Anatomy Lecture 5

Front 1

From where does the nervous system develop?

Back 1

Ectoderm of germ disc

Front 2

What are the precursors to the brain and spinal cord?

Back 2

Notochord and adjacent mesoderm induce the overlying ectoderm to form a neural plate that ultimately becomes the neural tube which will differentiate into brain and spinal cord

Front 3

Describe the formation of the neural tube

Back 3

1) Neural plate- thickened ectoderm
2) Neural folds
3) Neural tube
Fusion begins in midportion of neural groove and extends in both cranial and caudal directions
Cranial (anterior) neuropore closes about day 25, and the caudal (posterior) neuropore closes about 2 days later
The completely closed neural tube detaches from the ectoderm and sinks into the underlying mesoderm

Front 4

Describe the molecular regulation of the neural tube

Back 4

1) Noggin, chordin, and follistatin inactivates BMP-4 causing the ectoderm to become neuralized (neural plate- forebrain and midbrain)
2) WNT-3a and FGF are needed to allow induction of the caudal neural plate to form hindbrain and spinal cord
3) Initially, the PAX3, PAX7, MSX1, and MSX2 genes are expressed throughout the neural plate
4) Shh expression from notochord induces neural plate to ventralize and the floor plate to form by repression of PAX and MSX (basal plate)
5) BMPs upregulate PAXs expression in the dorsal neural tube that will form the roof plate and alar plate

Front 5

What are the two main portions of the neural tube?

Back 5

1) Cranial portion- expands to form the brain
2) Caudal portion- elongates to form spinal cord

Front 6

What are the 3 formations of the cranial portion of the neural tube?

Back 6

1) Three vesicles form: prosencephalon (forebrain), mesencephalon (midbrain), and rhombencephalon (hindbrain)
2) Ventricle formation: lateral, interventricular foramena (monro), third, cerebral aquaduct (sylvius), and fourth
3) Brain flexures- cervical, cephalic (midbrain), and pontine

Front 7

Describe 9 aspects of the caudal portion of the neural tube

Back 7

1) Neural tube is formed from neuroepithelial cells that rapidly divide thereby thickening the wall of the tube
2) Some neuroepithelial cells become neuroblasts which form the mantle layer around the neuroepithelial layer. The mantle layer becomes the gray matter of the spinal cord
3) Neuroepithelial cells will also give rise to astrocytes and oligodendroglia. Microglial cells are derived from mesoderm which migrate into the neural tube
4) A layer of neuroepithelial cells will line the cavity of the neural tube. These become the ependymal cells of the ventricles and spinal cord
5) As neuroblasts differentiate into neurons they extend processes to the periphery of the neural tube. As the processes become myelinated, this layer is termed the marginal layer (white matter)
6) Mantle layer
7) Neural crest
8) Spinal nerve
9) Positional changes of spinal cord

Front 8

List the 5 components of the mantle layer

Back 8

1) Basal plate- ventral horn- motor
2) Alar plate- dorsal horn- sensory
3) Sulcus limitans
4) Roof plate and floor plate
5) Intermediolateral cell column- sympathetic T1-L3- ANS

Front 9

List 9 components of the neural crest

Back 9

1) Spinal ganglia (dorsal root)
2) Sympathetic ganglia
3) Schwann cells (neurilemma)
4) Leptomeninges (pia and arachnoid)
5) Melanocytes
6) Odontoblasts (dentin of teeth)
7) Head mesoderm- pharyngeal arches
8) Suprarenal medulla
9) Heart (septum)

Front 10

List and describe 4 components of spinal nerve

Back 10

1) Ventral root- axons from neurons in basal plate
2) Dorsal root- axons from neurons of spinal (sensory) ganglia
3) Dorsal and ventral roots combine peripherally to form the spinal nerve (mixed sensory and motor)
4) Spinal nerve will further subdivide into dorsal and ventral primary rami supplying epimeric and hypomeric musculature

Front 11

Describe the positional changes of the spinal cord

Back 11

1) Initially, spinal cord extends entire length of embryo
2) Dura and vertebrae grow faster than spinal cord
3) At birth, end of cord (conus medullaris) is at L3 level
4) Cord ends between L1 and L2 in adult

Front 12

List 4 possible neural tube defects

Back 12

1) Spina bifida- results from vertebral rachischisis
2) Cranium bifida- ossification defect of skull
3) Exencephaly- cranial neuropore remains open which results in the condition termed anencephaly
4) Hydrocephalus- caused by aquaductal stenosis

