ch 9 Flashcards
muscle tissue
skeletal: skeletal, striated and voluntary; multinucleated, long, cylindrically shaped cells bundled together, contractions are fast but easily fatigue
cardiac muscle: cardiac, striated and involuntary. makes up muscular layer of the heart, uninucleated, cells branched with specialized junctions called intercalated discs; contractions rhythmic, fast, and completely relax in between contractions preventing fatigue.
smooth muscle: visceral, non-striated, and involuntary
narrow cylindrical fibers; makes up wall of blood vessels, ducts, hollow organs, uninucleated. closely arranged cells form sheets. contractions slow and sustained
function of muscle tissue
- produce body movement
- maintain posture and body position: ability to stand upright
- support soft tissue: layers of muscle make abdominal wall and floor of pelvic cavity
- guard entrances and exits
- maintain body temperature:heat released by working muscles
- store nutrient reserves: source of amino acids as energy reserve
properties of muscle tissue
- -excitability or irritability: ability to receive and respond to stimulus
- -contractility: ability to shorten forcibly when adequately stimulated
- -extensibility: ability to be stretched or extended
- -elasticity: ability to recoil and resume its resting length after being stretched
gross anatomy
each skeletal muscle is discrete organ made up several kinds of tissues
blood vessels, nerve fibers, connective tissue are also present
nerve supply
somatic motor neuron –> skeletal muscle cant contract on its own.
each muscle served by one nerve, an artery and by one or more veins
microscopically each muscle fiber is supplied by one nerve ending
blood supply
contracting muscle uses a hug amount of energy
highly vascularized
connective tissue sheaths
epimysium: “overcoat” dense irregular connective tissue. connected or blends into the deep fascia; separates muscle from surrounding tissues and organs
perimysium: surrounds muscle fiber bundles called fascicles; contain dense irregular CT; blood vessels and nerves serve muscle fibers
endomysium: within the muscle; a delicate, flexible, elastic connective tissue layer (mostly reticular fibers)
surrounds each muscle fiber, loosely interconnects adjacent muscle fiber. contain: capillary networks, satellite cells and nerve cells
microscopic anatomy of skeletal muscle
the muscle fiber:
can be very long up to 12 in
develop through fusion of myoblasts: some myoblasts do not fuse and remain for tissue repair.
contain hundreds of nuclei
motor unit
motor neuron and skeletal muscle fibers innervated by that motor neuron’s axonal terminals
thin filaments: 4 proteins
- F-actin (filamentous actin): two twisted rows of G-actin (globular actin), each which contain a myosin binding site
- nebulin: holds F-actin strands together, long nonelastic protein,; helps anchor thin filament ot z disc, regulates length of thin filament during development
- tropomyosin: double stranded protein molecule; covers myosin binding sites on actin; spirals around actin core and helps stiffen F-actin
- troponin: globular protein composed of 3 subunits. binds to tropomyosin G-actin, controlled by calcium ions
TnT: binds to tropomyosin
TnC: binds to calcium
TnI: binds to actin
relaxed muscle
normal shape of sarcomere
contracted muscle
the A band stays the same width, but the z lines move closer together and the I band gets smaller, the sarcomere shorten simultaneously and the ends of the myofibril are pulled toward its center
partially relaxed
the i band partially gets shorter
length and tension
length-tension relationship: resting length at time of stimulation: determines degree of overlap, therefore, number of pivoting cross-bridges
the number of cross-bridges largely determines the amount of tension produced
Frequency of stimulation: affects concentration of Ca2+ in the sarcoplasm and bound to troponin
twitch
single stimulus-contraction-relaxation sequence in muscle fiber
latent period
begins at stimulation and lasts 2 msec (excitation-contraction coupling is occuring)
contraction period
tension rises to a peak contraction cycle begins 10-100 msec
relaxation period
relaxation cycle begins lasts 10-100 msec
treppe
stair-step increase in twitch tension
wave summation
successive stimuli arrive before relaxation phase has been completed. duration of a single twitch determines max. time available for wave summation
incomplete/ unfused tetanus
stimulus frequency increases further without allowing muscle to relax completely; tension rises further and reaches a peak
complete/fused tetanus
stimulus frequency is so high, relaxation phase is eliminated and tension plateaus at max levels
synchronous motor unit summation
all firing away at the same time for short period of time
peak tension occurs when all motor units in muscle contract in state of complete tetanus
asynchronous motor unit summation
relay team; takes turns firing away gives longer lasting contraction
motor units are activated on a rotating basis some are resting and recovering while others contract
muscle tone
normal tension and firmness of a muscle at rest
isotonic: concentric isotonic contraction
peak muscle muscle tension exceeds th load, the muscle shortens which decreases angle at joint and moves object
eccentric isotonic contraction
muscles elongates; very common and important
isometric contraction
same measure no change
muscle as a whole does not shorten or change and results in no motion: peak tension never exceeds the load
atp
provides energy; demands are great during muscle contraction. resting muscles only contain enough ATP to sustain a contraction until additional ATP can be generated.
3 pathways to get ATP
- direct phosphorylation: coupled reaction of creatin phosphate and ADP: way to store energy; unique high energy molecule stored in muscles
- anaerobic pathways: glycolysis and lactic acid fermentation
- aerobic pathway
