Skeletal Muscle Contraction Flashcards
define epimysium
connective tissue surrounding entire muscle
define muscle
made up of multiple fascicles (each containing fiber)
define perimysium
connective tissue surrounding individual fascicle (typically thinner than epimysium)
define fascicle
a bundle of myofibers
define endomysium
delicate connective tissue around each myofiber
define sarcolemma (=plasmalemma)
cell membrane of muscle fiber
define myofiber (=muscle cell)
individual multinucleate muscle cell
define myofibril
chain of sarcomeres within a myofiber (intracellular configuration)
define myofilament
actin and myosin filaments that make up a sarcomere
what does sarco mean in greek
flesh
what are T-tubules
- invaginations of sarcolemma
- live close to cistern of SR
- form triads with cistern
- 2 per sarcomere
what are Z discs (lines)
anchor actin filaments
located at each of a sarcomere
what are I bands
composed of entirely actin
width changes during contraction
reflection of light
what are A bands
composed of actin and myosin
width does not change during contraction
reflection of light
what are H bands
composed entirely of myosin
width changes during contraction
what are the short-hand steps of muscle contraction
- action potential in alpha motor neuron
- Ca++ influx into axon terminal
- exocytosis of synaptic vesicles
- acetylcholine release into synaptic cleft
- diffusion of Ach across cleft
- binding of Ach to Ach receptors on sarcolemma
- opening of ligand-gated Na+ channels
- Na+ influx
- end-plate depolarization
- opening of voltage-gated Na+ channels
- sarcolemma action potential
- depolarization fo T-tubules
- Conformational change in DHP receptors
- conformational change in ryanodine receptors
- opening of ryanodine Ca++ channels
- release of Ca++ from SR
- Ca+ concentration in cytosol increases
- binding of Ca++ to Troponin
- Conformational change in troponin
- tropomyosin is pulled away from active sites on actin
- exposure of actin sites on actin
- binding of myosin heads to actin active sites
what are characteristics of DHP receptors
- voltage-sensitive L-type Ca++ channels arranged in quadruplets
- located on the sarcolemma T-tubules
- cause a conformational change in the ryanodine receptors
what are characteristics of ryanodine receptors
- located on the cisternae of SR
- open in response to conformational change in DHP receptors
- allow Ca++ into the cytosol from the SR
- SERCA uses ATP to pump calcium back into the SR
define preload
load on a muscle in the relaxed state before in contracts
what are the types of tension
passive: produced by pre-load
active: produced by cross-bridging
total: sum of active and passive tension
where is ATP required for muscle contraction
- most used for the sliding filament mechanism
- pumping Ca++ from Sarcoplasm back into SR
- pumping sodium and K+ through the sarcolemma to re-restablish resting potential
What is phosphocreatine
- releases energy rapidly
* reconstitutes ATP
compare isometric and isotonic contractions
isometric occurs when there is an increase in tension but not length while isotonic is when muscle length changes (lengthens=eccentric, shortens=concentric)
compare white and red muscle fibers:
white are more rapid, have fewer mitochondria, primarily are anaerobic, little myoglobin and larger concentration of ATPase when compared to red
