Anatomy and Physiology of Synovial Joints, Connective Tissues, and Muscular Function

SAID principle

Specific Adaptations to Imposed Demands

synovial joint components (all)

joint cavity, fibrous capsule, synovial membrane, hyaline cartilage, synovial fluid film, ligaments

some synovial joint components

bursa, fat pad, articular disk, accessory ligaments

synovial layer

produces hyaluronic acid

cartilage cell type

chondroblast/cyte

tendon cell type

tenoblast/cyte

bone cell type

osteoblast/cyte

mechanotransduction

The process by which the body converts mechanical loading into cellular responses

Extracellular matrix

proteins and water

fibrillar: collagen and elastin

interfibrillar: water, PGs, GAGs

collagen type I

resists tensile stress, found in all/most CT

collagen type II

resists compressive stress, found in cartilage and nuclei of IV discs

Elastin

found in tissues that require more deformation and elasticity

ligament component

type I collagen w/ varying elastin, fibroblasts

ligament structure

fibrils arranged in line with the applied tensile forces, not uniform, resist multiple angles of pull

What does the collagen/elastin ratio in a ligament depend on?

whether the ligament has a mobility or stability role

entheses

attachment site of ligament to bone

ligament nutrition

blood supply

tendon components

fibroblasts, tenoblasts/cytes; type I collagen

tendon structure

fibers are uniform and in the direction of tensile loading

collagen cross-linking

cross-linking resists slipping, combines fibers of collagen

tendon insertion

increased type II collagen closer to bone

myotendinous junction

interdigitation between collagen and muscle cells

tendon nutrition

blood supply, requires tensile loading to stay healthy

hyaline cartilage component

chondroblast/cyte, 90-95% type II collagen, PGs, GAGs

hyaline cartilage nutrition

avascular, relies on diffusion of synovial fluid

fibrocartilage composition

type II collagen, relies on diffusion

bone composition

type I collagen, hydroxyapatite crystals

cancellous bone

spongy inner layer/trabeculae

cortical bone

outer layer; thin, dense, compact

periosteum

fibrous outer layer covering bone

wolffs law

bone modeling consistent with the stress it's exposed to

bone maintenance

nutrition via circulatory system, osteoblast/clast activity

load

any force applied to a tissue

deformation

the result of an applied force

stiffness

resistance to deformation

compliance

ease of deformation

tendonitis

repeated microfailure (plastic region)

tendon rupture

single bout of excessive loading that results in macrofailure

ligament instability

repetitive sub-maximal loading into late elastic region of curve without sufficient recovery before the next

ligament sprain

a bout of loading into the plastic region

ligament rupture

single bout of excessive loading that resuls in macrofailure

creep

force is sustained while length changes over time

stress-relaxation

The force to maintain a certain strain decreases over time

strain rate sensitivity

stiffness is increased when loaded rapidly (hopping on toes vs calf stretch)

Role of skeletal muscle

1. produce movement of a bony lever

2. stabilize joint segments

3. respiration

4. produce body heat

actin

-thin filament

-binding site for myosin head

-troponin and tropomyosin

myosin

-thick filament

-head region

determinants of active tension

number of muscle fibers, size of muscle fibers, number of myofibrils in parallel

motor unit

an alpha motor neuron and all the muscle fibers it innervates

Large Motor Unit

large axon, many fibers (type II), recruited in forceful contractions

Small Motor Unit

small axon, fewer fibers (type I), recruited for fine motor

size principle

first choice is to recruit small motor units (save energy)

type 1 (slow oxidative) fibers

small, red, capillarity dense, high myoglobin content, slow speed, slow fatigue

type 2x (fast glycolytic) fibers

large, white, capillarity sparse, low myoglobin, fast speed, fast fatigue

active insufficiency

inability for a muscle to produce sufficient torque to shorten fully across all of the joints it crosses

passive insufficiency

inability for a 2 joint muscle to be stretched maximally across both joints it crosses

fusiform properties

good ROM, fewer long fibers

pennate properties

good force production, more short fibers

muscle spindle

sensitive to quick stretches (refelxes)

golgi tendon organ

the stretch of golgi tendon organ causes reflex inhibition