Risher - Development of Central Nervous System

Question 1

Embryonic Germ Layers - Gives Rise to?

Answer 1

Ectoderm - CNS / PNS, parts of skin

Mesoderm - Blood vessels, bones, muscles

Endoderm - Inner lining of organs such as liver and pancrease

Question 2

Germ layer origin of notochord?

Role?

Answer 2

Mesodermal

Induces neural plate development

Question 3

Neurulation

Answer 3

Fusion of the Neural Tube (complete by day 28)

Question 4

Brain Vesicle Formation and Differentiation:

Developing Structure - Mature Structure

1. Telencephalon - ?
2. Diencephalon
3. Mesencephalon
4. Metencephalon
5. Myelencephalon

Answer 4

1. Telencephalon - Cerebral Hemispheres
2. Diencephalon - Thalamus
3. Mesencephalon - Midbrain
4. Metencephalon - Pons, Cerebellum
5. Myelencephalon - edulla`

Question 5

3 Vesicle Stage

Developing Structure - Mature Structure

Answer 5

Prosencephalon - Forebrain

Msesncephalon - Midbrain

Rhombencephalon - Hindbrain

Spinal Cord

Question 6

5 Vesicle Stage

Developing Structure - Mature Structure

Answer 6

Telencephalon - Cerebral Hemisphere

Diencephalon - Thalamus

Optic Vessicle - Retina

Mesencephalon - Midbrain

Metencephalon - Pons

Myelencephalon - Medulla

Question 7

Neural portion of the eye is derived from what?

Answer 7

Retina dericed from prosencephalon that gives rise to diencephalon

Question 8

Spinal cord derivation?

Layers of Neural Tube?

Answer 8

Spinal cord derived from Posterior region of Neural Tube

In order of formation:

1. Ventricular
2. Mantle
3. Marginal

Question 9

Mantle Layer

Contains?

Becomes?

Marginal Layer

Becomes?

Answer 9

Contains primary neuronal cell bodies

Becomes grey matter in CNS

Axons extend into the Marginal Layer

- - -

Becomes white matter in CNS

Question 10

What is neurocyte (immature neuron) migration organized around in spinal cord development?

What is the difference between Dorsal and Ventral Neurocytes?

Answer 10

Sulcus Limitans

Dorsal - Alar Plate (sensory)

Ventral - Basal Plate (motor)

Question 11

Myelencephalon

Develops to?

Organization of Sensory / Motor

Answer 11

Medulla

Lateral = Sensory

Medial = Motor

Question 12

Choroid Plexus

Answer 12

2 areas where neural tube does not fuse or close initially, main function is to produce cerebrospinal fluid (CSF)

Also act as blood/CSF barrier

Question 13

Metencephalon

Develops to?

What are these derived from?

Answer 13

Pons & Cerebellum

Pons - Tegmentum, Basilar Pons

Cerebellum - Derived from Dorsal Alar Plate

Question 14

Mesencephalon

Develops into?

Alar Plate develops?

Basal Plate develops?

What does the anterior portion contain?

Answer 14

Midbrain

Alar Plate - Superior (visual) Colliculus, Inferior (auditory) Colliculus

Basal Plate - CN IV, CN III

Anterior portion contains cerebral peduncle, motor tracts from cortex

Question 15

Origin of Diencephalon?

What does it develop to?

What are these all derived from?

Answer 15

Prosencephalon

Epithalamus, Thalamus, Hypothalamus, Subthalamus

All derived from various aspect of the Alar Plate

Question 16

Thalamus and Hypothalamus

Answer 16

Thalamus - Sensory relay center of the brain

Hypothalamus - Controls autonomic function through hormones (via pituitary gland)

Question 17

Hypophysis (Pituitary Gland)

Answer 17

Most common cause of hypopituitarism in childrin

Remnant of Rathke’s Pouch, congenital cystic tumor

Question 18

Telencephalon

Develops to?

Direction of migration?

Answer 18

Develops to Cerebral Cortex

Migrates from mantle into marginal layer

Question 19

Neocortex vs Allocortex

What regions belong to the Allocortex?

