intro to muscles

8/6/2019 Intro to Muscles

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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 !

intro to muscles

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