Evolutionary Anatomy - My week 12 lecture notes for Human Locomotor Systems PDF

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My week 12 lecture notes for Human Locomotor Systems...

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Evolutionary Anatomy – summarise into tables Locomotion -

Vertical clingers - lemurs Semi brachiators – new world monkeys Terrestrial quadrupeds – old world monkeys Arboreal quadrupeds – old world monkeys Brachiating apes – gibbons, orangutans Knuckle-walking apes – chimps, gorilla Bipedal – humans

Skull -

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Frankfurt horizontal: orbital to porion Foramen magnum – humans more anterior, places on inferior skull, axis vertically orientated (oblique chimps), nuchal muscles smaller, chimps have additional muscle to help traps, apes rhomboids stat at nuchal region Humans – short face, back skull pushed down, shorter snout, inferior occipital condyles (chimps post/oblique) Nuchal muscles help with skull stability and head position, help balance skull against weight of face – why head slumps forward when sleeping up right Human – brain case large and globular Basicranial flexion – happened in humans when anterior skull flex inward so no snout like apes

Thorax -

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Monkey’s: quadrupedal locomotion (weight centred) – deep thorax (vent to dorsal), but narrower bilaterally. Scapular on side rib cage, glenoid cavity faces ventral side (and deep), humerus has greater congruency (non-brachiating). Clavicle – short. Apes: brachiating – vent-dorsal shallow (but wider), therefore organs remain close to COG and don’t fall too far forward, scapular on back of rib cage + shallow glenoid cavity greatly increases range of motion. Clavicle – long: allows excursion shoulder joint away from midline, long in all brachiators but longest in brachiating apes (orangutans) Humans barrel shape (12 ribs) vs apes funnel shape (13 ribs) Apes short lumbar region – large abdominal viscera so large ribcage and short lumbar support needed

Vertebral Column -

Humans: s-shaped, secondary curvatures, C7/T12/L5/S5/C4 Apes: C-shaped, only primary curvature, C7/T12/L3/S6/C3-4 Cervical: C2/axis – dens posterior position (retroflexion) in apes and monkeys (allows hyperextension of head to look up), Apes – long spinous process, end in knobs (thickenings). Humans – bifid spinous processes – nuchal ligament lies in space (vestigle in apes), allows us to keep head habitually upright.

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Thoracic – apes/humans; trans proc post orientation, vertebral column sits inside rib cage – allows weight to be centred. Wide sternum associated with wider rib cage. Monkeys; trans lat orient, vertebral column sits outsit ribcage. Lumbar – apes 3-4; width remains constant, orientation articular facets does not change in transitional vertebrae – due to lack of secondary curvature (facet orientation in humans stops vertebrae slipping forward at transition vertebrae in curvature) Sacrum/coccyx – apes = long sac, short coccyx. Tails – short sacrum, long caudal region (1735). Neural canal ends at proximal end caudal vertebrae except in new world monkeys with prehensile tails neural canal and spinal cord ends at distal end – end of tails = good nerve supply All primates have some angle between sac and coc regions to allow to give birth to large brain offspring Back muscles: Apes: erector spinae fused, humans: ES prevent too much lr

Upper Limb: Primitive in humans -

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Intermembral index: H+R/F+T. If >1 then upper limb longer then lower limb Humans II greater than clingers/leapers (lemurs) but less than others. Brachiators >1 Scapula: monkeys lateral placement – movement restricted to sagittal plane. Apes and humans; dorsal placement increases ROM. Humans (compared to apes): not as mobile, not as adept to quadrupedal locomotion, smaller supraspinous fossa (large in apes to help abd), acromion not as lateral (apes – more lateral attachment for abd, increasing moment arms) Glenoid cavity: monkeys; narrow, elongated, concave. Humans/apes: flat, wide round, lack congruence Supraglenoid tubercle projects in monkeys to limit hyperflexion in arm (Biceps long head), apes humans can hyperflex Prox humerus: Apes/humans; deltoid tub lower – creates great moment arm, greater leverage, greater ROM, GT and LT’s inferior to hum head Rotators: Apes – traps (insert on scap spine) and sa (insert ax/lat border scap) greater cranial rotation – scap/thoracic motion increased, allows scap to go further upward: increasing abd, long head triceps wider insertion on lat scap, dorsoepitrochlearis present (extension of lats): increases arm extension. Muscles also bigger. Humero-ulnar joint: Apes – olecranon fossa deeper (more extension, 4 limns pronated in knuckle-walking) , sharp lat troch ridge (stops lat displacement of olecranon process - absent in humans), olecranon process (lower in humans) of trochlear notch does not project too far anteriorly – shallow notch means tighter joint with ulna Distal Radius – knuckle-walking apes have a distal -dorsal projection from margin, stops hyperextension of wrist (absent in humans) Phalanges – apes: long (but short thumb) curved manual phalanges – allow for a hook grip, humans – flat, broad phalanges, long opposable thumb – precision grip, power grip Hand muscles – Apes: FDS, FDP better developed for hook grip, contrahentes muscle (sup to PI/DI muscles, PA to lat 3rd 4th digit, adductors). Humans: FPL, FPB well-developed, addP is only contrahentes muscle kept.

