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Questions and Answers
What is a unique characteristic of cardiac muscle?
What is a unique characteristic of cardiac muscle?
- It is striated and voluntary.
- It is striated and interconnected. (correct)
- It is non-striated and branched.
- It is smooth and involuntary.
What is the function of intercalated discs in cardiac muscle?
What is the function of intercalated discs in cardiac muscle?
- They insert into bones.
- They anchor cardiac cells together. (correct)
- They act as tendons.
- They separate cardiac cells.
What is a characteristic of heart muscle behavior?
What is a characteristic of heart muscle behavior?
- It has a short refractory period.
- It is stimulated by hormones.
- It contracts independently.
- It behaves as a functional syncytium. (correct)
What is the duration of the absolute refractory period in heart muscle?
What is the duration of the absolute refractory period in heart muscle?
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What type of ions is involved in the rising phase of the action potential in autorhythmic cells?
What type of ions is involved in the rising phase of the action potential in autorhythmic cells?
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What is the function of the sinoatrial (SA) node?
What is the function of the sinoatrial (SA) node?
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Where do the bundle branches split?
Where do the bundle branches split?
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What is recorded by electrocardiogram (ECG)?
What is recorded by electrocardiogram (ECG)?
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What corresponds to ventricular repolarization in the ECG?
What corresponds to ventricular repolarization in the ECG?
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Study Notes
Cardiac Muscle Characteristics
- Cardiac muscle is striated, short, fat, branched, and interconnected
- Connective tissue endomysium acts as both tendon and insertion
- Intercalated discs anchor cardiac cells together and allow free passage of ions
- Heart muscle behaves as a functional syncytium
Properties of Heart Muscle
- Heart muscle is stimulated by nerves and is self-excitable (automaticity)
- Contracts as a unit
- Has a long (250 ms) absolute refractory period
- Contraction is similar to skeletal muscle contraction
Intrinsic Conduction System
- Autorhythmic cells initiate action potentials
- Unstable resting potentials called pacemaker potentials
- Use calcium influx for rising phase of the action potential
SA Node and AV Node
- Sinoatrial (SA) node generates impulses about 75 times/minute
- Atrioventricular (AV) node delays the impulse approximately 0.1 second
Electrical Conduction
- Impulse passes from atria to ventricles via the atrioventricular bundle (bundle of His)
- AV bundle splits into two pathways in the interventricular septum (bundle branches)
- Bundle branches carry the impulse toward the apex of the heart
- Purkinje fibers carry the impulse to the heart apex and ventricular walls
Regulation of Heart Rate
- Heart is stimulated by the sympathetic cardioacceleratory center
- Heart is inhibited by the parasympathetic cardioinhibitory center
Electrocardiogram (ECG)
- Electrical activity is recorded by electrocardiogram (ECG)
- P wave corresponds to depolarization of SA node
- QRS complex corresponds to ventricular depolarization
- T wave corresponds to ventricular repolarization
- Atrial repolarization record is masked by the larger QRS complex
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