Cardiac Physiology

what are the types of Muscle Tissue

Cardiac, Skeletal, and Smooth.

Traits of Muscle Tissue

All muscle tissues share four traits: Irritability, Contractility, Extensibility, and Elasticity.

Connections in Cardiac Muscle

Cardiac muscle cells are connected by intercalated discs.

Fatigue in Cardiac Muscle

Cardiac muscles do not get fatigued like skeletal muscles because they contract longer and do not go into tetanus.

Importance of Calcium in Cardiac Muscle

Calcium is important in cardiac muscle because it triggers contractions.

Electrical Linkage in Cardiac Cells

Cardiac cells are electrically linked for synchronized contraction.

Heart Type

The heart is myogenic, meaning it beats on its own.

SA Node

The SA Node is the natural pacemaker of the heart, setting the rhythm at approximately 70–80 bpm.

Autorhythmic Cells Function

Autorhythmic cells leak ions and depolarize on their own, making the heart beat without nerves.

Electrical Pathway of the Heart

The electrical path through the heart is: SA Node → AV Node → Bundle of His → R/L Bundle Branches → Purkinje Fibers.

Function of the AV Node

The AV Node delays the impulse to allow the atria to contract before the ventricles.

Role of Purkinje Fibers

Purkinje fibers spread the signal through the ventricles for synchronized contraction.

SA Node Failure

If the SA node fails, the AV node or Purkinje fibers take over as ectopic pacemakers, but at a slower pace.

Sympathetic Nervous System and Heart Rate

The sympathetic nervous system speeds up the heart rate.

Parasympathetic Nervous System and Heart Rate

The parasympathetic nervous system slows down the heart rate, mainly via the vagus nerve.

ECG Measurement

An ECG measures electrical activity, not contraction.

P Wave in ECG

The P Wave represents atrial depolarization.

QRS Complex in ECG

The QRS Complex represents ventricular depolarization.

T Wave in ECG

The T Wave represents ventricular repolarization.

Types of Electrical Cells in the Heart

The three electrical cell types in the heart are Nodal (starts signal), Conductile (spreads it), and Contractile (contracts).

Nodal Cells

Nodal cells have an unstable resting membrane potential (RMP) and are self-depolarizing.

Contractile Cells

Contractile cells have a stable resting membrane potential (RMP), a sharp action potential spike, and a long plateau for strong contraction.

Supraventricular Arrhythmias

Supraventricular arrhythmias start in the SA node, AV node, or atria.

Ventricular Arrhythmias

Ventricular arrhythmias start in the Bundle of His, bundle branches, Purkinje fibers, or ventricles.

Danger of Arrhythmias

Ventricular arrhythmias are more dangerous than supraventricular arrhythmias, such as ventricular fibrillation.