Cardiac Physiology Lecture – Vocabulary Review

Vocabulary flashcards covering key terms from the lecture on cardiac muscle characteristics, heart conduction pathways, and autonomic regulation of heart function.

Contractility

The ability of muscle tissue to shorten and generate force, producing movement or pumping action.

Extensibility

The capacity of muscle fibers to be stretched or lengthened without damage.

Excitability

The property of muscle cells that allows them to respond to a stimulus by generating an electrical impulse.

Elasticity

The tendency of muscle tissue to recoil to its original length after being stretched.

Autorhythmicity

The capability of certain cardiac cells to depolarize spontaneously and rhythmically without external signals.

Myocardium

The muscular middle layer of the heart wall, comprising roughly 65 % of heart mass.

Contractile Myocardial Cells

The 99 % of heart muscle cells specialized to generate force and pump blood during each heartbeat.

Conductive (Conductile) Myocardial Cells

The 1 % of modified cardiac muscle cells that generate and rapidly transmit electrical impulses rather than contract forcefully.

Sinoatrial (SA) Node

A cluster of autorhythmic cells in the right atrium that initiates each heartbeat.

Pacemaker (of the heart)

Functional name for the SA node because it sets the heart’s intrinsic rhythm at about 100 beats per minute.

Internodal Pathways

Conductive tracts that distribute impulses from the SA node across both atria.

Atrioventricular (AV) Node

Node of conductive tissue at the atrial–ventricular junction that receives impulses from the atria.

Conduction Delay (AV nodal delay)

The slowing of impulse transmission in the AV node (~0.03 m/s) that allows ventricles time to fill before they contract.

Annulus Fibrosis

Fibrous rings that support heart valves and electrically insulate the atria from the ventricles.

Atrioventricular (AV) Bundle / Bundle of His

Bundle of conductive fibers that carries impulses from the AV node through the annulus fibrosis into the interventricular septum.

Bundle Branches

Left and right divisions of the AV bundle that conduct impulses down the septum to each ventricle.

Purkinje Fibers (Subendothelial Conductive System)

Fast-conducting fibers that distribute impulses from the bundle branches throughout ventricular myocardium, starting at the apex.

Conduction Velocity (0.3 m/s)

Average speed at which electrical impulses travel through ordinary myocardium.

Sympathetic Nervous System (cardiac)

Autonomic division that accelerates heart activity during stress or exercise.

Accelerators (T1–T6)

Sympathetic cardiac nerves originating from spinal segments T1–T6 that release norepinephrine.

Norepinephrine / Noradrenaline

Sympathetic neurotransmitter that increases sodium and calcium influx, raising heart rate and contractile force.

Chronotropic Effect

A change in heart rate produced by a stimulus (e.g., sympathetic stimulation increases rate).

Inotropic Effect

A change in the strength of cardiac contraction produced by a stimulus (e.g., calcium-mediated force increase).

Parasympathetic (Vagus) Nerve

Cranial nerve X providing most parasympathetic input to the heart, slowing its activity.

Acetylcholine

Parasympathetic neurotransmitter that opens potassium channels and decreases heart rate.

Cholinergic Receptors

Cardiac receptors that bind acetylcholine to mediate parasympathetic effects.

Hyperpolarization

Increase in membrane negativity due to potassium efflux, moving cells further from threshold and slowing depolarization.

Beta-1 Receptors

Cardiac adrenergic receptors that bind norepinephrine to increase heart rate and contractility.

Filling Time

Interval created by AV nodal delay that lets ventricles receive the final 30 % of blood before contraction.

Autorhythmic Rate (SA node ~100 bpm)

The intrinsic firing rate of SA node cells before any nervous or hormonal modulation.