Locomotion

Locomotion

1. Bones

   • Types of bone
     • long bones- act as levers found in limbs
     • Short bones- multiple articulation and complex movement, found in joints e.g tarsal and carpal bones
     • Flat bones- large surface for muscle attachment and protection e.g. scapula
     • irregular- e.g wedge bones like vertebrae/ splanchic in soft organs, phneumatic contain air
     • sesamoid- ease passage of a tendon e.g patella
   • Macroscopic structure
     • periosteum- outer membrane
     • cortical bone (compact bone)
     • Trabecular- spongey bone
     • medullary cavity In middle coated by endosteum
   • bone cells
     • osteoblasts- create bone
     • osteocytes- generalise bone cells
       • -mechanosensors -
     • osteoclasts- absorb bone
   • bone growth
     • woven bone=quickly formed irregular produced rapidly in fracture healing will eventually be replaced by lamellar bone
     • Intramembranous ossification
       • 1-mesenchymal cells become osteoblasts which secrete osteoids
         • osteoid is the non-mineral component of the matrix
         • osteoid forms a scaffold around osteoblast which is mineralised
       • 2-osteoblast is trapped in mineralised matrix and becomes osteocyte= bone formation
     • endochondral ossification
       • long bone development v common
       • 1-cartilage template, perichondrium lays down a bone collar in the diaphysis region using intramembranous ossification
         • perichondium is the membrane which surrounds the cartilage template
       • 2-cartilage in the diaphysis region degenerates leaving space for blood vessels creating a primary ossification centre. the matrix becomes impregnated with calcium salts
       • 3-epiphysis become vascularised creating secondary ossification centres
     • length
       • at growth plates to push epiphysis further apart
       • 1-proliferation and maturation of cartilage cells on epiphyseal growth plates
       • 2-hypertrophy of chondrocytes
       • 3- calcification of cartilage matrix
       • 4- chondrocytes die and are replaced by osteocytes
     • Girth
       • 1-build up bone on the outside and then either keep thick bone or delete bone from medullary cavity
       • 2- osteoblasts on periosteum lay down new bone forming ridges parallel to blood vessels eventually forming a pocket = an osteon
       • 3-osteoclasts on endosteum remove bone lining medullary cavity
     • what influences bone growth?
       • hormones
       • nutrition
   • Microscopic structures
     • cells suspended in a specialised matrix of hydroxyapatite
     • very vascularised
       • blood vessels enter bone via foramen and run under the periosteum, enter cortical bone through canals
       • blood vessel surrounded by concentric "doughnuts" of bone called lamellae
         • collagen orientated differently in neighbouring lamellae giving the bone strength
     • sandwiched between lamellae are cells called osteocytes
       • whole structure of blood vessel and surrounding lamellae is called an osteon
   • Structural Properties- 70% hydroxyapetite. of organic, 90% collagen

2. Muscles

   • skeletal muscle
     • epimysium> muscle belly> fasicle> fibre (cell)> myofibril> sarcomere
       • sarcomere composed of
     • striated
     • multiple peripheral nuclei
     • voluntary
     • musculoskeletal system
   • cardiac
     • single central nucleus
     • striated
     • involuntry
     • irregular arrangement separted by intercalated disks
     • Heart
   • smooth muscle
     • no striations
     • involuntary
     • longer contractions
   • architecture
     • Pennate
       • feather like
       • increases PCSA muscle force greater
     • Parallel
       • greater shortening since parallel, greater ability to do work/ more powerful
   • Muscle Contraction
     • uses
       • locomotion/ joint movement
       • stabilisation
       • continence
       • mastication
     • Sliding Filament Recap
       • 1-resting state myosin can't bind to actin as binding sites are blocked by troponin/tropomyosin complex
         • Myosin head has ADP and Pi attached
       • 2-Excitation- calcium ions bind to troponin changing shape, displaces tropomyosin from actin
       • 3-Binding- myosin head forms a cross bridge with the actin binding site, ADP and Pi detach from myosin head
       • 4- Power stroke, myosin head changes angle dragging actin filament toward sarcomere centre
       • 5-Detachment- ATP binds to myosin head causing it to detach from actin. ATP hydrolysed using ATPase to return myosin head to original position
     • Use of ATP
       • return myosin head to original position
       • reabsorb calcium ions to sarcoplasmic reticulum
     • muscle fibre types
       • Type 1- slow oxidative
         • slow because of low myosin ATPase activity
         • high oxidative capcity- fatigue resistant used to maintain posture
         • smaller diameter= weaker
       • Type 2a- fast oxidative glycolytic
         • high myosin ATPase activity
         • both oxidative and glycolytic capcity more common in body
       • Type 2 b- fast glycolytic
         • high ATPase activity
         • larger diameter- stronger
     • Types of contraction
       • Concentric- brings about movement and the muscle shortens
       • Eccentric- Slows movement/ controls motion the muscle elongates
       • Isometric- no shortening the filaments shorten but the muscle streaches passively so overall no change

3. tendons

   • and a little bit on ligaments
   • Tendon attach muscle to bone, ligament bone to bone etc
   • minimise distal limb mass
     • more efficient locomotion easier to raise leg & swing
   • used as springs- store and release elastic energy reduces the cost of running at high speed
   • can be used as power amplifiers, like a catapult slowly store energy then rapidly release
   • fasicles, sub fasicles> collagen fibres
     • majority composed of collagen in a helix then crimped structure
     • collagen gives tensile strength
   • Structural Properties- mostly type 1 collagen allows resist high tensile load. 1-5% PG resist compression. 2% elastin
     • ligament has less collagen than tendon and more PG since so close to joints need to resist compressive forces

