Locomotion Flashcards
Reasons animals move
Get food
Avoid predation
Find mates
Find/follow suitable habitat
Types of muscle shape
Longitudinal
Pennate
Convergent
Circular
Types of longitudinal muscles
Fusiform
Parallel
Types of pennate muscles
Multipennate
Bipennate
Unipennate
Resistive forces to motion
Friction - terrestrial
Gravity
Drag - aquatic
Crawling
Peristaltic/pedal waves associated with
-loops
-anchors
2 anchor system the simplest
Types of peristaltic/pedal waves
Retrograde
Direct
Retrograde waves
Waves move from back to front
Mostly in septate animals
Direct waves
Waves move from back to front
Mostly in non-septate animals
Pedal waves
Move forward
Interwaves = stationary
Pedal waves move faster than the animal
Friction in interwaves must be stronger than friction in the waves
Net direction of movement is forward
Movement via pedal waves
Pedal waves- animal lifts the body away from the ground but only marginally
Interwaves- animal presses down against the ground, providing thrust
Types of pedal waves
Monotaxic - single line of waves
Ditaxic - 2 asynchronous lines of waves
Tertrataxic - 4 asynchronous lines of waves
Pedal mucus
Combination of sticky pedal mucus with a thinner lubricating mucus (comprising the snail slime) provides lubrication while allowing sufficient grip to overcome gravity
Pressure beyond a critical value causes the mucus to lose adhesive property
The change in pressure is caused by the animal pressing against the surface.
Animal would have to press down in pedal waves instead of lifting, thus exceeding the critical stress yield value of the mucus
Sidewinding
More efficient in plain surfaces with few irregularities to provide grip, such as desert plains
Types of crawling
Pedal waves
Sidewinding
Lateral undulation
Vertebrate crawling
Galloping
Lateral undulation
A variation of anchor and loop movement in invertebrates
Made easier and more efficient by the presence of the spinal chord
Structure of muscle
Sarcomere
Myosin and actin
ZIAHMHAIZ
What are septate animals
Segmented
Peristaltic waves
Works because the animal is surrounded by soil
Thickening of the body increases contact with the surrounding soil, increasing friction (with the help of specialized setae)
Thinning of the body has the opposite effect
Frictional anisotropy
Difference in friction on snake scales depending on direction on the ground
Stride definition
One full cycle of leg movement
2 phases in one stride: swing phase and stance phase
How is leg movement achieved
a set of muscles that connect inside of the thorax to the coxa of the leg
Leg flexing and extension controlled by muscles in the Femur
Muscles attach to the inside surface of the exoskeleton.
Arthropod biomechanics
Exoskeleton constraints the size and positioning of the muscle
Insect legs have a wide range of movement but produce relatively little work
Muscles are often pennate, which have shorter contraction distances, but produce more force
They also don’t change volume with contraction
Leg posture in arthropods
Horizontal sprawled leg postures allow some insects to take advantage of gravity for leg movement
Vertical sprawled leg postures can decouple weight loading from movement muscles
What descriptors describe different gaits
- Leg position
- Stepping pattern
- Stride period (time for one leg to complete one movement cycle)
- Stride length (distance the centre of mass covers in one stride cycle
- Stride cycle (rate at which segments are cycled)
- Speed = stride length x stride frequency
- Duty factor (fraction of time one leg supports load)
- Phase (fraction of a cycle on leg leads or lags another)
Walking
For walking to occur, potential energy must be converted to kinetic energy
Bipedal walking similar to an inverted pendulum mechanism
Because gravity acceleration is constant, there is a limit to how fast animals can walk
To move faster, animals must change gait
Sprawled gait
Sprawled vertebrates increase speed by moving legs faster and exaggerating sideways movement to increase step distance; energetically costly
Running
Takes advantage of gravity and body elasticity to preserve energy
Duty factor is lower in running than in walking
In most animals, duty factor = 0.5 marks the boundary between walking and running
Under this criteria, cockroaches never run
Quantifying gaits- froude number
Fr = V^2/gL
V = velocity
g = gravity acceleration
L = length of leg
Ratio of centripetal forces and gravity
Why are insects size limited
Insects are small and lightweight, so little work is required to move them
There is a maximum size an insect can attain, beyond which the animal muscles cannot produce enough work to sustain their own weight.
