14lecture muscular system

7/27/2019 14lecture Muscular System

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Muscular system

Dr.Eman Khammas ALsadi

Embryology lacturer


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Muscular System

the muscular system develops from the mesodermal germlayer and consist of

1. Skeletal.

2. Smooth.

3. cardiac muscle.

With the exception of some smooth muscle tissue

Skeletal muscle is derived from paraxial mesoderm,

which forms

1-somites from the occipital to the sacral regions

2-somitomeres in the head.


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Smooth muscle differentiates from1. visceral splanchnic mesoderm surrounding the gut and its

derivatives

2. and from ectoderm (pupillary, mammary gland, and sweatgland muscles).

Cardiac muscle is derived from

visceral splanchnic mesoderm surrounding the heart tube.


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STRIATED SKELETAL MUSCULATUREHead musculatureis derived from seven somitomeres, from paraxial

mesoderm

somites, will give rise to Musculature of the1- axial skeleton 2-body wall 3-andlimbs

somites, which initially form as somitomeres and extend from the occipital regionto the tail bud.

Immediately after segmentation, these somitomeres undergo a process ofepithelization and form a ball of epithelial cells with a small cavity in thecenter


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Sclerotomethe bone-forming cells arise from the ventral region of each somite when

becomes mesenchymal again and forms the sclerotome

dermatome

Cells in the upper region of the somite form the dermatomeand two muscle-forming areas at the ventrolateral (VLL) and dorsomedial

(DML) lips (or edges), respectively


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Cells from these two areas migrate and proliferate to formprogenitor muscle cells ventral to the dermatome, therebyforming the

dermomyotome

. Some cells from the ventrolateral region also migrate intothe adjacent parietal layer of the lateral plate mesoderm


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they form

1. infrahyoid,

2. abdominal wall muscles

3. and limb muscles.

The remaining cells in the myotome form

1. muscles of the back,2. shoulder girdle,

3. and intercostal muscles


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lateral somitic frontierInitially, there is a well-defined

border between each somiteand the parietal layer of lateralplate mesoderm called thelateral somitic frontier

This frontier separates twomesodermal domains in theembryo:

(1) the primaxial domain thatcomprises the region aroundthe neural tube and containsonly somite-derived (paraxialmesoderm) cells

(2) the abaxial domain thatconsists of the parietal layer oflateral plate mesoderm togetherwith somite cells that havemigrated across the lateral

somitic frontier

b i l l


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abaxial muscleprecursors

Muscle cells that

1. cross this frontier from theventrolateral edge of themyotome) and enter the lateralplate mesoderm

2. receive many of theirsignalsfor differentiation from lateralplate mesoderm

primaxial muscle cellprecursors

those that remain in the paraxialmesoderm and

1. do not cross the frontier

2. and receive many of theirdevelopmental signals fromthe neural tube and notochord

E h t i it i ti f i l


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Each myotome receives its innervation from spinal nervesderived from the same segment as the muscle cells.Regardless of their domain

The lateral somitic frontierdefines

1. the border of dermis derived from dermatomes in theback

2. and dermis derived from lateral plate mesoderm in the

body wall.3. It also defines a border for rib development with the bony

components of each rib derived from primaxialsclerotome cells and the cartilaginous parts of those ribs(abaxial cells).


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INNERVATION OF AXIAL SKELETAL

MUSCLES

The new description of muscle development characterized by

1. primaxial

2. abaxial domains

is based on the actual embryological origin of muscle cellsand not their innervation.

The epaxial (above the axis) muscles (back muscles) areinnervated by dorsal primary rami, whereas

hypaxial (below the axis) muscles (body wall and limbmuscles) are innervated by ventral primary rami


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Cross section through half the embryo showing innervation to

developing musculature. Epaxial (true back muscles) are innervated by

dorsal (posterior) primary rami. Hypaxial muscles (limb and body wall)

are innervated by ventral (anterior) primary rami.

D i diff i i


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During differentiation,1) In somits : the precursor cells ( myoblasts), fuse and form long,

multinucleated muscle fibers. Myofibrils soon appear in thecytoplasm. by the end of the third month, cross-striations, typical ofskeletal muscle, appear.

2) A similar process occurs in the seven somitomeres in the headregion. Somitomeres never segregate into sclerotome anddermomyotome segments.

3) Tendons for the attachment of muscles to bones are derived fromsclerotome cells

4) The transcription factorSCLERAXIS regulates development of thesecells.


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Drawing showing musculature in the head and neck derived from somitomeres

and myotomes that form from the occipital region caudally in a 7-week

embryo.