4. ECM

   • ECM + cells from a tissue
   • ECM= network of discrete molecules maintain the integrity of the tissue
   • GAGs
     • glycosaminoglycans
     • long polysaccharide chians
     • hydrophilic- attract water and trap like a sponge
     • Difficult to compress
     • Examples
       • Hyaluronic Acid
         • synovial fluid
         • no PG
         • lubricate
       • Chondrotin Sulphate/ Keratin Sulphate
         • negatively charged sulphate groups repel each other= difficult to compress
         • Form PGs
           • proteoglycans
   • Elastin
     • coiled protien
     • has cross links between molecules which allows it to maintain structural integrity
   • Collagen
     • resist high tensile load
     • CRIMP pattern allows compliance
     • fibrous protein wrapped in a helix
   • cartilage- chondrocytes synthesise collagen
     • 10-20% collagen, 10-20% PG mostly water

5. Neuromuscular junctions

   • Structure nervous system
     • CNS
       • brain and spinal cord
     • PNS
       • Efferent (motor)
         • somatic (skeletal muscle)
         • autonomic (cardiac/ smooth/ exocrine glands)
       • Afferent (Sensor)
         • somatic vc visceral
   • Transmission across NMJ
     • 1- action potential arrives at presynaptic membrane causing voltage gated ca2+ channels to open
     • 2- Calcium ions diffuse into cytoplasm of presynaptic neurone
     • 3- calcium ions trigger synaptic vesicles to bind with the presynaptic membrane, releasing ACH into synaptic cleft via exocytosis
     • 4- ACH binds to receptors postsynaptic membrane causing ligand gated sodium ion channels to open
     • 5-sodium ion enter the cell depolarising the motor end plate
     • 6- acytlcholinesterase breaks down acytlchline into acytl and choline which diffuse back across the cleft
   • Excitation-contraction coupling
     • 1- Muscle action potential propagates along T tubule
     • 2- Depolarisation of T tubule causes Ca2+ channels to open between myoplasm and sarcoplasmic reticulum
     • 3- calcium binds to troponin allowing muscle contraction to begin
   • Skeletal Muscle Unit
     • one motor neurone and the fibres it innervates
       • strong muscle? few motor units
       • coordinate intricate movement? lots of motor units

6. Forelimb

   • Role in Locomotion
     • Support Bodyweight
     • Manipulation (feeding/digging/ carrying/displays)
   • Shoulder
     • extensors- brachiocephalicus, supraspinatus, biceps brachi
       • at the front of the shoulder
     • flexors- teres major, deltoids, triceps brachii long head
       • behind shoulder
     • Scapula specialisation
       • acromion- process at end of scapula spine
         • large= lots of shoulder flexor muscle attachment e.g animal adapted for digging
         • small on a horse since horse is adapted for locomotion not digging, larger on dog
       • scapula cartilage in horse- lengthens scapula and increases range of movement= greater stride length and more efficient locmotion
   • Elbow
     • Flexors- brachialis, biceps brachii,
     • extensors- triceps brachii
   • carpus + digits
     • know position of carpal flexors/ extensors
   • Hand + forearm specialisation
     • Interosseus muscle- small muscles that allow independent digit movement
       • dog has lots, cow has much fewer, horse has none

7. Hindlimb

   • Role of pelvic limb
     • propulsion (rear wheel drive)
     • power body upwards
     • defence
   • plantigrade- whole planter surface on ground, calcaneus sits on ground. tend to be bipedal
   • Digigrade- stands on digits, calcaneus is in air, shortened femur
   • unguligrade- foot segment longer, calcenius is almost vertical femur is short and robust
   • Femur
     • Horse
       • horse- large greater trochanter for muscle attachment
       • 3rd trochanter for gluteal attachment
       • distal trochlear groove large and uneven allows ability to lock patella
       • Short and Robust
     • Dog
       • slender and pronounced neck
       • distal trochlear grove much more even- no patella locking
   • Patella
     • apex always faces distally
     • asymetrical in horse- linked to locking ability?
   • Tibia and Fibula- fibula very short/ vestigal in horse to minimise distal limb mass
   • Tarsus- first and second tarsal bones fused in horse- no need for complex motor skill
   • Specialisation- reciprocal apparatus in horse
     • 1- superficial digital flexor and peroneus tertieus span tibia and are stripped of most muscle
     • 2- act as struts crossing both the tarsus and stifle
     • 3- tarsus can't flex without flexing stifle, tarsus can't extend without extending the stifle
     • 4- more efficient locomotion

8. Gait

9. Joints

   • Structure Synovial Joint
     • In limbs, v mobile
     • two articulating bones separated by fluid filled space
     • joint surrounded by synovial membrane, strengthened by fibrous joint capsule
     • Articular Cartilage
       • provides smooth gliding surface
       • transmits joint load
       • no nerves or blood supply= limited capacity for healing
     • Synovial Fluid
       • secreted by synovial membrane provides nutrient and waste transportation to articular cartilage
   • facilitators of joint function
     • Menisci
       • fibrocartilage discs provide cavity for femoral condyles gives joint stability
     • Bursae
       • fluid filled sacks ease tendon passage close to joint
     • tendon sheaths
       • like bursae but wrap all the way round
   • Types of joint
     • Joint Types