L14: Muscle Tissue Flashcards
muscle tissue types
skeletal
smooth
cardiac
skeletal muscle characteristics
- multinucleated
- peripheral nuclei
- striated
- each fiber innervated via single motor axon
- all or none AP
- myocyte = 50-60 microm
Myofiber types
type I
type IIA
type IIB
Myofiber type I
- intense oxidative staining
- rich in NADH, myoglobin
- posses many mitochondria
- primarily uses aerobic metabolism
- slow contractions
- dark or red fibers
Myofiber type IIA
-intermediate O2 staining
-aerobic and anaerobic
-more rapid than I
resistant to fatigue
Myofiber type IIB
- light staining
- anaerobic respiration
- rich in ATPase
- rapid contraction
- fatigue quickly
- white or light fibers
smooth muscle characteristics
- single nucleated cells
- no sarcomeric arrangement
- innervated via ANS
- not all or none
- cells connect via gap junctions
cardiac muscle characteristics
- single nucleated cells
- central nuclei
- cell branching
- sarcomeric arrangement
- cells communicate via gap junctions called intercalated discs
- cells are not directly innervated
hierarchy of skeletal muscle
epimysium muscle perimysium fascicle endomysium myofiber myofibrils =liner string of sarcomeres myofilaments
myofilaments
thick and thin
or
myosin and actin
epimysium
CT covering a muscle
perimysium
CT covering a fascicle
consists of fibroblasts and type I collagen
sarcolemma
a Myofiber = muscle cell
sarcolemma = muscle cell membrane
endomysium
CT covering the Myofiber
also covers sarcolemma
consists of basal lamina and reticular collagen fibers
basal lamina of endomysium
- secreted by muscle cells
- anchors muscle fibers to each other
- helps distribute the force of contraction
skeletal muscle fiber structure
- muscle fiber = muscle cell = bundle of fibrils made up of sarcomeres stacked on top of each other
- each sarcomere consists of Z lines, I bands, A band and H band
sarcomeres are separated from each other by ?
transverse discs called Z lines or discs
the A band consists of
the length of the myosin filament including the actin cross over section
the length of the A band is equal to ?
the length of the bundle of myosin filaments
the I band consists of?
the portion of actin filaments not overlapped by myosin at rest
the H band consists of?
only thick myosin, the portion not overlapped by actin
changes in band width with contraction
the I band shortens
H band may disappear
A band does not change
what happens to sarcomere length during contraction
it shortens, the Z discs get closer together
which results in the shortening of the muscle fiber during a contraction
3 dimensional shape of the sarcomere
hexagonal shaped
during contraction, forces develop between the actin and myosin filaments, to cause …..
sliding/contraction
sliding filament theory
when the concentration of ATP decreases, a back up source of energy
hydrolysis of creatine phosphate
thick filaments
- myosin
- myosin is a dimeric protein w/ long tails and 2 heads
myosin heads
- actin binding region
- ATP binding region
- light chain binding region
myosin light chains
- lost ability to bind Ca
- might stabilize heads
- required to stabilize myosin II: sites for phosphate binding
myosin arrangement in sarcomere
arranged tail to tail in center w/ heads attached to actin
results in myosin pulling actin inward from 2 directions
F-actin
- polymer of G-actin
- consists of 2 polymers in helical arrangement
- plus end inserts on Z-discs
actin-associated molecules
- troponin
- tropomyosin
actin: tropomyosin
- each one sits in groove between 2 actin strands of a filament
- each tropomyosin spans 7 actin monomers
troponin: actin
complex of 3 molecules
- troponin I
- troponin C
- troponin T
troponin I
inhibits binding between actin and myosin
troponin C
binds calcium ions
troponin T
binds to tropomyosin
location of T-tubules in skeletal muscle
located at the A-I junctions
location of mitochondria in skeletal muscle fibers
located between myofilaments
nebulin
-extends from Z disc to end of actin filament
template to regulate length of actin
titin
large fibrous protein
- spans Z to mid H
- connects ends of thick filaments to Z-line
- gives myosin elasticity
- centers myosin
ab-crystallin
heat-shock protein that protects desmin from mechanical stress
dystrophin
- links a-actin/desmin complex to cytoplasmic side of sarcolemma
- links actin to transmembrane proteins
- anchors actin
- reinforce sarcolemma
dystroglycan complex
links dystrophin intracellular to laminin-2 (extracellular)
a-actinin
attaches thin filaments to z-line
desmin intermediate filaments
- framework of desmin filaments which surround the Z-line and extend into each sarcomere
- link myofibrils laterally to sarcolemma
plectin
binds desmin filaments
myasthenia gravis
antibodies bind to ACH ligand receptors inhibiting full muscle contractions
muscular dystrophy
inherited disease resulting in progressive degeneration of skeletal muscle
dystrophin is absent/abnormal in Duchenne’s or becker’s muscle dystrophy (respectively)
satellite cells
- attach to myotubes before basal lamina is laid down
- function as stem cells
- become mitotic under stress
- give rise to myogenic precursor cells
myogenic precursor cells
replace damaged muscle by proliferating, fusing and differentiating into skeletal muscle fibers
satellite cells are involved in ?
