CH 44 THE MUSCULAR SKELETAL SYSTEM & LOCOMOTION
44.1 Types of Animal Skeletons
- A skeleton is a structure that serve functions related to support, protection, and locomotion.
o 3 types of skeletons are: Hydrostatic skeletons, exoskeletons, and endoskeletons.
o First 2 found in invertebrates, endoskeletons found in sponges, echinoderms, vertebrates.
Hydrostatic Skeletons Consist of Fluid-Filled Body Compartments
- A hydrostatic skeleton uses water pressure to support bodies.
- Water is almost incompressible, so if animal exerts a force on the water, it can use the hydrostatic pressure created
to move the body.
o Cnidarians (hydras) body and tentacles will either be elongated/shortened by movement of water into
and out of different regions of the body.
o Segmented worms moves by passing a wave of muscular contractions along length of body; circular
muscles squeeze elongate body and longitudinal muscles shortens it.
Exoskeletons are on the outside of an animal’s body
- Arthropods have an exoskeleton, an external skeleton that surrounds and protects most of the body surface,
- The skeleton is made of chitin and strengthened with calcium and other minerals.
- To allow growth, exoskeletons are shed, regrown and strengthened – ecdysis.
- Exoskeletons vary in their complexity, thickness, and durability.
o Ex. A fly maggot exoskeleton allows it to move through decaying organic matter while the lobster
exoskeleton provides defence against sea predators.
Endoskeletons are Internal Support Structures
- Protects only the internal organs and other structures.
- Made of calcium, magnesium, phosphate, and carbonate.
- Echinoderms and sponges have spiky networks of proteins and minerals in a platelike structure that extend into
spines and arms radiating from main body.
- Vertebrate skeletons are composed of either cartilage or bone.
44.3 Skeletal Muscle Structure and the Mechanism of Force Generation
- Vertebrates have 3 types of muscle – cardiac muscle, smooth muscle, skeletal muscle.
- Skeletal muscles can generate action potentials in response to a stimulus, these potentials cause increase in cytosolic Ca2+,
which triggers force generation.
- Invertebrate skeletal muscles have graded membrane potentials but do not have action potentials.
A skeletal muscle is a contractile organ that supports and moves bones
- A muscle is a grouping of cells – muscle fibres – bound into fascicles by a succession of connective tissue layers.
- In vertebrates, skeletal muscles are linked to bones by bundles of collagen called tendons, which can be long.
- Weightlifting enlarges fibres but doesn’t form new ones.
Muscle Fibres Contain Myofibrils Composed of Arrays of Filaments
- Skeletal muscles have a series of light and dark bands perpendicular to muscle’s long axis, so it can be called
striated muscle. Jan/26/11
- The pattern comes from cylindrical bundles called myofibrils, which extends from one end of the fibre to the
other and is linked to the tendons at the ends of the fibre.
- In each myofibril, thick and thin filaments arrange in a re