Lecture 8 Muscle Physiology

Question 1

How long are muscle cells?

Answer 1

As long as the whole muscle

Question 2

What kind of nucleation does skeletal muscle have?

Answer 2

multinucleated

Question 3

How do muscle cells become a multinucleated syncitium?

Answer 3

By fusing myoblasts together into muscle fibers

Question 4

T/F CT around and within skeletal muscle is continuous with the CT of bones.

Answer 4

True

Question 5

What are the CT layers from the endomysium of muscle to the periosteum of bone?

Answer 5

Endo-peri-epi-deep fascia-tendon-periosteum

Mnemonic: Every Person Eats Donuts for The Paste

Question 6

What are the series-elastic components of the musculoskeletal system?

Answer 6

All of the interconnected tissues in muscles that are attached to the bone membrane from endomysium to the periosteum

Question 7

What is the specialized plasma membrane of muscle cells?

Answer 7

Sarcolemma

Question 8

The sarcolemma is _______ at rest.

Answer 8

Polarized

Question 9

What can depolarize the sarcolemma?

Answer 9

Acetylcholine released by motor neurons

Question 10

What are the tubular infoldings of the sarcolemma?

Answer 10

T-tubules (transverse tubules)

Question 11

What do T-tubules do?

Answer 11

Penetrate into the cell and carry the electrochemical current into the cell

Question 12

What is sarcoplasm made of?

Answer 12

Highly organized myofibrils (actin and myosin), glycogen, and myoglobin

Question 13

What does glycogen do in the sarcoplasm? What does myoglobin do in the sarcoplasm?

Answer 13

Stores energy. Stores oxygen

Question 14

What is the specialized endoplasmic reticulum of muscle cells?

Answer 14

Sarcoplasmic reticulum

Question 15

What storage sacs is the sarcoplasmic reticulum connected to? What do these sacs store?

Answer 15

Termincal cisternae. They store calcium ions

Question 16

What protein complex anchors myofibrils inside muscle cells?

Answer 16

Dystrophin

Question 17

How does dystrophin attach myofibrils to the endomysium?

Answer 17

Dystrophin attaches the myofibrils next to the sarcolemma to integral membrane proteins that extend into the endomysium

Question 18

What is the difference between the sarcolemma, sarcoplasm, and sarcoplasmic reticulum?

Answer 18

Sarcolemma is the outer plasma membrane of muscle cells.
Sarcoplasm is the cytosol (flesh)
Sarcoplasmic reticulum is the series of interconnected tubules connected to the terminal cisternae

Question 19

Are the T-tubules of the sarcolemma and the interconnected tubules of the sarcoplasmic reticulum the same thing?

Answer 19

No. The T-tubules are larger invaginations of the sarcolemma. The t-tubules are surrounded on either side by the terminal cisternae. The terminal cisternae are interconnected by the tubules of the sarcoplasmic reticulum

Question 20

What is the triad formed surrounding the myofibrils?

Answer 20

The T-tubule surrounded on either side by the calcium storing terminal cisternae

Question 21

T/F The sarcolemma is surrounded by the endomysium.

Answer 21

True. Endomysium surrounds individual muscle cells made of myofibrils

Question 22

What is the difference between a myofiber and a myofibril?

Answer 22

The myofiber is the muscle cell which is composed of myofibrils making up its cytoplasm (sarcoplasm)

Question 23

What are the three bands of a sarcomere?

Answer 23

A band, H band, and I band

Question 24

Which of the three sarcomere bands does not change in size?

Answer 24

A band is the length of the thick myosin filaments

Question 25

Which sarcomere band changes in size and is a region of pure myosin? Pure actin?

Answer 25

H band is pure myosin. I band is pure actin

Question 26

What starts a wave of depolarization in the muscle cell?

Answer 26

The binding of ACh to the AChR (acetylchone receptor)

Question 27

How far does the wave of depolarization spread over the sarcolemma?

Answer 27

The sarcolemma down to the T-tubules

Question 28

Where are calcium channels found that open to release calcium on the sarcomeres?

Answer 28

On the sarcoplasmic reticulum buried deep among the myofibrils

Question 29

What must calcium bind to for the release of tropomyosin off of the active sites on actin?

