Case 1 Flashcards
What does the central nervous system contain what is it composed of?
It is enclosed withing the meninges and consists of the brain and spinal chord.
Which of the three primary germ layers does the nervous system originate from?
The ectoderm.
What structure is formed by the thickening of the edges of the neural plate?
The neural groove
What embryonic structure present by roughly three weeks is thought to be the origin of the entire CNS including neurones neuroglia ependymal cells and the epithelial cells of the choroid plexus?
The neural tube.
What is the function of the choroid plexus? Where is it located?
There are four choroid plexuses each one located in a separate ventricle of the brain. Their function is the production of cerobrospinal fluid (CSF).
What parts of the developing spinal chord does the sulcus limitans divide?
The alar and basal plates
Which of the alar and basal plates are the most ventral?
The basal
Which of the alar and basal plates are the most dorsal
The alar
Neurons derived from the basal plate are predominantly what type?
Motor
Neurons derived from the alar plate are predominantly what type?
sensory
What structures are derived from the expansion of the anterior end of the neural tube, what structures do these develop into
The primary brain vesicles, these develop into the ventricular cavities of the brain.
What three distinct layers can be observed in the spinal cord once a syncytium has been formed by the cells of the spinal cord side wall, list them from most central outwards?
the ependymal , mantle and marginal layers.
What does the ependymal layer of the embryonic spinal cord go on to form?
The ependyma of the spinal chord (the lining of the inside of the spinal canal partially responsible for the production of CSN)
What are the two types of cell present in the mantle layer?
spongioblasts and germinal cells
What do the spongioblasts of the mantle layer go on to form?
neuroglia cells
What do the germinal cells of the mantle layer go on to form?
neuroblasts or young nerve cells.
What does the marginal layer go on to form
the white funiculi of the spinal cord
The filaments of syncytium connecting spongioblasts are the precursor to what trait of mature neuroglia cells
The thin processes extending from each of them.
What shape are the germinal cells where are they found?
The are large oval or round shaped cells found in the side walls of the central canal between the ependymal cells but not on the roof or floor plates.
The germinal cells give rise to the neuroblasts where do these migrate from in between the ependymal cells of the side wall of the neural canal
into the mantle layer and towards the neural crest
At what stage of development do nerve fibers begin to be present in the marginal layer
Roughly 4 weeks
What do the intersegemntal fibers of the spinal cord originate from?
The neuroblasts in the mantle zone.
What do the dorsal nerve root fibers grow into where do these cells originate from?
They grow into the spinal cord, they originate from the cells of the spinal ganglia.
Until roughly what point in development is the spinal cord the same length as the vertebral canal?
Up until roughly three months.
Where does the end of the spinal cord reach in the vertebral canal at both birth and adulthood, what causes this shift?
At birth it is level with the 3rd lumbar vertebrae and by adulthood it has reached the 1st or second lumbar vertebrae this shift is caused by the vertebral canal growing more than the spinal cord.
What is the name of the thin filament that reaches from the end of the spinal cord to the the end of the coccyx?
The filum terminale
What the three primary vesicles present from three weeks of development what are these bulges filled with?
The prosencephalon, mesencephalon and rhombencephalon. they are filled with a fluid that will become CSF.
What does the prosencephalon develop into?
The cerebral hemispheres and the diencephalon.
What does the rhombencephalon develop into, what is it continuous with?
The pons, medulla and cerebellum, it is continuous with the spinal cord.
What is the first brain flexure to form?
The ventral cephalic fissure.
What are the three brain flexures which of these only appears in the secondary vesicle stage?
The ventral cephalic, the cervical and the pontine. the pontine only appears after the secondary vesicles are formed.
When does the cervical flexure develop the relation of what two structures causes it?
It appears between the 3rd and 5th week of development and is caused by the relation of the rhombencephalon the spinal chord.
What is the one brain flexure that persists after birth how is this observable in adult anatomy?
The cephalic fissure persists and is why the axis of the forebrain is at an angle to the rest of the CNS.
What are the two secondary vesicles derived from the proencephalon?
Telencephalon and diencephalon
What happens to the telencephalon throughout development?
