Types of Skeletal Muscle

Report
Muscle Tissue
Mamoun Kremli
Al-Maarefa College
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
Muscle Tissue Types
Skeletal Muscle - Units
Muscle
Fascicle
Fiber
Skeletal Muscle - Coverings
Epimysium
surrounds whole
muscle
Epimysium
surrounds whole
muscle
Skeletal Muscle - Coverings
Perimysium
Perimysium is around fascicle
Skeletal Muscle - Coverings
Endomysium
Endomysium is around each muscle fiber
Skeletal Muscle - Coverings
• Epimysium, Perimysium, Endomysium
Skeletal Muscle - Coverings
Skeletal Muscle – Blood Supply
• Muscles must have plenty of blood supply
• High demand for O2 and nutrients
Vessels injected with plastic material
Skeletal Muscle
•
•
•
•
Voluntary movement
Long and cylindrical
Transverse striations
Each fiber is multinuclear
(multinucleated cells –
embryonic cells fuse)
• 40% of body weight
Skeletal Muscle
Figure 4.14a
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 bands (dark-stained)
• I bands (light-stained)
• Z lines
A bands
I bands
Z line
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 Structure
Bloom W, Fawcett DW: A Textbook of Histology, 9th ed, Saunders
Skeletal Muscle – Sarcomere structure
Bloom W, Fawcett DW: A Textbook of Histology, 9th ed, Saunders
The Thin Filament - Actin
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)
titin_____
______actin
_____________myosin
Sliding Filament Model
__relaxed sarcomere__
_partly contracted_
fully contracted
Sarcomere shortens
because actin pulled
towards its middle by
myosin cross bridges
Titin resists overstretching
“A” band constant
because it is caused
by myosin, which
doesn’t change
length
Sliding Filament Model
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 nerve
signal: this initiates
calcium ion release
and muscle contraction
Neuromuscular Junction
• Motor Unit: a motor neuron and all the
muscle fibers it innervates (these all contract
together)
Motor Unit
Motor Unit
Motor End-plate
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
• Striations
• Involuntary
• One nucleus
– Deep center
• Heart muscle
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
Cardiac Muscle
Figure 4.14b
Cardiac Muscle
Cardiac Muscle
Cardiac Muscle
Cardiac Muscle
Smooth muscle
6 major locations:
•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
1. inside the eye 2. walls of vessels 3. respiratory tubes
4. digestive tubes 5. urinary organs 6. reproductive organs
Smooth Muscle
•
•
•
•
•
Spindle shaped
Not striated
Single nucleus
Involuntary movement
Internal organs
Smooth Muscle
Smooth Muscle
• Centrally located nucleii
Smooth Muscle
• Cells are surrounded by a net of reticular
fibers
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.
Summary
Some sites showing animations
of muscle contraction
• http://entochem.tamu.edu/MuscleStrucContr
actswf/index.html
• http://www.brookscole.com/chemistry_d/tem
plates/student_resources/shared_resources/a
nimations/muscles/muscles.html

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