Lecture on Bilateral Symmetry, Muscles and Locomotion

[Lecture] Bilateral Symmetry, Skeletal Muscle Structure, Regulation of Contraction, Specialized Muscles, Force Production, Invertebrate Muscles, Energetics of Contraction, Ecophysiology of Locomotion [Active & Non-Active Animals] - movement was thought to be the definition of life - ever...

[Lecture] Bilateral Symmetry, Skeletal Muscle Structure, Regulation of Contraction, Specialized Muscles, Force Production, Invertebrate Muscles, Energetics of Contraction, Ecophysiology of Locomotion [Active & Non-Active Animals] - movement was thought to be the definition of life - everything that moves = alive - everything that doesn't move = dead - [sessile animals:] - fixed in one place & don't move freely - attached to the surface (rocks, coral, reefs, ocean floor,...) - e.g. sponges, corals, barnacles - [planktonic animals:] - free-floating organisms that drift in the water/carried by currents - often limited swimming ability - e.g. jellyfish, zooplankton (e.g. krill), some larvae stages of marine animals, ectoparasites like sucker fish - [active animals:] - capable of independent movement - actively swim, crawl, fly - active work against forces like gravity just because something isn't moving on their own doesn't mean that they don't have muscles for active movement! - e.g. many corals can move their arms - e.g. motor proteins force generated movement via ATP-usage [Symmetry in Organisms] - Asymmetry: - no symmetry body has an irregular shape - e.g. sponges - usually sessile without active movement - Circular Symmetry: - body parts are arranged in a circle around a center point - e.g. some microscopic organisms - often sessile or planktonic - Radial Symmetry: - body parts are arranged around a central axis & the organism can be divided into multiple similar sections - e.g. sea anemones, starfish - often sessile of planktonic - Bilateral Symmetry: - body can be divided into 2 equal halves along a single axis - have right & left side - have a front & a back - have a head (often where the main processing organs/power lies) - have streamlining smooth, aerodynamic/hydrodynamic body shape for directional movement (radial symmetric organisms like sea stars can move equally well in multiple directions) - e.g. vertebrates, insects strongly adaptive (found in almost all groups) - 99% of animal species are bilaterally symmetric - often associated with active movement & directional movement - strong fitness factor - big factor for sexual selection more symmetric is often thought to be more attractive active movement is strongly linked to evolution of bilateral symmetry - bilateral symmetry is ancient - evolved very early on - BUT has been lost at least 4 times - e.g. Cnidarians are thought to be only secondary radial symmetric [striated vs. smooth muscles] - striated muscles - long, cylindrical, multinucleated cells - multiple cells build a syncytium - striated appearance under the microscope due to the organized sarcomere structure - responsible for voluntary movements (somatic NS) - generates force by contracting & pulling bones via tendons - specialized straited muscle: cardiac muscle - branched, single nucleus per cell - BUT connected via intercalated discs to help synchronize contraction - involuntary, rhythmic movement (autonomic NS) - smooth muscles - spindle-shaped, uninucleate cells with no sarcomere organization - arranged in layers around organs & blood vessels - controls involuntary movements for e.g. digestion, blood flow & respiration through the autonomic NS & hormones - usually endogenous & under parasympathetic control - contracts slowly but for long durations without fatigue - Ca^2+^ is mostly extracellular (no large intracellular stores) Types of Muscles \| BioNinja [Structure of Vertebrate Skeletal Muscles] - are striated muscles - skeletal **[&] **cardiac muscles - attached to bones - attachment can be different in different organisms - in insects to the exoskeleton - to soft body in soft-bodied organisms - or just to themselves - are organized into multiple levels - muscle = organ level - made up of many bundles (= fascicles) - surrounded by connective tissue layer (= epimysium) - fascicles = tissue level - bundle of individual muscle fibers - surrounded by connective tissue layer (=perimysium) - muscle fibers = cellular level - long, cylindrical, multinucleated cell - surrounded by a connective tissue layer (= endomysium) - contains many myofibrils functional contractile units - myofibrils = subcellular level - rod-like structures - made up of repeating