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Anatomy and Physiology 111 > chapter 9 - muscle structure/function > Flashcards

chapter 9 - muscle structure/function Flashcards

muscle function

1
Q

what are the three types of muscle tissue and are they voluntary/involuntary and striated/non-striated?

A

skeletal muscle tissue (voluntary, striated)

cardiac muscle tissue (involuntary, striated)

smooth muscle tissue (involuntary, non-striated)

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2
Q

what are the 4 functional characteristics of muscle tissue?

A

Excitability - can be stimulated
Contractility - able to decrease in length
Extensibility - is able to stretch
Elasticity - is able to recoil to original length

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3
Q

what is the formula for heat generation in muscles?

A

glucose + O2 -> ATP + CO2 +heat + H2O

this is a dehydration

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4
Q

what is the structural grouping order for muscles

A

muscle cell - groups into fascicles - groups into muscles

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5
Q

what are the three connective sheaths that surround the muscle?

A

Epimysium - (dense irregular) surrounds entire muscle
Perimysium - (fibrous) surrounds fascicles (groupings of muscle cells)
Endomysium - (areolar) surrounds each muscle cell (fiber)

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6
Q

what are the two ways a muscle can attach?

A

directly - epimysium attaches directly to periosteum of bone

indirectly - CT wrapping extend beyond muscle as a ropelike tendon/aponeurosis

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7
Q

Where is the nuclei located in the muscle cell?

A

along the outside

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8
Q

what is a myofibril?

A

a bundle of actin and myosin myofilaments enclosed in sarcoplasmic reticulum.

composes 80% of cell volume

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9
Q

what is the sarcolemma?

A

membrane around the outside of the muscle cell (lies inside endomysium)

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10
Q

what is the sarcoplasm and what does it contain?

A

cytoplasm of a muscle cell

contains: many mitochondria, glycosomes (glycogen storage), myoglobin (oxygen storage), and myofibrils (for contraction)

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11
Q

what is the sarcoplasmic reticulm?

A

a specialized smooth endoplasmic reticulum with terminal cisternae which store calcium ions

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12
Q

What are t-tubules?

A

channels of sarcolemma that form encircle each A and I band junction. allows the sarcolemma to penetrate deep into the muscle cell to allow the AP to act at each sarcomere..

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13
Q

What is a triad?

A

a pair of terminal cisternae and a T- tubule. Allows for the action potential (AP) to penetrate deep into cell allowing immediate release of Ca ions.

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14
Q

What are thin filaments composed of?

A
  • actin filaments with binding sites for myosin crossbridges

- tropomyosin and troponin (control switches for contraction)

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15
Q

What is the role of tropomyosin?

A

blocks the binding sites on actin in relaxed muscles

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16
Q

What is the role of troponin

A

holds the tropomyosin in position.

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17
Q

What is a sarcomere?

A

It is the smallest contractile unit (functional unit) of a muscle fiber

  • the region of a myofibril between successive z discs
  • composed of thick and thin myofilaments made of contractile proteins
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18
Q

What role does CA 2+ play in muscle contraction?

A
  1. floods the axon stimulating synaptic vessels to release ACH
  2. in the sarcomere, binds with the troponin changing its shape which then moves tropomyosin off of the active binding sites of actin. This is necessary to allow myosin heads to bind.
  3. after the contraction, Ca is pumped back into SR and remaining reacts with calmodulin->kinase->convert glycogen to glucose (fuel for ATP production)
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19
Q

What happens to the ACH after the AP of the sarcolemma has been generated?

A

Quickly broken down by the enzyme acetylcholinesterase found in the synaptic cleft.

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20
Q

What is the refractory period?

A

represents the interval after muscle contraction before another can begin (membrane needs to be repolarized before it can be stimulated again)

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21
Q

what is the latent period?

A

time between AP initiation and the beginning of the contraction

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22
Q

How is Ca released into the muscle cell?

A

AP travels along sarcolemma into t-tubules to triads and stimulates the release of Ca from the terminal cisternae of the sarcoplasmic reticulum (Ca storage site)

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23
Q

Define isotonic contraction.

A

muscle shortens because muscle tension exceeds the load

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24
Q

Define concentric isotonic contraction.

A

muscle shortens as it contracts (most common)

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25
Q

Define eccentric isotonic contraction.

A

muscle contracts as it lengthens (is stretched by another muscle). 50% more force than concentric. ex quadriceps during squats.

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26
Q

Define isometric contraction.

A

muscle does not shorten because tension does not exceed the load.

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27
Q

What is a motor unit?

A

it is a motor neuron and all muscle fibers (cells) it supplies.

it breaks down the muscle into smaller functional groups.

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28
Q

what is the purpose of a motor unit?

