Cardiac Electrical Activity and Rhythm

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Questions and Answers

What does the QRS complex in an ECG specifically represent?

Ventricular depolarization and atrial repolarization simultaneously (correct)

Atrial depolarization only

Ventricular repolarization only

Atrial repolarization only

Which part of the heart is primarily responsible for initiating a rhythm at a rate of 60-100 BPM?

Sinus node (correct)

AV node

Atrial tissue

Ventricular tissue

What occurs during atrial depolarization in relation to arterial pressure?

It leads to a large increase in blood volume in vessels.

It causes a significant decrease in ventricular pressure.

It has no effect on arterial pressure.

It results in a slight increase in pressure on ventricular walls. (correct)

Which neurotransmitter is involved in the sympathetic stimulation of the heart?

Norepinephrine (NE) (A) Signup and view all the answers

What is the primary effect of parasympathetic influence on heart rate?

Decrease the heart rate through vagal influence (B) Signup and view all the answers

Which physiological change occurs during the onset of exercise related to heart rate?

Inhibition of parasympathetic nervous system (C) Signup and view all the answers

How does the AV node function in terms of heart rhythm and intrinsic rate?

Acts as a backup pacemaker at 20-40 BPM (D) Signup and view all the answers

What is the impact of sympathetic control on blood flow through small arteries and arterioles?

Causes vasoconstriction in inactive tissues (A) Signup and view all the answers

Which event primarily triggers ventricular depolarization in the cardiac cycle?

Atrial depolarization (D) Signup and view all the answers

What abnormality in the ST segment can indicate a myocardial infarction (MI)?

ST segment depression (B) Signup and view all the answers

What is the intrinsic rate of the AV node?

40-60 BPM (B) Signup and view all the answers

Which of the following describes the relationship between ventricular contraction and electrical signaling?

Ventricular depolarization and atrial depolarization occur simultaneously. (C) Signup and view all the answers

What effect does sympathetic stimulation have on heart rate?

Increases heart rate by accelerating SA node depolarization. (B) Signup and view all the answers

During exercise, how does the parasympathetic nervous system influence heart rate?

Inhibits HR by enhancing vagal influence. (A) Signup and view all the answers

Which mechanism is primarily responsible for vasoconstriction in inactive tissues?

Catecholamine effect via adrenergic fibers. (B) Signup and view all the answers

What occurs immediately following atrial depolarization in terms of blood pressure changes?

A transient increase in ventricular pressure is generated. (B) Signup and view all the answers

What is the typical heart rate range during intense physical activity for a well-conditioned individual?

20-200 BPM (B) Signup and view all the answers

ST segment depression in an ECG may indicate which of the following conditions?

Myocardial infarction. (B) Signup and view all the answers

What type of response does the heart exhibit when the sympathetic nervous system is activated?

Tachycardia with enhanced contractility. (D) Signup and view all the answers

Study Notes

Heart Electrical Activity

Ventricular contraction begins 0.06 seconds after stimulation.
Electrocardiogram (ECG/EKG) records electrical heart activity.
- P wave: Atrial depolarization.
- QRS complex: Ventricular depolarization and atrial repolarization occur simultaneously.
- T wave: Ventricular repolarization.
- ECG abnormalities may indicate coronary heart disease.
  - ST segment depression can indicate a myocardial infarction (MI).

Heart Rhythm Areas

Sinus node: 60-100 BPM
Atrial Tissue: 60-100 BPM
AV node: 40-60 BPM
Ventricular Tissue: 20-40 BPM

Heart Rate Regulation

Extrinsic Neural Influences: Superimpose on inherent myocardial rhythm.
- Range: 20-200 BPM, dependent on physical fitness.
Sympathetic Stimulation:
- Catecholamines (NE/Epinephrine)
- Tachycardia:
  - Increases SA node depolarization, increasing the heart rate.
  - Increases contractility.
Parasympathetic Influence:
- Acetylcholine (Vagal Influence)
- Bradycardia:
  - Slows SA node depolarization, decreasing heart rate.

Parasympathetic Nervous System

Periphery:
- Excitation: Iris, gallbladder, coronary arteries.
- Inhibition: Gut sphincters, intestines, and skin vasculature.
- During exercise onset, heart rate increases by inhibition of the parasympathetic nervous system.

Sympathetic Nervous System

Mechanism: NE via adrenergic fibers within smooth muscle of small arteries, arterioles and precapillary sphincters.
- Inactive Tissue (Vasoconstriction): Renal, splanchnic, and inactive skeletal muscle.

Heart Electrical Activity & ECG

Ventricles contract 0.06 seconds after stimulation.
Electrocardiogram (ECG/EKG) records the heart's electrical activity.
- P wave: Atrial depolarization.
- QRS complex: Ventricular depolarization and atrial repolarization occur simultaneously.
- T wave: Ventricular repolarization.
- ECG abnormalities can indicate coronary heart disease.
  - ST segment depression might suggest a myocardial infarction (MI).

Heart Pressure Changes & ECG

Atrial depolarization triggers atrial contraction, leading to a slight increase in blood volume.
This volume increase slightly raises pressure on the ventricular walls.
Ventricular depolarization causes contraction, generating maximum pressure.
Ventricular repolarization signals the end of ventricular contraction.

Heart Rhythm Initiation & Intrinsic Rate

The slower the intrinsic rate of the tissue, the lower on the heart it is located.
Sinus node: 60-100 beats per minute (BPM).
Atrial tissue: 60-100 BPM.
AV node: 40-60 BPM.
Ventricular tissue: 20-40 BPM.

Extrinsic Heart Rate Regulation

Neural influences adjust the inherent rhythm of the myocardium.
- Accelerate heart rate (HR) in anticipation of exercise.
- Adjust HR as exercise intensity changes.
HR range: 20-200 BPM (dependent on physical fitness).

Sympathetic & Parasympathetic Control

Sympathetic stimulation:
- Releases catecholamines (norepinephrine/epinephrine).
- Results in tachycardia:
  - Increases SA node depolarization, leading to faster HR.
  - Increases contractility.
Parasympathetic influence:
- Releases acetylcholine (vagal influence).
- Results in bradycardia:
  - Slows SA node depolarization, leading to slower HR.

Exercise & Blood Flow

During the onset of exercise, heart rate increases due to inhibition of the parasympathetic nervous system.

Parasympathetic Neural Control

Periphery:
- Excitation of iris, gallbladder, and coronary arteries.
- Inhibition of gut sphincters, intestines, and skin vasculature.

Sympathetic Control on Blood Flow

Norepinephrine (NE) via adrenergic fibers located in the smooth muscle of small arteries, arterioles, and precapillary sphincters.
Inactive tissue (vasoconstriction):
- Renal, splanchnic, and inactive skeletal muscle.

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Description

Explore the fundamentals of heart electrical activity and rhythm in this quiz, focusing on the components of an electrocardiogram (ECG) such as the P wave, QRS complex, and T wave. Understand the physiological significance of heart rate regulation and the impact of neural influences and catecholamines on cardiac function.