Exam 1 Review:  Chapter 18:  Histology of the Heart

cardiac muscle tissue - The specialized involuntary, striated, uninucleate, contractile cells/fibers and the specialized conduction or pacemaker cells/fibers which comprise the bulk of the tissue of the heart; forming the myocardium in which the contractile cells are connected to each other by intercalated discs; autorhythmic.

contractile fibers - One of the two types of cardiac muscle cells; the majority of cardiac muscle cells which are involuntary, striated, branched, uninucleate cells connected to each other by intercalated discs and specialized to constrict by means of the sliding filament mechanism using actin and myosin proteins; contractile fibers are rapid in contraction and relaxation, have a long refractory period, do not readily fatigue, and are autorhythmic.

cell nucleus - The large, membrane-bound, usually oval or spherical organelle within the cytoplasm of (almost all) living cells, containing the cell's hereditary material (DNA in the form of chromosomes) and controlling tthe cell's metabolism, growth, and reproduction.

sarcomere - One of the segments into which a myofibril of striated muscle is divided; "the unit of contraction;" the sarcomere has dark a central A band split in the middle by the lighter H zone which contains the M line and, at each end, has one half of a lighter I band which is split by the Z line; the borders of the sarcomere are the Z lines. 

striations - The series of parallel lines or light and dark bands observed in the cytoplasm of striated muscle cells, the bands are perpendicular to the long axis of the muscle cell; the banding pattern is due to the orderly arrangement of contractile myofilaments organized into repeating sarcomeres within each myofibril.

myofibril.- The non-membrane-bound cell organelle of skeletal and cardiac muscle cells which is a long cylindrical mass of contractile protein fibers (actin + myosin), organized as a series of repeating sarcomeres,

myofilament - Any of the ultramicroscopic protein filaments, made up of actin and myosin, that are the structural units of a myofibril.

intercalated disc- the specialized intercellular junction between individual cardiac muscle cells which appears as a dark line in microscopic specimens; at the molecular level it contains both electrical synapses provided by gap junctions and structural connections provided by desmosomes and tight junctions.

gap junction - An intercellular junction which consists of a network of integral membrane protein channels called connexons which facilitate the cell-to-cell passage of small molecules, e.g., ions, small second messengers, etc., because these junctions are relatively non-selective in their permeability, i.e., they provide direct cytoplasmic connections; they are common in cardiac muscle and in some smooth muscle tissues.

desmosome - the specialized cell junction which links two cells by tying their outer cell membranes together with a tuft of intermediate filaments = tonofilaments embedded in a mass of dense anchoring material; desmosomes are particularly prevalent in tissues such as the epidermis and myocardium which have to withstand mechanical stress; nicknamed the "spot weld" junction.

Sketch and Label:

1. the histological features of cardiac muscle.