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HAN 200 > Chapter 9: Muscles > Flashcards

Chapter 9: Muscles Flashcards

1
Q

Muscle Tissue

A
  • Half of body’s mass
  • transforms chemical energy (ATP) to directed mechanical energy-> exerts force
  • three types:
  • skeletal
  • cardiac
  • smooth

Myo, mys, and sarco-prefixes for muscle

every muscle has a nerve attached to it

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2
Q

skeletal muscles

A
  • Elongated cells called muscle fibers
  • Striated (striped)
  • Voluntary (i.e., conscious control)
  • Contract rapidly; tire easily; powerful
  • Require nervous system stimulation
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3
Q

Cardiac muscle

A
  • Only in heart; bulk of heart walls
  • Striated
  • Can contract without nervous system stimulation
  • Involuntary
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4
Q

smooth muscle

A
  • In walls of hollow organs, e.g., stomach, urinary bladder, and airways
  • Not striated

-Can contract without
nervous system stimulation

-Involuntary

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5
Q

Special characteristics of muscle tissue

A
  • Excitability:
  • (responsiveness or irritability): ability to receive and respond to stimuli
  • Contractility:
  • ability to shorten forcibly when stimulated
  • Extensibility:
  • ability to be stretched
  • Elasticity:
  • ability to recoil to resting length
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6
Q

Muscle functions

A
  • 4 important functions:
    1. Movement of bones or fluids (blood)
    1. Maintaining posture and body position
    1. stabilizing joints
    1. Heat generation (especially skeletal muscle)

Additional functions:
-protects organs, forms valves, controls pupil size, causes “goosebumps”

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7
Q

Skeletal muscle

A

-Each muscle served by one artery, one nerve, and one or more veins.

  • Connective tissue sheaths of skeletal muscle:
    • Epimysium: dense irregular connective tissue surrounding entire muscle
    • Perimysium: connective tissue surrounding fascicles (groups of muscle fibers)
    • Endomysium: fine areolar connective tissue surrounding each muscle fiber
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8
Q

Muscle attachment sites: origin and insertion

A

Attach in at least 2 places:
*Insertion- moveable bone

*Origin- immovable (less movable) bone

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9
Q

Microscopic anatomy of a skeletal muscle fiber (cell)

A
  • Long, cylindrical cell
    • less than a diameter of human hair; up to 30 sm long
  • multiple peripheral nuclei
  • sarcolemma= plasma membrane
  • sarcoplasm= cytoplasm
  • glycosomes for glycogen storage
  • myoglobin for O2 storage
  • modified structures; myofibrils, sarcoplasmic reticulum, and T tubules
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10
Q

Myofibrils

A
  • Densely packed, rodlike elements
  • 80% of cell volume
  • contain sarcomeres-contractile units
    • sarcomeres contain myofilaments

-Exhibit striations- perfectly aligned repeating series of dark A bands and light I bands

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11
Q

Striations

A
  • Thick filaments: run entire length of an A band
  • Thin filaments: run length of I band and partway into A band
  • H zone: lighter region in midsection of dark A band where filaments do not overlap
  • Z disc (line): coin-shaped sheet of proteins on midline of light I band that anchors thin filaments and connects myofibrils to one another
  • Sarcomere: region between two successive Z discs
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12
Q

actin myofilaments

A

thin filaments

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13
Q

myosin myofilaments

A

thick filaments

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14
Q

Sarcoplasmic reticulum (SR)

A

-Network of smooth endoplasmic reticulum (organelle) surrounding each myofibril What was role of rough ER?

Pairs of terminal cisternae form perpendicular cross channels

Stores and releases Ca2+

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15
Q

Transverse (T) tubules

A

-Continuations of sarcolemma (plasma membrane)

Penetrate cell’s interior

Associate with paired terminal cisterns (part of SR) to form triads that encircle each sarcomere

**T tubules conduct impulses deep into muscle fiber; every sarcomere

Triad = 2 terminal cisterns + 1 T tubule (part of sarcoplasmic reticulum)

T tubules are transverse tubules formed by inward extensions of the sarcolemma.
-Function is to allow electrical impulses traveling along the sarcomere to move deeper into the cell.

