Annexe: Axon Growth Mechanisms and Characteristics

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to Lesson

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

How does axon growth occur in mature axons that have already contacted their target tissue?

  • By stretching existing microtubules.
  • By adding new microtubules throughout the axon. (correct)
  • By a combination of stretching and adding new microtubules at the growth cone.
  • By adding new microtubules exclusively at the growth cone.

What is the shape of a growth cone when the axon is growing rapidly?

  • Wide and fan-shaped with many filopodia.
  • Irregular with a complex network of filopodia.
  • Slim and pointed with few filopodia. (correct)
  • Small and round with short filopodia.

What happens to the growth cone at a choice point in the axon's path?

  • It changes shape to match the shape of the choice point.
  • It splits into multiple growth cones to explore different paths.
  • It grows larger and extends filopodia in various directions. (correct)
  • It shrinks and becomes inactive.

Where does the growth cone's speed tend to slow down?

<p>All of the above. (D)</p> Signup and view all the answers

What is a non-permissive substrate, and what effect does it have on axon growth?

<p>A substrate that repels the growth cone. (C)</p> Signup and view all the answers

What is CSPG, and how does it affect axon growth?

<p>A carbohydrate that inhibits axon growth. (D)</p> Signup and view all the answers

What two cytoskeleton components meet in the peripheral zone of vertebrate growth cones?

<p>Actin filaments and microtubules. (D)</p> Signup and view all the answers

How can the growth of microtubules in an axon be visualized?

<p>By using fluorescent labels. (D)</p> Signup and view all the answers

What is the role of profilin in the treadmilling cycle of actin filaments?

<p>Profilin promotes the addition of actin monomers to the plus-end of filaments. (C)</p> Signup and view all the answers

What happens to the growth cone when actin filaments are depolymerised by cytochalasin?

<p>The growth cone loses its ability to find the target tissue. (A)</p> Signup and view all the answers

Which of the following statements accurately describes the 'clutch mechanism' in axon guidance?

<p>It describes the interaction between guidance molecules on the outside of the growth cone and the cytoskeleton on the inside, mediated by linker proteins. (B)</p> Signup and view all the answers

What is the difference between long-range and short-range cues in axon guidance?

<p>Long-range cues specify the direction of growth, while short-range cues specify the exact pathway. (A)</p> Signup and view all the answers

How do microtubules contribute to axon branch formation?

<p>Microtubules stabilize the protrusions, allowing them to develop into mature side branches. (C)</p> Signup and view all the answers

Which of the following statements correctly describes the role of cofilin in the treadmilling cycle of actin filaments?

<p>Cofilin enhances the depolymerization of actin filaments at the minus-end. (C)</p> Signup and view all the answers

What is the main difference between axon collaterals and bifurcations?

<p>Collaterals are more frequent than bifurcations because they are less energetically costly. (A)</p> Signup and view all the answers

What is the function of guidance cues in axon guidance?

<p>Guidance cues provide information to the growth cone that enables it to navigate towards its target tissue. (D)</p> Signup and view all the answers

How does the stabilization of microtubules affect the growth cone's movement?

<p>Microtubule stabilization causes the growth cone to turn in the direction of the stabilized microtubules. (C)</p> Signup and view all the answers

Which of the following is NOT a characteristic of the engorgement phase of the growth cone?

<p>The engorgement phase is characterized by the formation of new axon shafts. (C)</p> Signup and view all the answers

Flashcards

Axon Growth Mechanism

Methods by which axons increase in length, including adding microtubules and stretching.

Growing by Adding Microtubules

New microtubules are added at the distal end of the axon, allowing growth in length.

Bleached Area Experiment

Experiment showing that microtubules are added to the distal end while the midsection remains stationary.

Growth and Stretching

Process where mature axons can add material along their length, not just at the growth cone.

Signup and view all the flashcards

Growth Cone Characteristics

The shape of the growth cone changes based on growth phase and environment, affecting its exploration behavior.

Signup and view all the flashcards

Growth Cone at Choice Points

When navigating, growth cones enlarge and produce more filopodia to explore different directions.

Signup and view all the flashcards

Non-Permissive Substrates

Surfaces like CSPG that cause growth cones to turn away at boundaries.

Signup and view all the flashcards

Cytoskeleton in Axon Growth

Actin filaments and microtubules work together in vertebrate growth cones to support growth.

