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Muscle Part 1

Muscle part 1

What control is skeletal muscle under? Striated? voluntary control by CNS. Yes
What are the principal cells of skeletal muscle? Large multinucleated syncytium
What constitutes a myofiber? Small myoblasts that fuse together to form a tube that matures
What is each cell lined with? A basement membrane and endomysium
What is a fasicle? What is it enclosed by? A bundle of fibers enclosed by perimysium
How are fasciles held together? By Epimysium
Where is the nuclei located in skeletal muscle? At the periphery
In muscle disease where do the nuclei end up? In the interior of the fiber
What is the plasma membrane referred to? Sarcolemma
Each fiber is innervated by how many nerves? A single nerve for each fiber
What makes up a motor unit? A single nerve that branches off and one nerve will innervate a set of fibers
When is recruitment of motor units important? When you are using all of your strength
What are myofibrils? Contractile organells that are embedded in the cyoplasm and ends of fibers
When are myofibrils triggered to shorten? when the cells are activated my a nerve
What is the sarcoplasmic reticulum? internal membranes. It surrounds each myofibril which is important in the activation mechanism
Why are most of the ribosomes free in skeletal muscle? Because they are not making a lot of proteins for export but for internal use
What makes up a sarcomere? From one Z line to another Z line
What forms an A band in the sarcomere? Thick myofilaments
What do the thick myofilaments contain? Myosin which has 2 globular heads and 2 helical tail regions that wrap around each other
What does the globular head of myosin conatin? Myosin light chains:Noncovalently sit on globular heads(conatin ATPase. Also actin binding sites.
What type of process does myosin assemble? By a bipolar process
Describe thin filaments and components Formed by actin. A double helix (that can't be separated). Tropomyosin sits on groove of helix and troponin sits on tropomyosin.
What do thin filaments insert into? Into the Z line
What interconnects the Z lines? Intermediate filaments that resist pulling
What proteins are Z lines comprised of? Alpha-actin and desmin(glue function)
Describe the titan protein and its functions Extends from the Z-lines along thin filaments and touches thick filaments. It is a molecular spring to sense tension. It can bind to transcription factors important in protein degradation inf the mulscle. It can translate tension into growth stimulation
What does cross bridges refer to? The crossing of thin and thick filaments. The overlap changes
What is riggermortus? Stiffening of the muscle due to death of a cell
How is cross-bridges regulated? Tropomyosin-Troponin position that blocks myosin from binding to actin. When a muscle is activated calcium is relased and binds to the troponin C-subunit which causes a rotation of tropomyosin-troponin and exposes the myosin-binding site on actin
What causes calcium to rise? Depolarization. T-tubules have voltage sensor which triggers change in calcium channel. Calcium is released through ryanodine channel and goes to cytosol to bind to troponin
What can anesthetics trigger and how is it treated? Excessive, uncontrolled release of calcium through ryanodine channel and cause muscles to heat up and super contract. Dantrolene blocks calcium channel.
What is a muscle spindle? where is it found? Encapsulated structure in usually perimysium. It functions in proprioception, sensing muscle tension to feed back to CNS for regulation



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