MCAT Biology › Heart
Which group of cells is responsible for the autoregulation of heart contraction?
Sinoatrial node
Atrioventricular node
Bundle of His
Purkinje fibers
The heart beats automatically through stimulation from the sinoatrial node. The group of neurons found in this node depolarize in a coordinated, spontaneous manner to allow for the contraction of the atria and ventricles in the heart. Without the sinoatrial node, heart contraction may be possible, but it would not be regular and would require additional regulation.
Depolarization of the sinoatrial node specifically leads to atrial contraction. The signal is then transmitted through the atrioventricular node and bundle of His to the purkinje fibers, which coordinate the contraction of the ventricles.
Blood returning from the lungs enters into which chamber of the heart?
Left atrium
Right atrium
Left ventricle
Right ventricle
Oxygenated blood returning to the heart from the lungs enters the left atrium. It then goes to the left ventricle and out the aorta.
Which of the following accurately shows the electrical pathway through the heart?
SA node, AV node, bundle of His, purkinje fibers
Purkinje fibers, SA node, AV node, bundle of His
Purkinje fibers, bundle of His, AV node, SA node
AV node, SA node, bundle of His, purkinje fibers
The correct electrical path through the heart is the SA (sinoatrial) node, AV (atrioventricular) node, bundle of His (AV bundle), then purkinje fibers.
The sinoatrial node initiates the electrical signal and acts as the heart's natural pacemaker. Innervation from the parasympathetic nervous system is crucial in maintaining a normal heart rate from the SA node, but is not required to initiate electrical signals. The signal travels to the atrioventricular node and is briefly delayed, allowing the atria to finish contracting before initiaing ventricular systole. The signal travels down the bundle of His and is quickly distributed to the purkinje fibers, which initiate ventricular systole.
Which nerve, as part of the parasympathetic nervous system, serves to decrease heart rate?
Vagus nerve
Radial nerve
Subcostal nerve
Femoral nerve
The vagus nerve is a major nerve of the parasympathetic nervous system, responsible for mediating numerous responses in the body. In relation to the heart, the vagus nerve provides constant inhibition to the sinoatrial node, slowing the heart rate. The sinoatrial node naturally fires at about 80 to 100 beats per minute, while a healthy resting heart rate is closer to 60 due to innervation by the vagus nerve.
The radial nerve is located in the forearm; the femoral nerve is located in the thigh; the subcostal nerve is located along the lower ribs.
What specialized area of tissue delays the proliferation of electrical stimulation in the heart, allowing the heart chambers to fill with blood?
Atrioventricular node
Sinoatrial node
Purkinje fibers
Bundle of His
Bundle branches
The atrioventricular (AV) node is located in the lower intratrial septum and receives impulses from the sinoatrial node. The sinoatrial node is termed the pacemaker of the heart and is located in the wall of the right atrium. It initiates normal heart beats and is innervated by the vagus nerve, which helps control the rate of impulses. Once an impulse causes the atria to contract, it travels to the atrioventricular node. Once the AV node receives the impulse, cellular mechanisms initiate a delay. This prevents simultaneous atrial and ventricular systole, allowing the ventricles to receive the blood exiting the contracted atria. Following the delay, the impulse travels from the AV node to the bundle of His.nThe bundle of His is a pathway for electrical signals to be transmitted to the ventricles. The Purkinje fibers spread through the myocardium and distribute electical stimuli to cause contraction of the ventricular myocardium. The bundle branches supply the two ventricles with electrical stimuli.
Which of the following is true about cardiac muscle?
It is striated
It is voluntary
Each muscle cell contains multiple nuclei
It does not utilize sarcomeres
All of these are true about cardiac muscle
The correct answer is "it is striated." Similiar to skeletal muscle, cardiac muscle is striated. It has only one nucleus per cell, and its action is involuntary. Futhermore, it is composed of sarcomeres, which give it its striated appearance.
Both the sympathetic and the parasympathetic nervous systems are essential for homeostasis and for survival. For example, when we are trying to run away from a threat, the sympathetic nervous system is in full effect to allow us to escape from danger. However, when there is no obvious threat, the parasympathetic nervous system tends to be more in control.
There are similarities and differences between the sympathetic and the parasympathetic nervous systems. In preganglionic nerve fibers, both the sympathetic and the parasympathetic nervous system utilize the neurotransmitter acetylcholine. Closer to the target organ, the parasympathetic nervous system remains dependent on acetylcholine whereas norepinephrine and epinephrine are the predominant neurotransmitters utilized by the sympathetic nervous system.
When norepinephrine and epinephrine bind to their receptors, different effects are carried out based on the type of receptor, affinity, and location of the receptor. For example, epinephrine has a higher affinity for the beta-2 receptor. When epinephrine binds to the beta-2 receptor, common effects include vasodilation and bronchodilation. Norepinephrine has a stronger affinity for the alpha-1, alpha-2 and beta-1 receptors. When norepinephrine binds to its receptor, common effects on the body include vasoconstriction (alpha-1), increased heart rate (beta-1) and uterine contraction (alpha-1).
In patients with heart failure, the physician might prescribe a beta blocker to help with the condition. How will a beta blocker be useful in patients with heart failure?
Blocking the beta-1 receptor, which prevents the heart from having to work as hard.
Blocking the beta-2 receptor, which prevents the heart from having to work as hard.
Blocking the beta-2 receptor, which will make the heart work harder.
Blocking the beta-1 receptor, which will make the heart work harder.
Blocking the beta-1 receptor, which will cause vasoconstriction.
The heart has the beta-1 receptor on its surface. When norepinephrine binds to beta-1 receptors on the heart, the effect is an increase in heart rate. In patients with a heart problem, increasing the heart rate might exhaust the heart and provoke heart failure. By blocking this receptor with a beta blocker, agonists to the beta-1 receptor cannot increase the heart rate.
Which valve in the heart separates the right atrium from the right ventricle?
Tricuspid valve
Bicuspid valve
Pulmonic valve
Mitral valve
The tricuspid valve separates the right atrium from the right ventricle. The bicuspid valve (also known as the mitral valve) separates the left atrium from the left ventricle. The pulmonic valve separates the right ventricle from the pulmonary artery and the aortic valve separates the left ventricle from the aorta (these are known as the semilunar valves).
Which cardiac valve prevents backflow of blood from the left ventricle into the left atrium?
Mitral Valve
Tricuspid Valve
Pulmonary Valve
Aortic Valve
This a simple anatomy question. The mitral (bicuspid) valve lies between the left atrium and ventricle, therefore the answer must be the mitral valve. The tricuspid valve lies between the right atrium and ventricle.
What are the valves between the right atrium and right ventricle, and between the left atrium and left ventricle, respectively?
Tricuspid valve; mitral valve
Bicuspid valve; tricuspid valve
Mitral valve; pulmonary valve
Aortic valve; bicuspid valve
The valve between the right atrium and ventricle is the tricuspid valve. The valve between the left atrium and ventricle is called the bicuspid, or mitral, valve. "Bicuspid" and "mitral" can be used interchangeably.
The pulmonary valve connects the right ventricle with the pulmonary artery, while the aortic valve connects the left ventricle with the aorta.