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BIOD27H3 Study Guide - Endoplasmic Reticulum, Myocyte, Myosin Head


Department
Biological Sciences
Course Code
BIOD27H3
Professor
Catherine Nash

Page:
of 26
FINAL EXAM REVIEW
Lecture 17 – Skeletal Muscles
oattached to bones of the skeleton by tendons (collagen)
opositions and moves the skeleton
o40% total body weight
ocontracts in response to a signal from a somatic motor neuron
o cannot initiate own contraction
o contraction not influenced by hormones
Smooth Muscle
oprimary muscle of internal organs (except heart)
o influence the movement of materials around and in and out of the body
o multiple levels of control
o primary extrinsic control arises from autonomic nervous system (ANS)
o some can contract spontaneously – i.e without signals from CNS
omodulated by endocrine system
Cardiac Muscle
oonly found in the heart
omoves blood through circulatory system
omultiple levels of control
oprimary extrinsic control arises from autonomic nervous system (ANS)
o some can contract spontaneously – i.e without signals from CNS
Skeletal Muscle
oOrigin:
- point of musclebone attachment closest to the trunk.
- usually more stationary.
oInsertion:
- The point of muscle bone attachment more distal (distant) from the trunk.
- usually more mobile
Flexor and Extensor muscles
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oFlexor muscles: brings bones closer together
e.g bicep
oExtensor muscles: moves bones away from each other
e.g tricep
oMost joints have pairs of muscles: 1 flexor, 1 extensor
o Antagonistic muscle groups:
- flexor-extensor pairs exert opposite effects
- when one contracts, the other relaxes
Skeletal muscles are composed of muscle fibres
oMuscle cells are the largest cells in body
oGroups of muscle cells function together as a unit
oLong, cylindrical with up to several 100 nuclei each muscle fibre (or cell)
oFibres arranged in parallel
oEach muscle fibre is covered in connective tissue
oGroups of adjacent fibres are contained in fasicles
oCollagen, elastic fibres, nerves and blood vessels are found between the fasicles
oEntire muscle is enclosed in connective tissue and tendons
Components of muscle fibres
oMuscle fibre: comprised of myofibrils, which contain thick and thin filaments
- the contractile machinery of the muscle
oSarcolemma = Cell membrane
oTransverse tubules (T-tubules) = Invaginations of the sarcolemma
oSarcoplasm = Cytoplasm (contains mitochondria and glycogen for muscle contraction)
Sarcoplasmic reticulum (SR) = Modified endoplasmic reticulum
- Wrapped around myofibrils
- releases Ca during muscle contraction
oMitochondria : provides ATP for muscle
contraction
T Tubules allow conduction of the Action
Potential
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Transverse tubules (T-tubules): invaginations of the sarcolemma, closely associated with terminal
cisternae to form a triad.
- membrane of t tubules is continuous with muscle fibre
- lumen of t-tubules are continuous with extracellular fluid
- allow depolarisations of sarcolemma to quickly reach interior of a muscle fibre.
- transport Action Potentials from NMJ to interior of fibre
Sarcoplasmic reticulum (SR) : releases Ca2+ ions from the terminal cisternae
- terminal cisternae gathers and stores Ca2+
Myofibrils are the contractile units of muscle fibres
-highly organised bundles of contractile and elastic
proteins that carry out
work for contraction
- one muscle fibre contains a 1000 or more
myofibrils
Components of myofibrils
Sarcomere: fundamental contractile unit of myofibril that repeats throughout the length of the myofibril
Sarcomeres contain:
Myosin (thick filaments)
Actin (thin filaments)
Two Z lines per sarcomere
Actin (thin) and Myosin (thick) filaments are sandwiched between Z lines
Z lines: Zig-zag protein structures
Attachment site (anchor) for thin (actin) filaments
M line: proteins that form attachment sites for
thick (myosin) filaments
- equivalent to Z disk for thin filaments
A Band: Darkest band
Encompasses entire length of thick filament
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