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16
Q

Skeletal Muscle

Epimysium

A

dense irregular connective tissue surrounding entire muscle

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17
Q

Skeletal muscle

Perimysium

A

connective tissue surrounding fascicles (groups of muscle fibers)

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18
Q 
Skeletal muscle 
(Endomysium)
A

fine areolar connective tissue surrounding each muscle fiber

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19
Q

Skeletal muscle fiber cell:

SARCOLEMMA

A

plasma membrane

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20
Q

Skeletal muscle fiber cell:

SARCOPLASM

A

cytoplasm

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21
Q

Skeletal muscle fiber cell:

MODIFIED STRUCTURES

A

myofibrils, sarcoplasmic reticulum, T tubules

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22
Q

Thick filaments

A

run entire length of an A band

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23
Q

Thin filaments

A

run length of I band and partway into A band

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24
Q

H zone

A

lighter region in midsection of dark A band where filaments do not overlap

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25
Q

Z disc (line)

A

coin shaped sheet of proteins on midline of light I band that anchors thin filamnets and connects myofibrils to one another

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26
Q

M line

A

line on midline of H zone

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27
Q

Sarcomere

A

region between 2 successive Z discs

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28
Q

Sliding filament theory of muscle contraction

A
  • Skeletal muscle fiber contracts, Myosin heads bind to actin; sliding begins
  • Cross bridges form and break several times, ratcheting thin filaments toward center of sarcomere
  • When this happens:
    1. H bands & I bands get smaller
    2. Zones of overlap get larger
    3. Z lines move closer together
    4. Width of A band remains constant

shortening of myofibril during a contraction

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29
Q

Nervous system control of skeletal muscle

A
  • A skeletal muscle fiber contracts when stimulated by a motor neuron
  • Neuromuscular junction: site where motor neuron meets midpoint of muscle fiber
  • Each muscle fiber has only one NMJ
  • A single neuron may branch to control more than one muscle fiber
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30
Q

Excitation-contraction coupling

A

-Events that transmit AP along sarcolemma lead to sliding of myofilaments

  • Excitation – AP traveling
  • Coupling – actual contraction
  • AP brief; ends before contraction
    • Causes rise in intracellular Ca2+ which ->contraction

-Latent period:
Time between AP initiation and beginning of contraction

31
Q

Excitation

A

AP propagated along sarcomere to T tubules

32
Q

Steps in excitation-contraction coupling

A
  1. The action potential (AP) propagates along the sarcolemma and down the
    T tubules.
  2. Calcium ions are released.

(The AP travels along sarcolemma and down into the T tubules, this impulse causes release of Ca from sarcoplasmic reticulum)

  1. Calcium binds to troponin and removes the blocking action of tropomyosin. When Ca2+ binds, troponin changes shape, exposing binding sites for myosin (active sites) on the thin filaments.
  2. Contraction begins: Myosin binding to actin forms cross bridges and contraction (cross bridge cycling) begins. At this point, E-C coupling is over

This Ca assists in exposing active binding sites on actin filaments

33
Q

Homeostatic imbalance: Rigor mortis

A

-Cross bridge detachment requires ATP

3–4 hours after death muscles begin to stiffen with weak rigidity at 12 hours post mortem

  • Dying cells take in calcium ->cross bridge formation
  • No ATP generated to break cross bridges
34
Q

During depolarization, the sarcolemma is most permeable to

A

sodium ions

35
Q

What is calcium’s function during muscle contraction?

A

Calcium binds to troponin, changing its shape and removing the blocking action of tropomyosin.

