Embryology of the Nervous System

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  • Created by: Becca
  • Created on: 29-12-13 12:40
What does the primitive node develop into? What is its embryological origin?
Develops into the notochord which is solid mesoderm, signals come from it to induce neuroectoderm formation in overlying ectoderm. The region around this is called the neural plate
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What happens to the neural plate during development?
The neural plate starts to curl up (folds form in the neural groove) and will pinch off as the neural tube
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What is the difference between the primitive streak & the notochord/neural plate as they grow?
The primitive streak stays the same length but the notochord and neural plate grow until they reach the procordal plate
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What develops at the beginning of the 4th week?
Paroxial mesoderm form somites: medial part -> sclerotome (skeleton) & vertebral body (adjacent to neural tube). Intermediate -> myotome (muscle) & nephrotome (genitourinary sys). Lateral -> dermotome/skin, parietal (body wall) or visceral (gut wall)
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What genes are involved in the development of the neural plate?
Neural plate starts to form by inducing the expression of PAX3, 7 followed by notochord secretion of SHH which induces PAX6 -> folding of neural tube
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What controls neural folding?
Organising centre: anterior neural ridge & FGF8 - SHH is secreted by prochordal plate & notochord, BMPs are secreted by adjacent non-neural ectoderm
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What physical route does neural tube formation occur in?
Begins centrally - central canal (partially formed neural tube) is in communication with amniotic cavity via the anterior (cranial) and posterior (caudal) neuropores
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What is spina bifida? What is common to each sub-type?
Failure of closure of a posterior/caudal neuropore. All types involve a failure in vertebral arch formation
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What is each sub-type of spina bifida? (commom/symptomless -> rare/no neural function)
SB occulta: failed arches of bone to form to protect neural cord. SB cystica meningocoel: swollen meninges. SB cystica meningomyelocoel: whole neural tube protrudes from body wall. SB cystica myeloschisis: neural tube hasn't closed, sits on surface
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During brain development, what closes initially? What does this closure form? What is this formation controlled by?
Closure of rostral neuropore -> formation of 3 primary brain vesicles: prosencephalon (forebrain), mesencephalon (midbrain) & rhombencephalon (hindbrain). Controlled by a pattern of HOX gene expression in overlapping rhombomeres
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When do brain flexures form? Where are the flexures?
Flexures form during week 4: midbrain flexure in the midbrain region, cervical flexure at the junction of hindbrain & spinal cord and pontine flexure, later divides hindbrain to myelencephalon (medulla oblongata) & metencephalon (pons + cerebellum)
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What is holoprosencephaly?
Defective formation of the brain where the lateral ventricles merge to form a single large ventricle. Results in facial abnormalities: midline facial defects and hypotelorism (eyes too close together)
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When does myelin sheath formation occur? What are the different types of myelin sheath?
Begins mid-foetal life, continues postnatally. Myelin = lots cell membrane with cytoplasm 'squeezed out'. Differs in the CNS (single oligodendrocyte, myelination of several axons) & PNS (Schwann cell, responsible myelinating short stretch of axon)
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Ectoderm along crests of neural folds form neural crest which detaches & migrates to either side of the neural tube. What can then form?
Cells of dorsal root ganglion i.e primary sensory neurons, sensory ganglia of CN, autonomic ganglia i.e post ganglionic cell bodies, adrenal medulla, Schwann cells, pigment cells and some meninges & bone/muscles of the head
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How does the nervous system develop?
A single layer of pseudostratified columnar cells divide & migrate outwards to increase tube size. Form either neurons or supporting cells (dorsal root/sympathetic ganglia->oligodendrocytes/astrocytes). Original germinal layer remains as ependyma
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How does the spinal cord & vertebral canal develop?
Initially cord fills vertebral canal, spinal nerves emerge horizontally at all levels. Bones grow more rapidly, cord 'left behind'. Nerve roots fuse to form spinal nerves at intervertebral foramen therefore cauda equina consists of spinal nerve roots
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Other cards in this set

Card 2

Front

What happens to the neural plate during development?

Back

The neural plate starts to curl up (folds form in the neural groove) and will pinch off as the neural tube

Card 3

Front

What is the difference between the primitive streak & the notochord/neural plate as they grow?

Back

Preview of the front of card 3

Card 4

Front

What develops at the beginning of the 4th week?

Back

Preview of the front of card 4

Card 5

Front

What genes are involved in the development of the neural plate?

Back

Preview of the front of card 5
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