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Lecture 6

KINE 1P90 Lecture Notes - Lecture 6: Catecholamine, Sympathetic Nervous System, Ventricular Fibrillation

Physical Education and Kinesiology
Course Code
Klentrou Panagiota

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Electrical Activity of the Heart
Intrinsic Control
oMeans "starts from within"
oHeart controls function from within
Only muscle in the body that does not depend on the brain to function
Generates its own electrical impulses from within
oCardiac muscle generates its own electrical signal: autoconduction
Generates its own action potentials
oContracts without nervous stimulation
o1% of cardiac muscle cells are specialized and spontaneously initiate contraction
Autorhythmic Cells
Contractile cells are 99% of the cardiac muscle cells and do the
mechanical work
Autorhythmic cells are 1% of the cardiac muscle cells
Autorhythmic cells do not have a resting potential bit rather they have a
pacemaker potential
Unlike other cells with a resting potential (a stable electric
difference across the membrane), cells with a pacemaker potential have an
electric difference across the membrane that is constantly changing, by
Continuous depolarization
The electric charge across the cell membrane is constantly
changing , due to the movement of potassium, sodium, and calcium ions
across the membrane
When the cycle starts, the cell has a negative electrical charge of
about -60mV, this means;
At the beginning of the cycle, the inside of the cell is
-60mV relative to the outside
On the inside there is a high concentration of potassium
ions and on the outside there is a high concentration of sodium ions
How do action potentials occur in the pace maker cells
To reach threshold, ion gated in the membrane must
open, permitting ions to move from one side to the other
There is a constant slow influx of sodium
regardless of the membrane potential
There is a constant efflux of potassium
Before the threshold is reached, voltage gated
calcium channels (t-type) open for a short time, this leads to a
brief influx of calcium and threshold is released
\Their membrane potential depolarizes slowly, or drifts, until threshold is
reached and an action potential results
This drift and the resulting action potential occurs in repeating cycles.
The action potentials spread throughout the heart and trigger its repetitive beating
oAutoconduction System
5 specialized tissues in the heart
They generate and distribute the electrical impulses
Electrical impulses stimulate the heart muscle to contract
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