contractile units = sarcomeres - sarcomeres = molecular level - basic contractile unit - consist of thick (myosin) & thin (actin) filaments - Z-lines mark the boundaries of each sarcomere - t-tubules system as an extension of the sarcoplasmic reticulum (stores Ca^2+^ needed for contraction) that helps transmit nerve impulse deep into the muscle  - invertebrates also have striated muscles! - functional unit = sarcomere - composed of thick & thin filaments - thick filaments = myosin - has 2 head-groups - BUT just one is biologically active - thin filaments = actin - G-actins units make F-actin - 2 F-actin structures intertwine in a helical structure - also contain troponin & tropomyosin - sit in regular intervals - key components: - Z-lines/-disc - boundaries of the sarcomere - M-line - where the myosin filaments are anchored - I-band - \~light band - only contains actin - A-band - \~dark band - contains both myosin & thin filaments - H-zone - central region of the A-band where only myosin is present - disappears during contraction! - very organized structure looks different at different stages - how the sarcomere works [Sliding Filament Theory] - form Huxley & Huxley - key steps: - nerve impulse arrives most muscles are neurogenic! - ACh gets released at the neuromuscular junction - Ca^2+^ release - depolarization triggers release of Ca^2+^ from the sarcoplasmic reticulum (Ca^2+^ cell storage) - Dihydropyridine receptor gets activated & pulls open the Ryanodine receptor in the SR membrane (they are physically connected) - Ca^2+^ flows into the Moplasm - Ca^2+^ binds to Troponin - binding shifts tropomyosin binding sites on actin gets free - cross bridge formation - myosin starts in a low energy state = 45° (no ATP is bound) - ATP binds which leads to cocked stage (=90°) of the myosin head due to angle change, the myosin head moved slightly up & is now in front of a new G-actin in the actin-filament - ATP gets hydrolyzed to ADP+Pi making new binding possible - Mg^2+^ needed for contraction because ATP is almost always bound to Mg^2+^ no Mg^2+^ = no available ATP for the cell - reason for cramps (due to lack of Mg^2+^ & therefore lack of available ATP) - actin + myosin-ADP-Pi = Actomyosin (weak bond) - actin + myosin-ADP = Actomyosin (strong bond) - filament sliding = power stroke - myosin releases Pi & tilts back to 45° pulls the actin filament - detachment & resetting - a new ATP molecule binds to myosin, causing it to release actin - cycle just continues & the filaments slide against each other - relaxation - when the nerve signal stops, Ca^2+^ is pumped back & tropomyosin covers actin's bindings sites again sarcomere returns to its original length!  - force production = function of the overlap between myosin & actin - sarcomere changes length BUT the overall position just changes & not the molecules themselves - sarcomere length at rest & during force generation is quite similar/the same amongst all vertebrates - max. force generation at 2 -- 2,2 µm sarcomere length - at different length the overlap is not optimal - all animals use this principle! - dose dependency of Ca^2+^ can be observed - certain concentration needed for the interactions to be possible otherwise the binding sites are blocked of - Ca^2+^ & (lack of) ATP are reason for rigor mortis: - actin & myosin can bind to each other because Ca^2+^ frees binding sites by removing/redirecting tropomyosin strong bond between filaments - with no new ATP, the binding cannot be broken up stiff muscles (until everything deteriorates) - 24-48h until the proteins in the muscles break down - every step was carefully researched using different scenarios with different molecules (ATP, Mg^2+^, Ca^2+^) present in different constellations & concentrations [Energetics of Muscle Contraction] - different frequency of APs lead to different tension in the muscle - single AP = twitch - low frequency APs = continuous twitching most cramps - phase where muscles produce tension but no true force for body movement - high-frequency APs = muscle tension quickly reaches a maximum (= tetanus) - point where all productive muscle movements happen tonic phase - different types of muscles in the body - red muscles slow-twitch, Type I fibers - dark red color due to high number of mitochondria in the cells - uses aerobic respiration (**oxidative metabolism**) - has slow but sustained contraction - can work for long periods without tiring ATP is always generated in the mitochondria BUT it needs time - used during endurance activities from long-distance runs to maintaining upright posture - also