A
  • allows partial (weaker) contraction of the muscle

- contraction is asynchronous (all motor units do not fire at the same time). This helps prevent fatigue.

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29
Q

What are the three phases of a muscle twitch?

A

latent - excitation (small period from stimulus to reaction)
contraction - cross bridge formation and generation of tension
relaxation - Ca ions drawn into SR and tension decreases to 0

30
Q

what are the 4 types of reactions as you increase the stimulus’ frequency?

A
  1. single stimulus produces a twitch
  2. inc the freq, muscle does not have time to relax and forms a wave summation
  3. further inc and get unfused (incomplete) tetanus
  4. if freq is increased enough, can no longer see waves and get fused (complete) tetanus
31
Q

How does the stimulus strength affect the response?

A

inc in stimulus -> more motor units stimulated -> inc strength of contraction

32
Q

Define threshold stimulus.

A

the minimum stimulus strength that causes first visible contraction.

33
Q

Define maximum stimulus.

A

stimulus strength at which maximum contraction occurs.

34
Q

Define recruitment.

A

recruitment refers to the number of motor units contracting.

35
Q

What effect does stimulus strength have on recruitment.

A
  1. increases number of motor units contracting

2. motor units with larger and larger fibers are stimulated.

36
Q

What are the three ways that ATP is produced

A
  1. Direct phosphorylation of ADP by creatine phosphate (CP)
  2. Anaerobic pathway (glycolysis)
  3. Aerobic respiration
37
Q

Explain direct phosphorylation of ADP by creatine phosphate (CP).

A

CreatinePO4 -> PO4 + creatine
then : PO4 + ADP -> ATP

this is a bilateral reaction. Occurs during activity, but during rest excess ATP will convert to phosphatecreatine. Therefore, it acts as a buffer for ATP concentration.

note that this depends on the supply of creatinePO4 and will deplete rapidly 1-7 seconds of intense activity.

38
Q

Explain the anaerobic (glycolysis) pathway.

A
  • occurs at 70% muscle contractile activity
  • bulging muscles compress blood vessels and restrict oxygen supply.

Glucose undergoes glycolysis to make pyruvic acid releasing 2 ATP then pyruvic acid is converted to lactic acid - > diffuses into blood - > used for fuel by liver/heart/kidneys and converted back to pyruvic

Faster than the aerobic pathway. Stores last about 1 min
change of PH in the muscle causes fatigue

39
Q

Explain the aerobic pathway.

A

-produces 90% of ATP during rest and light moderate exercise

Uses glycogen first, then blood glucose, pyruvic acid from glycolysis, then fatty acids

-most efficient production of ATP (generates 36)

40
Q

What effects muscle fatigue?

A
  1. ionic imbalance (note that this includes PH changes)
  2. Ca 2+ depletion (prolonged exercise interferes with Ca regulation and release)
  3. lack of ATP (needed for breaking bridges and cocking heads)
  4. lack of oxygen
41
Q

What happens in complete lack of ATP?

A

a state of continuous contraction and causes contractures/cramps.

42
Q

What is oxygen necessary for?

A
  1. replenishment of oxygen reserves and myoglobin, glycogen stores, ATP and CP reserves
  2. conversion of lactic acid to pyruvic acid, glucose, and glycogen
43
Q

When is muscle contraction most strong

A

at 80-120% of their normal resting length (stretched)

44
Q

How are muscle fiber classified?

A
  1. speed of contraction

2. metabolic pathway

45
Q

What are the three types of muscle fiber?

A
  1. slow oxidative - slow contracting and fatiguing (good for marathons)
  2. fast oxidative - intermediate (walking)
  3. fast glycolytic - fast contracting and fatiguing (short term high energy activities)
46
Q

What are the affects of aerobic (endurance) exercise on the muscle?

A
  • increased muscle capillaries, number of mitochondria, and myoglobin synthesis
  • may convert fast glycolytic fibers to fast oxidative fibers
47
Q

What are the affects of resistance exercise (typically anaerobic)?

A
  • muscle hypertrophy due to inc in fiber size

- inc mitochondria, myofilaments, glycogen stores, and CT

48
Q

What is disuse atrophy?

A

degeneration of a muscle as a result of inactivity

49
Q

What shape are smooth muscle cells?

A

spindle shaped

50
Q

What are the difference in microscopic structure of smooth from skeletal muscle?

A
  • spindle shaped
  • uninucleate
  • only has endomysium containing blood vessels and nerves is found between cells
  • SR is less developed and Ca stored in caveolae
  • no striactions
51
Q

What is a caveolae?

A

indentations in the plasma membrane that store Ca ions.

52
Q

Why is smooth muscle not striated?

