muscles Flashcards
syncytium
contains many nuclei in a common cytoplasm; skeletal muscle cell
what are contractile proteins synthesized into in cytosol
myosin thick and actin thin filaments
what is muscle fiber made of?
myofibrils
what is muscle fiber further organized into?
fascicles, and into anatomically identifiable muscles
myofiber
each muscle cell, made up of myofibrils
sarcomere I band
only actin
sarcomere H band
only myosin
M line
bisects H and A bands
Z line
bisects the I band (*made of alpha actinin)
titin
large thick filament associated protein
nebulin
thin filament associated protein
desmin
intermediate filament protein
calsequestrin
calcium binding protein
neuromuscular junction
where myofiber and axon terminus meet
primary synaptic cleft
shallow trough in which the axon terminal lies
secondary synaptic clefts, or junctional folds
sarcolemma invaginations to increase surface area at site of junction
how is muscle stabilized
basal lamina and reticular fiber
how does dystrophin work?
anchors the cortical actin network ot the extracellular matrix through the interaction of its N-terminus with F0actin, and the interaction of its C termninus with a transmembrane complex of dystrophin-associated proteins and dystrophin-associated glycoproteins.
dystrophin-transmembrane protein/ glycoprotein complex
stabilizes association between myofibrillar proteins inside the muscle cell and the extracellular basal lamina. protects physical integritiy of the muscle.
three types of connective tissue that organize myofibers
endomysium, perimysium, epipysium
endomysium
surrounds each myofiber
perimysium
bundles several myofibers into groups called fascicles
epimysium
dense CT sheath that finds fascicles together to form the muscle body
role of mytendinous junction
attaches skeletal muscle to bone via tendon
muscle spindle
encapsulated, lymph filled, fusiform structures that lie parallel to the skeletal myofibers in connective tissue bet. bundles of myofibers.
intrafusal fibers
contained by muscle spindle. modified muscle fiber. has a central nonstriated area where nuclei are concentrated.
two types of intrafusal fibers
nuclear bag fibers
nuclear chain fibers
two types of sensory fiber receptors associated with intrafusal fibers
annulospiral endings
flower-spray endings
what happens when muscle is stretched
sensory fiber receptors are distorted and stimulated, and the relay of this info leads to contraction
satellite cells
stem cells in adult muscle. proliferate after injury to generate new myoblasts. reside underneath the basal lamina.
where are cardiac muscle cells found
myocardium of heart and in the walls of the large veins at their junction with the heart. mononucleated
organization of cardiac muscle includes
myofibrils in sarcomers, intercalated disks, abundant mitochondria
role of intercalated disks
organize several specialized junctions for stable adhesion and communication
what kind of junctions in intercalated disks
desmosomes, fascia adheres, gap junctions
what does desmin do in cardiac muscle cells?
the intermediate filament protein associated with desmosomes
diads
formed between SR and T tubules in cardiac myocytes. Present at the Z lines.
cardiac T tubules
are thicker
SR in cardiac myocytes
less extensive; uses extracellular calcium
delicate CT endomysium
surrounds individual cardiac myofibers.
where is a rich capillary network present
cardiac myocyte
role of perimysium in cardiac myocytes
myofibers are bundled into groups. collagenous fibers are coarser than those of endomysium
Purinje fibers
modified cardiac myocytes. conduct impulses from AV node through ventricular septum into the ventricles. these cells have few poorly organized myofibrils. no t tubules.
myofilaments in smooth muscle contain mostly
actin; not arranged in sarcomeres or myofibrils
dense bodies
in sarcoplasm. contain alpha-actinin and are analogous to Z lines of striated myofibers. serve as anchoring sites for actin myofilaments
attachment plaques
anchoring site for actin myofilament
what role does desmin play in smooth muscle?
intermediate filaments associated with attachment plaques
what happens during smooth muscle contraction?
their nuclei coil up
does smooth muscle have SR?
yes, but it is poorly elaborated
two types of smooth muscle tissue
unitary (visceral); multi-unit
visceral (unitary) smooth muscle
found in walls of many hollow organs. exhibit sustained contractions or waves of contraction. few are innervated. connected by gap junctions. spontaneous depolarization.
multi unit smooth muscle
rely upon neural stimulation of contraction. cells receive individual innervation. undergo relatively rapid, precisely graded contraction. sphincter pupillae of eye and arrector pili muscles of skin
