muscles Flashcards
myofiber
muscle cell
myofibril
collection of myofilaments
myofilaments
actin and myosin
thin filament
made of F-actin, 1um long, double helix, bound to tropomyosin and troponin
thick filament
made of myosin, 1.6 um long
sarcomeres
on myofibrils, mainly made of actin and myosin, muscles are repeating units of sarcomeres, myosin pulls the Z lines towards the center of the sarcomere by the pulling of thick filaments on thin filaments. One sarcomere is Z-line to Z-line
skeletal muscle contraction
relaxed state, binding myosin to actin is prevented because the binding site is covered by tropomyosin, Ca2+ binds to troponin, troponin (bound to the end of tropomyosin) releases tropomyosin from actin, myosin can bind to actin, binding ATP allows myosin to dissociate from actin and hydrolysis of ATP puts myosin in high energy state
molecular structure of sarcomere
contractile proteins are actin and myosin, troponin has calium sensor with 4 binding sights and rotates tropomyosin for myosin binding, tropomyosin: rod shpaed that binds 6-7 actin units, Titin: looks like a slinky is an elongatable component and keeps thick filaments centered in the sarcomere, nebulin runs along the actin, Z-line is alpha-actinin, M-line is myomesin and C protein on outside
muscle conection to CT
sarcolemma is plasma membrane of myofiber, epi- peri- and endomysium are CTs that invest different muscle regions, epimysium = tough covering of muscle, perimysium = CT surrounding muscle fascicle, endomysium = CT within fasicles, surround and invest muscle cells. Vessels and nerves course these
nerves and muscles
nerve synapse on center of muscle, AP spread toward tendon, each muscle innervated by group of motor neurons in spinal cord, damage to neurons produces paralysis, each neuron innervated one muscle and a subset of the total muscle fibers in said muscle, motor unit = muscle fibers innervated by motor neuron. when neuron fires AP activates all muscle fibers
muscle contraction and relaxation
AP => Ach release => Ach receptor binds Ach => opens causing depolarization => AP propagates down fiber => AP and depol occur at t-tuble => protein links at t-tubles/Srjunction (triad) altered to allow Ca release from SR => Ca bind troponin, exposing myosin binding sites on actin => while Ca and ATP present the myosin-actin cycle continues => Ca ATPase pumps Ca back into SR => tropomyosin moves back into place and muscle relases
transverse-tubule system (t-system) in skeletal and cardiac muscle
needed because extracellular Ca would take too long to diffuse to center of muscle cells, outside would contract before inside and muscle would tear apart. Each myofibril has Ca store it needs for contraction
pathway for AP transmission to interior via t-tubule
depol in t-tubule doesn’t go directly to SR, no electrical continuity, AP goes toward tendon and inward toward t-system, membrane depols in t-system this translates to Ca release from SR (called E-C coupling).
Excitation-contraction (E-C) coupling
DHPR is a voltage gated Ca channel, RyR is one of these with a channel in SR. depol causes conformational change in DHP receptor causing Ca release channel to open and Ca flows out of the SR
skeletal muscle tension grading and regulation
Increase AP frequency or increase motor unit recruitment
muscle fatigue
reduced perforance during prolonged or intense activity, decrease in force production and speed of contraction, in principle can be impairment at any point from motor neuron to SR. steps affected: 1) propagation of AP to t-tubule, 2) release of CA from SR, 3) effect of Ca on myofilament interaction, 4) force generation by myofilament
sarcomere length in resting, contractile, and stretched
resting = 2.4 micrometer (um), contractile = shorter (close to 1.6 um), stretched to breaking point = 3.6 um
muscle fiber classes
slow, fast and an intermediate. Have different myosin isoenzymes, different proportions of mitochondria and oxidative enzymes, different resistance to fatigue, and different speeds of contraction
slow oxidative fibers
used for postual or relatively maintained contractions, reddish in color due to high myoglobin content
intermediate fibers
fast with both glycolytic and oxidative enzymes
fast twitch fibers
high in glycolytic content, used for rapid bursts of activity. Each motor unit is homogeneous
satellite cells
stem cells, repair damaged muscles cells
myofiber growth
number of cells don?t change, cell size increases by adding myofilaments as additional myofibrils so there is always a Ca store nearby
Cardiac muscle
need Ca, have pacemaker, one nucleus, 50-100 um in length, are striated, 5-15 um in diameter, has SR, have t-system, yes troponin, use Ach and norepinephrine, no motor units, Na dependent (NaCh), fast tension development
smooth muscle
no aligned filament, mononucleated, yes and no on gap junctions, 100s of um long, 2-5 um wide, some have SR, no t-system, no troponin, use Ach, norepinephrine, NO, many peptides, some have motor units, some CaCh, some no AP, have pacemaker, slow rate of tension development
