Embriology Flashcards
What is the morula?
microscopic cluster of cells (the 16 cell stage), appearance similar to mulberry, occurs before the blastocyst stage
What is blastulation?
process of going from morula to blastocyst
What is a blastocyst?
has an outer (trophoblast - differentiates into cytotrophoblast and synchitiorophoblast, important for formation of the placenta) and inner cell mass (embrioblast - turns into bilaminar disc - later forms the embrio)
Two layers of the bilaminar disc?
1) epiblast (above it is the amniotic cavity)
2) hypoblast (beneath it is the yolk sac)
What is the prechordal plate?
temporary cellular plaque situated rostral to the notochordal process/plaque, comes to underline the rostral part of the neural plate
What is gastrulation?
A process of cellular rearrangement which involves migration, invagination and differentiation of the epiblast, getting from bilaminar to trilaminar disc. Gastrulation occurs in the following sequence: (1) the embryo becomes asymmetric; (2) the primitive streak forms; (3) cells from the epiblast at the primitive streak undergo an epithelial to mesenchymal transition and ingress at the primitive streak to form the germ layers.
Three locations with no mesoderm
procordal plate, notochord, cloacal plate
Formation of the neural tube
neural plate -> neural fold -> neural tube
What is the neural crest and what does it develop into?
At about the time the neural groove deepens, a cluster of cells appears and forms the neural crest at the area where the neural fold borders on the ectoderm. The
neural crest detaches from the ectoderm to become ganglia of
the cranial and spinal nerves.
Where does the closure of the neural groove start?
in the middle of the embrio and proceeds towards the cephalic and caudal ends
Explain the three primary developing brain vesicles and which 5 vesicles do they turn into?
1) forebrain (prosencephalon) -> telencephalon + diencephalon
2) midbrain -> mesencephalon
3) hindbrain -> metencephalon, myelencephalon
(2 + 3 = rhombencephalon)
Which cells are precursors to neurons and which to glial cells?
Ectodermal cells of the neural groove and neural tube:
1) neuroblasts -> neurons
2) spongioblasts -> glial cells
What are radial glia cells?
cells of the embrionic neural tube that function as guides to developing immature neurons.
However, it is now recognized that these radial glia may also undergo postnatal differentiation into immature neurons, astrocytes, oligodendrocytes, and ependymal cells. After development is completed, the undifferentiated radial glial cells populate the subventricular zone, which is most evident rostrally in association with the lateral ventricle of the frontal lobe. Here, these radial cells function as neuronal stem cells and as a source of astrocytes and oligodendrocytes.
What is the mantle layer?
it is the primordium of the spinal cord’s gray
matter, develops from the cell proliferation of neuroblasts
and spongioblasts that forms the thick, multilayered wall of the neural tube (the mantle layer).
What are the alar and basal plate?
Further differentiation of the mantle layer.
Alar plate -> dorsal horn
Basal plate -> ventral horn
Name 2 signaling centres responsible for the development of the spinal cord
1) surface ectoderm adjacent to the ectoderm that formed the neural plate (secrets BMP-4 /bone morphogenetic protein 4/ - responsible for the formation of dorsal horn neurons
2) notochord - secretes SHH (sonic hedgehog) - responsible for directing the development of the ventral portion of the neural tube with its ventral horn neurons
Which structures of the adult animal are formed from the neural crest cells?
dorsal root ganglia,
sympathetic trunk ganglia, collateral ganglia (associated with arteries),
terminal ganglia (associated with visceral organs)
The eyes develop from which cephallic vessicle?
diencephalon
Which part of the ventricular system of the brain does not contain a choroid plexus?
cerrebral (mesencephallic) aqueduct
Which plate (alar or basal) forms the prosenceohalic structures?
alar (the sulcus limitans disappears rostral to the mesencephalon)
Explain why the term optic nerve is a misnomer
By definition, a nerve is a collection of axons outside the CNS that are myelinated by Schwann cells, which arise from the neural crest. Therefore, optic nerves are misnamed because they develop as extensions of the prosencephalon. They form in the optic stalk that extends from the diencephalon to the optic cup. Their axons are myelinated by CNS oligodendroglial cells, covered by meninges, and bathed in CSF. This is important to remember because the optic nerves may be affected by diseases that are specific to the CNS. Therefore, optic neuritis is a form of encephalitis. Conversely, polyneuritis does not affect the optic nerves.
