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Chapter 18: Development of the Structures of Head and Neck - Part 3
1. True/ False- Ectodermal cells of the embryo form the periderm. (After neurulation, ectodermal cells
proliferate to form the periderm, a new outer squamous cell layer on top of the original basal cell layer)
2. True/ False- Neural crest cells invade the skin dermis to form melanocytes. (Invade epidermis)
3. True/ False- All the cutaneous glands of the skin are derived by ectodermal invaginations into
dermis. (Sebaceous, sweat, mammary, and scent-marking glands)
4. True/ False- The mammary gland is basically a cutaneous gland, similar to a sweat gland in origin.
5. True/ False- The neurocranium of the skull houses the nasal cavity. (Houses the brain, whereas the
maxilla houses the nasal cavity)
6. True/ False- The rhomboncephalon forms cerebrum. (The hindbrain forms the cerebellum, pons,
and medulla oblongata)
7. True/ False: The infundibulum is a part of the midbrain. (Part of the diencephalon of the forebrain)
8. True/ False-In the adult lens of the eye, only the posterior surface has an epithelium. (Anterior
surface exhibits epithelium in the adult eye)
9. True/ False- The primary lens fibers are formed by the epithelium of the lens on its rostral surface.
(The primary lens fibers are formed from cells of the caudal wall of the lens vesicle. Cells of the
rostral wall form the secondary lens fibers)
10. True/ False- The outer layer of the optic cup gives rise to the photoreceptors. (The most caudal
layer of the inner epithelium give rise to rods and cones)
11. True/ False- SSA fibers innervate the otic vesicle.
12. True/ False- The hyaloid artery supplies developing lens.
13.
Describe the development of the inner ear.
The first indication of formation of the inner ear is the appearance of an ectodermal thickening called
the otic placode on the dorsolateral aspect of the head next to the rhombencephalon. The otic placode
gradually invaginates, first forming an otic pit. This pit deepens, the lips of the pit fusing to form the
otic vesicle. This vesicle detaches from the surface ectoderm and sinks deeper into the underlying
mesenchyme. It then develops a dorsal appendage called the endolymphatic appendage, which forms
the endolymphatic sac. The rest of the otic vesicle differentiates into a utricle (dorsal) and a saccule
(ventral). The tip of the saccule extends and curls to forms the cochlear duct. The utricle differentiates
into a flattened diverticulum that will form the 3 semi-circular canals.
The inner ear is very complex and is innervated by CN VIII. Because the inner ear is derived from
ectoderm, the type of fibers within CN VIII are considered special somatic afferent (SSA).
14.
Describe the 3 primary parts of the neural tube that form the brain, and their divisions.
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The neural groove forms the neural tube, which develops into the CNS. The cranial part of the neural
tube exhibits 3 dilations: the proencephalon (forebrain), mesencephalon (midbrain), and the
rhombencephalon (hindbrain), which contribute to the formation of the brain.
Forebrain
The development of the proencephalon takes place after the closure of the cranial neuropore. At this
point, the forebrain gives rise to 2 ventrolateral diverticulae called the optic vesicles. It also forms
telencephalic vesicles, which are forerunners of the cerebral hemispheres. The neural tube cavity is
retained within the forebrain and eventually forms the lateral ventricles of the brain. The caudal part
of the forebrain develops into a midline structure, the diencephalon, which houses numerous centers
including the hypothalamus, thalamus, epithalamus, and pineal gland.
Midbrain
The mesencephalon undergoes little change compared to the forebrain and hindbrain, but contains
numerous ascending and descending tracts. The original neural canal is retained as the cerebral
aqueduct, a short canal connecting the 3rd and 4th ventricles. Neuroblasts aggregate at the roof of the
midbrain to form the rostral and caudal colliculi.
