Animal Movement Chapter 30

Overcoming Forces

Skeletal Support Hydrostatic Exoskeleton Endoskeleton Soft bodies: hydra, earthworm Fluid filled cavity – remember water is not compressible Exoskeleton Hard external skeleton: arthropods (chitin ), mollusks (calcium carbonate) Shell of nonliving material secreted by living cells Exoskeleton is molted occasionally during growth or outer edge is added Endoskeleton Hard elements alongside soft tissue Vertebrates – cartilage and bone, echinoderms – inorganic material

Human Skeleton Ancestral traits – 375 myo tetrapod body plan Axial skeleton Appendicular skeleton Bipedalism frees hands for other uses Vertical backbone supports weight unevenly Flexible joints provide versatility Ligaments hold bones together Ball-and-socket joint Hinge joint Pivot joint

Bone Structure Bones are complex living organs Living cells secrete the bone matrix Calcium and phosphate (hard) and collagen (flexible) make up the matrix Yellow bone marrow stores fat Red bone marrow produces RBCs

Bone Health Bone repair – bones are continually being repaired Bone fractures heal stronger so long as the bone remains immobilized for a period of time Osteoporosis is the result of slow replacement of bone tissues Becoming more common, even in men Bones need stress to remain strong

Muscle-Skeleton Pairing Muscles attach to bone via tendons To move in two directions muscles are arranged in antagonistic pairs Ex. Triceps and biceps One muscle is contracted while one is relaxed

Structure of Skeletal Muscle Skeletal muscle attaches to bone, moves body One muscle fiber contains many myofibrils Sarcomeres are the repeating units of myofibrils Thin filament – actin Thick filament – myosin

Muscle Contraction Sliding-filament model of muscle contraction – follow z-lines Motor neuron allow interaction between actin and myosin, ATP allows for movement

Sliding filament

Motor Neurons Neuron cell bodies in CNS transmit action potential via axon Axon forms neuromuscular junctions with muscle fibers Acetylcholine is released across junctions making muscle fibers contract Acetylcholine in muscle cells causes the release of calcium ions (Ca2+) from the ER (endoplasmic reticulum) Ca2+ allows for interaction between thick and thin filaments by removing the barrier (regulatory protein) between them Muscle contraction force is dependent on the number of motor neurons activated