P tt f l f ti t ll d b


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Patterns of muscle formation are controlled byconnective tissue into which myoblasts migrate.

In the head region,

these connective tissues are derived from neural crest cells;

in cervical and occipital regions,

they differentiate from somitic mesoderm;

and in the body wall and limbs,

they originate from the parietal layer of lateral platemesoderm.


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HEAD MUSCULATURE

All voluntary muscles of the head region are derived fromparaxial mesoderm including the tongue and the eyes

(except )1. that of the iris, which is derived from ectoderm),

2. and that associated with the pharyngeal (visceral) arches

Patterns of muscle formation in the head are directed byconnective tissue elements derived from neural crest

cells.


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LIMB MUSCULATURE

in the seventh week of development limb start as acondensation of mesenchyme near the base of the limb

buds which is derived from DLC of the somites

the pattern of muscle formation is derived from the parietal

layer of lateral plate mesoderm, which also gives rise to the

bones of the limb.the radial nerve,

which supplies the extensor musculature, is formed by a

combination of the dorsal segmental branches,

whereas the ulnar and median nerves, which supply theflexor musculature, are formed by a combination of the

ventral branches


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Spinal nerves

1)play an important role in differentiation and motor

innervation of the limb musculature

2)also provide sensory innervation for the

dermatomes.


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Forelimbs with their dermatome

segments indicated.


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CARDIAC MUSCLE

Cardiac muscle develops from splanchnic mesodermsurrounding the endothelial heart tube.

1-Myoblasts adhere to one another by special attachmentsthat later develop into intercalated discs.

2- Myofibrils develop as in skeletal muscle,

3- but myoblasts do notfuse.

4- During later development, the Purkinje fibers, form theconducting system of the heart


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SMOOTH MUSCLE

1) Smooth muscle for the dorsal aorta and large arteries isderived from lateral plate mesoderm and neural crest

cells.

2) In the coronary arteries, smooth muscle originates fromproepicardial cells and neural crest cells (proximalsegments).

3) Smooth muscle in the wall of the gut and gut derivativesis derived from the splanchnic layer of lateral platemesoderm that surrounds these structures.

4) Only the sphincter and dilator muscles of the pupil andmuscle tissue in the mammary and sweat glands arederived from ectoderm.

5) Serum response factor (SRF) is a transcription factorresponsible for smooth muscle cell differentiation.


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Clinical CorrelatesPartial or complete absence of a muscle is common

e.g :the palmaris longus serratus anterior,or quadratusfemoris muscles.

Poland sequence A more serious defect occurs in1\20,000 individuals and is characterized by

1. absence of the pectoralis minor and partial loss of thepectoralis major (usually the sternal head) muscles

2. The nipple and areola are absent or displaced,

3. digital defects (syndactyly [fused digits] and brachydactyly[short digits]) on the affected side.

4. The disfiguring nature of the defects can be problematic,especially in females because of breast development


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Poland

sequence.

The pectoralis

minor and part of

the pectoralis

major musclesare missing on

the patient's left

side.

Notedisplacement of

the nipple and

areola.


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prune belly syndrome :

1) Partial or complete absence of abdominal musculature,Usually, the abdominal wall is so thin that organs are

visible and easily palpated.

2) This defect is associated with malformations of the urinarytract and bladder, including urethral obstruction.

3) These defects cause an accumulation of fluid that distendsthe abdomen, resulting in atrophy of the abdominalmuscles.

.


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Prunebellysyndrome:a distended

abdomen

from

atrophy of

abdominal

wallmusculatur

e.

Muscular dystrophy


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Muscular dystrophy1) is the term for a group of inherited muscle diseases

2) cause progressive muscular wasting and weakness.

3) There are a large number of these types of diseases of

which4) Duchenne's muscular dystrophy (DMD) is the most

common.

5) The disease is inherited as X-linked recessive such thatmales are much more often affected than females.

6) Both Duchenne's muscular dystrophy and Becker'smuscular dystrophy are caused by mutations in the genefor dystrophin on the X chromosome


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8 Infant with

arthrogryposis

(congenitaljoint

contractures).


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Arthrogryposis or congenital joint contractures

1. usually involves more than one joint

2. and may be caused by neurological defects (motor

horn cell deficiency, meningomyelocele),

3. muscular abnormalities (myopathies, muscle

agenesis),

4. joint and contiguous tissue problems (synostosis,

abnormal development),

5. and fetal crowding and constraint (multiple births,

oligohydramnios).


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14lecture muscular system

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