intro to muscles
TRANSCRIPT
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Dr. Maung Myint
muscles
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One of the basic essential property of an organism ability to react to the changes in their environment
Reaction may be
chemical
electrical mechanical ( movement )
cytoplasmic streaming
cilia
flagilla( containing actin and myosin protein)
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4 uniquecharacteristics ofmuscletissue
Excitability - ability to respond to stimuli by producingaction potential
Contractility - ability to contract when stimulated.
Elasticity - ability to return to its original length whentension is released.
Extensibility - ability to stretch without being damaged inresponse to the contraction of opposing muscle fibers.
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Functions of muscular tissue
Producing body movements walking and running
Stabilizing body positions
posture
Moving substances within the body heart muscle pumping blood moving substances in the digestive tract
Generating heat contracting muscle produces heat shivering increases heat production
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muscle Contractile apparatus containing A&M and also
specialized excitable plasma membrane capable ofinitiating cellular contraction
Developed mainly
fromthe meschymal tissue ( paraxial mesoderm, lateralplate mesoderm, splanchnopleuric mesoderm etc)
also from ectodermal tissue
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mesenchyme
myoblasts
smooth muscle cellsability to proliferate
Skeletal muscleproliferating myoblasts fuse and differentiate to form a
multinucleated muscle fibresatellite cells undifferentiate mucle precursor cells
cardiac myocytes
single or bi-nucleatedno myogenic stem cells in the cardiac muscle
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Skeletal muscle proliferating myoblasts fuse and differentiate to form amultinucleated muscle fibre satellite cells undifferentiate mucle precursor cells
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Development ofskeletalmuscle
during the fourth week of embryonic development mesodermal cells form thick blocks along each side
of the developing neural tube.
blocks, called paraxial mesoderm, form structures calledsomites.
sclerotome separates from the rest of the somite andgives rise to the vertebral skeleton
dermatome forms the connective tissue of the skin
myotome gives rise to the skeletal muscles
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Muscles
The three types of muscle
skeletal muscle smooth muscle and
cardiac muscle
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cardiacmuscle
STRIATED / BRANCHING
INTERCALATED DISC
INVOLUNTARY
e.g,muscles oftheheart
heart muscle
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functionalandstructuralcharacteristic
strong contraction, utilize great deal of energy
more resistant to fatigue
contractions are continuous, initiated by inherentmechanism though modulated by external autonomicand hormonal stimuli
rhythm (spontaneous contraction and relaxation)
specialized cardiac muscle fibers (Purkinjee fibres) form the conducting system of the heart.
cardiac muscle
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Musclecell
long cylindrical, one ( or most two ) centrally placed nuclei end of the fibres are split longitudinally into few branches, which
abut on similar branches of another cell ( syncytium ) intercalated disc delicate collagenous tissue in between, rich capillary network striations
cardiac muscle
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smoothmuscle
NO STRIATIONS / SMOOTH
INVOLUNTARY
e.g,
muscles ofthe GI tractmuscles of bloodvessels
muscles of bladder,uterus
smooth muscle
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capable ofslow sustainedcontraction
involuntary ( muscles may be made to contract ) by local stretching of fibres by nerve impulses from autonomic nerves by hormonal stimulation
arrangements in tubes that undergo peristalsis, ( GITmuscles,
ureter ) muscles are arranged in longitudinal and circular fashion
in viscera that undergo mass contraction ( bladder,uterus ) muscles are arranged in whorls and spiral fashion
smooth muscle
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long, spindle-shaped cells closely arranged in bundles or sheets. exhibit no striations (smooth muscle) found in the walls of
hollow viscera (e.g., the gastrointestinal tract, some of thereproductive tract, and the urinary tract),
blood vessels, larger ducts of compound glands, respiratory passages, and within the dermis of skin.
is not under voluntary control; regulated by the autonomicnervous system, hormones (such as bradykinins), and localphysiological conditions. involuntary muscle.
