Support and Locomotion

Muscles Muscles work by contracting: getting smaller in size Three types of muscles Skeletal (Striated, voluntary) Cardiac (Heart) Smooth (Involuntary)

Skeletal Muscle Called striated because of how it looks Responsible for voluntary actions Human body has over 700 different skeletal muscles (this makes up ~35% to 45% of the total body weight!) SkM contracts by having two proteins, actin and myosin, slide past each other

Skeletal Muscle The sarcomere is the functional unit of muscle contraction Thin filaments consist of two strands of actin and one tropomyosin coiled about each other Thick filaments consist of myosin molecules

Actin (thin filament) and myosin (thick) slide past each other Myosin has little “feet” called cross-bridges

Skeletal Muscle At rest, tropomyosin blocks the myosin binding sites on actin

Skeletal Muscle When Ca2+ binds to the troponin complex, a conformational change results in the movement of the tropomyosin- tropinin complex and exposure of actin’s myosin binding sites

Skeletal Muscle Using ATP, cross-bridges from myosin “grab” binding sites on actin and pull the filaments closer This action occurs over and over until the muscle fiber is completely contracted

Muscles are controlled by the Nervous System Action potentials run along a neuron until they reach a synapse, where they release neurotransmitters (ACh) Once at the muscle cells, the action potential releases Ca2+ from the sarcoplasmic reticulum The Ca ions allow the proteins on the actin and myosin to bind, forming the cross-bridges

Cardiac Muscles Cardiac muscles are those that power the heart Very similar to SkM, except CM is controlled by the SA node, not a motor neuron

Smooth Muscles SmM surround blood vessels and most hollow organs: uterus, bladders, GI tract Most SmM contraction is slow and sustained, sometimes rhythmic (peristalsis)

Smooth Muscles SmM contraction can be initiated by stretching, hormones, or the nervous system Most are involuntary, but some can be controlled (urinary bladder)

ATP Large amounts of ATP are required for muscle contraction AND relaxation Breaks/reforms connections between actin and myosin Powers pumps that return Ca2+ to the sarcoplasmic reticulum

Rigor mortis Stiffening of muscles after death Muscles run out of ATP after death Connection between actin and myosin cannot be broken – muscle remains contracted After ~72 hours, relaxation occurs because of decomposition

Skeletons What do skeletons do? Provide the framework for support of the body Three basic types: Hydrostatic Skeleton Exoskeleton Endoskeleton

Hydrostatic Skeletons fluid pressure provides support (Cnidarians, Annelids)

Exoskeleton Encase the bodies of Arthropods (insects, crustaceans, and arachnids) Made of proteins, chitin, or are calcareous Thin exoskeleton where the animal needs to bend or move

Crustacea, Molluska, and Insecta

Endoskeleton Found in Echinoderms, Chordates, and Sponges Serve several functions for vertebrates: Supports body and protects internal organs Used as muscle attachment sites to allow locomotion

Produce blood parts (RBC’s, WBC’s, and platelets Serve as storage sites for Calcium and Phosphorus Some even aid in sensory transduction (hammer, anvil, and stirrup of the middle ear)

Cartilage Consists of chondrocytes embedded in a collagen/elastin matrix Located at ends of long bones and between vertebrae Functions as shock absorber

Bones Compact bone provides strength and rigidity as well as attachment sites for muscles Spongy bone is very porous; site where blood cells are produced (bone marrow)

How does the body move? Muscles work in antagonistic pairs One always extends (bends out) while the other always flexes (bends in)

How does the body move? A muscle attaching two bones is attached to one fairly immovable bone (origin) and one that moves (insertion) Tendons connect muscle to bone Ligaments connect bone to bone

Joints are where two bones meet Three basic types of joints: Fixed: Skull Hinge: Elbows and knees Ball-and-Socket: Shoulders and hips

Arthritis (joint inflammation) Osteoarthritis (“wear-and-tear” arthritis) Cartilage covering the ends of bones slowly wears away, causing stiffness and soreness Rheumatoid arthritis Autoimmune disease in which the body’s immune system attacks the synovial membranes