Muscular Tissue Skeletal Cardiac Smooth Muscular (contractile) tissue is composed of cells called muscle fibers. Muscle fibers contain actin and myosin filaments; interactions result in animal movement. Three types of vertebrate muscle tissue are: Skeletal Cardiac Smooth

Microscopic Anatomy & Physiology Myofibrils are contractile portions of fibers that lie parallel and run length of fiber. Protein filaments: thick (made of myosin) thin (made of actin) Sarcomere has repeating bands of actin and myosin that occur between two Z lines in myofibril. I band contains only actin filaments. H zone contains only myosin filaments. Anatomy of skeletal muscle2.ram

Sliding Filament Model As a muscle fiber contracts, sarcomeres within myofibrils shorten. As sarcomere shortens, actin filaments slide past myosin; I band shortens and H zone disappears. Sliding filament theory: actin filaments slide past myosin filaments because myosin filaments have cross- bridges that pull actin filaments inward, toward their Z line.

Sliding Filament Model Contraction process involves sarcomere shortening, filaments themselves remain same length. ATP supplies energy for muscle contraction. Myosin filaments break down ATP to form cross- bridges that attach to and pull actin filament.

Muscular Contraction Ca2+ ions bind to troponin, which causes tropomyosin threads to shift position. Change in structure of tropomyosin exposes myosin heads with ATP binding sites. The myosin heads function as ATPase enzymes, splitting ATP into ADP + P After attaching to actin filaments, myosin cross-bridges bend forward, actin filament is pulled along.

Muscular Contraction While ATP and Ca2+ ions are available, cross-bridges attach; as ADP + P are released, the cross-bridges change their positions and cause a power stroke as filaments pull together. When another ATP molecule binds to myosin head, cross- bridge detaches and the cycle begins again. When nerve impulses cease, active transport proteins in the sarcoplasmic reticulum pump calcium ions back into storage sites.

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Fast twitch & slow twitch muscles Slow twitch muscle fibers contract slowly, but keep going for a long time more mitochondria for aerobic respiration less SR  Ca2+ remains in cytosol longer long distance runner “dark” meat = more blood vessels Fast twitch muscle fibers contract quickly, but get tired rapidly store more glycogen for anaerobic respiration sprinter “white” meat

Diseases of Muscle tissue ALS amyotrophic lateral sclerosis Lou Gehrig’s disease motor neurons degenerate Myasthenia gravis auto-immune antibodies to acetylcholine receptors Stephen Hawking

Botox Bacteria Clostridium botulinum toxin blocks release of acetylcholine botulism can be fatal muscle

Rigor mortis no life, no breathing no breathing, no O2 no O2, no aerobic respiration no aerobic respiration, no ATP no ATP, no Ca2+ pumps Ca2+ stays in muscle cytoplasm muscle fibers continually contract tetany or rigor mortis eventually tissues breakdown & relax measure of time of death

Signal Transduction Pathway Fig. 49.2 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Sensory reception begins with the detection of stimuli by sensory receptors. Exteroreceptors detect stimuli originating outside the body. Interoreceptors detect stimuli originating inside the body. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Sensory Processing Transduction. Amplification. Transmission. The conversion of stimulus energy into a change in membrane potential. Amplification. The strengthening of stimulus energy that is can be detected by the nervous system. Transmission. The conduction of sensory impulses to the CNS. Integration. The processing of sensory information. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Sensory Receptors Mechanoreceptors respond to mechanical energy. Pain receptors = nocioceptors. Different types of pain receptors respond to different types of pain. Thermoreceptors respond to heat or cold. Respond to both surface and body core temperature. Chemoreceptors respond to chemical stimuli. Electromagnetic receptors respond to electromagnetic energy. Photoreceptors respond to the radiation we know as visible light. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

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