36
Q

Principles of muscle mechanics

A
  • Contraction produces muscle tension,
  • Contraction may/may not shorten muscle

-Isometric contraction:
no shortening; muscle tension increases but does not exceed load

-Isotonic contraction:
muscle shortens because muscle tension exceeds load

37
Q

Isometric contraction:

A

no shortening; muscle tension increases but does not exceed load

38
Q

Isotonic contraction:

A

muscle shortens because muscle tension exceeds load

39
Q

Motor unit: the nerve-muscle functional unit

A
  • Each muscle served by at least one motor nerve
  • Motor nerve contains axons of up to hundreds of motor neurons
  • Motor unit = motor neuron and all (four to several hundred) muscle fibers it supplies
  • Smaller number = fine control

Motor units in muscle usually contract asynchronously; helps prevent fatigue

40
Q

motor unit

A

motor neuron and all (four to several hundred) muscle fibers it supplies
*Smaller number = fine control

41
Q

Muscle twitch

A

Motor unit’s response to single action potential of its motor neuron

3 phases:

  • Latent period
  • period of contraction
  • period of relaxation
42
Q

Muscle twitch:

LATENT PERIOD

A

Events of excitation-contraction coupling; no muscle tension

43
Q

Muscle twitch:

PERIOD OF CONTRACTION

A

cross bridge formation;tension increases

44
Q

Muscle twitch:

PERIOD OF RELAXATION

A

calcium ions reentry into SR; tension declines to zero

45
Q

Graded muscle responses

A

Graded muscle responses:
*Varying strength of contraction for different demands

-Required for proper control of skeletal movement

  • Increased force graded by:
    1. Changing frequency of stimulation
  1. Changing strength of stimulation (recruitment)
46
Q

single twitch

A

a single stimulus is delivered. the muscle contracts and relaxes

47
Q

summation

A

if another stimulus is applied before the muscle relaxes completely, then more tension results. this is WAVE (or temporal) summation and results in unfused (or incomplete) tetanus

low stimulation frequency-> unfused (incomplete) tetanus

48
Q

tetany

A

at higher stimulus frequencies, there is no relaxation at all between stimuli. this is fused (complete) tetanus

high stimulation frequency-> fused (complete) tetanus

49
Q

recruitment

A
  • The smooth ↑ in muscular tension produced by the ↑ in the number of active motor units
  • Contraction starts w/ activation of the smallest motor units in a stimulated muscle
  • As movement continues, larger motor units are activated & tension production rises steeply
50
Q

response to change in stimulus strength

A
  • Recruitment works on size principle:
  • Motor units with smallest muscle fibers recruited first
  • Motor units with larger and larger fibers recruited as stimulus intensity increases
  • Largest motor units activated only for most powerful contractions
51
Q

isotonic contractions

A
  • Muscle changes in length and moves load
  • Isotonic contractions either concentric or eccentric:
  • Concentric contractions—muscle shortens and does work
  • Eccentric contractions—muscle generates force as it lengthens
52
Q

Isotonic: CONCENTRIC CONTRACTIONS

A

muscle shortens and does work

53
Q

Isotonic: ECCENTRIC CONTRACTIONS

A

muscle generates force as it lengthens

54
Q

Isometric contractions

A
  • Load greater than tension muscle can develop
  • Tension increases to muscle’s capacity, but muscle neither shortens nor lengthens
  • Cross bridges generate force but do not move actin filaments
55
Q

Muscle contraction requires ATP

A

Anaerobic and Aerobic pathway

56
Q

Anaerobic pathway

A
  • Glycolysis – does not require oxygen
  • Small amount of ATP produced
  • At 70% of maximum contractile activity:
  • Bulging muscles compress blood vessels; oxygen delivery impaired

*Lactic acid is produced which changes pH Results in MM fatigue

57
Q

Aerobic pathway

A
  • Requires oxygen

- Produces 95% of ATP during rest and light to moderate exercise

58
Q

Excess postexercise oxygen consumption

A

To return muscle to resting state:
*Oxygen reserves replenished

  • Lactic acid converted to pyruvic acid
  • Glycogen stores replaced
  • ATP and creatine phosphate reserves replenished
  • All require extra oxygen; occur post exercise

***Paying back the Oxygen Debt

59
Q

Force of muscle contraction

A

Force of contraction depends on number of cross bridges attached, which is affected by:
*Number of muscle fibers stimulated (recruitment)

  • Relative size of fibers—hypertrophy of cells increases strength
  • Frequency of stimulation

*Degree of muscle stretch
(Length-tension relationship – muscle fibers at 80–120% normal resting length ->more force

60
Q

Velocity and duration of contraction

A

Influenced by:

