Block 1 Development Flashcards
Where does neural tube fusion begin?
In the region of the 5th somite
When does Neurulation begin?
Between 18 and 19 weeks
When do the two neuropores close?
Rostal closes about day 24
Caudal close about day 26
What somites form the spinal cord and the brain?
Rostal to the 4th is the brain.
4th to caudal is the spinal cord.
What do neuralcrest cells develop into?
They form the PNS, primary neurons, Schwann cells, satellite cells, melanocytes, and chromaffin cells of the adrenal medulla.
What are the three layers of the neural tube?
Ventricular layer - initially the entire tube wall, rapidly divides and thickens, differentiates into neuroblasts and after becomes the ependyma, a single layer of cells lining the spinal cord.
Intermediate layer - becomes populated by the neuroblasts from the ventricular layer, becomes the gray matter where all the cell bodies are located (dorsal, ventral, and lateral horns)
Marginal layer - becomes white matter where all the axons of the intermediate layer travel
What cells maintain their mitotic ability?
Glial cells only
Where are the alar and basal layers located?
The intermediate layer
What divides the alar and basal layers?
Sulcus limitans
What do the alar and basal layers become and what are their orientations?
Alar - forms the dorsal horn, secondary sensory neurons
Basal - forms ventral and lateral horns, motor neurons
They eventually become neurites and form axons and dendrites.
What forms the dorsal root ganglion?
Neural crest cells. They start bipolar and become psuedounipolar
When does Myelination start and end?
It starts the 4th month Prenatally and continues into the 2nd year.
At 12 weeks the dura grows faster than the spinal cord. At what vertebrae does the spinal sit for an infant and adult?
Infant - L2/3
Adult L1
Where are lumbar punctures done?
Between L3/4 or L4/5
What are the three areas of the brain?
Forebrain or Prosencephalon
- telencephalon becomes the cerebral hemispheres
- diencephalon becomes the thalamus
Midbrain or mesencephalon
- stays the midbrain
Hindbrain or rhombencephalon
- metencephalon becomes the pons and cerebellum
- Myelencephalon becomes the medulla
Where are the ventricles located?
2 lateral ventricles - in the cerebral hemispheres
Third ventricle - diencephalon with the thalamus
Cerebral aqueduct - within the mesencephalon or midbrain
Fourth ventricle - within the rhombencephalon
What are the three flexures of the brain?
Cervical (hindbrain and spinal cord)
Cephalic (midbrain)
Pontine (mid of diencephalon)
How is the cerebellum formed and what are the lobes and composition?
- It is formed by the thickening of the alar plate (rhombic lip)
- the anterior and posterior lobes are divided by the primary fissure
- the floccunodular is separated by the posterolateral fissure
- the cortex is gray matter, the middle is white, the center is gray
What does the diencephalon form?
The thalamus, hypothalamus, epithalamus, optic nerve and retina, and posterior lobe of the pituitary gland neurohypophysis.
Has the third ventricle.
What is the makeup of the pituitary gland?
Both neuroectoderm and ectoderm origins
The infundibulum is a downward extension from the floor of the diencephalon giving rise to the posterior half (neuroectoderm)
Rathk’s pouch is outgrowth of ectoderm lined from the stomoduem, gives rise to the anterior portion called the adenohypophysis, glandular part.
Located in the sella turcica of the sphenoid bone
Anatomically and physiologically associated with the hypothalamus
What does the telencephalon form?
It is the rostal part of the prosencephalon
Forms the frontal, parietal, temporal, and occipital lobes
Forms the insula, an area buried in the cortex (grey matter)
Basal ganglion, fiber bundles, internal capsule, and corpus callosum, lateral ventricles, olfactory tract
What does the choroid plexus do and how is it formed?
Makes CSF
Formed by pia with ependyma called the Choroidea
Where do the different cranial nerves come from?
I telencephalon
II diencephalon
III, IV mesencephalon
V - XII brainstem
What is the composition of the basal and alar plates?
Basal plate - three columns of cells on each side of the brain stem
Alar plate - four columns of cells on each side of the brainstem
How are NTDs determined?
By measuring AFP and acetylcholine esterases
When does defective closure of the neural tube result is malformations like NTDs?
Weeks 3 and 4
What is Craniorachischisis?
Complete failure of the neural tube resulting in neural tissue outside the skull.
What is Anencephaly?
Failure of the rostal neuropore to close and subsequent failure of the cranial vault to form.
Total absence of brain tissue
What is meroanencephaly?
Failure of the rostal neuropore to close and subsequent failure of the cranial vault to form.
Remnants of brain tissue may be present
What is Encephalocele?
Protrusion of the brain through a defect in the skull.
What is spina bifida?
Failure of the caudal neuropore to close
What is spina bifida occulta?
Spinal malformation of vertebral arch
May be a tuft of hair on back
Spinal cord may be tethered to SQ tissue
What are the types of spina bifida cystica?
Meningocele - spinal cord in tact but meninges herniate through defect in the vertebral arch and skin usually lumber
Myelomeninocele - spinal cor and meninges herniate through the opening. May have Arnold-Chiari malformation resulting in hydrocephalus.
Occult spinal dysraphism - (tethered spinal cord) failure of tube to detach from surface ectoderm. Usually in sacral/coccygeal. May connect to central canal
What are some factors of NTDs?
Diabetes mellitus
Abnormal folic acid metabolism
What is Holoprosencephaly (HPE)?
Cyclops eye
Failure of normal of development so that the forebrain has no divisions.
What is hydrocephalus?
A. Dilation of CSF ventricles due to overproduction, obstruction to flow, or failure of reabsorption.
B. Often seen in others, dandy walker of Arnold Chiari
What are Arnold-Chiari malformations?
Type II - includes NTDs. Displacement of cerebellum and brainstem into the cervical spinal canal
Type I - milder. Many have syringomyelia and some have hydrocephalus. May be asymtomatic.
What are Dandy-Walker malformations?
Posterior fossa abnormalities that include cerebellar vermis, formation of a large cyst, and blockage of Luschka and Magendie foramen
Symptoms in infants - slow motor development, irritability, vomiting
In older children lack of muscle coordination, jerky eye movements
What is syringomyelia?
- Tubular cavitation of spinal cord, usually in cervical/upper thoracic
- Affects central canal fibers
- Initially loss of sensation in pain/temp over shoulders and arms due to damage of fibers crossing in the ventral white commissures
- Often with Arnold-charia type I
Unknown cause
What are some characteristics of alcohol and the prenatal vein?
It is teratogenic at all times during development.
Lesions may not be visible
Most common cause of mental retardation.
One drink in the 1st trimester can lower IQ by three points
