2 Embryology Nervous System Flashcards
How is the neural tube formed from the notochord after gastrulation has occurred?
Notochord- induces neurulation- neural plate- lateral edges elevate- depressed mid region= neural groove- neural folds approach in midline and fuse= NEURAL TUBE
What effect does the notochord have on the overlying ectoderm?
Directs conversion of overlying ectoderm to neuroectoderm
What is the notochord?
Early forming midline structure in the trilaminar embryo mesoderm layer initially ventral to the ectoderm, then neural plate and finally neural tube- has important signalling role
By what day of pregnancy has the neural tube completely closed? How long does the whole process take (from the neural plate stage)?
Neural tube closed: 28-32 days pregnancy
Process takes: 10 days
Failure in the closure of the neuropores can cause neural tube defects. What effect will a cranial defect have and what effect will a caudal defect have?
Cranial defect: anencephaly(absence of a major portion of the brain, skull, and scalp)
Caudal defect: spina bifida
What is spina bifida? Where does it occur? What consequence can it have?
What?
Spinal column is either incompletely formed or absent
Where?
Can occur anywhere along length of neural tube
Most occur in lumbrosacral region
Consequence?
Neurological deficits: sensory dysfunction, flaccid paralysis and areflexia below the affected level
What is hydrocephalus? How can it occur and how can it be treated?
What?
increase in the volume of cerebrospinal fluid (CSF) occupying the cerebral ventricles
How it can occur?
Blockage between ventricles (CSF drains down) eg tumour, infection, occurs with spina bifida
Treated?
Treated using a shunt into the peritoneum
Apart from spina bifida, give 2 other consequences that can occur as a result of spinal cord defects.
- Anencephaly (failure of notochord closure cranially–> absence of cranial structures–> incompatible with life)
- Rachischisis (failure of neural fold elevation)
In some cases it is possible to diagnose and potentially reduce the incidence of neural tube defects. How can this be done (diagnosis and prevention)
Diagnosis
- Raised maternal serum α-fetoprotein
- Take into account maternal age
- USS
Prevention
Folic acid pre-conceptually (3 month and for first trimester)
Reduces incidence by 70%
Outline how the neural tube develops into the spinal cord, the divisions of the brain, the ventricular system (and the flexores and neural crest cells)).
-
Explain how and why the cauda equina is formed.
- Neural tube gives rise to spinal cord
- After 3rd month- vertebral column grows faster than spinal cord
- Spinal roots must elongate before they exit their intervertebral foramen
- Forms CAUDA EQUINA
What are the 3 primary brain regions (dilations) that can be seen during neural fold formation?
Name the 5 secondary brain vesicles that develop from the 3 primary brain vesicles?
Where do the 2 flexures of the neural tube occur? Why do they occur?
Why?
Growth of cranial neural tube exceeds available space linearly so must fold
Where?
Cervical flexure: spinal cord- hindbrain junction
Cephalic flexure: midbrain region
Give some of the derivatives of the neural crest cells in the: 1) nervous system, 2) head, neck and midline, 3) other (2)
(REMEMBER= extremely vulnerable to environmental insult esp alcohol)
Odontoblasts: large columnar cells, whose cell bodies are arranged along the interface between dentin and pulp, from the crown to cervix to the root apex in a mature tooth
Give some examples conditions caused by abnormalities of neural crest cell migration (2)
What do each of the secondary brain vesicles develop into? (5)
Useful diagram- parts of brain derived from secondary brain vesicles:
Useful schematic- showing how ventricles form in nervous system.
