What are the adult derivatives of the primary brain vesicles?
What are the adult derivatives of the secondary brain vesicles?
telencelphalon - cerebral hemisphers
diencephalon - optic nerve, thalamus, hypothalamus, etc
mesencephalong - midbrain still
metencephalon- pons, cerebellum
myeloencephalon - medulla
What are the neuropores? What is the clinical significance of their failure to close properly?
they are the open ends of the neural tube - caudal and rostral. they communicate with the amniotic fluid that runs through the neural canal.
rostral is supposed to close aorund day 24. caudal is supposed to close around day 26
if they don't close, you can get ossification defects of the skull and vertebral column - severe abnormalities of the brain and spinal cord.
How does the neural tube differentiate into gray and white matter?
after the neural tube closes, the neuroepithelial cells begin to proliferate into 3 layers; the ventricular layer, the intermediate layer and the marginal layer
the ventricular layer is where the cells proliferate before they migrate out - these will eventually become the glia
the intermediate layer has the cell bodies of neurons - this will be the gray matter
the marginal layer has the axons of the neurons in the intermediate layer - this will be the white matter
Describe the relationship of the alar and basal plates to the organization of the adult nervous system.
the alar plate will form the sensory neurons of the dorsal horn and brain
the basal plate will form motor neurons of the ventral horn and brain
Describe the development of the cranial nerve nuclei.
Cranial nerve ganglia are formed by neural crest cells that migrate into the territory of the brainstem
CN 1 and 2 develop as outgrowhts directly from the telencephalon and diencephalon respectively, so these are extensions of the brain and have no nuclei
Describe the development of the hypothysis (pituitary gland)
It has dual ectodermal origin
1. the neural ectoderm forms the infundibulum, which is a downgrowth of the hypothalamus that becomes the neual portion (and posterior lobe)
2. Oral ectoderm forms Rathke's pound, which becomes the glandular anterior portion of the hypophysis
the two parts fuse as the anterior and posterior cartilages of the greater wing and body of the sphenoid fuse to form the definitive sell turcica
What is the origin of the neural crest?
they are motile neuroextodermal cells that lie dorsal and lateral o the neural tube- originally in the neural folds
they will migrate throughout the embryo
What are the adult derivatives of the neural crest cells?
peripheral nervous system
- most sensory neurons, autonomic ganglia, enteric ganglia/nerves, schwann cells, satellite cells
arachnoid and pia mater, aorta CT, merkel cells, chromaffin cells of adrenal medulla, odontoblasts, cartilage and bones of head and neck, melanocytes
What is spina bifida oculta?
mildest form of of spina bifida where the vertebral arch is malformed with no obvious involvement of the spinal cord, meninges or skill
onlyevidence is a tuft of hair overlying the defect
What is spina bifida cystica
(meningocele vs. myelomeningocele)
this is the more serious form when the caudal neuropore fails to close.
meningocele is when the spinal cord is intact, but the meninges filled with CSF herniate thorugh the defect in the lumbosacral region
myelomeningocele is the most severe form because the spinal cord and the meninges herniate out
What is anencephaly?
failure of the rosetral neuropore to close and subsequent failure of the cranial vault to form
anencephaly - total absence of brain tissue
meroanencephaly = remnants of the brainstem tissue may be present
What is waardenburg syndrome?
When neural crestcell migration is diffusely disrupted during development
broad range of seemingly unrelated symptoms..
abnormal appearance of face, deafness, pale eyes, shock of white hair
lack of pigmentaiton (melanocytes missing)
what is hydrocephalus?
this is dilation of the cerebral ventricles by CSF due to CSF overproduction, obstruction of flow, or failure of CSF reabsorption
in kids this will make hte head huge
often seen with other malformations like Dandy-walker or Chiari
What is Hirschsprung disease?
failure of neural crest cells to migrate tot he colon, most commonly the rectum and sigmoid colon
the parasympathetic ganglia don't form, so normal peristalsis can't occur
fecal retention with formatoin of megacolon
What does the neural canal develop into?
ventricular system of the brain and central canal of the sinal cord
How do nerves pick up their myelin?
when they pass through the marginal layer of the neural tube.
Why does the babinski sign disappear aorund age 2?
because infants aren't fully myelinated
it disappears when the higher cortical function that suppresses the reflex is fully myelinated