04 Wiring the Brain

Question 0

Corticospinal and Corticobulbar tracts reside where in brain?

Answer 0

within Pyramidal tract.

Question 1

What areas of the body have relatively greater representation in the cortex?

Answer 1

Areas for which there needs to be enhanced somatosensory sensitivity.

Question 2

Describe how a phantom limb might be felt in another part of the body

Answer 2

if no sensation/information is being received by a part of the cortex (due to loss of limb), nerves from other parts of the cortex might grow into that place and infiltrate area of phantom.

Question 3

One theory about the etiology of schizophrenia

Answer 3

disruption/improper migration of neurons. ALSO, deficits in signaling between neuregulin 1 and its receptor, ErbB4.

Question 4

During cortical development, excitatory neurons derive from where? how do they migrate?

Answer 4

the pallium. Radial migration.

Question 5

during cortical development, inhibitory neurons derive from where? how do they migrate?

Answer 5

derive from subpallium, migrate tangentially.

Question 6

What are neuregulin 1 and ErbB4?

Answer 6

Neuregulin 1 is expressed in the pallium, guides inhibitory neurons which express ErbB4 receptors.

Question 7

inhibitory neurons: what do they synthesize?

Answer 7

GABA. (neurotransmitter)

Question 8

describe gamma oscillations. in what disease are they decreased?

Answer 8

gamma oscillations are an index of synchronized neural network activity. decreased in schizophrenia. impt for cognition, memory, learning.

Question 9

what Calcium binding protein plays a big role in gamma oscillation frequency control?

Answer 9

parvalbumin. a set of fast-spiking GABAergic interneurons express parvalbumin.

Question 10

parvalbumin interneurons rely on what for migration and differentiation?

Answer 10

rely on interneuron 1/ErbB4 signaling. Loss results in a decrease of power in gamma oscillatins that mimics the pattern seen in schizophrenia.

Question 11

define the thalamocortical afferents (TCA). what guides them in their developmental path?

Answer 11

TCA: axon pathways between thalamus and cortex. corridor cells act as guideposts steering the growth cones of TCA cells as they traverse the developing brain.

Question 12

describe the path of corridor neurons.

Answer 12

derive from the LGE (lateral ganglionic eminence) but migrate into MGE. Form a permissive zone between MGH and primordial globus pallidus (which would normally repel TCAs). Corridor cells express neuregulin1, and TCAs growth cones express ErbB4.

Question 13

describe guidepost cells. how do they guide pioneer neurons?

Answer 13

guidepost cells act as kiosks for pioneer neurons that grow from the periphery to the CNS. Growth cones of pioneer neurons are guided by guidepost cells

Question 14

name 3 types of guidepost cells in vertebrates

Answer 14

corridor neurons (thalamocortex)
Cajal-Retzius cells (hippocampus)
subplate neurons (cortex)

Question 15

what are the main excitatory cells called?

Answer 15

principal cells.

Question 16

name 2 features of growth cones.

Answer 16

lamellipodia (sheet like structures)
filopodia (finger like projections)
highly specialized structures that direct the movement of the growth cone.

Question 17

general qualities of axon guidance molecules that are SECRETED?

Answer 17

tend to be long-range signals, expressed as gradients in target tissue.

Question 18

general qualities of axon guidance molecules that are TETHERED?

Answer 18

tend to be short-range signals, local acting.

Question 19

Feature of pioneer neurons?

Answer 19

have many active filopodia. some of pioneer neurons are transitory, and will be primary sensory cells until other cells follow and replace them.

Question 20

Trophic molecules vs tropic molecules?

Answer 20

Trophic: support growth and survival
Tropic: guide
some molecules function as both

Question 21

Describe ECM molecules. examples?

Answer 21

ECM = extracellular matrix. proteinaceous molecles, interact with receptors (integrins) in the axons to regulate the extent of adhesion of the growth cones.
Examples: laminin, fibronectin.

Question 22

how do axons change their sensitivity to ECM proteins?

Answer 22

alter expression of integrins. (receptors that interact with ECM molecules).

Question 23

what are CAMs?

Answer 23

Cell Adhesion Molecules. bind to promote adherence amongst axon processes. expressed by both pioneer and follower axons.

Question 24

Netrin: receptor is what?

Answer 24

DCC

Question 25

Slit: receptor is what?

Answer 25

Robo

Question 26

Semaphorins: receptor is what?

Answer 26

Various neuropilins and plexins

Question 27

Ephrins: receptor is what?

Answer 27

Eph

Question 28

Netrins are impt for what? Receptors expressed where? Netrins expressed by what cells/where?

Answer 28

Netrins are multifunctional, can either repel or attract depending on circumstance. Receptors are DCCs. Receptors expressed in retinal ganglion cell axons. Netrins expressed by midline floorplate neurons at optic chiasm.

Question 29

Netrin turning response is dependent on what?

Answer 29

Dependent on cAMP concentration in growth cone.
If HIGH, attraction
if LOW, repulsion.

Question 30

Slit is expressed where, by what cells? Receptor is what? Role is what?

Answer 30

Expressed by midline floorplate neurons at optic chiasm. Can be multifunctional. Receptor is Robo. Slit plays role in preventing ipsilateral axons from crossing at optic chiasm, and preventing REcrossing from crossed axons.

Question 31

Semaphorins are expressed where? Can cause what? Receptors are what? Receptors expressed where?

Answer 31

Semaphorins expressed on cell surfaces or ECM (can be either secreted or membrane bound). Can cause immediate growth cone collapse. Receptors are various neuropilins and plexins, some expressed on growth cones.

Question 32

Ephrins do what?

Answer 32

Regulate formation of topographical maps in retina and tectum.

Question 33

Which ephrins regulate Anterior-Posterior topography?

Answer 33

Ephrin A and EphA receptors. Cells with lowest Ephrin A map to axons with highest EphA receptors.

Question 34

Which ephrins regulate Dorsal-Ventral topography?

Answer 34

Ephrin B and EphB in retina and tectum. Signals are purely attractive.

Question 35

Ephrins exist where in the brain? their receptors exist where?

Answer 35

Ephrins exist on tectum (colliculi).

Eph receptors exist on retinal ganglion cell axons.

Question 36

At choice points, what happens morphologically to filopodia?

Answer 36

The whole axon growth cone slows when it senses a choice point, and filopodia extend outwards.