smoothmuscle
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smooth muscle
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striatedmuscle
Muscle fibre
single cell, elongated (long) cylinders ( 30cm in length)
fibres are arranged in bundle
connective tissue are present in between the fibres
( endomyseum, perimyseum, epimyseum )
possesses many hundreds of nuclei located at theperiphery within the cell membrane ( sarcolemma)
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Each skeletal muscle is composed of
muscle ( wrapped by epimysium ) containing bundles of fascicles
fascicle ( wrapped by perimysium ) made up of bundles of muscle fibers
muscle fiber ( wrapped by endomysium )
contain myofibrils. myofibrils
composed of myofilaments
skeletal muscle
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Skeletalmuscle
attached mainly to the bones / exceptions
contraction causes the movements of the skeleton voluntary muscles / innervated by somatic nerves
muscle fibers have characteristic alternating light anddark cross-bands. ( striations )
skeletal muscle
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cross one or more joints
contraction cause movements at these joints
exceptions:- subcutaneous muscles ( facial muscles) extraocular muscles
muscles associated with resp & digestive systems
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Muscles are attached either directly or by means of their
tendons, aponeurosis to bones, cartilages,ligaments or fascia
to organs
to skin
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Most skeletal muscles extend between bones and crossat least one movable joint.
Upon contraction, one of the bones moves while theother bone usually remains fixed.
Less movable attachment of a muscle is called its origin.(Origin typically lies proximal to the insertion.)
More movable attachment of the muscle is its insertion.( Insertion is pulled toward the origin. )
skeletal muscle
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originandinsertion
skeletal muscle
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S
keletalmusclesare classified according to
the way fascicles are organized, andtheir relationships to tendons.
fascicle arrangement4 patterns of fascicle arrangement are:
parallel pennate
convergent ( triangular ) circular
skeletal muscle
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arranged parallel to the long axis of the muscle.( fusiform muscle )e.g. sternocleidomastoid m, rectus abdominis m, sartorius m
a muscle shortens by one third to one half its resting lengthwhen it contracts,
the muscles whose fibers run parallel to the line of pull will bringabout a greater range of movement
skeletal muscle
Skeletalmuscle with parallel fibres
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multipennate muscle
arranged as a series of bipennate muscles lyingalongside one anothere.g., acromial fibers of the deltoid muscle
the tendon lying within its center and the musclefibers passing to it from all sides, converging asthey goe.g., tibialis anterior muscle
skeletal muscle
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The muscle has a broad origin, andits fibers converge on to a tendon
e.g. pectoralis major muscle
skeletal muscle
Muscle withcircularfibres
The muscle fibers are arranged incircular concentric circles.
e.g. sphincters, orbicularis oris muscle
Muscle withconverging fibres
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Blood supply supplied by the adjacent vessels
different pattern
Nerve supply supplied by one or more nerves containing both motor
and sensory fibres
(Skeletal muscle can not function without a nerve supply)
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Each skeletal muscle receives
motor
the motor nerve functions in eliciting contraction,
sensory the sensory fibers pass to muscle spindles.
in addition, there are autonomic fibers that supply thevascular elements of skeletal muscle.
skeletal muscle
Innervation ofaskeletalmuscle
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motorunit
Composed of a single motor neuron, the muscle fibers it controls, and the neuromuscular junctions between the motor
neuron and the muscle fibers.
Typically controls only some of the muscle fibers in anentire muscle.
Most muscles have many motor units. many motor neurons are needed to innervate an entire muscle
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The muscle fibers of a motor unit contract in unison andfollow all-or-none law of muscle contraction.
motorunit
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Neuromuscular junction
Where motor neuron meets muscle fiber
Components
Synaptic knob Synaptic vesicles
Acetylcholine (ACh)
Motor end plate ACh receptors
Synaptic cleft acetylcholinesterase
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If a muscle is devoid of nerve supply flaccid (loss of tone of a muscle fibre)
atrophy ( decrease in the size of m fibre )
spontaneous contractions ( fibrillation)
histological features are retained for years, thenm fibres are replaced by fat and conn tissue
If the nerve regenerates may regain fairly normal function
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All movements are the result of the
coordinated action of many muscles.
However, to understand a muscle's action it isnecessary to study it individually.
