APK 2105C Study Guide - Quiz Guide: Endoplasmic Reticulum, Skeletal Muscle, Myocyte

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Chapter 12 All Lectures
Muscle Physiology
Lecture 1
Chapter 12, Lecture 1
Muscle Physiology
Skeletal muscle structure
o CT covering the outside of the
muscle = epimysium
o Fascicles = bunches within the
muscle
Paramysium =
surrounds the fascicles
and fills in gaps
between fascicle
o Myocyte = individual skeletal
muscle cell
Extremely longspan
the length of the muscle
Need multiple nuclei
Endomysium =
surrounds the individual
myocyte
Contains normal organelles and myofibrilscontractile organelle
Myofibrils push other organelles to the edges of the cell
o Nuclei are on the outside of the cell
Myofibrils are composed of protein filaments
o Actin
o Myosin
o Have dark and light stripescauses striated appearance
o Blood vessels and nerves throughout each layer of cells
o Sarc = flesh
o Sarcolemma = plasma membrane of skeletal muscle cell
o Sarcoplasm = cytoplasm inside a skeletal muscle cell
Myofibrils = contractile organelle that runs the length
of the myocyte
o Overlapping arrangement of myosin and actin
Thick filament = myosin
Thin filament = actin
Actin fills up most of the
structure
o Lots of mitochondria in myocyte
o T (transverse) tubule
Around and between the myofibrils
Invaginations of the sarcolemma into
the cell’s interior
o Sarcoplasmic reticulum (SR) = type of ER in
skeletal muscles
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Surrounds each myofibril and comes in contact with T tubule
Membranous organelle that surrounds the myofibrils
Terminal cisternae = enlarged regions of the SR that make contact with
the T tubules
Have 2 of them around a T tuble
Terminal cisternae + T tubule = triad
o 2 triads for every sarcomere
Function = store Ca
Normally, the muscle cell does not contain much Ca
Motor neurons travel down sarcolemma as T tubule to trigger
release of Ca
Ca is dumped into everything in the myofibrils
o Sarcomere = functional unit of
organization of the myofibril and its
overlapping arrangement of actin
and myosin to give the striated
appearance
Myofibril is formed by a
series of sarcomeres
Fills up the cells from end to
end
Goes from one Z disk to
another Z disk (Z disk = Z
line)
Myosin runs all the way
across the sarcomere
Actin has space in between
themallows for contraction
M line
Running down the middle of the sarcomere
Midline
Ends of myosin thick filaments are holding onto each other
o Heads on myosin are pointing towards the Z disk
A band = length of myosin
Darker than the I band
Actin myofilaments overlapping the myosin give the dark color
I band = only have actin myofilamentsmysosin myofilaments do not
encroach
Surrounds either side of the Z disk
Lighter than the A band
H zone = bare zone
No myosin headscannot attach to the actin myofilaments
No actin myofilaments in a relaxed muscle
6 actin surround each myosin
Contractile proteins
o Thin myofilaments = actin
Double helix structure
Each strand is made of individual protein structures = G actin
Have specific spots on protein = myosin binding site
Every G actin has a myosin binding site on it
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Tropomyosin
Long strand (longer name)
Covers myosin binding site
o When myosin binding site is
exoposedwill ALWAYS have
contraction
Troponin is associated with this protein
o Troponin
Ca binds to a protein in
the troponin complex
Ca causes shape change
in troponin to roll the
tropomyosin off of the binding site
Binding site is exposed so contraction can occur
Attached at the Z disks
o Thick myofilaments = myosin
Has fibrous and globular structure
Fibrous portion = double helix tail
o Bare zone = where the
tails all come together
Globular structure = glob tail that
the tail terminates at
o Heads are evenly
distributed throughout the
filament
o Actin-binding site
Connects to G
actin on the actin
myofilaments
o ATPase site
Enzyme on the head of myosin that functions to
hydrolyze ATP (dephosphorylate)
Releases energy to use in contractile
process
Stretched across the middle of the sarcomere
Actin and myosin overlap in outer region of A band
Titin
Coil at the end of myosin
Attaches the myosin to the Z disk
Very large protein
Highly elastic
o Allows muscle to stretch
o Allows muscle to recoilgo back to resting length without
damage
Lecture 2
Chapter 12, Lecture 2
Muscle Physiology
Sliding-filament mechanism of contraction
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