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BIO241 CH9 Muscles > Muscles > Flashcards

Muscles Flashcards

1
Q

Three Types of Muscle Tissue

A
  1. Skeletal muscle tissue:
  2. Cardiac muscle tissue:
  3. Smooth muscle tissue:
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2
Q

DESCRIBE Skeletal muscle tissue:

hint: VASP

A

** *VASP**

  • Attached to bones and skin
  • Striated
  • Voluntary (i.e., conscious control)
  • Powerful
  • Primary topic of this chapter
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3
Q

DESCRIBE Cardiac muscle tissue:

Hint: ISOh

A

**ISOh*

  • Only in the heart• Striated
  • Involuntary
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4
Q

DESCRIBE _ Smooth muscle_ tissue:

HINT: INN

A

_*INN_

• In the walls of hollow organs, e.g., s_tomach, urinary bladder, and airways_

  • *• Not striated**
  • *• Involuntary**
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5
Q

Special Characteristics

of Muscle Tissue

Hint: CEEE

A

*CEEE

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

Muscle Functions are?

Hint: HMMS

A

** *HMMS**

  1. Movement of bones or fluids (e.g., blood)
  2. Maintaining posture and body position
  3. Stabilizing joints
  4. Heat generation (especially skeletal muscle)
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7
Q

IN Skeletal Muscle
_Each muscl_e is served by

one_____, one ______, and one or more _____.

Hint: ANV

A

_*ANV_

1 artery, 1 nerve,** 1+ **veins

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8
Q

• Connective tissue sheaths of skeletal muscle are?

Hint: PEE

A

**• Epimysium:
• Perimysium:
• Endomysium: **

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9
Q

WHAT Connective tissue sheaths of skeletal muscle has
dense regular connective tissue surrounding entire muscle?

A

**
• Epimysium **

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10
Q

WHAT Connective tissue sheaths of skeletal muscle has
fibrous connective tissue surrounding fascicles (groups of muscle fibers)??

A

**• Perimysium: **

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11
Q

WHAT Connective tissue sheaths of skeletal muscle has
fine areolar connective tissue surrounding each muscle fiber?

A

**• Endomysium **

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12
Q

2 Ways Muscles attach:

A

**• Directly
• Indirectly **

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13
Q

• Muscles attach when the

_epimysium of muscle is fused to the periosteum of bone or perichondrium of cartilage
_

A

**
Directly **

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14
Q

• Muscles attach when the
—connective tissue wrappings extend beyond the muscle as a ropelike tendon or sheetlike aponeurosis?

A

**• Indirectly **

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15
Q

Microscopic Anatomy of a Skeletal Muscle Fiber are?

A
  • Cylindrical cell 10 to 100 μm in diameter, up to 30 cm long
  • Multiple peripheral nuclei
  • Many mitochondria
  • Glycosomes for glycogen storage, myoglobin for O2 storage
  • Also contain m_yofibrils, sarcoplasmic reticulum, and T tubules_
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16
Q

DESCRIBE

Myofibrils

A
  • Densely packed, r**odlike** elements
  • ~80% of cell volume
  • Exhibit striations: p_erfectly aligned repeating_ series of_ **dark A bands and light I bands **_
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17
Q

DESCRIBE

_Sarcomere
_

A
  • Smallest contractile unit (functional unit) of a muscle fiber
  • The region of a myofibril between two successive Z discs
  • Composed of thick and thin myofilaments made of contractile proteins
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18
Q

Features of a

Sarcomere are?

A

• Thick filaments: run the entire length of an A band

  • Thin** filaments: run the **length of the I band** and **partway** into the **A band
  • Z disc: coin-shaped sheet of proteins that anchors*** the ***thin filaments*** and ***connects myofibrils to one another
  • H zone: lighter midregion where filaments do not overlap
  • M line: line of protein myomesin that holds adjacent thick filaments together
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19
Q

Ultrastructure of Thick Filament
is Composed of?

A

protein myosin

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20
Q

• Myosin tails contain?

