Comparative Vertebrate Anatomy - Biol 161A - Week 4
Comparative Vertebrate Anatomy - Biol 161A - Week 4 Biol 161A
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This 11 page Class Notes was uploaded by Anastassia Erudaitius on Monday February 22, 2016. The Class Notes belongs to Biol 161A at University of California Riverside taught by Dr. Reznick in Fall 2015. Since its upload, it has received 48 views. For similar materials see FUNCTIONAL ANATOMY: VERTEBRATES in Biology at University of California Riverside.
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Date Created: 02/22/16
Lecture 10 Notes – Limb adaptations for specialized functions Diversity of limb structures in mammals o Plantigrade o Digitigrade o Unguligrade o Take note of process length (olecranon in horse vs armadillo) o Overall limb length Different limb structures adapted for different functions Line of action of a muscle = direction in which a muscle pulls or the direction in which it contracts Force = function of how heavy an object is and the friction against which the object is being moved o Examples: A muscle pulling on a point of attachment triceps pulling up on olecranon Foot striking the ground when running Jaw crushing food o All of these examples involve muscles contracting and applying force to bones which in turn move and apply force to objects outside of the body Work = the end product of force o W = (force required to move object)(distance over which the object is moved) o Units = force x distance = joules or N-m Torque = moment = turning force o = (Li(F) o Force that is applied to a lever or by a lever o Torque can be increased by applying more force or by applying that force further from the fulcrum (greater Li) o Any bone-muscle lever system is creating circular motion Almost all limbs and jaws involve rotation around a fixed point The outforce is applied along a circular arc Forces are generally not applied in the direction in which an object is moving so we subdivide it into two components perpendicular to one another o Effective force (F – lines up with the direction of motion of the object e) (is tangent to the circular motion of the object) o Wasted force (F )w– perpendicular to direction of motion Confused: in his drawings the wasted force is always perpendicular to the F e Red = Fm Green = Fe Black = Fw Fo= F icos) o Cos(0) = 1 o Cos(90) = 0 Fw= a proportion of the Fe Because the direction of the olecranon is always changing the Fe is also always changing Movable joint = diarthroses bone rotates around this single point Length of Fe = Fm (force applied by muscle) Force exerted by a muscle is maximized when the line of action lines of perfectly with the direction of motion of the appendage More than one muscle may act on a joint combFtemporaliss of muscles can be visualized by lining them up in a head to tail fashion Femasseter Fw Fetemporalis The independent force vectors are lined up above, resulting in a combined force represented by the two effective forces Multiple muscles that seemingly all do same thing o Masseter, temporalis, pterygoideus all close jaw o Having multiple muscles that insert at different angles enables the appendage to have a more complex range of motion Movement in vertebrates is governed by the coordinated contractions of groups of muscles rather than individual muscles or opposing muscles Limb specialization – diggers o Moles and armadillos are diggers and therefore need powerful limbs o Fo = Fi (Li/Lo) o Increase Fo by increasing length of in arm or decreasing length of out arm o In respect to runners, an Armadillo has a shorter radius (Lo) and a longer olecranon (Li), giving it a larger MA (and therefore larger force) than those exhibited by runners How to increase speed o Runners: Lever = entire leg tip of limb (foot) = end of out arm hip joint = fulcrum lever rotates around fulcrum Vo = Vi(Lo/Li) o Longer out arm (Lo) If you compare two limbs identical in every respect except the length of the out arm (Lo), then you’ll notice that even though Lo is different the angle swept by the limb when the muscle contracts is the same The circle created by rotation of the limb the radius of that circle is Lo The length of the arc (d) is directly proportional to Lo therefore a longer Lo results in the limb covering a longer distance when the muscle contracts o Shorter in arm Angle proportional to distance covered by tip (arc) Tip moves more quickly Summary: o Shortening the Li Larger angle Larger distance covered o Lengthening the Lo Larger distance covered Note: when you insert the muscle closer to the joint that means you are shortening the Li (think about it) the joint is the fulcrum Tradeoff between speed and force o A limb cannot be adapted to maximize both output speed and force Plantigrade animals specialized for high Fo digging Specialists extreme adaptations for a given function most animals are not specialists Generalists moderate abilities retained for both force and speed, but are not as good as specialists for either function Not ALL input force (Fi) is effective in moving the bone, the Fe is actually what determines actual out force (Fo) o Fo = Fie (li/lo) o Where Fie is the effective in force o Alternative notation Fo = Fi (cos0)(li/lo) o The “effective in arm” = moment arm Fie Lie Fi = Li =cos0 MA= Fo= Li Fi Lo Lecture 11 For Vo = Vi(Lo/Li) o Vi is the rate of contraction of muscles (increasing this results in a minor increase in speed) o Vo is the speed of the object/limb Man-made structures are simpler than animals they are rigid bodies propelled by an engine Cursorial locomotion o Adapted/specialized for running limbs specialized for speed o Long limbs Length increased by adding segments of ankle and foot (or wrist and hand) to the vertical component of the limb o Unguligates Hoofed animals (Artiodactyla, Perrisodactyla), dogs, cats, Carnivores, many dinosaurs, many birds, some rodents, some marsupials, some extinct order of mammals o Cursors are able to move efficiently at moderate speeds and are capable of high maximum speeds o Ecological advantage = can forage for food over large areas can exploit resources sparsely distributed in either time or space o Red Queen Hypothesis – while cursorial prey have higher escape speeds, their predators have become faster as well No prey is so fast that it is immune to predation No predator is so fast that it Is free of the risk of starvation Wide applicability in biological sciences also used in interaction between pathogens/parasites and their hosts o Limb length increased by adding segments to limb because of summation of velocities and distal lightening Summation of Velocities o The limb actually works as four