locomotor overview

synovial joint

• most common

• most moveable

• articulating bones separated by fluid filled spce

• joint space surrounded by synovial membrane which is strengthened bya fibrous joint capsule

articular (hyaline) cartilage

• interface between bones at a synovial joint

• lubrication

• shock absorption - stiff to compression

• load transmission

• no nerves or blood vessels

synovial fluid

• secreted by synovial membrane

• clear/straw coloured viscous fluid

• contains hyaluronic acid

• lubrication

• shock absorption

• nutrient and waste transportation

menisci

• shape

• where are they located

• function

• medial and lateral are c shaped fibrocartilage rings located within knee joint

• deepens articular surface of tibia- increases joint stability

• act as shock absorber- increase SA to dissopate force

bursae

• structure and what does it contain

• function

• sac like structure containing small amount synovial fluid

• decrease friction between tendon, skin and bones

tendon sheath and clinical importance

-like bursae but wrap around tendon where they pass over joints

especially important clinically in horse

blood and nerve supply of

• articular cartilage

• free sensory fibres from where

• what kind of fibres to blood

• what kind of fibres from blood vessels

• what kind of fibres from joint capsule

• articular cartilage is avascular

• blood vessels supply epiphysis and joint capsule/ synovial membrane

• nerves for pain ,reflex, posture, and locomotion

• 1. free sensory fibres from joint capsule and synovial membrane

• efferent fibres to blood vessles

• sensory fibres from blood vessels

• proprioceptive fibres from joint capsule

other types of joint

planar

• articular surfaces

• movement

• rotation?

• examples

• flat or slightly curved articular surfaces

• gliding

• no rotation

• carpal/tarsal

pivot

• rounded end of one bone fits into ring of another

• rotation

• eg proximal radioulnar or antlantoaxial

hinge

• slightly rounded eg of one bone fits into slightly hollow of another

• one bone moves, the other is stationary

• elbow

• equine MCP

condylar

• oval convex surface fits into hollow

• angular movement

• biaxial

• femoro tibial, radiocarpal

saddle

• 2 surfaces

• convex in one direction

• concave in the other at right angles to the first

• eg DIP (distal interphalangeal) joint

ball and socket

• greates range of motion

• eg hip

joints

why are osteoprogenitor cells hard to see

they are difficult to distinguish from the surrounding connective tissue

how do oesteoblasts appear

closely arranged in a dense single layer of cells covering the bone surface

where bone formation is active there may be several layers

osteocyte shape

• where does it reside

• feature of mature osteocyte

star which reside in lacunae

mature osteocyte contains single nucleus

osteoclast shape

• very large up to 100um

• multi nucleated

• attach themselves to the bone matrix and sit within deep indentations of the bone matrix that are formed by their activity:resorption bays or howship lacunae

osteoclast

trabeculae

osteocyte in matrix

osteoblast

bone marrow

which collagen type predominates the annulus fibrosus

collagen type i

why is the cytoplasm of the osteoblast basophilic

because of the well developed rer

characteristic of cell specialised in the secretion of proteins

where are the volkmann

where are the bone lining cells found

on quiescent bone surfaces

tooth

aperneurosis

flat sheet of dense connective tissue connecting muscle to bones/ fascia

epimysium

dense irregular connective tissue surrounding each muscle protecting it from friction

fasicle

a bundle of muscle fibers

perimysium

connective tissue surrounding a bundle of muscle fibres

endomysium

surrounds individual muscle fibres

muscle belly

fleshy, thickest part of the muscle, is encased in the epimysium

skeletal muscle structure

• multiple peripheral nuclei

• voluntary

• striated

• regular parallel bundles

• outermost layer surrounded by epimysium

cardiac muscle structure

• striated

• single central nucleus

• involuntary

• irregular arrangement

• intercalated disks

• intercalated disks have extensive gap junctions allowing cell to cell communication

smooth muscle contraction

• not striated

• single nucleus

• involuntary

• longer contractions

• overlapping sheets of spindle shaped cells

• microscopically appear homogenous

• connected through end to end junctions called gap junctions creating a watertight seal

