Transcript Lecture - Tele Anatomy

• I seek protection of ALLAH against the
rejected Shaitan
• I seek refugee in ALLAH against the accused
Shaitan
• Most of the structures of head and neck
regions are derived from mesenchyme.
• The epidermis of skin develops from surface
ectoderm.
• Brain and spinal cord develop from neuroectoderm.
• Mesenchyme for the formation of head region
is derived from:
• 1. Neural Crest cells
• 2. Paraxial mesoderm
• 3. Lateral Plate mesoderm
• 4. Ectodermal Placodes
• Neural Crest cells form
• Facial and pharyngeal arch skeletal structures
and all other tissues in these regions including
cartilage, bone, dentin, tendon, dermis, pia
mater, arachnoid mater, sensory neurons,
glandular stroma and neurons of fifth,
seventh, ninth and tenth cranial sensory
ganglia.
• Paraxial mesoderm forms
• Floor of skull and a small portion of occipital
region, voluntary muscles of craniofacial
region, dermis and connective tissue in the
dorsal region of head and meninges caudal to
prosencephalon
• Lateral Plate mesoderm forms
• Laryngeal cartilages and connective tissue in
this region
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• Ectodermal Placodes forms
• Neurons of fifth, seventh, ninth and tenth
cranial sensory ganglia
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Pharyngeal apparatus
Arches
Pouches
Clefts
Membranes
• Most of the structures of head and neck
regions are derived from mesenchyme.
• Obviously the epidermis of skin develops from
surface ectoderm.
• Brain and spinal cord develop from neuroectoderm.
• Mesenchyme for the formation of head region
is derived from:
– Neural Crest cells
– Paraxial mesoderm
– Lateral Plate mesoderm
– Ectodermal Placodes
• Diagram showing skeletal structures of head and
neck.
•
• Structures developing from paraxial mesoderm
(somitomeres and somites) are colored green.
• Structures developing from lateral plate
mesoderm are colored blue.
• The rest of the structures develop from the
mesenchyme derived from neural crest cells.
• Neural Crest cells form
• Facial and pharyngeal arch skeletal structures
and all other tissues in these regions including
cartilage, bone, dentin, tendon, dermis, pia
mater, arachnoid mater, sensory neurons,
glandular stroma and neurons of fifth,
seventh, ninth and tenth cranial sensory
ganglia.
• Paraxial mesoderm forms
• Floor of skull and a small portion of occipital
region, voluntary muscles of craniofacial
region, dermis and connective tissue in the
dorsal region of head and meninges caudal to
prosencephalon
• Lateral Plate mesoderm forms
• Laryngeal cartilages and connective tissue in
this region
•
• Ectodermal Placodes forms
• Neurons of fifth, seventh, ninth and tenth
cranial sensory ganglia
• The pharyngeal or branchial apparatus
contributes greatly to the formation of head
and neck.
• Pharyngeal Apparatus consists of:
• Pharyngeal or branchial arches
• Pharyngeal or branchial pouches
• Pharyngeal or branchial clefts or grooves
• Pharyngeal or branchial membranes
• In humans, they develop during the fourth
week in utero as a series of mesodermal
outpouchings on the left and right sides of the
developing pharynx
• These grow and join in the ventral midline.
The first arch, is the first to form, separates
the mouth pit or stomodeum from
the pericardium.
• By differential growth the neck elongates and
new arches form, so the pharynx has six
arches ultimately.
• Each pharyngeal arch has a cartilaginous stick,
a muscle component which differentiates
from the cartilaginous tissue, an artery, and
a cranial nerve.
• Each of these is surrounded by mesenchyme.
Arches do not develop simultaneously, but
instead possess a "staggered" development.
• Pharyngeal pouches (or branchial pouches)
form on the endodermal side between the
arches, and pharyngeal grooves (or clefts)
form from the lateral ectodermal surface of
the neck region to separate the arches
• The pouches line up with the clefts, and these
thin segments become gills in fish.
• In mammals the endoderm and ectoderm not
only remain intact, but continue to be
separated by a mesoderm layer.
• More is known about the fate of the first arch
than the remaining four.
