Post on 17-Dec-2015
Objectives• Identify basic structure of Muscles• Recognize types of muscular tissues and the
difference between them• Recognize the relation between structure and
function of various muscular tissues
Tissues • Four fundamental tissues are recognized:– Epithelial tissue– Connective tissue– Muscular tissue– Nervous tissue
Muscle Tissue - Characteristics• Cells are referred to as fibers because they are
elongated• Contracts or shortens with force when
stimulated• Contraction depends on myofilaments– Actin– Myosin
• Plasma membrane is called sarcolemma– Sarcos = flesh– Lemma = sheath
Special functional characteristics• Contractility– Only one action: to shorten– Shortening generates pulling force
• Excitability– Nerve fibers cause electrical impulse to travel
• Extensibility– Stretch with contraction of an opposing muscle
• Elasticity– Recoils passively after being stretched
Muscle Tissue Types• Skeletal:– attached to bones
• Cardiac:– muscle of the heart
• Smooth:– muscles associated with tubular structures and
with the skin
Skeletal Muscle – Blood Supply
Vessels injected with plastic material
• Muscles must have plenty of blood supply• High demand for O2 and nutrients
Skeletal Muscle• Voluntary movement• Long and cylindrical• Transverse striations• Each fiber is multi-
nuclear(multinucleated cells – embryonic cells fuse)
• 40% of body weight
Skeletal Muscle• Large, elongated, multinucleated fibers. • Nucleii are in periphery of cells, just under cell
membrane
Skeletal Muscle• A band (dark-stained)• I band (light-stained)• Z line
A band
I band
Z line
Giemsa stain
Skeletal Muscle• A-band (actin & myosin )• I-band( actin only)• Z lines(attachment of
actin)• H-band(myosin only)• M-line (Myomesin,
creatine kinase)
Skeletal Muscle Structure• Invaginations of the T system
at transition between A and I bands (twice in every sarcomere)
• They associate with terminal cisternae of the sarcoplasmic reticulum (SR)(which is the specialized calcium-storing smooth endoplasmic reticulum).
• Abundant mitochondria is present between myofibrils.
Skeletal Muscle – Sarcomere structure
Bloom W, Fawcett DW: A Textbook of Histology, 9th ed, Saunders
Skeletal muscle• Fibers have striations• Myofibrils are
organelles of the cell: these are made up of filaments
• Sarcomere– Basic unit of contraction– Myofibrils are long rows
of repeating sarcomeres– Boundaries: Z discs (or
lines)
-an organelle
Myofibrils• Made of three types of filaments (or
myofilaments):– Thick (myosin)– Thin (actin)– Elastic (titin)
______actin_____________myosin
titin_____
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
Sarcoplasmic reticulum is smooth ER• Tubules surround myofibrils• Cross-channels called “terminal
cisternae”• Store Ca++ and release when
muscle stimulated to contract• Two thin filaments triggering
sliding filament mechanism of contraction
• T tubules are continuous with sarcolemma, therefore whole muscle (deep parts as well) contracts simultaneously
Neuromuscular Junction• Motor neurons innervate muscle fibers• Motor end plate is where they meet• Neurotransmitters are
released by nervesignal: this initiatescalcium ion releaseand muscle contraction
Neuromuscular Junction• Motor Unit: a motor neuron and all the
muscle fibers it innervates (these all contract together)
Types of Skeletal Muscle:Type I fibres (red fibres). • Red muscles (large amounts of myoglobin and
mitochondria). Type II fibres(white fibers). • White muscles (less amounts of myoglobin and
mitochondria). Type III Fibres (Intermediate).• Have characteristics between type I & II In
humans, skeletal muscles are composed of mixtures of these 3 types of fibres.
• Red muscles are used when sustained production of force is necessary, e.g. in the control of posture.
• White muscles are for rapid accelerations and short lasting maximal contraction e.g. extraocular muscles of the human eye)
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• Rhythmicity: • More T-Tubules
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
Smooth Muscle• Cytoplasmic filaments
insert on dense bodies located in the cell membrane and deep in the cytoplasm.
• Contraction of these filaments decreases the size of the cell and promotes the contraction of the whole muscle.
• During the contraction the cell nucleus is deformed.
Smooth Muscle• A rudimentary sarcoplasmic reticulum is present • T tubules are not present in smooth muscle cells.• Caveoli(look like pinocytotic or endocytotic vesicles)
function like T tubules.• Contains thin filaments made of actin and
tropomyosin and thick filaments made of myosin• Intermediate filaments (Desmin and Vimentin)• Dense bodies are 2 types • - Membranous(membrane associated) -Cytoplasmic• Both thin and intermediate filaments insert into
dense bodies.
Regeneration of Muscle Tissue• Injured cardiac fibers after childhood are replaced
by fibrous tissue.
• Injured skeletal fibers have limited potential for
regeneration. Satellite cells (Undifferentiated
myoblasts) within the basal lamina of skeletal
fibers become activated and proliferate and fuse
together to give new muscle fibers.
• Injured smooth fibers have active regenerative
activity.