A

**
• 2 interwoven, heavy polypeptide chains**

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21
Q

• Myosin heads contain:

A
  • 2 smaller, light polypeptide chains that act as cross bridges during contraction
  • Binding sites for actin of thin filaments
  • Binding sites for ATP
  • ATPase enzymes
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22
Q

Ultrastructure of Thin Filament

A
  • Twisted double strand of fibrous protein F actin
  • F actin consists of G (globular) actin subunits
  • G actin bears active sites for myosin head attachment during contraction
  • Tropomyosin and troponin***: regulatory proteins ***bound to actin
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23
Q

DESCRIBE

Sarcoplasmic Reticulum (SR)

A
  • Network of smooth endoplasmic reticulum surrounding each myofibril
  • Pairs of terminal cisternae form perpendicular cross channels
  • Functions in the regulation of intracellular Ca2+ levels
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24
Q

DESCRIBE

T Tubules

A
  • Continuous with the sarcolemma
  • Penetrate the cell’s interior at each A band–I band junction
  • Associate with the paired terminal cisternae to form triads that encircle each sarcomere
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25
Q

Explain

Triad Relationships

A
  • T tubules conduct impulses deep into muscle fiber
  • Integral proteins protrude into the intermembrane space from T tubule and SR cisternae membranes
  • T tubule proteins: voltage sensors
  • SR foot proteins: gated channels that regulate Ca2+ release from the SR cisternae
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26
Q

What is

Contraction?

A
  • The generation of force
  • Does not necessarily cause shortening of the fiber
  • Shortening occurs** when **tension generated by cross bridges on the thin filaments exceeds forces opposing shortening
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27
Q

DESCRIBE

Sliding Filament Model of Contraction

A
  • In the relaxed state***, ***thin and thick filaments slightly overlap
  • During contraction, myosin heads bind to actin, detach, and bind again, to propel the thin filaments toward the M line
  • As H zones shorten and disappear, s**arcomeres shorten, muscle cells shorten, and the whole muscle shortens
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28
Q

WHAT are

Requirements for Skeletal Muscle Contraction

A

**1. Activation: **

**2. Excitation-contraction coupling:

• Final trigger: a brief rise in intracellular Ca2+ levels**

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29
Q

WHAT is-

neural stimulation at a
neuromuscular junction

_ _

A

** Activation **

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30
Q

What is
Generation and propagation of an action potential along the sarcolemma?

_ _

A

**
Excitation **

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31
Q

Events at the Neuromuscular Junction
• Skeletal muscles are stimulated by somatic motor neurons
• Axons of motor neurons travel from the central nervous system via nerves to skeletal muscles
• Each axon forms several branches as it enters a muscle
• Each axon ending forms a neuromuscular junction with a single muscle fiber
Neuromuscular Junction
• Situated midway along the length of a muscle fiber
• Axon terminal and muscle fiber are separated by a gel-filled space called the synaptic cleft
• Synaptic vesicles of axon terminal contain the neurotransmitter acetylcholine (ACh)
• Junctional folds of the sarcolemma contain ACh receptors
Events at the Neuromuscular Junction
• Nerve impulse arrives at axon terminal
• ACh is released and binds with receptors on the sarcolemma
• Electrical events lead to the generation of an action potential

A

Events at the Neuromuscular Junction
• Skeletal muscles are stimulated by somatic motor neurons
• Axons of motor neurons travel from the central nervous system via nerves to skeletal muscles
• Each axon forms several branches as it enters a muscle
• Each axon ending forms a neuromuscular junction with a single muscle fiber
Neuromuscular Junction
• Situated midway along the length of a muscle fiber
• Axon terminal and muscle fiber are separated by a gel-filled space called the synaptic cleft
• Synaptic vesicles of axon terminal contain the neurotransmitter acetylcholine (ACh)
• Junctional folds of the sarcolemma contain ACh receptors
Events at the Neuromuscular Junction
• Nerve impulse arrives at axon terminal
• ACh is released and binds with receptors on the sarcolemma
• Electrical events lead to the generation of an action potential

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32
Q

DESCRIBE

Destruction of Acetylcholine

A
  • ACh effects** are quickly **terminated by the enzyme acetylcholinesterase
  • Prevents continued muscle fiber contraction in the absence of additional stimulation
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33
Q

Events in Generation of an Action Potential?

A
      1. Local depolarization (end plate potential):
  1. Generation and propagation of an action potential:
  2. Repolarization:**
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34
Q

Events in Generation of an Action Potential

Describe Local depolarization (end plate potential):

_ _

A

• ACh binding opens chemically (ligand) gated ion channels

• Simultaneous diffusion of Na+ (inward) and K+ (outward)

• More Na+ diffuses, so the interior of the sarcolemma becomes less negative

  • *• Local depolarization – end plate potential
    • *
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35
Q

Describe Generation and propagation of an action potential:

A
  • End plate potential spreads to adjacent membrane areas
  • Voltage-gated Na+ channels open
  • Na+ influx decreases the membrane voltage toward a critical threshold
  • If threshold is reached, an action potential is generated
  • Local depolarization wave continues to spread, changing the permeability of the sarcolemma
  • Voltage-regulated Na+ channels open in the adjacent patch, causing it to depolarize to threshold
36
Q

Events in Generation of an Action Potential
_ _
Describe

_ Repolarization:_

A

• Na+ channels close and voltage-gated K+ channels open

• K+ efflux rapidly restores the resting polarity

• Fiber cannot be stimulated and is in a refractory period until repolarization is complete

• Ionic conditions of the resting state are restored by the Na+-K+ pump

37
Q

DESCRIBE

Excitation-Contraction (E-C) Coupling

A
  • Sequence of events by which transmission of an AP along the sarcolemma leads to sliding of the myofilaments
  • Latent period: T_i_me when E-C coupling events occur & Time between AP initiation and the beginning of contraction
38
Q

_ Events of_ Excitation-Contraction (E-C) Coupling

A

• AP is propagated along sarcomere to T tubules

• Voltage-sensitive proteins stimulate Ca2+ release from SR

• Ca2+ is necessary for contraction

39
Q

Role of Calcium (Ca2+) in Contraction

At low intracellular Ca2+ concentration:

A
  • Tropomyosin blocks the active sites on actin
  • Myosin heads cannot attach to actin
  • Muscle fiber relaxes
40
Q

Role of Calcium (Ca2+) in Contraction

• At higher intracellular Ca2+ concentrations:

A

** • Ca2+ binds to troponin**

• Troponin changes shape and moves tropomyosin away from active sites

• Events of the cross bridge cycle occur

• When nervous stimulation ceases, Ca2+ is pumped back into the SR and contraction ends

41
Q

DESCRIBE

**Cross Bridge Cycle
**

A
  • Continues as long as the Ca2+ signal and adequate ATP are present
  • Cross bridge formation—high-energy myosin head attaches to thin filament
  • Working (power) stroke—myosin head pivots and pulls thin filament toward M line
  • Cross bridge detachment—ATP attaches to myosin head and the cross bridge detaches
  • “Cocking” of the myosin head—energy from hydrolysis of ATP cocks the myosin head into the high-energy state
42
Q

Review Principles of Muscle Mechanics

  1. Same principles apply to contraction of a single fiber and a whole muscle
  2. Contraction produces tension, the force exerted on the load or object to be moved
  3. Contraction does not always shorten a muscle:
    • Isometric*** contraction: ***no shortening; muscle tension increases but does not exceed the load
    • Isotonic contraction: muscle shortens because muscle tension exceeds the load
  4. Force and duration of contraction vary in response to stimuli of different frequencies and intensities
A

Review Principles of Muscle Mechanics

  1. Same principles apply to contraction of a single fiber and a whole muscle
  2. Contraction produces tension, the force exerted on the load or object to be moved
  3. Contraction does not always shorten a muscle:
    • Isometric contraction: no shortening; muscle tension increases but does not exceed the load
    • Isotonic contraction: muscle shortens because muscle tension exceeds the load
  4. Force and duration of contraction vary in response to stimuli of different frequencies and intensities
43
Q

What is

The Nerve-Muscle Functional Unit

A

• Motor unit = a motor neuron and all (four to several hundred) muscle fibers it supplies

44
Q

**• Small motor units in muscles that controls? **

A

** fine movements (fingers, eyes)**

45
Q

• Large motor units Control

A

** weight-bearing muscles (thighs, hips) **

46
Q

STUDY

• Muscle fibers from a motor unit are spread throughout the muscle so that a single motor unit causes weak contraction of entire muscle

  • _**• Motor units in a muscle usually contract asynchronously; helps prevent fatigue
    • _
A

Study

• Muscle fibers from a motor unit are spread throughout the muscle so that a single motor unit causes weak contraction of entire muscle

• Motor units in a muscle usually contract asynchronously; helps prevent fatigue

47
Q

Describe

Muscle Twitch?

A

• Response of a muscle to a single, brief threshold stimulus

• Simplest contraction observable in the lab (recorded as a myogram)

48
Q

WHAT are the

Three phases of a twitch:

A
  • Latent period: events of excitation-contraction coupling
  • Period of contraction: cross bridge formation; tension increases
  • Period of relaxation: Ca2+ reentry into the SR; tension declines to zero
49
Q

Explain

Muscle Twitch Comparisons

A

_Different strength and duration of twitches are due to variations in metabolic properties and enzymes between muscles _

50
Q

Graded Muscle Responses

Responses are graded by?