  • Muscle fiber type
  • Slow and fast fiber type
  • Load
  • Greater the load, slower the contraction
  • Recruitment
  • More motor units contracting, the faster and more prolonged the contraction.
61
Q

Muscle fiber type

A

3 types:
-Slow oxidative fibers (long distance)

  • Fast oxidative fibers
  • Fast glycolytic fibers (short sprints)
  • Most muscles contain mixture of fiber types
  • All fibers in one motor unit same type
  • Genetics dictate individual’s percentage of each
62
Q

Muscle fiber types- FAST FIBERS

A
  • Large diameters, densely packed myofibrils, large glycogen reserves & few mitochondria
  • Produce powerful contractions
  • Use massive amounts of ATP & fatigue quickly
  • Use anaerobic glycolysis

Classified according to two characteristics: speed of contraction and metabolic pathway

63
Q

muscle fiber types- SLOW FIBERS

A
  • Half the diameter as fast fibers
  • Specialized for long periods of contraction
  • Large capillary network supports oxygen demand
  • Myoglobin: red pigment that binds oxygen
  • Oxidative fibers (slow) use aerobic pathways

Classified according to two characteristics: speed of contraction and metabolic pathway

64
Q

influence of load

A

Muscles contract fastest when no load added

increase load -> increased latent period, slower contraction, and decreased duration of contraction

If load exceeds muscle maximal tension speed of contraction is 0. (isometric

65
Q

Aerobic (endurance) exercise

A

Leads to increased:

  • Muscle capillaries
  • Number of mitochondria
  • Myoglobin synthesis
  • Results in greater endurance, strength, and resistance to fatigue
  • May convert fast glycolytic fibers into fast oxidative fibers
66
Q

Resistance exercise

A

typically anaerobic

Muscle hypertrophy:
*Due primarily to increase in fiber size

-Increased myofilaments, glycogen stores, and connective tissue leads to Increased muscle strength and size

67
Q

Homeostatic imbalance

A
  • Disuse atrophy
  • Result of immobilization
  • Muscle strength declines 5% per day
  • Neurogenic atrophy
  • Without neural stimulation muscles atrophy to ¼ initial size

-Fibrous connective tissue replaces lost muscle tissue leads to rehabilitation impossible

68
Q

Smooth muscle

A
  • Found in walls of most hollow organs (except heart)
  • Usually in two layers (longitudinal and circular)

Allows peristalsis - Alternating contractions and relaxations of smooth muscle layers that mix and squeeze substances through lumen of hollow organs

69
Q

Smooth muscle

A
  • Spindle-shaped fibers - only one nucleus; no striations
  • Lacks connective tissue sheaths; endomysium only

SR - less developed than in skeletal muscle

Pouchlike infoldings (caveolae) of sarcolemma store Ca2+ - most calcium influx from outside cell; rapid

No sarcomeres, myofibrils, or T tubules

70
Q

Innervation of smooth muscle

A

No NMJ as in skeletal muscle

Autonomic nerve fibers innervate smooth muscle at diffuse junctions

Varicosities (bulbous swellings) of nerve fibers store and release neurotransmitters into diffuse junctions

Slow synchronized contractions

May be initiated by pacemaker cells, hormones or local chemicals

71
Q

types of smooth muscle

A
  • Unitary (visceral) smooth muscle:
  • In all hollow organs except heart
  • Electrically coupled by gap junctions
  • Contract synchronously
  • Multi unit smooth muscle:
  • Located in large airways, large arteries, arrector pili muscles, and iris of eye

*Contractions are rarely synchronously

72
Q

Unitary (visceral) smooth muscle:

A

In all hollow organs except heart

  • Electrically coupled by gap junctions
  • Contract synchronously
73
Q

Multi unit smooth muscle:

A

Located in large airways, large arteries, arrector pili muscles, and iris of eye

*Contractions are rarely synchronously

74
Q

developmental aspects

A

With age, connective tissue increases and muscle fibers decrease

  • By age 30, loss of muscle mass (sarcopenia) begins
  • Regular exercise reverses sarcopenia
  • Atherosclerosis may block distal arteries, leading to intermittent claudication and severe pain in leg muscles

HAN 200 (15 decks)

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