in the diaphragm - white muscles fast-twitch, Type II fibers - white/pale color with fewer mitochondria - uses anerobic respiration (**glycolysis**) - has fast but short-lived contraction - ATP is used up quickly & then the muscle relies on glycolysis - designed for quick, powerful movement sprinting, jumping, weightlifting - fast oxidative Type IIa fibers mix between the two - uses both aerobic & anaerobic metabolism - fatigue resistance: white muscles \< Type IIa fibers \< red muscles - found in muscles that need both speed/power & endurance (e.g. middle-distance runners) - all muscles are a mix of both types (white & red) BUT the composition can be changed through certain types of training aerobic/endurance training (running, swimming) increases red muscle efficiency strength training (lifting weights, sprinting) enhances white muscle power - huge potential in plasticity [Invertebrate Muscles] - in vertebrates a single AP leads to a single twitch of uniform size - summing the APs can lead to summoning of the force - BUT in invertebrate the AP itself can differ in size which means, that the contraction can be modulated in shape in size Ein Bild, das Text, Diagramm, Reihe, Origami enthält. KI-generierte Inhalte können fehlerhaft sein. [Moving the Whole Organism: Different Adaptations] - no 'darwinian demons' (no bad muscle) often just trade offs - muscles are organized specifically for the animals needs adapted to operate at max. efficiency in different environments - [frogs] - frogs always jump in a standardized way (it's always the same) - catapult-like mechanism - before jumping the leg muscle shortens to a specific length (loading energy into tendon) - then stretched tendon recoils like a spring  - during jumping, the muscles operate at optimal activation level - skeletal system is specially adapted for jumping - elongated hind limbs bigger lever effect & therefore more powerful - pelvis is highly flexible & can rotate backwards during takeoff, which increases power in each jump (pelvic girdle rotation) - last vertebrae are fused together, building a rod-like structure (urostyle) which provides rigid base for better force transfer - they jump when force/power is optimal - jump hat the perfect sarcomere length (around 2µm) - jump at the perfect velocity frogs prioritize power! - [toadfish] - make very load noises! - sound = physical waveform distortions measured in Hz - have superfast muscles (SFM) they can contract at very high twitch frequencies - fastest-contracting vertebrate muscle known - can contract & relax their muscles at rates of 100-250 Hz - rapid contractions create continuous hum ("boat whistle") - short bursts of contraction generate grunts & growls - generate sound using the swim-bladder - physiological specializations to be able to sustain rapid contractions - specialized Ca^2+^ handling - have highly developed sarcoplasmic reticulum (SR) allows rapid Ca^2+^ cycling - Ca^2+^ then trigger contraction & are then quickly removed for relaxation - Ca^2+^ gets pumped back into the SR at very fast rates to completely relax the muscle before the next contraction starts - very fast removal 50x faster than in normal muscles - overall intracellular Ca^2+^ is very low contraction is possible even at small concentration changes - high ATP-turnover & mitochondria density - fast contraction cycles consume large amounts of ATP but due to the high mitochondrial count, the continuous ATP production is provided for - fast cross-bridge cycle - overall very fast troponin kinetics binding sites are free very quickly - express myosin isoform for rapid attachment & detachment cycles allows quick force generation & release - possible that neurons also work very quickly - through e.g. a strong ACh-esterase which clears neuromuscular junction - single muscle twitches are not summed! toadfish prioritize speed! - [swimming in fish] - have 2 types of different muscles along the body - Type I = slow-twitch oxidative along the sites of the body - mainly for normal swimming patterns - sustained force - Type IIb = fast-twitch glycolytic spiraled inside the body - mainly for escape reflex when they feel threatened - bending body at a strong angle to quickly get away - rapid burst - much faster & much stronger contraction possible - escape reflex = C-Bend/-Shape - fast-twitch musles on one side contract forcefully, bending the fish into a tight C-shape - can occur in less than 10 ms - during normal swimming patterns the white muscle fibers operate at optimal force generation regarding length-tension relation & power-velocity