S1) Embryology of the Nervous System Flashcards
Describe the five steps involved in the formation of the neural tube in early embryonic development
⇒ Gastrulation produces the notochord
⇒ Notochord induces neurulation
⇒ Neurulation induces the neural plate
⇒ Elevation of lateral edges of neural plate
⇒ Neural folds gradually approach each other in the midline and fuse, producing the neural tube
What is the role of the notochord during neurulation?
The notochord directs the conversion of the overlying ectoderm to neurectoderm
What is a neuropore?
A neuropore is a region corresponding to the opening of the embryonic neural tube in the anterior/posterior portion of the developing prosencephalon
Defects in closure of the neuropores underlie serious and common birth defects of the nervous system.
What are neural tube defects?
- Neural tube defects are defects which result from failure of the neutral tube to close
- Failure can occur caudally or cranially
What are the results of the following:
- Cranial neural tube defect
- Caudal neural tube defect
- Cranial neural tube defect results in anencephaly
- Caudal neural tube defect results in spina bifida
What is spina bifida?
- Spina bifida is a type of neural tube defect occurring when the vertebrae don’t form properly around part of the baby’s spinal cord
- It arises from the failure of neural tube closure caudally
Spina bifida can occur anywhere along the length of the spine.
What is the most common location?
Spina bifida most commonly occurs in lumbosacral region
What is anencephaly?
- Anencephaly is a neural tube defect resulting in the absence of cranial structures, including the brain
- It results from the failure of neural tube closure cranially and is incompatible with life
What is rachischisis?
Rachischisis is a neural tube defect occuring due to the failure of neural fold elevation
How can one diagnose a neural tube defect?
- Raised maternal serum α-fetoprotein
- USS
How can a neural tube defect be prevented?
Folic acid pre-conceptually (3 month) and for the first trimester reduces incidence by 70%
Most of the length of the neural tube gives rise to the spinal cord.
In four steps, explain how the cauda equina forms
⇒ A 3 months, the spinal cord is the same length as the vertebral column
⇒ Thereafter, the vertebral column grows faster
⇒ The spinal roots must elongate in order to exit at their intervertebral foramen
⇒ Cauda equina is formed
During neural fold formation three primary brain regions can be distinguished.
Identify these primary brain vesicles
- Embryonic forebrain (prosencephalon)
- Embryonic midbrain (mesencephalon)
- Embryonic hindbrain (rhombencephalon)
At 5 weeks of development, the three primary brain vesicles become five secondary brain vesicles.
Identify these
Identify the mature derivatives of the following secondary brain vesicles:
- Telencephalon
- Diencephalon
- Mesencephalon
- Metencephalon
- Myelencephalon
How are flexures formed in the embryological development of the nervous system?
Growth & development at the cranial neural tube exceeds available space linearly, so it must fold up to form flexures
Which two flexures are formed in the embryological development of the nervous system?
- Cervical flexure
- Cephalic flexure
Where are the cervical and cephalic flexures located respectively?
- Cervical flexure – hindbrain junction
- Cephalic flexure – midbrain region
What is the role of the ventricular system?
The ventricular system cushions the brain & spinal cord within their bony cases
Compare and contrast the ventricular system in development and adults
- In development, it is a tubular structure of the developing CNS persisting as development proceeds
- In the adult, it is comprised of interconnected “reservoirs” filled by CSF, produced by cells of ventricular lining
Relate the secondary brain vesicles to their corresponding ventricle in the ventricular system
- Telencephalon → lateral ventricle
- Diencephalon → third ventricle
- Mesencephalon → cerebral aqueduct
- Metencephalon & myelencephalon → fourth ventricle
What is hydrocephalus?
- Hydrocephalus is a condition characterised by excessive accumulation of fluid in the brain
- Is is most common in newborns with spina bifida occur due to a blockage of the ventricular system e.g. tumour, infection
How can hydrocephalus be treated?
Hydrocephalus is readily treatable by use of shunt
Explain the early organisation of the neural tube by describing its three layers
- Inner: neuroepithelial layer
- Intermediate: mantle layer (neuroblasts)
- Outer: marginal layer (processes)
What is the function of the roof and floor plates of the neural tube?
Roof & floor plates regulate dorsal & ventral patterning
Describe the modality of the alar and basal plates respectively
- Alar plate = sensory
- Basal plate = motor
Describe the location and function of neural crest
- Location: cells of the lateral border of the neuroectoderm tube
- Function: become displaced and enter the mesoderm and undergo epithelial to mesenchymal transition
Identify 8 neural crest derivatives in the nervous system
- Cranial nerve ganglia
- Spinal root ganglia
- Sympathetic ganglia (chain & pre-aortic)
- Parasympathetic ganglia
- Schwann cells
- Glial cells
- Leptomeninges (arachnoid & pia)
- Connective tissue & bones of the face & skull
Identify 3 neural crest derivatives in the head, neck and midline
- Odontoblasts
- Dermis (face & neck)
- C cells of the thyroid gland
Identify 3 miscellaneous neural crest derivatives
- Conotruncal septum (heart)
- Melanocytes
- Adrenal medulla
