unit 4 Flashcards
what are the four properties of muscle?
excitability, contractility, extensibility, elasticity
what does a skeletal muscle consist of?
contractile tissue composed of muscle cells
a series of collagen-based connective tissue coverigs
what do the connective tissue coverings do?
bind muscle fibers, link skeletal muscle to bone, transduce force to attached structures, convey neurovasculature
how are skeletal muscle cells developed?
myoblasts fuse to form a single skeletal muscle cell
once fusion occurs, muscle fibers cannot divide
how do muscles enlarge?
by hypertrophy
what are satellite cells?
myoblasts that remain in muscle
stem cell like cells
how does muscle fiber regeneration occur?
satellite cells divide and fuse to form new muscle fibers
they are activated when needed for healing
features of skeletal muscle
long cylindrical cells, multinucleate, appears striated due to overlapping thick and thin filaments
longitudinal skeletal muscle
cross section skeletal muscle
endomysium
layer of reticular fibers that surrounds individual muscle fibers
perimysium
CT layer that surrounds a group of fibers to form a fascicle
epimysium
dense CT that surrounds a collection of fascicles
deep fascia that surrounds muscle
what is a fascicle
multiple muscle fibers grouped
functional unit of muscle
denervation atrophy of skeletal muscle due to motor neuron damage
what is the myotendinous junction?
site of attachment of a muscle fiber and the contiguous CT of the tendon
what is the purpose of a myotendinous junction?
increase SA of contact and enhance adhesion
what surrounds each muscle fiber?
capillary beds
where are the parts of a nerve that go to skeletal muscle?
cell body - SC or brain
axon - in neurovascular bundle to muscle
fine movement
a few branches innervate a small number of muscle fibers
gross movement
many branches innervate thousands of muscle fibers
red fibers
type I, slow
slow contraction speed, fatigue resistant
intermediate fibers
type IIa, fast oxidative-glycolytic
fast contraction speed, relatively fatigue resistant
white fibers
type IIb, fast glycolytic, fast twitch
fastest contraction speed, fatigue quickly
structure of myofibrils
long bundles of myofilaments that extend the entire length of the fiber and occupy most of the sarcoplasm
A band
contain thick filaments and overlapping thin filaments
I band
remaining thin filament
Z line
protein dense regions separating sarcomeres
H zone
portion of A band containing only thick filaments and no myosin heads
M line
protein dense region in the middle of the H zone
how are adjacent sarcomeres structured?
they are aligned
what is myosin?
a molecular motor protein that is a major component of thick filaments
what are myosin composed of?
2 heavy chains and 4 light chains
structure of myosin
tails associate in antiparallel fashion with a central bare zone and myosin heads that radiate around ends
what does a myosin head contain?
actin binding site and ATP binding site
what is actin?
a major component of thin filaments that contains a binding site for myosin head
what does tropomyosin do?
covers myosin binding sites on actin
what does troponin T, I, and C do?
T - binds to tropomyosin
I - binds to actin
C - binds to calcium
what does the binding of TnC and Ca do?
causes conformational change where tropomysoin moves to make the binding site on actin accessible
which filament slides during muscle contraction?
thin filaments slide over thick filaments toward M line
what zones/bands change during muscle contraction?
Z discs, I bands, H zone
what is the sarcoplasmic reticulum?
a special type of sER that is composed of membranous sacs and anastomosing channels encircling each myofibril
terminal cisternae
dilated sacs at ends of each sarcoplasmic reticulum networks
what is the function of the sarcoplasmic reticulum?
stores high concentrations of stored Ca2+ in terminal cisternae
where are mitochondria and glycogen deposits located?
adjacent to sarcoplasmic reticulum
what are transverse tubules (T-tubules)
invaginations of sarcolemma into the cell
what do T-tubules form?
a network of channels lined by specialized plasma membrane that wrap around each myofibril
triad
t-tubules associate with terminal cisternae of two sarcomeres
neuromuscular junction structure
axon forms a dilation called axon terminus that houses synaptic vesicles
axon termini lie in a depression of the sarcolemma
function of neuromuscular junction
initiate events that lead to skeletal muscle contraction:
Ach released and binds to AchR on sarcolemma, leads to influx of Na+, depolarizes membrane, action potential is reached
once an action potential is reached at the NMJ, what happens?
Ca2+ released from SR into sarcoplasm cause troponin to move tropomyosin, the contraction cycle begins
contraction cycle
longitudinal cardiac muscle
cross section cardiac muscle
three types of cell junctions in intercalated discs
fascia adherens, desmosomes, gap junctions
fascia adherens
hold cells together, link to actin in nearest sarcomere
similar to adherens junctions
desmosomes
hold cells together, link to IF network
similar to maculae adherens
gap junctions
spread action potential , allow for coordinated contraction
how is contraction of cardiac muscle initiated?
by cardiac conducting cells (modified cardiomyocytes)
cardiac muscle contraction
membrane is depolarized which extends to T-tubules
signals SR, releases Ca2+
Ca2+ binds to TnC…
how does the depolarization signal travel in cardiac cells?
from one cell to the next via gap junctions, slower than skeletal muscle
cross section smooth muscle
longitudinal smooth muscle
unique features of smooth muscle
no T-tubules
non-striated
stretchier and greater contractile time
can contract in wave pattern or along the entire length
robust cell proliferation
visceral smooth muscle
in walls of vasculature and hollow organs
connected via gap junctions for rapid spread of action potential
multiunit smooth muscle
few gap junctions, each cell acts independently
myofilaments in smooth muscle
organized into bundles that are oriented in all directions
initiation of smooth muscle contraction
electrical, mechanical, chemical
smooth muscle contraction
thin filaments slide past thick which generates tension transmitted to IFs, IFs pull on sarcolemma
shortening occurs in all directions
