1. Cardiac Action Potential
By Jenny R. Sheriff, EMT-P, I/c

2. Action Potential The ability of a muscle cell to depolarize
Happens in 3 stages
Stimulation
Depolarization
Repolarization

3. Regulatory Properties
Chronotropic state
Rate of contraction
Dromotropic state
Rate of electrical conduction
Inotropic state
Strength of contraction (contractility)

4. Regulatory Properties
Controlled by the brain
Autonomic NS
Sympathetic
Parasympathetic
Endocrine system
Insulin
Sympathetic nervous system – fight or flight. Major neurotransmitters are epinephrine and norepinephrine, which are classified as catecholemines.These are made in the adrenal glands which lie on top of the kidneys and secreted by the adrenal medulla.
Parasympathetic NS – feed or breed. Neurotransmitter is acetylcholine, which is produced in the brain and nerves. Glucose plays a part in production of acetylcholine. Acetylcholine is classified as a cholinergic.

5. Receptors Triggered by changes in chemicals or pressure
Are found throughout the body

6. Baroreceptors Sense changes in pressure and send signals to the brain.
Aortic Arch
Carotid Sinus
Changes in pressure against the walls of the aorta (particularly in the arch) and the carotid sinus cause the baroreceptors to signal the brain to act. For example, if the blood pressure drops, baroreceptors signal the brain. The brain then sends a signal to the parasympathetic NS via the vagal nerve to inhibit acetylcholine, which increases the availability of catecholemines, resulting in increased HR, peripheral vasoconstriction, and increased BP.

7. Chemoreceptors Sense chemical changes Acid/base balance
Chemoreceptors can be found throughout the vascular system and in the brain. They sense chemical changes, like CO2 and O2, and try to make the body compensate for the changes.

8. Adrenergic Receptors Alpha 1 Alpha 2 Beta 1 Beta 2
Peripheral vasoconstriction
Alpha 2
Peripheral vasodilation
Beta 1
Increases HR, conductivity, automaticity, and contractility
Beta 2
Bronchodilation
In cases of acidosis, the chemoreceptors in the brain identify increased levels of CO2 and trigger the sympathetic nervous system. RR increases, while sympathetic outflow to the heart is also triggered, resulting in increased HR, via the vagus nerve and adrenergic receptors on the heart.

9. Ions Na is the major extracellular ion
K is the major intracellular ion
Ca is an extracellular ion necessary for neurologic and muscle function
Ca can enter cells through calcium channels and into the sarcoplasmic reticulum of cardiac muscle fibers, resulting in muscle contraction. Ca is regulated through the parthyroid hormone.

10. Cardiac Action Potential
Electrical Potential
Polarized state
Depolarization
Repolarization

11. Electrical Potential
The difference between the electrical charges on opposite sides of a cell wall.

12. Polarized State Resting phase
The inside of the cell has a negative charge in relation to the outside of the cell
The polarized state is the electrical charge of the cell when it’s at rest. This is true for all muscle cells.

13. Depolarization Muscle contraction
The charge inside the cell becomes positive in relation to the outside of the cell
During depolarization, neurons stimulate fast NA channels open, allowing an influx of sodium to enter the cell. Calcium also enters the cell, and small amounts of potassium leave the cell. The calcium acts on actin and myosin filaments, causing muscle contraction.

14. Repolarization Sodium/potassium pump Muscle begins to relax
Refractory period
Absolute refractory period
Relative refractory period
In repolarization, ATP is used to pump potassium and sodium against the concentration gradient. That is, potassium is pumped back into the cell and sodium is pumped back out through the sodium/potassium pump.

16. Scenario
Your 60 yof patient is c/o chest pain and flu like symptoms. She states she has been taking calcium supplements because she is afraid of osteoporosis. She’s been taking these for about a year. She states severe diarrhea for the last week, with some vomiting. She also feels weak and seems lethargic.

17. Scenario
Your patient is a 54 yom c/o chest pain. Hx of diabetes, CAD, HTN, lung CA.

18. Questions??