Transcript Muscular System

Muscular System
• As with the skeltal system most
of the
• muscular system also develops
from the
• mesodermal germ layer
• Smooth muscle develops from
splanchnic
• mesoderm which surrounds gut
/derivatives.
• • Cardiac muscle develops from
splanchnic
• mesoderm which surrounds the
heart tube.
TRUNK MUSCULATURE
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Skeletal muscle of the
trunk develops from
paraxial mesoderm
(which forms somites &
somitomeres)
• Somites differentiate
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Somites differentiate
into:1. Sclerotome → Axial
skeleton &
2. Dermomyotome →
a.Dermatome dermis
and subcut tissues & b.
Myotome segmental
muscles (& takes with it
FATE OF MYOTOME CELLS
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Myotome cells split
off, move to their
definitive locations, &
become elongated &
spindle shaped
(called myoblasts)
Many myoblasts fuse
to become
Multinucleated muscle fibres.
• Myofibrils appear
in
• cytoplasm.
• By 12/52 cross
• striations typical for
• skeletal muscle
• appear.
• Somites: form body wall musculature. It
forms a dorsal epimere & a
• ventral hypomere.
• The epimere forms the vertebral
extensors; while the hypomere forms
• the muscles of the body wall and limbs.
• Note the different innervation viz. dorsal
and ventral primary rami
Somitomeres
• same process in head and neck region i.e.
form myoblasts which will form extra
ocular eye muscles, face, larynx, tongue
etc
Head Musculature
Limb Musculature
• Condensation of mesenchyme near the
base of limb buds (7th week)
• Mesenchyme is derived from dorsolateral
cells of somites
• Migrate into limb bud to form the muscles
• Connective tissue dictates the pattern of
muscle formation
• Upper limb buds lie opposite the lower five
cervical and upper two thoracic segments
Limb Musculature
• Lower limb buds lie
opposite lower foua
lumbar and upper two
sacral segments
• There is a 180°
medial rotation of the
lower limb compared
to developing upper
limb (angle of flexion
differs)
Cardiac Muscle
• Develops from splanchnic mesoderm
surrounding the endothelial heart tube
• Myoblasts adhere to one another by
intercalated discs
• Myofibrils develop as in skeletal muscle
but do not fuse
• Few special bundles become visible
(Purkinje fibers)
Smooth Muscle
Clinical Correlations
INTRAEMBRYONIC COELOM
INTRAEMBRYONIC COELOM
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Appears as isolated spaces in the lateral
mesoderm
• In the 4th week, the spaces fuse to form
a single horseshoe-shaped (U-shaped)
cavity
• The coelom divides the lateral
mesoderm into:
1. Somatic (parietal) layer: under ectoderm
2. Splanchnic (visceral) layer: over
endoderm
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Somatopleure = somatic mesoderm +
overlying ectoderm
Splanchnopleure = splanchnic
mesoderm + underlying endoderm
INTRAEMBRYONIC COELOM
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DERIVATIVES: It gives rise to three
body cavities:
1. A pericardial cavity: the curve of U
2. Two pericardioperitoneal canals
(future pleural cavities): the proximal
parts of the limbs of U
3. Two peritoneal cavities: the distal
parts of the limbs of U
• Each cavity has a parietal layer
(derived from somatic mesoderm) & a
visceral layer (derived from visceral
DEVELOPMENT OF
PERITONEAL CAVITY
• Major part of intraembryonic coelom
• Develop from the distal parts of the
limbs of the U-shaped cavity
• Originally, it is connected with
extraembryonic coelom (midgut
herniates to the outside through this
connection)
• At 10th week, it looses its connection
with extraembryonic ceolom (when
midgut returns to abdomen)
DEVELOPMENT OF
PERITONEAL CAVITY
• Originally, there were 2 peritoneal
cavities
• After lateral folding of embryo, the
peritoneum becomes a single cavity
HOW?
MESENTERIES
• A MESENTERY is a double layer of
peritoneum that begins as an extension
of the visceral peritoneum covering an
organ
• The mesentery connects the organ to
the body wall and transmits vessels
and nerves to it
• Transiently, the dorsal & ventral
mesenteries divide the peritoneal cavity
into right & left halves
• The ventral mesentery disappears
EXCEPT where stomach develops
PERICARDIAL CAVITY
• Develops from the curve of the Ushaped cavity
• During formation of head fold, the heart
& pericardial cavity move
ventrocaudally & become anterior to
the foregut (esophagus)
• It is bounded by an outer somatic & an
inner visceral layer, forming the serous
pericardium
PERICARDIAL CAVITY
• Originally, it is connected with the 2
pericardioperitoneal canals
• Later on, it become separated from the
2 pericardioperitoneal canals
HOW?
