MSK Biomechanics

What are the roles of muscle

-dynamic motion

-stabilization

-balance

Myosin are ___ filaments, actin are ___ filaments

thick, thin

What is the motor unit of muscle?

alpha motor neuron and skeleton muscle fiber

How does contraction occur?

1. Nerve releases Ach at NMJ

2. Ach binds to receptors

3. Ach activates sarcolemmal gated Na channel

4. Action potential is generated and travels along sarcolemma

5. DHPR receptors activate and release Ca2+

6. Ca2+ binds troponin allowing for myosin actin binding

7. contraction

What is concentric contraction?

muscle length shortens as it activates

What is eccentric contration?

muscle lengthens as it activates

What is isometric contraction?

muscle length stays the same as it activates

What are type 1 muscle fibers?

-slow twitch

-large number of capillaries

-high oxidative capacity

-slow repetitive movement

-postural muscles

What are type 2 muscle fibers?

-fast twitch

-low oxidative capacity

-power generators

-larger with greater dynamic motion

T or F: muscle fiber types can change

True

T or F: certain myopathies effect certain kinds of fibers

True

What is a muscle spindle cell?

detects too much stretch, located in muscle belly

What is the golgi tendon organ?

detects too much contraction, located at musculotendinous junction

What is a myopathy?

muscle dysfunction

What is muscle damage?

strains or tears

How do muscles heal?

1. ruptured myofibers retract forming a gap between stumps allow access for inflammatory cells

2. contraction bands plug myofiber stumps preventing further damage

3. satellite cells get activated and migrate to damage (5 days)

4. myotubes differentiate into myofibers (months)

T or F: scar tissue can cause mechanical contriction

True

How does muscle necrosis occur?

cell damage allows for Ca2+ to enter the cytoplasm, activating destructive proteases

T or F: bone is a dynamic tissue that undergoes regular remodeling

True

What are the functions of bone?

-support

-motion with muscles and ligaments

-storage of fat, marrow, and minerals

-regeneration

What is the composite of bone?

-mineral (hydroxyapatite)

-type 1 collagen

What is cortical/compact bone?

-dense and strong

-located in diaphysis of long bones

-important for resisting torsion

What is cancellous/trabecular bone?

-lightweight and porous structure

-common in metaphysis and epiphysis

-excellent at distributing loads

-high metabolic activity

The nutrient artery supplies what bone?

the inner 2/3 of cortical bone

The periosteal vessels supply what bone?

outer 1/3 of cortex

The metaphyseal and epiphyseal artery supply what bones?

proximal and distal ends of long bones

Adequate ______ from blood supply is required for osteoblast and osteoclast activity

perfusion

What does the bone multicellular unit consist of?

-osteocytes

-osteoblasts

-osteoclasts

-type 1 collagen

-osteoid

-hydroxyapatite

What is the main function of osteoblasts?

growth

What is the main function of osteocytes?

maintenance and communication with neighboring cells

What is the main function of osteoclasts?

resporption

What does it mean that bone is anisotropic?

it is stronger along the axis

What does it mean that bone is viscoelastic?

its response depends on rate at which load is applied

Describe how bones take a load....think about a graph

load->elastic->yield->plastic->failure

What is bone remodeling?

resorption and formation occur on the same bone surface

What occurs during cortical remodeling?

an osteoclast tunnel is formed within cortex

What occurs during cancellous remodeling?

osteoclasts dig a trench rather than a tunnel

What is Wolff's law?

bone remodels in response to the mechanical loads placed upon it

T or F: bone adapts well to increased habitual loading

True

What does repetitive cyclic loading cause in bones?

focal microdamage

What is primary bone repair?

direct/contact healing facilitated by fracture compression

What is secondary bone repair?

indirect healing where the gap is large and forms a callus

What is the inflammatory stage of secondary bone repair?

soft callus forms from type 3 collagen

What is the remodeling phase of secondary bone repair?

mineralized cartilage is replaced by woven bone

What are the complications associated with bone repair?

infection, necrosis, fixation failure, delayed/non-union, laminitis, angular limb deformity

What can contribute to non-union occuring?

-age

-comorbidities

-metabolic disease

-nutritional deficits

What are fractures their weakest?

2 weeks post injury

Why would a plate be placed on a fracture?

-to prevent forces

-place plate on tension side to resist bending

T or F: bone can heal 100%

True

______ induces bone adaptation

strain

What are positional tendons?

-extensors

-low strain

-low water content

-low GAG

-low collagen

What are energy storing tendons?

-flexors

-high strain

-high water content

-high GAG

-high collagen

What is the structure of tendons?

crimp pattern of collagen fibers with small cellular fraction

T or F: tendon fibers are arranged into fascicles

True

What type of collagen make up the vast majority of tendons?

type 1

Tenocytes and tenoblasts are arranged according to the ______ environment of the tissue

mechanical

What does it mean for tendons to have CRIMP?

at rest, tendons have slack and a wavy like appearance

T or F: blood supply to tendons increase with age and mechanical loading

False

What does it mean for a tendon to heal extrinsicly?

blood comes from outside of the tendon

What two vessels supply tendons intrinsically?

paratenon and mesotenon

What phase are flexor tendons in while under tensile stress?

stance phase

How is kinetic energy stored during the first half of stance phase load?

elastic energy

T or F: the safety margins of a tendon are very wide

False

What is hysteresis?

loss of energy as heat during tendon loading and unloading

Damage to intrinsic tendon vasculature will increase reliance on extrinsic healing and result in what?

adhesion

Tendon injury can cause ____ disruption and release _______

extracellular matrix, degrading enzymes

What factors impair healing?

-location

-age

-immobilization

-NSAIDS

-steroids

-decreased growth factors

-decreased gene expression

What are the kinds of tendon injury?

-overstrain

-trauma

-degeneration

What ae the stages of tendon healing?

-inflammatory

-reparative

-remodeling

Scar tissue has an increased level of what kind of collagen?

Type 3

Controlled loading during tendon healing is important to prevent what?

-reinjury at original location

-adjacent injury

-contralateral injury

What occur during the inflammatory tendon healing stage?

-hematoma

-increased blood supply and edema

-infiltration of WBC

What occurs during the reparative tendon healing stage?

-accumulation of fibroblasts

-increased type 3 collagen

What occurs during the remodeling tendon healing stage?

-gradual transformation to type 1 collagen

-thickened collagen

-increased crosslinks

-improved fiber allignment

T or F: COMP increased with growth and exercise

True

T or F: after skeletal maturity, tendons have plenty of time to adapt

False

T or F: tendons can heal 100%

False