Embryology Flashcards
at what week does the nervous system begin to develop
week 3
why is the nervous system not fully functional after birth
as the neurones are not fully myelinated
describe the formation of the neural tube from gastrulation
gastrulation produces a notochord in the mesoderm
this causes the overlying ectoderm to differentiate into neuroectoderm. this region then thickens and theres elevation of the lateral edges which come together and fuse to form the neural tube
what are the ends of the neural tube called before they close
anterior and posterior neuropore
what do cranial defects in the failure of the neural tube to close cause
anencephaly - without a brain
what do caudal defects in the failure of the neural tube to close cause
spina bifida
what is spina bifida
when the neural tube fails to fuse leading to problems with the spinal cord and closure of the spinal vertebrae itself
true or false spina bifida is often associated with hydrocephalus
true as it could lead to CSF circulation difficulties
what is Rachischisis
failure of neural fold elevation so the neural tube never actually forms
what protein is often raised in the mothers blood when there is a neural tube defect
alpha fetoprotein
what are the 3 types of spina bifida
occulta, meningocele, myelomeningocele
what is spina bifida occulta
where there is no protrusion/lumps of CSF or anything only a failure of the posterior vertebral arch to fuse
what is spina bifida meningocele
where meninges and CSF herniates through the region of the posterior vertebral arch which failed to fuse
what is spina bifida myelomeningocele
where meninges, CSF and spinal cord all herniate through the poorly fused vertebral column giving neurological defects
at what level does spina bifida usually occur
L5-S1
how does folic acid prevent neural tube defects
helps the epithelial folds to fuse together to close the neural tube
at what spinal level does the cauda equina begin
L1
why does the cauda equina develop
the vertebral column begins to grow faster than the spinal cord and so the spinal roots must elongate so that they can exit at their respective vertebral foramen
at what level should a lumbar puncture be administered and why
L3/4 as the spinal cord is finished and it is at the level of the cauda equina so there is less risk for neurological damage
name some functions of neural crest cells
endocardial cushions, dorsal root ganglion, sympathetic ganglion, Schwann cells
what is Hirschsprung’s disease
where the neural crest cells fail to develop into the enteric ganglion
what is diGeorges syndrome
where the neural crest cells fail to migrate properly leading to problems with the thymus, thyroid, face and CVS
what are flexures
a change in the axis of the nervous system as the neural tube grows too much for the room it has and so it must fold
what are the 2 flexures
cephalic - bend in the midbrain
cervical - bend in the hindbrain-spinal cord junction
what are the 3 dilations of the neural tube called
forebrain - prosencephalon
midbrain - mesencephalon
hindbrain - rhombencephalon
what are the primary brain vesicles
the 3 areas of dilation of the cranial end of the neural tube when the tube has closed
what are the secondary brain vesicles
the 5 divisions resulting from the change in shape from the 3 primary brain vesicles
what are the 5 secondary brain vesicles called
telencephalon dincephalon mesencephalon metencephalon myelencephalon
which secondary brain vesicle do the cerebral hemisphere develop from
telencephalon
which secondary brain vesicles does the thalamus develop from
diencephalon
which secondary brain vesicle does the midbrain develop from
mesencephalon
which seoncdary brain vesicle does the cerebellum and pons develop from
mesencephalon
which secondary brain vesicle does the medulla oblongata develop from
myelencephalon
what cells produce CSF
choroid plexus cells found in the ventricles
what are the ventricles
fluid filled spaces in the CNS
how much CSF is produced per day
600 ml
what is the function of CSF
to cushion the brain and spinal cord
what connects the lateral ventricles to the 3rd ventricles
intraventricular foramen
what connects the 3rd ventricle to the 4th ventricle
cerebral aqueduct
how does CSF drain
drains through the ventricles to the 4 ventricle where it can then drain through the central canal or the lateral and medial apertures. from the apertures it goes into the subarachnoid space where its reabsorbed by arachnoid granulations in the superior sagittal sinus to join the venous circulation
what is hydrocephalus
where there is a build up of CSF in the ventricles due to a mismatch between CSF production and drainage
what may cause hydrocephalous
tumour, infection, stenosis, spina bifida
how is hydrocephalous treated
ventricular-peritoneal shunt. this is where a shunt goes from the ventricle to the abdominal cavity so that CSF is drained in the abdomen instead
what are the disadvantages of ventricular-peritoneal shunts
infection
may outgrow them in the case of children
