MECHANISMS OF AXON GUIDANCE 1 Flashcards
WHAT ARE THE TWO HYPOTHESIS FOR SPECIFIC NEURONAL CONNECTIONS
- WEISS RESONANCE THEORY
2. SPERRY CHEMOAFFINITY
WHAT WAS WEISS THEORY
RANDOM AND DIFFUSE NEURONAL OUTGROWTH OCCURS TO ALL TARGET FOLLOWED BY ELIMINATION OF NON FUNCTIONAL CONNECTIONS
WHAT WAS SPERRY THEORY
DIRECT SPECIFIC OUTGROWTH OCCURS THROUGH AXONS FOLLOW IDENTIFICATION TAGS CARRIED BY THE CELLS AND FIBRES IN THE EMBRYO
HOW DID THEY TEST WHETHER THE SPERRY OR WEISS TEST WAS CORRECT
- CUT THE OPTIC NERVE (AMPHIBIAN) AND REMOVED THE TEMPORAL RETINA ALLOWING JUST NASAL AXONS TO GROW BACK
- IF WEISS WAS RIGHT THE AXONS WOULD GROW ALL ALONG THE PATHWAY AND THEN BE ELIMINATION
- IF SPERRY WAS RIGHT THE MOTOR AXONS ARE GUIDED SPECIFICALLY TO THEIR TARGET
WAS THE WEISS RESONANCE THEORY OR THE SPERRY CHEMOAFFINITY THEORY CORRECT
THE SPERRY
IN THE EARLY CHICK EMBRYO, IF THE NERUAL TUBE IS CUTE AND REPLACED OR REVERSE BEFORE MOTOR AXONS GROW OUT, WHAT IS THE RESULT
DESPITE THIS NORMAL INNERVATION OCCURS AND MOTOR AXONS STILL FIND THEIR TARGETS
WHAT COULD BE CONCLUDED FROM THE CHICK NEURAL TUBE EXPERIMENT
THIS SUGGESTS THE AXONS ARE ACTIVELY NAVIGATED
ENVIRONMENT CONTAINS GUIDANCE CUES THAT AXONS CAN USE TO FIND THE CORRECT TARGETS
WHY DO WE DO EXPERIMENTS ON INSECTS
- SIMPLE NS
- EASY TO MANIPULATE
- LARGE INSECT CELLS EASY TO ABLATE
EG GRASSHOPPER
UPON EXPERIMENTS ON INSECTS SUCH AS GRASSHOPPER WHAT HAS BEEN FOUND IN RELATION TO AXON PATHWAYS
ALL PATHWAYS ARE STEREOTYPED EMBRYO TO EMBRYO, SEGMENT TO SEGMENT.
THIS HAS ALLOWED A MAP TO BE MADE - COREY GOODMAN
WHAT DOES REPRODUCIBILITY OF AXON BEHAVIOUR SUGGESTS WHAT
GROWTH CONES ARE RESPONDING TO CUES IN THE ENVIRONMENT
PATHWAYS SEEM TO CHANGE UPON ENCOUNTERING SPECIFIC …………………..
AXONS
IN ABLATING CELLS, FOUND THAT MOST AXONS ……………… TO BEHAVE NORMALLY BUT OTHER AXONS …………….. IT MUST BE THAT SOME GROWTH CONES ARE LOOKING FOR ……………….. CUES FROM THE ……………….. AXON.
