Muscle Tissue Lecture 2 Flashcards
Contractile Proteins
- Main components generating force
- Found inside myofibrils
Myosin
- Makes up thick filaments
- Shaped like twisted golf clubs
- Has actin binding sites
Actin
- Makes up thin filaments
- Shaped like golf balls
- Has myosin binding sites
Regulatory Proteins
Aid in alternating between contraction & relaxation
Troponin
- Found in thin filaments
- Functions as a binding site for calcium
Tropomyosin
- Found in thin filaments
- Functions to block the myosin binding site during muscle relaxation
Structural Proteins
- Stabilize the structure
- Provide elasticity and extensibility
Titin
- Anchors thick filaments from M-line to Z-disc
- Helps return filaments to original positions after stretch or contraction
Myomesin
- Forms the M-line
- Helps stabilize thick filaments
Nebulin
Anchors thin filaments (actin) to the Z-discs
Dystrophin
- Links thin filaments to the sarcolemma for stability
- Lacking in muscular dystrophy
Sarcomere
- Functional unit of striated muscle
- Contracts during muscle contraction
Z Disc
- Protein structures at sarcomere edges
- Stabilize filaments
- Sarcomere spans from Z disc to Z disc
A Band and I Band
A band: Full length of thick filaments, overlaps thin filaments
I band: Lighter, thin filaments only, no thick filaments
M Line and H Zone
M line: Midline of sarcomere, through thick filaments
H zone: Middle of A-band, thick filaments only, no thin filaments
Zones During Contraction
- Z-lines closer together, sarcomere shortens
- H band shrinks/disappears
- I band shrinks
- A-band remains constant length
ATP Hydrolysis
Sliding Filament Theory Step 1
- ATPase in myosin head cleaves ATP into ADP and releases phosphate
- Positions myosin head correctly
Formation of Cross Bridges
Sliding Filament Theory Step 2
- Ca2+ released from SR binds to troponin upon signaling
- Alters troponin-tropomyosin complex, exposing myosin binding sites
- Allows myosin and actin binding
Power Stroke
Sliding Filament Theory Step 3
- ADP detaches from myosin head
- Myosin heads move towards sarcomere center, causing shortening
Breaking of Cross Bridges
Sliding Filament Theory Step 4
- Another ATP molecule binds to cross bridge
- Releases myosin from actin
Continuation of Process
- Continues with ATP and Ca2+ presence
- Nerve impulses trigger calcium release
- Without ATP, muscle stays contracted, leading to rigor mortis
Excitation-Contraction Coupling
- Link between sarcolemma action potential and muscle contraction initiation
- Action potential from motor neuron triggers muscle response
Neural Control
- Action potential in motor neuron initiates process at neuromuscular junction
Excitation
- Action potential causes ACh release from motor neuron
- Leads to sarcolemma excitation
Calcium Ion Release
Excitation-Contraction Coupling #1
- Muscle fiber action potential travels through T tubules/triads
- Triggers release of stored Ca2+ from sarcoplasmic reticulum
Contraction Cycle Begins
Excitation-Contraction Coupling #2
- Ca2+ binds troponin, exposing active sites on actin
- Cross-bridges form; continues with ATP/Ca2+ availability and action potentials
Sarcomeres Shorten
Excitation-Contraction Coupling #3
- Interaction of thick and thin filaments (sliding filaments)
- Shortens sarcomeres, pulls ends of muscle fibers closer
Muscle Tension Produced
Excitation-Contraction Coupling #4
- Fiber shortening causes entire muscle to shorten
- Contraction generates pull/tension on tendons
Delayed Onset Muscle Soreness (DOMS)
- Strenuous exercise leads to microscopic muscle tears
- Within 24-72 hours, inflammation causes:
- Pain, tenderness, muscle stiffness, and swelling (edema)
Muscle Strain
Result from excessive force causing muscle and tendon tears
Muscle Cramps
Painful, sudden, spasmodic muscle fiber contractions
