Lecture 9: Anatomical Components of Muscle (Hayward) Flashcards
what property is common to all muscles?*
contractility
why does skeletal muscle have banded appearance?*
regular arrangement of actin and myosin
cytoplasm of muscle cell = *
sarcoplasm
endoplasmic reticulum of muscle cell = *
sarcoplasmic reticulum
muscle cell = *
myofiber
components of myofibril*
actin and myosin myofilaments
hierarchy of skeletal muscle structure*
myofilament –> myofibril –> myofiber –> muscle fascicle –> muscle belly
what are a bunch of myofibrils surrounded by to make a myofiber (muscle cell)?*
endomysial layer
what structure surrounds a muscle belly?*
fascia
name the bands in a sarcomere*
A (anisotropic), I (Isotropic), M, H, and Z bands
What happens to the length of the different bands in a sarcomere during a muscle contraction?**
I and H bands shorten. A and M bands stay the same length. Total sarcomere length (distance between Z bands) decreases.
what happens to sarcomere if only one Z band contracts?*
no force is produced. Z bands on both ends of sarcomere must contract to produce force.
fx of M-line*
anchors adjacent thick filaments (myosin)
fx of Z bands*
anchor thin filaments (actin)
H-band is composed of thick and/or thin filaments?*
Thick filaments only
What are Z-lines composed of?*
alpha-actinin and Z-line filaments
What are M-lines composed of?*
M-line filaments and creatine kinase enzyme
intermyofibrillar space*
space between adjacent myofibrils. Contains SR, mitochondria, glycogen, and lipids
alpha-actinin*
an anchoring filament that helps anchor thin-line filaments to the Z band
3 intermediate anchoring filaments**
vimentin, desmin, and vinculin
fx of vinculin*
scaffold protein that connects myofibrils adjacent to the sarcolemma to the sarcolemma
fx of vimentin*
scaffold protein that extends b/w Z lines of the same sarcomere
fx of desmin*
scaffold protein that hold Z-lines of adjacent myofibrils together
fx of titin***
large springy globular protein that anchors M-bands and imparts a portion of passive elastic component of muscle. Connects thick myofilaments with the Z-line. Spans distance between M and Z lines. Elasticity of titin helps restore the stretched sarcomere (muscle) back to its correct length and transfers force down to the tendon.
In which band of sarcomere is there never overlap of thin and thick filaments?*
H band region (thick only)
fx of T (transverse) tubule system*
an invagination of surface membrane into the muscle cell. Connects to the intracellular SR and facilitates Ca release from SR following a depolarization
dystropin**
cytoskeletal protein located on the inner surface of the sarcolemma. Involved in the structural integrity of the sarcolemma (anchors actin, regulates membrane proteins). Main fx = transmission of force to extracellular matrix of muscle cell.
what happens to muscle cell in absence of dystropin?*
muscle cell can’t generate force and degenerates. Cause of muscular dystrophy
what enzyme is a good marker for cardiac disease/muscle death/abnormalities of skeletal muscle?
creatine kinase (will be elevated in muscular dystrophy)
myostatin
a SKELETAL muscle growth inhibitor. If inhibited, will facilitate muscle growth. Potential cure for muscular dystrophy. Not effective in cardiac muscle.
follistatin
muscle growth activator. Potential cure for M.D.
Could myostatin regulate hypertrophy or fibrosis?
No. Thus, myostatin may prevent muscle wasting without causing cardiac dysfunction in cases of cardiac failure.
where is T tubule system located?
at interconnection of A and I bands in the sarcolemma
fx of Ca in sarcomere
allows actin and myosin to interact
describe path of Ca from release to reuptake in sarcomere
wave of depolarization moves down T tubules, conformationally changes the DHP and RyR receptors, allowing Ca to be released from SR, diffuse around cell and bind to regulatory proteins before being re-taken up by longitudinal proteins of the SR via Ca ATPase
what stimulates Ca ATPase on SR?
increases in intracellular Ca
sliding filament hypothesis
there must be a central component (A band) that doesn’t change but has the capacity to pull other bands over it. In other words, globular heads on A bands bind to thin filaments and pull other them inward. This is accomplished by the formation and breaking of bonds between actin and myosin at the crossbridges in the presence of ATP.
conductility
the propagation of membrane depolarization over the cell surface
What corresponds to the dark staining bands of muscle fibers on light microscope?
A-bands. Composed of parallel arrays of thick myofilaments composed of myosin. Have cross-bridges that extend toward adjacent thin myofilaments
What corresponds to the light staining bands of fibers on light microscope?
I bands. (thin filaments of actin). Attach at one end to Z lines.
sarcomere =
repeating Z-line to Z-line interval of myofibrils
myofilament ratio
6 thin myofilaments to 1 thick myofilament. Each thick filament is surrounded by a hexagonal array of 6 thin filaments.
2 main components of muscle membrane system that serve to activate the contractile apparatus
1) transverse (t) tubular system
2) Sarcoplasmic reticulum
What is a triad?
complex of T-tubule flanked by 2 terminal cisternae on the SR. There are 2 triads per sarcomere. Forms a gap which is bridged by junctional feet. A conformational change in the junctional feet leads to Ca release from the SR.
components of junctional feet
DHP and RyR receptors
sarcotubules
netowork of longitudinally arranged tubular membranes. Fx in re-uptake of Ca back into SR
main fx. of SR
reservoir of Ca. Controls the Ca conc. of the sarcoplasm surrounding myofibrils and myofilaments through its ability to concentrate and release Ca.
Ca ATPase pumps Ca from where to where?
from sarcoplasm to lumen of SR
fx of calsequestrin
binds Ca. Regulated by intracellular concentrations
How does the length of thin and thick filaments change during muscle contraction?
They don’t change! The filaments slide over one another, but they don’t actually change in length
general fx of myosin
generates force of contraction, ATPase activity
general fx of actin
interacts with myosin for muscle contraction, activates myosin ATPase
general fx of alpha-actinin
structural; harnesses thin filaments
general fx of tropomyosin
regulation; limits availability of myosin binding sites on actin
general fx of troponin
regulation; calcium sensitive “switch” to initiate myosin-actin interactions
principal protein comprising thick myofilaments
myosin
principal structural protein of thin myofilaments
actin
length-tension relationship
tension generated is directly proportional to the number of cross-bridges overlapped by thin filaments
state of actin and myosin during rigor mortis
they are bound and unable to disassociate in the absence of ATP
