Module 1 Flashcards
The heart is composed of three layers:
- The inner layer is the endocardium.
- The middle layer is the myocardium.
- The outer layer is the epicardium.
The muscular layers contain specialized
electrical cells of the cardiac conduction system
Electrical cells of the cardiac conduction system are responsible for
automaticity, contractility, and conductivity,
automaticity, contractility, and conductivity, function together to produce
contractions sequentially.
The electrical conduction system of the heart synchronizes
the atria and ventricles to properly empty and fill the ventricles.
specialized myocardial conduction cells form
bundles of fibers that spread the action potential to the muscles. This electrical signal contracts the muscles in the atria and ventricles.
The action potential has two phases
depolarization (activation) and repolarization (recovery)
Specific cellular ion channels open and close during depolarization and repolarization as an
action potential travels throughout the heart
electrolytes (sodium (Na+), potassium (K+), and calcium (Ca2+)) exchange between intracellular /extracellular
ions are
polarized charged particles that generate the electrical activity of the action potential.
These electrical currents transmitted to the skin’s surface and recorded using electrodes during an EKG. However, only atrial and ventricular contractions record since other electrical impulses are too small to deliver towards the skin surface.
SA node - sinoatrial node
- small oval structure
- located in right atrium
- contains highly specialized cells - able to depolarize without stimulation or discharge.
Automaticity
spontaneous depolarization of an action potential.
SA node can activate an action potential about
- 70 times or beats per minute,
- considered the primary pacemaker of the heart.
The autonomic nervous system can modify the rate of
spontaneous depolarization of the SA node.
Stimulation of the sympathetic nervous system during vigorous exercise or excitement does what to the SA node.
While the parasympathetic nervous system during activities such as resting or sleeping does this to the SA node
increases the rate while parasympathetic cause a decrease.
Sympathetic and parasympathetic divisions of the ANS have opposite effects on the body and keep the body in
homeostasis
Three branches of autonomic nervous system
Sympathetic, parasympathetic, and enteric
Parts of the atrial myocardium, the muscle surrounding the AV node, and the His-Purkinje network also have
automaticity and the ability to serve as secondary pacemakers for the heart.
The fastest pacemaker, the SA node, determines
the heart rhythm
The SA node will reset the secondary pacemakers because
it will depolarize first
. The pacemaker rate decreases with
increased distance from the SA node and is slowest in the Purkinje fibers.
An escape rhythm occurs when
an ectopic rhythm ( 3 or more ectopic beats produced from an ectopic focus )replaces a normal sinus rhythm.
If a secondary pacemaker other than the SA node produces an action potential resulting in myocardial depolarization, that structure is the
ectopic focus and produces ectopic beats
An ectopic rhythm occurs if
three or more ectopic beats produce from the ectopic focus.
An increased vagal tone causes
Why?
- slower automaticity of the SA node
- slower conduction through the AV node,
- results in a lower heart rate.
- Increased vagal tone activates parasympathetic nervous system
- higher Vagal tone - can relax faster after stress
