MUSCLE Flashcards
MUSCLE CELL CALSSIFICATION
Striated (muscle cells with a banded appearance) or nonstriated (not banded) * Muscle cells can have a single nucleus or be multinucleate * Muscle cells can be controlled voluntarily (consciously) or involuntarily (automatically)
SKELETAL MUSCLE
Striated, “voluntary”, and multinucleated * Cells can be very long * Contracts rapidly but tires easily * Is extremely adaptable and can exert forces ranging from a fraction of an ounce to over 70 pounds * Satellite cells: Like a muscle “stem cell,” can divide to become new skeletal muscle cells (adult skeletal muscle cells do not divide).
CARDIAC
Occurs only in the heart * Is striated, not voluntary, uni- or bi- nucleate * Contracts at a fairly steady rate set by the heart’s pacemaker cells * Cells are called cardiac myocytes * Form branching networks connected at intercalated disks * Neural controls allow the heart to respond to changes in bodily needs Limited capacity for repair
SMOOTH MUSCLE
Nonstriated, involuntary, and have a single nucleus * Smooth muscle cells are small and tapered * can divide and regenerate * Found in walls of hollow organs and blood vessels * Contract alone or under nervous system control * Smooth muscle helps maintain blood pressure, and squeezes or propels substances (i.e., food, feces) through organs
FUNCTIONAL CHARACTERISTICS OF MUSCLE TISSUE
ExCoExEl
Excitability, or irritability – the ability to receive and respond to stimuli * Contractility – the ability to shorten forcibly * Extensibility – the ability to be stretched or extended * Elasticity – the ability to recoil and resume the original resting length
functions of skeletal muscle
roduce skeletal movement * Maintain body posture * Support soft tissues * Stabilize joints * Guard body openings * Generate heat
n overcoat of dense regular and irregular connective tissue that surrounds the entire muscle; Separates muscle from surrounding tissues
epimysium
fibrous connective tissue that surrounds groups of muscle fibers called fascicles; Contains blood vessel and nerve supply to fascicles
perimysium
– fine sheath of connective tissue composed of collagen and reticular fibers surrounding each muscle cell/fiber; Contains capillaries and nerve fibers contacting muscle cells; Contains satellite cells (stem cells) that repair damage
Endomysium
surrounds muscle (which are bundles of fascicles) *
epimyseum
surrounds fascicles
perimyssium
which are bundles are fibers/cells
fascicle
surrounds muscle fibers (which are filled with myofibrils)
ENDOMYSIUM
long cylinders of sarcomeres
MYOFIBRIL
contract to shorten muscles. (Made up of myofilaments)
Sarcomeres
2 TYPE OF MUSCLE ATTACHMENT
DIRECT AND INDIRECT
epimysium of the muscle is fused to the periosteum of a bone
DIRECT MUSCLE ATTACHMENT
onnective tissue wrappings (endomysium, perimysium, and epimysium) come together at ends of muscles and extend beyond it as a tendon (bundle) or aponeurosis (sheet)
INDIRECT MUSCLE ATTACHMENT
INNERVATION AND VASCULARIZATION
Nerves * Skeletal muscles are voluntary muscles, controlled by nerves of the somatic nervous system * Muscles have extensive vascular systems: * supply large amounts of oxygen and nutrients * carry away wastes
Formation of Skeletal Muscle Fibers
- Skeletal muscle cells are called fibers * Myoblasts join to form muscle fibers
SKKELETAL MUSCLE FIBERS
Are very long cylindrical cell with hundreds of nuclei just beneath the sarcolemma * Each cell is a syncytium produced by fusion of embryonic mesodermal cells (myoblasts) * Fibers are 10 to 100 m in diameter, and up to hundreds of centimeters long
re densely packed, rod-like contractile elements * Make up most of the muscle cell volume * Made up sarcomeres, which are themselves bundles of protein filaments (myofilaments)
MYOFIBRIL
The smallest contractile unit of a muscle * The region of a myofibril between two successive Z discs * Composed of myofilaments made up of contractile proteins * The repeating pattern of myofibrils notice the presence of a repeating portion known as a sarcomere
SARCOMERE
Myofibrils and sarcomeres consist of thick and thin myofilaments * These filaments are responsible for the striations of muscle, which are alternating dark and light bands * Myofilaments are responsible for muscle contraction * Thin filaments: * made of the protein actin * Thick filaments: * made of the protein myosin
