Muscle

Question 1

What are the boundaries of a sarcomere?

Answer 1

from one Z line to another Z line

Question 2

What are myofibrils?

Answer 2

• bundles of contractile filaments
• make up a muscle fiber
• covered with its own network of sarcoplasmic reticulum

Question 3

What are the regulatory proteins of myofibrils?

Answer 3

tropomyosin and troponin

Question 4

What are the thin filaments in a muscle fiber?

Answer 4

• what myosin binds to
• made of actin
• tropomyosin and troponin (regulatory proteins) bind to the actin filaments

Question 5

What are the thick filaments in a muscle fiber?

Answer 5

• made of myosin
• myosin heads interact with actin
• actin-myosin work together for contraction with ATPase

Question 6

What prevents the binding of myosin to actin in the relaxed state?

Answer 6

tropomyosin

Question 7

How is the binding site for myosin uncovered?

Answer 7

troponin binds to Ca2+ and undergoes a conformational change -> induces conformational change in tropomyosin

Question 8

Why does myosin exert force as soon as it binds?

Answer 8

the energy is released upon binding because it does not need ATP in order to exert force

Question 9

What causes myosin to release from actin?

Answer 9

ATP binding and hydrolysis puts myosin into a high energy state

Question 10

How do we get so much muscle shortening?

Answer 10

• lots of sarcomeres in series will summate linearly

- many myosin-actin cycles occur during a single contraction

Question 11

Is regulation of cardiac muscle like skeletal muscle?

Answer 11

yes

Question 12

How is smooth muscle regulated?

Answer 12

• 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

Question 13

Is the process of smooth muscle activation faster or slower than skeletal and cardiac muscle?

Answer 13

much slower

Question 14

How is calcium removed in smooth muscle?

Answer 14

Ca pumps and Na-Ca exchangers in the sarcolemma

Question 15

Each skeletal muscle cell of a mammal is innervated at _____ spot.

Answer 15

one

Question 16

An action potential in the motor axon causes release of ___________.

Answer 16

acetylcholine

Question 17

What do large muscle cells use for action potentials (re. Ca2+)?

Answer 17

the T-system and sarcoplasmic reticulum

Question 18

What would happen if skeletal or cardiac muscle cells did not contract uniformly?

Answer 18

the shear forces would destroy the cells

Question 19

What is diffusion r^2 (mean distance) proportional to?

Answer 19

time

Question 20

What is the transverse tubule system?

Answer 20

• 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

Question 21

Why is the sarcoplasmic reticulum important for skeletal and cardiac muscle contraction?

Answer 21

• each myofibril has a SR around the bundle

- Ca2+ is stored in the SR (small distance for Ca2+ to diffuse)

Question 22

Myofilaments are bundled to form ________.

Answer 22

myofibrils

Question 23

What protein can bind to approx 50 Ca2+ and is in muscle cells?

Answer 23

calsequestrin

Question 24

At muscle relaxation, ______________ pumps Ca2+ back into the _______.

Answer 24

Ca2+ ATPase pump; sarcoplasmic reticulum

Question 25

What is a motor unit?

Answer 25

the muscle fibers innervated by a motor neuron

Question 26

Are cardiac and smooth muscle innervated?Can they function without nerve innervation?

Answer 26

they are innervated but can function without nervous innervation

Question 27

How can skeletal muscle tension be gradated?

Answer 27

- increase the frequency of action potentials | - recruit additional motor units

Question 28

What are satellite cells regarding skeletal muscle?

Answer 28

stem cells | - source of new myoblasts to repair injured muscle

Question 29

What regulates the proliferation of satellite cells?

Answer 29

fibroblasts in the connective tissue

Question 30

Can cardiac muscle repair itself?

Answer 30

no

Question 31

Can smooth muscle repairs itself?

Answer 31

yes | - cells can dedifferentiate and regenerate new muscle cells

Question 32

What happens to your muscles when you lift weights?

Answer 32

- no new skeletal muscle fibers | - new myofibrils are formed (cross sectional area of each cell is increased)

Question 33

What is the key difference between E-C coupling of skeletal and cardiac muscle?

Answer 33

- 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

Question 34

What occurs in hypertrophic cardiomyopathy?

Answer 34

- cardiac murmur - cardiac pump failure - sudden death - cardiomyocyte and cardiac hypertrophy - myocyte disarray - interstitial and replacement fibrosis - dysplastic intramyocardial arterioles

Question 35

What is the disorder that results in hypertrophic cardiomyopathy?

Answer 35

- autosomal dominant (most) - missense mutation - incomplete penetrance - disease of the sarcomere (mostly)

Question 36

What does myostatin do?

Answer 36

normally negative feedback for muscle growth

Question 37

What does myostatin deficiency look like?

Answer 37

- very muscular and strength

Question 38

What causes malignant hyperthermia?

Answer 38

- RyR 1 mutation | - exposure to halothane and/or succinylcholine

Question 39

What is the phenotype of malignant hyperthermia?

Answer 39

- hypermetabolism - skeletal muscle damage - hyperthermia - death if untreated

Question 40

What are the clinical signs of malignant hyperthermia?

Answer 40

- muscle rigidity (masseter spasm) - increased CO2 production - rhabdomyolysis - hyperthermia

Question 41

What is the treatment for malignant hyperthermia?

Answer 41

dantrolene 2.5 mg/kg