Hindbrain
During early development, the rhombencephalon exhibits 7 segments, rhombomeres, which contribute
to the formation of pharyngeal arches. Later, the hindbrain is separated from the spinal cord by the
development of the cervical flexure (not apparent in domestic animals). The pontine flexure also
divides the hindbrain into a rostral metencephalon, which develops into the cerebellum and pons, and
a caudal myelencephalon, which forms the medulla oblongata.
15.
What is palatine raphe, and how is it formed?
The palate develops from 2 primordia: the primary palatine process and the secondary palatine process.
The primary palatine processes is small and contributes to the formation of the incisive bone
(premaxilla) and later the incisive papilla. The secondary palatine processes grow towards the midline,
separate the nasal cavity from the oral cavity, and fuse. Their line of fusion in the adult is retained as
the palatine raphe.
16.
Describe the development of the optic cup, and its developmental fate.
The optic vesicles are a pair of outgrowths from the diencephalon (caudal part of forebrain). These
vesicles grow towards the surface ectoderm. The ventral aspects of the optic stalks exhibit grooves
(choroidal fissure) to accommodate hyaloid arteries that supply the developing eye (but disappear in
the mature eye). Eventually, the fissure will close to surround the artery. The distal ends of the optic
vesicles invaginate to form optic cups. As this happens, the surface ectoderm near the cups thickens to
form the lens placodes, which eventually invaginate to form a lens pits, which soon close to form lens
vesicles. These vesicles detach from surface ectoderm, sink into the underlying mesenchyme, the optic
cups, and are supplied by hyaloid arteries.
The optic cups gave external and internal layers of epithelium that fuse. The outer layer differentiates
into the pigment layer of the retina, while the inner layer forms the retina proper. The retina proper
consists of several layers of cells. The most cranial layer forms the ganglion cell layer. The middle
layer forms the bipolar cell layer. The most caudal cells become photoreceptors (rods and cones).
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17.
Describe where retinal detachment usually occurs.
Because the retina proper develops from the inner epithelial layer of the optic cup, the retina is not
firmly attached to the outer pigment layer. As the eye ages, the vitreous gel within the inner epithelium
tends to shrink and detach from the outer retinal epithelium, a process known as posterior (caudal)
vitreous detachment, which is normally benign but can sometimes tear the retina.
18. Most of the adult nasal mucosal epithelium is derived from:
a. Nasal pit ectoderm (Neural plate cells (neuroepithelium, neuroectoderm) invade nasal pit and
differentiate into olfactory cells)
b. Neural crest cells
c. Olfactory placode
d. Encroaching gut endoderm
e. Nasomedial processes
19. All of the following are part of the brain except:
a. Metencephalon
b. Myelencephalon
c. Telencephalon
d. Procencephalon
e. Cranial neural crest
20. Select the wrong item:
a. The Rhinencephalon is part of procencephalon developmentally
b. The 2 lateral ventricles of the brain develop within the mesencephalon (From the retention of
the neural tube cavity within the forebrain)
c. The pia mater and arachnoid coverings of the brain are derived from neural crest
d. The diencephalon is part of procencephalon
e. Only telencephalic lobes of the developing brain are paired
21. For the following bones of the skull- mention their developmental origin, and type of ossification
process involved:
Bone
Malleus
Mandible
Ethmoid
Basioccipital
Basisphenoid
Parietal
Incisive
Basihyoid
Vomer
Maxilla
Embryological Origin
Ossification Type
Mandibular (Meckel’s) cartilage of branchial arch I (neural crest cells) Endochondral
Mandibular cartilage (neural crest cells)
Membranous
Medial wall of left and right cartilaginous nasal capsules (neural crest) Endochondral
Sclerotome
Endochondral
Sclerotome
Endochondral
Sclerotome
Membranous
Upper jaw component of the intermaxillary segment (neural crest cells) Membranous
Hyoid (Reichert’s) cartilage of branchial arch II (neural crest cells)
Endochondral
Nasal septum (neural crest cells)
Membranous
Neural crest cells
Membranous
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