Movement and Support Notes

Animals must generate physical force and apply it against air, water, or land to move.
Skeletal Support:
- Rigid body parts enhance movement efficiency.
- Legs push against the ground.
- Bird wings push against air.
- Fins or flippers apply force against water.
- Each body part is supported by a skeleton.
Three Main Skeletal Systems:
- Hydrostatic skeletons
- Exoskeletons
- Endoskeletons

Found in invertebrates like cnidarians and annelids.
Consist of fluids held in a gastrovascular cavity.
Fluids alter body shape via contractile cells in the body wall.
Example: Hydra
- When a hydra closes its mouth, water is trapped causing it to elongate.
- When the mouth opens water is released, and it becomes shorter.
- Constricting the cavity elongates the animal.
- Longitudinal cells contract, shortening the body when disturbed.

Found in many arthropods and most mollusks.
Arthropod exoskeletons are made of chitin (a protein).
Mollusk shells are made of calcium carbonate.
Jointed exoskeletons allow arthropods to swim, fly, burrow, walk, crawl, and leap.
Provide watertight coverings for arthropods in dry places.
Offer physical protection from predators.
Bivalves (e.g., clams) can close shells to avoid drying out.
Disadvantages:
- Pose a problem for growth.
- Arthropods molt (break out of their exoskeleton and grow a new one).
- Relatively heavy; larger arthropods have heavier skeletons relative to body weight.

Found in echinoderms and vertebrates.
Structural support system within the body.
Echinoderms have endoskeletons made of calcified plates.
Vertebrates have endoskeletons made of cartilage or a combination of cartilage and bone.
Sharks and some fishes have skeletons made mostly of cartilage.
Four-limbed vertebrates have limb girdles to support limbs.
Vertebrate endoskeletons enable swimming, flying, burrowing, walking, crawling, or leaping.
Internal skeletons cannot protect like exoskeletons.
Internal skeletons grow as the animal grows, so there is no need to molt.
Lightweight relative to the bodies they support, allowing even land-dwelling vertebrates to grow very large.

Rigid skeletons must be divided into parts connected by joints to allow movement.
Joints are places where parts of a skeleton are held together to enable movement.
In vertebrates, bones are connected at joints by ligaments (strong connective tissues).
Most joints have ligaments, cartilage, and lubricating joint fluid.

Muscles produce physical force by contracting (getting shorter) when stimulated.
Muscles relax when not stimulated but cannot actively get longer.
Muscles work together in pairs or groups attached to a supporting skeleton.
Muscles are attached to bones around joints by tendons (tough connective tissue).
Tendons pull on bones when muscles contract.
Muscles are arranged in groups that pull parts of the skeleton in opposite directions.

Arthropod muscles attach to the inside of the exoskeleton.
Vertebrate muscles attach around the outside of bones.
Pairs or groups of muscles pull across joints in different directions.
When one muscle group contracts, it flexes the joint.
When the first group relaxes and the second group contracts, the joint straightens.
Flexor: muscle that bends (flexes) a joint
Extensor: muscle that straightens a joint

Complex combinations of bones, muscle groups, and joints have evolved in vertebrates.
In many fishes and snakes, muscles are arranged in blocks on opposite sides of the backbone and contract in waves bending the body from side to side to generate thrust.
Limbs of some amphibians and reptiles stick out sideways, using sideways movements of their backbone to move their limbs.
Mammals stand with their legs straight under them.
Mammalian limbs have evolved for different kinds of movement.
Shapes and relative positions of bones and muscles, and the shapes of joints, are linked to their functions.
Paleontologists can reconstruct habits of extinct animals by studying joints of fossil bones and tendon/ligament attachment sites.

The 3 Types of Human Muscle include Cardiac (heart muscle), Smooth (found in intestinal track) and Skeletal muscle which is attached to bones
Ligaments connect bone to bone.
Tendons attach muscle to bone.
Muscles work in pairs.
Muscles must be attached to something in order to be effective.
Humans have 206 bones (adult). Babies have nearly 300 bones.
Animal: Multicell heterotroph, some don't move.

Hydrostatic skeleton: A structure found in invertebrates, consisting of fluid-filled cavities that help maintain body shape and allow movement through pressure changes in the fluids.
Exoskeleton: A rigid external covering found in many arthropods and mollusks made of materials like chitin or calcium carbonate, providing support and protection to the animal.
Molting: The process by which arthropods shed their old exoskeleton to allow for growth and the development of a new, larger exoskeleton.
Endoskeleton: An internal support structure found in echinoderms and vertebrates, which can consist of cartilage or bone and supports the body from within.
Joint: The connection point between two skeletal parts that allows for movement.
Ligament: A type of strong connective tissue that connects bones to one another at joints, providing stability.
Tendon: A tough connective tissue that attaches muscles to bones, enabling the muscles to exert force on the bones during movement.