Answer 19

Neo = 6 layers

Allo = 3 layers (smaller)

Allocortex regions:

1. Paleocortex (Olfactory)
2. Archicortex (Hippocampal)

Question 20

Corpus Striatum

Emerges from?

Gives rise to?

Answer 20

Emerges from floor of lateral telencephalic vesicle

Gives rise to:

1. Caudate nucleus
2. Putamen
3. Amygdaloid Nucleus
4. Claustrum
5. Globus Pallidus
   - - -

2 & 5 Together make lentiform nucleus, which is separated from the caudate nucleus by the internal capsule

Question 21

What makes the basal ganglia?

What clinical conditions are involved with this structure?

Answer 21

Caudate, Putamen, Globus Pallidus, Substantia Nigra

Vulnerable in movement disorders such as Huntington’s and Parkinson’s

Question 22

Critical Periords for Neuronal/Synaptic Development

Answer 22

1st Critical Period: Rapid neuronal proliferation between 4th and 6th month (Zika Virus infects neural stem cells and reduces their numbers)

2nd Critical Period: Neuron process (axon/dendrite) growth and formation of synaptic connections from 3rd trimester to 2 y.o.

Question 23

Astrocyte

Answer 23

Predominant cell type in the brain

Secrete instructive signals that facilitate the formation of synapses between appropriate axon/dendrite pairs

Question 24

Synaptic Refinement

Answer 24

Elimination of weak inputs and strengthening of active ones by astrocytes and microglia from 0 - third decade of life

Question 25

Myelination

Answer 25

Axon insulation that facilitates synaptic transmission Begins in 4th fetal month and continues until the end of 2nd postnatal year (corticospinal tracts) compared to decade 3 in the neocortex

Question 26

CNS vs PNS Myelination

Answer 26

CNS - Oligodendrocytes PNS - Schwann Cells

Question 27

Lissencephaly

Answer 27

Cephalic disorder resulting form faulty neuronal migration, children have developmental delay, seizure and shortened life expectancy

Question 28

Spina Bifida Spinal Bifida Occulta Meningomyelocele Myeloschisis

Answer 28

Neural tube defect where **posterior neuropore** fails to close properly Occulta - Vertebral arch defect (least severe) Meningomyelocele - Most common variation, typically present in Arnold-Chiari malformation Myeloschisis - Most severe, no skin/meningeal covering

Question 29

Anencephaly

Answer 29

Neural tube defect where anterior neuropore fails to close, **not compatible with life**

Question 30

Encephalocele (cranium bifidum)

Answer 30

**Ossification** defect Skull fails to close/ossify May result in hydrocephalus, lumb paralysis, ataxia Requires reparative surgery; shunts can be insrted to drain CSF

Question 31

Dandy Walker Syndrome

Answer 31

Posterior fossa cyst leads to 4th ventrical dilation Poor cerebellum development, lack of general brain development

Question 32

Hydrocephalus

Answer 32

Excess CSF from blockage of circulation or overproduction leads to dilation of ventricles

Question 33

Post Closure Defects: Holoprosencephaly

Answer 33

Failure of cleavage and rotation, **single ventricle** Can be caused by **maternal diabetes, fetal alcohol syndrome risk factors**

Question 34

Encephaloclastic Defects

Answer 34

Porencephaly/Schizencephaly (loss of tissue) Hydraencephaly (tissue loss replaced with fluid) = Loss of tissue Risk Factor: **Materal Coccaine Use**

Question 35

Tethered Spinal Cord (Filum Terminale Syndrome)

Answer 35

Filum Terminale attached to wall of spinal canal Weakness and sensory deficits in lower extremities Transection can significantly alleviate symptoms

Question 36

Cells Derived from Neural Crest during Neural Tube formation?

Answer 36

Melanocytes Schwanna Cells Adrenal Cells (Chromaffin) Dorsal Root Ganglion Cells, Cranial Nerve Sensory Cells Autonomic Ganglion Cells