By: Rodrigo Vilaro, Peyton Maclay, and Maria Walts Chapter 49 Motor Mechanisms By: Rodrigo Vilaro, Maria Walts, and Peyton Maclay

Introduction Most organisms need some form of support. Many animals wear their support on the outside. They have Exoskeleton- a hard covering or shell -Insects, for example, have exoskeleton made of chitin. Cicada’s Exoskelton All vertebrates ( animals with backbones) possess an endoskelton - their entire skelton is on the inside. Examples: humans, fish, amphibians, reptiles, birds, and all other mammals are considered vertebrates

Hydrostatic Skeleton A hydrostatic skeleton consists of fluid held under pressure in a closed body compartment. Peristalsis - a type of movement on land produced by rhythmic waves of muscle contractions passing from front to back.

The Human Skeletal System In humans, the supporting skeleton is made of cartilage and bone. Cartilage is found in the embryonic stages of all vertebrates. It is later replaced by bone, except in your external ear or the tip of your nose. - Bone is a connective tissue that contains nerves and blood vessels. - Cartilage lacks nerves and blood vessels.

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Bones Bone is made up of two substances: 1. Collagen 2. Calcium Salts Bone is a dynamic tissue that changes shape when osteoblasts ( bone-building cells) and osteoclasts (bone-breaking cells) remodel it. Bones are held together by joints, like the ball-and-socket joint in your shoulder. Bones not only serve as support but together with muscles also help move us. The connective tissue that attach muscles to bones are called Tendons.

Joints Joints hold bones together. So what holds the joints together? They are held together by tough connective tissues called ligaments. Ligaments attach bone to bone. Ball and Socket: shoulder- enables rotation Hinge: allows only one type of movement Pivot: allows for rotation (neck)

8 Organizations of Skeletal Muscles Organizations of Skeletal Muscles Muscles are made up of muscle bundles, which subdivide into muscle fascicles. Within each muscle fascicle are units called muscle fiber cells. Within each muscle fiber are contractile fibrils called myofibrils. A single myofibril is subdivided, by Z lines, into sarcomeres or contractile units.

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The Sliding-Filament Model of Muscle Contraction  According to the sliding-filament model of muscle contraction, neither the thin filaments nor the thick filaments change in length when the sarcomere shortens; rather, the filaments slide past each other longitudinally, producing more overlap between the thin and thick filaments. 10

Result of longitudinal Slide 11

12 Muscle Contraception What happens during muscle contraction? When acetylcholine is released by a motor neuron, it binds with receptors on a muscle fiber and causes an action potential. The impulse stimulates the release of calcium ions from the sarcoplasmic reticulum. Calcium ions bind to troponin molecules, exposing the myosin-binding sites on the actin filaments. ATP (which is bound to the myosin head) is split and Pi and ADP are released. Myosin, binds to the exposed site on the actin molecules and actin- myosin cross bridges form, In creating these cross bridges, myosin pulls on the actin molecule, drawing it toward the center of the sarcomere. Then the actin-myosin complex binds ATP and myosin releases actin.

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Muscle Contraction Review A nerve impulse is sent to a skeletal muscle. The neuron sending the impulse releases a neurotransmitter onto the muscle cell. The muscle depolarizes. Depolarization causes the sarcoplasmic reticulum to release calcium ions. These calcium ions cause the actin and myosin filaments to slide past each other. The muscle contracts.

Smooth Muscles  Found mainly in the walls of blood vessels, the digestive tract, and internal organs.  They are long and each has a single nucleus.  The contractions are relatively slow and may be initiated by the muscles themselves.  Contractions may also be caused by stimulation from neurons in the autonomic nervous system. This explains why they are responsible for involuntary movements. 15

Cardiac Muscles  Are only found in the heart  The difference between Cardiac Muscles and Skeletal is that these consist of striated cells that are electrically connected by intercalated discs.  They can also generate action potentials without neural input. 16

Locomotion Swimming- Overcoming friction is a major problem for swimmers. Gravity is less of a problem for swimming animals than for those that move on land or fly. Locomotion on Land - Walking, running, hopping, or crawling on land requires an animal to support itself and to move against gravity.

Locomotion continued Flying- Flight requires that wings develop enough lift to overcome the downward force of gravity. Comparing Costs of Locomotion - Animals that are specialized for swimming spend less energy per meter traveled than equivalently sized animals specialized for flying or running.