Lecture 2 - Development Of CNS

Question 1

What is gastrulation?

Answer 1

The process where the bilaminar disc becomes the trilaminar disc

Question 2

Briefly describe the process of gastrulation:

Answer 2

Outer layer of the bilayer germ disc invaginates at the primitive streak to produce a three layered germ disc

Question 3

What are the 3 layers of the trilaminar disc?

Answer 3

Ectoderm
Mesoderm
Endoderm

Question 4

What are some derivatives of the ectoderm?

Answer 4

Skin
Neural tissue and neural crest

Question 5

What are the derivatives of the mesoderm?

Answer 5

Heart,vessels and muscles
Notochord (made of endoderm)

Question 6

What are the derivatives of the endoderm?

Answer 6

Digestive and respiratory tracts

Question 7

What is the function of the notochord?

Answer 7

Induces neuraltion

Induces the neural plate of ectoderm above it to start to fold in on itself to generate the neural tube = neurulation

Question 8

What is notogenesis?

Answer 8

Formation of the notochord

Question 9

Briefly describe notogenesis (formation of the notochord):

Answer 9

Made from the primitive node and migrates to form a rod like structure in the mesoderm during gastrulation

Question 10

What is neuralation?

Answer 10

Formation of the neural tube

Question 11

What structure induces neuraltion?

Answer 11

Notochord

Question 12

What happens in neuraltion?

Answer 12

Notochord and paraxial mesoderm send signals to the overlying ectoderm causing it to thicken forming the neural plate
Neural plate thickens and begins to fold forming neural folds
Neural folds elevate and fuse in the midline at mid cervical level;
Neural crest cells detach and migrate

Question 13

What way does the neural tube zip up/fuse?

Answer 13

Rostrally and caudally (pinches in the middle then moves rostrally and caudally)

Question 14

What condition is caused if the neural tube fails to fuse in the rostral direction?

Answer 14

Anencephaly

Question 15

What is anencephaly?

Answer 15

When the brain doesn’t form at all

Question 16

What condition can be caused by failure of the neural tube to fuse in the caudal direction?

Answer 16

Spina bifida

Question 17

How many main swellings form at the rostral neural tube?

Answer 17

3

Question 18

What are the 3 main swellings from the rostral neural tube which become major parts of the adult brain?

Answer 18

Prosencephalon
Mesencepohalon
Rhombencephalon

Question 19

What structures form from the prosencephalon, mesencephalon and Rhombencephalon?

Answer 19

Prosencephalon = forebrain
Mesencephalon = midbrain
Rhomencephalon = hind brain (4th ventricle that comes from this region is shaped like a rhombus)

Question 20

Which of the 3 main swellings from the rostral neural tube are further subdivided into 2 swells?

Answer 20

Prosencephalon and Rhombencephalon

Question 21

What does the prosencephalon subdivide into?

Answer 21

Telencephalon
Diencephalon

Question 22

What does the rhombencephalon get subdived into?

Answer 22

Metencephalon
Myelencephalon

Question 23

What forms fromt he telencephalon?

Answer 23

Most of the cerebral hemisphere

Question 24

What forms from the diencephalon?

Answer 24

Thalamus
Hypothalamus
Optic nerve/retina

Question 25

What is the function of the mesencephalon?

Answer 25

Boundary between fore and hindbrain

Question 26

What does the metencephalon form?

Answer 26

Pons and cerebellum Meta analysis happens after main research and pons and cerebellum sit behind or after the cerebrum

Question 27

What does the myelencephalon form?

Answer 27

Medulla

Question 28

What are the functions of the signals that the notochord produces during neuraltion?

Answer 28

Are BMP-4 inhibitors so causes ectoderm cells to proliferate

Question 29

Generally, what part of the brain has the motor structures and what part of the brain has the sensory structures?

Answer 29

Motor = anterior (motor forwards) Sensory = posterior (think occipital lobe for sight is posterior)

Question 30

What structure determines the orientation of the brain and the spinal cord so that motor structures are anterior and sensory structures are posterior?

Answer 30

Notochord

Question 31

What does the notochord produce to determine the orientaion of the brain and spinal cord structures?

Answer 31

Morphogens

Question 32

What affect does the notochord have on the neural tube due to the morphogens?

Answer 32

Produces sonic hedgehog so that the cells of the spinal cord nearest to it becomes the ventral side

Question 33

What does the ectoderm produce to stimulate dorsal fate?

Answer 33

BMP

Question 34

What does the notochord stimulate the ventral portion of the neural tube/spinal cord to produce?

Answer 34

Basal/floor plate which gives rise to motor neurones

Question 35

What forms in the dorsal portion of the neural tube in absence of influence of the notochord?

Answer 35

Alar/roof plate which gives rise to the sensory neurones

Question 36

What roots are sensory and what roots are motor in the nervous system?

Answer 36

Sensory = dorsal root Motor = ventral root

Question 37

What neurones are found in the dorsal and ventral horns of the spinal cord?

Answer 37

Dorsal horn = sensory neurones Ventral horn = motor neurones

Question 38

How are the dorsal columns and the motor corticospinal tract postioned in the spinal cord?

Answer 38

Dorsal columns posterior Corticospinal tract anterior

Question 39

What forms from the neural tube central canal?

Answer 39

Brains ventricular system

Question 40

What reflex is the superior colliculus important in?

