14lecture Muscular System
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Transcript of 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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