Exam 2: Muscles Flashcards
Thin filaments consist primarily of protein
actin
thin filaments are made of
F-actin, Troponin complex, Tropomyosin
G-actin monomers assemble to form
a polymer - 2 polymers become twisted to form a double-stranded helix (filamentous actin)
Troponin complex is made of
3 subunits (TnT, TnC, TnI)
TnT
attaches to Tropomyosin
TnC
binds Ca ions
TnI
binds troponin complex to actin
Inhibits actin-myosin interaction
Tropomyosin molecule consists of
2 polypeptide chains which form an alpha helix
Each tropomyosin molecule rests on
7 G-actin molecules and covers their active sites for myosin
Thick filaments consist of protein
myosin II
Myosin consists of
2 heavy chains (golf club heads) and 4 light chains
Heavy meromyosin
4 light chains + 2 globular heads (2 S1 moieties), and a short twisted tail (S2 segment)
Light meromyosin
long twisted tail - 2 chains wrapped around each other in an alpha-helix
sarcomere
overlapping actin (thin) and myosin (thick) myofilaments
myofibrils
long cylindrical series of end-to-end sarcomeres
Extend length of muscle cell
Muscle Fiber (cell)
many parallel myofibrils
Contractile unit of skeletal muscle is
a sarcomere
Z-line to Z-line
A-band
Dark band
thick and thin filaments
widest band
H-band
Thick filament only
bisects A-band
I-band
light band, thin filament only
Made of portions of adjacent sarcomeres
Z-line (disk)
attachment for thin filaments
Contains alpha-actinin, which anchors actin filaments to Z-disk
bisects I-band
M-line
consists of protein structures lying between thick filaments, holding them
Bisects H-band
Major protein in M-line
creatine kinase
Titin molecules
elastic protein
4 molecules anchor thick filament to Z-discs
alpha-actinin
component of Z-disk
anchors thin filament to Z-disk
nebulin
nonelastic protein, wrapped around each thin filament
anchors thin filament to Z-disk
Myomesin
secures thick filament at M-line
C protein
secures thick filament at M-line
Dystrophin
cytoplasmic protein that binds actin to laminin of external lamina surrounding muscle fiber
Sarcolemma
cell membrane, external lamina, and reticular lamina
Sarcoplasmic reticulum
muscle cell smooth endoplasmic reticulum
Endomysium
surrounds each muscle fiber (cell)
delicate layer of reticular fibers
perimysium
surround many fibers as a group to form a fascicle (bundle)
thin, collagenous connective tissue
epimysium
dense, irregular collagenous connective tissue that encloses fascicles to form gross muscle
Skeletal muscle
striated muscle
voluntary movement
quick and forceful contractions
Cardiac muscle
heart, striated, involuntary
contraction is rigorous and rhythmic
Smooth muscle
non-striated, involuntary
slow contraction
Muscle cell nuclei are
oval-fusiform shape and euchromatic
Skeletal muscle nuclei are located
on cell periphery
Transverse tubules (T-tubules)
invaginations of cell membrane (sarcolemma)
Lumen continuous with extracellular space and contain extracellular fluid
Carries nerve impulses deep into cell
Terminal cisternae
store calcium in lumen
form triad at A-I junction of sarcomere
Satellite cells
regenerative cells that lie between skeletal muscle and its external lamina
Proliferate after injury and form new myoblasts
Myasthenia Graves
autoimmune disease causing muscle weakness
Antibodies bind to acetylcholine receptors, preventing muscle contraction
Muscular Dystrophy
genetic, degenerative disease affecting striated muscles
Duchenne muscular dystrophy (DMD)
most common and severe form
Protein dystrophin is absent
causes muscle weakness and atrophy of shoulder, hip, pelvic, and thigh muscles
As disease progresses affects heart and breathing muscles, leading to death
Cardiac muscle
weakly striated (sarcomeres and myofibrils present) Cells short and branched Contain glycogen deposits
Lipofuscin
aging pigment, present in cardiac muscle cells of older people
Cardiac muscle nuclei
are located in center of cell
Atrial granules (membrane bound granules)
Contain atrial natriuretic factor and brain natriuretic factor
Most numerous in muscle fibers of right atrium
Diuretic hormones, act on kidneys to lower blood pressure
Cardiac muscle cells are covered in
endomysium - contain many capillaries
Intercalated discs
specialized intercellular junctions of myocardium
Transverse portion of intercalated disc
perpendicular to long axis of muscle fiber
Contains Fascia adherens - anchor actin filaments & Maculae adherents (desmosomes) - bind cells together
Lateral portion of myocardial intercalated discs
parallel to cells fibers
Contain gap junctions - permit flow of ions from cell to cell
Purkinje fibers
specialized cardiac muscle cells located in endocardium
Large, pale staining, contain glycogen deposits
Form impulse-conducting system of heart - relay electrical impulses to myocardial fibers
Heart muscle damage can be detected by
high troponin blood levels
Smooth muscle
forms sheets, no striations
Nucleus in center of cell - largest width
Dense bodies
myofilament bundles attach on internal surface of smooth muscle cell membrane
Caleolae
bubble-like structures on inner surface of cell membrane in smooth muscle cells - release Ca into cell for contraction
A nerve impulse is transmitted
down the nerve cell axon until it reaches the pre-synaptic membrane
What ions enter the pre-synaptic terminal following a nerve impulse?
Calcium ions
Ca ions trigger
synaptic vesicle to release their neurotransmitters into the synaptic cleft
What neurotransmitter triggers muscle contraction
Achetocholine
Following Ach receptor binding, what is the ion exchange in the skeletal muscle cell?
Na ions enter the cell, K ions leave the cell - sarcolemma is depolarized
Nerve impulse is carried deep into the muscle cell by
T-tubules
Sarcoplasmic reticulum contains what protein?
calsequestrin, which stores Ca ions
After the sarcoplasmic reticulum is depolarized, what ion is released?
Calcium ions, which bind to the TnC subunit of troponin complex
Binding of Ca ions to troponin causes
a conformation change, causing TnT subunit to push tropomyosin deeper into the actin groove uncovering actin active sites
Uncovering the actin active sites allows
myosin head to bind to the actin monomor, pulling the actin filament over the myosin filament
What is needed for myosin to move the actin filament?
ATP energy
Myosin slides the actin filament in which direction during contraction
closer to the midline of the sarcomere (M-band), shortening the sarcomere
During contraction the length of the thin and thick filaments
remains the same, their relative position is what changes
During contraction the A-band
remains the same size
During contraction the H-band and I-band
become smaller
During contraction the Z-discs
come closer toward the midline
Rigor mortis
at death, the actin-myosin complexes can’t dissociate since ATP is not available, so muscles stiffen
