muscle (skeletal, cardiac, and smooth) Flashcards
from largest to smallest, list the organization/components of skeletal muscle
- whole muscle
- fascicle
- muscle fiber
- myofibril
- sarcomere
- filaments (thick and thin)
- protein
what is the structure of thin filaments
intertwined chains/strands of ACTIN molecules
tropomyosin vs troponin
- tropomyosin covers the active sites/myosin binding sites on actin (looks like a strand)
- troponin is bound periodically to tropomysosin and contains 3 subunits
what are the 3 subunits of troponin
TnC= ca2+ binding
TnT=binds to tropomyosin
TnI= inhibitory role
what is the structure of thick filaments
composed of myosin….with myosin heavy chains and myosin light chains. also contains the “cross-bridge”. there is an ATP binding site and an actin binding site
what is an isoform
same protein but slightly different a.a and still has similar fn
what is a sarcomere
functional unit of contractile muscle that can shorten to generate force
what is a sarcomere composed of (3)
thick and thin filaments are z-discs
I-band
composed of only thin filaments…changes length during a contraction
A-band
composed of thick and thin filaments (overlapping)
H-zone
only thick filaments…changes length during a contraction bc the thin filaments move in towards the m-line
what are titin filaments for
they have rigid compenent that are anchored at z-discs and at the m-line on thick filamens. they STABILIZE thick filaments in the center of the sarcomere
do the lengths of thick and thin filaments vary from different muscle fibers
thick filaments DONT…always 1.6 microns in all mm fibers
thin filaments can vary in length
what is nebulin
it is a protein within thin filaments to determine the length of the thin filament…it spans the whole length of the thin filament and is anchored at the z-line along with the thin filament
describe the “pseudo crystalin” structure of a myofibril
- every thin filament surrounded by 3 thick filaments
- every thick filament surrounded by 6 think filaments
what is excitation-contraction coupling
mechanism by which AP (excitation) in sarcolemma (membrane) initiates a contraction
in excitation-contraction coupling there is a very large increase in what
rapid, large increase in the free Ca2+ within the muscle cell
what is the mechanism for excitation coupling
- a.p reaches the sarcolemma and enters the T-TUBULE
- this causes Ca2+ to be released from the LATERAL SACS of the sarcoplasmic reticulum out into the sarcoplasm
- Ca binds to TnC and removes the tropomyosin block on the actin active sites
- Ca2+ is removed from TnC (reblocking the actin active sites)
- Ca2+ is uptaken into the fenestrated collar of the sarcoplasmic reticulum= relaxation
uptake of Ca2+ into the fenestrated collar during muscle relaxation is what kind of transport
active transport…uses ATP via the Ca2+-ATPase pump in the s.r
free Ca2+ is stored where
lateral sacs of the sarcoplasmic reticulum
what does free Ca2+ bind to in order to be held in the lateral sacs
calsequestrin
what is the DHP receptor
receptor in the sarcolemma/t-tubule region of a muscle cell. contains 2 components:
- Ca2+ channel that is INACTIVE
- a voltage sensor that senses the a.p that reach the muscle cell
the DHP receptor voltage sensor contacts what other receptor
ryanodine receptor
what is the ryanodine receptor
a receptor located on the s.r membrane that is a Ca2+ channel that releases Ca from the lateral sac of the s.r