axon growth and guidance Flashcards
How many neurons and connections
10’11 neurons 10’14 connections
Weiss resenonce theory
random then non functional removed. it is wrong
Sperry chemoreceptivce theory
axons with id tags with directed and specific outgrowth. is right
name the 4 types of growth cone
long/short atractive/repelant
what was found from insect experiments into the growth cone?
Pathways are stereotyped embryo to embryo and segment to segment.
Cajals groth cone
is the growing tip of the axon.
what are CAMs and CDCs egs
cell adhesion molecules eg IgG and NCAM and calcium dependant cahderin molecues.
give examples of experiments that prove Sperry right
Chick embryo notocord reversed still got to targets. Frog cut and removed optic nerve it regrew to original position. grass hopper ti1 uses cx1 as a gidance cell.
decribe pineer and follower cells
pioneer cells use cell cues and floor plate interaction to lay the scaffold, then follower or secondary cells use cell adhesion moleucles on the axons to giude them to their destination both are steriotyped.
how does c axon sensitivity change
becomes sensitive to repellant after crossing floor plate, before floor plate sensitive to netrin. Semaphorins and slits protein inhibit after floor plate.
X levels determine if axon will be comissural, What is X
X is slits receptor.
FASII
causes fascicluation, regulated by BEAT.
ROBO
Roundabout-encodes for slits receptor lots on non crossing axons. vetebrate homologue ROBO1
Commisureless (COMM)
Expressed in C neuons then turned off after crossing. Comm controls ROBO-encodes traficing protein that stops ROBO getting to the cell surface.
COMM in veterbrates
trick question you cheeky monkey, However Rig 1 or ROBO3 is expressed only precrossing blocks ROBO 1 until midline.
Keep working you’re doing well furry kitten
keep on going otherwise you might get bittern
Structure of lamella and filopodia f actin
lamela actin bundles crosslinked net. Filopodia polarised bundles that form larger bundles.
Chat about treadmilling (not the gym)
in a resting growth cone treadmilling occurs. If it reaches a target molecular clutch stops the actin movement. a actinmyosin tubule pulls the myosin tuble to the end.
Ephrins
non-permissive used in early patterning.detected by eph receptors. Together they make the longitudinal lateral grid for topograhic mapping. ephrins posterior (hi) and anterior. Ephs tempral (hi) to nasal. Ephrins cause repulsion between cells. cause rhombomeres. Can channel axon growth but still need permissive.
Semaphorins
membrane bound or secreated sema3. Cause growth cone to turn or inhibit guidance.
Lamin
localised in optic nerve permissive but not directive
long and short work together example
Sema1 short and Sema2 long direct Ti1
Netrin
secreated protien that can associated with extracellular matrix
Target derived factors
determine morphology and connection. GDNF turns off Pea 3 so cutaneous maximus and lats have internueron pecs and triceps dont <-monosynaptic.