A
  • Variations in the degree of muscle contraction
  • Required for proper control of skeletal movement
  1. Changing the frequency of stimulation
  2. Changing the strength of the stimulus
51
Q

*STUDY

Response to Change in Stimulus Frequency
• A single stimulus results in a single contractile response—a muscle twitch
• _Increase frequenc_y of stimulus (muscle does not have time to completely relax between stimuli)
• _Ca2+ release stimulate_s further contraction → temporal (wave) summation
• Further increase in stimulus frequency → unfused (incomplete) tetanus
• If _stimuli are given quickly enou_gh, fused (complete) tetany results

A

*STUDY

Response to Change in Stimulus Frequency
• A single stimulus results in a single contractile response—a muscle twitch

  • Increase frequency of stimulus (muscle does not have time to completely relax between stimuli)
  • Ca2+ release stimulates further contraction → temporal (wave) summation
  • Further increase in stimulus frequency → unfused (incomplete) tetanus
  • If stimuli are given quickly enough, fused (complete) tetany results
52
Q

STUDY

Response to Change in Stimulus Strength
• Threshold stimulus: stimulus strength at which the first observable muscle contraction occurs

  • Muscle contracts more vigorously as stimulus strength is increased above threshold
  • Contraction force is precisely controlled by recruitment (multiple motor unit summation), which brings more and more muscle fibers into action
  • Size principle: motor units with larger and larger fibers are recruited as stimulus intensity increases
A

STUDY

Response to Change in Stimulus Strength
• Threshold stimulus: stimulus strength at which the first observable muscle contraction occurs

  • Muscle contracts more vigorously as stimulus strength is increased above threshold
  • Contraction force is precisely controlled by recruitment (multiple motor unit summation), which brings more and more muscle fibers into action
  • Size principle: motor units with larger and larger fibers are recruited as stimulus intensity increases
53
Q

• Isotonic contractions are either?

A

** concentric**

or

eccentric

54
Q

_______________contractions—the muscle shortens and does work

A

** • Concentric **

55
Q

______________contractions—the muscle contracts as it lengthens

A

**
• Eccentric **

56
Q

STUDY

Isotonic Contractions

  • Muscle changes in length and moves the load
  • Isotonic contractions are either concentric or eccentric:
  • The load is greater than the tension the muscle is able to develop
  • Tension increases to the muscle’s capacity, but the muscle neither shortens nor lengthens
A

STUDY

Isotonic Contractions

  • Muscle changes in length and moves the load
  • Isotonic contractions are either concentric or eccentric:
  • The load is greater than the tension the muscle is able to develop
  • T_ension increases_ to the muscle’s capacity, but the muscle neither shortens nor lengthens
57
Q

During Muscle Metabolism: What happens in _Energy for Contraction? _

A

• ATP is the only source used directly for contractile activities

• Available stores of ATP are depleted in 4–6 seconds

**• ATP is regenerated **

58
Q

**
• ATP is regenerated by?**

A

• Direct phosphorylation of ADP by creatine phosphate (CP)

• Anaerobic pathway (glycolysis)

• Aerobic respiration

59
Q

During Anaerobic Pathway what happens
at 70% of maximum contractile activity?

Hint: BOP

A

BOP

• Bulging muscles compress blood vessels

• _Oxygen deliver_y is impaired

• Pyruvic acid is converted into l_actic acid
_

60
Q

During Anaerobic Pathway
_ What happens to ** Lactic acid_?**

Hint: DUC

A

DUC

  • Diffuses into the bloodstream
  • Used as fuel by the liver, kidneys, and heart
  • Converted back into pyruvic acid by the liver
61
Q

Study

Aerobic Pathway

  • Produces 95% of ATP during rest and light to moderate exercise
  • Fuels: stored glycogen, then bloodborne glucose, pyruvic acid from glycolysis, and free fatty acids
A

Study

Aerobic Pathway

  • Produces 95% of ATP during rest and light to moderate exercise
  • Fuels: stored glycogen, then bloodborne glucose, pyruvic acid from glycolysis, and free fatty acids
62
Q

WHAT is Muscle Fatigue

and Occurs when:

A

• Physiological inability to contract

• Occurs when:
• Ionic imbalances (K+, Ca2+, Pi) interfere with E-C coupling

• Prolonged exercise damages the SR and interferes with Ca2+ regulation and release

• Total lack of ATP occurs rarely, during states of continuous contraction, and causes contractures (continuous contractions)

63
Q

Muscle Fatigue during

  • Oxygen Deficit*
  • Extra O2 needed after exercise for?*
A

Replenishment of

• Oxygen reserves

• Glycogen stores

• ATP and CP reserves

** Conversion of lactic acid to pyruvic acid, glucose, and glycogen

64
Q

What happens during

Heat Production During Muscle Activity?

