Transcript Movement on land

Movement on land
Neuroethology
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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
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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
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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
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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)
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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
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flexing the spinal cord
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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?
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levers increase torque, reduce role of front legs, speed
limited by metabolism, rescued by changes in gait and
elastic storage