Histology Flashcards
A Band
Anisotropic, only colored in polarized light, thick and thin. Bisected by M line.
I band
Isotropic, bisected by Z disc, only actin
Z disc
Bisects I bands. Area between 2 z discs = sarcomere.
H band
Only thick. Area around M line.
Types of striated muscle
Skeletal (move skeleton), visceral striated (tongue, pharynx, diaphragm, upper esophagus), cardiac (in the walls and base of large veins of the heart)
Structure of troponin
3 subunits: TnC (calcium), TnI (actin), TnT (tropomyosin)
Tropomyosin
masks myosin binding site on actin
Triad
At A-I junction. 2 terminal cisterna of sarcoplasmic reticulum and 1 T-tubule. depolarization of the t tubule membrane triggers release of calcium from the terminal cisternae to initiate uscle contraction.
dystrophin
binds ECM to actin filaments through dystroglycans
Titin
spring, centers thick filament (@ z disc)
Myosin II structure
dimer, 2 heads (globular). 1 ATP ginding site, 1 actin binding site. 2 necks: regulatory light chain x 2, essential light chain x 2. Tail: coiled coil –> bipolar arrangement –> bare zone (no heads)
alpha actinin
binds actin to z disc
desmin
intermediate filament binding sarcomeres to each other around z discs
m line proteins
hold thick together
What happens in contraction
Calcium binds to troponin –> tropomyoin moves out of the way –> ATP regulates muscle contraction –> shortening of I band.
Types of muscle fibers
Type I: slow twitch, A. Type 2A: fast-twitch. Type 2B: fast twitch anaerobic.
Type 1 muscle fiber
slow twitch, A (aerobic), small force, sustained activity, dark meat, myosin- ATPase rxn is slowest. Resistant to fatigue
Type 2A muscle fiber
fast-twitch, glycolitic “I”, larger, pink (myoglobin), intermediate force, resistant to fatigue
Type 2B muscle fiber
fasttwitch glycolitic, anaerobic. Fatigable, large force, lots of glycogen, fastest myosin ATPase activity –> lots of lactic acid
terminal cisternae
serve as reservoirs for calcium. Plasma membrane contains an abundance of gated calcium release channels called ryanodine receptors.
Ryanodine receptors
gated calcium release channels involved in releasing calcium into the sarcoplasm.
calsequestrin
highly acidic calcum-binding protein capable of binding up to 50 internalized calcium ions; allows storage at high concentration.
Myasthenia gravis
ACh nicotinic receptors are blocked by antibodies directed to the body’s own receptor proteein. Autoimmune disease caused by the reduced number of functional ACh receptor sites. –> weakening of the muscle fiber response to nerve stimulus. Begins with extraocular muscles. AChE inhibitors = pharmacological treatment. (extend the life of released ACh within the synaptic cleft).
curare
paralyzing poison used on arrow tips in South America, binds to nictinic ACh receptors without opening the ion channels. –> paralysis of skeletal muscles including the diaphragm) without affecting contraction of cardiac muscle.
