Lecture 10
Locust jump
Joints: coxal monocondylic joint: many axes of rotation
Pinnate muscle, apodemes: adaptation
Heitler W.J. 1974. The locust jump. Specializations of the
metathoracic femoral-tibial joint. Journal of comparative
Physiology 89: 93-104
• Announcements:
• Snow cancellation adjustment: we will get back into phase by taking 2 wks
to complete lab 4 [jump]; those that missed this week will do lab 4 next
week and for everybody else: there will be no labs Feb 8,10,11
• Content for term test: questions drawn from material presented in lecture
and lab preambles
• Four labs completed by term test time (Feb 17): skeletons, tentoria, fluids,
jump
• See Locomotion Augmented on course website for: squid locomotion,
polychaete parapodia body waves, slug locomotion, flea jump, locust
jump, levers [ignore non-click flight for the moment and white muscle
fibres fishes]
• First class lever: insect flight: good answer
Tettigoniidae (katydid) from Papua New Guinea: particularly elongate femur and tibia
feature shared with grasshoppers
Saltatorial adaptation
locust jump
Some insects are adapted to run: cursorial adaptation: e.g., tiger beetle,
Cicindellidae [photo.net]
When grasshoppers
evolved to use their
metathoracic legs for leaping;
they compromised their ability
to run: an adaptive tradeoff.
Igor Siwanowicz
Anatomy Tibial levator, Tibial
depressor
Levator muscle (extensor): raises
an appendage
Depressor muscle (flexor: lowers
an appendage
tibia levator takes up much of
femur volume
depressor of tibia and its
apodeme much smaller
pinnate: muscle fibres angled to
insert on apodeme
Apodeme: adaptation
• Increases surface area available for muscle insertion
• Improves mechanical advantage: farther from axis of rotation
• Relocates muscle to regions remote from appendage: leg extremities tarsi,
lighter (roach); bulk where there is room for it, adductor muscle in head;
rope apodeme
• Stabilizes: resists stresses and strains: tentorium acts as tie and as a strut
Pinnate ‘feather-like’ muscle arrangement: adaptation
•Parallel-fibred muscles, individual fibres longer so insertion point
moved through greater distance; pinnate improves force at expense
of distance an appendage is displaced
•Muscle fibres dilate toward the middle when they contract; angling
fibres minimizes problems of expansion within confines of
exoskeleton
Rope apodeme and
its elastic antagonist
Resilin? Muscles a,b,c
contract to pull rope
tendon and depress
claw (of pretarsus)
first class lever
Resilin antagonist is
third class lever
•
A grasshopper gets extra force into its leap by simultaneous contraction of the antagonists:
tibial depressor and tibial levator. It prepares to jump by contracting both muscles
simultaneously and isometrically (no movement at the joint). This distorts the exoskeleton in
the neighbourhood of the joint and so stores elastic ‘deformation’ energy that can be
released later during the jump and so contribute to the forces the leg exerts against the
ground.
How is it that during this isometric contraction stage the smaller muscle is able to match the effort of
the much larger muscle? Ans. Two things are involved: 1) mechanical advantage [‘pulley’ effect of
lump changes force direction] which favours the flexor at maximum flexion and 2) a bifurcated
apodeme ‘cap’ that catches behind the lump.
This involves a pulley-like arrangement that changes the direction of
forces. A bifurcated ‘pocket’ or ‘cap’ is part of the tibial flexor apodeme; at
maximal flexion of tibia on the femur the bifurcation is pulled over the
lump and helps to hold the weaker flexor muscle during the isometric
preparatory (to the jump) contraction.
The force advantage of the
flexor muscle is different at
different angles of flexion of the
femorotibial joint. Part of the
answer is that when the angle
of flexion is less than 5 degrees,
the force advantage of the
flexor muscle is superior to that
of the extensor.
***As mentioned in class: the lump in
this diagram should be coloured to match
the purple of the femur not the blue of the tibia.
•
***As mentioned in class: the lump in
this diagram should be coloured to match
the purple of the femur not the blue of the tibia: the
lump is part of the ventral wall of the femur.
1) The apodeme of the flexor makes
an angle with the effort arm of the
lever that is almost 90 degrees; this is
because it rides up over the 'lump'
located between the dicondylic joints.
The lump functions as a pulley in that
it changes the line of action of the
force of the flexor muscle; it changes
the direction in which the apodeme
pulls on the tibia, making it nearly 90
degrees; by contrast the stronger
extensor pulls at a very poor angle of
5 degrees.
2) The effort arm (the distance
between the point of insertion of the
apodeme on the tibia and the axis of
rotation) is quite short for the
extensor; much longer for the
flexor. So the moments of force can
be balanced.