DPT 756 Lec 9 pt 1 (up to Exam II)

Define transsynaptic neuronal death

A neuron will die when all of it's friends die (no more inputs from surrounding neurons)

Define transneuronal atrophy

A neuron will atrophy when 2/3rds of it's friends die (reduced inputs from surrounding neurons0

Describe PNS nerve regeneration. Do they have good axonal regrowth? Rate of regrowth per day?

Good axonal regrowth

1/2mm/day

Describe CNS nerve regeneration. Does it have good axonal regrowth?

Axons do not regenerate effectively, only a few mm at most

Why is CNS regeneration slow?

Glial scar tissue takes up a lot of space

Describe the influence of genetics vs brain orchestration on early synapse development

Human genome not big enough provide exact specification of each synapse

Instead, brain orchestrates synapse connections

Define vulnerable periods of development

Periods where injuries to the developing fetus or most devastating

Define windows of opportunity

Periods of time during which development is primed to occur

Define silent synapses ("benchwarmers")

Synapses that aren't actively transmitting synapses, but act as a reserve in the brain

Can be turned into functional units by repetitive stimulation

Found in rodent cortices

Define synaptogenesis

The formation of new synapses via experiences

Who experiences more synaptogenesis, humans or other vertebrates?

Humans experience more

Synaptogenesis occurs secondary to the formation of these types of synapses

Random, unspecified early synapses in more complex brains

In a simple system (lower vertebrates) without the requirement of a lot of synapses, connections are more driven by...

Genetics

Describe the amount of synapses we have at birth

Most of the cortical neurons that will ever exists are in their correct cortical location

Do we have most of our cortical connections at birth?

No, most of the connections are not there at birth

During the first year of life, there is a tremendous burst of...

Synaptogenesis

Compare the amount of synapses in a one-year-old vs an adult

By the end of the first year, over double the # of synapses than an adult has

Synaptogenesis has this effect on febrile seizures in young children

Increased excitability of the cortex may contribute to febrile seizures

Synaptogenesis in the first year is followed by a much longer period of this process

Pruning of excess synaptic connections

When does pruning stop happening in the brain?

Late adolescence

Early synapses that aren't pruned are:

Incorporated into functioning units ("stabilized")

What brain areas have the highest # of synapses? Compared to another area? (general)

More synapses in human association cortices

Fewer in primary sensory areas

The prefrontal cortex and visual cortex experience these changes to synapses during the first 5 years of life

First year: Tons of synaptogenesis

Years 1-5: Pruning of the unnecessary synapses

Define apoptosis. Why does it occur?

Normal or programmed cell death during development

Removes unnecessary or redundant cell populations

Apoptosis removes these type of cells

Neurons that fail to find targets for innervation

Compare the amount of apoptosis in humans vs lower vertebrates

More apoptosis in lower vertebrates

What was the effect of caspace 9 (inhibits apoptosis) on knock-out mice?

Overgrowth of cortex with resultant gyri and sulci

Did not survive past neonatal period

Abnormal enlargement of the brain in humans (megalencephaly) has this effect on cognition

Reduced cortical functioning

Overgrowth of synapses can be concluded to lead to...

Lower overall brain function

Define the crowding hypothesis, and relate it to children with cerebral palsy

When areas of the developing brain "take over" (multi task) to take on more tasks than they are able because the original area of the brain has died

Results in overall lower functioning (like in CP)

If multiple brain regions are crowded into one physical area of the brain, will the brain be able to do all of it's functions to the same level as a typical brain?

No

Is initial synaptogenesis in the cerebral cortex under environmental control?

No, it's just happening for everything (build build build)

How does environmental influence play a role in early vs late synaptogenesis?

Early synaptogenesis: No effect

Late synaptogenesis: Pruning begins earlier if sensory stimulus is blunted

This brain area is present at birth and does not need to develop any further

Somatosensory cortex

This brain area myelinates rapidly postnatally

Visual cortex

This brain area myelinates heavily in the first 12 months of life, and will continue until about age 10

Prefrontal cortex

This brain area is myelinated into young adulthood

Corpus callosum

Environmental enrichment has been shown to have this effect on dendritic arbors

Increase in size and complexity

Do more synapses = more intelligence?

No, they have to be synapses made in the right configuration

Second language teaching and musical training are likely to be more effective if they are started...

Early

Most of the windows of opportunity for development occur before this age

Before age 10

Define long term potentiation and long term depression. What type of changes are these?

Both are functional changes

LTP: Ramping up ion receptor production

LTD: Ramping down ion receptor production

What will cause LTP or LTD in a synapse?

The frequency of use

LTP caused by using the synapse more

LTD caused by using the synapse less

Name the structural changes that occur d/t plasticity (4)

Neurogenesis (rare)

Synaptogenesis

Pruning

Synaptic remodeling

Which comes first, structural or functional plasticity?

Functional plasticity must happen before structural plasticity can occur

Mechanisms of plasticity (4)

Horizontal connections

Uncovering silent synapses

Activity-dependent synaptic plasticity

LTP

Why is LTD important?

It's a mechanism to decrease synaptic strength and prevent runaway potentiation leading to synapse saturation

What does LTP and LTD tell us about the strength of a synapse?

It's modifiable

Do synapses have a range of operation?

Yes

Learning puts synapses at this part of the range of operation (1) What is the effect on LTP?

Puts them at the top of their modification range (saturates them)

No more LTP once it's saturated

Describe the effect of unilateral visual deprivation on connections between the deprived eye and V1 (visual cortex)

Weakening of synapses between deprived eye and V1

Define strabismus. How does it present? Why does it occur?

Disconjugate eye movements

Looks like inturning of the abnormal eye, dominant eye for fixation, squinting eye on the opposite side

Defect is in binocular interaction, not in the function of the eye muscles

Define amblyopia. How is it corrected?

When an eye with strabismus starts to lose vision

Can be prevented via a patch worn on the stronger eye

What is the effect of skilled reaching tasks on cortical movement representations?

Skilled reaching caused cortex to reorganize. Skill caused cortical change

Which develops first, motor skill or structural brain changes? How long does it last?

Motor skill develops before structural reorganization

Persists without continued performance for months

Cortical reorganization is associated with this change to synapses

An increase in synapse number

Describe the rate of motor skill acquisition and developmental plasticity in the motor cortex

Occur at different rates

Skill, reorganization and synaptogenesis occur at different rates during training

Which induces cortical reorganization: Skill learning or strength training?

Skill learning, not strength training

Which induces cortical reorganization: Skill learning or endurance training?

Skill learning, not endurance training

Which of the following causes motor map reorganization? Skill, endurance, strength training

Skill training

Endurance causes angiogenesis

Strength training causes synaptogenesis in SC