.
skeletal muscle
muscleaction
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Contraction
Isometric length of the muscle does not change because the
tension produced never exceeds the resistance (load)
tension is generated, but not enough to move the load
Isotonic tension produced exceeds the resistance (load), and
the muscle fibers shorten, resulting in movement
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Classification ofmuscles
According to the shape of the muscle
Quadrilateral muscle Strap muscle
Fusiform muscle
Digastric muscle
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According to the direction of muscle fibres muscle with parallel muscle fibres
e.g. sternomastoid m, rectus abdominis m, sartorius m
(force of contraction is great when
muscle fasciculi are arranged parallel to the line of pull )
muscle with oblique muscle fibres (Pennate muscles) Unipennate e.g. extensor digitorum longus m
Bipennate e.g. rectus femoris m
Multipennate muscles e.g. deltoid m, tibialis anterior m
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According to the number of heads of origin
biceps, triceps, quadriceps
According to the action flexors, extensors, rotators, levators
Combination of action and shape pronator quadratus
Combination of action and location flexor digitorum profundus, FD superficialis
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According to the function
Prime movers - A muscle or a group of muscles that directly brings about
the desired movement. Q femoris extension of knee jt
Antagonists - Muscles that directly oppose the movement under
consideration
Fixators - Muscles that stabilize joints or parts thereby maintain
posture or position while the prime movers act
Synergists - Special type of fixator muscles that prevent undesired
action at the intermediate joint & stabilize theintermediate joints
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axial muscles (60% of the bodys skeletal muscles) Axial muscles position the head and spinal column, and move the
rib cage
appendicular muscles (40%). Appendicular muscles support the pectoral and pelvic girdles,
and the limbs.
Others in case of limbs, muscles of anterior & posterior compartments
skeletal muscle
In relation to the body meridian
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Criteria fornaming ofmuscles
Names incorporate appearance, location, function,orientation, and unusual features
Names provide clues to their identification orientation of muscle fibers muscle attachments specific body regions muscle shape muscle size muscle heads/tendons of origin muscle function or movement muscle position at body surface
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Naming ofskeletalmuscles
The correct names of all muscles (except the platysma
and the diaphragm) include the word muscle.
We may use the descriptive term alone, but the word
muscle is always implied.
skeletal muscle
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Names ofskeletalmusclesinclude
descriptiveinformationabout:
1. Location in the body: identified by body regions
e.g. temporalis muscle
2.O
rigin and insertion the first part of the name indicates the origin the second part of the name indicates the insertion
e.g. genioglossus muscle
3. Fascicle organization describes the fascicle orientation within the muscle
e.g. rectus (straight), transversus, and oblique
skeletal muscle
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4. Relative position
externus (superficialis) are visible at the bodysurface
internus (profundus) are deep muscles extrinsic muscles are outside an organ
intrinsic muscles are inside an organ
5. Action muscles may be named after movements
(flexor, extensor, retractor, etc.) or common occupations and habits(e.g. risor = laughter)
skeletal muscle
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6. structural characteristics
number of heads, attachment (bi = 2, tri = 3) shape (trapezius, deltoid, rhomboidius) size
longus (long)
longissimus (longest) teres (long and round) brevis (short) magnus (large) major (larger) maximus (largest) minor (small) minimus (smallest)
skeletal muscle
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Description of a muscle
Muscles are usually described according to their
origin insertion
nerve supply
action
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Effects ofaging onskeletalmuscle
Slow, progressive loss of skeletal muscle mass begins as adirect result of increasing inactivity.
Size and power of all muscle tissues also decrease Lost muscle mass is replaced by either adipose or fibrous
connective tissue. Muscle strength and endurance are impaired. Decreased cardiovascular performance thus.
Increased circulatory supply to active muscles occurs much more slowly Tolerance for exercise decreases. Tendency toward rapid fatigue.
Muscle tissue has a reduced capacity to recover fromdisease or injury. Elasticity of skeletal muscle also decreases.
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Clinicalrelevance
Deformities
Contractures
Administration of drugs Exercise / stretching
Body building
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Thank you !