• The first three contribute to structures above
the larynx, while the last two contribute to
the larynx and trachea.
• The mesenchymal tissue is derived from two
sources:
• Paraxial and lateral plate mesoderm. This forms
the central core of mesenchymal tissue. It is
mesodermal mesenchyme. It will develop into
muscles and arteries of the respective arches.
• Neural crest cells. These migrate into the arches
and form the peripheral part of mesenchymal
tissue. It is ectodermal mesenchyme. The
cartilaginous bars of different arches develop
from it.
• First pair of pharyngeal arches plays a major role
in facial development.
• Two prominences or processes develop from first
pharyngeal arch.
• Maxillary process. It gives rise to maxilla (upper
jaw), zygomatic bone, and squamous part of the
temporal bone
• Mandibular process. It forms mandible and
sphenomandibular ligament
• Dorsal end of first arch forms ossicles of middle
ear.
• Following statements regarding first pharyngeal arch
are true EXCEPT:
• First pair of pharyngeal arches plays a major role in
facial development.
• Two (maxillary and mandibular) processes develop
from first pharyngeal arch.
• Maxillary process gives rise to maxilla, zygomatic bone,
and petrous part of the temporal bone A
• Mandibular process forms mandible and
sphenomandibular ligament
• Dorsal end of first arch forms ossicles of middle ear.
• The second pharyngeal arch forms upper part
of body of hyoid bone and lesser horn of hyoid
bone. So it is usually called hyoid arch.
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• Third pharyngeal arch forms lower part of
body and greater horn of hyoid bone.
• The pharyngeal arches support the ventrolateral wall of the primordial pharynx, which is
derived from the cranial part of the foregut.
4 components of arch
• An aortic arch, an artery that arises from the
truncus arteriosus of the primordial heart and
runs around the primordial pharynx to enter the
dorsal aorta
• A cartilaginous bar that forms the skeleton of the
arch
• A muscular component that forms muscles in the
head and neck
• A nerve that supplies the mucosa and muscles
derived from the arch
• The nerves grow into the arches from the
brain and are derived from neurectoderm.
• The cartilaginous bars develop from neural
crest cells.
• The muscles and arteries are derived from
local paraxial and lateral plate mesoderm.
• The muscles of different arches do not always
attach to the bony or cartilaginous components
of their own arch but sometimes migrate into
surrounding regions.
• The muscular components of each arch carry
their own nerve, and wherever the muscle cells
migrate, they carry their cranial nerve
components with them. Thus the origin of these
muscles can always be traced, since their nerve
supply comes from the arch of origin.
• The dorsal end of the first arch cartilage
(Meckel’s cartilage) is closely related to the
developing ear and forms two middle ear
ossicles (malleus and incus) and anterior
ligament of malleus.
• The middle part of the cartilage regresses, but
its perichondrium forms sphenomandibular
ligament.
• Ventral part of the first arch cartilages form
the horseshoe-shaped primordium of the
mandible and, by keeping pace with its
growth, guide its early morphogenesis (Hall,
1982).
• Each half of the mandible develops lateral to
and in close association with Meckel’s
cartilage.
• The cartilage disappears as the mandible
develops by intramembranous ossification.
• Some endochondral ossification occurs in the
median plane of the chin and in the
mandibular condyle.
• The dorsal end of the second arch cartilage
(Reichert cartilage), also closely related to the
developing ear, ossifies to form the stapes of
the middle ear and the styloid process of the
temporal bone.
• The part of the cartilage between the styloid
process and hyoid bone regresses; its
perichondrium forms the stylohyoid ligament.
• The ventral end of the second arch cartilage
ossifies to form the lesser cornu or horn of
hyoid bone and the superior part of the body
of the hyoid bone.
• The third arch cartilage, located in the ventral
part of the arch, ossifies to form the greater
cornu and the inferior part of the body of the
hyoid bone.
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• The fourth and sixth arch cartilages fuse to
form the laryngeal cartilages, except for the
epiglottis.
• Hyoid bone develops from
• Third pharyngeal arch which forms the body of hyoid bone
• Third arch cartilage, located in the ventral part of the arch.
