Muscle Flashcards
What are the boundaries of a sarcomere?
from one Z line to another Z line
What are myofibrils?
- bundles of contractile filaments
- make up a muscle fiber
- covered with its own network of sarcoplasmic reticulum
What are the regulatory proteins of myofibrils?
tropomyosin and troponin
What are the thin filaments in a muscle fiber?
- what myosin binds to
- made of actin
- tropomyosin and troponin (regulatory proteins) bind to the actin filaments
What are the thick filaments in a muscle fiber?
- made of myosin
- myosin heads interact with actin
- actin-myosin work together for contraction with ATPase
What prevents the binding of myosin to actin in the relaxed state?
tropomyosin
How is the binding site for myosin uncovered?
troponin binds to Ca2+ and undergoes a conformational change -> induces conformational change in tropomyosin
Why does myosin exert force as soon as it binds?
the energy is released upon binding because it does not need ATP in order to exert force
What causes myosin to release from actin?
ATP binding and hydrolysis puts myosin into a high energy state
How do we get so much muscle shortening?
- lots of sarcomeres in series will summate linearly
- many myosin-actin cycles occur during a single contraction
Is regulation of cardiac muscle like skeletal muscle?
yes
How is smooth muscle regulated?
- no troponin
- increased Ca2+ binds to calmodulin
- Ca-calmodulin binds to CaM kinase and phosphorylates the myosin head
- phosphorylated myosin binds to actin and generates force
Is the process of smooth muscle activation faster or slower than skeletal and cardiac muscle?
much slower
How is calcium removed in smooth muscle?
Ca pumps and Na-Ca exchangers in the sarcolemma
Each skeletal muscle cell of a mammal is innervated at _____ spot.
one
An action potential in the motor axon causes release of ___________.
acetylcholine
What do large muscle cells use for action potentials (re. Ca2+)?
the T-system and sarcoplasmic reticulum
What would happen if skeletal or cardiac muscle cells did not contract uniformly?
the shear forces would destroy the cells
What is diffusion r^2 (mean distance) proportional to?
time
What is the transverse tubule system?
- membrane structure that allows the action potential to propagate through the cross section of the cell
- the action potential propagates rapidly along the length and depth of the cells
Why is the sarcoplasmic reticulum important for skeletal and cardiac muscle contraction?
- each myofibril has a SR around the bundle
- Ca2+ is stored in the SR (small distance for Ca2+ to diffuse)
Myofilaments are bundled to form ________.
myofibrils
What protein can bind to approx 50 Ca2+ and is in muscle cells?
calsequestrin
At muscle relaxation, ______________ pumps Ca2+ back into the _______.
Ca2+ ATPase pump; sarcoplasmic reticulum
What is a motor unit?
the muscle fibers innervated by a motor neuron
Are cardiac and smooth muscle innervated?Can they function without nerve innervation?
they are innervated but can function without nervous innervation
How can skeletal muscle tension be gradated?
- increase the frequency of action potentials
- recruit additional motor units
What are satellite cells regarding skeletal muscle?
stem cells
- source of new myoblasts to repair injured muscle
What regulates the proliferation of satellite cells?
fibroblasts in the connective tissue
Can cardiac muscle repair itself?
no
Can smooth muscle repairs itself?
yes
- cells can dedifferentiate and regenerate new muscle cells
What happens to your muscles when you lift weights?
- no new skeletal muscle fibers
- new myofibrils are formed (cross sectional area of each cell is increased)
What is the key difference between E-C coupling of skeletal and cardiac muscle?
- Ca2+ binding is needed via DHPR entry to trigger Ca2+ release from SR in the heart (via RyR)
- DHPRs in skeletal muscle make direct physical contact with the RyR after binding to Ca2+ and produce Ca2+ release
What occurs in hypertrophic cardiomyopathy?
- cardiac murmur
- cardiac pump failure
- sudden death
- cardiomyocyte and cardiac hypertrophy
- myocyte disarray
- interstitial and replacement fibrosis
- dysplastic intramyocardial arterioles
What is the disorder that results in hypertrophic cardiomyopathy?
- autosomal dominant (most)
- missense mutation
- incomplete penetrance
- disease of the sarcomere (mostly)
What does myostatin do?
normally negative feedback for muscle growth
What does myostatin deficiency look like?
- very muscular and strength
What causes malignant hyperthermia?
- RyR 1 mutation
- exposure to halothane and/or succinylcholine
What is the phenotype of malignant hyperthermia?
- hypermetabolism
- skeletal muscle damage
- hyperthermia
- death if untreated
What are the clinical signs of malignant hyperthermia?
- muscle rigidity (masseter spasm)
- increased CO2 production
- rhabdomyolysis
- hyperthermia
What is the treatment for malignant hyperthermia?
dantrolene 2.5 mg/kg
