development of the nervous system

Question 1

what features are involved at the beginning of the development of the spinal chord *

Answer 1

neural plate ectoderm mesoderm endoderm - internally

Question 2

how does the neural tube develop *

Answer 2

the ectoderm over the trilaminar embryonic disk thickens to form the nerual plate

the neural plate folds in on itself to form the CNS, first becoming the neural fold - this forms the neural canal

the neural tube is lined by neuroepithelial cells

the neural crest tissue forms alomng either side of the neural tube

Question 3

what do neuroepithelial cells form *

Answer 3

the CNS

Question 4

what are neural crest cells *

Answer 4

they are cells either side of the neural tube that develop into the peripheral NS

• sensory neurons of the dorsal root ganglia and cranial ganglia
• postganglionic autonomic neurons
• schwann cells
• non-neuronal derivitives eg melanocytes

Question 5

describe the differentiation of neuroepithelium *

Answer 5

it ahs to make lots of different cell types including neuroblasts, glioblasts and ependymal cells

Question 6

describe neuroblasts *

Answer 6

they are of developmental origen turn into neurons with cell bodies in CNS

Question 7

describe glioblasts *

Answer 7

developmental they form astrocytes, oligodendrocytes

Question 8

describe astrocytes *

Answer 8

involved in neurotransmission support neurons involved in the blood brain barrier

Question 9

describe oligodendrocytes *

Answer 9

wrap around neurons - myelination

Question 10

describe ependymal cells *

Answer 10

line the ventricles and central canal of spinal cord

Question 11

descrinbe the differentiation of the neural crest cells *

Answer 11

form the sensory neurons - cell bodies sit in the dorsal root ganglia form ganglia in the periphery - postganglionic autonomic neurons form shwann cells form non-neuronal derivitives eg melanocytes

Question 12

where does proliferation of the neuroepithelium occur *

Answer 12

cell division happens at the inside of the neural tube

Question 13

describe the formation of the layers in the neural tube *

Answer 13

ependymal cells stay at the inner membrane - germinal layer

neuroblasts migrate away from the inner membrane to the grey matter layer - the mantle layer

the neurobast axons are directed out to form the white matter layer - marginal layer

glioblasts migrate to both the white and grey matter

Question 14

describe the layers of the neural tube *

Answer 14

at the dorsal side - roof plate

at the ventral - floor plate

ependymal/germinal layer lines the canal

grey matter/mantle layer

white matter/marginal layer

in brain, grey outside and white beneath

Question 15

what controls neural differentiation *

Answer 15

sequential secretion of different selective signalling molecules that interact with recpetors on neuroblasts that determine how far, where and what the blast cells differentiate to they control migration and axonal growth by attraction and repulsion (atrophic and inhibitory factors) depends on the conc gradient and timing of secretion of signalling molcules

Question 16

summarise the developing spinal cord *

Answer 16

the grey matter layer differentiates into the alar plates dorsally and the basal plates ventrally

alar plates develop into dorsal horns

basal plates develop into ventral horns

the neural crest develops into the dorsal root ganglia (sensory)

ventral neurons are motor neurons and interneurons - in the ventral grey matter

neurons in the dorsal grey matter are the interneurons

sensory info comes from the dorsal root ganglia and synapse on the interneurons in the dorsal horns and the information goes up to the brain.

Question 17

describe a simple reflex pathway *

Answer 17

the sensory info goes into the dorsal horn and then there is a single synsapse between the dorsal and ventral neurons - then the motor neurons take the signal away via ventral root and the spinal nerve

Question 18

describe the developing brainstem *

Answer 18

the ventral/motor nuclei are more medial, the dorsal/sensory are more lateral because the neural plate hasn’t folded properly (because of the presence of the 4th ventricle) - this dictates the pattern of the cranial nerve nuclei in the brainstem

there is the 4th ventricle - large just under the cerebellum, this is formed becasue of lateral proliferation of teh root plate

Question 19

describe the dorsal view of an embryo brain at 4wks - dorsal view of embryo *

Answer 19

it is the anterior part of the neural tube there is the future forebrain - PROSENCEPHALON the future midbrain (brainstem) - MESENCEPHALON the future hindbrain (cerebellum) - RHOMBENCEPHALON future spinal cord

Question 20

describe the developing brain at 5 weeks - dorsal view of embryo *

Answer 20

the forebrain (cortex) has the telencephalon and the diencephalon - thalamus and hypothalamus midbrain - brainstem pons - brainstem medulla - brainstem

Question 21

describe the developing brain at 8wks - dorsal view of embryo *

Answer 21

neural tube forms ventricles - lateral ventricles (forebrain) drain into 3rd ventricle in the forebrain there are developing hemispheres midbrain - aqueduct drains into 4th ventricle hind - developing cerebellum, behind this - have the 4th ventricle

Question 22

explain how flexures in the brain give rise to development of the mature brain *

Answer 22

at 4wks there are - cephalic flexure, pontine flexure (level of pons) and cervical flexure (develop spinal cord below) 5wk - increase in flexures 8wk - have the cortex, diencephalon subcortically, and the cerebellum in hind brain term - still growth - myelination and formation of pathways

Question 23

summarise how the cotical layers form from the neuroepithelium *

Answer 23

in the subventricular zone there are developmental cells - even in adult in ventricular zone there are vertically orientated radial glial cells - astrocytes which scaffold from ventricle to pia surface using growth and inhibitory factors, neurons migrate along radial glia - ultimately end with 6 layers - layer 1 is just fibres

Question 24

what are the zones in the cortex *

Answer 24

ventricular zone subventricular zone intermiediate zone ???

Question 25

what does the normal developmet depend on *

Answer 25

proliferation, differentiation, migration, axon growth and synapse formation

Question 26

how can things go wrong in development

Answer 26

genetics and environment, - lifestyle, diet, teratogens can interfere with processes

Question 27

describe cranioachischisis

Answer 27

completely open brain and spinal cord

Question 28

describe anencephaly

Answer 28

open brain and lack of skull vault anterior portion of neural tube hasn’t fused and brain hasn’t developed

Question 29

describe encephalocele

Answer 29

herniation of the meninges and brain - brain develop out of the cranial cavity

Question 30

describe iniencephaly

Answer 30

extreme retroflexion of the head

Question 31

describve meningocele

Answer 31

meninges bulging out of defect of skull/spine - filled with CSF

Question 32

describe closed spine dysraphism

Answer 32

deficiency of at least 2 vertebral arches - covered by lipoma - hernia

Question 33

describe spina bifida occulata

Answer 33

closed asymptomatic, some of the vertebrae are not completely closed no closure of the base of the spinal tube

Question 34

describe myelomeningocele

Answer 34

open spinal cord - externally visible

Question 35

what is a neural tube defect

Answer 35

defecit at top of bottom of neural tube can be prevented by folic acid in pregnancy

Question 36

describe neuronal stem cells and their use for regeneration *

Answer 36

in development many are lost by apoptosis some are left behind - especially in the hippocampus in degenerative diseases you can’t regenerate nerve cells - if we can access progenitor cells we might be able to treat

Question 37

summarise how developmental neurobiology can be used in the repair of the nervous system *

Answer 37

stem cells

use axonal guidance mechanisms to induce regeneration of the CNS