Muscle Tissue Part 2 Flashcards
Smooth muscle characteristics
Simplest type of muscular tissue. No cross striations. Contractile filaments are not well organized in cell. Specialized for slow/rhythmic prolonged contractions (visceral organs) or rapid/precise (eye). Are involuntary
Shape of smooth muscle cells
Fusiform cells. aka Elongated spindle-shaped
Where is the nuclei of smooth muscle cells?
Centrally placed. Long/cigar shaped with tapered ends
What does the sarcoplasm of smooth muscle cells consist of?
Myofilaments and organelles, numerous mitochondria
How are the myofilaments arranged in smooth muscle?
Randomly distributed throughout the cytoplasm
What do the thin filaments of smooth muscle anchor to?
Dense bodies
What are dense bodies of smooth muscles anchored to and by what are they anchored?
Dense bodies are anchored to intermediate filaments via desmin (analogous to Z-lines of skeletal muscle fibers)
What does the sarcolemma of smooth muscle posses a large number of ?
Caveolae
Communicating junctions
gaps in the smooth muscle to connect the muscle cells
Reticular fibers in smooth muscle
Cover the smooth muscle cells. Play an important role in the force transduction in the smooth muscle tissue
Thin filaments of smooth muscle
F-Actin, tropomyosin, Caldesmon (NO TROPONIN is present)
Caldesmon
Smooth-muscle specific actin-binding protein that mass the myosin-binding site on the actin fibers
Thick filament of smooth muscle
Myosin II
Composition of myosin II
2 heavy polypeptides and 4 light chains (2 essential and 2 regulatory)
When does smooth muscle myosin bind to actin?
Only when phosphorylated
Where does the neural stimulation of smooth muscle occur?
Thru the post ganglion of the autonomic system
How are neuromuscular junctions different in the smooth muscle compared to skeletal muscle?
The neurotransmitters are released near to the muscle cells and diffuse to the cells as opposed to precise release (skeletal muscle)
How do smooth muscle cells without terminal nerves receive neural impulses?
Impulse transmission occurs via gap junctions
What can elicit chemical stimulation in smooth muscle?
Hormones, angiotensin II, vasopressin
What effect does mechanical stimulation of smooth muscle elicit?
Can lead to the initiation of muscular contraction
What drives the contraction of smooth muscle?
High concentrations of Ca++
Ca++’s effect on smooth muscle fibers
Binds to calmodulin. Complex releases actin, thus opening the myosin-binding sites on F-actin. Complex activates myosin light-chain kinase
What does myosin light-chain kinase do?
Phosphorylates the regulatory (light) chain of the myosin molecule
What happens after the light chain of myosin in the smooth muscle in phosphorylated?
Myosin unfolds and the actin-binding site becomes open. Myosin binds to actin. Filaments slide. Cells shorten. Nucleus folds and becomes corkscrew-shaped. Slow action.
Smooth muscle relaxation
Ca++ pumped back into the sarcoplasmic reticulum. Calmodulin deactivates from Ca being disassociated and rebinds to myosin-binding site on actin. Uses 10% ATP that skeletal muscle uses
Latch state
For long-term contraction in smooth muscle. Used to sustain tone of blood vessels. Resembles rigor mortis
Smooth muscle blood supply
Blood supply is moderate via capillaries in connective tissue immediately surrounding the muscle cells
Active regeneration response
Smooth muscle cells can go thru mitosis and replace damaged/lost cells
Cardia muscle blood supply
Extensive blood supply thru a network of capillaries
Regeneration of cardiac muscle
limited regeneration. localized injury results in scar tissue of fibrous connective tissue. muscle function is lost in scar tissue area
Characteristics of cardiac muscle CELLS
Cylindrical cells arranged end to end. Centrally placed rounded nuclei. Large/flattened mitochondria densely packed between myofibrils. Form a long chain of muscle cells with intercalated disks between. Branching between fibers.
Intercalated disks
Junctions between individual muscle cells. Has a transverse and lateral portion.
Transverse portion of the intercalated disks
Runs at a right angle from the fiber. Provides mechanical stability for the tissue. Prevents cells from being pulled apart
Adherens junctions
In transverse portion of intercalated disks. Connect myofilaments of 3 neighboring cardiac muscle cells
Desmosomes
In transverse portion of intercalated disks. Connect intermediate filaments of 2 adjacent cells
Lateral portion of intercalated disks
Run parallel to myofilaments. Contains communicating/gap junctions. Provides ionic continuity between adjacent cells. Allows contraction signal to pass from cell to cell
T-tubules in cardiac muscle
Found at the Z-disks (NOT at junction of A and I bands)/ Sarcoplasmic reticulum not as well developed and have smaller cisternae than skeletal muscle.
Diads
One T-tubule and its surrounding small terminal cisternae
Purkinje fibers
Cardiac conducting cells that are modified for the conduction of electric impulses.
Nodes/bundles of Purkinje fibers
Sinoatrial node, atrioventricular node, bundle of His
Layers of Arteries/Veins
Tunics: Tunica intima, tunica media, tunica adventitia
Artery characteristics
Thicker walls, narrower lumens, usually round when cut
Vein characteristics
Walls are not distinctly separate, bundles of smooth muscle, much thinner wall than arteries
Lymphatic vessels
Very thin walls, only endothelial lining, may contain valves
