The Musculoskeletal System Flashcards
What are the properties of muscle?
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Contractility
- Ability to shorten with force
-
Excitability
- Capacity to respond to a stimulus
-
Extensibility
- Ability to stretch
-
Elasticity
- Ability to recoil after stretched
Describe the classification of the three types of muscle tissue
-
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
Voluntary VS Involuntary muscle
- Voluntary: Actions directed by thought via nervous system
- Involuntary: Actions not under conscious control via autonomic nervous system
Describe the structure of muscle fiber
- Each fiber packed with myofibrils
- Each myofibril packed with myofilaments
- Myofilaments: Thick and thin filaments
Describe the structure of myofibril
-
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)
Describe the skeletal muscle structure
-
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
Flexor VS Extensor Muscle
- 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
What are sarcomeres?
- Contractile units of skeletal muscle
- Consists of components between 2 Z discs
Describe the sliding filament theory of contraction
- Calcium ions released from sarcoplasmic reticulum
- Ca2+ bind to troponin
- Troponin molecule changes position
- Tropomyosin molecule moved away from actin active sites
- Active sites on actin exposed
- Energized myosin binds to actin active sites, forming cross-bridges
- Pi released, pivoting myosin heads, causing power stroke
- ATP binds to myosin head, detaching cross-bridges
- Splitting of ATP to ADP+Pi reactivates and recocks myosin head
Describe how contraction is controlled
- Control of cross bridge attachment
- Troponin-tropomyosin system
- Tropomyosin filament in grove between double row of 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
Describe the Excitation-Contraction Coupling Neuromuscular Junction (NMJ)
- Neuromuscular Junction (NMJ): Action potential reaches the axon terminal of a motor neuron
- Acetylcholine released into synaptic cleft
-
Sarcolemma
- ACh binds to receptors
- Opens ligand-gated channels
- Na+ diffuses in
- Causes depolarization
- Produces action potential
-
Transverse Tubules
- Propagation of Action Potential
- Opens voltage-gated calcium channels
-
Sarcoplasmic Reticulum
- Release Ca2+ ions to sarcoplasm
-
Myofibrils
- Ca2+ binds to troponin
- Troponin-Tropomyosin system
- Muscle Contraction
- Sliding filament theory of contraction
What is a motor unit?
- A motor neuron and all the muscle fibers it innervates
- The number of fibers varies based on the muscle’s required control
How do skeletal muscles generate energy at different exercise intensities?
- Rest & Mild Exercise: Fatty acids
- Moderate Exercise: Equal use of fatty acids and glycogen
- Heavy Exercise: Primarily glycogen and blood glucose
Describe glucose uptake
- With increased intensity of the exercise and longer exercise time
- More GLUT4 channels are inserted into the sarcolemma to allow more glucose into cells
What is VO2 max?
- Aerobic capacity (Maximal oxygen uptake)
- Varies based on age, sex, size, and training
What happens when exercise is intensified?
- 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
What is the lactate threshold?
- 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
Describe the differences between Type I and Type II muscle fibers.
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)
Describe Type IIA and Type IIX fibers
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
What is phosphocreatine and its function?
- 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
What causes muscle fatigue?
- 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
How can endurance training effect skeletal muscles?
- Improved ability to obtain ATP from oxidative
phosphorylation - Increased size and number of mitochondria
- Less lactic acid produced per given amount of exercise
- Increased myoglobin content
- Increased intramuscular triglyceride content
- Increased lipase
- Increased proportion of energy derived from fat; less from carbohydrates
- Lower rate of glycogen depletion during exercise
- Improved efficiency in extracting oxygen from blood
- Decreased number of type IIX (fast glycolytic) fibers; Increased number of type IIA (fast oxidative) fibers
What is hypertrophy?
- 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)
How are muscles repaired?
- 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
Describe muscle decline with aging
- 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
Describe sensory feedback to control skeletal muscle movements
-
Golgi tendon organs: respond to tension a
muscle puts on a tendon - Muscle spindle apparatus: respond to muscle length
What is the muscle spindle apparatus?
- Intrafusal fibers (thin muscle cells)
- Types:
- Nuclear bag fibers
- Nuclear chain fibers
- Sensory cells:
- Primary (annulospiral):
- Secondary (flowerspray): stimulated if sustained stretch
- Muscle stretches
- Spindles stretch
- Both the primary (1st) and secondary sensory endings
What is the monosynaptic-stretch reflex?
- 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
What is the Golgi tendon organ reflex?
- 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
Describe Huntington’s disease
- Degeneration of caudate nucleus
- Chorea: involuntary movements
- Random, quick, uncontrolled, jerky
movements
Describe Parkinson’s disease
- 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
Compact bone VS Spongy bone
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
What are the four different bone cells?
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
Describe how bone is remodeled
- 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
