Week 8 Flashcards
What is the anatomical relevance of brain asymmetry?
- Functional Specialization:
Each hemisphere tends to specialize in different tasks.
For example:
Left hemisphere: Often responsible for language, logic, and analytical thinking.
Right hemisphere: More involved in spatial awareness, creativity, and emotional processing.
- Lateralized Structures:
Certain brain structures, like the Habenulae and Motor Cortex, show lateralization, meaning each side of the brain controls specific functions. The left side of the brain usually controls the right side of the body, and vice versa. - Brain Efficiency:
Asymmetry can make brain functions more efficient by dividing labor between the two hemispheres. This division of tasks allows each hemisphere to specialize, improving the overall speed and effectiveness of cognitive processes. - Neurodevelopment:
Brain asymmetry plays a role in development. Structures like the parapineal organ influence how the brain becomes asymmetrical during early development, helping guide brain organization.
In short, brain asymmetry helps the brain organize, specialize, and optimize various functions for more efficient processing.
What is the functional relevance of brain asymmetry?
Implicated in:
Circadian control of behaviour
Motor inhibition
Pain inhibition
Social and emotional responses
Spatial cognition
What disorders involve habenula dysfunction?
Depression
Schizophrenia
Drug-induced psychosis
What is symmetry?
Symmetry - homologous tissues facing each other around an axis are equivalent e.g. left and right hands look the same
What is asymmetry?
Homologous tissues facing each other around an axis are NOT EQUIVALENT e.g. left and right work differently
What is laterality?
Dominance of one part of the body over the homologous part on the other side e.g. my left hand is dominant over my right
Laterality depends on the presence of asymmetry
Is the epithalamus symmetric or asymmetric?
Asymmetric
What genes are expressed in the epithalamus?
Nodal pathway genes
When does nodal pathway gene expression change?
When the midline is damaged
What happens to parapineal and habenula when nodal signalling is abrogated?
The laterality changes
Whether Nodal expression is absent or bilateral, the outcome is the same
Absent or bilateral nodal results in 50% left, 50% right parapineal organ
Absent of bilateral nodal results in the larger habenula being 50% left and 50% right
parapineal organ and large habenula are always on the same side
Nodal and the midline regulat laterality of epithalamus
Nodal and the midline are not required for asymmetry
What is the epithalamus divided into?
The dorsal and ventral
What do anterior/dorsal cells of the epithalamus give rise to?
The parapineal organ
What do the ventral cells of the epithalamus give rise to?
The habenulae
What does left ablation give rise to?
A partial loss of habenular asymmetry
Results in midline or right sided parapineal organ and a switch in habenular laterality
What do left habenular ablation results not depend on?
changes in nodal signalling
Suggests that a competitive mechanism is determining laterality in absence of Nodal
What is the ace epithalamus?
Symmetric
What is expressed in the epithalamus?
fgf8
What is fgf8 required for?
To initiate and maintain parapineal migration
Rescues parapineal migration to the left
What is Tg expression found at?
The leading edge of the parapineal organ and lost in fgf8-/-
Where is parapineal organ migration rescued?
In fgf8-/- when CA-FgfR1 is expressed in a few parapineal cells
What is left sided Tg expression dependent on?
Nodal signalling
What is the neural crest?
A migratory cell
Can differentiate into many cell types
Neural crest develops from the neural tube very early in development
Where is the neural crest ‘born’?
At the dorsal edge of the neural tube along the whole A-P axis of the embryo
What tissues are involved in neural crest induction?
Neural crest develops at the intersection of the ectoderm, the dorsal neural tube and the mesoderm
