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Physiology 209 > Muscle > Flashcards

Flashcards in Muscle Deck (43):
1

Three types of muscle

-skeletal muscle
-cardiac muscle
-smooth muscle

2

Skeletal Muscle

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

3

Cardiac Muscle

responsible for the rhythmic contractions of the heart

4

Smooth Muscle

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

5

Muscle fibers

-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

6

tendons

-attaches muscle to bone on both sides of a joint

7

What causes the striations within each myofibril

-caused by light I-bands and dark A-bands
-in the center of each light band is a dark like called the Z-line

8

Sarcomere

-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.

9

Myofybril is a lattice of what?

thick and thin filaments

10

I-band

Mostly thin filaments

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H-zone

Mostly thick filaments

12

A band

thick and thin filaments

13

Actin

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

14

Myosin

-thick filaments are made myosin
-thick filaments --> alot = myosin bundles.

15

Sliding Filament Model

-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

16

What does the contraction of sarcomeres do?

It shortens the entire myofibril

17

Length-tension relation

-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.

18

The cross bridge cycle

-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.

19

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

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

20

Structure of neuromuscular junction

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

21

How does Neuromuscular transmission work?

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

22

How does Ca released from the SR affect the Muscle fibers

- 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.

23

Twitch

-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.

24

What does the duration of the contraction reflect

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

25

Tension

-force generated by a muscle

26

Generation of muscle tension

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

27

Recruitment

an increase in the number of active fibers

28

Summation

-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.

29

Tetanus

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

30

What is an important part for increasing muscle tension

the recruitment of additional motor units

31

Creatines Roles in Skeletal Muscle Energy Metabolism

-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

32

What sustains levels of ATP during prolonged muscle activity?

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

33

Types of Skeletal Muscle Fibers

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

34

Fast glycolytic Fibers

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

35

Slow oxidative fibers

-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

36

Fast Oxidative Fibers

-intermediate properties. "fast" myosin and oxidative metabolism

37

Muscle fatigue

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

38

Diseases of the Motor Unit

-Neurogenic Disorders
-myopathic disorders
-Upper motor neuron

39

Neurogenic disorders

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

40

Myopathic Disorders

-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.

41

Upper motor neuron diseases

-cause overactive reflexes, spasticity

42

Myopathies

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

43

Smooth muscle

-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.