Front 13

List 3 types of spinal bifida

Back 13

1) Occulta
2) Cystica- meningocele and meningomyocele
3) Myeloschisis (spina bifida aperta)- Arnold-Chiari malformation- herniation of cerebellum due to tethering of cord in spina bifida cystica

Front 14

List 3 types of cranium bifida

Back 14

1) Meningocele
2) Meningoencephalocele
3) Meningohydroencephalocele

Front 15

Describe the formation of the pituitary gland (hypophysis)

Back 15

1) Rathke's Pouch- adenohypophysis, pars tuberalis, and pars intermedia
2) Infundibulum- stalk and pars nervosa

Front 16

List 4 characteristics of spinal nerves

Back 16

1) All cranial nerves except olfactory (I), optic (II), and spinal accessory (XI) arise from brainstem
2) All that arise from brainstem do so from the rhombencephalon except oculomotor (III) and trochlear (IV) which arise from mesencephalon
3) Rhombomeres- induction is by signaling of underlying somitomeres formed from paraxial mesoderm, give rise to motor nuclei of cranial nerves V, VI, VII, IX, X, and XII
4) Ectodermal placodes- give rise to sensory ganglia along with neural crest cells

Front 17

List the 3 types of ectodermal placodes

Back 17

1) Nasal- sensory epithelium in nose
2) Otic- ear
3) Epibranchial (4)- contribute ganglia to the cranial nerves V, VII, IX, and X which supply the pharyngeal arches

Front 18

What are the 2 divisions of the autonomic nervous system?

Back 18

1) Sympathetic
2) Parasympathetic

Front 19

List 3 characteristics of the parasympathetic nervous system

Back 19

1) Fibers carried by cranial nerves III, VII, IX, and X
2) Ganglia are derived from neural crest
3) Also in sacral spinal nerves S2, S3, and S4

Front 20

List 2 characteristics of the sympathetic (T1-L2 or L3) nervous system

Back 20

1) Thoracic neural crest migrates the entire length of the developing spinal cord and these neuroblasts form the chain ganglia
2) Other neural crest derived neuroblasts migrate further to form the preaortic (collateral) ganglia and sympathetic organ plexus ganglia (cardiac, pulmonary, and gastrointestinal)
Preganglionic cell fibers (intermediolateral cell column)
White ramus communicans
Postganglionic fibers
Gray ramus communicans

Front 21

What does the blocking of BMP4 expression cause?

Back 21

Formation of the neural plate in the middle of the ectoderm

Front 22

What do PAX3 and PAX7 become?

Back 22

Bipolar sensory neurons

Front 23

What does Shh signaling initiate?

Back 23

Invagination of the neural plate into the embryo

Front 24

When does the cranial neuropore close? The caudal neuropore?

Back 24

Around day 25
Two days later

Front 25

What is the fate of neuroepithelial cells?

Back 25

Remain on central canal and will form part of CSF

Front 26

Ganglia are derived from what?

Back 26

Neural crest

Front 27

What direction does epimeric musculature grow?

Back 27

Dorsally

Front 28

What direction does hypomeric musculature grow?

Back 28

Ventrally

Front 29

What part of the vertebrae is missing in spina bifida occulta?

Back 29

Pedicle and part of lamina

Front 30

What is lacking to complete development in spina bifida aperta?

Back 30

Shh

Front 31

What is Arnold-Chiari malformation?

Back 31

The brain stem and cerebellum are pulled through the formen magnum due to a stretching of the spinal cord. Spinal cord is tethered in place due to spina bifida aperta

Front 32

Define exencephaly

Back 32

Cranial neural tube failed to close

Front 33

Define craniorachischisis

Back 33

Skull failed to completely form

Front 34

Molecular signaling from where influence development of the rhombencephalon (hindbrain)?

Back 34

Occipital somites

Front 35

Where do motor nuclei develop?

Back 35

Rhombomeres of neural tube

Front 36

Describe ectodermal placodes

Back 36

Form from surface ectoderm
Move into embryo then populated by neural crest cells which form neurons of the sensory ganglia of cranial nerves

Front 37

What do neural crest cells of the caudal neural tube form?

Back 37

Neurons of the DRG and sympathetic ganglia