3.2 - Skeletal Muscle Flashcards
What % of the body weight do the skeletal muscles make up?
around 40%
What is the function of the skeletal muscles?
to position and move the skeleton
Muscles are attached to bones via _____
tendons
What are tendons composed of?
dense regular connective tissue = collagen
What is collagen?
protein arranged into cable-like fibers
What is the outer connective tissue surrounding the whole skeletal muscle?
epimysium
What are fascicles?
bundles of muscle tissue
Fascicles are covered by a connective tissue sheath called _____
perimysium
What are muscle fibers covered by?
endomysium
What are myofibrils?
functional units of skeletal muscle, contractile and elastic protein bundles
What is the shape of a muscle fiber?
long and cylindrical
The cell membrane of a muscle fiber is called the ____
sarcolemma
The specialized endoplasmic reticulum of the muscle fiber is called _____
sarcoplasmic reticulum
What are T-tubules?
transverse tubules
branching tubes associated with the SR
What is the function of the terminal cisternae?
sequester Ca2+ with the help of Ca2+ ATPase in SR membrane
What is a triad?
1 t-tubules with flanking cisternae
What are the muscle equivalent of these terms?
- muscle cell
- cell membrane
- cytoplasm
- modified endoplasmic reticulum
- muscle fiber
- sarcolemma
- sarcoplasm
- SR
What structures occupy most space in the muscle fiber?
contractile structures of the myofibril
Myofibrils are made up of proteins. Name the:
- Contractile proteins
- Regulatory proteins
- Accessory proteins
contractile proteins:
- myosin
- actin
Regulatory proteins:
- tropomyosin
- troponin
Accessory proteins:
- nebulin
- titin
- others
The repeated patters of striations in a muscle fibre forms a _____
sarcomere
What is a sarcomere made up of?
z-line
I-band = isotropic = reflects light uniformly
A-band = anisotropic = scatters light unevenly
H zone = lighter part of A band
M line = middle
What causes these striations?
the organization of the protein components of the myofibrils
What is the structure of myosin?
- consists of 2 coiled protein chains/mols
- head and tail region
- tails are together, heads are at the ends
About 250 myosin mols join to form the _____
thick filament
What are the individual actin subunits called?
G-actin (globular)
G actin subunits polymerize to form ____
F-actin chains
f for filamentous
What forms the basis of a thin filament?
When 2 F-actin chains twist together
The F-actin associates with _____
regulatory proteins; troponin and tropomyosin
What are known as crossbridges?
The direct interaction of myosin heads with actin filaments
What forms a completed thin filament?
coiled F actin + troponin + tropomyosin
The I band contains:
ONLY thin filaments
TRUE OR FALSE:
The Z-line is the attachment site for ____ and the M-line is the attachment site for ____
z-line: thin filaments
m-line: thick filaments
The H-zone contains _____
only thick filaments
How are cross sections taken at the outer edge of an A band lined out?
each thin filament is surrounded by 3 thick filaments
6 thin filaments surround 1 think filament
Accessory proteins ensure that ____
filaments are properly aligned within a sarcomere
What is the function of titin?
- stabilizes position of contractile filaments
- returns stretched muscles to their resting length
What is titin?
largest known elastic protein stretching from z line to m line
What is nebulin?
non-elastic protein
Where does nebulin attach?
z disc
What is the function of nebulin?
helps to align actin filaments in the sarcomere
