Lab 8: Chick 72 hours
Lab 8: Chick, 72 hours
Nervous system Cranial nerves Cranial nerves Digestive system
72 hour chick embryo
• Cranial nerves and ganglia are quicklyCranial nerves and ganglia are quickly
developing, with one new cranial ganglion per neuromere.
p
• The organs of the digestive system areThe organs of the digestive system are forming.
• At this stage the embryo has a foregut, hindgut, and the beginnings of organs hindgut, and the beginnings of organs along the midgut.
Neural crest cells
• So versatile that they could be called a fourth germ layer. They help form many ti
tissues:
– Melanocytes, adrenal glands, peripheral
system neurons including spinal ganglia, and system neurons including spinal ganglia, and bones and cartilage of the head, and parts of the cranial trigeminal and glossopharyngeal and vagus ganglia
and vagus ganglia...
• They arise along the neural tube startingThey arise along the neural tube starting around 27 hours and are migratory along specific paths. Two movies show the
fluorescently labeled cells moving away fluorescently labeled cells moving away from the neural tube over 10-12 hrs.
Neural crest cells can be fluorescently Neural crest cells can be fluorescently labeled with a specific antibody (HNK-1)
Immunocytochemistry for neural crest cells HNK 1 HNK-1 expressing cells in color
Neural crest cell derivatives
Neural crest cell derivatives
• Neural crest cells play a large role in
vertebrate evolution because they form so vertebrate evolution because they form so many of the structures in the head and
pharyngeal arches that are characteristic pharyngeal arches that are characteristic of a vertebrate body type.
• They are therefore the main cells
responsible for changes in craniofacial evolution.
The avian bill is formed in part from the cranial neural crest migrating from the fore and midbrain
i t th b hi l h
region to the branchial arches
(A): Migration of neural crest cells (shown in red) (B) and (C): Maxillary (mx) and mandibular arches (B) and (C): Maxillary (mx) and mandibular arches (md)
(D): Beak bone (red) from NCC (D): Beak bone (red) from NCC.
The avian bill is not entirely made from NCCs – they contribute but do they determine its pattern?
contribute but do they determine its pattern?
A grafting
experiment was experiment was done to test this.
Chick neural crest The duck beak of course is
cells were put in the quail embryo
(“quck”) or quail
of course is longer. The
quail beak has ill
( quck ) or quail neural crest cells
were put in the duck embryo (“duail”) The
a maxillary
bump near the tip (egg tooth). embryo ( duail ). The
results are on the next slide.
A. Quail NC
cells B. Duck NC cells cells transplanted in a duck embryo ( k) lt transplanted in a quail embryo (a duail) results in a (a quck) results in a stubby quail type bill and
)
longer duck type bill.
having the egg tooth bump.
• The results of the reciprocal transplants indicate that it is the neural crest which indicate that it is the neural crest which forms not only the cartilage and bone but directs the overlying ectoderm and the
directs the overlying ectoderm and the
mesoderm as well in the formation of the avian beak
Cranial nerves and ganglia
Sensory organs
Sensory organs
• Most of the paired cranial nerves (bundled collections of neurons) have a cell body
collections of neurons) have a cell body containing the nucleus and most of the
cytoplasm in ganglia (singular ganglion). The
thi d f th d i th h li
third, fourth and sixth have no ganglia.
• Nerves are made up of neurons extending back • Nerves are made up of neurons extending back
to the central nervous system or to some target sensory organ or muscle.
• The next slide shows a typical migrating
embryonic neuron with a leading edge growth embryonic neuron with a leading edge growth cone which extends the axon from the cell body.
The migrating neuron as shown in lecture.
Cranial nerves
• The sources of the neurons can be alongside the neuromeres (rhombomeres), or from
ectoderm just under the epidermis (epibranchial ectoderm just under the epidermis (epibranchial placodes) or growth from the developing
sensory organ (nose, eye, ear).
• The olfactory sensory nerve (I) forms axons
growing from the nasal pits toward the cerebral hemispheres.
hemispheres.
• The optic nerve (II) forms from the sensory
retina and later axons grow back to join to the diencephalon
diencephalon.
• The oculomotor (III) nerves are motor and later innervate the eye muscles (not yet formed).y ( y )
Cranial nerves of the hindbrain
• The trigeminal (V) is both sensory and motor
with the semilunar ganglion sending branches to the eye (ophthalmic) and maxillary/mandibular processes. Placode cells and neural crest form p
this nerve.
