Muscle Physiology Flashcards
describe muscles in a simple manner
excitable tissues (like neurons)
how does the action potential affect muscles
induces contractions to generate force for movement
what are the types of muscles
- smooth
- cardiac
- skeletal
what are the main parts of a skeletal muscle structure
- tendons
- epimysium
- fascicles
- perimysium
- muscle fibres
- endomysium
describe tendons
thick connective tissue that connects to bones
describe epimysium
- continuation of tendon
- thin outer covering of entire muscle
describe fascicles
bundles of muscle fibres
describe perimysium
covering of fascicle
describe muscle fibres
= muscle cells
describe endomysium
covering of muscle fibres
what is gross muscle made of
bundles of fascicles
what are the main components of a muscle fibre
- sarcolemma
- sarcoplasm
- sarcoplasmic reticulum
- transverse (T) tubules
- (multi)nuclei
describe the sarcolemma
muscle plasma membrane
describe the sarcoplasm; what does it consist of
muscle cell cytoplasm; consists of mitochondria and myofibrils
describe the sarcoplasmic reticulum; what does it consist of
muscle ER; consists of lateral sacs/terminal cisternae
what is a triad and what does it do
1 t-tubule in middle and 2 terminal cisternae at ends (swelling), which plays a role with propagating AP leading to muscle contraction
draw out the structure of sarcolemma to triad
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draw out the components of a muscle fibre
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draw out the skeletal muscle structure
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how do the SR and terminal cisternae work together
calcium pumps on SR membrane which allows for active transport of calcium ions into SR for storage in TC
how do SR and T-tubules work together
activate muscle contractions (propagating AP); transmit signals from sarcolemma to myofibrils
describe myofibrils; what protein fibres does it contain
lowest level of bundles (molecular level) and contains actin and myosin protein fibres
describe the functional unit of myofibril
sarcomere; has A and I bands, M and Z (start and end) lines, H zone
describe the arrangement of muscle that makes it look the way it does
thick and thin filaments arranged in a manner that gives stripey appearance
what type of a filament is myosin; actin?
thick; thin
draw out a myofibril
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what is the Z-line
the area where thin filaments are held together (edge of sarcomere)
what is the M-line
middle of sarcomere where thick filaments are linked together
what is the I-band
area of sarcomere with only thin filaments (light in colour)
what is the H-zone
area of sarcomere with only thick filaments
what is the A-band
area of sarcomere with mainly thick filaments with overlap of thin filaments at edges (dark in colour)
what are the main parts of thin filament structure
G-actin with binding site making actin protein making F-actin making thin filament
what are the regulatory proteins of the thin filaments
tropomyosin, troponin
what is the role of tropomyosin
overlaps myosin binding sites on actin
what is the role of troponin
complex of 3 proteins; attaches to actin and tropomyosin which then binds Ca (reversibly) and allows for regulation of skeletal muscle contraction
describe the thin filament structure shape
double stranded, helical/twining
describe the thick filament structure shape
many hockey stick structures bound together, each end of hockey stick is myosin head binding site (crossbridge)
what do the myosin heads bind for
actin and ATPase
draw flow of main parts of sarcomere structure at the molecular level
z-line -> titin -> thick and thin filaments overlapped -> z-line
what is titin
- elastic and structurally supportive protein
- when muscle contracts and expands, titin produces elastic force allowing sarcomere to stretch and return back to shape
list the mechanisms of generating force in muscles
- sliding filament model
- crossbridge cycle
- excitation-contraction coupling
describe the sliding filament model
- thin and thick filaments overlap
- slide past e/o
- individual filaments do not shorten but appearance turns short of muscle
how does sliding happen
cyclical formation and breaking of crossbridges
describe the steps of crossbridge cycle
- myosin head goes through conformation change due to ATP hydrolysis
- cyclic binding/unbinding of crossbridges to thin filaments
- results in thin filaments moving toward M line of sarcomere
the crossbridge cycle alters the energy content of myosin molecules. describe the energy forms
- high energy: ADP + P bound to myosin so it stores energy (high affinity for actin)
- low energy: ATP bound to myosin (low affinity for actin)
draw out the crossbridge cycle
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why are crossbridges out of sync but go through the cycle simultaneously
to allow for gradual movement
what would happen if crossbridges were in sync
inefficient use/generation of power
describe excitation-contraction coupling
- explains how muscle contractions turn on and off
- sequence of events where an AP in the sarcolemma cause contraction
- dependent on neural input from motor neuron
- requires Ca release from SR
describe the role of the neuromuscular junction
- nerves and muscle fibres meet here
- essential synapse for muscle contraction and movement
- motor neuron innervates several muscle cells which releases acetylcholine
- potential generated in end plate to trigger AP in muscle cell
motor neuron AP ______ creates muscle cell AP
always
what are the roles of Ca, troponin and tropomyosin in excitation-contraction coupling
- low/no Ca: troponin holds tropomyosin over myosin binding sites on actin
- Ca present: binds to troponin causing movement of troponin then tropomyosin and exposes binding sites for myosin on actin
- cycle occurs and muscle contracts
draw a diagram of excitation-contraction coupling
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what are the receptors and releases that cause AP in T-tubule membrane to lead to calcium release from SR membrane
- DHP and ryanodine receptors
- calcium-induced calcium release
draw gating of SR calcium channels before and after AP
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