MOVEMENT IN ANIMALS

The Earthworm

• Belong to the phylum Annelida, the ringed worms.
• They have a hydrostatic skeleton – muscles work against a fluid filled sac, the coelom.
• The body of worms is adapted to burrowing, streamlined with no limbs.
• The body plan is segmented.
• Circular blocks of muscles are present in each segment.
• Longitudinal muscles run the length of the body.
• Chaetae (bristles), 8 per segment, with retractor muscles project from the body providing traction.

• Extension: the circular muscles contract, squeezing the body forwards and the longitudinal muscles relax.
• Anchoring: The chaetae project and grip the substrate.
• Contraction: The longitudinal muscles contract and the circular muscles relax, pulling the body forwards.

The Arthropod

• Exoskeleton made of chitin – reinforced with calcium in crustaceans.
• Limbs segmentally arranged .
• Flexible joints permit movement.
• Antagonistic muscles attach inside the tubular limbs.
• Flexors and extensors are on the opposite sides of the limb to a vertebrate with its endoskeleton.
• Movement is programmed by the nervous system.
• Movement can be very fast (a cockroach can run at 1ms^-1).
• Legs rise and fall in sequence down one side – a locomotory wave.
• Alternating locomotory waves pass on each side of the body.
• Evolution of the arthropods has resulted in a reduction of limbs:
   

  ▪ Crustacea 10 pairs

  ▪ Arachnida 4 pairs

  ▪ Insecta 3 pairs

The Bony Fish

• Streamlined shape for cutting through water.
• Bony skeleton for support of muscles.
• Myotome muscle blocks flex the body, especially the tail.
• Anal and dorsal fins control roll.
• Paired pectoral (front) and pelvic (back) fins control pitch (up-down) and yaw (side to side)
• Caudal (tail) fin provides thrust.
• Swim bladder provides neutral buoyancy.
• Lateral line organ detects changes in pressure so it can indicate the depth.

Bird flight

• Feathers: Stiff flight feathers extend the surface area of the arm to produce an aerofoil wing.
• Stiff tail feathers control direction and velocity (air braking on landing).
• Body feathers insulate providing protection at high altitude and conserve body heat to maintain a high metabolic rate.
• Well developed chest muscles to power the wings.
• Keel bone projects from thorax to attach flight muscles.
• Hollow air-filled bones provide strength but remain light.
• A horny beak is lighter than jaws and teeth.
• Air sacs in the abdomen permit breathed air to travel twice through the lung tissues.
• Haemoglobin with a high affinity for oxygen permits flight at high altitude.
• The embryo develops externally in a shelled egg. Female birds are not weighed down by pregnancy.

• Muscle contraction
• The Nerve Impluse
• The Synapse
• Top of Page

© Paul Billiet 2004