Brain and Behaviour: Neurodevelopment & Neuronal Plasticity

Flashcards for reviewing Brain and Behavior lecture notes, focusing on Neurodevelopment and Neuronal Plasticity.

Brain Development

Basic processes prenatally and postnatally.

Neuroplasticity

Experience-dependent plasticity.

Stages of Brain Development

1. Cell birth/ Proliferation (Neurogenesis and Gliogenesis) 2. Cell migration 3. Cell differentiation and maturation 4. Synaptogenesis and synaptic pruning 5. Cell death 6. Myelination (myelogenesis)

Cell birth/ Proliferation

Process by which 250,000 neurons are born per minute at its peak

Neurogenesis

Does not take place with neuronal division – neurons do not divide

Stem cells

Immature cells that divide to form progenitor (precursor) cells.

Ventricular zone (brain’s nursery)

Cells undergoing mitosis were always closer to the inner surface of the neural tube, known as this.

Cell Migration

Movement of the newly formed cells towards the outer layers

Occurs with the help of:

Chemical signals (immunoglobulins and cytokines) and physical support provided by radial glia.

Migration with the help of radial glia

Cells ‘climb’ along radial glia with the help of extensions

Extensive Migration of Young Neurons into the Infant Frontal Lobe

Neurons are still migrating in the frontal cortex after birth (most prominent in the first few months of life, mostly up to 3m with some persisting up to 7m)

Most of these

Will become inhibitory GABAergic interneurons

Differentiation and Maturation

Immature neurons begin to express genes that will allow them to become a particular type of cell.

Dendritic development

Region where dendritic arborization (branching) and growth of dendritic spines occur.

Induction

Ongoing cell-cell interactions via the secretion of chemicals, where cells influence the fate of their neighbouring cells

Synaptogenesis and Synaptic Pruning

Synaptogenesis is guided by a variety of cues and signals

Growth cone

The growing end of the axon, which was characterised as “a battering ram, endowed with exquisite chemical sensitivity, with rapid ameboid movements”

Growth cones are attracted to:

Chemicals released from target sites include Cell adhesion molecules (CAMs) and Tropic molecules

Successful contact has been made

Axon and target induce each other to construct machinery to help them attach to one another and to form a synapse (postsynaptic density proteins, PSDs)

Growth cones

Detects and selects among a wide range of guidance cues.

Synaptic pruning

Those that are not successful are eliminated.

Synaptic Rearrangement

Occurs throughout life and it is related to learning or experience

Adolescence

A period of increased synaptic pruning starting from the back to the front by early adulthood.

Apoptosis

This type of cell death.

Programmed Cell Death (PCD)

Conserved process in animals and plants.

Apoptosis is an active process

Cells that undergo apoptosis are expressing genes that enable them to die – death genes (caspases)

Rita Levi-Montalcini

Proteins secreted by target cells promote the survival and growth of neurons - survival signals

neurotrophins (growth factors)

Proteins, a family of these factors named neurotrophic factors (Brain-Derived Neurotrophic Factor (BDNF), Neurotrophin-3(NT-3) etc.

Myelination

Occurs when glia form a fatty sheath that covers the axons of neurons.

Myelin speeds up the transmission of neural impulses and allows for its ‘saltatory conduction’

First occurs in the spinal cord and then in the hindbrain, midbrain and forebrain (back -to-front)

SO…

Immature neurons are created, they migrate, differentiate and mature, form synapses and compete for survival

Lack of exposure to language at an early age

May lead to the inability to use language

Critical Periods

A period during which the brain is most sensitive to a specific experience

Epidemiological studies

Show evidence for environmental factors that lead to pathology later in life such as epilepsy, autism spectrum disorders, schizophrenia etc.

In people blind since infancy

There is enhanced tactile (finger sensitivity) and auditory ability

Collateral Sprouting

New branches formed by non-damaged axons attach to vacant spots of dendrites and cell bodies

Hippocampus

The granular layer of the dentate gyrus of the hippocampus, was the first neurogenic area to be discovered

Synapses and dendritic branches of a neuron are not fixed…

Axons extend, retract or even disappear

Myelination is a job for glia and it is a slow process

Some processes extend beyond prenatal life and continue to shape our brains well into adulthood

Neurotrophic factor

Is a family of these factors named neurotrophic factors (Brain-Derived Neurotrophic Factor (BDNF), Neurotrophin-3(NT-3) etc

Immature neurons

Neurons are created, they migrate, differentiate and mature, form synapses and compete for survival.

Neuroplasticity

Allows for great potential and susceptibility to environmental influences throughout life, but especially during the critical periods of development.

Summary

Our brains are more adaptive than we thought previously.