Animal Locomotion PDF

Different animal locomotor designs - Driven by selection pressure aka drivers of evolution o To obtain resources: habitat, food, mates o Environmental changes: temperature, weather, geography(natural habitat) o Biological: predators, pathogens(disease) ⇒ aim: Use minimum energy(to conserve energy) w...

Different animal locomotor designs - Driven by selection pressure aka drivers of evolution o To obtain resources: habitat, food, mates o Environmental changes: temperature, weather, geography(natural habitat) o Biological: predators, pathogens(disease) ⇒ aim: Use minimum energy(to conserve energy) while - Moving on different substrates and terraces - Moving in more than one directions - At varying speeds - Function o Support body mass o Move center of mass(COM) o Move limbs in cyclic fashion by individual muscles and joints Bipedal Quadrupedal 1. Small base of support --> strategies for 1. Large base of support --> COM would be stability to compensate e.g. vertical spine -less likely outside the base of support --> > maintain center of mass in the base of more stable support 2. Differentiate f(x) between fore and 2. Thoracic limb is freed for other f(x) hindlimbs --> different limbs have different designs --> ✓specialize --> optimize for e.g. flight/ prehension(grasping) responsible locomotion - Forelimbs: maneuvering, braking, body weight support - Hindlimbs: provide power for propulsion - Body adaptations examples (Adaptation for economy of locomotion) o o o o Mammal stances (Plantigrade/ Digitigrade/ Unguligrade) ▪ Plantigrade: walking with the toes and metatarsals flat on the ground ▪ Digitigrade: walking on the toes with the heel and wrist permanently raised ▪ Unguligrade: walking on the nail or nails of the toes (the hoof) with the heel/wrist and the digits permanently raised Loss of digit are often seen ∵↓use →lose to ↓NRG to maintain tissue ↑length of feet/ distal limb segment →larger steps →↑travel distance using same amount of energy Limb Geometry ▪ Jump/ walking ⇒ long hindlimbs ▪ Brachiation (limb geometry) ⇒ Long forelimbs act as long levers (See notes for lever principle) Size and location of bony processes/prominences ▪ Digging ⇒ Large bony prominence @ knee joint Limb posture ▪ Large body size When mass ↑, area ↑ relatively less ∴↑mass→↓area; while, muscle area = muscle force ∴mass↑, muscle force↓ ⇒Straight limbs → force travels straight up the limb i.e. more efficient energy transfer o less energy is needed to sustain posture and withstand ground reaction force(GRF) experienced o Limited capability in locomotion o Muscle anatomy(number, size, morphology[shape], where it’s attached, fiber type, firing patterns) + tendon structure & f(x) COMPARE QUADRUPEDAL HERBIVORES & CARNIVORES ▪ Large quadrupedal herbivores ▪ ✓ need of flight and migration for food(of low energy value)→ adapted for endurance, low energy cost, fleeing ⇒ ↓muscle, ↑ tendon in distal limb →↓NRG cost to swing limb → fast runners+↓NRG during locomotion Quadrupedal Carnivores ✓ need for hunting prey(unstable locomotion chasing prey vs lie in ambush)→ adapted for speed(acceleration, deceleration), agility, claws for gritting and grasping prey ⇒ upstraight forelimbs for braking, angular hindlimbs ↑efficiency for acceleration(limb posture); ⇒ Digitigrade: gritting and grasping prey(mammal stance); ⇒ muscular long tail for counter balance; ⇒ Large muscle groups: Spinal muscles: facilitate power & propulsion Proximal forelimb muscles: facilitate maneuvering and rapid braking Proximal hindlimb muscles: facilitate power & propulsion - Comparing different bipedals Walking Long columnar hindlegs + upright spine →COM directly above base of support Shorter forelimbs freed for tool use/carrying Plantigrade → foot act as lever Jumping (saltatorial locomotion) Crunch postures Long legs act as long distal levers Huge proximal hindlimb muscles → maximize force, contraction speed, series compliance Use of long tendons → amplify power produced by proximal structures Flight Hollow bones → reduce weight Limbs and feet are adapted for perching and catching prey Forelimbs as wings for flapping, hovering, gliding (flight) Connective tissues - Composed of cells and extracellular matrix(ECM) o ECM: Cells secrete new ECM and enzymes to degrade matrix macromolecules → ECM continuously renewed to stay healthy ▪ ECM transmits force to cells ∴↑mechanical load ↑turnover rate Types of mechanical stress F(x): ▪ Provides extracellular ‘scaffold’ structure for