Development of Neurons

Question 1

when does human brain development begin

Answer 1

3rd post conception week

Question 2

what factors influence the intrauterine environment

Answer 2

maternal health and disease

insults which may be continuous/episodic throughout pregnancy (eg alcohol, cytomegalovirus)

placental function and foetal nutrition

Question 3

what factors influence the extrauterine environment

Answer 3

physical factors eg nutrition

emotional and social factors

exposure to alcohol, drugs etc

Question 4

when is the embryonic period

Answer 4

conception to week 9

Question 5

describe the development during the embryonic period

Answer 5

at first there is a 2 layered embryo - epiblast and hypoblast (epiblast becomes us and hypoblast forms sac, placenta and cord etc)

epiblast forms primitive streak and primitive node

cells migrate through streak and then rostro-caudal migration

this is determined by nodal signalling

Question 6

gastrulation

Answer 6

results in the development of a 3 layered embryo (germ layers)

Question 7

describe the development of the 3 germ layers

Answer 7

• Ectoderm – skin, nails, hair and neural tissue
• Mesoderm – muscle, bone, cartilage and vascular system
• Endoderm – gut and respiratory system

Question 8

when does the neural tube form

Answer 8

day 20-27

Question 9

describe the formation of the neural tube

Answer 9

neural progenitor cells form the neural plate, which forms the neural groove and then neural tube

Question 10

describe the further development of the neural tube

Answer 10

neural progenitors line the inside of the tube - form the ventricular zone

hollow centre of the tube becomes ventricular system and central channel of spinal cord

anterior/rostral tube becomes the brain

caudal tube becomes the spinal cord

Question 11

define neural patterning

Answer 11

cells acquire distinct identities according to their specific spatial positions

Question 12

describe neural patterning in the mature neocortex

Answer 12

the mature neocortex has distinct functional and strucutral areas, and genes are expressed differently in these areas

there is continuous and complex refinement

Question 13

give an example of neural patterning in the mature neocortex

Answer 13

signalling molecules Emx2 and Pax6

• a high concentration of Pax6 and low of Emx2 inducecs progenitor cells to differentiate into motor neurons
• the converse induces visual cortical neurons

Question 14

when is the foetal development period

Answer 14

week 9 to 40/42 (term)

Question 15

how is the brain initally formed in the foetal development period

Answer 15

smooth in contour - lissencephalic

gradually develops sulci and gyral pattern

Question 16

why is the development of gyri and sulci required

Answer 16

to accomodate the proliferating neuronal populations

Question 17

describe the division of the NPC in the ventricular zone

Answer 17

divide intially symmetrically then asymmetrically

• In symmetrical cell division, both daughter cells are progenitor (stem) cells
• In asymmetrical cell division, one progenitor (stem) cell is produced and one neuron (cannot divide further)

progenitor cells remain in VZ and continue to divide, and neurons migrate to their place in the developing neocortex

Question 18

what are the 3 ways in which neurons migrate to the cortex from the ventricular zone

Answer 18

somal translocation

radial glial guides

tangetial migration and signalling pathways

they end up in an orderly 6 layered structure with an inside out arrangment of migrated neurons

Question 19

what do neurons develop once they reach their target cortical regions

Answer 19

axons - longer and communicate with other neurons

dendrites - gather information and transmit to neurons

Question 20

programmed neuronal cell death

Answer 20

babies are made with all the neurons they need- half of these will die (apoptosis), mostly prenatally

Question 21

synaptic exuberance

Answer 21

development of connections between the neurons

Question 22

synpatic pruning

Answer 22

axons and dendrites

process of synapse elimination that occurs

Question 23

oligodendrocytes

Answer 23

form myelin sheaths in the CNS

(schwann cells in the PNS)

Question 24

post natal development

Answer 24

limited neuronal proliferation from the VZ

• olfactory bulbs
• dentate gyrus of the hippocampus
• oligodendrocytes

myelination

Question 25

when does myelination occur

Answer 25

post natally

Question 26

myelination

Answer 26

OPC develop processes which wrap around axons to form myelin sheaths - increase axonal conduction rates also maintain axonal integrity, survival, neuronal size and axonal diameter

Question 27

when does myelination mainly occur

Answer 27

first 2 years of life ongoing into 20s

Question 28

why is there an increased risk to health during adolescence

Answer 28

risk taking behaviour and extreme emotions

Question 29

effect of hormones on development of the brain during adolescence

Answer 29

Pubertal hormones affect brain restructuring and result in permanent reorganization Hormones have different effects on the HPA axis in males and females: * Oestrogens make girls more prone to stress * Androgens are supposed to make boys more resilient to stress

Question 30

how is the nerichment and deprivation effect illustrated

Answer 30

monocular visual deprivation: * This is associated with altered patterns of organization within the primary visual cortex * When both eyes are stimulated pathways known as ocular dominance columns develop equally * If one eye is blocked, the bands/columns representing the deprived eye shrink and the inputs from the active eye invade and subsume territory in the PVC normally occupied by the blocked eye * Squint development

Question 31

what is faults in neural tube formation associated with

Answer 31

spina bifida and anencephaly

Question 32

what is failure of the brain vescile to form called

Answer 32

holoprosencephaly

Question 33

PLP1 related disorders

Answer 33

* The **PLP1** **gene** encodes a transmembrane proteolipid protein, the predominant myelin protein present in the CNS. It is responsible for compaction, stabilization and maintenance of myelin sheaths, oligodendrocyte development and axonal survival * Located on the X chromosome (X-linked inheritance) * Mutations in the PLP1 gene cause a spectrum of disorders, Pelizaeus-Merzbacher is the most severe * Presents in infancy/early childhood with nystagmus, hypotonia and cognitive impairment. Progresses to severe spasticity and ataxia * Shortened life span * Spastic paraparesis 2 manifests as spastic paraparesis with/out CNS involvement and usually normal life span

Question 34

impact of malnutrition on brain development

Answer 34

impact on brain growth and volume impact on myelination a lack of energy and deprivation leads to a lack of post natal stimulation and experiences