Traffic - week 8 Flashcards
3 types of muscle
- skeletal (striated, voluntary, multinucleate) a. movement of whole body or parts
- cardiac (striated, involuntary, one nucleus) a. pump blood
- smooth (unstriated, involuntary, one nucleus) a. movement of substances through hollow
organs
skeletal muscle (long)
functional anatomy
- whole muscle
a. made up of long cells bundled with connective tissue
b. connective tissue extends to form tendons attaching muscle to bone
muscle cell
contains myofibrils (specialized organelles) which are made up of protein filaments (myofilaments)
thick filaments
(1) made of myosin molecules, each of which has a head and tail end
(2) heads form cross bridges, have an actin binding site and ATPase site
thin filaments
(1) made mostly of actin molecules, each of which has a myosin binding site (cross bridge binding site)
(2) tropomyosin blocks binding sites when cell at rest
(3) troponin holds tropomyosin in place, has Ca2+ binding site
thick and thin filaments arranged into…
sarcomeres (functional units that contract) this arrangement results in striations
plasma membrane of muscle fiber also called
sarcolemma (1) forms T tubules, which project into cell (continuous with surface membrane, allowing electrical activity at cell surface to be transmitted throughout cell)
sarcoplasmic reticulum is modified..
smooth ER
(1) network of tubules surrounding myofibrils
(2) ends of each portion expand into sacs called terminal cisternae (a.k.a. lateral sacs, stores Ca2+)
other important points during contraction (gg)
during contraction, at any given time, only some cross bridges are attached - as they release others attach so thin filaments don’t slide backward
b. latent period is time between AP and contraction
c. contraction and relaxation last about 100 m sec
d. contraction of an individual cell is an all-or- none response
Skeletal muscle mechanics (car battery)
gradation of whole muscle tension
- a single AP to a muscle fiber results in a weak contraction (twitch) - muscle cells work together to produce more force
- recruiting more motor units➝ more tension (more force, stronger contraction)
a. a motor unit is a motor neuron plus all the fibers it innervates (fibers spread throughout muscle)
smaller motor units in muscles..
needing precise control (eyes, fingers)
asynchronous recruitment of motor units
prevents fatigue - alternate motor units (e.g., postural muscles, holding a heavy object)
influencing tension in each fiber..
increased frequency of stimulation➝ increased tension
if there is no relaxation between APs,
tetanus occurs (a smooth, sustained contraction of maximal strength)
length-tension relationship
maximal force possible at optimal length - myosin cross bridges have maximal access to actin binding sites. less fatigue ➝ increased tension
types of contractions
isotonic and isometric
isotonic
tension constant, muscle changes length
(1) concentric contraction - muscle shortens (lifting a load)
(2) eccentric contraction - muscle lengthens (lowering load)
isometric
tension develops, length stays the same (trying to lift too heavy a load, pushing against a wall)
muscles accomplish work…
(force x distance), but most of the energy muscles use (about 75%) converted to heat
lever systems
muscles provide force to move bones (levers) around joints (fulcrum)
2. depending on construction of system, allows a given effort to move a heavier load, or to move it farther and faster
Skeletal muscle metabolism (arms and legs)
- muscle cells have enough ATP reserves to last 4-6 seconds of strenuous activity