugs, such as caffeine, nicotine, or cocaine, can stimulate other pacemaker cells to speed up and temporarily "escape" the SA node rhythm. If this ectopic focus consists of Purkinje fibers, then ventricular contraction will occur prematurely, prior to ventricular filling. Without proper filling, this abnormal contraction pumps little blood and is not sensed. However, the following normal beat generated from the SA node has augmented filling and is sensed, resulting in the missed beat sensation.
The "rest and recovery" period, where the muscle restores depleted reserves, includes all of the following processes EXCEPT
Pyruvic acid is converted back to lactic acid. this is NOT a part of the "rest and recovery" period. When oxygen is available, lactic acid is converted back to pyruvic acid (not vice versa) that then enters the Krebs cycle. Lactic acid is the end product of the anaerobic pathway.
There are a total of four mechanical events of the cardiac cycle, all of which are associated with their own electrical events. Recall that in order for a muscle to contract, it must receive an electrical signal that leads to a depolarization phase. If the heart is to perform a series of contractions, then, for each contraction, the muscle must relax as well. Relaxation of the muscle is correlated with the repolarization of the muscle and indicates a time in which the chambers are filling with blood. Which portion of a normal ECG represents ventricular depolarization?
QRS complex
Which part of the intrinsic conduction system normally initiates the depolarizing impulse that causes a heartbeat?
SA node Like the rest of the intrinsic conduction system, the SA node contains pacemaker cells that spontaneously depolarize. The cells within the SA node, however, depolarize faster than the other cells within the system. This causes action potentials to initiate in the SA node rather than in any of the other structures.
Which part of the conduction system initiates the depolarizing impulse, which spreads throughout the heart?
SA node the SA Node spontaneously depolarizes, causing the wave of depolarization that spreads through the rest of the conduction system and heart.
Arrange these elements of the intrinsic conduction system in the order that a depolarizing impulse travels during a normal heartbeat.
SA node Internodal pathways AV node AV bundle Bundle branches Purkinje fibers
Events at the Neuromuscular Junction in Order
Somatic motor neuron delivers action potential Acetylcholine is released from the axon terminal onto the motor endplate Net Na+ influx through nicotinic receptors Muscle fiber depolarizes Action potential travels down the T-tubule of the muscle fiber
How does the myosin head obtain the energy required for activation?
The energy comes from the hydrolysis of ATP. Myosin is a large, complex protein with a binding site for actin. It also contains an ATPase. The energy released during the hydrolysis of ATP activates the myosin head.
Action potential propagation in a skeletal muscle fiber ceases when acetylcholine is removed from the synaptic cleft. Which of the following mechanisms ensures a rapid and efficient removal of acetylcholine?
The inside surface of the sarcolemma is negatively charged compared to the outside surface. Sodium ions diffuse inward along favorable chemical and electrical gradients. The resting membrane potential of all cells is negative (inside compared to outside). Therefore, given the direction of the chemical and electrical gradients, more sodium ions diffuse inward than potassium ions diffuse outward.
During contraction, what prevents actin myofilaments from sliding backward when a myosin head releases?
There are always some myosin heads attached to the actin myofilament when other myosin heads are detaching. During contraction, about half of the myosin heads are attached, preventing the actin myofilament from sliding backwards when any single myosin head detaches. The situation is analogous to a game of tug-of-war. In tug-of-war, individual hands release after they pull on the rope, but not all hands release at the same time.
How does troponin facilitate cross bridge formation?
Troponin controls the position of tropomyosin on the thin filament, enabling myosin heads to bind to the active sites on actin. For cross bridges to form, tropomyosin must not block the active sites. The position of tropomyosin is controlled by the regulatory protein troponin. This protein-protein interaction couples the binding of calcium (to troponin) to the exposure of active sites.
In a neuromuscular junction, synaptic vesicles in the motor neuron contain which neurotransmitter?
acetylcholine (ACh) acetylcholine is the neurotransmitter found in neuromuscular junctions.
What causes the release of calcium from the terminal cisternae of the sarcoplasmic reticulum within a muscle cell?
arrival of an action potential Yes, an action potential in the T tubule causes the release of calcium from the terminal cisternae of the sarcoplasmic reticulum.
Which of the following hormones is currently thought to decrease plasma calcium levels in pregnant women and children?
calcitonin calcitonin is currently thought to decrease plasma calcium levels in children and pregnant women.
PTH promotes the formation of which hormone?
calcitriol parathyroid hormone promotes the formation of calcitriol.
An increase in sympathetic stimulation of the heart would increase stroke volume by increasing __________.
contractility Increased sympathetic activity increases heart contractility. This causes cardiac fibers to contract more forcefully at all levels of preload. Regardless of end diastolic volume, this mechanism increases stroke volume by reducing end systolic volume.
How would a decrease in blood volume affect both stroke volume and cardiac output?
decreased stroke volume and no change in cardiac output a decreased blood volume would decrease the end diastolic volume, thus lowering the stroke volume. Although this would initially lead to a decrease in the cardiac output, heart rate would increase because of increased activity of the sympathetic nervous system in an effort to maintain cardiac output.