A

does not contain sacromeres, myofibrils or t-tubules, but does contain myosin and actin.

53
Q

How is smooth muscle innervated?

A

autonomic nerve fibers innervate at diffuse junctions. Along these fibers are varicosities - bulbous swellings of nerve fibers that store and release neurotransmitters.

54
Q

How are the myofilaments differ in smooth muscle compaired to those of skeletal?

A
  • ratio of myosin to actin is much less (1:13) than in skeletal (1:2)
  • myosin filaments have heads along whole length
  • no troponin complex: calmodulin binds Ca ions
  • myofilaments are spirally arranged not in sarcomeres and contracts like a corkscrew.
  • has dense body proteins that anchor the non-contractile intermediate filaments (resist tension) to the sarcolemma
55
Q

What is the role of intermediate filaments?

A
  • the contractile filamants cause the cell to bulge to the sides when they contract.
  • the intermediate filamants provide a harness that limits/controls the bulging
56
Q

What are the contraction characteristics of smooth muscle?

A
  1. slow and synchronous
  2. cells are electrically coupled by gap junctions
  3. rate and intensity of contractions can be modified by neural and chemical stimuli
  4. stress-relaxation response: responds to stretch only briefly then adapts. Retains ability to contract on demand despite stretching.
  5. length-tension: can still contract when between half and twice its resting length
  6. exhibits hyperplasia: cells can multiply
  7. neural regulation of contraction: neurotransmitter binds and inc or dec Ca in the sarcoplasm
  8. contains pacemaker cells: stimulate contraction of whole sheets of cells
  9. same basic mechanism of contraction: inc Ca causes sliding of filaments
  10. contraction is very energy efficient (slow ATPases) and contractions are slower and longer
57
Q

What is the roll of pacemaker cells?

A

stimulates the contraction of whole sheets of cells.

58
Q

What are the two types of smooth muscle?

A

single-unit (visceral) smooth muscle

multi-unit smooth muscle

59
Q

what are the characteristics of single-unit (visceral) smooth muscle?

A
  • sheets contract as a unit because of gap junctions
  • often exhibit spontaneous AP
  • arranged in opposing sheets and exhibit stress-relaxation response
  • found in hollow organs and is the most common
60
Q

what are the characteristics of multi-unit smooth muscle?

A
  • located in large airways, arteries, arrector pili muscles, and iris of the eye
  • rare gap junctions
  • arranged in motor units with no synhronicity
  • graded contractions that involve recruitment in response to neural stimuli
61
Q

Describe muscular dystrophy.

A
  • Many types of diseases
  • Muscles enlarge due to fat and CT deposits
  • Muscle fibers undergo atrophy

ex. Duchenne muscular dystrophy (DMD)

62
Q

Describe Duchenne muscular dystrophy (DMD).

A
  • sex linked genetic disorder
  • lack protein dystrophin which anchors cytoskeleton to extracellular matrix and stabilizes the sarcolemma
  • sarcolemma tears during contraction resulting in no control over Ca ion entry
  • often die of respiratory failure in early 20s
  • no cure, but stem cell research shows promise
63
Q

What is the effect of aging on muscles?

A
  1. muscle replaced by CT
  2. decreased muscle bulk/strength
  3. decreased number of muscle cells
  4. arteriosclerosis (failure of the cardiac system due to aging) can impede blood supply
64
Q

Explain the striation and what causes it

A

I bands: light bands with just actin

Z disc: in the middle of I band, has alpha actinin to anchor actin

A bands: darker band with myosin and actin

H zone: lighter band in middle of A band that has myosin only

M line: middle of h zone, dark line containing myomesin which anchors myosin

titin which stretches from z disc to m-line through myosin to give it elasticity

65
Q

What is excitation-coupling?

A

the sequence of events by which transmission of an AP along the sarcolemma leads to sliding of the myofilaments

this is the latent period

66
Q

What are the two proteins that regulate cytoplasmic concentrations of Ca2+ to keep it low?

A

Calmodulin

Calequestrin

67
Q

what is the purpose of muscle tone?

A

to keep muscles firm, healthy, and ready to respond

68
Q

What is the force of muscle contraction affected by?

A
  1. number of muscle fibers stimulated and size of the fibers (recruitment)
  2. Frequency of stimulation
  3. Length-tension relationship (80-120%)
69
Q

What affects the speed of the contraction fibers?

A

the speed of acetylcholinesterases. Faster ACPases means faster contractile fibers

70
Q

explain the stress-relaxation response of smooth muscles.

A

stretching in smooth muscles provokes contraction, which automatically moves things along a tract. This only lasts briefly and then the muscle adapts to its new length and relaxes.

allows hollow organs to fill or expand slowly

Anatomy and Physiology 111 (9 decks)

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