function of skeletal muscle

• voluntary movement of skeleton controlled by somatic nervous system

• maintain body position and posture

• stabilise joints

• support underlying organs and soft tissue

• store nutrient reserves

• maintain correc body temperature

smooth muscle function

• involuntary contrction controlled by autonomic nervous system

• lines inner wall of vasculature, hollow visceral organs, major bodily tracts

• regulate blood pressure by altering systemic vascular resistance

• peristalsis

• regulate bodily secretion

• lines respiratory tract

• iris controls light entering

• hair follicles

what is muscle architecture

• the arrangement of muscle fibres relative to the axis of force

• maximum force developed by muscle is proportional to the number of sarcoeres hence fibre length

pennate muscle

• short fibres at an angle to internal tendon/aperneurosis

• increases PCSA

• PSCA is directly proportional to force

• short fibres mean less contraction distance so it is economical

• however trade off with speed

parallel muscles

• fibres run parallel to line of pull of muscle

• more sarcomeres in series mean more total muscle fibre shortening so more work

• work= force x distance

• moves joints through a large range of motion

• speed= distance/time

roles of tendon

• minimise distal limb mass

• join muscle to bone

• store elastic energy

• conserve energy

• power amplification: stretched tendons recoil faster than muscle shortens so more power. only a small amount of work is done but in a shorter time so power output is higher

• power= rate of doing work

tendon structure

• tenoblasts and tenocytes

• chondrocytes, synovial cells and vascular cells

• tendon collagen fibres are in a crimped pattern

• collagen fibrils- collagen fibres- fascicles (surrounded by endotenon) 

• fascicles are bound together by the endotenon a dense irregular connective tissue sheath to form the tendon

type i

• slow oxidative

• low myosin ATPase activity

• high oxidative capacity

• smaller diameter

• fatigue resistant

• less force production

• steady fatigue curve

type iia

• fast oxidative glycolytic

• high myosin ATPase activity

• high oxidative AND glycolytic capacity

type iib

• fast glycolytic

• high myosin ATPase activity

• high glycolytic capacity

• larger diameter (stronger) fatigue easily

what can fibre types be influenced by

• genetics

• training

• age

• lifestyle

• diet

isometric contraction

• muscle contracts but does not change length

• produces force but it is equal to resistance

• eg holding something

concentric contraction

• shortens as it generates force

• force greater than resistance

• movement

eccentric contraction

• muscle lengthens under tension

• lowering

• high force and low energy

• eg control or resist flexion of the elbow caused by the ground reaction force during landing impact

lactertus fibrosis

horse

Biceps stretches during stance when carpus locked in extension

– LF stores ELASTIC ENERGY

– When carpus buckles in late stance this rapidly releases the stored energy

– The leg swings forward

myosin

• thick filaments

• polypeptide chains

• 2 globular heads and a long tail

• heads are the site of myosin ATP enzyme

thin filaments

• 2 intertwned chains of actin molecules plus

• tropononin- small globular protein bound to actin and tropomyosin

• tropomyosin- rod shaped, located end to end along thin filament

sliding filament theory

• tropononin controls position of tropomyosin on the thin filament. myosin cant bind with tropomyosin on its binding site

• acetylcholine diffuses from neuron and ca ions are released into sarcoplasm and bind to troponin

• calcium acts on tropomyosin and the myosin binding site is exposed

• myosin head binds to actin at newly exposed site. pi and adp are released

• thin filament moves in the direction of its negative end because the myosin head is firmly attached to the thin filament during its power stroke

• the two heads of each myosin molecule work independently. only one head attaches to actin at a given time

• myosin head and atp bind. myosin head detaches from the thin filament

• atp is hhydrilysed

events during a muscle contraction

• resting state- troponin controls the position of tropomyosin on the thin filament- here tropomyosin blocks the myosin binding site on the actin molecules

• excitation contraction coupling- calcium ions bind to troponin which changes shape. this moves tropomyosin on the thin filament away from the myosin binding site

• myosin heeads bind to actin on the thin filament. causes detachment of adp and phosphate molecules

• power stroke: myosin heads move performin a power stroke which drags the thin filament towards the centre of the sarcomere