MYOFILAMENT
The contractile units of muscle * Structural units of myofibrils (that is, myofibrils are made up of many sarcomeres postioned end to end) * Form visible striated patterns within myofibrils: * alternating dark, thick filaments(A bands) and light, thin filaments(I bands)
SARCOMERE
the center of the A band
M LINE
MIDLINE OF SARCOMERE
M LINE
the centers of the I band
Z LINE/DISC
at 2 ends of sarcomere
Z LINE
coin-shaped sheet of proteins (connectins) that anchors the thin filaments and connects myofibrils to one another
Z LINE
The densest, darkest area on a light micrograph * Where thick and thin filaments overlap
ZONE OF OVERLAP
The area around the M line * Has only thick filaments but no thin filaments
H ZONE
- Strands of protein that reach from tips of thick filaments to the Z line * Stabilize the filaments
titin
re extensions of the sarcolemma that join with the SR at specialized regions
transverse tubules
The cell membrane of a muscle cell * Surrounds the sarcoplasm (cytoplasm of muscle fiber) * Muscle contractions are started by a change in transmembrane potential (electrical charge on either side of the membrane)
sarcolemma
A rapid, transitory reversal of the transmembrane potential that propagates quickly along the length of an electrically excitable cell. * Huh? Basically, a portion of a cell goes from negative to positive charge very quickly and this spreads from one part of the cell to the next to the next and so on.
action potential
are continuous with the sarcolemma and have the same properties * They conduct action potentialsto the deepest regions of the muscle * These impulses signal for the release of Ca2+ from adjacent terminal cisternae * Allow entire muscle fiber to contract simultaneously
transverse tubules
- Transverse tubules encircle the sarcomere near zones of overlap (why?) * Ca2+ released by SR causes thin and thick filaments to interact
zone of overlap andt tubules
n elaborate membranous structure that runs longitudinally, surrounding each myofibril * Similar in structure to smooth endoplasmic reticulum * Helps transmit action potential to myofibril * Forms chambers (terminal cisternae) attached to T tubules that release calcium during muscle contraction
sarcoplasmic reticulum
Concentrate Ca2+ inside (via ion pumps) * When stimulated by an action potential, they release Ca2+ into sarcomeres to begin muscle contraction
terminal cisternae
Structure formed by 1 T tubule and 2 terminal cisternae (thickenings of the SR) * T tubules and SR provide tightly linked signals for muscle contraction * T tubule proteins act as voltage sensors * SR has receptors that regulate Ca2+ release from the terminal cisternae
a triad
caused by interactions of thick and thin filaments * Structures of protein molecules detemine interactions
muscle contraction
Thin filaments are chiefly composed of the protein actin held together bynebulin * The subunits contain the active sites to which myosin heads attach during contraction * Tropomyosin strands block active sites * Troponin holds tropomyosin and actin together (at rest)
Myofilaments: Thin Filaments
Longitudinal section within one sarcomere
filaent
binds tropomyosin to actin
troponin
3 suvbsunit of troponin
consists of three subunits * TnI: binds to actin * TnT: bonds to tropomyosin * TnC: binds calcium * controlled by Ca2+, kind of like the “lock” and Ca2+ is the “key”
2+ binds to receptor on troponin molecule * Troponin–tropomyosin complex changes shape, moves troponin out of the way * Exposes the active site of each actin molecule (bead)
initiating contraction
During contraction, myosin heads: * interact with actin filaments, forming cross-bridges * pivot, producing motion It is the pivoting of myosin heads that causes muscle contraction and therefore all movements
myosin action
sliding filament model of contraction
hin filaments slide past the thick ones so that the actin and myosin filaments overlap to a greater degree * In the relaxed state, thin and thick filaments overlap only slightly * Upon stimulation, myosin heads bind to actin and sliding begins * Myosin heads pull the actin thin filaments closer together, sliding them in between the thick filaments * As this event occurs throughout the sarcomeres, the muscle shortens * Z lines move closer together * width of A band stays the same * width of the I band and the H zone both shrink
