Development of the Nervous System

Question 1

3 distinct layers in the early development?

Answer 1

Ectoderm
Mesoderm
Endoderm

Question 2

What forms the neural plate?

Answer 2

Proliferation of the ectoderm

Question 3

What happens to the neural plate as it proliferates?

Answer 3

As the neural plate thickens, it folds on the sides, fusing dorsally - the space in the middle is called the NEURAL CANAL

Question 4

What forms the neural crest?

Answer 4

A little strip at EITHER end of the dorsal tip of the neural fold forms the neural crest

Question 5

Neural tube vs. neural crest?

Answer 5

Neural tube - all CNS cells (wall of tube made up of neuroepithelium cells)

Neural crest = all PNS cells

Question 6

Cells that form the neural tube?

Answer 6

Neuroepithelium

Question 7

What 3 cells can the neuroepithelium differentiate into?

Answer 7

Neuroblasts (all neurone w. cell bodies in the CNS inc. upper motor neurones)

Glioblasts (become neuroglia - astrocytes + oligodendrocytes)

Ependymal cells (line ventricles and central canal)

Question 8

What 4 cells can the neural crest cells differentiate into?

Answer 8

Sensory neurones of dorsal root ganglia & cranial ganglia

Postganglionic autonomic neurones

Shwann cells

Non-neuronal derivatives e.g. melanocytes

Question 9

Differentiation of neuroepithelium?

Answer 9

3 layers - inner membrane layer w. mitosis occuring, neuronal soma layer (white matter) and axonal layer (grey matter)

ALSO have an ependymal layer

Question 10

Layers of the neural tube?

Answer 10

Innermost - ependymal layer (germinal layer)

Middle - grey matter (mantle layer)

Outer - white matter (marginal layer)

Question 11

What control differentiation?

Answer 11

Signalling molecules - secreted by tissues which interacts with receptors on neuroblasts

These control migration & axonal growth via. excitatory and inhibitory action - this depends on [gradient] and timing

Question 12

What are 2 significant features of the developing spinal cord?

Answer 12

1. NEURAL CANAL is much SMALLER than the thickness of the wall
2. GREY MATTER is split into 2 distinct types:
   o Alar plate (dorsal)
   • receives sensory info
     o Basal plate (ventral)
   • has interneurones and motoneurones to send info out of ventral roots

Question 13

What does the fully developed spinal cord consist of?

ONENOTE!!

Answer 13

Neural canal
o becomes CENTRAL CANAL - now carries CSF

Alar plate
o develops into the DORSAL horns

Basal plate
o develops into the VENTRAL horns

Whole spinal cord becomes surrounded by a thick layer of WHITE MATTER

Question 14

Where is the Notochord found?

Answer 14

Found just below the BASAL plate (ventral side)

Question 15

What is the function of the Notochord?

Answer 15

Produces several signalling molecules
o establishes a [gradient] (highest near the notochord)

The cells within the neural tube closest to the notochord are therefore induced to become MOTOR NEURONES (in basal plate)

Question 16

Where is the ectoderm found?

Answer 16

Dorsal to the neural tube

Question 17

Function of the ectoderm?

Answer 17

Also produces signalling molecules
o establish a [gradient]

BUT
o tend to INHIBIT cell differentiation into MOTOR neurones

Question 18

How is the brainstem developed?

Answer 18

Brainstem is a tubular structure
o BUT the 4th ventricle is in the middle so messes the organisation (developed first!)

The
o ROOF PLATE - proliferates rapidly
- this pushes the ALAR PLATES aside, so are NO longer dorsal to the roof plate

o DORSAL part - expands laterally

Question 19

What does the development of the brainstem mean for the CNs?

Answer 19

CNs within the brainstem that have MOTOR FUNCTION
o tend to lie more MEDIALLY (as where basal plates end up)

Motor = medial
Sensory = lateral
Autonomic = in-between

Question 20

What does the brain develop from?

Answer 20

Only the ANTERIOR portion of the NEURAL TUBE develops into the brain

Question 21

Development of the brain at 4 weeks?

Answer 21

3 PRIMARY VESICLES form:
o Prosencephalon = future FOREBRAIN
o Mesencephalon = future MIDBRAIN
o Rhombencephalon = future HINDBRAIN

Question 22

What happens in the week following the 4th week for brain development?

Answer 22

The most SUPERIOR VESICLE divides into 2
and
The THIRD (inferior) VESICLE also divides into 2

i.e. this produces 5 SECONDARY VESICLES

Question 23

Development of the brain at 5 weeks?

Answer 23

Forebrain
o Telencephalon - will become cerebral hemisphere
o Diencephalon - less expansion occurs here (eventually becomes thalamus, hypothalamus, epithalamus & subthalamus)

Midbrain

Hindbrain
o Pons
o Medulla

Question 24

Development of the brain at 8 weeks?

Answer 24

As development continues, neural tube proliferates more & more

Space within the NEURAL TUBE (central canal) becomes smaller relative to wall
o becomes the VENTRICULAR SYSTEM

Development of the CEREBELLUM also beings
o out-pouching from the back of the pons

Question 25

Folding of the brain during development?

Answer 25

The VESICLES are NOT in a straight line
o there are 3 FLEXURES

Name of FLEXURES based on position
o Cephalic flexure
o Pontine flexure
o Cervical flexure

Question 26

Flexures during development of the brain?

Answer 26

Becomes more & more exaggerated upon development

ONENOTE!!

Question 27

Grey matter and white matter in the brain?

Answer 27

Brain has
o a CORE of WHITE MATTER
o GREY MATTER is on the outside

Grey matter - nuclei that have migrated from the inner membrane of the neural tube

Question 28

Where do neuroblasts proliferate?

Answer 28

Inner membrane

Question 29

Explain the proliferation of neuroblasts in the development of the cortex

Answer 29

Some neuroblasts will stay in the MIDDLE
o forms the BASAL GANGLIA

Some neurones migrate towards the OUTER membrane:

o migration occurs by neuroblasts attaching themselves to radial glial cells

o the RADIAL GLIAL CELLS have their soma attached to the INNER membrane and have a SINGLE LONG PROCESS to the OUTER membrane

o the neurones hence CLIMB TOWARDS the OUTER membrane

Question 30

How do the layers of the cortex develop?

Answer 30

The proliferations & migrations of the neuroblasts occur in WAVES
o this forms the layers of the cortex
o until you reach the 6th layer!

Each layer in unique

Question 31

How do neural developmental disorders arise?

Answer 31

Genetic or environmental abnormalities!

Occurs early in gestation OR pregnancy

Question 32

What environmental abnormalities can give rise to developmental disorders?

Answer 32

Schizophrenia - malfunction of neural development

Spina bifida - deficiency of folic acid

Question 33

How to replace lost neurone?

Answer 33

Regulate stem cell differentiation

Question 34

How to induce CNS regeneration?

Answer 34

Guidance mechanism for axons