repair, maintenance and regeneration of skeletal muscle tissue
mitotic satellite cells
C-Met receptor is binding site for HGF
hepatic growth factor
satellite cell staining
stain like the nuclei but have a dark band around them
use stain CD56 specifically
satellite cells can also play a role in ?
hematopoiesis
components of the neuromuscular spindle
- extrafusal fibers
- intrafusal fibers
- alpha motor neurons
- gamma motor neurons
- primary and secondary afferent fibers
fusal = ?
fusiform shape
spindle = fusiform shaped structure
intrafusal fibers
- nuclear bag region
- nuclear bag fibers
- nuclear chain fibers
nuclear bag region
- -intrafusal fibers
- -the sensory region of the neuromuscular spindle
what supplies the extrafusal fibers ?
alpha motor neurons
extrafusal fibers = skeletal muscle fibers
gamma motor neurons
supply the intrafusal fibers
afferent fibers are _____ fibers
sensory
A1-motor fibers
supply ends of the nuclear bag or chain fibers
characteristics of cardiac muscle tissue
- single central nuclei
- branching of cells
- sarcomeric arrangement
- intercalated discs
- cells not directly innervated
cardia T-tubule system
- not as extensive as skeletal muscle
- 1 tubule per 1 cisternae = diad
- diads at Z-lines
purpose of intercalated discs
allow cardiomyocytes to communicate via gap junctions
composition of intercalated discs
- macula adherents = desmosomes
- fascia adherents
- gap junctions
intercalated disc macula adherents
=desmosomes
- -link intermediate filaments of adjoining cardiomyocytes
- -transverse component
intercalated disc fascia adherents
- -anchor actin filaments of sarcomeres
- -transverse component
cardiac macula adherents link ?
desmin (intermediate filaments) to adjoining cells
transverse components
hold cardiomyocytes together
intercalated discs: longitudinal component
gap junctions
what secretes ANP?
cardiac muscle cells in atria
ANP
atrial natriuretic peptides
function of ANP
- regulate fluid electrolyte balance
2. relax vascular smooth muscle to reduce blood vol. and press.
storage of ANP
stored in atrial muscle cells as a prohormone in secretory vesicles
release of ANP
release is stimulated by atrial stretch—when larger volumes of blood enters atria
resulting in cleavage of the prohormone so ANP is released
other names for smooth muscle
involuntary
visceral
smooth muscle cell characteristics
- single central nuclei
- no banding pattern
- innervated via ANS
- not “all or none”
- cells connected via gap junctions
smooth muscle cells can also be innervated by ?
the enteric system
GI system
smooth muscle actin and myosin bundles are incorporated into a _______ arrangement, found throughout the ______ except in ______ area.
meshwork arrangement
throughout cytoplasm
except nuclear area
dense bodies are associated with what type of muscle tissue
smooth muscle tissue
functions of dense bodies
- anchor actin to each other and cell membrane
2. communicate force of contraction to cytoskeleton and cell membrane
structure of dense bodies
- contain a-actinin
2. interconnected by desmin
location of dense bodies
cytoplasm
cell membrane
of smooth muscle cells
smooth muscle cells do not have ?
T-tubule system
or
extensive SR
where does smooth muscle get it’s Ca for contraction?
all extracellular
purpose of pinocytotic vesicles in smooth muscle
–transport Ca from extra to SR
caveolae of smooth muscle
vesicles that appear
not sure of their purpose
probably involved in trafficking of particles
initiation of caveolae formation
caveolin binds to cholesterol in lipid rafts
stims caveolae formation
smooth muscle lipid rafts
a depression of cell membrane involved in fluid and electrolyte transport
lipid raft composition
composed of cholesterol and sphingolipids
innervation of smooth muscle cells may either ____ or ______ contraction of muscle cells.
facilitate or inhibit
most organs have smooth muscle ….. ?
smooth muscle sheets that are poorly innervated
excitation is conducted via many gap junctions
adrenergic and muscarinic receptors
linked to G-proteins
nicotinic cholinergic receptors
cation channel
caveolae start as ….
a lipid raft that is taken inward as a pinocytic vesicle
