unit 4
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Unit 4. The Muscular System. Muscle Cells. There are 3 types of muscle cells Cardiac, Smooth, and Skeletal All muscles can contract (shorten) When muscles contract, part of the body moves. Cardiac Muscles. Striated, tubular, and branched Have one nucleus per cell Contract involuntarily - PowerPoint PPT PresentationTRANSCRIPT
Unit 4The Muscular System
Muscle CellsThere are 3 types of muscle cells– Cardiac, Smooth, and SkeletalAll muscles can contract (shorten)When muscles contract, part of the body moves
Cardiac MusclesStriated, tubular, and branchedHave one nucleus per cellContract involuntarilyFound in the walls of the heart
Smooth MusclesNon-striated, arranged in sheetsHave one nucleus per cell Contract involuntarily, and can sustain prolonged contractions
Smooth Muscles
Found in the walls of internal organs (cavities and tubes) such as:– Blood vessels, iris of the eye,
internal organs such as the stomach, intestines, uterus, and esophagus for peristalsis
Skeletal MusclesStriated and tubularHave many nuclei per cellAttached to the bones of the skeleton
Skeletal Muscles
Contract voluntarily, controlled consciously by the nervous systemDue to structure and having many nuclei they are referred to as fibres
Compare the muscle types!Type Structure Voluntary/
Involuntary?Location
in the Body
Cardiac
Smooth
Skeletal
Type Structure Voluntary/ Involuntar
y?
Location in the Body
Cardiac Tubular, arranged in a branched network, striated, one nucleus per cell
involuntary Heart
Smooth Long, tapered, arranged in sheets, non-striated, one nucleus per cell
involuntary Walls of digestive system, blood vessels, other internal organs
Skeletal Tubular, very long, striated, many nuclei per cell.
voluntary Attached to the bones of the skeleton,
Muscle ContractionMuscles contract they shorten!Muscles can only pull they cannot pushMuscles that permit movement are found in pairs, as each muscle in the relaxed state needs an opposite muscle to stretch it.Antagonistic muscles- pairs of muscles that work against each other to make a joint move
Muscle contraction – bundle of fibres
Skeletal muscles consist of many bundled muscle fibres held together with connective tissueMuscle fibre consists of: – Myofilaments a thread of
contractile proteins found within muscle fibres
Muscle Contraction - bundles of fibres
Two types of Myofilaments– Thick filament – fine myofilament
composed of bundles of protein called myosin. Each myosin molecule consists of two polypeptide chains wrapped around each other. Binds to actin
Two types of MyofilamentsThin filament – fine myofilament composed of strands of protein called actin. Consist of globular actin proteins. Binds to myosin
Myofilament ContractionFour steps:1. The myosin head is attached to actin
Myofilament Contraction2. The myosin head flexes, advancing the actin filament
Myofilament Contraction3. The myosin head releases and unflexes, powered by ATP.
Myofilament Contraction4. The myosin reattaches to actin farther along the fibre
Sliding Filament ModelActin is anchored in the striated muscle tissue called the Z-LineSince it is ‘anchored’ like this, when actin moves it drags the Z-line with it, toward the myosinThis causes the entire muscle to contract
Sliding Filament ModelThe heads of the two ends of the myosin filament are orientated in opposite directions. When the heads attach to the actin, they bend toward the centre of the myosin.
Sliding Filament ModelAs one end of the myosin filament draws the actin filament and its attached Z line toward the centre, the other end of the myosin filament does the same
Sliding Filament ModelBoth Z lines move toward the centre, and contraction occurs