Which strucutres form the neopallium, archipallium and paleopallium?
1) Neopallium: gyri and sulci of the cerebral hemispheres
2) Archipallium: hippocampus
3) Palleopalium: olfactory bulbs, olfactoru peduncles and the piriform lobe
Name the basal nuclei
1) caudate nucleus
2) lentiform nucleus (globus pallidus + putamen)
3) claustrum
4) amygdaloid body
The gray matter of the spinal cord derives from the:
A Marginal layer
B Mantle layer
C Neural crest
b
Submucosal and myenteric ganglia of the intestine derive from the:
A Neural crest
B Alar plate
C Basal plate
D Marginal layer
a
Name the 3 types of white matter axon groups
(1) association (course between cortical areas within one cerebral hemisphere)
(2) projection (leave the cerebral hemisphere where their cell bodies are located and enter the brainstem via the internal capsule)
(3) commissural (cross from one cerebral hemisphere to the other)
Where does postnatal neurogenesis occur in the brain?
1) olfactory system
2) hippocampus
3) subependymal/ subventricular layer
Which malformation is present in this image, and which is the only domestic animal species with this disease?
A calf with prosencephalic hypoplasia. Note the area in the center of the calvaria devoid of hair. The malformed diencephalon is fused to the skin here, and cerebrospinal fluid leaked out of the third ventricle at this site. The calvarial defect here is called a cranioschisis or cranium bifidum. In human newborns, this is called anencephaly, which is an incorrect term because it implies complete absence of brain development. Only observed in calves.
Which anomaly is present in the image
Lateral view of the brain of a calf with prosencephalic hypoplasia. Note the abnormally shaped brainstem and cerebellum.
Which anomaly is shown in the image?
Meningocele/meningoencephalocele (PHD needed to verify which)
Which anomaly is shown in the image?
Head of a stillborn Belgian foal with a small meningoencephalocele. The hairless mass protruded through a small midline cranioschisis. On microscopic examination of the mass, brain tissue, including choroid plexus, was found adjacent to the dermis.
Which anomaly is shown in the image?
A newborn Burmese kitten with a large meningoencephalocele associated with facial duplication. A very large meningoencephalocele occurs as part of an inherited craniofacial malformation in Burmese cats. The superior jaws and nasal areas were shortened and had no recognizable nares, planum nasale, or nasal cavities. Olfactory bulbs or peduncles were absent in the malformed cerebrum. A philtrum was present on either side of the rostral midline of the face and vibrissae on both sides of the cleft. Duplication was also evident in the two pairs of maxillary bones and two sets of maxillary canine teeth. No gross evidence of any eyes was seen, but one pair of orbits was present. No optic nerves or chiasm was associated with the diencephalon. The mandibles were prominent, and the tongue was enlarged and protruded from the mouth.
What is exencephaly?
brain tissue that protrudes out of the cranial cavity and is not covered by skin (PHD needed to differentiate between this and meningocele/meningoencephalocele)
Which anomaly is shown in the image?
A 2-year-old Holstein cow with a calvarial lipomeningocele. This malformation was associated with the meninges of the falx cerebri with no cerebral involvement. This cow was clinically normal. A lipomeningocele, as the term suggests, is a meningocele that has a large amount of fat associated with it, usually without neuro signs.
Which anomaly is shown in the image?
