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
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
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
4
Q
Describe the structure of muscle fiber
A
- Each fiber packed with myofibrils
- Each myofibril packed with myofilaments
- Myofilaments: Thick and thin filaments
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)
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
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
8
Q
What are sarcomeres?
A
- Contractile units of skeletal muscle
- Consists of components between 2 Z discs
9
Q
Describe the sliding filament theory of contraction
A
- 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
10
Q
Describe how contraction is controlled
A
- 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
11
Q
Describe the Excitation-Contraction Coupling Neuromuscular Junction (NMJ)
A
- 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
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
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
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
15
Q
What is VO2 max?
A
- Aerobic capacity (Maximal oxygen uptake)
- Varies based on age, sex, size, and training
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
- 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
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
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
26
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*
27
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
1. Muscle stretches
2. Spindles stretch
3. Both the primary (1st) and secondary sensory endings
28
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**
29
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
30
Describe Huntington's disease
* Degeneration of **caudate nucleus**
* **Chorea**: involuntary movements
* Random, quick, uncontrolled, jerky
movements
31
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
32
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
33
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**
34
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
