U3 Lecture 19 Flashcards
- describe the organization of muscle and the connective tissues surrounding each structure - diagram and label the major structural and contractile elements of a muscle fiber, and describe the function of each element - diagram and label the major contractile and regulatory elements of the sarcomere - diagram and label the thin and thick filaments including all of the proteins that make up each myofilament - give a general description of the sliding filament mechanism
Structural organization of skeletal muscle
- Muscles covered by epimysium are made of groups called fasicles covered by perimysium which is made of groups called individual muscle fibers surrounded by endomysium
What level of organization is each layer of skeletal muscle?
- organ level : muscle
- Tissue level : fasicles
- Cellular level : muscle fibers
- Chemical level : myofibrils
What are muscle cells called?
Fibers
Why are muscle fibers multinucleated?
The develop from the fusion of myoblasts
Define hypertrophy
the growth of muscles due to an increase in muscle cell size
Define hyperplasia
growth of muscle due to an increase in muscle cell number
How do muscles develop and grow?
- after birth, growth of muscle fibers happens by hypertrophy (not hyperplasia) bc muscle fibers cannot undergo mitosis
What type of cells are able to undergo mitosis and aid in muscle regeneration?
Satellite cells
What are the 3 C’s of skeletal muscle physiology?
- Conduction
- Control
- Contraction
Define conduction
Conduction of electrical signals
- It results from EXCITATION of a muscle fiber
- occurs @ sarcolemma
Define sarcolemma
the plasma membrane of skeletal muscle fibers
- forms transverse tubules (T-Tubules) that run through the muscle fiber
Define control
Control of muscle contraction
- regulates activities of smooth ER in skeletal muscle fiber (= sarcoplasmic reticulum SR)
What does the SR do in muscle fibers?
SR stores Ca2+
Surrounds myofibrils
E-C coupling releases Ca2+ from the SR to start contractions
The SR stops contractions later by recovering more Ca2+
Define contraction
Contraction of muscle
- carried out by the cross bridge cycle
- results from the shortening of organelles called myofibrils in the cytoplasm of skeletal muscle fibers
What is myofibril made of?
Sarcomeres composed of actin and myosin
What causes striations on muscle fibers?
The alignment of sarcomeres
Structure of sarcomeres
Z disc, I band, Zone of overlap, H zone, M line, thin filament (actin) and thick filament (myosin)
What increases in a sarcomere during contraction?
Zone of overlap
What stays the same in a sarcomere during contraction?
A band
What are the contractile proteins in muscle?
Actin and myosin
What are the regulatory proteins in muscle?
Troponin and tropomyosin
What are the structural proteins in muscle?
Titin, dystrophin, alpha-actin, myomesin, and nebulin
Define actin
- found in thin filaments
- has myosin binding sites for crossbridge formation with myosin
- actin is the “red” circles on models in class
Define myosin
- in thick filament
- myosin heads connect to myosin binding sites on actin
Define tropomyosin
- in thin filaments
- covers the myosin binding sites on actin when its relaxed
- its the band that actin and troponin is attached to
Define troponin
- in thin filaments
- holds tropomyosin in place when relaxed
- during contraction, Ca2+ binds to it and causes tropomyosin to move away from myosin binding sites on actin
- other colored balls on thin filament
Define titin
- spans half of sarcomere length (z disc to M line)
- stabilizes the position of thick filament, eleasticity and extensibility, lets sarcomere return to length after contraction
- spring by z disc extends to m line
Define Dystrophin
- cytoskeletal protein that links the thin filament to the sarcolemma
- attached to the extracellular proteins in the connective tissues surrounding the muscle fibers
- helps transmit tension from the sarcomeres to tendons
Define nebulin
- spans the length of the thin filament (little protein line in middle of actin line)
- anchors thin filament to Z disc
Define alpha-actinin
- protein in Z disc
- binds to actin molecules of the thin filament and to titin
Define myomesin
- protein in M line (“paper chains”)
- binds to titin and thick filaments at m line
Define sliding filament model of muscle contraction
Actin and myosin filaments slide over each other to shorten the length of muscle fibers
Steps of sliding filament model
- myosin heads bind to actin to form cross bridge
- conformational change (energized by ATP hydrolysis) causes thin filaments to slide along thick filaments
- Myosin head group releases, forms new cross bridge, sliding cycle repeats
