Early brain development 3

Question 1

Intrinsic axon guidance molecules

Answer 1

These are molecules present on the growth cone or nearby cells that mediate direct interactions between the growth cone and its immediate environment.

Extracellular Matrix (ECM): Proteins in the extracellular space that provide structural support and guidance.
Cell Adhesion Molecules (CAMs): Proteins on cell surfaces that help the growth cone stick to or interact with other cells.
Cadherins: A type of CAM that helps in stable cell-cell adhesion during axon guidance.
Ephrins and Eph Receptors: Molecules that provide repulsive or attractive cues, guiding axons away from or toward specific areas.
Mechanism: These molecules guide the growth cone via contact attraction or repulsion, meaning:

Contact Attraction: The growth cone is drawn toward a molecule it interacts with.
Contact Repulsion: The growth cone moves away from molecules it finds repulsive

Question 2

Extracellular guidance molecules

Answer 2

These are diffusible signals (molecules secreted into the environment) that guide the growth cone from a distance.

Chemo-attractants: These molecules attract the growth cone, leading it toward the source (e.g., Netrins).
Chemo-repellents: These molecules repel the growth cone, steering it away from the source (e.g., Semaphorins, Slits).
Some of these molecules are bound to the ECM, while others diffuse freely through the extracellular space.

Question 3

Axon guidance at the midline

Answer 3

This is the crossing of axons at the ventral midline of the spinal chord and corpus callosum.
Netrin stimulates the crossing of axons at the midline.
Netrin attracts axons and stimulates crossing at the midline of the spinal cord
After crossing axons become insensitive to netrin and are repelled by slit/semaphorin