Health Science 2211- Lecture 2

myocardium

spiral and circular bundles

organized manner

when an electrical impulse moves across it

cardiomyocytes

short, fat, branched, striated cells with a central nucleus interconnected by intercalated discs

areas where the plasma membranes intermesh

• desmosomes
• gap junctions

tight seals that weld the plasma membranes together

ionic channels responsible for propagation of electrical signal from cell to cell during muscle contraction

enable synchronized contraction of muscle fibers (atria and ventricles contract at the same time)

plasma membrane of muscle cell

tiny invaginations of the sarcolemma that quickly spread electrical signal to all parts of the muscle fiber during contraction

myofibrils

consist of thick and thin filaments which are the contractile structure of muscle

• group of overlapping thin and thick filaments
• each sarcomere is found between 2 Z discs

when a thick and thin filaments overlap each other in a pattern

they slide past each other

single sequence of atrial contraction followed by a ventricular contraction

• special tissue called nodal tissue
• has characteristics of both nerve and muscle tissue

• self-excitable
• can generate electrical impulses without an external stimulus

in the cardiac conduction system

• it's the pacemaker of the heart
• cluster of cells in wall of right atrium

begins an action potential followed by contraction of both atria, expelling contents into ventricles

• transmits electrical signals to AV Bundle (bundle of His)
• located in atrial septum

• Bundle of His
• only place where signal can be transmitted from atria and ventricles

• systole: contraction
• diastole: relaxation; filling

a recording of the electrical changes that accompany the cardiac cycle

atrial contraction

rapid ventricular contraction

ventricular relaxation

Nervous

• hormones (epinephrine)
• age
• gender
• physical fitness
• body temperature