Lecture 6B: CNS Development Flashcards
T/F: As a consequence of developmental events, structures belonging to functionally unrelated systems often come to lie next to one another.
True.
What is Down’s Syndrome?
A chromosomal disorder caused by the presence or all or part of an extra 21st chromosome.
An agent or environmental factor that causes malformation of an embryo is known as a ______.
Teratogen
In fetal alcohol syndrome, there is an association between the severity of facial structural defects and _______.
Midline brain anomalies.
T/F: Fetal Alcohol syndrome is the most common genetic cause of mental retardation.
False.
Down’s Syndrome is the most common genetic cause of mental retardation.
What structure of the brain is often associated with structural anomalies in a child born with fetal alcohol syndrome?
Corpus callosum
List 4 characteristics of children with fetal alcohol syndrome.
1) Small birth weight
2) Problems eating and sleeping
3) Difficulty seeing and hearing
4) Physical disabilities (ie. abnormal muscle tone)
5) Trouble following directions
6) Difficulty paying attention and learning in school
7) Behavioural deficits: trouble getting along with others and controlling behaviour
T/F: The embryonic stage is from conception to 2 weeks.
False.
This is the pre-embryonic stage.
The fetal stage is from _____ until ____.
End of 8th week; birth
What major milestone occurs during the embryonic stage?
Development of systems and organs (ball of cells has begun to differentiate).
What major milestone occurs during the fetal stage?
Nervous system continues to develop and mylelination of neurons begins.
____ to _____ marks the embryonic stage.
End of week 2; end of week 8
At what developmental stage in utero does the basic nervous system (besides myelination) begin to form?
Embryonic stage
When do three germ cell layers become established for form the embryo?
Beginning of 2nd week
What germ layer develops into all major tissues of the nervous system and the skin?
Ectoderm
T/F: The endoderm is the outermost layer of the the three germ cell layers.
False.
The endoderm is the innermost layer.
T/F: The mesoderm develops into bones of skeleton, muscles and the digestive tract.
False.
The mesoderm develops into bones of the skeleton, muscles and circulatory system.
The endoderm develops into the digestive tract, liver and ______.
Respiratory system.
What is the thickening of the ectoderm, form which the nervous system begins, known as?
Neural plate
The neural plate begins to fold at its lateral edges to form the ______. The neural folds then progressively fuse to form the _____.
Neural groove; neural tube
What is the name of the process by which the neural plate becomes the neural tube?
Neurulation
Closure of the neural tube is initiated at the precursor area to the _____.
Upper cervical spine
On what day does neurulation occur in embryonic development?
Day 22
What are 2 cephalic and 1 caudal conditions that can result from failure of the neural tube to completely close?
1) Anencephaly
2) Encephalocele
3) Spina bifida - caudal
What condition involves an absence of a large part of the brain and the skull (mostly fatal)?
Anencephaly
A herniation of intracranial contents through a defect in the cranium can be seen in what condition?
Encephalocele
What is spina bifida?
Developing vertebrae do not close around the incomplete neural tube, resulting in a bony defect at the distal end of the neural tube.
What are the two types of spina bifida?
Spina bifida occulata; spina bifida cystica
T/F: In spina bifida cystica, the neural tissue does not protrude through the bony defect.
False.
This occurs in spina bifida occulata.
Explain the difference between meningocele and meningelomyelocele.
Meningocele - meninges and CSF protrude through the bony defect (spinal cord does NOT)
Meningelomyelocele - defect is large enough for meninges and a portion of the spinal cord to protrude through the defect.
Meningocele and meningelomyelocele are the subtypes of what condition?
Spina bifida cystica
Many neural tube defects have been traced to deficiencies in what in the maternal diet?
Folic acid
What is a possible mechanism by which folic acid helps to reduce the incidence of neural tube defects?
Folic acid may accelerate cell proliferation and thereby overcome any genetic/environmental defect that impairs cell proliferation.
What structure results from a pinching off of the ectoderm during neurulation and lies lateral to the neural tube?
Neural crest
T/F: Neural crest cells give rise to neurons and glia in the PNS.
True
The caudal portion of the neural tube gives rise to the _____, while the expanded cephalic (rostral) portion of the neural tube will form the ___.
Spinal cord; brain
When does brain formation occur?
Day 28 (week 4)
What are the 3 primary vesicles (enlargements) that form from the expanded cephalic portion of the neural tube?
1) Forebrain
2) Midbrain
3) Hindbrain
What what week are there 5 secondary brain vesicles?
Week 5
What will the anterior forebrain become? What will the posterior forebrain become?
Anterior: 2 cerebral hemispheres
Posterior: diencephalon
The hindbrain develops into the ____, ____ and ____.
Pons, cerebellum and medulla.
Why do flexures form?
Flexures form as a result of unequal growth of different parts of the developing brain.
What are the 3 flexures that form?
1) Cephalic flexure
2) Pontine flexure
3) Cervical
The cephalic flexure forms in the region of the _____. The pontine flexure occurs in the region of the developing ____. The cervical flexure forms at the junction between ____ and ____.
1) midbrain
2) pons
3) hindbrain
4) spinal cord
Which flexure is permanent?
Cephalic flexure
T/F: The typical brain has 100 million nerve cells at birth.
False.
The typical brain has 100 billion nerve cells at birth.
What does secondary neurulation allow for the formation of?
Sacral and coccygeal segments of the spinal cord and dorsal and ventral horns.
Developing gray matter of the spinal cord separates into what?
1) Dorsal alar plate
2) Ventral basal plate
The alar plate gives rise to the ____ horn of the spinal cord, while the basal plate gives rise to the ____ horn, sites of ___ and ___ function respectively.
Dorsal horn
Ventral horn
Sensory
Motor
The dorsal gray and ventral gray columns segregate the white matter into ____, ____ and ____ funiculi.
Anterior, posterior, lateral
Up until what point are the spinal cord segments adjacent to corresponding vertebrae.
3rd fetal month
At what segment of the vertebral column would the S1 nerve root exit from during the 2nd fetal month?
S1 vertebrae (roots of sinal nerves project laterally from spinal cord until the 3rd fetal month)
At birth, the tip of the spinal cord lies at ___ vertebrae level, while in adults, the spinal cord extends to ____.
L3; L1 or L2
What is a condition associated with a defect in secondary neurulation? Explain.
Tethered cord syndrome - abnormal stretching of the spinal cord
From medulla through the midbrain, the alar and basal plates form sensory and motor columns of cells that supply _____.
Cranial nerves
How does the alar and basal plates in the developing brain differ from that of the spinal cord?
The alar plate is located slightly laterally in the developing brain to accommodate for other structures forming in the posterior direction (ie. fourth ventricle). The basal plate remains anterior in both.
Cells in alar plate differentiate into sensory neurons for ___, ___, ___, ____ and ____ from the face.
taste, hearing, balance, visceral sensation, somatic sensation from the face
Cells from what plate will develop into parasympathetic preganglionic neurons and muscles of the eyes, head and neck?
Basal plate
When do ventricles begin to form?
Day 28 (after the appearance of the three ventricles)
Why are the lateral ventricles “C” shaped?
Expansion of the cerebral hemispheres affects the shape of the lateral ventricles.