Answer 29

Troponin

Question 30

What do the AHM I Z regions of the sarcomere stand for?

Answer 30

``` A anisotropic (dark appearance of myosin) H helle (german for bright) region of myosin w/o actin M middle I Isotropic (light appearance of actin) Z Zwischen (german for between) anchor site of titin ```

Question 31

T/F Thin filaments are globular subunits. Myosin is composed of two entwined polypeptides each shaped like a golf club

Answer 31

True

Question 32

The heads of myosin can also be called which enzyme?

Answer 32

ATPase

Question 33

Are actin and myosin filaments elastic?

Answer 33

No, They stay the same size

Question 34

If actin and myosin are not elastic how are they considered contractile?

Answer 34

Because they contract the cell (myofiber) by moving over each other in a series of sarcomeres

Question 35

Which muscle filament is elastic?

Answer 35

Titin

Question 36

Where are the cell bodies of somatic motor neurons?

Answer 36

Brainstem and spinal cord

Question 37

What is the range of branching in the axons of motor neurons?

Answer 37

From 3-6 to over 200 branches

Question 38

T/F Each axon branch of a somatic motor neuron contacts one muscle fiber (cell)

Answer 38

True

Question 39

What is a motor unit?

Answer 39

A motor neuron and all the muscle fibers it innervates

Question 40

What kind of control are small motor units good for? Large motor units?

Answer 40

Fine control (eye muscles). Strength (can have as many as 1000 muscle fibers per nerve fiber)

Question 41

Much of the intracellular protein is _______ (anionic or cationic

Answer 41

anionic

Question 42

What four actions are involved in Muscle contraction and relaxation?

Answer 42

1. Excitation 2. Excitation-Contraction Coupling 3. Contraction 4. Relaxation

Question 43

What is excitation-contraction coupling?

Answer 43

action potentials on the sarcolemma activate myofilaments

Question 44

How is the resting membrane potential disrupted?

Answer 44

When ligand-gated Na+ channels on the motor end plate bind to ACh and open to let Na+ into the cell which depolarizes the membrane

Question 45

During the powerstroke in which direction does the myosin head pull the thin actin filament relative to the z line?

Answer 45

Towards the Z line

Question 46

With out ATP where is the myosin head relative to the active site of the actin?

Answer 46

The myosin head is bound to the active site of actin

Question 47

T/F ATP is required for the myosin head to release actin.

Answer 47

True

Question 48

During Rigor Mortis, where does the Ca++ come from to activate the actin-myosin cross bridges?

Answer 48

The SR releases Ca++ as it deteriorates

Question 49

What molecule is needed for the myosin to bind with the actin? What molecule is needed for the myosin to release the actin?

Answer 49

Ca++. ATP

Question 50

How does Botox work?

Answer 50

It blocks the ACh release from motor neurons. Muscles cannot contract to cause wrinkles in those areas

Question 51

What are paralytic neuromuscular toxins?

Answer 51

Muscle relaxants such as Botox, Curare, TTX

Question 52

What are spasmodic neuromuscular toxins?

Answer 52

Muscle stimulants that cause uncontrollable muscle contraction and spasms

Question 53

What is the role of glycine in muscle contraction?

Answer 53

It prevents overstimulation of muscles

Question 54

Which autoimmune disease mimics the effects of curare?

Answer 54

Myasthenia Gravis

Question 55

How does myasthenia gravis inhibit the generation of an end-plate potential?

Answer 55

Antibodies bind and inhibit ACh receptors from sensing ACh

Question 56

How is myasthenia gravis treated?

Answer 56

With acetylcholinesterase inhibitors, thymus removal or immunosuppressive agents

Question 57

What is the only source of energy for muscle contraction?

Answer 57

ATP

Question 58

Which enzyme system regenerates ATP from ADP and Pi?

Answer 58

Phosphagen enzyme system.

Question 59

What are the two main phosphogen enzymes?

Answer 59

Myokinase and Creatine Kinase

Question 60

Where does myokinase get its Pi in ATP formation?

Answer 60

From ADP producing ATP and AMP

Question 61

Where does creatine kinase get its Pi for ATP formation?

Answer 61

