T1L20 plasticity and regeneration

Question 1

2 things that determine gene expression in particular cells

Answer 1

1. inducing factors
   - signalling from other cells
   - freely diffusing or tethered to cell surface acting locally
   - modify gene expression, cell shape and motility
2. competence
   - the ability of a cell to respond to inducing factors
   the exact cellular sets of:
   - surface receptors
   - transduction molecules
   - transcription factors expressed

Question 2

neural stem cells

Answer 2

infinitely regenerating

after terminal division and differentiation they can give rise to the full range of cell classes within relevant tissue

eg inhibitory &excitatory neurons, astrocytes, oligodendrocytes

Question 3

neural progenitor cell

Answer 3

incapable of self renewal

can give rise to only one class of differentiated progeny eg

oligodendroglial progenitor cell gives rise to oligodendrocytes until its mitotic capability is exhausted

Question 4

dividing precursor cells

Answer 4

s8,9

asymmetrical division to generate
> neuroblast
> progenitor cell (limited mitotic potential)

notch proteins > neuroblast
numb proteins > progenitor

Question 5

neuroblast

Answer 5

post mitotic immature nerve cell that will differentiate into a neuron

fate determined by:

• position in ventricular zone
• environment at time of division
• age of precursor cell

neuroblast differentiation:
growth cone and filopodia

1. pathway selection eg retinal ganglion cell reaching thalamic nucleus
2. target selection eg to the correct thalamic nuclei
3. address selection eg which LGN layer

guidance:
- chemoattractants eg NETRIN
- chemorepellants eg SLIT
s13,14

Question 6

development of the cortex

Answer 6

inside out

Question 7

trophic interactions

Answer 7

• neurotrophic factors eg nerve growth factor

apoptosis- relects competition for trophic factors

ensures proper match of postsynaptic and presynaptic neurons

Question 8

synapse elimination

Answer 8

activity dependant finetuning of neural connections:

• initially each muscle fibre connects to one motor neuron
• during maturation this changes so one motor neuron connects to many muscle fibres

Question 9

modification of circuits by experience

Answer 9

mostly during early life - in CRITICAL PERIODS

critical periods:

• time windows for different skills and behaviours
• eg sensorimotor skills, language acquisition, emotional functions, visual perception

2 important factors for success:

1. availability of appropriate influences eg exposure to language
2. neural capacity to respond to them

eg ocular dominance- development of sensory perception requires sensory experience - window open only while young

monocular deprivation leads to ocular dominance on other side if during critical period

Hebbian modification

Question 10

plasticity in adult cerebral cortex

Answer 10

eg motor map of hand changes on losing a digit.

s30

functional remapping

Question 11

PNS vs CNS axon regen after injury

Answer 11

peripheral:
- macrophages clear debris from degenerating nerve stump
- schwann cells proliferate and secrete neurotrophins
- the neuron which the axon is regenerating from express genes that return it to growth state
- growth cone and regeneration

CNS:

• degeneration of myelin
• debris cleared by microglia
• glial scar formation
• astrocytes/oligondendrocytes/microglia produce inhibitory factors

Question 12

adult neurogenesis - the only 2 places we can make new cortical neurons

Answer 12

1. subventricular zone (SVZ) to olfactory bulb
2. hippocampus
   - primarily interneurons
   - some integrate in functional networks, but most die