skeletal muscle structure and function Flashcards
__ muscle is multi-nucleated
skeletal
___ muscle has intercalated discs
cardiac
Name the general features of skeletal muscle
Voluntary control, striated, triads with t tubules, long multinucleated cells
- Describe the organization of muscle from deep to superficial
-Muscle fibrils are bundled together and surrounded by endomysium to form a muscle fiber
-Muscle fibers are bundled together and surrounded by the perimysium to form a fascicle
-Fascicles are bundled together and surrounded by the epimysium to form a muscle structure
Name the major components of a sarcomere
z discs, A band, I band, H zone, M line
what is found in the I band?
thin filaments
what is found in the A band?
thick and thin filaments
what is found in the H zone?
thick filaments
what is the M line?
myomesin that stabilizes thick filaments
what is the function of desmin?
ties the sarcomere to the sarcolemma via z discs
what is the function of titin
stabilizes thick filaments by connecting z disc to M line
what connects thin filaments to the z disc?
alpha actinin
what is the function of tropomyosin?
regulates muscle contraction by covering the actin-myosin binding site
Describe the functions of the 3 tropnin types
TnT: attaches to tropomyosin
TnC: binds calcium
Tnl: regulates myosin-actin interaction
Describe the process of a muscle contraction in a sarcomere
-Calcium binds to TnC and actin binding site is exposed
-Myosin binds actin and ATP
-Hydrolysis of ATP occurs and the head cranks. This causes the sctin filaments to slide toward the center
-The ADP and Pi are released and a new ATP binds, releasing the myosin head and allowing the muscles to release from their contracted position
The ATP binding site is located on ___
the myosin head
Describe the molecular processes involved during excitation-contraction coupling
by which an action potential of a ventral motor neuron in the spinal cord leads to
contraction of a skeletal muscle
-Action potential causes a release of Ach at the synaptic cleft, which then binds to receptors at the motor end plate of the sarcolemma.
-The generated depolarization spreads along the t tubule
-Calcium ions release from terminal cisternae and into the sarcoplasm
-Calcium binds TnC and actin binding site is exposed
-Cross-cycling occurs
each muscle fiber is innervated by ___ neuron(s)
one
What is an innervation ratio? What is the significance of this?
The number of muscle fibers innervated by a single neuron; lower rations allow for finer movements, while larger ratios allow for bulkier, forceful movement
What are the components of a motor end plate?
Synaptic vesicles, synaptic cleft, and postsynaptic membrane
Describe DHPR and RYR receptors
DHPR are receptors in the membrane of t tubules. ATP spreading down the T tubules causes a conformational change in DHPR, which causes a mechanical opening of the RYR receptors in the cytoplasm. This allows calcium out of the sarcoplasmic reticulum.
what is calsequestrin?
a calcium binding protein in the terminal cisternae that stores calcium. this causes relaxation of muscle
what is Sarcalumenin
a calcium binding protein that aids SERCA by sequestering the calcium near the pump
describe SERCA
ATPase in the sarcoplasmic reticulum that pumps calcium into the terminal cisternae to sequester calcium
