Ach Flashcards
Bones of the skull are derived from ________ and _________.
paraxial mesoderm and neural crest
Viscerocranium
Viscerocranium = face; contains taste, sight and smell organs
forms around the gut tube, rostral to the notocord.
Neurocranium
Neurocranium forms around the rostral end of the neural tube, which is responsible for its induction.
Bone formation is via both endochondral (ethmoid, **sphenoid, **occipital base, **petrous temporal, **temporal- mastoid)** and intramembranous ossification (parietal, frontal, **squamous occipital)
Correlate the parts of the skull that are derived from occipital somites. Which are derived from neural crest mesenchyme? What type of ossification takes place in each?
Mesenchyme is derived from occipital somites
Somitomeres 1-7 and occipital somites 1-4 contribute to formation of the head.
neural crest mesenchyme –> Frontal bone and “face”
Craniosynostosis
skull abnormality caused by premature closure of one or more sutures that produces a misshapen skull.
Microcephaly
skull abnormality
**a small head due to a brain that fails to grow **
Cranioschisis
skull abnormality
is a skull defect through which the meninges and/or brain herniate. (NTD)
Autosomal dominant genetic disorder characterized by craniosynostosis and other congenital abnormalities e.g., syndactyly of hands and feet, mental retardation.
Apert Syndrome
Skull abnormalities: acrania, anencephaly, meroanencephaly
Acrania: no skull
Anencephaly: no brain, neural folds fail to elevate and fuse. Cranial neuropore remains open. Brain tissue degenerates in response to exposure to amniotic fluid. Extent of neurological deficit depends on amount of damage to brain tissue.
Meroanencephaly: some poorly formed brain stem tissue present
Hydrocephalus
Enlarged ventricles due to too much CSF. If this occurs prior to closure of the sutures, the head enlarges.
Dilation of the ventricles due to excess amount of CSF
Due to CSF overproduction, obstruction of flow or failure of CSF reabsorption
Holoprosencephaly
The forebrain does not divide into two hemispheres
Syringomyelia
Tubular cavitation of the spinal cord – generally cervical/upper thoracic
Pathogenesis unknown; probably diverse
Neural deficits begin with loss of pain & temperature sensation over shoulders and upper arms.
Occipital encephalocele
The brain and meninges protrude through a defect in the occipital bone.
This can also occur in the frontal area but more common in the occipital.
Craniorachischisis
Failure of a significant portion of the neural tube to close resulting in exposure of the malformed neural tissue along the back of the head and body
Hirschsprung disease or congenital megacolon
Due to failure of neural crest cells to migrate into the colon – most common in rectum and sigmoid colon.
The parasympathetic ganglia do not form, so normal peristalsis does not occur.
Fecal retention with ballooning of the colon and abdomen
