Invertebrate locomotion Flashcards
•Two types of mechanical work
- Two types of mechanical work
- The body moves with respect to environment (motile)
- The environment is moved past the fixed organism (sessile)
What are the principles of locomotion?
- If a body is at rest relative to its environment it can be set in motion only by the application of an external force
- The application of an unbalanced force to a mass in motion results in acceleration or deceleration in the direction of the force
- For every action there must be an equal and opposite reaction
- Energy within a closed system remains constant but may be changed from one form to another
A moving animal must overcome resistive forces in the medium in which it’s moving - friction, drag
These can change the rate of movement
F= m*a
W= f*d
What happens to the energy?
Energy is conserved and mechanical energy can be converted to kinetic energy (movement of a mass) and ultimately lost as heat
Aqueous environment - water is a viscous medium which creates drag.
- The mechanical work of locomotion is derived from energy generated by chemical reactions of the cell
- BUT chemical work (glycolysis ect) does not always = mechanical work
- Therefore must define the efficiency of locomotion
- Concept of useful work – measurement of mass and distance moved
•The efficiency of an animal can then be expressed as;
Output of useful work
Input of energy
- Some animals are more efficient than others, however efficient systems may have limited power (rate of work)
- Trade-off between efficiency and absolute power
•Locomotion = change in cell shape occurring against environmental resistance by the utilisation of metabolic energy
what Three types of cell contribute to locomotion??
- Flagellated cells
- Ciliated cells
- Muscle cells
Generation of force – by animal cells - cilia and flagella
Cilia produce constant propulsive forces by sequenced and coordinated movements of large numbers of cilia
Flagellum are much longer than cilia and move back and fourth in parallel to the direction of the cell. Chemical energy is required to create the protein links, allowing the locomotory work to take place.
Generation of force – by animal cells
Muscle fibres generate forces because they have the ability to shorten against resistance
- Myofibrils – tubular contractive element ~1µm in diameter
- Functional unit – sarcomere composed of thick and thin filaments – 2 proteins myosin and actin
- Cross-bridges are formed between myosin and actin filaments; cause thin filaments to slide over thick filaments
- Continued contraction requires a repeated cycle of formation and detachment of cross-bridges and at each cycle, high-energy phosphate must be supplied by ATP
- Rate of shortening – the rate of sarcomere shortening and number of sarcomeres
- Force generated – number of filaments in parallel; as the overlap of fibrils increases linkage sites become saturated and power drops
•Chemical energy is utilised in muscle cells to shorten muscle fibres
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•Skeletal systems are required to transmit the generated forces
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•2 fundamental types;
•2 fundamental types;
- Fluid skeletons - wide range of soft-bodied invertebrates
- Rigid skeletons – crustacea and some echinoderms
•Muscles can only generate power when they contract and force must be applied to restore fibres to original length
In an antagonistic muscle pair as one muscle contracts, the other muscle relaxes or lengthens. The muscle that is contracting is called the agonist and the muscle that is relaxing or lengthening is called the antagonist.
The fluid skeleton can be employed in a variety of ways but basic principles are the same – a simple hydraulic system, allowing a shape change in a fluid mechanism.
Layers of muscle in a polycheate allow a much greater variety of movement
Locomotion in soft-bodied organisms
Walking
- Many soft-bodied invertebrates can move over a firm substratum
- Must transmit a force to the substratum through a fixed point
- Many systems involve the propagation of waves of contraction and relaxation of muscles with longitudinal axis parallel to direction of travel
- Flatworms, some cnidarians and all gastropod molluscs move by pedal locomotory waves (how the wave is behaving).
Locomotion in soft-bodied organisms - what is the use of the Pedal retractor muscle
Pedal retractor muscle – attach to shell and dorsal mantle and act to shorten or raise and lower the sole of the foot
- Direct waves (A) depend on contraction of longitudinal and dorsoventral muscles beginning at posterior end (back to front)
- Picking up, retracting and pushing.
- Retrograde waves (B) involve contraction of transverse muscles interacting with haemocoelic pressure to extend anterior part of foot forward, followed by longitudinal contraction
- wave of retraction moving in the opposite direction to movement – stick a section out in front
How do Errant polychaete worms change their locomotion pattern?
- Each example changes with the number of segments being used.
- Uses bristles as contact points on that animal to move forward.
- Variations in length and amplitude of metachronal waves combine with parapodial movements to produce the different patterns
- Parapodia and chaeta retract on recovery stroke so parapodia on opposite sides of any given segment are exactly out of phase
Using bristles - contact points on that animal to move forward.
Ripple effect of cheate moving
What allows soft-bodied organisms to burrow?
- Good examples in the polychaete worms and bivalve molluscs
- Highly efficient burrowers have secondarily lost most of their intersegmental septa (or have perforated septa)
- Arenicola marina and Polyphysia crassa
- fluid shifts, loose intersegmental septa, allowing a greater shift in the fluid throughout that environment.
- Reduced parapodia
- Chaetae or surface or expanded body segments act as anchor points
- Burrow wall provides the antagonistic force resisting the hydraulic pressure
What are the steps in Burrowing in Arenicola marina
- Embed and anchor anterior region in substratum
- Contract posterior circular muscles forcing coelomic fluid anteriorly and causing segments to swell
- Posterior longitudinal muscles contract pulling back of the worm forward, cheate maintain the anchor point.
- Second phase of burrowing as anterior circular muscles contract and longitudinal muscles relax
- Posterior edges of each segment protruded as anchors
- Proboscis thrust forward deepening the burrow, creating lever
- Proboscis retracts anterior segments fill with fluid – process repeated
