MUSCULOSKELETAL SYSTEM I Flashcards
What is Titin
Filamentous protein which is very springy.
Anchored by Z-discs and stabilizes myofilaments during muscle contraction.
what is sarcoplasm?
Intracellular fluid found between myofibrils.
Suspends ions such as potassium, magnesium, phosphates and protein enzymes.
Mitochondria (which supply contracting muscle with energy-ATP) are also present.
What does sarcoplasmic reticulum do?
Regulates the release, reuptake of calcium ions and their storage; as well as muscle contraction.
Myosin Filaments: composed of multiple myosin molecules. Name the six polypeptide chain
a) 2 heavy chains: double helix = tails
b) 4 light chains: 2 heads = 2 light chains on each head
Central portion of myosin filament = body
Part of the body forms an arm (extends heads away from the body)
Myosin filament have 2 hinges: one between arm and body and the other where head attaches to the arm.
Explain Troponin molecule and its role in muscle contraction
Attached intermittently alongside of tropomyosin molecules.
Exists in 3 loosely bound protein subunits:
I) Troponin I: has a strong affinity for actin
II) Troponin T: has affinity for tropomyosin
III) Troponin C: has affinity for Ca2+ ions
Troponin C bound to Ca2+ ion initiates muscle contraction.
Explain tropomyosin molecule in details.
Contained by the actin filament.
Wrapped spirally on the sides of F-actin helix
At rest, tropomyosin covers active sites of actin filament, thus, preventing interaction between the myosin heads and actin.
Explain actin molecule in details
Double-stranded F-actin protein molecules: Backbone of actin filament.
G-actin molecules: part of F-actin
ADP molecule: attached to each G-actin, are active sites in actin filaments for attachment of myosin heads for muscle contraction.
Each bases of actin filament are strongly inserted into Z-discs.
Characteristics of whole muscle contraction
Relation of Velocity of Contraction to Load:
No load Skeletal muscle contraction rapidly
Load applied velocity of contraction progressively decreases as load is increasing.
Load applied = max force exerted by the muscle velocity of contraction becomes (0) with no resultant contraction, despite activation of muscle fibre.
Load on contracting muscle is a reverse force opposing contractile force produced by muscle contraction.
Molecular mechanism of muscle contractio
a) Calcium
b) Sodium
c) Magnesium
d) Adenosine Triphosphate (ATP):
e) Adenosine Diphosphate (ADP):
f) Acetylcholine (ACh):
a) Calcium: Troponin-initiation of contraction (inhibition of inhibitory effect of troponin-tropomyosin on actin filaments, induce Ca2+ release (cardiac muscles)
b) Sodium: NMJ-action potential generation
c) Magnesium: myosin head binding to actin active sites
d) Adenosine Triphosphate (ATP): myosin head binding to actin active sites,
e) Adenosine Diphosphate (ADP): power stroke action
f) Acetylcholine (ACh): NMJ-activation of ACh-gated cation channels in motor-end-plate
Activation of Actin Filament by Calcium ions:
explain
Large amounts of Ca2+ inhibits troponin-tropomyosin complex
Troponin C binds Ca2+ ions (can bind up to 4 Ca2+) causes conformational change of troponin complex tropomyosin molecule is pulled away, deep into the grooves between 2 actin strands exposure of active sites on actin attachment of energized myosin heads occurs muscle contraction.
Interaction of the Activated Actin Filament and the Myosin Cross-bridges- the Walk Along/Sliding Mechanism theory:
explain
Myosin heads attach to the exposed active sites on actin filament myosin heads tilt towards myosin arm leading to power stroke action release of energy (ADP + phosphate ion) actin filament gets dragged/pulled along with myosin head = walk-along/ sliding filament mechanism theory.
The Amount of Actin and Myosin Filament Overlap Determines Tension Development by the Contracting Muscle:
Draw the graph and explain all the points from A-D
Point D: No actin-myosin overlap
Actin filament pulled all the way to the end of the myosin filament.
Tension developed by activated muscle is zero (0).
Point C: Sarcomere begins to shorten
Actin and myosin filaments overlap each other. But actin has not reached the center of the myosin filaments.
Tension increases progressively until sarcomere length decreases to about 2.2 micrometers.
Point B: Sarcomere shortens further
Sarcomere maintains full tension at the length of 2 micrometers.
Ends of actin begin to overlap each other in addition to overlapping the myosin filaments.
Point A: sarcomere decreases in length (from 2 to ~1.65 micrometers)
The strength of contraction decreases rapidly.
The 2 Z-lines abut the ends of myosin filaments.
Contraction continues further, to shorter sarcomere lengths, ends of myosin filaments are crumpled.
Strength of contraction approaches (0) & sarcomere has contracted to its shortest length.
General mechanism of muscle contraction.
A. The action potential travels the motor nerve ending on the muscle fiber.
B. Neurotransmitters Ach is secreted at the synaptic cleft.
C. Ach acts on the sarcolemma causing the
Open of Ach-gated cation channel
D. Opening of Ach-gated cation channel (Na+) Allows the influx of Na+ into the muscle fibers.
E. Influx of Na+ results in depolarization of the muscle fiber, which causes the opening of Voltage-gated Na+ channels, which initiates an action potential.
F. AP travels along the sarcolemma
G. The AP travel along the center of the membrane (crosses T tubules) stimulates the SR to release the Ca2+.
H. Ca2+ initiates attraction force between actin and myosin, sliding to each other- contractive process.
I. After a second, Ca2+ is released back to the SR by the Ca2+ ATPase pump located in an SR membrane = muscle contraction ceases after the removal of Ca2+.
What is ATP activity of the myosin head
Myosin head function as ATPs enzyme= binds ATPs and use it for energy
What does the actin filament compose of?
Actin, Troponin and Tropomyosin
