Target Selection

Chemoattractants

Molecules like Netrin that attract growing axons toward specific targets through receptors like Frazzled.

Chemorepellents

Molecules such as Semaphorins and Ephrins that repel axons from certain regions.

Growth Factors

Substances like Fibroblast Growth Factor 2 (FGF2) and neurotrophins that guide axons by creating concentration gradients.

Combinatorial coding

The principle that axons respond to a combination of overlapping environmental cues and their relative levels.

Retinal Ganglion Cells (RGC) axons

Axons that accurately target specific layers within the Lateral Geniculate Nucleus (LGN) for visual processing.

Neurotrophins

Chemoattractant molecules critical for guiding axons to specific targets, such as NT-3 for sympathetic innervation.

Ephrins

Molecules that can establish repulsive barriers to restrict axons to specific regions.

Topographic mapping

A principle ensuring an ordered representation of the external world in the brain, seen in various sensory systems.

Retinotectal projection

The projection of retinal axons to the Superior Colliculus (SC) in a topographically organized manner.

Chemospecificity model

A hypothesis suggesting molecules guide axons to their specific targets based on chemical gradients.

Sperry's Chemospecificity Hypothesis

A hypothesis stating that axons follow gradients of signaling molecules to reach their targets.

Ephrin A gradients

Molecules concentrated in the posterior tectum that repel axons from the temporal retina, establishing an anterior-posterior axis.

Bidirectional Signaling in Ephrins

The ability of Ephrins to act as both ligands and receptors, mediating attractive interactions in the retinotectal system.

Summary of Lecture 11

Overview of target selection, molecular cues, mechanisms, and topographic mapping in establishing neuronal connections during development.