Dorsal-Ventral Patterning in the Brain

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18 Questions

What is the process where the axon needs to know what direction it needs to take called?

Axon guidance

Which molecules attract the axon during the process of axon guidance?

Netrin

What allows axons to grow together and form fasciculations?

CAMs

What do pre-synaptic and post-synaptic neurons use to communicate during synaptogenesis?

Neurotrophic factors

Which molecules allow axons to form white matter tracts after becoming myelinated?

CAMS

What is the role of growth cone at the tip of the axon during axon guidance?

Detecting environmental molecules

What is the main responsibility of Sonic hedgehog (Shh) signalling molecule in the brain?

Expression of neurones in the ventral aspect

Which type of neurons are associated with Parkinson's Disease due to their death?

Dopaminergic neurons

Which axis determines the basic plan for the location of neurones in the brain?

Dorsal-ventral axis

What happens when there is an interruption to the dorsal-ventral axis in the brain?

Neurones end up in the wrong place

When cortical layering does not work properly, what is the likely outcome?

Interruption to function

In which part of the brain do we observe more advanced organization characterized by identifiable layers?

Cortex

What is the main function of the dorsal-ventral patterning in the brain?

Controlling the migration of neurones to the right layer

Which layer is adjacent to the white matter in a fully formed brain?

Layer 6

What is the role of signalling molecules in neuronal organization within regions/nuclei?

Guiding the neurones to the correct layer

What may be a consequence of abnormal neuronal migration in the brain?

Misplacement of neurones within layers

Which process involves neurones starting to become functioning cells?

Differentiation

What is one potential impact of exposure to Zika virus on a developing brain?

Microcephaly due to fewer neurones

Study Notes

Brain Development and Structure

  • Different layers of the brain have varying densities of neurons, with each purple dot representing a nucleus.
  • The size of cell bodies also varies across layers.

Cortical Layering

  • The inner layer (layer 6) is adjacent to the white matter in a fully formed brain, but adjacent to the ventricles in the early stages of brain development.
  • Cells in layers 1-6 originate from a strip of cells adjacent to the fluid-filled vesicle in the early brain.

Process of Cortical Layering

  • Proliferation: Neurons proliferate at a high rate to populate the entire cortex, occurring at a rate of 250,000 cells per minute in the ventricular zone.
  • Migration: Neurons migrate to the correct layer, involving signaling and scaffolding.
  • Differentiation: Immature neurons differentiate into functioning neurons, forming dendrites, axons, ion channels, and NT receptors.

Abnormalities in Cortical Layering

  • Abnormalities in proliferation can result in fewer neurons and a smaller brain (microcephaly), e.g., exposure to Zika virus during pregnancy.

Axon Guidance and Connection Formation

  • Axons use growth cones to detect molecules in the environment, with chemoattractants attracting and repellents repelling them.
  • Axons stick together via cell adhesion molecules (CAMs), forming fasciculations, and eventually white matter tracts.
  • Synaptogenesis involves two-way signaling between pre-synaptic and post-synaptic neurons, with communication via neurotrophic factors (e.g., NGF).

Dorsal-Ventral Patterning

  • Signaling molecules (e.g., Sonic hedgehog) determine the dorsal or ventral location of neurons in the brain.
  • Examples of neurons in the ventral aspect of the brain include motor neurons of cranial nerves, dopaminergic neurons, and serotonergic neurons.

Basic Plan of Neuron Location

  • The location of neurons is determined by their position in the anterior-posterior, dorsal-ventral, and medial-lateral axes.
  • Any interruption to this plan can result in neurons ending up in the wrong place.

Organization Within Regions/Nuclei

  • The basic plan works well for subcortical structures, but cortical organization is more advanced, with identifiable layers and varying densities and types of neurons.
  • Cortical layering is essential for proper function, and disruptions can lead to functional interruptions.

This quiz explores the signals that determine whether neurones are located in the dorsal or ventral part of the brain, with a focus on the Sonic hedgehog (Shh) signalling molecule. Topics covered include the expression of neurons in different brain regions and their association with neurological conditions such as Parkinson's Disease.

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