axon targeting Flashcards
what is axon targeting?
growing axons navigate through the developing nervous system to reach their appropriate targets, forming precise and function connections with specific neurons, muscles or other tissues
what are the three main mechanisms involved in axon targeting?
pathway selection
target selection
address selection
what are axon guidance cues?
axon targeting is guided by various extracellular signals that help direct the growing axons to their appropriate targets, these can be long-rage of short-range
what two ways can guidance cues be classified?
attractive cues- promotoe axon growth toward the source of the signla
repulsive cues- push axons away from the signal’s source
what molecule can cause chemorepulsion and chemoattratcion?
netrins
what is fasiculation?
axon bundles or fascicles form when individual axons grow together and travel along the same path
fasciculation helps groups of axons follow a shared path toward their target regions, ensuring that they are guided along the correct routes
what is selective fasciculation?
selective fasciculation refers to a more specific form of axon bundling where only certain axons, often those with similar properties or targeting the same destination, adhere to one another and travel together along a shared pathway, while other axons do not join the same bundle
the growing axons use both positive (attractive) and negative (repulsive) cues to determine which other axons they will fasciculate with they might be repelled by axons targeting a different destination while being attracted to those with similar targets
what is defasciculation?
axons separate from a fascicle (a bundle of axons) and stop traveling together
this occurs when axons that were previously part of a group (fascicle) begin to move away from one another and follow different paths
what is selective defasciculation?
specific axons or subsets of axons within a fascicle separate or detach from the bundle, while the remaining axons stay together and continue to follow the same path
this process allows certain axons to break away from a fascicle to follow different routes, while the others continue along their shared trajectory
what type of cue is fasciculation an example of?
short term cue
what is a growth cone?
a growth cone is the dynamic, specialized structure at the tip of a growing axon or dendrite that plays a critical role in guiding the developing neurite toward its correct target during neural development. The growth cone is highly sensitive to environmental cues and is essential for axon pathfinding
structure of a growth cone
lamellipodium: a broad, flat, sheet-like region at the leading edge of the growth cone, responsible for exploratory movement and substrate interaction.
filopodia: long, finger-like protrusions that extend from the lamellipodium. they are more dynamic and sensitive to environmental cues, helping the growth cone to sense the surrounding area and make decisions about direction.
they both contain actin filaments that allow the cone to extend and retract dynamically, responding to external cues
two main growth cone components
actin (hand)- constantly remodeled
microtubules- stable
what are the two forms of actin?
globular (monomeric) actin and filamentous (multimeric) actin
treadmilling
in the filopodia, actin is in filament form along the finger and it is being acted on by myosin
myosin is attached to the membrne and pushes actin into the palm
more actin is made at the tip of the finger and is taking off at the palm
constant recycling in equilibrium