A

• ~ 40% of the energy released in muscle activity is useful as work

• Remaining energy (60%) given off as heat

• Dangerous heat levels are prevented by radiation of heat from the skin and sweating

65
Q

• The force of Muscle contraction is affected by:

A
  • Number of muscle fibers stimulated (recruitment)
  • Relative size of the fibers—hypertrophy of cells increases strength
  • Frequency of stimulation—↑ frequency allows time for more effective transfer of tension to noncontractile components
  • Length-tension relationship—muscles contract most strongly when muscle fibers are 80–120% of their normal resting length
66
Q

Muscle Velocity and Duration of Contraction

  • *Influenced by:
    • *

Hint MLR

A
      1. Muscle fiber type**

2. Load

3. Recruitment

67
Q

Muscle Fiber Type
Classified according to two characteristics?

A
  1. Speed of contraction: slow or fast, according to:
    • Speed at which myosin ATPases split ATP
    • Pattern of electrical activity of the motor neurons
  2. Metabolic pathways for ATP synthesis:
    • Oxidative fibers—use aerobic pathways
    • Glycolytic fibers—use anaerobic glycolysis
68
Q

Muscle Fiber Type has
Three types?

A

• _SLOW & FAST _oxidative fibers

• Fast glycolytic fibers

69
Q

WHAT HAPPENS

DURING

Influence of MUSCLE Load

A

↑ load → ↑ latent period,

↓ contraction,

and

↓ duration of contraction

70
Q

WHAT HAPPENS DURING MUSCLE

Influence of Recruitment

A

**Recruitment → faster contraction **

and

↑ duration of contraction

71
Q

Effects OF
Aerobic (endurance) exercise

Leads to increased?

A
  • **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
72
Q

Effects of Resistance Exercise
Resistance exercise (typically anaerobic) results in?

A

** • Muscle hypertrophy (due to increase in fiber size)**

• Increased mitochondria, myofilaments, glycogen stores, and connective tissue

73
Q

WHAT IS

The Overload Principle?

A

** • Forcing a muscle to work hard promotes increased muscle strength and endurance**

• Muscles adapt to increased demands

• Muscles must be overloaded to produce further gains

74
Q

WHAT IS Peristalsis?

A

• Alternating contractions and relaxations of smooth muscle layers that mix and squeeze substances through the lumen of hollow organs

• Longitudinal layer contracts; organ dilates and shortens

• Circular layer contracts; organ constricts and elongates

75
Q

Microscopic Structure

OF SMOOTH MUSCLE

A
  • Spindle-shaped fibers: thin and short compared with skeletal muscle fibers
  • Connective tissue: endomysium only
  • SR: less developed than in skeletal muscle
  • Pouchlike infoldings (caveolae) of sarcolemma sequester Ca2+
  • No sarcomeres, myofibrils, or T tubules
76
Q

WHAT IS

Innervation of Smooth Muscle

A

• Autonomic nerve fibers innervate smooth muscle at diffuse junctions

• Varicosities (bulbous swellings) of nerve fibers store and release neurotransmitters

77
Q

DESCRIBE

Myofilaments in Smooth Muscle

A
  • Ratio of thick to thin filaments (1:13) is much lower than in skeletal muscle (1:2)
  • Thick filaments have heads along their entire length
  • No troponin complex; protein calmodulin binds Ca2+
    • Myofilaments are spirally arranged, causing smooth muscle to contract in a corkscrew manner

• Dense bodies: proteins that anchor noncontractile intermediate filaments to sarcolemma at regular intervals

78
Q

Contraction of

Smooth Muscle

A

• Slow, synchronized contractions

• Cells are electrically coupled by gap junctions

• Some cells are self-excitatory (depolarize without external stimuli); act as pacemakers for sheets of muscle

• Rate and intensity of contraction may be modified by neural and chemical stimuli

• Sliding filament mechanism

• Final trigger is ↑ intracellular Ca2+

• Ca2+ is obtained from the SR and extracellular space

79
Q

STUDY

Contraction of Smooth Muscle
• Very energy efficient (slow ATPases)
• Myofilaments may maintain a latch state for prolonged contractions
Relaxation requires:
• Ca2+ detachment from calmodulin
• Active transport of Ca2+ into SR and ECF
• Dephosphorylation of myosin to reduce myosin ATPase activity