tissue ▪ Bears majority of mechanical stress ▪ Transmits chemical signals to the cells to regulate their migration growth and differentiation Common constituents: ▪ Fibrous proteins E.g. Elastin o Coiled structure o Cross links between molecules that are maintained when stretched out → maintains protein structure integrity when subjected to tensile forces → elastic E.g. Collagen o Compliant arrangement: triple helix of polypeptide chains form collagen microfibrils + hierarchical structure (microfibril→fibrils→fiber) → strong structure → high tensile strength o CRIMP structure → can be elongated and able to store energy o 29 forms (I-IV is most common) ▪ Ground substance: amorphous, vicious, gelatinous substance containing GAGs Glycosaminoglycans(GAGs) o Polysaccharides that link with proteoglycans ▪ Proteoglycans: large molecules → excellent for space filling o Hydrophilic → hold lots of water→ anti-compressive o E.g. Hyaluronan/Hyaluronic acid o ▪ Large molecule with high affinity for water ▪ Excellent lubricative properties ▪ Involved in tissue repair E.g. Chondroitin sulphate, keratan sulphate ▪ Highly charged sulphate groups → electrostatic repulsion → anti-compressive ▪ Forms proteoglycan with protein Bones - Living cells suspended in a matrix(65% mineral compounds; 30% organic material mainly collagen) o Organic: 90% type I collagen → structural organization, elasticity & flexibility o Inorganic: hydroxyapatite → mechanical rigidity, load bearing stregth - renewable and dynamic in behavior in response to the environment - Function o Organ protection e.g. ribs o Calcium storage in bone cells o Provide structural support o Blood cell production at red bone marrow o Lipid storage in yellow bone marrow o pH buffer for blood by releasing minerals - Different bones in the body a. Long Bone ▪ Anatomy 2 layers(outer&inner); Bone Periosteum membranes Act as protective layer; Site of sensory nerves: sense when bone is damaged → convey pain to CNS Site of blood & lymphatic nevers Osteogenic: contains osteoblasts Endosteum Bone Trabecular(spongy) type bone Single layer lining medullary cavity; Both osteogenic & osteolytic: contains osteoblasts & osteoclasts Particularly found in the epiphysis, surrounded by a layer of cortical bone Hexagonal structure → mechanically strong → provides good strength despite the air spaces → ↓bone weight → ↑effective use of NRG Thickness: diaphysis>epiphysis ↓thickness towards 2 ends Filled with bone marrow House of stem cells Cortical(compact) bone Medullary cavity marrow i.e. growth plate Epiphyseal plate @ end of epiphysis to join another plate Articular cartilage Penetrates cortical bone, extends into the internal of bone Blood vessels b. Non-long bones 1. Flat bones e.g scapular F(x): protect structure underneath/ provide s.a. for muscle attachment Characteristics: o No medullary cavity o 2 layers of compact bone surrounding either spongy bone/air o Develops differently from long bone 2. Short bones/ irregular bones Characteristics: o No medullary cavity o Developed from a single center of ossification o Found in areas with lot of action∵lots of short bones → lots of joints → greater range of motion e.g @ the carpus c. Sesamoid bones ▪ Small bone embedded within a muscle/tendon near a joint ▪ Function: Ease tendon path (i.e aid tendon movement) & prevent excessive tendon wear Increases moment arm (the length between a joint axis and the line of force acting on that joint) of muscles ↑moment arm → lift larger loads with smaller forces but less absolute movement for given force applied E.g. Patella in front of knee joint Provides leverage & momentum between knee joint and tendon o Facilitates quadriceps, tendons and ligaments → protects knee joint o ▪ - Microstructure of bone o Bone cells Name Osteogenic cells Location Periosteum Osteoblasts Osteocytes Periosteum within lacunae surrounded by mineralized bone matrix Endosteum Osteoclast Function Stem cells: differentiate into osteoblasts Forms new bone matrix Supports and maintains bone structure Reabsorbs unwanted bone (controlled by calcium homeostasis/damaged bone cells) o Structures Blood vessels Travels: Top to bottom through central(Haversian) canal Side to side through Perforating(Volkmann’s) canal Lamella(e) Finger-like projections surrounding canals F(x): - Allows communication between cells - Sense mechanical strain in bone A space where bone cells reside in Lacuna →↓distance between blood vessel & osteons → effective material exchange & transport - - o Osteon (haversian system) ▪ Basic functional unit of compact bone ▪ Collagen fibers run in different directions in neighboring lamellae →more resistant to twisting → bones X brittle → ↑resistance to fractures ▪ Structure of osteon gives bone strength and flexibility Surface markings (Bony Processes) o Function: ▪ Provide leverage to muscles when they cross joints to bring about movement ▪ Articulation with other bones → bone can join tgt ▪ Smooth surfaces for muscle attachment o Non-existent @ infancy ▪ ∵develops & changes according to pulls & strains produced by muscle on bone tissue Long bone formation 1. A bone collar is produced on the perichondrium of the diaphysis of the cartilage template by (Intra)membranous ossification → kicks starts long bone formation ▪ (Intra)membranous ossification #Produces flat/short/irregular bone while for long bone it only kick starts the formation process# Process: 1. Mesenchymal(stem) cells differentiate into osteoblasts 2. Osteoblasts secret osteoid (organic component of ECM) 3. (Osteoid mineralize) 4. Osteoblasts trapped in mineralized matrix becomes osteocytes 2. Cartilage tissue becomes bone tissue through endochondral ossification ▪ Endochondral ossification Occurs in the diaphysis(primary ossification center) and extends to the epiphysis(secondary ossification center) Process: 1. Bone collar prevents cartilage in its region to gain nutrients → chondrocytes at the primary ossification center start to degenerate → make space for bone tissue 2. Vascularization occurs in the degenerating area → osteogenic cells, other bone cells and calcium salts are introduced to the area 3. Matrix become impregnated with calcium salts 4. Cartilage cells die; Osteoblasts & osteocytes prevail as the main cell type 3. At the metaphysis, cartilage remains as the epiphyseal growth plate; At two ends of the epiphysis, hyaline cartilage remains as articular cartilage - Bone growth o in length @ epiphyseal growth plate Epiphyseal growth plate ▪ Cartilage → soft in nature → X provide mechanical strength & rigidity to cope with load imposed ▪ Growth plate of different bones and different species closes off at different times of life; Closes off when growth plate is ossified i.e. reaches skeletal maturity, meaning: 1. ↑ rate of ossification close to diaphysis 2. ↓ production rate of chondrocytes ▪ Femur is the first long bone to reach skeletal maturity Process: 1. Reserved chondrocytes in the growth plate is the basis of cartilage tissue → ensures cartilage tissue is attached to the bone of the epiphysis 2. (Proliferating) Chondrocytes proliferate by mitotic cell division → develops & matures (prehypertrophic chondrocytes) 3. Prehypertrophic chondrocytes grow in size until it reaches hypertrophy (Hypertrophic chondrocytes) 4. Hypertrophic chondrocytes pushes the growth plate apart, resulting in widening of growth plate → calcify and die → taken over by bone tissue by ossification 5. Deposition of bone in a organized manner as trabecular bone and osteoclastic resorption o In diameter/girth (Appositional growth) @ diaphysis of bone ▪ By osteogenesis at periosteum and osteolysis at endosteum Osteogenesis @ periosteum 1. Bone formation @ bone surface principally produced ridges that parallel a blood vessel on the surface of diaphysis 2. Ridges get higher and deeper channels are formed where blood vessels run 3. The ridges converge and fuse, trapping the vessel inside the bone → forming the structure of an osteon ▪ Occurs in targeted regions to gain the right organization & structure ▪ Results in more lamellae/osteon and bone widens o Type of bone formed Lamellar bone Slow production during growth in girth/ remodeling ∵organized structure requires time to develop Woven bone Rapid production in fracture healing, intramembranous & endochondral ossification ∵irregular arrangement. Bones can be deposited randomly by cells ∵regular concentric arrangement ∵irregular arrangement ∴strong ∴mechanically weak If bone is surgically repaired, ✓drive bone to repair and Laid initially in fracture healing (so there’s bone for adapt in certain ways e.g. form lamellar bone instead of support) → remodeled into lamellar/ trabecular bone woven o Nutritional influences ▪ Calcium and phosphate salts: raw materials of osteogenesis; insufficient→ ↓mineralization of new bone ▪ Vitamin D: affects absorption which depends on calcitriol (made only in presence of vit D.) ▪ Vit C, A, K , B12 o Hormonal influences ▪ Calcitonin, parathyroid