relation - during escape response the muscles gets pushed together a lot so they can't operate at the optimal range - reducing their ability to generate optimal force due to worse length-tension relationship - excessive overlap between myosin & actin which blocks some binding-sites - prioritize speed for contraction & not optimal working range - but due to C-shape, the red muscles on the other side gets stretched, allowing effective force generation to get away in the next phase Ein Bild, das Text, Diagramm, Reihe, Zahl enthält. KI-generierte Inhalte können fehlerhaft sein. - [insect flight muscles] - have high power & high frequency - two major flight muscle types found in insects - synchronous flight muscles - \~ direct flight muscles - muscles attach directly to the wings - when the dorsoventral/verti-cal muscle contracts, the wings go down - when the longitudinal/hori-zontal muscle contracts, the wings co up - under neurogenic control (one nerve impulse = one contraction) - leads to slower wingbeat (100-200 Hz) - found in more primitive insects (e.g. dragonflies, cockroaches, grasshoppers) - asynchronous flight muscles - \~ indirect flight muscles - muscles don't directly attach to the wings but to the thorax - wings move by deforming the thorax - dorsoventral/vertical muscles compress the thorax, making the wings go up - longitudinal/horizontal muscles expand the thorax, making the wings go down - also neurogenic BUT the muscles can contract faster than their NS can send signals! - turned on by neural input, but once activated, they can contract in an oscillatory manner - muscles start to twitch against each other - contraction of one set on muscles stretches the other set to activate subsequent contraction - mechanism avoid rate limitations form equilibrium dynamics of Ca^2+^ transient & pump-driven Ca^2+^ cycling - BUT Ca^2+^-concentrations need to be in a certain range - leads to high frequency wingbeat (up to 1000 Hz) - found in advanced fliers (e.g. flies, bees, mosquitos) - ATP costs in these muscles is extremely high highest recorded metabolic expense we know off! - most common flight fuel = fatty acids a lot of metabolic water is produced! (weight is greatly increased) - solution = flying insects need to pee often - [clams] - two adductor muscles (anterior & posterior) contract to close the shell & relax to open it - specialized catch muscle mechanism they can maintain tension without continuous ATP use - clam muscles lock into place using paramyosin - latch their fibers together, preventing relaxation - similar to how smooth muscles in vertebrates can maintain tone for long periods - can induce rigor mortis clear out ATP & Ca^2+^ to stay connected - need serotonin to get out of that state - they stay close to avoid predators or to retain moisture in intertidal zones during low tide - extremely cost effective mechanism mollusks use \~0,3% of the energy that vertebrate smooth muscle does to maintain the same force! [Physical Factors Affecting Locomotion] - relationship between size & locomotion - animal movement follows scaling principles size changes affect speed, energy use & efficiency - small animals have higher metabolic rates per gram of body mass which impacts endurance & speed efficiency - move quickly for their size but have lower absolute speed - larger animals can take longer strides while smaller animals increase stride frequency to move faster - strong but slower due to mass constraints - inertia & momentum - inertia = object's resistance to changes in motion - momentum = product of mass & velocity, describing how much motion an object has - different modes of locomotion - running using the ground for propulsion - force is limited - gravity works against animal - swimming facing drag forces - streamlining is critical - water increases buoyancy - flying balance lift vs. gravity - wings must support weight efficiently - medium has a big influence on movement: - water - buoyancy - low to high viscosity - low O~2~ - air - no buoyancy - low viscosity - high O~2~ - land - buoyancy is not an issue - low viscosity - high O~2~ - movement is dictated by animal size & physical properties of the medium! - shape/mass & type of locomotion determines the cost of transport across the whole animal kingdom! Ein Bild, das Text, Screenshot, Zahl, Diagramm enthält. KI-generierte Inhalte können fehlerhaft sein. - general trend: with increasing body mass, the cost of transport decreases - larger animals move more efficiently unit of mass - energy efficiency of different locomotion types: swimming \> flying \> running