Muscle Tissue I: Lecture 15 Flashcards
skeletal muscle tissue
voluntary long, cylindrical multinucleated muscle cells; connected by nerves
cardiac muscle tissue
involuntary, branched, uni or binucleated, connected by gap junctions
smooth muscle tissue
involuntary, short spindle shaped, uninucleated, connected by gap junctions
muscle extracellular matrix
endomysium- holds muscle cells together within muscle tissue
muscle cell characteristics
contractility, excitability, conductivity, distensibility, elasticity
contractility
ability of protein fibers within myocytes to draw together
excitability
responds to electrical or chemical stimuli
conductivity
conduct stimulus (electricity)
distensibility
can be stretched up to 3x resting length
elasticity
ability to regain original state after stretching
myocyte
muscle cell
sarcoplasm
myocyte cytoplasm
sarcolemma
myocyte plasma membrane
sarcoplasmic reticulum (SR)
modified endoplasmic reticulum; forms web-like network surrounding myofibrils, varies in structure in three types of muscle tissue
myofibrils
unique cylindrical organelles found in muscle cells; 50-80% of cell volume; bundles of specialized proteins that allow for contraction
muscle organelles
(such as nucleus, mitochondria) packed between myofibrils
structure of skeletal muscle fiber
thin cylinders consist of many fibers, surrounded by endomysium
length: up to 30 cm
thickness: up to 100 micrometers
transverse tubules (t-tubules)
deep inward extensions of sarcolemma that surround each myofibril; form tunnel-like network within muscle fibers
continuous with cell exterior, filled with extracellular fluid
terminal cisternae
enlarged sections of SR, flank each t-tubule
triad
two terminal cisternae plus corresponding t-tubule form triad
types of myofilaments
thick, thin, elastic
filament proteins
actin, myosin, titin, tropomyosin, troponin
thick filaments
-contractile protein myosin
-globular heads at each end linked by intertwining tails
-connected to tailes by hinge-like neck
-active site that binds with actin
thin filaments
-actin, tropomyosin, troponin
-multiple actin subunits string together; form two intertwining strands in functional thin filament
-each bead-shaped actin has active site, binds with myosin heads
thin filament function
tropomyosin: long, rope-like regulatory protein; twists around actin, covering up active sites
troponin: small globular regulatory protein; holds tropomyosin in place; assists with turning contractions on and off
I band
light band, only thin filaments
Z disc
middle of I band, composed of structural proteins; anchor thin filaments, attachment points for elastic filaments, attach myofibrils to one another across entire diameter of muscle fiber
A band
dark band “zone of overlap”; both thick and thin filaments generate tension during contraction
H zone
middle of A band with only thick filaments
M line
dark line in middle of A band; structural proteins hold thick filaments in place, anchoring point for elastic filaments
fascicle
bundle of multiple muscle fibers
endomysium
connective tissue surrounding muscle fibers
perimysium
connective tissue surrounding fascicle
epimysium
connective tissue surrounding bundles of fascicles that make up the skeletal muscle
tendon
perimysium and epimysium come together at end of muscle; bind muscle to its attaching structure (usually bone)
fascia
thick connective tissue layer that encloses skeletal muscles; anchors to surrounding tissues and holds muscle groups together
sliding-filament mechanism of contraction
tension generated
-both I band and H zone narrow, A band unchanged
-myosin heads attach to actin, pull thin filaments toward M line; brings Z-discs closer together (shorten sarcomere)
- sarcomeres arranged end to end; simultaneous contraction shorten whole muscle fiber
sarcomere
functional unit of contraction
membrane potential
result form unequal distribution of ions near plasma membrane resulting in polarized resting state
polarization
thin layer of negatively charged ions in cytosol on inside of cell; thin layer of positively charged ions on outside of cell
electrical gradient
created by separation of charges; source of potential energy
electrical potential
when barrier separating ions is removed, they follow their gradients, creating a flow of electrical charges; potential energy becomes kinetic energy
ion channels
ions cannot diffuse through lipid component of plasma membrane, must rely on specific protein channels
leak channels
always open; continuously allow ions to flow down concentration gradients between cytosol and ECF
gated channels
closed at rest; open in response to specific stimulus
ligand-gated, voltage-gated, mechanically-gated
ligand-gated channels
open in response to binding of specific chemical or ligand to a specific receptor
voltage-gated channels
open in response to changes in voltage across membrane
mechanically-gated channels
open or close in response to mechanical stimulation (pressure, stretch, or vibration)
protein channels
allow for movement of ions (Na+ and K+) through hydrophobic phospholipid bilayer
sodium/potassium pump
moves 3 Na+ ions out and 2 K+ ions into cell per ATP hydrolyzed
ATP hydrolysis
pump moves ions against concentration gradients
high concentration of Na+ outside cell, high concentration of K+ inside cell
voltage
difference in electrical potential between two points
