Transcript Movement on Land

Movement on land
Movement lectures
 On Land
 In water
 Insect singing
 Flight
 Muscle PowerPoint now on line
 http://biolpc22.york.ac.uk/632/
musclelectures.html
Planned Assessment
 Exam
 Short
answer 4/6 (2 Neural, 2 Movement)
 Paper 1/4
 take in
 handouts
 own
handwriting
 clean, unmarked copies of SET papers
 Past
paper for 2005 has same format
Books, CDs
 McNeill - Alexander R.
 Animal
mechanics
 How Animals Move [CD
Rom borrow in teaching]
 Schmidt-Nielsen (1997)
Animal physiology 5th
edition
Aim
 Staying still
 resistance
reflex
 Walking - and running
 neural
control
 energetics
 mechanics
 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
Central control
 Central pattern generator (CPG)
 Block
sensory input (deafferentation)
Stick insect: innervated
denervated
CPG
 Locusts flying,
Clione
swimming,
tadpole
swimming
…
 Reciprocal
inhibition
excitation
CPG
Role of sensory input
 why have sensory input if
CPG works anyway?
 initiate/end
rhythm
 adjust speed of rhythm
 cycle by cycle feedback
 adjust pattern (gait)
 examples from crustacean
stomatogastric ganglion
 ~40
neurons
Cycle by cycle feedback
 Switch from stance to swing
Initiate/end rhythm
 Simple : rhythm runs while stimulus is
maintained
Accelerate rhythm
 More complex : rhythm runs on after
stimulus is maintained
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
Summary so far
 resistance reflexes provide for stability

feedback loop
 Central pattern generation
 Sensory
control
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
Hind legs more powerful
 push back on the ground, lift
up tail (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)
Limits to 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
Walking and running
 You use more energy
 going
faster
 uphill
1 kW
5 miles / hour
Going uphill
 Extra work is force x distance up
 =10 J/kg
 if muscle efficiency is 20%, need 50J/kg
Going faster...
 more energy need to go faster for most
mammals
 horse
Going faster
 same (per kilo) for all animals
 percentage increase less for small animals
 larger
BMR
Per meter?
 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
 energy use increases with speed and
gradient
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
= speed ^2/(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
In running
 energy changes between
 potential
energy
 elastic strain energy
 Achilles tendon
 stretches
by 5%
 gives back 93%
Achilles tendon
In galloping
 second spring

flexing the spinal cord

with tendon above
And Kangaroos hop...
 elastically
Summary
 resistance reflexes provide for stability
 feedback
loop
 Central pattern generation
 Levers help & hinder
 energy use increases with speed and
gradient, but stays fixed per meter
 take off for running determined by gravity
and leg length
 in running, energy stored in tendons