CONTINUE
STALL
SPECIFIC
ABLATED
WHAT IS THE LABELLED PATHWAY HYPOTHESIS
AXONS SELECTIVELY BUNDLE WITH OTHER AXONS
AXON SURFACES CARRY LABELS/CUE
DIFFERENT AXON GROWTH CONES EXPRESS DIFFERENT SETS OF RECEPTORS FOR CUES
EARLY AXONS FOR AN AXON SCAFFOLD ON WHICH LATER AXONS CAN EXTEND
WHAT IS ANOTHER NAME FOR AN EARLY AXON
PIONEER
WHAT IS ANOTHER NAME FOR A LATE AXON
FOLLOWER
THE LABELLED PATHWAY HYPOTHESIS IS TRUE IN AMPHIBIANS, WHAT ABOUT MAMMALS
THIS IS TRUE FOR MAMMALS ASWELL
GIVE AN EXAMPLE OF PIONEER AND FOLLOWER NEURONS IN MAMMALIANS
SUBPLATE NEURONS IN THE CORTEX PROJECT FROM THE CORTEX TO THE THALAMUS BEFORE INNERVATION OF THE CORTEX BY LATERAL GENICULATE NUCLEUS
ABLATION OF THE SUBPLATE = LGN FAILURE
HOW DO THE PIONEER AXONS FIND THEIR WAY IF THERE ARE NO OTHER AXONS TO RESPOND TO
PIONEER AXONS ARE ALSO STEREOTYPED AND SEEM TO RESPOND TO SPECIFIC POINT IN THE PATHWAY
HOW DO PIONEER AXONS GO ABOUT FINDING THEIR TARGET
CELLS IN THE PATHWAY ARE STEPPING STONES/GUIDE POST CELLS
WHAT EXPERIMENT SHOWS PIONEER AXONS RESPOND TO ENVIRONMENTAL CUES
THE PIONEER TI1 GROWTH CONE MAKES A TURN AT THE LIMB BOUNDARY AND AGAIN AS IT APPROACHES A SPECIFIC CELL, CX1. ABLATION OF CX1 CAUSES STALLING OF THE GROWTH CONE
WHAT ARE THE FOUR FORCES OF AXON GUIDANCE
CHEMOATTRACTION AND REPULSION
CONTACT ATTRACTION AND REPULSION
NEURONS VARY GREATLY BUT ALL EXHIBIT ………………. IN TERMS OF SHAPE OR FUNCTION
POLARITY
WHAT DO DENDRITES DO
RECEIVE INCOMING INFORMATION
WHAT DO AXONS DO
CARRY INFORMATION AWAY FROM THE CELL BODY IN ACTION POTENTIALS
AXONS HAVE HIGHLY POLARISED ………….. (+ END TOWARDS GROWTH CONE. DENDRITES ALSO HAVE MICROTUBULES BUT THESE ARE LESS ORDERED AND HAVE MIXED ……………………… THE DIFFERENCE IS DUE TO LOCALISATION OF DIFFERENT TYPES OF ………………………………… ……………………………….. ……………………… (MAP)WHICH DETERMINE HOW THEY ARE CROSS LINKED
MICROTUBULES
ORIENTATIONS
MICROTUBULE ASSOCIATED PROTEINS
AXONS EXPRESS WHICH MAP
TAU
DENDRITES EXPRESS WHICH MAP
MAP2
WHAT IS A NEURITE
A NEURONAL PROJECTION - EITHER A DENTRITE OR AXON
KINESINS ARE PART OF ………………………….. STRUCTURE. IT IS …………. END DIRECTED AND SO WILL BE GOUND TOWARDS THE …………………. CONE OF AXONS. GFP LABELLING SHOWS KINESIN MOVING AROUND TO SEE WHICH SHOULD BECOME AN ……………..
MICROTUBULE
PLUS
GROWTH
AXON
WHAT UNDERLIES AXON CHOICE
NEW BORN NEURITES ARE TYROSINATED AND THEREFORE DYNAMIC MICROTUBULES
STABILISED ACETYLATED MICROTUBULES ARE PRESENT ONLY IN THE NEWLY POLARISED AXON
WHAT DOES ARTIFICIAL STABILISATION (BY TAXOL) OF MICROTUBULES IN A NEURITE CAUSE
AXON FORMATION
WHAT IS THE OUTCOME OF CUTTING OFF AN AXON
LEADS TO NEW AXON SELECTION IN A FEEDBACK LOOP