Movement on land. Neuroethology nMovement on land; reflexes and central pattern generators in the CNS; change of gait and its neural and energetic consequences.

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 motoneurons and Ia afferents

Resistance reflex

excitatory loop from muscle spindle

Ia afferent

Schematic

Resistance reflex - 2

inhibitory loop from muscle spindle to antagonistic muscle

needs interposed interneuron

interneuron

Active movementPrimary motor

cortex

in active movement, if a load is present, resistance reflex adds to motor command to make a stronger movement

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 CNSspread toes

Reflex reversal

Stimulate brain (MLR)to induce locomotion

Zap Ia interneuron afferentRecord motoneuron

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

burst

}interburst

expiratory muscle

How does the pattern change?

10s

Extra CO2 • accelerates rhythm• recruits extra muscles

(neck, abdomen)• recruits extra neurons

How do the bursts change?

ejps closer together?bigger ejps?less tonic activity?

+CO2

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

force

this is called Weight (or load) Transfer

the longer your legs, the more mechanical advantage you have

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 horse

speed

oxygen

co

nsu

mp

tion

Change of gait

walking, trotting, cantering, galloping

Pictures by Muybridge, 1870

Per meter?

it might be the energy needed to move a particular distance

oxygen

co

nsu

mp

tion

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...

elastically

speed

oxygen

co

nsu

mp

tion

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