Dicephalia/diprospia - prosencephalic duplication occurs most commonly in calves and is associated with varying degrees of duplication in the face. The brainstem usually becomes single somewhere in the mesencephalon. The pons, medulla, and cerebellum are all single structures. This is a partial dicephalus. These calves are usually born alive but are recumbent and unable to stand.
Which anomaly is shown in the picture and name the plant (and its toxin) associated with causing this defect if ingested during pregnancy.
holoprosencephaly (arrhinencephaly) with cyclopian malformation.
Common in lambs if the dams are exposed to Veratrum californicum (cyclopamine - effect on the sonic hedgehog signaling) on the 14th and 15th day of pregnancy. The image shows a newborn cyclopic lamb with a single median plane partially divided eyeball and the proboscis dorsal to the fused eye (an elongated sucking mouthpart that is typically tubular and flexible).
Which anomaly is show in the image?
Ventral view of the brain of a 6-month-old Morgan horse with partial holoprosencephaly. Note the absence of longitudinal cerebral fissure rostral to the optic chiasm and the absence of the olfactory bulbs and peduncles.
Which anomaly is shown in the image?
A beagle with cyclopia. Note the proboscis dorsal to the fused eye (an elongated sucking mouthpart that is typically tubular and flexible).
Which anomaly is shown in this image?
Brain of a calf with hydranencephaly caused by in utero infection with Akabane virus. The white structures on the floor of the lateral ventricles are the hippocampi.
Which anomaly is shown in this image?
Unilateral hydranencephaly in an 8-month-old miniature poodle. The calvaria has been removed, but the dura is still in place.
Which anomaly is present in this MRI image of a 2 YO dog w/ 1 Y history of seizures?
R sided hydranencephaly (also evident - hypoplasia of the ispilateral diencephalon
Name the anomaly and a typical breed in which it occurs. What are the typical clinical signs?
lissencephaly, Lhasa apso.
Difficulty in learning routine training programs such as house breaking, abnormal behavior, and occasionally slow postural reactions and poor menace responses. Generalized seizures may occur when the dogs are 10 to 12 months old.
Which anomaly is present? Lhasa apso 5 MO evaluated for abnormal mentation
Note the lack of gyration of the cerebrum consistent with lissencephaly. The cerebral cortex also is thickened and there is a paucity of white matter that would normally make up the corona radiata, internal capsule (large arrowhead) and corpus callosum (small arrowhead). The left lateral ventricle is enlarged compared with the right lateral ventricle.
Name the anomalies present
Lissencephaly and cerebellar hupoplasia
Name the anomaly, specie and clinical signs
Complex malformation of calves (Arnold-Chiari malformation).
These calves are usually born alert and with vision but are recumbent and unable to coordinate their neck, trunk, and limb functions to be able to stand. They often exhibit opisthotonus and abnormal nystagmus. A malformed tail with an associated loss of tone and reflexes in the anus and tail is present.
Name the anomaly
dyplomielia (note the 2 central canals)
Name the anomaly
Diastematomyelia
Name the anomaly
Lumbosacral myeloschisis and rachischisis in a puppy.
Which anomaly is shown in this MRI image of a 10-month old English bulldog with fecal and urinary incontinence?
Meningocele.
A sagittal T2-weighted image of the lumbosacral vertebral column of the dog. At the L6–L7 articulation, the vertebral canal is expanded and the meninges extend dorsally to exit the vertebral canal just caudal to the L6 spinous process. Note the hypointense linear connections to the overlying skin (arrowhead) where the skin margin is indented (arrow).
Which anomaly is shown?
cerebellar hypoplasia
calf
in utero infection with CDV virus
Which anomaly is shown?
hydranencephally
Two 1-week-old calf brains with severe hydranencephaly caused by an in utero infection by Akabane virus. At autopsy, the thin pial-glial membrane of the neocortical portion of the cerebral hemispheres was seen to have collapsed when cerebrospinal fluid (CSF) in the dilated lateral ventricles was released. CSF had replaced the absent cerebral tissue.