hormone: regulates calcium metabolism ▪ Insulin, growth hormone, thyroxine: regulates bone growth ▪ Oestrogen, testosterone: regulates growth plate closure (∴closure of growth plates near sexual maturity) ▪ Oestrogen: regulates osteoblast activity - Maintenance & renewal of bone tissue o Bone modelling(reshaping) ▪ Process of bone shape change in response to the load imposed o Bone remodelling ▪ A lifelong cyclical process of bone removal & addition ▪ For: maintaining mechanical strength; response to mechanical demands(Wolff’s law) bone was loaded → micro-cracks that would normally be repaired by ongoing remodelling → X cause fractures * micro-cracks would accumulate if X time for repair mechanism to take place + ongoing cycles of extreme loading mineral homeostasis: providing access to calcium and phosphorous stores by releasing minerals from skeleton ▪ Pathology related to imbalance of the cyclical process: Osteoporosis Osteopetrosis ∵ removal> ∵ production> removal production ⇒ the bone in almost entirely ⇒ enlarged mineralized → very dense → trabecular spaces → deformed bone ↓bone density → weak and vulnerable to fractures and damages Treatment: - Prescribe hormones/metabolites - Euthanasia (esp. production species where economics is considered) Muscle - Comparing muscles o Size o Shape (long & thin vs short & fat) o Number of bellies (biceps & triceps) o Tendinous origins/insertions o Internal architecture  primary determinant of muscle function ▪ Arrangement of muscle fibers at structural level relative to the direction the muscle’s pulling Affects muscle volume, muscle moment arms, tendons o Impacts muscle function e.g. holding a laser pointer on the palm i. Muscle force ∵natural motion of laser pointer is fall by gravity Push/pull on object with mass that causes it to change velocity ∴hand is exerting force on the pointer from precenting it to fall due to gravity ii. Muscle work e.g. rowing Force x Δdistance applying force on the paddle iii. Muscle power ↑ the extend of arm movement → ↑ work performed by muscle Rate of performing work(Δwork/Δtime) = rate of muscle contraction - Sarcomere o Basic functional/contractile/organizational unit of muscle fiber o Composed regular & repetitive arrangement of 2 main protein filaments: actin & myosin o Multiple sarcomere → micro fibril o Shortens to bring about contraction of muscle fiber o Sarcomere of skeletal muscle ▪ Arranged radially in myofibril ▪ Thick filaments: Myosin @ the center of sarcomere → form Anisotropic band(A-band): dark in color Polypeptide chains with 2 globular heads and a long tail Connected to Z disk and M-line by titin → stabilizes structure of thick filament Globular head o F(x): grab hold and anchor actin molecules to pull them towards the center during contraction o Site of myosin ATPase(f(x): drives cross bridge cycling mechanism) ▪ Thin filaments: 2 intertwined chains of actin molecules Troponin: small globular protein bound to actin and tropomyosin Tropomyosin: rod shaped, located end to end along thin filament ▪ Different compartments of the sarcomere: Z disk o Formed with α-actinin o Between each sarcomere H-zone o Distance between 2 thin filaments in the same sarcomere M-line o Accessory protein structure made of structural protein(myosin & cprotein) and a functional enzyme(creatine kinase) o @ center of each sarcomere Type of muscle o Cardiac muscle ▪ Histology slide characteristics 1. Single central nucleus 2. Striated 3. Irregular arrangement with intercalated disks ▪ Involuntary contractions o Smooth muscle ▪ Histology slide characteristics 1. Single nucleus 2. No striation ▪ Involuntary contractions ▪ Allow longer contractions compared with the other 2 types o Skeletal muscle ▪ Histology slide characteristics 1. One muscle cell has multiple peripheral nuclei ∵multiple nuclei allows muscle(regenerative tissue) to readily repair 2. Striated (cross hatchings → arrangement of contractile protein) 3. Regular parallel bundles/arrangement ▪ Voluntary contractions ▪ Types of muscle fiber All 3 muscle fibers can exist in the same muscle → can activate & control diff pop. of diff fiber types @ diff times dependent on muscle activity Distribution is affected by genetics, training to ↑SO%↓FG%, age, lifestyle, diet Muscle fibers types are interchangeable involving addition/removal of mitochondria Smaller diameter; Weaker Type I Slow oxidative Low myosin ATPase activity Aerobic respiration to drive cross bridge cycle → → high oxidative fatigue contractions