Muscle

Question 1

Three types of muscle

Answer 1

• skeletal muscle
• cardiac muscle
• smooth muscle

Question 2

Skeletal Muscle

Answer 2

used for posture and locomotion. This is the muscle that enables our arms and legs to contract, under our conscious control
-composed of bundles of long (up to 1 ft) thin cells called muscle fibers

Question 3

Cardiac Muscle

Answer 3

responsible for the rhythmic contractions of the heart

Question 4

Smooth Muscle

Answer 4

cuases involuntary contraction in blood vessels, gut, bronchi, and uterus.

Question 5

Muscle fibers

Answer 5

• generated during development by the fusion of a large number of small precursor cells called myoblasts.
• each myoblast has a single nucleus, whereas the fiber is a mutlinucleated cell.
• -is striped
• mature muscle fibers are long thin cells with many nuclei.
• consist of cylindrical bundles called myofibrils

Question 6

tendons

Answer 6

-attaches muscle to bone on both sides of a joint

Question 7

What causes the striations within each myofibril

Answer 7

• caused by light I-bands and dark A-bands

- in the center of each light band is a dark like called the Z-line

Question 8

Sarcomere

Answer 8

• the contractile unit of skeletal muscle.
• this unit is delineated by the I,A, and Z bands/line
• consists of two sets of parallel and partially overlapping protein filaments; thickfilaments extending from one of the A band to the other, and thin filaments attached to the Z lines and extending across the I band and part way into the A band.

Question 9

Myofybril is a lattice of what?

Answer 9

thick and thin filaments

Question 10

I-band

Answer 10

Mostly thin filaments

Question 11

H-zone

Answer 11

Mostly thick filaments

Question 12

A band

Answer 12

thick and thin filaments

Question 13

Actin

Answer 13

• thin filaments consist of actin.

- Each actin filament is formed from two chains of globular actin subunits, twisted into a helix.

Question 14

Myosin

Answer 14

• thick filaments are made myosin

- thick filaments –> alot = myosin bundles.

Question 15

Sliding Filament Model

Answer 15

• muscle contraction occurs when the thin filaments slide over the thick filaments.
• Note that neither the thick or think filaments change in length.
• the thin filaments are pulled over the thick filaments by the myosin head groups, which repeatedly grab, pull and release the thing filaments,
• the reaction is driven by ATP hydrolysis

Question 16

What does the contraction of sarcomeres do?

Answer 16

It shortens the entire myofibril

Question 17

Length-tension relation

Answer 17

• if the filaments are too close or too far the maximal tension is low.
• the maximal tension is reached at a mid point where the filaments are the perfect distance apart.

Question 18

The cross bridge cycle

Answer 18

-driven by ATP binding and hydrolysis by the myosin head groups.

myosin binds to action –> power stroke –> ADP + Pi release –> myosin dissociated –> ATP attaches –> ATP Hydrolysis to produce ADP + Pi –> back to start.

Question 19

The number of fibers that are innervated by a single motor neuron

Answer 19

-can range from 10 (e.g. extraocular muscles) to 100 (muscles of the hand) to several thousand (large flexor and extensor muscles of leg).

Question 20

Structure of neuromuscular junction

Answer 20

• Motor axon
• Active Zone
• ACh synaptic vesicles
• nACh receptors
• Basement Membrane (AChE)

Question 21

How does Neuromuscular transmission work?

Answer 21

1. Action potential in motor neuron
2. Acetylcholine Release at presynaptic terminal
3. Na+ influx through activated nicotinic acetylcholine receptors
4. Endplate potential
5. Fiber action potential fired

Question 22

How does Ca released from the SR affect the Muscle fibers

Answer 22

• calcium released from the SR binds to tropin on the thin filaments.
• this causes a conformational change in tropinin, which in turn moves the associated tropomyosin molecule away from from the myosin binding site on actin, which can then bind the heads of the thick filaments.

Question 23

Twitch

Answer 23

• contraction of muscle fiber in response to a single action potential
• lags behind the muscle action potential, because of the delays associated with excitation-contraction coupling.

Question 24

What does the duration of the contraction reflect

Answer 24

-primarily, the time it takes for the Calcium conc. in the muscle to return to baseline.

Question 25

Tension

Answer 25

-force generated by a muscle

Question 26

Generation of muscle tension

Answer 26

Tension is exerted by a whole muscle is controlled by: 1. recruitment 2. Summation *Skeletal muscle is adapted for large force generation over a narrow operating range

Question 27

Recruitment

Answer 27

an increase in the number of active fibers

Question 28

Summation

Answer 28

- additive effects of several closely spaced twitches. - applies to individual muscle fibers - Single action potentials in the motor neuron, spaced more than a few hundred milliseconds apart, cause a transient twitch of the muscle fiber - if the action potentials are applied more rapidly, the twitches begin to add together - Motor neurons typically fire in bursts, resulting in, sustained contraction of the muscle fiber.

Question 29

Tetanus

Answer 29

-motor neurons typically fire in bursts, resulting in, sustained contraction of the muscle fiber.

Question 30

What is an important part for increasing muscle tension

Answer 30

the recruitment of additional motor units

Question 31

Creatines Roles in Skeletal Muscle Energy Metabolism

Answer 31

- there is a transfer of a P from creatine phosphate to ADP via Creatine Kinase - this creates enough ATP for a few seconds of muscle activity

Question 32

What sustains levels of ATP during prolonged muscle activity?

Answer 32

- glycolysis and oxidative phosphorylation. | - Glycogen in the muscle, glucose and fatty acids from the blood provide fuel.

Question 33

Types of Skeletal Muscle Fibers

Answer 33

1. Fast glycolytic Fibers 2. Slow oxidative fibers 3. Fast oxidative fibers

Question 34

Fast glycolytic Fibers

Answer 34

- myosin with high ATPase activity - no myoglobin ("white muscle") - for generation of larger force over short periods of time

Question 35

Slow oxidative fibers

Answer 35

- myosin with low ATPase activity - Myoglobin to facilitate oxygen transport from blood ("red muscle") - for generation of low levels of force over long periods of time

Question 36

Fast Oxidative Fibers

Answer 36

-intermediate properties. "fast" myosin and oxidative metabolism

Question 37

Muscle fatigue

Answer 37

- not completely understood - failure of action potentials in muscle fibers - Lactice acid build up, which reduces muscle pH, altering protein structure and function.

Question 38

Diseases of the Motor Unit

Answer 38

- Neurogenic Disorders - myopathic disorders - Upper motor neuron

Question 39

Neurogenic disorders

Answer 39

- due to changes in motor neuron cell bodies of axons | - clinical features include muscle atrophy, fasciculations, decreased muscle tone

Question 40

Myopathic Disorders

Answer 40

- due to degeneration of muscle with little or no change in motor neurons - characterized by muscle weakness, myotonie, myoglobinurea (heme-containing proteins in urine), and increase in sarcoplasmic enzymes in plasma.

Question 41

Upper motor neuron diseases

Answer 41

-cause overactive reflexes, spasticity

Question 42

Myopathies

Answer 42

Duchene Muscular Dystrophy - inherited, X-linked disorder. Affects males only - starts in legs, Progresses rapidly - Caused by mutation in gene encoding dystrophin. 430 kDa protein. Critical component of muscle cytoskeleton

Question 43

Smooth muscle

Answer 43

- actin and myosin in smooth muscle do not have the highly ordered structure of skeletal and cardiac muscle, this smooth muscle lacks striations. - requires Ca, but involves different molecular mechanisms than contraction of skeletal or cardiac muscle.