Answer 40

Visual reflex’s

Question 41

What reflex is the inferior colliculi important in?

Answer 41

Auditory reflex

Question 42

How are the sensory alar and motor basal plates arranged in the neural tube at the brainstem?

Answer 42

Motor basal plates more medial close to canal and alar sensory more lateral

Question 43

On a basic level how does the cauda equina form?

Answer 43

Initially cord fills entire vertebral canal But as you get to L1 vertebra begin to grow faster than the spinal cord this stretches the lower portion of the cord producing the cauda equina

Question 44

What is hydrocephalus?

Answer 44

Dilation of the ventricles of the brain due to occlusion leading to build up of CSF

Question 45

How can neural tube defects predispose to hydrocephalus?

Answer 45

Cord gets tethered at site of defect Spine grows and cord cant move within the vertebral canal so the brainstem containing the 4th ventricles gets pulled down through Foramen magnum becoming occluded so CSF builds up

Question 46

What condition is caused by failure to close the neural tube in the cranial direction?

Answer 46

Anencephaly

Question 47

What condition is caused by the failure of closure in the caudal direction (involves the spine/spinal cord)?

Answer 47

Spina bifida

Question 48

What structure is failing to develop when the neural tube fails to zip up/fuse in the cranial or caudal direction?

Answer 48

Posterior vertebral arches

Question 49

What is craniorachischisis?

Answer 49

Most severe neural tube defect where the tube completely fails to fuse both cranially and caudally It is embryonically fatal since neither brain or spinal cord forms

Question 50

What are some conditions caused by failure of the cranial neuropore to fuse?

Answer 50

Anencephaly Cranial bifida Cranial meningocele

Question 51

What are the 4 main neural tube defects caused by failure of the caudal neuropore to fuse?

Answer 51

Spina bifida occulta Spina bifida cystica Meningocele Myelomeningocele

Question 52

Which neural tube defect involves the h spinal cord and so has neurological problems and which defect doesn’t? Meningocele or myelomeningocele

Answer 52

Meningocele doesn’t involve spinal cord only meninges Myelomeningocele involves spinal cord

Question 53

What is myelocele?

Answer 53

Spinal cord fails to develop so the lumen of the neural tube is exposed to the outside world and is associated with a CSF filled cyst

Question 54

Why are children with myelocoele at risk to meningitis and have neurological deficits?

Answer 54

Spinal cord doesn’t form properly Neural tissue is exposed to the world

Question 55

What is a Myelomeningocele?

Answer 55

CSF fillled cyst containing the spinal cord (meninges and neural tissue) The vertebral body doesn’t fully close Child will likely have neurological deficits A type of spinal bifida cystica

Question 56

What is a meningocele?

Answer 56

Presence of a CSF fille cyst that contains only the meninges Type of spinal bifida cystica

Question 57

How does myelomeningocele and meningocele present differently?

Answer 57

Meningocele transilluminates very well whereas Myelomeningocele doesn’t Meningocele normally has good neurological prognosis whereas Myelomeningocele doesn’t

Question 58

What are the 2 types of spina bifida c ystica?

Answer 58

Meningocele Myelomeningocele

Question 59

What is it called when the meninges herniate out of the fontanelles of the skull?

Answer 59

Cranial meningocele

Question 60

What is spina bifida occulta and how does it present?

Answer 60

Hidden spina bifida where the vertebral arches fail to fuse Site has an overlying tuft of hair and nothing else is really affected

Question 61

How do you prevent neural tube defects?

Answer 61

Take folic acid 400mg daily from 3months before conception until week 12 of pregnancy

Question 62

What other structure can folate deficiency lead to anomalies in except neural tube defects?

Answer 62

Palatial anomalies

Question 63

What are neural crest cells?

Answer 63

Cells at the Lateral border that during neuraltion dissociates from their neibouring cells to form neural crest cells (they migrate from the neural tube)

Question 64

What cells are derived from neural crest cells?

Answer 64

All neurones who’s cell bodies are in the PNS: -primary sensory neurones -autonomic postganglionic neurones -enteric neurones Schwann cells Cells of adrenal medulla Meloncytes Leptomeninges Head mesenchyme

Question 65

What are the leptomeninges?

Answer 65

Arachnoid and pia mater

Question 66

What tissue receives significant contribution from neural crest?

Answer 66

Thymus Thyroid Spiral septum of heart Parts of teeth

Question 67

Where do neural crest cells migrate from in the embryo?

Answer 67

Dorsal part

Question 68

As neural crest cells migrate dorsal to ventral what structures do they leave behind?

Answer 68

Dorsal root ganglia Sympathetic ganglia Preaortic ganglia (receive input from splanchnic nerves) Adrenal medulla (chromaffin cells) Gut wall enteric nervous system

Question 69

What are the 2 main neural crest cell defects?

Answer 69

Hirschsprungs disease Di George Syndrome

Question 70

What is Hirschsprung’s disease?

Answer 70

Neural crest cell defect Lack of enteric nerves in sections of large intestine leading the Denervation of smooth muscle causing hypomotility and constipation

Question 71

What is Di George syndrome?

Answer 71

Neural crest cell defect Immunodeficiency due to involvement of thymus (neural crest cells have big contribution) Facial anomalies (cleft/lip palate, low set ears, small jaw) Heart anomalies Hypocalcaemia (parathyroid involve