At what froude number do all vertebrates shift from walking to running
0.5 (0.3-0.8)
Quadrupedal running gaits
Symmetrical: trot, pace (camels), amble (elephants)
Asymmetric used at Fr>2.5
Jumping/hopping
Development of hind legs relative to body length
Smaller femur, with longer fibula/tibia and feet bones (only for vertebrates)
What force does walking take most advantage of
Gravity
Duty factor
How long the legs are on the ground
At what duty factor is the boundary between walking and running
0.5
Centripetal force equation
mV^2/L
Gravity equation
mg
Disadvantage of sprawled gaits
High energetic cost
What gave humans a locomotive advantage
Sweating system
Important forces in aquatic locomotion
Buoyancy
Drag
Gravity
What is the big opponent in aquatic locomotion
Drag
Moving through water
Positive buoyancy reduces effect of gravity
High density of water increases the effect of drag
Water must be pushed back to achieve forward thrust (wake)
Reynolds number
Inertial drag/ viscous drag
( Density x velocity x length ) / viscosity
Low Reynolds number <10
Fluid behaves like honey
High Reynolds number >100
Fluid behaves like water
What can affect the Reynolds number
How fast they swim
Size
Gaits in aquatic locomotion in invertebrates
Rowing (drag powered)
Tail-flipping
Lift powered
Jetting
Rowing
Works at low and high Reynolds numbers
Forward movement of the oars produces drag, making it relatively inefficient
Tail flipping
Works only at Reynolds numbers >500
Turns the shrimp into a hydrodynamic shape
Jetting
Provides fast acceleration but energetically costly over long periods
Good to escape predators
Works best at Reynolds numbers >2000
Jet orifice - shoot water out
Gaits in aquatic locomotion in vertebrates
Lift powered
Lateral undulation
Lift powered
Works great at Reynolds numbers >2000
Sinusoidal movement of pectoral fins provides lift on both forward and back strokes
Fluid moves faster on one side of the body , generating lift
Lateral undulation
Characterised by waves of contraction from front to back of body
Waves push against the water providing thrust
At high speeds the whole body of fish acts as a hydrofoil
Muscle used in lateral undulation
White muscle has low haemoglobin and mitochondria concentration; used during anaerobic swimming
Red muscle has high haemoglobin and mitochondria concentration; used during aerobic swimming
Proportion of red muscle varies from as little as 1% (cod), to 14% (mackerel) or more (tuna)
Muscle organization allows for even shortening through whole body
Undulation
Fish can use a combination of both
Lateral undulation moves a lot of water to the sides… thus increasing drag
More efficient to maintain a rigid body, and concentrate wave movement as far back to the tail as possible (keep an airfoil shape)
Swimming energetics
Water moves back at each stroke, thus dissipating some energy of such stroke
Drag increases with velocity squared (v*v)
Momentum is mass * velocity
More efficient to move large amounts of water at slow speeds, than small amounts of water at high speeds.
Most efficient swimmers in the ocean
Cetaceans
Size and swimming energetics
Larger —> more water displaced —> swim more efficiently
Type of muscle used in short term thrusts
Red muscle
Type of muscle used in long term swimming
White muscle
Tail lift
Geometry of tail affects type of lift and power generated
Wider tails with points at ends - long distance movement
Smaller tails- thrust and power
Thrust = momentum
Mass x velocity = momentum
Drag increases as velocity increases V^2
Therefore if double velocity of water drag increases by factor of 4
So moving more water, slower = same momentum but least lost to drag
Cetaceans
Whales
Dolphins
Porpoises
Why are whales migratory
Swimming is very energy efficient due to size
Important forces in aerial locomotion
Drag
Gravity
Wing properties
Faster you go
Drag changes as a function of velocity
Easier to generate lift
Easier to fight gravity
Physics of flying
Air behaves like a fluid
The same principles of drag and lift talked about in aquatic locomotion apply to aerial locomotion
The main differences relate to lower density of air relative to water, and the constant effect of GRAVITY
Reynolds number and aerial locomotion
Dependent on surface properties- bumpy = faster
Flight velocity and drag
Lift to drag ratio
Lift/drag
Birds = 2-20
Insects = 0.5-2
Gaits for aerial locomotion in vertebrates
Hovering
Forward powered flight
Gliding/soaring
Vertebrate wings
Muscles on endoskeleton
Hovering
Forward and backward stroke to generate lift
Hummingbirds = symmetrical - figure of 8 pattern
Kestrels = asymmetrical - bend their wings in the backstroke to reduce drag - push down to generate lift
Vertebrate wing muscles
Flight is promoted by the pectoral muscles, connecting the sternum to the humerus near the shoulder joint
Good distance advantage, but weak force advantage
Sternum is modified to allow the attachment of large muscles
Gliding
3 forces must be in balance: lift (provided by wings); drag (caused by air resistance); weight (promoted by gravity)
Gliding angle is changed by moving wings (backwards increase the angle), higher angles means higher speeds
Minimum sink speed is the forward speed at which downward speed is less
Maximum range speed is the forward speed at which gliding angle is minimum, thus travelling a higher distance for a given height loss
Maximum range speed is slightly faster than Minimum sink speed
Gliding farther means increasing speed at the expense of faster height loss
Minimum sink speed
Forward speed at which downward speed is less
Maximum range speed
The forward speed at which gliding angle is minimum, thus travelling a higher distance for a given height loss
Gliding and size
Larger birds glide faster
Remaining differences due to wing shape
Soaring
If there is a vertical component to the wind, then animals can keep gliding indefinitely
Many birds of prey take advantage of local upward winds to hover without flapping wings
Allow to scan for prey with minimum fuss
Types of soaring
Slope soaring
Thermal soarin- takes advantage of warm convection currents
Gaits of aerial locomotion in invertebrate s
Hovering
Forward powered flight
Difference in insects and birds flying
Wings can be smaller
Generating wing motions must be faster (smaller so must move faster in order to generate the necessary force)
Air is different when you’re small- Reynolds number- insects have a lower Reynolds number (air is more viscous)
Forward flight
Movement of wings similar to movement of fins in lift powered swimming
Wing is rotated in the upstroke to avoid downward lift
Insect flight muscles
Muscles that power flight attach to the inside of the thorax, not the wings themselves
Change in thorax shape forces the wings up and down
Maximizes power given the limited space inside exoskeleton
Muscles that attach to the wing are small and only control wing orientation
What powers soaring
Updraft of air
Where can slope soaring occur
Hills
Dunes
Waves
Wing morphology
Slope soarer- long and narrow
Thermal soarer- wide and large
Hunter- shorter and wide (can generate large amounts of thrust for strikes)
Why can insect wings be smaller and thinner
Mass is proportional to volume
Lift is proportional to wing area
How can insects combat a low Reynolds number
Increasing initial speed- take off by generating powerful jumps
Hovering in insects
Difference between hovering and forward flight depends on body angle relative to ground
Change angle of body- tilt up to change direction of lift - as cannot change direction of wings
Muscles in wings?
Insects must tilt whole body as cannot change direction of wings as have no muscles in wings
