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
what is soleus
muscles predominantly composed of dark fibers
what is gastrocnemius
muscle predominantly composed of light fibers
what is the difference between first-class, second-class, and 3rd class lever systems?
first class: fulcrum is in the middle (in force and out first move in opposite directions)
2nd class: resistance (outforce) is in the middle): both in and out forces are on the same side of the fulcrum
3rd: efforce (in force) is in the middle (both forces move in same direction)
what is referred to as a chain of sarcomeres
myofibril
which sarcoplasmic band does not undergo a change in length during the contraction of a skeletal muscle
A band
which sarcomeric band is composed entirely of actin filaments
I band
DHP channels are part of what structure
T tubules
Ryanodine sensitive calcium ion release channels is part of what structure
SR
what factor does the concentration of calcium increase in the cytosol after released from the SR
100
what helps maintain the optimum calcium concentration gradient to facilitate return of calcium to SR
calsequestrin
what is an example of eccentric contraction
the tricep muscle while lowering the body to the floor during a push up
what is anchored to the presynaptic membrane and associated with synaptic vesicles to which they are tethered by short filaments
dense bar
In order for acetylcholine-gated ion channels to open, how much Ach molecules are necessary to attach its alpha subunit
2
