Health Science 2211- Lecture 2
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what is the cardiac muscle called that forms the wall of the heart?
how are the muscles arranged in the myocardium?
spiral and circular bundles
The heart's four chambers must beat in an ______________.
When does a chamber of the heart contract?
when an electrical impulse moves across it
Concentric layers of cardiac muscle cells are called?
Describe the structure of cardiomyocytes.
short, fat, branched, striated cells with a central nucleus interconnected by intercalated discs
what are intercalated discs?
areas where the plasma membranes intermesh
what are the 2 ways that intercalated discs connect adjacent cardiac muscle cells?
tight seals that weld the plasma membranes together
Define gap junctions.
ionic channels responsible for propagation of electrical signal from cell to cell during muscle contraction
what does intercalated discs enable?
enable synchronized contraction of muscle fibers (atria and ventricles contract at the same time)
what is the sarcolemma?
plasma membrane of muscle cell
what are T (transverse) tubules?
tiny invaginations of the sarcolemma that quickly spread electrical signal to all parts of the muscle fiber during contraction
Muscle fibers are filled with bundles of threads called?
what do myofibrils consist of?
consist of thick and thin filaments which are the contractile structure of muscle
what is a sarcomere? (structure in myofibrils) Where is it found? (2)
- group of overlapping thin and thick filaments
- each sarcomere is found between 2 Z discs
what are striations?
when a thick and thin filaments overlap each other in a pattern
what happens to filaments during contraction and relaxation of the muscles?
they slide past each other
what is the heartbeat?
single sequence of atrial contraction followed by a ventricular contraction
what controls the heartbeat? Describe it.
- special tissue called nodal tissue
- has characteristics of both nerve and muscle tissue
Cardiac muscle cells in nodal tissue are authorthytmic, what does this mean?
- can generate electrical impulses without an external stimulus
where are the authorthytmic nodal cells located?
in the cardiac conduction system
What is the Sinoatrial (SA) node and where is it located?
- it's the pacemaker of the heart
- cluster of cells in wall of right atrium
what is the function of the SA node?
begins an action potential followed by contraction of both atria, expelling contents into ventricles
What is the atrioventricular (AV) node? and where is it located?
- transmits electrical signals to AV Bundle (bundle of His)
- located in atrial septum
what is the atrioventricular (AV) bundle?
- Bundle of His
- only place where signal can be transmitted from atria and ventricles
what is the difference between systole and diastole?
- systole: contraction
- diastole: relaxation; filling
what is the ECG or EKG?
a recording of the electrical changes that accompany the cardiac cycle
what does the P wave indicate?
what does the QRS complex indicate?
rapid ventricular contraction
what does the T wave indicate?
______________ system can increase or decrease heart rate.
what 5 things influence heart rate?
- hormones (epinephrine)
- physical fitness
- body temperature
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