It divides into two lateral bulges that develop into the two cerebral hemispheres and the basal ganglia.
What happens to the diencephalon throughout development?
Cells that make up the diencephalon develop into the thalmus, hypothalmus, pineal gland and pituitary gland.
What happens to the mesoencephalon throughout development?
it develops into four prominent structures know collectively as the corpora quadrigemina, the two of these nearest the diencephalon are known as the superior colliculi the two closest to the hind brain are known as the inferior colliculi.
What two secondary vesicles are derived from the rhombencephalon?
The metencephalon and myelencephalon.
What happens to the metencephalon throughout development?
It develops into the pons and cerebellum
What happens to the myelencephalon throughout development?
It becomes the medulla
What are the two main groups of cells found in the CNS and PNS
neurones and glial cells.
What is the most common type of glia cells?
Astrocytes
What protein is present in astrocytes that makes it able to distinguish them from neurones in the CNS?
glial fibrillary acidic protein
What is the term for the end of the processes that extyend from astrocyctes?
astrocytic endfeet
How do astrocytes help control the distribution of neurotransmitters?
They restrict diffusion, and absorb neurotransmitters for metaboloisation and recycling
What are the precursor cells to astrocytes what role do they play in brain growth?
radial glial cells they span the cerebral cortex allowing for the migration of new nerve cells.
What is the role of microglial cells before birth and in the adult body?
Before birth they help development by releasing growth factors and act as macrophages removing the debris from cells that have gone under apoptosis which happens on a large scale during this time. In adults they are mostly inactive but resume their phagocytic macrophage role during times of nerve damage and death.
What are the two kinds of myelinating cells?
Schwann cells and oligodendrocytes
Which type of mylinating cell has a role in the regeneration of peripheral axons following injury?
Schwan cells
What part of the nervous system are schwan cells mostly seen in?
The PNS
How many cells does a schwan cell typically insulate?
1
What is the term for the absence of the brain and skull what is the typical prognosis?
Anencephaly. Most children like this die in childbirth those that don’t typically die soon after due to cardiorespiratory arrest.
What is the alternate term for encephalocele, what is it and what effects it’s severity?
The alternate term is meningoencephalocele, this is where the brain and meninges extrude through the skull its severity is dependent on the size and location of the encephalocele.
What region of the neural tube fails to close in spina bifida?
the lumbosacral region.
what are the three categories of spina bifida?
Spina bifida occulta, spina bifida cystic (myleomeningiocele), meningocele.
which form of spina bifida usualy leads to some degree of disability in affected individuals?
myleomeningiocele/ spina bifida cystic
What is the term for excessive accumulation of cerebrospinal fluid in the brain
hydrocephalus
What abnormality of the cerebellum is often observed in spna bifida?
Type II arnold chiari malformation.
Why might a developing child with spina bifida have some degree of hydrocephaly what observable difference would this have to the structures of the brain?
The type II arnold chiari malformation causes the cerebellum to be forced into the foramen magnum of the skull disrupting the normal flow of CSF this can causeaccumulation of CSF in the skull/hydrocephally. This often leads to vetriculomegaly.
What is and what causes the lemon sign.
The lemon sign is a malformation of the skull where the skull becomes somewhat lemon shaped. It is caused by the decreased intracranial pressure resulting from the movement of the cerebellum in the arnold chiari malformation causing the frontal bone of the skull to be sucked in slightly changing the shape of the head.
When does the lemon sign usually disappear by what causes this?
The lemon sign is usually only resent up to 25 weeks due to the bones of the skull hardening allowing them to resist the drop in intracranial pressure.
What is the banana sign?
The observable deformation of the cerebellum often seen in spina bifida it often persists after the lemon sign
Why is the breach position more commonly seen in babies with spina bifida?
A baby with spina bifida will only have their leg undergo spontaneous spasms resulting in the legs not developing strongly enough to kick the baby round into the normal position.
How is a baby positioned in a breach birth position?
With its caudal end towards the cervix.
Why are are babies with spina bifida and encephaloceles often birthed via caesarean section?
Because it is though that the cysts present in these conditions may be damaged by the normal birth process.