It ossifies to form the greater cornu and the inferior part of
the body of hyoid bone A
• The fourth and sixth arch cartilages which fuse to form
hyoid bone
• The ventral end of the second arch cartilage which ossifies
to form the horns of hyoid bone and the superior part of
the body of the hyoid bone
• The dorsal part of the second arch cartilage which forms
the superior part of the body of hyoid bone.
• The cartilage of the epiglottis develops from
mesenchyme in the hypobranchial eminence,
a prominence in the floor of the embryonic
pharynx that is derived from the third and
fourth pharyngeal arches.
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• Note: Maxilla and Mandible develop by Membranous ossification.
• Maxillary process and Meckel’s cartilage are replaced by Maxilla and Mandible.
• Cartilages, Bones and Ligaments developing
from pharyngeal arches:
• First arch: Premaxilla, Maxilla, Zygomatic bone
and part of Temporal bone, Meckel’s cartilage,
Malleus, Anterior Ligament of Malleus, Incus,
Sphenomandibular Ligament, Anterior part of
Mandible.
• Second arch: Stapes, Styloid Process,
Stylohyoid Ligament, Lesser Horn and Superior
part of Body of Hyoid Bone.
• Third arch: Greater Horn and Inferior part of
Body of Hyoid Bone.
• Third and Fourth arch: Epiglottis.
• Fourth and Sixth arch: Laryngeal cartilages
(Thyroid, Cricoid, Arytenoid, Corniculate and
Cuneiform cartilages).
• Note: Three ligaments are developing from
Pharyngeal arches.
• They are:
• Anterior Ligament of Malleus
• Sphenomandibular Ligament
• Stylohyoid Ligament
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Muscles
• First arch:
• Anterior belly of Digastric, Mylohyoid, Tensor
Tympani, Tensor veli Palatini and muscles of
mastication (Temporalis, Masseter, Lateral
Pterygoid, Medial Pterygoid).
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The muscles developing from the first arch are
Posterior belly of Digastric A
Mylohyoid
Tensor Tympani
Tensor veli Palatini
Temporalis
Masseter
• Second arch:
• Stepedius, Stylohyoid, Posterior belly of
Digastric and Muscles of Facial expression
(Buccinator, Auricularis, Frontalis, Platysma,
Orbicularis oris, Orbicularis occuli etc.).
• Third arch: Stylopharyngeus.
• Fourth arch: Cricothyroid, Levator veli Palatini
and Constrictors of Pharynx.
• Sixth arch: Intrinsic muscles of Larynx and
Striated muscles of esophagus
• Each arch is supplied by its own cranial nerve.
The special visceral efferent (branchial)
components of the cranial nerves supply muscles
derived from the pharyngeal arches.
• Because mesenchyme from the pharyngeal
arches contributes to the dermis and mucous
membranes of the head and neck, these areas
are supplied with special visceral afferent nerves.
• The facial skin is supplied by trigeminal (fifth
cranial) nerve. However, only its caudal two
branches (maxillary and mandibular) supply
the derivatives of the first pharyngeal arch.
• Trigeminal nerve is the principle sensory nerve
of head and neck and is the motor nerve for
the muscles of mastication. Its sensory
branches innervate the face, teeth, and
mucous membranes of the nasal cavities,
palate, mouth, and tongue.
• Facial nerve (seventh cranial) nerve supplies
second pharyngeal arch.
• Glossopharyngeal (ninth cranial) nerve
supplies third pharyngeal arch.
• Vagus (tenth cranial) nerve supplies fourth and
sixth arches.
• The fourth arch is supplied by the superior
laryngeal branch of vagus and the sixth arch by
its recurrent laryngeal branch.
• The nerves of the second to sixth arches,
however, innervate the mucous membranes of
the tongue, pharynx, and larynx.
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• First arch: Trigeminal nerve or fifth cranial nerve
• Second arch: Facial nerve or seventh cranial
nerve
• Third arch: Glossopharyngeal nerve or CN IX
• Fourth arch: Superior laryngeal branch of Vagus
• Sixth arch: Recurrent laryngeal branch of Vagus