Exam 3 Review:  Chapter 09:  Smooth and Cardiac Muscle

smooth muscle tissue = nonstriated muscle tissue - The muscle tissue characterized by the absence of transverse stripes or a banding pattern observed in microscopy, due to the diffuse network arrangement of the contractile proteins, actin and myosin, which are not organized into myofibrils; the cytoplasm also lacks the T tubule system and the connective tissue around this muscle tissue never unites to form tendons or aponeuroses; the spindle-shaped, uninucleate, involuntary contractile cells controlled by the autonomic nervous system; it may be autorhythmic; it is the muscle type found in the walls of tubular internal organs, in the iris of the eye, in the arrector pili muscles, uterus, etc.

dense body - The dark-staining cell organelles (peripheral proteins) within smooth muscle cells which are attached to the sarcolemma, internally to the thin (actin + myosin) intermediate filaments which move these structures during contraction, and, externally to surrounding endomysium.

intermediate filaments - One of three types of cytoskeletal elements (the other two are thin filaments (actin) and microtubules); frequently the three components work together to enhance both structural integrity, cell shape, and cell and organelle motility; intermediate filaments are stable, durable, intermediate in size compared with thin filaments and microtubules; they are prominent in cells that withstand mechanical stress.

cardiac muscle tissue - The specialized involuntary, striated, uninucleate, contractile tissue of the heart; comprising the myocardium in which the uninucleate cells are connected to each other by intercalated discs; autorhythmic.

autorhythmicity - A property of cardiac muscle cells (and some smooth muscle cells); the ability to depolarize and contract at a set rate on their own with no outside stimulus or regulation necessary.  aka automaticity.

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.