A

STUDY

Contraction of Smooth Muscle
• Very energy efficient (slow ATPases)
• Myofilaments may maintain a latch state for prolonged contractions
Relaxation requires:
• Ca2+ detachment from calmodulin
• Active transport of Ca2+ into SR and ECF
• Dephosphorylation of myosin to reduce myosin ATPase activity

80
Q

WHAT 2 THINGS HAPPEN

DURING

Regulation of Contraction

A

1)Neural regulation:
• Neurotransmitter binding → ↑ [Ca2+] in sarcoplasm; either graded (local) potential or action potential

• Response depends on neurotransmitter released and type of receptor molecules

2)Hormones and local chemicals:
• May bind to G protein–linked receptors

• May either enhance or inhibit Ca2+ entry

81
Q

What are the

Special Features of Smooth Muscle Contraction?

A

Stress-relaxation response:
• Responds to stretch only briefly, then adapts to new length

  • Retains ability to contract on demand
  • Enables organs such as the stomach and bladder to temporarily store contents

Length and tension changes:
• Can contract when between half and twice its resting length

82
Q

Special Features of Smooth Muscle Contraction

_Hyperplasia?
_

A

• Smooth muscle cells can divide and increase their numbers

• Example:
• estrogen effects on uterus at puberty and during pregnancy

83
Q

2 Types of Smooth Muscle?

_ _

A

1)Single-unit (visceral) smooth muscle:
• Sheets contract rhythmically as a unit (gap junctions)
• Often exhibit spontaneous action potentials
• Arranged in opposing sheets and exhibit stress-relaxation response

2)Multiunit smooth muscle:
• Located in large airways, large arteries, arrector pili muscles, and iris of eye
• Gap junctions are rare
• Arranged in motor units
• Graded contractions occur in response to neural stimuli

84
Q

_**STUDY_ Developmental Aspects
• All muscle tissues develop from embryonic myoblasts
• Multinucleated skeletal muscle cells form by fusion
• Growth factor agrin stimulates clustering of ACh receptors at neuromuscular junctions
• Cardiac and smooth muscle myoblasts develop gap junctions
• Cardiac and skeletal muscle become amitotic, but can lengthen and thicken
• Myoblast-like skeletal muscle satellite cells have limited regenerative ability
• Injured heart muscle is mostly replaced by connective tissue
• Smooth muscle regenerates throughout life
• Muscular development reflects neuromuscular coordination
• Development occurs head to toe, and proximal to distal
• Peak natural neural control occurs by midadolescence
• Athletics and training can improve neuromuscular control
• Female skeletal muscle makes up 36% of body mass
• Male skeletal muscle makes up 42% of body mass, primarily due to testosterone
• Body strength per unit muscle mass is the same in both sexes
• 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

A

_**STUDY_ Developmental Aspects
• All muscle tissues develop from embryonic myoblasts
• Multinucleated skeletal muscle cells form by fusion
• Growth factor agrin stimulates clustering of ACh receptors at neuromuscular junctions
• Cardiac and smooth muscle myoblasts develop gap junctions
• Cardiac and skeletal muscle become amitotic, but can lengthen and thicken
• Myoblast-like skeletal muscle satellite cells have limited regenerative ability
• Injured heart muscle is mostly replaced by connective tissue
• Smooth muscle regenerates throughout life
• Muscular development reflects neuromuscular coordination
• Development occurs head to toe, and proximal to distal
• Peak natural neural control occurs by midadolescence
• Athletics and training can improve neuromuscular control
• Female skeletal muscle makes up 36% of body mass
• Male skeletal muscle makes up 42% of body mass, primarily due to testosterone
• Body strength per unit muscle mass is the same in both sexes
• 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

85
Q

What is Muscular Dystrophy
and what is DMD

A

• Group of inherited muscle-destroying diseases
• Muscles enlarge due to fat and connective tissue deposits
• Muscle fibers atrophy

_Duchenne muscular dystrophy (DMD):_
• Most common and severe type
• Inherited, sex-linked, carried by females and expressed in males (1/3500) as lack of dystrophin
• Victims become clumsy and fall frequently; usually die of respiratory failure in their 20s
• No cure, but viral gene therapy or infusion of stem cells with correct dystrophin genes show promise

BIO241 CH9 Muscles (1 decks)

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