muscle histology
DESCRIPTION
Muscle Histology. Functions of muscle tissue. Movement Joint stabilization Heat generation. Special functional characteristics of muscle. Contractility ability to shorten and thicken (when muscles work they contract that is they get shorter and thicker) Excitability - PowerPoint PPT PresentationTRANSCRIPT
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Muscle Histology
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Functions of muscle tissue Movement
Joint stabilization
Heat generation
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Special functional characteristics of muscle
Contractility ability to shorten and thicken (when muscles
work they contract that is they get shorter and thicker)
Excitability ability to respond to stimulus
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Special functional characteristics of muscle
Extensibilityability to stretch (when muscle is relaxed it
becomes longer and thinner) *some muscles work while others relax *
Elasticityability to return to original length
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Types of Muscle Tissue
Skeletal muscle
Cardiac muscle
Smooth muscle
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Types of Muscle TissueSkeletal
•Attach to and move skeleton•40% of body weight•Fibers = multinucleate cells (embryonic cells fuse)•Cells with obvious striations•Contractions are voluntary
Cardiac: only in the wall of the heart
•Cells are striated•Contractions are involuntary (not voluntary)
Smooth: walls of hollow organs•Lack striations•Contractions are involuntary (not voluntary)
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Similarities…
Their cells are called fibers because they are elongated
Contraction depends on myofilamentsActinMyosin
Plasma membrane is called sarcolemmaSarcos = fleshLemma = sheath
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Skeletal muscle
Epimysium: surrounds whole muscle
Perimysium is around fascicle
Endomysium is around each muscle fiber
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Skeletal Muscle
AttachmentsTendon ~ strong, tough connective
tissue cord, connect muscle to bone *Achilles Tendon (attaches to calf muscle and heel bone) *lumbodorsal fascia (surrounds the deep muscles of the back and trunk)
Origin: the less movable attachment
Insertion: the end of the muscle that attaches to a bone that moves
-where the muscle ends Usually one bone moves while the
other remains fixedNote: origin and insertion may
switch depending on body position and movement produced
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Attachments continued
Many muscles span two or more jointsCalled biarticular or multijoint musclesCause movements at two joints
Direct or “fleshy” attachmentsAttachments so short that muscle appears to
attach directly to bone Indirect: connective tissue extends well
beyond the muscle (more common)Tendon: cordlike (most muscles have tendons)Aponeurosis: flat sheetRaised bone markings where tendons meet
bones○ Tubercles, trochanters, crests, etc.
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Skeletal muscle Fibers (each is one
cell) have striations Myofibrils are
organelles of the cell: these are made up of filaments
SarcomereBasic unit of
contractionMyofibrils are long
rows of repeating sarcomeres
Boundaries: Z discs (or lines)
This big cylinder is a fiber: 1 cell -an organelle
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Myofibrils Made of three types of filaments (or
myofilaments):Thick (myosin)Thin (actin)Elastic (titin)
______actin_____________myosin
titin_____
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Sliding Filament Model__relaxed sarcomere__ _partly contracted_
fully contracted
“A” band constant because it is caused by myosin, which doesn’t change length
Sarcomere shortens because actin pulled towards its middle by myosin cross bridges
Titin resists overstretching
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Another pic
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EM (electron microscope): parts of 2 myofibrils
Labeled and unlabeled
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Sarcoplasmic reticulum Tubules surround myofibrils Cross-channels called “terminal cisternae” Store Ca++ and release when muscle stimulated to contract To thin filaments triggering sliding filament mechanism of contraction T tubules are continuous with sarcolemma, therefore whole muscle
(deep parts as well) contracts simultaneously
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Some sites showing animations of muscle contraction
http://entochem.tamu.edu/MuscleStrucContractswf/index.html
http://www.brookscole.com/chemistry_d/templates/student_resources/shared_resources/animations/muscles/muscles.html
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Types of skeletal muscle fibers Fast, slow and intermediate Whether or not they predominantly use oxygen to
produce ATP (the energy molecule used in muscle contraction) Oxidative – aerobic (use oxygen) Glycolytic – make ATP by glycolysis (break down of
sugars without oxygen=anaerobic) Fast fibers: “white fibers” – large, predominantly
anaerobic, fatigue rapidly (rely on glycogen reserves); most of the skeletal muscle fibers are fast
Slow fibers: “red fibers” – half the diameter, 3X slower, but can continue contracting; aerobic, more mitochondria, myoglobin
Intermediate: in between
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A skeletal muscle contracts when its motor units are stimulated
Amount of tension depends on1. the frequency of stimulation2. the number of motor units involved
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Muscle hypertrophy Weight training (repeated intense workouts): increases diameter and
strength of “fast” muscle fibers by increasing production of○ Mitochondria○ Actin and myosin protein○ Myofilaments containing these contractile proteins○ The myofibril organelles these myofilaments form
Fibers enlarge (hypertrophy) as number and size of myofibrils increase[Muscle fibers (=muscle cells) don’t increase in number but increase in diameter producing large muscles]
Muscle atrophy: loss of tone and mass from lack of
stimulation Muscle becomes smaller and weaker
Note on terminology: in general, increased size is hypertrophy; increased number of cells is hyperplasia
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Cardiac muscle
Bundles form thick myocardium
Cardiac muscle cells are single cells (not called fibers)
Cells branch Cells join at intercalated
discs 1-2 nuclei in center Here “fiber” = long row of
joined cardiac muscle cells Inherent rhythmicity: each
cell! (muscle cells beat separately without any stimulation)
Intercalated disc__________
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Smooth muscle•Muscles are spindle-shaped cells•One central nucleus•Grouped into sheets: often running perpendicular to each other•Peristalsis•No striations (no sarcomeres)•Contractions are slow, sustained and resistant to fatigue•Does not always require a nervous signal: can be stimulated by stretching or hormones
6 major locations: 1. inside the eye 2. walls of vessels 3. respiratory tubes 4. digestive tubes 5. urinary organs 6. reproductive organs