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24-25 HUMAN PHYSIOLOGY > The Musculoskeletal System > Flashcards

The Musculoskeletal System Flashcards

1
Q

What are the properties of muscle?

A
  • Contractility
    • Ability to shorten with force
  • Excitability
    • Capacity to respond to a stimulus
  • Extensibility
    • Ability to stretch
  • Elasticity
    • Ability to recoil after stretched
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2
Q

Describe the classification of the three types of muscle tissue

A
  • Skeletal
    • Attached to bones
    • Multiple nuclei peripherally located
    • Striated
    • Both voluntary and involuntary
  • Smooth
    • Walls of hollow organs, blood vessels
    • Single nucleus centrally located
    • Gap junctions
    • NOT striated
    • Involuntary
  • Cardiac
    • Heart muscle
    • Single nucleus centrally located
    • Intercalated discs
    • Striated
    • Involuntary
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3
Q

Voluntary VS Involuntary muscle

A
  • Voluntary: Actions directed by thought via nervous system
  • Involuntary: Actions not under conscious control via autonomic nervous system
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4
Q

Describe the structure of muscle fiber

A
  • Each fiber packed with myofibrils
  • Each myofibril packed with myofilaments
  • Myofilaments: Thick and thin filaments
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5
Q

Describe the structure of myofibril

A
  • A (Dark) band
    • Length of myosin (thick)
    • H zone: Light area where actin and myosin do not overlap
  • I (Light) band
    • Distance between A bands
    • Mostly actin (thin)
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6
Q

Describe the skeletal muscle structure

A
  • Skeletal Muscle
    • Surrounded by epimysium
    • Contains muscle fascicles
  • Muscle Fascicles
    • Surrounded perimysium
    • Contains muscle fibres
  • Muscle Fibres
    • Surrounded by endomysium
    • Contains myofibrils
  • Myofibrils
    • Surrounded by sarcoplasmic reticulum
    • Consists of sarcomere
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7
Q

Flexor VS Extensor Muscle

A
  • Flexor: decrease the angle between two bones at a joint
  • Extensor: increase the angle between two bones at a joint
  • The agonist (i.e. the muscle that is contracting) is responsible for movement
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8
Q

What are sarcomeres?

A
  • Contractile units of skeletal muscle
  • Consists of components between 2 Z discs
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9
Q

Describe the sliding filament theory of contraction

A
  1. Calcium ions released from sarcoplasmic reticulum
  2. Ca2+ bind to troponin
  3. Troponin molecule changes position
  4. Tropomyosin molecule moved away from actin active sites
  5. Active sites on actin exposed
  6. Energized myosin binds to actin active sites, forming **cross-bridges **
  7. Pi released, pivoting myosin heads, causing power stroke
  8. ATP binds to myosin head, detaching cross-bridges
  9. Splitting of ATP to ADP+Pi reactivates and recocks myosin head
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10
Q

Describe how contraction is controlled

A
  • Control of cross bridge attachment
    • Troponin-tropomyosin system
    • Switch for muscle contraction and relaxation
    • Tropomyosin filament in grove between double row of G-actins
    • Troponin attached to tropomyosin at intervals of every 7 actins
  • In relaxed muscle…
    • Ca2+ levels are low
    • Tropomyosin blocks binding sites on actin
    • Preventing formation of cross-bridges
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11
Q

Describe the Excitation-Contraction Coupling Neuromuscular Junction (NMJ)

A
  1. Neuromuscular Junction (NMJ): Action potential reaches the axon terminal of a motor neuron
  2. Acetylcholine released into synaptic cleft
  3. Sarcolemma
    • ACh binds to receptors
    • Opens ligand-gated channels
    • Na+ diffuses in
    • Causes depolarization
    • Produces action potential
  4. Transverse Tubules
    • Propagation of Action Potential
    • Opens voltage-gated calcium channels
  5. Sarcoplasmic Reticulum
    • Release Ca2+ ions to sarcoplasm
  6. Myofibrils
    • Ca2+ binds to troponin
    • Troponin-Tropomyosin system
  7. Muscle Contraction
    • Sliding filament theory of contraction
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12
Q

What is a motor unit?

A
  • A motor neuron and all the muscle fibers it innervates
  • The number of fibers varies based on the muscle’s required control
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13
Q

How do skeletal muscles generate energy at different exercise intensities?

A
  • Rest & Mild Exercise: Fatty acids
  • Moderate Exercise: Equal use of fatty acids and glycogen
  • Heavy Exercise: Primarily glycogen and blood glucose
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14
Q

Describe glucose uptake

A
  • With increased intensity of the exercise and longer exercise time
  • More GLUT4 channels are inserted into the sarcolemma to allow more glucose into cells
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15
Q

What is VO2 max?

A
  • Aerobic capacity (Maximal oxygen uptake)
  • Varies based on age, sex, size, and training
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16
Q

What happens when exercise is intensified?

A
  • Produce energy faster than our bodies can deliver O2
  • Muscles generate energy anaerobically
  • Only lasts for 1-3 minutes
  • Lactate levels accumulate
  • Side effects: ↑ acidity of the muscle cells
17
Q

What is the lactate threshold?

A
  • Anaerobic threshold
  • Determines exercise intensity for a given person
  • % of maximal oxygen uptake at which a rise in blood lactate levels occurs
  • Occurs at about 50−70% VO2 max
  • Potential causes
    • Low muscle oxygen
    • Accelerated glycolysis
    • Recruitment of fast-twitch fibres (fast fatigue muscles)
    • Reduced rate of lactate removal
18
Q

Describe the differences between Type I and Type II muscle fibers.