Signup and view all the flashcards

Actin Treadmilling

A cycle where actin filaments rapidly grow at the plus-end and shrink at the minus-end.

Signup and view all the flashcards

Profilin

A protein that promotes the addition of actin monomers to the growing plus-end of filaments.

Signup and view all the flashcards

Cofilin

A protein that enhances the depolymerization of actin filaments at the minus-end.

Signup and view all the flashcards

Growth Cone Phases

Four stages of growth cone behavior: encounter, protrusion, engorgement, and consolidation.

Signup and view all the flashcards

Growth Cone Steering

The mechanism by which the growth cone changes direction based on actin dynamics.

Signup and view all the flashcards

Long-range Cues

Guidance molecules that act over long distances to direct axons without specifying a direct path.

Signup and view all the flashcards

Short-range Cues

Guidance signals that specify the precise pathway for the growth cone, based on receptor interactions.

Signup and view all the flashcards

Clutch Mechanism

A linkage system that transmits signals from surface receptors to the cytoskeleton for movement.

Signup and view all the flashcards

Collaterals

Side branches of an axon that allow it to contact multiple target tissues.

Signup and view all the flashcards

Axon Protrusions

Small extensions formed by actin that can develop into side branches if stabilized by microtubules.

Signup and view all the flashcards

Study Notes

Axon Growth Mechanisms

  • Axons grow by adding new microtubules at their distal ends. Fluorescently labeled microtubules show growth occurs distally, leaving a bleached area mid-axon.
  • Mature axons, already in contact with their target tissues, grow by adding material along their entire length, not just at the growth cone. Young axons, not yet in contact, grow primarily at the growth cone.

Growth Cone Characteristics

  • Growth cone shape varies based on environment and growth phase.
    • Fast growth: Slim, pointed, few filopodia.
    • Choice point: Enlarged, many filopodia in various directions.
    • Target area: Smaller than choice point, still exploring with filopodia.
  • Growth cone speed varies by location. Faster in optic tracts, slower at choice points (e.g., between optic tract and tectum) and in the tectum itself.
  • Non-permissive substrates (like CSPG) cause growth cone turns.

Cytoskeletal Factors in Axon Growth

  • Actin filaments and microtubules interact in the growth cone's peripheral zone.
  • Treadmilling of actin filaments uses profilin and cofilin to control polymerization and depolymerization at the plus and minus ends, respectively. This dynamic balance influences growth.
  • Four Phases of Growth Cone:
  • Encounter substrate: Filopodia contact attractive surface.
  • Protrusion: Filopodia extend further,
  • Engorgement: Filopodia pull growth cone into substrate.
  • Consolidation: Axon shaft forms, filopodia seek new substrates.
  • Cytoskeletal control of growth direction:
    • Depolymerizing actin (cytochalasin) causes turn towards stable filaments.
    • Stabilizing microtubules (taxol) causes turn towards stable microtubules.
    • Destabilizing microtubules (nocodazole) causes turn towards stable microtubules.
  • Guidance cues from receptors influence the growth cone through stabilization signaling
    • Long-range cues (secreted), specify direction but not path.
    • Short-range cues specify pathway (same molecule may be attractive or repulsive).
  • Actin depolymerization halts axon growth and target tissue finding.

The Clutch Mechanism

  • Explains how growth cones generate traction. Guidance molecules, cytoskeleton, and linker molecules are involved in transmitting signals from environment to cytoskeleton.

Axon Branching

  • Collateral branching (main axon with side branches) is the most common branching method.
  • Branch formation: Protrusions form containing actin filaments. Microtubule migration stabilizes these into branches. Without stabilization/attractive signal, protrusions will regress.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Quiz Team

More Like This

Lecture 5
43 questions

Lecture 5

WellIntentionedSloth avatar
WellIntentionedSloth
Farrer Lecture on Nerve Growth
21 questions

Farrer Lecture on Nerve Growth

UsableDysprosium8038 avatar
UsableDysprosium8038
Cours: Axon Growth and Survival
17 questions

Cours: Axon Growth and Survival

FormidableJadeite611 avatar
FormidableJadeite611
Annexe: Growth Cone and Axon Guidance
48 questions

Annexe: Growth Cone and Axon Guidance

FormidableJadeite611 avatar
FormidableJadeite611
Use Quizgecko on...
Browser
Open
Browser
Browser