Creatine phosphate

Question 62

Where does the immediate source of ATP come from? How long does the immediate source provide ATP?

Answer 62

Aerobic metabolism using O2 released from myoglobin in muscles. Also, from Phosphagen system. Lasts about 10 seconds

Question 63

Where does the short-term energy source of ATP come from? How long does it last?

Answer 63

Anerobic metabolism thru the glycogen-lactic acid system? Lasts for about 30-40 seconds

Question 64

Where does the long term energy source of ATP come from? When does it begin?

Answer 64

Respiratory and cardiovascular systems catch up to the O2 demand for aerobic respiration. Begins after 40 seconds of sustained exercise and supplies more than 90% of ATP at this stage

Question 65

Which muscle fiber type has lots of myoglobin and syntesizes ATP aerobically?

Answer 65

Red Slow Twitch (Type 1)

Question 66

Which muscle fiber type uses anaerobic metabolism to produce ATP? Which one uses both anaerobic and aerobic metabolism?

Answer 66

White Fast Twitch (Type IIb). Pink Intermediate (Type IIa)

Question 67

Which muscle type has striated muscle cells linked to each other by intercalated discs?

Answer 67

Cardiac muscle

Question 68

What junctions line the intercalated discs?

Answer 68

Gap junctions and desmosomes

Question 69

What do gap junctions facilitate in cardiac muscle?

Answer 69

The facilitate the synchronization of muscle contractions

Question 70

Where does the Ca++ come from in cardiac muscle? What facilitates the Ca++ absorption?

Answer 70

From the extracellular fluid. Large T-tubules

Question 71

Which striated muscle type forms triads of the SR with the T-tubules? Which one forms diads?

Answer 71

Triads are formed in skeletal muscle where the T-tubule is sandwiched between two terminal ciseternae of the SR. Diads are formed in cardiac muscle - the T-tubule is paired with the SR only on one side

Question 72

What kind of respiration does cardiac muscle use almost exclusively?

Answer 72

Aerobic. Cardiac muscle is an obligate aerobe

Question 73

How are damaged cardiac cells repaired?

Answer 73

By fibrosis not mitosis.

Question 74

Which muscle cells are fusiform and have only one nucleus?

Answer 74

Smooth muscles

Question 75

What kind of nucleation does cardiac muscle have in humans? (mono or multi-nucleated)

Answer 75

Mononucleated just like smooth muscle. Skeletal muscle is multinucleated

Question 76

Where do the thin filaments attach to in smooth muscles?

Answer 76

Dense bodies scattered throughout the sarcoplasm, which are attached to dense plaques on the sarcolemma

Question 77

T/F Both cardiac and smooth muscles can be described as a functional syncitium

Answer 77

True. They both are mononucleated but have gap junctions that allows depolarization to spread from cell to cell

Question 78

Where does smooth muscle get its Ca++ for contractions?

Answer 78

From a poorly developed SR and extracellular fluid

Question 79

What does the poorly developed SR have instead of T-tubules?

Answer 79

Caveolae which are shallow invaginations of the SR

Question 80

What doe stretching do to smooth muscles?

Answer 80

Opens mechanically-gated calcium channels causing contraction

Question 81

What happens when smooth muscle is stretched gently?

Answer 81

It briefly contracts and then relaxes

Question 82

How can smooth muscle be made to contract forcefully?

Answer 82

By being stretched greatly. The contraction force matches the degree of stretching.

Question 83

T/F Smooth muscles responds to hormones, low pH, and high CO2

Answer 83

True

Question 84

What regulatory protein must calcium bind to in the cytoplasm of smooth muscle in order to activate the MLCK?

Answer 84

Calmodulin

Question 85

What is MLCK?

Answer 85

Myosin light chain kinase. It uses ATP to phosphorylate the myosin head

Question 86

What do the actin thin filaments pull on to shorten Smooth muscle?

Answer 86

the interconnected dense bodies which may be seen as the Z discs in skeletal muscles

Question 87

How many ATP are needed for the power stroke in smooth muscle?

Answer 87

Two ATP. One used by the MLCK to activate the myosin head and a second to ratchet the myosin head causing contraction