A

Type I (Red Slow-Twitch)
* Aerobic
* Resistant to fatigue
* Rich in capillaries and mitochondria
* Used for endurance activities

Type II (Fast-Twitch)
* Quick to fatigue
* Larger glycogen stores
* Type IIA (aerobic) and Type IIX (glycolytic)

19
Q

Describe Type IIA and Type IIX fibers

A

Type IIX fibers (White fast glycolytic)
* Contracts fast
* Anaerobic
* Large stores of glycogen
* Few capillaries and mitochondria
* Little myoglobin
* e.g. eye muscles

Type IIA fibers (Pink fast oxidative)
* Contracts fast
* Aerobic
* Intermediate to Type I and Type IIX
* e.g. gastrocnemius muscle

20
Q

What is phosphocreatine and its function?

A
  • ATP used faster than produced during exercise
  • Fast renewal of ATP: Combining ADP with ‘phosphocreatine’
  • Made in the liver and kidneys
  • Found in meat and fish
  • ‘Creatinemonohydrate’ dietary supplements: Increase muscle phosphocreatine by 15-40%
  • Damages liver in the long-term
21
Q

What causes muscle fatigue?

A
  • Lactic acid accumulation and lower pH
  • Increased concentration of PO4 due to phosphocreatine breakdown
  • Less ATP
  • Buildup of ADP
  • Central Fatigue: Fatigue of upper motor neurons, impaired function of CNS
22
Q

How can endurance training effect skeletal muscles?

A
  1. Improved ability to obtain ATP from oxidative
    phosphorylation
  2. Increased size and number of mitochondria
  3. Less lactic acid produced per given amount of exercise
  4. Increased myoglobin content
  5. Increased intramuscular triglyceride content
  6. Increased lipase
  7. Increased proportion of energy derived from fat; less from carbohydrates
  8. Lower rate of glycogen depletion during exercise
  9. Improved efficiency in extracting oxygen from blood
  10. Decreased number of type IIX (fast glycolytic) fibers; Increased number of type IIA (fast oxidative) fibers
23
Q

What is hypertrophy?

A
  • Muscle adaptation to strength training
  • Type II muscle fibers become thicker due
    to more sarcomeres
  • Thicker fibers may split into two fibers
  • Addition of three more proteins:
    1) Titin (protein attaching myosin to Z disc)
    2) Nebulin (protein associated with actin)
    3) Obscurin (protein that surround Z discs)
24
Q

How are muscles repaired?

A
  • Satellite cells: Stem cells of skeletal muscle
  • Fuse to damaged muscle cells for repair or forming new muscle fibres
  • Myostatin: Paracrine regulator that inhibits
    satellite cells
25
Q

Describe muscle decline with aging

A
  • Reduced muscle mass (usually type II)
    • Helped with strength training
  • Reduction in capillary blood supply
    • Helped with endurance training
  • Fewer satellite cells
    • Increased myostatin production to inhibit satellite cells
26
Q

Describe sensory feedback to control skeletal muscle movements

A
  • Golgi tendon organs: respond to tension a
    muscle puts on a tendon
  • Muscle spindle apparatus: respond to muscle length
27
Q

What is the muscle spindle apparatus?

A
  • Intrafusal fibers (thin muscle cells)
  • Types:
    • Nuclear bag fibers
    • Nuclear chain fibers
  • Sensory cells:
    • Primary (annulospiral):
    • Secondary (flowerspray): stimulated if sustained stretch
      1. Muscle stretches
      2. Spindles stretch
      3. Both the primary (1st) and secondary sensory endings
28
Q

What is the monosynaptic-stretch reflex?

A
  • Only 1 synapse within CNS
  • Striking patellar ligament passively stretches spindles activating annulospiral sensory neurons
  • Synapse on alphas that stimulate extrafusals
  • Produces knee-jerk reflex
29
Q

What is the Golgi tendon organ reflex?

A
  • Disynaptic reflex: 2 synapses in the CNS
  • Sensory axons synapse on interneurons
  • Make inhibitory synapses on motor neurons
  • Monitors tension, prevents excessive muscle contraction or passive muscle stretching
30
Q

Describe Huntington’s disease

A
  • Degeneration of caudate nucleus
  • Chorea: involuntary movements
  • Random, quick, uncontrolled, jerky
    movements
31
Q

Describe Parkinson’s disease

A
  • Degeneration of dopaminergic neurons from
    the substantia nigra to the caudate nucleus
  • Rigidity, resting tremor, and difficulty in
    initiating voluntary movements
  • Treated with l-dopa (the precursor of
    dopamine), but has side-effects of involuntary movement
32
Q

Compact bone VS Spongy bone

A

COMPACT BONE
* Dense and solid
* Basic functional unit: osteon
* Directional arrangement of osteons

SPONGY BONE
* Less dense; an open network
* Presence of bone plates, called trabeculae
* No blood vessels and osteon

33
Q

What are the four different bone cells?

A

OSTEOCYTES
* Mature bone cells

OSTEOBLASTS
* Immature bone cells
* Secretes organic components of matrix

OSTEOPROGENITOR CELLS
* Stem cells
* Produce osteoblasts

OSTEOCLAST
* Multinucleated
* Secretes acid and enzymes to dissolve bone matrix

34
Q

Describe how bone is remodeled

A
  • Organic and mineral components of bone matrix are continuously recycled and renewed
  • 1/5 of adult skeleton is demolished and
    rebuilt yearly
  • Homeostasis of Ca2+ balance

24-25 HUMAN PHYSIOLOGY (10 decks)

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