Axon Guidance

Question 1

Intrafusal muscle fibre

Answer 1

Can sense stretch - knee jerk reflex

Question 2

Axon pathfinding

Answer 2

Uses cues (molecular factors) for growth cone to navigate to target.

Question 3

Axon Growth Cone

Answer 3

Specialised organelle. Contains:
Lamellipodia
Filopodia
A ‘core’ and ‘periphery’ - different cytoskeletal components.
Both found in periphery

Question 4

Lamellopodia

Answer 4

‘webbed’ sections between filopodia.

Question 5

Filopodia

Answer 5

Reach out into environment to discover waymarkers.
Ligand Receptors on edge of F.
Produce polymerised actin - for growth.
Sliding filament theory of growth.

Question 6

Microtubule

Answer 6

Tubulin polymerises in a spiral pattern to form microtubule. Found inside axon, help send proteins from cell nucleus to growth cone.

Question 7

Substrate interaction

Answer 7

growth cones can follow physical grooves - eg grooves
Cell adhesion molecules are important for growth. (CAMs) eg LAMININ, ADHERIN

Question 8

Guidance Factors

Answer 8

Contact factors - either repulsive or adhesive.
Diffusion factors - either repulsive or adhesive. Usually ligands

Question 9

Growth cone change of direction

Answer 9

Signal (chemical) causes local depolymerisation of actin filaments. Axon turns other way.
Either stabilise or destabilise microtubules, axon turns towards or away respectively.

Question 10

Tracts

Answer 10

Spinal tracts form from bundling of axons together. Like an axon highway.
Formed by pioneer axons and then follower axons. But there are still choice points.

Question 11

Dendritic arbour growth

Answer 11

Dendrites also have growth cones.
Polarity of the neurons is determined by extraellular factors. Chemical signals allow dendrites to grow in the right direction.