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Movement on land Neuroethology Movement on land; reflexes and central pattern generators in the CNS; change of gait and its neural and energetic consequences. Jumping flying swimming. Evolution of neurons and behaviour; from ethology to neuroethology. ….. Fly jump [last lecture] Integration of behaviour Books, CDs, Papers McNeill - Alexander R. Animal mechanics How Animals Move [CD Rom borrow in teaching] Biewener, AA (2003) Animal Locomotion OUP Library check Amazon Dickinson, M.H. et al 2000. How animals move: An integrative view. Science 288, 100-106. Aim Staying still How do we stay still? Resistance reflex Walking - and running How does the nervous system control activity? How do mechanics and energetics limit/enhance limb coordination? Muscle spindle main sense organ used maintain constant position Modified muscle cell innervated by g motoneurons and Ia afferents Resistance reflex Ia afferent excitatory loop from muscle spindle Schematic Resistance reflex - 2 inhibitory loop from muscle spindle to antagonistic muscle needs interposed interneuron interneuron Active movement in active movement, if a load is present, resistance reflex adds to motor command to make a stronger movement Primary motor cortex Summary so far resistance reflexes provide for stability feedback loop Now onto: what is the role of the CNS in patterned movement? What is the role of the brain ? Central pattern generator (CPG) Block sensory input (deafferentation) Stick insect: innervated denervated CPG Locusts flying, breathing Clione swimming, tadpole swimming crustacean stomach cockroaches & cats walking snail feeding… Clione swimming Reciprocal inhibition excitation CPG http://neuromajor.ucr.edu/courses/Clione.mov Tadpole swimming in Xenopus tadpoles reciprocal inhibition + excitation Summary so far Resistance reflexes provide for stability feedback loop Rhythmic patterns encoded in CNS network. Now onto: what is the role of the sensory systems in patterned movement? Role of sensory input why have sensory input if CPG works anyway? examples from crustacean stomatogastric ganglion ~40 neurons Initiate/end rhythm Simple : rhythm runs while stimulus is maintained Accelerate rhythm More complex : rhythm runs on after stimulus is maintained Cycle by cycle feedback Switch from stance to swing Babinski reflex Healthy adult reflex - curl toes Infant & damaged CNS spread toes Reflex reversal Zap Ia interneuron afferent Record motoneuron Stimulate brain (MLR) to induce locomotion Role of sensory input Sensory neurons: initiate/end rhythm adjust speed of rhythm cycle by cycle feedback adjust pattern (gait) Sensory input is gated by the CNS Summary so far resistance reflexes provide for stability feedback loop Central pattern generation Sensory control Now onto: what did the locust breathing practical show us about neuronal organisation? Locust practical Visual observations of coordination Recordings of muscle activity } interburst expiratory muscle burst How does the pattern change? 10s Extra CO2 • accelerates rhythm • recruits extra muscles (neck, abdomen) • recruits extra neurons How do the bursts change? +CO2 ejps closer together? bigger ejps? less tonic activity? How are bursts organised? Big ones at start or end? Summary so far resistance reflexes provide for stability feedback loop Central pattern generation Sensory control Now onto: what can we do with the muscle work? Generating force =mass x acceleration measured in Newtons force delayed by elastic elements Muscles helped by Levers torque : force x distance 3 types Force / fulcrum / load Class 3 most common Each muscle contraction moves limb further than muscle contracts Legs as levers inertia the longer your legs, the more mechanical advantage you have force this is called Weight (or load) Transfer Why are hind legs more powerful? push forwards on the ground, lift up front legs (balance) some animals avoid using their front legs T rex kangaroos Power rate of working work = force x distance therefore power = force x speed measured in Watts litres O2 / kg /hour at rest, basic metabolic rate Metabolic rate basal metabolic rate determine from food ingested heat produced oxygen consumed 70 W (1 light bulb) What limits our power output? <1sec 4500 W muscle output <2 min 1500 W anaerobic energy store kettle <2 hours 350 W oxygen transport All day 150W need to eat/sleep 2 light bulbs Going faster... more energy need to go faster for most mammals oxygen consumption horse speed Change of gait Pictures by Muybridge, 1870 walking, trotting, cantering, galloping Per meter? oxygen consumption it might be the energy needed to move a particular distance Summary so far resistance reflexes provide for stability feedback loop Central pattern generation Levers help & hinder power is not unlimited! energy use increases with speed (and gradient) Now onto: can we beat the laws of physics when we run? Why do we run? to keep foot on ground, circular acceleration must be less than gravity speed ^2 < gravity * radius speed < ( gravity * radius ) speed < ( 9.8 * 0.9) = 3m/s When do we run? This gives us the Froude Number F = speed2/(gravity * leg length) at 0.5 walk -> run [trot] at 2.5 trot -> gallop Gravity on moon 5 times less Children run sooner as they have shorter legs bend legs in running to reduce radius In running energy changes between potential energy elastic strain energy Achilles tendon stretches by 5% gives back 93% Achilles tendon In galloping energy stored/released in a second spring flexing the spinal cord with tendon above And Kangaroos hop... oxygen consumption elastically speed Summary Staying still How do we stay still? Resistance reflex & feedback loops Walking - and running How does the nervous system control activity? CPG, sensory input, gating of sensory input How do mechanics and energetics limit/enhance limb coordination? levers increase torque, reduce role of front legs, speed limited by metabolism, rescued by changes in gait and elastic storage