What is the type of chemical reaction used to rebuild ADP into ATP?
dehydration synthesis a water molecule is removed, thus it is called dehydration synthesis. Building ATP from ADP requires a synthetic enzyme plus a source of energy to rebuild the high energy bond.
Where in the cross bridge cycle does ATP hydrolysis occur?
during the cocking of the myosin head As ATP is broken down, its energy is used to cock the myosin head in preparation for the next power stroke.
Which of the following would increase heart rate?
epinephrine and norepinephrine secreted by the adrenal medulla as a result of sympathetic stimulation, these hormones act as part of the sympathetic response, increasing heart rate.
What means of membrane transport is used to release the neurotransmitter into the synaptic cleft?
exocytosis the synaptic vesicles (where the neurotransmitter is stored) merge with the membrane and release the neurotransmitter by exocytosis.
Action potentials travel the length of the axons of motor neurons to the axon terminals. These motor neurons __________.
extend from the brain or spinal cord to the sarcolemma of a skeletal muscle fiber The cell bodies of motor neurons to muscles in the head and neck are located in the brain. The cell bodies of motor neurons to the rest of our muscles are located in the spinal cord.
Action potentials generated by the autorhythmic cells spread to the contractile cells through what structures in the membrane?
gap junctions action potentials generated by the autorhythmic cells spread waves of depolarization to contractile cells through gap junctions. If the depolarization causes the contractile cells to reach threshold, they will in turn generate an action potential.
Which of the following processes produces molecules of ATP and has two pyruvic acid molecules as end products?
glycolysis glucose is broken down in the process called glycolysis. This process takes place in the cytoplasm and does not require oxygen - hence it is called anaerobic respiration. If oxygen is available, the pyruvic acid moves into the mitochondria and glycolysis contributes to aerobic respiration.
Which of the following would NOT be a way that parathyroid hormone (PTH) could alter plasma calcium levels? (Which one of the following is FALSE?)
increase osteoblasts on bone This answer is false. PTH would NOT increase osteoblasts. Osteoblasts store calcium on bone, thus lowering plasma calcium levels.
How would an increase in the sympathetic nervous system increase stroke volume?
increased contractility an increase in sympathetic nervous system activity would increase contractility (by increasing available calcium), thus increasing stroke volume. Contractility causes an increase in stroke volume by decreasing end systolic volume; it does not change end diastolic volume.
Put the phases of the cardiac cycle in the correct order, starting after ventricular filling.
isovolumetric contraction, ventricular ejection, isovolumetric relaxation the ventricles must contract and eject blood before they relax and fill again.
What, specifically, is a cross bridge?
myosin binding to actin The attachment of a myosin head from the thick filament to an active site on actin on the thin filament is a cross bridge. As soon as the cross bridge forms, the power stroke occurs, moving the thin filament toward the center of the sarcomere.
What causes the power stroke?
release of ADP and Pi the hydrolysis of ATP provides the energy for the power stroke. Energy is transferred from ATP to the myosin head.
How is acetylcholine (ACh) removed from the synaptic cleft?
simple diffusion away from the synaptic cleft and acetylcholinesterase (AChE; an enzyme) Acetylcholinesterase breaks down acetylcholine in the synaptic cleft.
The action potential on the muscle cell leads to contraction due to the release of calcium ions. Where are calcium ions stored in the muscle cell?
terminal cisterns (cisternae) of the sarcoplasmic reticulum calcium is stored in the terminal cisterns (cisternae) of the sarcoplasmic reticulum until it is released by an action potential.
In order to cause cardiac muscle contraction, the contractile cells must also depolarize. What causes the depolarization of the contractile cells?
the flow of positive ions from adjacent cells the flow of positive ions from the autorhythmic cells (or adjacent cells) brings the membrane to threshold initiating depolarization of the contractile cell.
Acetylcholine binds to its receptor in the sarcolemma and triggers __________.
the opening of ligand-gated cation channels These channels permit sodium ions to diffuse inward and potassium ions to diffuse outward.
What is name given to the regularly spaced infoldings of the sarcolemma?
transverse or T tubules T tubules penetrate a skeletal muscle fiber and provide a pathway for excitation into the interior.
What does the QRS complex represent in the ECG wave tracing?
ventricular depolarization the QRS complex represents depolarization in the ventricles, which have greater mass than the atria.
When an action potential arrives at the axon terminal of a motor neuron, which ion channels open?
voltage-gated calcium channels the action potential opens voltage-gated calcium channels and calcium rushes into the axon terminal, leading to the release of the neurotransmitter.
Repolarization of an autorhythmic cell is due to the opening of which channels?
voltage-gated potassium channels opening of voltage-gated potassium channels causes positive potassium ions to move out of the cell. This efflux of potassium causes the cell to become more negative inside thus, repolarizing the cell.
Which type of muscle fiber has a large quantity of glycogen and mainly uses glycolysis to synthesize ATP?
white fast twitch fibers white fast twitch fibers have high glycogen content for a readily available source of glucose for glycolysis. They appear white because of the reduced amount of myoglobin and fewer capillaries surrounding them. Because these fibers have reduced myoglobin and very few capillaries surrounding them, they have very little oxygen available for the Krebs cycle and oxidative phosphorylation. They also have fewer mitochondria (where the Krebs cycle and oxidative phosphorylation would take place).
