Development Of Nervous System Flashcards
What is the notochord?
Refers to a rod of cells
Where is the notochord located?
Runs in the midline of the embryo
In the mesoderm layer
During what process is the notochord formed?
Gastrulation
What is the function of the notochord?
Releases signalling molecules
Which diffuse upwards to the overlying ectoderm
Stimulate it to differentiate into neuroectoderm
What is the neural plate?
Refers to a thickening of neuroectoderm
What are neural folds?
Refers to the edges of the neural plate moving upwards
What is the neural groove?
Refers to the depression in the neural plate between the neural folds
What is neurulation?
Refers to the formation of the neural tube
How does neurulation occur?
Elevated edges of neural plate curl towards each other
Meet each other in the midline
Fuse together to form neural tube
What are neuropores?
Refers to openings at the ends of the neural tube
Where are the anterior and posterior neuropores located?
Anterior neuropore - cranial end of neural tube
Posterior neuropore - caudal end of neural tube
What happens to the neuropores during development?
Close up completely
What developmental abnormality causes neural tube defects?
Neuropores do not close up completely
What are two types of neural tube defects?
Spina bifida/cleft spine
Anencephaly
What developmental abnormality causes spina bifida?
Posterior neuropore doesn’t close up completely
Where does spina bifida occur in the spine?
Lumbo-sacral region
What is the structure of a low-severity spina bifida?
Spinal cord is deep
Cyst made up of meninges and CSF is near the surface
What is the structure of a high-severity spina bifida?
Cyst made up of meninges and CSF is deep
Spinal cord is near the surface
What are the signs of spina bifida? Why do they occur?
Neurological deficits, due to problems with spinal cord
But no cognitive delay because no problem with brain
Hydrocephalus, due to meninges being abnormally tethered to spinal cord
What developmental abnormality causes anencephaly?
Anterior neuropore doesn’t close up completely
What is meant by anencephaly?
Cranial structures do not develop, including the brain
How are neural tube defects diagnosed?
Raised maternal serum alpha-fetoprotein
Ultrasound scan
Why is maternal serum alpha-fetoprotein raised with neural tube defects?
This is an embryonic protein that leaks out of the neural tube defect into amniotic fluid and then maternal circulation
How are neural tube defects prevented?
Folic acid pre-conceptually for 3 months and during the first trimester
What does the spinal cord develop from?
Most of caudal end of neural tube
How does the cauda equina develop?
Initially vertebral column and spinal cord are same length
But then vertebral column grows faster
Spinal nerve roots elongate downwards to exit at their corresponding intervertebral foramina
How many primary brain regions are there? What are they called?
Three
Forebrain, midbrain and hindbrain
When do the primary brain regions develop?
As the neural folds form
When do the primary brain vesicles develop?
As the neural tube forms
How many secondary brain vesicles are there?
Five
What are flexures?
Folds in the cranial neural tube
Why do flexures form?
Cranial neural tube grows and runs out of space
So it folds to maximise its use of space
How many flexures are there? What are they called?
Two
Cervical and cephalic
Where along the cranial neural tube is the cervical flexure?
Between the spinal cord and hindbrain
Where along the cranial neural tube is the cephalic flexure?
In the midbrain
What does the ventricular system develop from?
The lumen of the neural tube
What is hydrocephalus?
Accumulation of CSF in the ventricular system
How is the neural tube organised?
Deep layer
Intermediate layer
Marginal layer
Dorsal end
Ventral end
What is the deep layer of the neural tube made up of?
Neuroepithelial cells
What is the function of the neuroepithelial cells of the deep layer of the neural tube?
Line the ventricular system
Produce CSF
What is the intermediate layer of the neural tube made up of?
Neuroblast cell bodies
What is the marginal layer of the neural tube made up of?
Processes of neuroblasts
What are the dorsal and ventral ends of the neural tube made up of?
Dorsal end is made up of roof plate
Ventral end is made up of floor plate
What is the function of the roof and floor plates of the neural tube?
Regulate dorsal and ventral patterning of the neural tube
Divide intermediate layer into alar plate and basal plate
Where are neural crest cells located in the embryo?
Lateral border of neuroectoderm
What happens to neural crest cells during development?
Become displaced and enter the mesoderm
Undergo epithelial to mesenchymal transition
Migrate to other regions of embryo
What do neural crest cells develop into?
Wide range of structures
E.g. cranial nerve ganglia, dorsal root ganglia, autonomic ganglia, Schwann cells, connective tissue of face and skull, septum of heart, melanocytes
What developmental abnormalities can occur with neural crest cells?
Problems with migration
Problems with morphogenesis
What is an example of a condition with abnormal development of neural crest cells?
DiGeorge syndrome
What abnormalities are present in people with DiGeorge syndrome due to abnormalities in neural crest cell development?
Congenital aphasia of thymus gland
Aplastic parathyroid glands
Cardiac defects
What body system is the first to begin development?
Nervous system
Which body system is the last to complete development?
Nervous system
When does the nervous system complete development?
End of first year after birth
Which body system is the most susceptible to damage during pregnancy? Why?
Nervous system
Because it is developing throughout the entire pregnancy
What is the relative position of the alar plate?
Dorsal
What is the function of the alar plate?
Sensory functions
What is the relative position of the basal plate?
Ventral
What are the functions of the basal plate?
Motor functions
What causes hydrocephalus?
Blockage of ventricular system
E.g. stenosis, infection, tumour
How is hydrocephalus treated?
Use of shunt
How does the brain develop?
Primary brain regions develop
Then primary brain vesicles
Then secondary brain vesicles
How does the ventricular system develop?
When the five secondary brain vesicles form, there is an empty space in each one
These empty spaces develop into the ventricles
