muscle Flashcards
primary function of all muscle
and the other functions
The primary function of all muscle is to generate force and/or movement in response to stimuli.
body movement
posture maintenance
respiration
production of body heat
communication
constriction of organs and vessels
heartbeat
skeletal muscle
attached to
tendons
myofilaments
think/thick filaments
F-Actin: backbone of thin filaments, contains the binding site for thick filaments
tropomyosin: two identical alpha helices that coil around each other, regulating the binding of myosin to actin
troponin complex: consists
troponin C: ca binding to site
troponin T: binds to tropomyosin
troponin I: bound to actin
thick filament is myosin.
myosin head contains a region for binding actin as well as a site for binding and hydrolyzing ATP
light chains regulate Myosin ATPase
sarcomere
z-discs: zigzag protein structure that is the attachment site for thin filaments
I bands: lightest band of the sarcomere, only actin
a band: darked band, contains both thick and thin filaments
h zone: central region of A band, only myosin
line: proteins from the attachment site for thick filaments, same thing z disk for think filaments
neuromuscular junction
the area where the lower motor neuron makes synaptic contact with the muscle fiber
three components:
presynaptic motor neuron filled with synaptic vesicles
the synaptic cleft
postsynaptic membrane of the skeletal muscle fiber
initiation of the AP
AP travels down motor neuron into axon terminal.
Ca channels activated, and Ca enters
vesicles containing ACh bind to the presynaptic membrane
ACh binds and opens ion channels
Na entry
the entry of Na generates an excitatory end plate potential. (EPP) that spreads to adjacent voltage-gated Na channels and initates an action potential
ceasing neural transmission
must get rid of
once AP stops firing in the alpha motor neuron, ACh must be removed and will diffuse away or be broken down into acetate and choline by acetylcholinesterase.
excitation-contraction coupling
what is it
how can we get Ca in the sacroplasm?
triggers contraction in all muscle types is a rise in intracellular calcium.
depending on the muscle type, Ca can enter the sarcoplasm from the extracellular space via voltage-gated Ca channels or
can be released into the sarcoplasm from the intracellular Ca storage reservoir of the SR
electrical excitation of the membrane triggers an increase of Ca is EC coupling
what are the channels? Ca can enter the sacroplasm with
DHP receptor: L-type Ca channel
RyR: ryanodine receptor
Ca release channel on SR
besides mechanically, they can open by Ca (Ca induced Ca release)
how does an increase in Ca allow contraction?
it removes the inhibition of cross-bridge cycling.
Ca2+ binds low-affinity sites of troponin C, which changes the troponin complex.
causes the troponin complex as well as tropomyosin to move revealing the myosin binding site of actin
cross bridge cycling
before it starts, tropomyosin must be shifted
1) ATP binding: ATP binds to the head of myosin heavy chain, which breaks the bond of myosin and actin
2) ATP hydrolysis: ATP is broken down to ADP and Pi inorganic phosphate, resulting in the movement of the myosin head into the cocking position. allows for binding of new actin
3) the power stroke: PI is dropped and strengthens bond between myosin and actin, triggering the power stroke, myosin head returns to un cocked state well doing so pulls the actin.
4) ADP release: disassociation of ADP from myosin casuses myosin to remain bound to actin until until ATP initiates the cycle again.
termination of contraction requires removal of CA
Ca must be removed so that the myosin binding site on actin can be covered by tropomyosin
Ca can be removed to the extracellular space by the Na-Ca exchanger or by the Ca pump which uses ATP.
SERCA type Ca pump
calquestrin and calreticulin maximize CA uptake by the SR
rigor mortis
development of rigid muscle several hours after death
what is ATP needed for and whre can you get it from
needed for:
myosin ATPase (contraction)
Ca ATPase: SERCA (relaxation)
Na/K ATPase (after AP in muscle fibre)
sources:
free intracellular ATP
ATP formed from phosphocreatine
anaerobic metabolism
aerobic metabolism
anaerobic metabolism vs
aerobic metabolism
anaerobic: ATP is needed so glycogen is converted back into glucose (glucogenesis).
glucose is broken down into pyruvate by glycolysis resulting in 2 ATP molecules.
occurs in the sacroplasm
aerobic: O2 is present, pyruvate enters the citric acid cycle, producing 2 more molecules of ATP as well electrons H
the electrons and H combine with O2 in the ETC to produce 26-28 ATP
occurs in mitochondria