Lower Limb: derived in humans -

Apes knuckle walking apes less reliant on lower limbs than humans

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Humans gait – same efficiency Weight transfer – effect of gravity causes rotational axes in joints and result in moment arms that cause flex and ex. Effects of gravity resisted by ligaments. Gait cycle: movement from heel strike to terminal swing of the same limb: mostly single limb support, some moments offer double limb (2 leg) support. DF, PF and abd (weight to midline) important Pelvis: last phase of human evolution from leaving apes – Apes: flexed hip, flexed knee gait. Long iliac blade, lat positioned femur; glutes = ex. Humans: bowl shaped pelvis, shortened iliac blade allows well developed sciatic notch – Sacro tuberous ligament passes to provide passive support. Glutes act as abd, MR which are important for our gait where weight remains at midline. Femur - Humans: LL med rotated, long robust shafts, high bicondylar angle femur – valgus knee, large fem head, long neck fem – increases moment arm of gluteal muscles. Elliptical outline fem condyles allow greater contact with knee – places patella further forward increasing congruence in knee joint. Apes: LL Lat orientation, shorter, slender, curved shafts (helps grab branches with lower limbs), narrow bicondylar angle of femur, shorter neck of femur. Round fem condyles. Tibia and Fibula – Humans: tibia robust, WB, perpendicular to prox articular surface, lat tib plateau 92% of medial (important for locking mechanism where (smaller) lateral condyle contacts tibia plateu, anglulation of femur condyles to perpendicular tibia, femur rotates medially so that medial fem condyle keeps contact). Slender, NWB fib. Apes: tibia less robust, fib mobile and robust (allows weight transfer from tib to fib in rotation), lat tib plateau 84% of medial (therefore can do more knee rotation (LR) for grasping tree branches) Foot: human – large adducted big toe, robust calcaneus, strong heel, well developed longitudinal transverse arches, weight transfer from heel – lat margin foot – ball – big toe. Big toe aligns with other toes. Apes: abd big toe (grasp braches), not arch, 2 nd, 3rd toes lat to leave the ground. Muscles: Apes – pmin inserts onto pelvis (helps maintain hip flexion), gmax wider insertion, glutes are thigh extensors, AbdHLongus muscle (additional muscle), QP absent

Fossil Evidence -

Species – mate with viable offspring Natural selection – diversity, adaptation to environment, differential fitness, reproductive advantage Fossilization – convert organic to mineral material. Depends on how/where animal lived, died, anatomy, how quickly buried, likelihood of finding Australopiths (Aus) and Genus Homo

Skull -

Foramen Magnum – posterior to anteriorly Projecting snout – Only sapiens have forehead/globular brain case, face gets flatter Post orbital constriction (in gorilla) gets lost down lineage Nuchal plane – gets smaller

Thorax

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Aus: cone shaped, but human like pelvis, large gut but not as stable as modern humans. Homo: barrel shaped, NEAN - broad thorax, long clavicle, robust muscle markings

Vertebral Column -

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AUS: longer spinous process in cervical region, longer trans proc in lumbar region, afarensis – thoracic kyphosis, africanus – 6 lumbar vertebrae – monkey like (more than apes…don’t know why) H.ergaster modern human like but 6 Lumbar vertebrae H.neanderthalis modern human like, lumbar lordosis, BUT more robust and no bifid cervical spinous processes – less well developed nuchal ligament, nuchal muscles probs more developed

Upper Limb -

Humerofemoral index – more human like in all Distal radius: (projection in knuckle-walking apes prevents hyper DF), humans only a little projection, australpiths have projection Hand: AUS; long ape like curved digits but also long thumb, developing opposition (not likely able to do opposition and precision grip like us). Nean – robust, human like but distal digits have flattened end, more capable of power grip than precision grip.

Pelvis -

Aus – iliac shortened, rotated anteriorly to coronal plane (allows glutes to work as abd, mr), distinct sciatic notch. Wider side to side, unlike humans (widest ant-post) and hamstring position on ischium ape-like. H.ergaster – narrow hips, modern pelvic shape. Nean – anterior placement of sacrum (indicates lumbar lordosis and balance at joint), wide pelvis, long pubis – neonate had further to travel in birth canal.

Obstetric behaviour -

Humans – neonates makes 90 degree turn on way through canal. Apes – ant/pos position on way out. Afarensis – lat position on way out.

Lower Limb -

Femur – humans: robust head, long neck, angulated shaft. Chimp: small head, short neck, vertical shaft. Aus, Homo transitional Tibia – humans – more robust, vertical orientation, thicker cortical bone for WB Foot – AUS: bipedal features, deep heal, add Hallux...