fibers - slow cross bridge cycle → slow contractions capacity→ ↑ATP for contraction Type IIa Fast oxidative glycolic fibers High myosin ATPase activity Mix of aerobic and anerobic respiration → high oxidative+glycolytic capacity Type IIb Fast glycolytic fibers High myosin ATPase activity Anerobic respiration →high glycolytic capacity → ↓ATP for contraction ▪ resistant→ For postural activities e.g. core muscles Larger diameter; fatigue easily→ For short bursts during high intensity exercise but for long periods Produce reasonable amount of force for a longer period of time Stronger when contract but only for short periods Type of muscle fiber arrangement Pennate muscle o Short fibers at an angle to internal tendon/aponeurosis→ feather-like o Benefits 1. Uses less energy to contract ∵shorter fibers = shorter distance to contract → more economical 2. Generate great force ∵Arrangement allows more muscle fiber to be packed → ↑contractile unit per fiber → generate stronger forces while longer but smaller in size →↑muscle PCSA (physiological cross sectional area) → ↑muscle force ➔ great @ braking, preventing joints from moving Parallel muscle o Fibers run parallel to the line of pull of the muscle o Benefits 1. Longer muscle fibers → more sarcomeres joining end to end → ↑ total muscle fiber shortening →↑potential for performing muscle work → ↑Δdistance per contraction → ↑velocity(distance/time) of contraction→ allow larger range of motion at joint ➔great @ moving joints ▪ Structure Hierarchical structure: myofibril → muscle fiber → fascicle → muscle belly Connects muscle to bone; vary in length Helps anchor tendon to muscle Unit of muscle, bundle of fascicle Sub-unit of muscle, bundle of muscle fiber Tendon Aponeurosis Muscle belly Fascicle Epimysium Perimysium Endomysium Fiber A muscle cell Myofibril Formed by multiple sarcomere Sarcolemma the plasma membrane of the muscle cell - Skeletal muscle control o Skeletal muscle only contract with innervation from motor neurons ▪ Each skeletal muscle fiber is innervated by a motor neuron ▪ A neuron can innervate more than one fiber → one neuron + all the fiber it innervate= 1 motor unit Ratio is dependent on muscle function (↑for strength ↓for fine control) ▪ Motor neurons are excitatory → +ve response only ▪ Patter of activity of motor neuron determines strength, speed and duration of contraction o Neuromuscular junction ▪ One-way communication only ▪ Shown as white blots on muscle surface when acetylcholinerase is stained Synaptic vesicles Junctional folds Contain Acetylecholine(ACh): neurotransmitters for motor neurons Highly folded sarcolemma with receptor @ mouth of each fold →↑s.a. for efficient & effective synaptic communication Acetylcholinesterase @ cleft of fold → breakdown ACh ▪ Initiation of muscle contraction by motor neuron Action potential travels down the axon & reaches the terminal end → depolarization of pre-synaptic membrane → voltage-gated Ca2+ channels in the membrane open up → Ca2+ ions diffuses into presynaptic nerve cytoplasm → stimulates movement of synaptic vesicles containing ACh to move downwards and fuse to presynaptic membrane → release ACh into the synaptic cleft → ACh diffuses across the clef by simple diffusion to bind to ACh receptors @ mouth of junctional folds of postsynaptic membrane → ligand-gated ion channels open up →Na+ ions enter, K+ ions exit muscle cell (exchange of ions) → depolarization of motor end plate = end plate potential - →further voltage-gated ion channels along the fiber open up → action potential is propagated → depolarization of T-tubule → T-tubule voltage sensor changes shape → Ca2+ channel of SR changes shape → Ca2+ channel between myoplasm and SR opens up → Ca released from SR = calcium transient → cross bridge cycling Force generation/Contraction of skeletal muscle brought by sarcomere o Types of contraction 1. Isometric contraction ▪ Contracts but X shorten ∵ working to counteract passive stretching of muscle caused by a weight ∴ f(x): hold something at its place 2. Concentric contraction ▪ F(x): actively create movement of joint 3. Eccentric contraction ▪ F(x): resist/control movement of joint E.g. preventing dislocation of elbow joint when weight is applied Biceps undergo eccentric concentration to work against the stretch in order to control the speed of elbow extension → prevent damaging bicep muscles and elbow joint when the joint is stretched out of motion o Sliding filament theory ▪ Thick & thin filaments slide pass each other →↑ overlap of thick & thin filament → shortening of sarcomere → shortening of muscle fiber o brought by Actom yosin Cross Bridge Cycle ▪ @ resting state, tropomyosin blocks myosin binding site on the actin molecule Troponin controls the position of tropomyosin on the thin filament Tropomyosin coils around actin → blocks active sites when muscle is @ rest 1. Excitation-contraction coupling: links electrical signals from the somatic nervous system to mechanical muscle contractions → Initiation of muscle contraction ▪ Acetylcholine stimulates the release of Ca2+ ions into sarcoplasm → Ca2+ ions bind to Ca2+ binding site(Tn-C) of troponin → tropomyosin binding site(Tn-T) changes in shape → pulls on tropomyosin → opens up myosin binding site 2. One of the myosin head binds to myosin binding site on actin → detachment of ADP and phosphate molecules from myosin head ▪ 2 myosin head work independently 3. Myosin head performs a ‘power stroke’ that drags the thin filament towards the center of sarcomere → shortening of sarcomere 4. ATP binds to myosin head causing it to lose affinity for actin → detach from actin binding site ▪ ATP is hydrolyzed by ATPase in myosin head into ADP and phosphate → release energy → reenergizes myosin head to return to previous position Step 3 repeats if Ca2+ ions are present Returns to resting state if Ca2+ ions are absent o Ca2+ ions can be stored back into the sarcoplasmic reticulum when CaATPase hydrolyses ATP → end muscle contraction o Sources of ATP for contraction ▪ Phosphorylation of ADP by creatine phosphate(CP) Simple reaction → very rapid ATP generation Muscle stores finite amount of CP and creatine kinase → CP is the limiting reagent → only used for onset of muscle contraction to kick start the cycle ∴for short durations of muscle activity ▪ Aerobic respiration: oxidative phosphorylation of ADP in mitochondria Requires a number of step → require time → slow generation of ATP Uses blood borne fuels(glucose, fatty acids, oxygen) and muscle glycogen → more raw material to generate ATP →can support endurance type of muscle activity Produces 34 ATP per cycle →↑ATP supply → supports moderate levels of activity ▪ Anaerobic/glycolytic respiration: Phosphorylation of ADP in cytosol During high intensity exercise(>70% max rate of ATP use), the body system is at maximal → X get a lot of O2 and that delivered to tissue → aerobic respiration is limited → ATP supply is limited → anaerobic respiration is used to provide additional ATP Performed under the absence of oxygen Requires muscle glycogen &/ blood borne fuel Produces lactic acid as by-product → excessive amount can cause pain in muscle and limits muscle f(x) - Classes of neurotoxin o Presynaptic/transmitter release inhibitor o Receptor inhibitor (by binding/destroying) o Acetylcholinesterase inhibitor (ACh X broken down → prolonged sustained contractions) Tendon - Work in a controlled and regular manner - Structure: o Hierarchical arrangement of tendon fiber parallel to long axis of tendon ▪ Collagen fibril –bundle tgt → collagen fiber → subfascicle(primary fiber bundle) → fascicle → tendon o Regular arrangement o Composition ▪ 86% Collagen (predominantly type I) ▪ 1-5% proteoglycans ▪ 2% elastin ▪ Tenocytes ▪ water - Benefits of tendon o Join muscle to bone → transmit muscle force to skeleton o More economical use of energy ▪ Tendons are stretchy → shorter muscle fibers are needed →∵short ∴contraction is limited → ↓NRG cost of contraction ▪ Tendons stretches to store elastic energy and when released, it recoils quickly → performs work more quickly than muscle → amplify power when same amount of energy [only applies when limited work is needed] In distal limb of horses, tendons are used to compensate big bulks of muscle ➔Minimizes distal limb mass swing distal limb freely with less NRG Tendons act as catapults in limbs of horses: stores elastic energy → release and recoils quickly when carpus buckles → all force is on tip of hoof → propels Ligament - Composition o 75% Collagen o >1-5% Proteoglycan ▪ To withstand high compressive forces @ joints which are very mobile o 2% elastin o Fibrocytes Cartilage - Composition o 10-20% Collagen(mostly type II) o 10-20% proteoglycan (mostly chondroitin sulphate) o Hyaluronan o 68% water o Chondrocytes ▪ - Spheroid in shape, flattened in shape near articular surface to provide friction free gliding @ joint ▪ ∵X blood supply to cartilage →↓[O2] → depends on anaerobic respiration Cartilage adaptation in different regions