Topographic mapping

Question 1

Topographic mapping

Answer 1

Many systems are mapped to specific areas of sensory and motor cortex.
Learnt during brain surgeries.

Question 2

Zebrafish mapping

Answer 2

Basic anatomy of the system is similar in amphibia.
Retinotectal system - optic nerve to tectum - region of brain.
Have complete crossing in brain, left eye to right brain and vice versa.

Question 3

Steps leading to connection

Answer 3

Defasiculation of axon from tract.
Enters target.
Finds topographical location.
Find layer.
Covered with target cells.

Question 4

Finding topographical location

Answer 4

Roger sperry demonstrated topographical mapping by rotating the eye of frogs.
Dorsal axon still goes to specific tectum of brain.
He proposed latitude and longitude gradient cues.

Question 5

Ephrin signalling in the retinotectal system.

Answer 5

Within a tectum, diffusion gradient of EPH signals to axon where to connect.
This is the longitude/latitude system.
May either be reverse signalling or regular.

Question 6

Chemical based targeting for layer specificity

Answer 6

Eg layers of cerebral cortex, contain specific molecules targeted by certain axons.
CAMs important.

Question 7

Refinement of axonal projections

Answer 7

1. refinement of topography eg 3 projections to 1.
2. refinement of convergence.
3. refinement of postsynaptic compartment.
   ‘Hebbian’ process.

Question 8

Hebbian learning

Answer 8

Neurons that fire together wire together.

Question 9

Hubel and Weisel

Answer 9

Occular dominance columns. Experience dependant process

Question 10

Critical periods of development

Answer 10

6 week period where if eye is closed then other eye gains ocular dominance.
May be mammalian trait only though.

Question 11

Frogs and fish

Answer 11

Lesions to part of the tecta will produce experience driven rewiring.

Question 12

Olfactory (smell) system

Answer 12

1000 different receptors vs 4 in visual system.
All receptors lead to olfactory bulb.