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 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

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 CNSspread toes

Reflex reversal

Stimulate brain (MLR)to induce locomotion

Zap Ia interneuron afferentRecord motoneuron

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