Neurodevelopment

Question 1

Subventricular zone

Answer 1

• active zone of cell production seen immediately around the ventricles of the neural tube
• neurons that are produce here migrate outwards to the cortical plate

Question 2

Subplate neurons

Answer 2

• thalamic axons that project to the cortical plate initially synapse on a transient layer of neurons called the subplate neurons
• axons subsequently detach from the subplate neurons and process superficially to synapse on the true cortical cells
• subplate neurons then degenerate
• can sometimes remain in schizophrenia

Question 3

Neurogenesis

Answer 3

• neurogeneisis takes place in certain brain regions in adults- dentate gyrus of the hypocampus and olfactory bulb
• stress reduces hippocampal neurogenesis
• enriched environments, exercise and antidepressants promote hippocampal neurogenesis

Question 4

Neuronal migration

Answer 4

• takes place in the first 6 months of gestation

- two types of migration are noted: radial and tangential

Question 5

Radial migration

Answer 5

• primary mechanism by which excitatory neurons reach the cortex
• radial glial cells form scaffolding through their foot processes to guide the migrating neuronal cells
• successive populations of migrating neurons travel past the previously settled nuerons to form radial stacks of cells (Rakic’s cortical columns)

Question 6

Tangential migration

Answer 6

-most inhibitory interneurons in the external and internal granular layers are tangentially migrated

Question 7

Heterotopia

Answer 7

-abnormalities in the neuronal migration resulting in neurons failing to reach the cortex and residing in ectopic positions

Question 8

Myelination

Answer 8

• begins prenatally at around 4th gestational month
• largely complete in early childhood (by 2 years) but does not reach it’s full extent until late in third decade of life

Question 9

Synaptogenesis

Answer 9

• occurs very rapidly from the second trimester through the first 10 years of life
• peak synaptogenesis occurs within the first 2 years

Question 10

Synaptic pruning

Answer 10

• by mid-childhood more neurons and cellular processes are established than required in adult brains
• pruning takes place and eliminates unnecessary neuronal connections

Question 11

Dopamine receptions

Answer 11

• before 5 years of age dopamine 2 receptor is more dense than in adults but regresses during the second decade
• dopamine receptors continue to decrease in adult years but at a considerably slower rate of 2.2% reduction per decade
• Rate is faster in males than in females
• in schizophrenia the rate of D2 receptor loss is faster

Question 12

Pruning

Answer 12

• excessive or prolonged pruning is associated with schizophrenia
• relative underpruning is implicated in autism

Question 13

Cerebral plasticity

Answer 13

• refers to the capability of the brain to be moulded
• cortical sensory maps change with variations in sensory input
• patients with phantom limb show reorganisation of sensory maps after amputation so that the representation of the amputated limb may occur on the cortical face area
• repeated practice also leads to a reorganization of brain’s functional regions -seen in musicians etc