lecture 11: soft bodies 1 Flashcards
criteria for hydrostatic skeletons (3)
1) fluid maintained at constant volume
2) container for fluid must be deformable
3) container for fluid is wrapped in muscle and connective tissue
*** fluid in a deformable container that is wrapped in muscle transmits the force of muscle contraction
examples of conventional hydrostats
the fluid is water in conventional hydrostats
- tube feet of echinoderms (urchins, stars, etc)
– coelomic fluid in
coelomic compartment - lophophoric tentacles of bryozoan
– coelomic fluid in
coelomic compartment - sea anemones
– no coelom or coelomic
fluid - marine annelid
– each metamere has
coelomic fluid in coelomic
compartment
examples of muscular hydrostats
ex// muscular foot of gastropods
ex// arms of cephalopods
ex// parenchymal cells of turbellarians - circular and longitudinal muscles
- muscles themselves can act as hydrostatic skeletons
- muscles themselves can transmit the force of muscle contractions as they contain water and a bunch of them contracting can act as hydrostatic skeleton
what can be used for hydrostatic skeleton?
Any deformable, incompressible material maintained at constant volume
comparing stiff levers and hydrostats
both transmit force created by muscle shortening - to do work
both re-extend antagonistic muscles
both exploit mechanical advantage
how can hydrostatic skeletons exploit mechanical advantage?
diagram showing different lengths and diameters of cylinders –> all have same volume
exponential function shows that this is not a straight line - not linear
the relationship between diameter and length in a cylinder that maintains constant volume = is not linear — the curve is not a linear line
As a cylinder of constant volume changes shape there is a non-linear relationship between its diameter & length
*** this shows how hydrostatic skeleton can take advantage of the mechanical advantage
discuss 2 appendages of squids
resting lengths of each are different
tentacles much longer than arms when resting
- tentacles capture fast moving prey
if want cylinder longer, need to decrease diameter
how to EXTEND tentacles (or arms)?
*****contract any muscles that reduce cross-sectional diameter upon shortening
- circular muscles: decrease diameter (an therefore increase length)
- radial and transverse muscles will result in elongation
How to SHORTEN tentacles (or arms)?
*****contract any muscles that reduce length
- only one type of muscle that can shorten length = longitudinal muscles
what is the difference in changing diameter of the tentacle versus the arm
the resting length of the arm is shorter than the tentacle, so if there is a change of diameter by 1 unit on the input side, then the output side would be a change of 10 units
the resting length of the tentacle is longer, so if there was a input change of diameter of 1 unit, the output is much larger, at change of length of 25 units
** this is important for prey capture as needing to move fast
– amplification of output and speed
tentacle muscles
- longitudinal muscles:
- change the length of arm or tentacle
- Obliquely striated = longer effective length range
- Circular muscles
- Transverse muscles
- Radial muscles
^ - Cross-striated = speed important!
- helping to change diameter of arm or tentacle
- fast shortening speed
Internally pressurized cylinders: wall tension
what are 2 types of tension and explanation
**as internal pressure increases, the wall experiences tension or tensile stress — going to be both Circumferential tensile stress and Axial tensile stress
Circumferential tensile stress
- threaten to produce longitudinal rips in the material of the wall
- 2x axial stress –> will experience more circumferential stress than axial direction
Axial tensile stress
- threaten to blow off ends of internalized pressurized cylinders
***** if a thin sausage and fat sausage in a pan– the fat sausage will rip open sooner
as radius of cylinder increases, the more tension on the wall of the cylinder
Circumferential tensile stress =
internal pressure x
radius of cylinder
————————————–
wall thickness
EXAMPLE:
- peristaltic body movements of annelid
– more tension when short and fat
how is the wall of a hydrostatic skeleton reinforced so it doesnt break?
consider an anemone:
- need to increase tension a lot in stalk to have pressure in tentacles
consider tube feet of echinoderms
- circumferential stress is 2x axial stress, so the tube foot must be reinforced so doesnt get short and fat
***importance of collagenous connective tissue
- latticework of crossed helical fibres (collagen)
- collagen has very steep stress strain curve — meaning that if u pull on end of collagen fibre u hv to use a lot of force (stress) to extend it even a little (very stiff material
- use instead lattice work of fibres, on angles — the material readily gives intitially bc pulling on the extracellular matrix of the fibres, not the fibres themselves
- eventually, as the material gets pulled, the individual fibres start to line up and become parallel to the direction of the pull —>
now when pulling on either end, the extension is limited bc then pulling on collagen fibres themselves bc they get parallel
- when gets parallel, becomes still and stops extending
Internally pressurized cylinders
- Need to prevent ruptures
- Need to limit/control shape change
**importance of collagenous connective tissue
- collagen has steep stress strain curve –> v stiff material
- these fibres on an angle to still be deformable - reinforce without limiting their ability to be deformable
stress strain curve of collagen
j shaped
steep
initially extends readily
eventually pulls parallel to collagen fibres, making hard to break or apply too much force
