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
Describe the features of slow and fast twitch muscles.
Slow motor units: resisting gravity, sustained movement, posture
Fast oxidative motor unit: sustained locomotion
Fast glycolytic motor unit: burst power
Describe the two modes of growth for skeletal muscle
Hypertrophy: seen in strength training; increase in size of cells
Hyperplasia: seen in endurance training; increase in number of cells
