Muscle

• In muscle tissue, contractility is the key feature of muscle
• In muscle tissue, actin and myosin are microfibrillar proteins
• In muscle tissue, sarcolemma is the muscle cell membrane
• In muscle tissue, sarcoplasm is the cytoplasm
• Skeletal muscle, is large, elongated, multinucleated fibers that have strong, quick voluntary contractions
• Cardiac muscle are irregular branched cells (centrally, located nuclei) bound together longitudinally by intercalated discs that perform strong involuntary contractions
• Smooth muscle are grouped, fusiform cells that perform weak involuntary contractions
• In skeletal muscle, the endomysium surrounds individual muscle
• In skeletal muscle, perimysium encloses a group of muscle fibers called a fascicle
• Intercalated discs are fibers consisting of cells in a series joined at interdigitating regions
• Transverse regions of intercalated disc have abundant of desmosomes and adherent junctions
• Intercalated disks regions serve as "electrical synapses" promoting rapid impulse conduction through cardiac cells and contraction of many adjacent cells as a unit
• Longitudinal regions in cardiac muscle have gap junctions
• Fiber contraction of the heart is intrinsic and spontaneous
• Ischemia, which is tissue damage due to lack of oxygen, is the most common injury, commonly when coronary arteries are occluded by heart disease
• Smooth muscle is a major component of the digestive, respiratory, urinary and reproductive tracts, blood vessels and their associated organs.
• Smooth muscle fibers are elongated, tapered and unstriated
• In smooth muscle contraction, thin filaments attach to dense bodies located at the cell membrane, which are attachment sites between muscle cells. This allows the multicellular tissue to contract as a unit, providing better efficiency and force
• The dilated terminal end of an axon that contacts the muscle cell is called the terminal bouton or axon terminal
• Fast glycolytic is the muscle fibers experience rapid fatigue
• The all-or-nothing contraction of cardiac muscle cells (as opposed to the modulation of contraction) is under the control of autonomic nervous system
• Calcium triggers the contraction of the sarcomere
• A group of mesenchymal satellite cells help to repair skeletal muscle cells after injury. They do this by differentiating to produce new muscle cells that fuse with existing muscle cells.
• Actin, troponin and tropomyosin are the proteins contained in a thin filament
• The role of titin in a muscle contraction is to prevent overstretching of the sarcomere and also acts like a spring to recoil the sarcomere after it is stretched.
• A band is the darker region of the sarcomere, as seen in TEM, is where the thick and thin filaments overlap
• Smooth muscle will increase in number as well as size in response to increased load
• Function of muscle spindle is to involuntary contract by stretch reflex
• Cardiac and smooth cells are under autonomic control and have a centrally located nuclei in cell
• Cardiac and skeletal cells are striated and the contractions are all-or-none
• In a sarcomere, the I band is bisected by a z-disk
• The repeated functional units of a myofibril, arranged end to end, are called sarcomeres
• Epimysium is the sheath of dense irregular connective tissue that completely surround a muscle
• Skeletal muscle contains fascicles made up of muscle fibers which contains myofibrils that contain myofilaments that consist of think filaments (myosin) and thin filaments (actin)
• A skeletal muscle is enclosed within the epimysium, a thick layer of dense connective tissue, that is continuous with fascia and the tendon binding muscle to bone
• Large muscle contains several fascicles of muscle tissue, each wrapped in a thin, dense connective tissue layer called the perimysium
• Within fascicles, individual muscle (skeletal) fibers are surrounded by a delicate connective tissue layer called the endomysium
• Endomysium form paths for nerves, blood vessels and lymphatics, and they are continuous with the tough connective tissue of a tendon
• Striated skeletal muscle contains three layers. The endomysium surrounding individual muscle, the perimysium encloses a group of muscle fibers comprising a fascicle, and a thick epimysium surrounding the entire muscle.
• In a myotendinous junction, tendons develop together with skeletal muscles and join muscle to the periosteum of bones