PERICARDIAL CAVITY
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Originally, the bronchial buds are
small relative to the heart
• Bronchial buds grow laterally into
pericardioperitoneal canals (future
pleural cavities)
• Pleural cavities expand ventrally
around heart & splits mesoderm into:
1. Outer layer: forms thoracic wall
2. Inner layer: pleuropericardial
membrane
PLEUROPERICARDIAL
MEMBRANES
• THE PARTS SURROUNDING THE
SEROUS PERICARDIUM: form the
fibrous pericardium
• THE PARTS BEHIND THE HEART: fuse
with the ventral mesentery of the
esophagus (at 7th week), forming the
mediastinum & separating pericardial
from pleural cavities
• N.B.: The right pleural cavity separates
from pericardial cavity earlier than left
PLEURAL CAVITIES
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Develop from the 2 pericardiperitoneal
canals
• Originally, they are connected with
pericardial & peritoneal cavities
• Later on, they become separated
from:
1. Pericardial cavity
2. Peritoneal cavity (HOW?)
PLEUROPERITONEAL
MEMBRANES
• Produced when developing lungs &
pleural cavities expand into the body
wall
• During 6th week, they fuse with dorsal
mesentery of esophagus & septum
transversum, separating pleural
cavities from peritoneal cavity
• N.B.: The right pleural cavity separates
from peritoneal cavity earlier than left
DEVELOPMENT OF
DIAPHRAGM
DEVELOPMENT OF
DIAPHRAGM
• The diaphragm develops from:
1. Septum transversum: forms the
central tendon
2. Dorsal mesentery of esophagus:
forms the right & left crus
3. Muscular ingrowth from lateral body
wall: posterolateral part (costal part)
4. Pleuroperitoneal membranes: small
portion of diaphragm
SEPTUM TRANSVERSUM
• At 3rd week, it is in the form of mass of
mesodermal tissue in the cranial part of
embryo (opposite the 3rd, 4th & 5th
cervical somites)
• At 4th week (during formation of head
fold), it moves ventrocaudally forming a
thick incomplete partition between
thoracic & abdominal cavities
• At 6th week, it expands & fuse with
dorsal mesentery of esophagus &
pleuroperitoneal membranes to form
INNERVATION OF
DIAPHRAGM
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Myoblasts from 3rd, 4th & 5th cervical
somites migrate into diaphragm &
bring their nerve fibers from them
• Nerve fibers derived from ventral rami
of 3rd, 4th & 5th cervical nerves fuse to
form phrenic nerve that elongate to
follow the descent of diaphragm
1. Both motor & sensory supply of the
diaphragm is derived from phrenic
nerve
2. The part of diaphragm derived from
lateral body wall receives sensory
ANOMALIES OF DIAPHRAGM
1. CONGENITAL DIAPHRAGMATIC
HERNIA
2. EVENTRATION OF DIAPHRAGM
3. CONGENITAL HIATAL HERNIA
CONGENITAL
DIAPHRAGMATIC HERNIA
CONGENITAL
DIAPHRAGMATIC HERNIA
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A posterolateral defect of diaphragm
Cause: defective formation and/or
fusion of pleuroperitoneal membrane
with other parts of diaphragm
• Effects:
1. Herniation of abdominal contents into
thoracic cavity
2. Peritoneal & pleural cavities are
connected with one another
• The defect usually occurs in the left
side (WHY?)
EVENTRATION OF
DIAPHRAGM
EVENTRATION OF
DIAPHRAGM
• Cause: failure of muscular tissue from
body wall to extend into
pleuroperitoneal membrane on one
side
• Effects: superior displacement of
abdominal viscera (surrounded by a
part of diaphragm forming a pocket)
CONGENITAL HIATAL
HERNIA
• Herniation of part of the stomach
through a large esophageal hiatus
(opening)
Reference
• clanatomy.ukzn.ac.za/...Embryology/EMB
RYOLOGY_OF_MUSCULAR
• HENRY Gray 1821-1865 anatomy of the
human body.
• http://www.youtube.com/watch?v=8VFAF_
piggl
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