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Lecture 3

Lecture 3 - Lower Limbs

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Sherry Fukuzawa

Human Bipedalism BiomechanicsPrimary problem balancendHuman Centre of GravityJust anterior to 2 sacral vertebraHumans are the only species who are bipedsusing the locomotionBalance is a key problem for bipedialism We have a small center of gravity that sits on our feet As opposed to quadrupeds where they have four limbs on the ground they have a large distribution of weight and therefore their balance in terms of their upper bodies is not much of an issue since they have a larger center of gravity Modified brachiates the majority of the weight is towards their hindlimbsThere are two key ligaments that allow us to maintain this up right posture without us having to spend so much energy Maintain standing positionIliofemoral ligament pelvisoIt attaches the illium of the pelvis to the femur of the hip It sits in the front of the hips Attaches to the proximal end of the femuroBinds femur to iliumoPrevents hyperextension This is how we maintain an upward positionCruciates knee jointoLock knees to prevent upper bodyfemur from falling forwardoWhen we stand we are standing with our knees in an extended position up right But what prevents us from falling forwardoBinds the distal end of the femur to the proximal end of the shin boneVertebral ColumnHUMANS4 curves They wrap around the center of gravity that allows us to maintain an upright postureThe line of gravity runs from the side of the head in front of ears running through the knee joints and the arches of our feet The spine curves around the spine of gravity again allowing us to maintaining this posture 1Cervical 72Thoracic 12oKyphosis3Lumbar 5olordosis4Sacral 5 fused5Caudal 4APESLack extreme curvature of spineLumbar region greatly reducedWhen they pull themselves us they still have a C shape to the spine while their knees are still in a flexed positionThis is why apes cannot walk long distances in a bipedal locomotion This is a huge engery expenditure to maintain this position MONKEYSMost have only kyphosis throughout the vertebral columnRib CageRib CurvatureThe most curvature of the ribs is humans then apes then monkeys and prosimians which are largely in a quadrupedal system We have a widening of the thorax barrel chest once of the system becomes bipedalApes are a transition towards thatdistributing their weight to a more upright positionProsimiansmonkeysRibs are less curved on vertebral endTransversely narrow rib cageRibs hang downward in thoraxVertebral column forms dorsal edge Apesconicalhumans barrel shaped rib cageHigh degree of bending Ribs extend backward near vertebral columnRibs expand ventrally to articulate via costal cartilage with sternumSacral regionIlliumIshiumfor like butt musclesPebuisforms the front of the pelvic boneIn between the two pelvic bones is the sacrum tail boneDifferences in the sacral regions are related to differences of weight differences through the hindlimbs which is usHumans Humans Wide sacrumIncreases distance between sacroiliac joints5 sacral vertebrae fusedoMonkeys usually have around 3 Apes have 37 humans have 56 good way to tell on a bell ringeroSegments increase as tail length decreases Sacraul illicac bonehip attaches to sacrumoIt will be greatest with the greaoWe have very large sacral ilicac joint in comparison to iliac bone monkeys is smallerNeural canalruns along the back spine endsoIf you do not have a tail it will end off quickly at the bottom of the sacrum Similarly if you look down the neural canal of a chimp it will also disappear new the end oNEW WORLD MONKEYSEMI BRACHIATOR SWING WITH TAILSO IF IT GETS LARGER OR STAYS THE SAME YOU ARE LOOKING AT NWMoOld world monkeys it doesnt decrease in much in size as you move downPositioned at a more acute angle to the lumbar vertebraSacrum posteriordistal to hip jointSacrum is the widest and shortest superiorly and inferiorly ApesNarrowerVariableof sacral vertebrae 37Positioned in line with the vertebral columnLess longitudinal curvatureSmaller auricular surfaceSacrum anteriorsuperior to hip jointSacral Region The shape of the sacrum often indicates weight bearingtail length
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