• detachment- ATP binds to myosin causing it to lose affinity for actin and to detach from the actin binding site

  • atp is hydrolysed into adp and phosphate which reenergises myosin head to return to prevous poition

    • no calcim- resting state

    • if calcium is oresent then return to stage 3

what are the 3 functions of ATP in skeletal muscle contraction

• energy released from atp hydrolysis re enrges the myosin head providing enery for cross bride movement and force generation

• binding of atp to myosin causes the release of the myosin head from actin allowing repeated contractions

• in the sacoplasmic reticulum ca-atpase hydrolyses atp in order to take ca ions back to the sr to end a muscle contraction

what is the mechanical safety factor

• what is it

• example

• ratio of failure stress to typical stress experienced during locomotion

• the superficial digital flexor tendon has a small cross section and experiences relatively high streses operating near its mechanicl limit

• this is bcause it plays an important role in elastic energy cycling during locomotion

• to fulfill its locomotor function it must operate at a low safety factor

what do extrinsic muscles do

hold scapula to thorax

what flex distal joints

carpal and digital flexors

what happens during stance in forelimb

• withstand ground reaction force

• stabilise joints

• reisst over extension of joints

which muscles elevate and protract limb during swing

• cranial extrinsic muscles- protracting limb

• dorsal extrinsic- elevating

events during hindlimb stance

withstand ground reaction force

ressit over extension of joints

create propulsion

swing phase

• protraction of limb

• clearing foot away from ground

• preparing limb/foot position for stance

how do GRF change with speed

increase

how do GRF alter during incline

• forelimb vertical forces decrease uphill

• hind limb peak vertical forces increase uphill

what are gaits based on

• footfall patterns

• biomechanical properties

PE and KE during

• braking

• midstance

• propulsion

• braking and propulsion PE low KE high

• other way in midstance

basic structure of the ECM

• fibroblasts in most connective tissue

• GAG polysaccharide chains (repeating dissacharides)

• GAGs which covently bond to proteins- proteoglycans

• fibrous proteins such as collagen

• proteoglycans form a gel like substance where fibrous proteins are embedded which resists compressive forces, allow diffusion

glucosaminoglycans

• structure

• branched or unbranched

• hydorphobic or hydrophilic

• how do they withstand compression

• unbranched polysaccharide chains

• repeating disaccharide chains

• hydrophilic

• porous gels (hydrated) filling up most of the extracellular space

• attract cations so water in by osmosis- turgor- withstand compression

collagen

• how many polypeptide chains

• how many forms

• triple stranded helical structure

• 3 polypeptide chains

• 29 forms

elastin

• hydrophobic or hydrophilic

• what is the precursor molecule

• how does the precursor form elastin

• highly hydrophobic protein

• precursor is tropoelastin

• tropoelastin is secreted into the extracellular space and assembled into elastic fibres close to the plasma membrane, which then cross link

• coiled

• stretch and recoil

tendon

• collagen

• proteoglycans

• elastin

• tenocytes

ligament

• fibrocytes

• ecm

• lower collagen, more proteoglycan

• elastin

cartilage

• which collagen

• which is the predominant proteoglycan

• other molecules

• how much percent of water

• chondrocytes

• type ii collagen mostly

• proteoglycan predominantly chondrotin sulphate

• hyaluoran

• 68 percent water

• regional variation

ecm of bone

• what gives rigidity and compressive strength and where is this deposited?

• which gives tensile strength and elasticity

• hydroxyapatite gives rigidity and compressive strength

• this is deposited on collagen fibres

• load bearing

• inorganic

• type i collagen gives tensile strength and flexibility, elasticy, structural organisation, organic

what is mechanical loading

• ecm turnover is triggered by mechanical loading

• involves cell signalling

• loading increases synthesis of new ecm proteins and degrading enzymes

• loading can alter the molecular conformation of proteins changing how enzymes bind and degrade (change in collagen type and organisation)

• tissue properties influence how they degrade eg stiffness

wolffs law

• increase in loading causes architecture of spongy bone to strengthen and cortical layer strengthening whilst decrease causes bones to weaken and bone tissue to be resorbed