skeletal, smooth and cardiac muscle Flashcards
describe structure and ultrastructure of skeletal muscle
striated muscle fibres multinucleate form in utero from mononucleate myoblasts increase fibre size during growth
bundles of fibres encased in connective tissue sheaths
cells replaced after injury by satellite cells -> differentiate to form new muscle fibres
explain process of excitation-contraction coupling
muscle action potential propagated
Ca2+ released from lateral sac
Ca2+ binding to troponin removes blocking action of tropomyosin
cross-bridge moves
Ca2+ removal from troponin restores tropomyosin blocking action
explain mechanics of skeletal muscle contraction
contraction with…
constant length = ISOMETRIC
shortening length = ISOTONIC (concentric)
increasing length = LENGTHENING (eccentric)
define isometric
contraction with constant length
define isotonic
contraction with shortening length
explain sliding filament theory and relationship to length-tension properties
describe generation of controlled force by recruitment of motor units
explain tetanus
AP is 1-2ms long, but twitch may last up to 100ms
may get more APs during contraction
these add up = SUMMATION
tetanic tension > twitch tension since Ca2+ never gets low enough to allow troponin/tropomyosin to re-block myosin binding sites
describe aerobic and anaerobic properties of muscle
describe structure and function of smooth muscle
no striations
innervated by ANS, not somatic NS
has X-bridge cycle and uses Ca2+
exists in hollow organs (eg GI tract, uterus, airways, ducts)
spindle-shaped
mononucleate and divide through life
thick myosin and thin actin filaments
filaments arranged diagonally across cells and are anchored to membranes and cell structures by dense bodies (like Z-lines)
filaments still slide together to contract cell
explain contraction and relaxation in smooth muscle
increased Ca2+ -> Ca2+ binds calmodulin -> Ca2+-Calmodulin binds to myosin light chain kinase -> kinase phosphorylates myosin X-bridges with ATP -> phosphorylated X-bridges bind to actin filaments -> CONTRACTION + TENSION
relaxes via action of myosin light chain phosphatase -> dephosphorylates X-bridges
persistent stimulation and increased Ca2+ in some smooth muscle
how do differences in elastic properties of muscles contribute to force production?
by influencing speed of contractile elements , elastic structures have profound effect on muscle force, power and work
define actin
protein found in microfilaments - active in muscular contraction, cellular movement and maintenance of cell shape
define myosin
fibrous protein, motor protein
converts chemical energy released from ATP into mechanical energy - this mechanical energy used to pull actin filaments along , causing muscle fibres to contract , therefore, generating movement
define titin
large protein
contributes to elasticity of striated muscle fibres
stabilise thick filament, prevent overstretching of sarcomere, and to recoil sarcomere after its stretched
how are skeletal muscle fibre types characterised?
fibres are fast/slow-shortening
oxidative or glycolytic ATP forming pathways are used
FAST -> myosin has high ATPase activity
SLOW -> has low ATPase activity
oxidative fibres
increased mitochondria -> increased oxid. phosphorylation
increased vascularisation to deliver more O2 and nutrients
contain myoglobin -> increased O2 delivery
fibres are red and have low diameters
glycolytic fibres
few mitochondria
increased glycolytic enzymes and glycogen
lower blood supply
white fibres with larger diameters
3 types of muscle fibres
slow oxidative (I) - resist fatigue fast oxidative (IIa) - intermediate resistance to fatigue fast glycolytic (IIb) - fatigue quickly
smooth muscle types
single or multiunit
single unit smooth muscle
GIT, uterus, small blood vessels many cells linked by gap junctions signals travel between cells contract synchronously may contain pacemaker cells stretch evokes contraction
multiunit smooth muscle
airways, large arteries, hairs
few or no gap junctions
richly innervated by ANS
don’t respond to stretch
most smooth muscles in organs are a mixture of single and multiunit populations of cells
means an organ can have a mixture of properties in different areas