• The facial nerve (VII with acousticofacialis
ganglion) is a mixed nerve for the face Trace it ganglion) is a mixed nerve for the face. Trace it to the second mainly, but mandibular arch too. Placode cells and neural crest contribute to this nerve It is close to the auditory nerve (VIII)
nerve. It is close to the auditory nerve (VIII) which innervates the nearby developing ear (auditory vesicle).
• The glossopharyngeal (IX) and associated superior ganglion is a sensory nerve can
superior ganglion is a sensory nerve can be traced to the third arch. Epibranchial placodes and neural crest form this nerve placodes and neural crest form this nerve. • The vagus (X) and associated jugular
ganglion is a mixed nerve for the fourth ganglion is a mixed nerve for the fourth arch. Epibranchial placodes contribute to the neural crest forming these neurons
Glossopharyngeal Spinal Spinal cord Glossopharyngeal ganglion (IX) Otic vesicle p accessory nerve (XI) Otic vesicle Acousticofacialis ganglia (VII/VIII) left right Neuromeres of myelencephalon Metencephalon Yolk sac Semilunar ganglion of Mesencephalon Yolk sac g g trigeminal nerve (V) anterior
Spinal cord Notochord Facial nerve Semilunar ganglion (V) ganglion (V) of trigeminal nerve Isthmus Metencephalon Isthmus Mesencephalon
Digestive system and endoderm derivatives
• At 72 hours the endodermal derivatives such as the lung buds begin to rapidly expand into the
the lung buds begin to rapidly expand into the mesenchyme of mesoderm origin.
• The esophagus, stomach, liver and duodenum p g , , are just beginning to form. Try to trace the
connections between these tissues as they all branch off the same original endodermal tube. • Note the closeness of the ductus venosus to the
li di t l t th li ill d thi
liver rudiment; later the liver will surround this vessel. Why would later much more vitelline blood be directed to the liver?
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Pharyngeal region
• The four pharyngeal (branchial) arches are characteristically found in all vertebrates
characteristically found in all vertebrates during development whether or not gills are formed. This is an example of the retention of common structures and
developmental pathways in vertebrate l ti
evolution.
• The derivatives of the endoderm and
l t ll th t i
neural crest cells vary the most in evolution.
Posterior endoderm derivatives
• The hindgut is the region posterior to the caudal intestinal portal The hindgut ends caudal intestinal portal. The hindgut ends in the cloaca. Note how the allantois
branches off ventrally The cloaca is a branches off ventrally. The cloaca is a
blind ending but will later form an opening at the site of the cloacal membrane
at the site of the cloacal membrane (proctodeum). Try to find possible
functional openings of the mesonephric functional openings of the mesonephric ducts into the cloaca.
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Sagittal section to show how allantois g branches off of the hindgut
Neural tube cell organization
• The dividing population of cells is closest to the lumen in the ependymal (ventricular) layer as mentioned in the lecture. At the early stages seen in the next slide the division into three
layers (ependymal mantle and marginal) is not layers (ependymal, mantle and marginal) is not completed.
• Because all tube cells are attached at the
ependymal end and extend the full width, the tube is considered to be a pseudostratified epithelium Pseudo meaning that there is only epithelium. Pseudo meaning that there is only one cell layer but because cell bodies are at various positions it looks like there are many y strata or layers.
Chick embryo neural tube cells before the formation of the three neural layers.
Dividing cells can sometimes be seen close to the lumen in the ventricular zone.
• In the spinal cord or brain of the 72 hour chick embryo the thin outer
marginal zone sometimes is seen (i.e rarely) as distinct from the two darker and denser inner layers. Try to find it.
and denser inner layers. Try to find it.
In viewing sections note how the
thi k f th l i b t
thickness of the layers varies between brain regions.
• In the next slide the adult spinal cord
structure is shown with the dorsal sensory structure is shown with the dorsal sensory and ventral motor nerves.
In the 72 hr chick the nerve axons are • In the 72 hr chick the nerve axons are
growing toward the targets (such as the limb bud which is very early in its
limb bud which is very early in its
development) but the staining method used for these sections does not allow used for these sections does not allow nerve fibers to be easily seen.
• The oculomotor nerves (cranial nerve III) can sometimes be seen as thin usually
can sometimes be seen as thin usually
non-continuous streaks extending from the mesencephalon floor toward the internal
mesencephalon floor toward the internal carotid arteries. These nerves will
innervate the muscles of the eyes (The innervate the muscles of the eyes. (The oculomotor nerves may not be seen in all sets of sections
Body cavities
• The coelom is beginning to become divided into the pericardial cavity
divided into the pericardial cavity
surrounding the heart, the pleural cavity surrounding the lungs and the peritoneal surrounding the lungs, and the peritoneal cavity around the gut.