separate levers connected in a series rather than one long lever therefore the speed of the tip of the limb is actually the speed of all the levers in the series o Adding more segments to tip of limb adds potential for more speed at point of contact with ground o Retaining plantigrade posture and only increasing the length of the two limb segments would result in less of a gain from the summation of velocities therefore cursorial locomotion animals would benefit more by increasing number of segments o Reduction or loss of the clavicle frees the scapula and allows it to rotate with the limb - contributes to the multiplication of velocity Animals with no clavicle or a reduced clavicle should be faster Horses have a somewhat rigid spine but very long legs which compensate for it makes it fast Horses also have scapulas that rotate adding several inches to their stride length (cheetahs do as well) Cheetahs however have the advantage of both rotating scapula’s and a flexible spine making it even faster Distal lightening = lightening of the segments of the limb that are more distant from the body o Reduction of distal weight and concentration of muscles near the center of gravity o In order to run one must constantly accelerate and decelerate the limbs Must accelerate limb to bring forward, then bring it to a standstill, then accelerate it backwards to make contact with the ground and generate forward propulsion, then once again bring it to a standstill and reverse the motion o Power stroke – thrust component which propels your body forwards (the back swing) o Recovery stroke – forward component, sets leg up for another power stroke, essentially wasted energy o Cursorial limbs have evolved to make the energetic costs of this system as little as possible o Configuration of animals constantly changing during locomotion ventroflexion of vertebral column, rotation of scapula, power and recovery stroke o The muscles that move the limb also move with it forward and backwards o The limb moves faster when the mass of the limb is concentrated closer to the body This is because the pendulum oscillates faster when the counterweight is closer the fulcrum think of the counterweight as the muscles of the limb while the pendulum is the tip of the foot Heavy ankles vs heavy thighs heavy thigs results in faster limbs because mass of limb is closer to body Lengthening limbs by adding segments is more efficient in keeping mass of muscles close to body than is increasing the length of the first two segments of the leg The muscles that are centered close to the body transmit force to the foot through the use of tendons force generated by these muscles is transmitted to more distal elements The length of the tendons is also increased in order to transmit force over a longer distance The intervening segments (digits and metapodials) are stretched into supporting pillars These joints are powered by muscles located in the second segment of the limb (close to body) so the length is simply increased by adding segments of bone and connective tissue making them light Limb has increased from 2 to 4 segments but the muscles that power the limb remain concentrated in the two segments closest to the body Lower limbs primarily contain connective tissue and little muscle Lengthening of the limb is concentrated in more distal elements can be seen in difference of proportions in plantigrade, digitigrade, and unguligrade organisms o The bulk of the lengthening occurs at the metapodials and digits o The femur length is relatively the same o The tibia/fibula is slightly elongated relative to the femur here is where most of the muscles are concentrated Loss and fusion of bone o Reduction or loss of shaft of the ulna or the fibula o Bones in metapodial and digital segments tend to be either lost or fused o Fused units provide equal strength as separate units but are less weight but they become restricted to just forward or backwards movement Muscles used for twisting limb or digit mobility is reduced or lost Joints also altered joint of cursorial organisms are hinge-like in structure, which allows forward and backward swinging but restricts circular or side to side motion Limb becomes lighter further from body and requires less force to move it Elasticity o Elastic tissues store energy and then return the energy in a way that contributes to locomotion o Suspensory ligaments of fetlock joint in horses – store energy as they stretch and release it as foot is lifted off of the ground (limb pushed back and up) o Slingshot biceps Continuous force applied to elastic element stretches element input force is stored stored force instantly released when input force is released Stretching force is applied while foot is on ground during power stroke elastic recoil powers the recovery stroke Mass of biceps = 0.4 kg Without elastic recoil, 50kg of muscle would be required to power recovery stroke Loss of function – tradeoff o Cursorial limbs adapted for speed, but digits no longer effective for manipulating objects o Cursorial adaptations are a good example of convergent evolution o Independent origin evident because there are differences in the bones that contribute to lengthening and lightening of the limb cheetah, birds, and horses are all cursorial yet have 3 and 4 segments (respectively) How can you tell convergent evolution versus inherited traits? o Subtle differences of morphology among groups Ex: Cursors may have different number of metapodials o Molecular data o Development how skeleton has been modified since early stages in development Juvenile antelope has splints of two digits that are later lost these modifications are typical of ancestors but not seen in the adults of the species Low and high gear muscles o Speed specialists still need ability to produce force Horses need to exert force for fast acceleration Cat needs to exert force when leaping on prey o Both functions can be retained by having high and low gear muscles Analogous to gears of car low gears get the car moving from standstill, high force/low speed high gears used to maintain speed once attained, low force/high speed o Gluteal muscles vs ischio-pubic series of muscles Both have same out arm (Lo) – distance from hip joint to foot In arm (Li) for gluteal muscles is short – distance from greater trochanter to pivot specialized for speed In arm (Li) for I-P series is long – insert lower on femur, tibia, or fibula exert more force, suited for slow movements or acceleration Greater Gluteal – Fi Lie Ischo-pubics – Fi for Glut. Lie for I- Moment arm for glutal P muscle is shorter than moment arm for I-P series Vo = Vi(Lo/Lie)
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