NEUROTRANSMITTER released from the parasympathetic nervous system.
ANOMALOUS (INWARD) RECTIFICATION
A DECREASE in potassium permeability that occurs when the ELECTRICAL OR CHEMICAL DRIVING FORCE on potassium is INCREASED. This is an inherent property of the cardiac cell membrane
A disturbance in the normal electrical activity of the heart due to either abnormal 1) IMPULSE FORMATION or 2) IMPULSE CONDUCTION or 3) BOTH.
An INTRINSIC property of SPECIALIZED cardiac cells to INITIATE their own electrical activity i.e., PACEMAKER activity.
Heart rate of less than 60 beats/minute.
Affecting the pacemaker RATE (frequency).
The spread of electrical activity FROM CELL TO CELL in the heart.
The speed with which conduction occurs; expressed in meters/second. CONDUCTION VELOCITY IS INVERSELY RELATED TO CONDUCTION TIME.
DELAYED AFTERDEPOLARIZATION (DAD)
A transient depolarization of the membrane FOLLOWING an action potential. DADs are an ABNORMAL form of electrical activity caused by ABNORMALLY HIGH INTRACELLULAR Ca2+.
When the membrane potential becomes more POSITIVE than the resting membrane potential.
DIASTOLIC DEPOLARIZATION (phase 4)
A SLOW depolarization of the membrane potential that is responsible for the AUTOMATICITY of cardiac PACEMAKER cells
A general term that refers to any CARDIOTONIC STEROID or GLYCOSIDE that INCREASES THE CONTRACTILE FORCE OF THE MYOCARDIUM (heart).
EARLY AFTERDEPOLARIZATION (EAD)
A transient depolarization of the membrane DURING the later portion of the plateau phase or phase 3 repolarization of an action potential. EADs are abnormal electrical events that may underlie some types of prolonged Q-T syndrome and other dysrhythmias.
EFFECTIVE REFRACTORY PERIOD (absolute refractory period)
The period of TIME during an action potential when a stimulus (regardless of strength) CANNOT produce a REGENERATIVE action potential.
The ELECTRICAL POTENTIAL and CONCENTRATION GRADIENT acting on ion to cross the membrane; these TWO factors influence the movement of ions ACROSS the membrane (ionic current flow).
A THEORETICAL value at which the CONCENTRATION GRADIENT and the ELECTRICAL GRADIENT acting on a SINGLE ION are balanced. This value is calculated by the NERNST EQUATION
When the membrane potential becomes more NEGATIVE than the resting membrane potential.
Affecting the CONTRACTILITY of muscular tissue.
Visualized as PORES within the sarcolemma through which ions move into and out of a cell.
The flow of ions ACROSS the sarcolemmal membrane via ION CHANNELS; POSITIVE ions flowing into the cell represent INWARD CURRENT and POSITIVE ions flowing out of the cell represent OUTWARD CURRENT.
Reduced BLOOD FLOW to a region of tissue or an entire organ, usually as a result of an obstruction, such as a narrowed artery. Not synonymous with a lack of oxygen (hypoxia).
Neurotransmitter released from the SYMPATHETIC nervous system.
When a pacemaker cell is electrically stimulated at a rate FASTER than its own intrinsic rate (OVERDRIVE), stopping the stimulation results in a temporary SUPPRESSION of pacemaker activity.
RATE OF RISE (dV/dt)
This term refers to the RATE OF VOLTAGE CHANGE during the action potential UPSTROKE; expressed in volts/second. DO NOT CONFUSE THIS TERM WITH SPONTANEOUS RATE.
RE-ENTRY OF EXCITATION
An ABNORMAL form of CONDUCTION in which an impulse will RE-EXCITE PREVIOUSLY EXCITED tissue, resulting in SUSTAINED REPETITIVE activity.
RELATIVE REFRACTORY PERIOD
The period of TIME during an action potential when a stimulus can produce SOME TYPE of REGENERATIVE action potential.
When the membrane potential RETURNS to more negative levels FOLLOWING a depolarization.
RESTING MEMBRANE POTENTIAL
The electrical potential DIFFERENCE across a cell membrane; the INSIDE BEING NEGATIVE with respect to the outside positive
The plasma membrane of a muscle cell.
A protein within the sarcolemma which functions to REMOVE SODIUM from the inside the cell and to RESTORE POTASSIUM to the inside of the cell. The movement of sodium and potassium are COUPLED and METABOLIC ENERGY (ATP) is required.
A protein in the sarcolemma which extrudes INTRACELLULAR Ca2+ from the cell in EXCHANGE for EXTRACELLULAR SODIUM flowing down its concentration gradient into the cell. This process DOES NOT depend DIRECTLY on metabolic energy.
The FREQUENCY (beats/minute) of pacemaker activity. DO NOT CONFUSE THIS TERM WITH RATE OF RISE OR CONDUCTION VELOCITY.
Heart rate greater than 100 beats/minute
The membrane potential at which a REGENERATIVE action potential is produced. This value depends on the type of action potential (slow vs. fast) as well as the ionic environment or presence of drugs.
ABNORMAL form of PACEMAKER activity usually lasting a short time, resulting from DADs or EADs.