Histology - Muscle Tissues Flashcards
degrades ACh in synaptic cleft.
ACh esterase (AChE)
a protein complex that connects the cytoskeleton of a muscle fiber to the surrounding extracellular matrix through the cell membrane.
dystrophin
dervied from mesoderm, striated, capilaries in intercellular spaces. Slow and fast fiber types.
skeletal muscle
aggregate at top of junctional folds
ACh receptors (AChRs)
associated with sweat glands, contain both actin and myosin. contraction mechanism similar to smooth muscle cells, but ectoderm derived.
myoepithelial cells
Contains the entire length of a single thick filament.
A-band
Dense bodies (where actin attatches) instead of Z disks as in skeletal muscle; have noncontractile intermediate filaments (along w/dense bodies, form intracellular cytoskeleton); has slower contraction speed than skeletal.
Difference in Smooth and Skeletal Muscles
calcium interacts with calmodulin, causing interaction between actin and myosin
Ca2+ in smooth muscle
presynaptic element
lower motor neuron (LMN)
cylinder-shaped, paralell, multinucleated, periferal nuclei. Mitochondria and myoglobin in high quantity.
skeletal muscle fibers structure
great capacity for hyperplasia and hypertrophy, (ex: uterus in pregnancy)
smooth muscle regenration
fast glycolitic muscle fibers, anaerobic respiration.
type II skeletal muscle
type III collagen are located external to the basal lamina. Hugh compnent of endomesium fround smooth muscle.
reticular fibers
calcium storage and release
Sarcoplasmic reticulum
Purkinje fibers
Purkinje fibers
receptors on t-tubule and SR interact to release calcium
depolarization down t-tubule
On perfery of muscle fibers, can undergo hyperplasia (mitosis) and hypertrophy by fusing with other skeletal muscles.
satellite cells
is the zone of thin filaments that is not superimposed by thick filaments.
I-band
Autoimmune disorder. Autoantibodies bind acetylcholine receptors in skeletal muscle, causing muscle weakness and potential death. Treatment includes AChE inhibitors
myasthenia gravis
branched, layered, mononucleated, central nucleus. Intercalcated discs with gap junctions, high mitochondria and myoglobin. diad at the Z disc.
structure of cms
enzyme that aids in active calcium reuptake by SR after contraction.
calsequestrin
A paler region within the A-band, zone of the thick filaments that is not superimposed by the thin filaments.
H-zone
Stain dark and lie just inside sarcolema. Interaction between them and reticular fibers that harnesses the force of contraction of the myofilaments, like wringining a sponge, Causes “corkscrew nucleus”.
dense bodies
Autonomic nervous system, Purkinje fibers (modified cardiac muscle cells), gap junctions.
cardiac muscle innervation
indentations in surface of sarcolemma, may act like T tubules and sarcoplasmic reticulum of skeletal muscle
Caveolae of Smooth Muscle
a layer of connective tissue, which ensheaths the entire muscle. dense irregular connective tissue, continuous with fascia.
epimysium
derived from mesoderm, striated, rich capillary beds in intracellular connective tissue, located in proximal portion of heart and pulmonary vessels.
cardiac muscle
a wispy layer of areolar connective tissue that ensheaths each individual muscle fiber. It also contains capillaries andnerves. It overlies the muscle fiber’s cell membrane: thesarcolemma.
endomysium
(from the German “Mittelscheibe”, the disc in the middle of the sarcomere) formed of cross-connecting elements of the cytoskeleton.
M-line
anchors thin myofilaments to Z disc.
a-actinin
two chains of F-actin, tropomyosin and troponin associate. Ca2+ causes conformational change.
thin myofilaments
two Z discs are brought closer together as myofilaments slide past each other.
Huxley’s sliding filament theory
Dystrophin or sarcolemma molecules absent or reduced causing muscle weakness and potential death. Treatment controls symptoms to maximize quality of life.
muscular dystrophies
fusiform-shaped, often in perpendicular layers, surrounded by basal lamina.
structure of smooth muscle fibers
new myofibrils form to increase fiber diameter
hypertrophy of skeletal muscle fibers
200-300 myosin molecules, 2 heavy and 2 light chains per myosin.
thick myofilaments
Ca2+ required to initiate contractions, binds to calmodulin (no troponin is smooth muscle) which regulates myosin kinase (transfers P+ group from ATP to light myosin on heads), cross-bridging occurs(enzymes are slower than skeletal, so slower formation)
Chemical Reaction of Smooth Muscle
Occurs following death because the lack of ATP preventing the dissassociation of actin and myosin. ATP important for relaxing muscle, dissociation of thin and thick myofilaments.
rigor mortis
prominent in wound contraction and tooth eruption deriving from connective tisues.
myofibroblasts
lower motor neuron (LMN) + muscle fibers
motor unit
They connect heart muscle cells, allowing them to work as a single functional organ. Have lateral and transverse portions. Lateral has gap junctions, and faces less stress in contraction. Transverse region contains adherens junctions.
Intercalated discs
Functional units of muscle fiber. Defined by Z lines.
sarcomere
anchors thick myofilaments to Z discs
titin
triad of structures at A-I junction, t-tubule, terminal cisternal of SR.
triad of structures at A-I junction
monitors length and changes in length of muscle, and participates in stretch reflexes. In OMM, an important target for effective treatment, i.e. counter-strain technique.
muscle spindle
slow oxidative muscle fibers, aerobic respiration
type I skeletal muscle
indicating the contracted state of the cell
“cork-screw” nucleus
a sheath ofconnective tissue that groupsmuscle fibers into bundles (anywhere between 10 to 100 or more) or fascicles.
Perimysium
mononucleate, central nucleus
no striations or sarcomeres
no t-tubules, but have caveolae
involuntary control by ANS
differences from skeletal muscle
Interferes with the release of acetylcholine from LMN causing muscle paralysis and potential death. Treatment can include an anti-toxin.
botulism
derived from mesoderm (and ectoderm), no striations, loacted in walls of hollow viscera, blood vessels, glands, dermis.
smooth muscle
Skeletal Muscle regulation of contraction
By binding of Ca2+ to TnC, causes tropomyosin movement and exposes myosin-binding sites on actin filaments
Cardiac muscle regulation of contraction
By binding of Ca2+ to TnC, causes tropomyosin movement and exposes myosin-binding sites on actin filaments
Smooth muscle regulation of contraction
By phosphorylation of myosin light chain by myosin light chain kinase in the presence of Ca2+-calmodulin complex
Muscle spindle function
monitors length and changes in length of muscle, and participates in stretch reflexes
T-Tubule Structure and Function
deep invagination of the sarcolemma that allow depolarization of the membrane to quickly penetrate to the interior of the cell, signaling Ca2+ release from sarcolema.
Transverse Portion of Intercalcated Disc
Adhering Junctions: Zonula Adherens and Macula Adherens (Desmosomes)
Lateral Portion of Intercalcated Disc
Gap Junctions
triad
A transverse tubule surrounded by two SR cisterna. Contact between these structures is located at the junction of the A and I bands.
Terminal Cisternae
Enlarged areas of the SR surrounding the t-tubules that store calcium (increasing the capacity of the SR to release calcium) and release it when an action potential courses down the t-tubules, eliciting muscle contraction.
Contraction mechanism of smooth muscle - detailed
Ca2+ binds to and activates calmodulin, which then binds to caldesmon. This binding causes the caldesmon protein to disengage from the actin filament, exposing the myosin-binding sites on the actin filament. Myosin motor heads are phosphorylated by myosin light-chain kinase, allowing the myosin head to interact with the actin filament and cause contraction.
