Chapter 23: Wiring the Brain

Question 1

brain development begins as ()

Answer 1

tube

Question 2

wiring in the brain is determined by:
1. nature - ()
2. nurture - ()

Answer 2

1. establishing correct pathways and targets by genetic programs
2. fine-tuning based on experience and sensory info from envi

Question 3

organization of the LGN

inputs are segregated by ()

Answer 3

eye and ganglion cell type

Question 4

() cells give rise to neurons and astrocytes.

Answer 4

Radial glial

Question 5

neuronal cell structure developes in 3 major stages

Answer 5

1. cell proliferation
2. cell migration
3. cell differentiation

Question 6

In humans, the majority of neocortical neurons are born between the () of gestation, peaking at the astonishing rate of 250,000 neurons per minutes

Answer 6

5th week and the 5th month

Question 7

cell proliferation

(1) and (2) during cell division determine fate of daughter cells.

Answer 7

1. Transcription factors
2. cleavage plane

Question 8

Ultimate fate of migrating daughter cells determined by the (1) of the precursor cell, its (2), and its (3) at the time of division.

Answer 8

1. age
2. position
3. environment

Question 9

cell migration

() migrate vertically from the dorsal ventricular zone by moving along thin radial glial fibers.

Answer 9

Pyramidal cells and astrocytes

Question 10

cell migration

() generate from the ventral telencephalon and migrate laterally.

Answer 10

Inhibitory interneurons and oligodendroglia

Question 11

cell migration

Radial processes disappear when () is complete

Answer 11

cortical assembly

Question 12

cell migration

• First cells to migrate take up residence in (1), which eventually disappears.
• Next cells to divide migrate to the (2).
• The first to arrive become layer VI, followed V, IV, and so on: “(3).”

Answer 12

1. subplate layer
2. cortical plate
3. inside out

Question 13

• Consequence of a specific spatiotemporal pattern of gene expression
• process by which a cell takes on the appearance and characteristics of a neuron

Answer 13

cell differentiation

Question 14

Order of cell differentiation: ()

Answer 14

neurons, astrocytes (peaks at the time of birth), then oligodendrocytes

Question 15

evidence for idea that cell differentiaton is rogrammed well before reaching final destination

Answer 15

neural precursor cell will still differentiate even when extracted from brain and placed in tissue culture

Question 16

(), a protein secreted by cells in the marginal zone, repels the growing axon and attracts the growing apical dendrite, giving the pyramidal neuron its characteristic polarity.

Answer 16

Semaphorin 3A

Question 17

Adult cortical sheet like a “()”; many structurally distinct areas stitched together; in humans, many specialized cortical areas are precisely stitched

Answer 17

patchwork quilt

Question 18

Ventricular zone contains cortical ‘()’; migrating cells are precisely guided by radial glial fibers (for majority of cortical neurons)

helps for “patchform quilt” arrangement of cortical sheet

Answer 18

protomap

Question 19

Some (~1/3) neurons migrate laterally. How? Neurons in different areas have distinct ().

Answer 19

molecular identities

Question 20

() input contributes to cortical differentiation

Answer 20

Thalamic

Question 21

• concept that an entire radial column of cortical neurons originates from the same birthplace in the ventricular zone

Answer 21

radial unit hypothesis

Question 22

In the fetal telencephalon, () are expressed by neural precursor cells in complementary gradients

• sizes of different cortical areas change when these concentration gradients are also changed

Answer 22

Pax6 and Emx2

Question 22

describe how thalamic inputs are able to influence cortical development

Answer 22

Subplate neurons attract appropriate thalamic axons

Question 22

3 phases of pathway selection

(1) : which side of the optic tract?
(2) : which nucleus of the thalamus?
(3) : which layer of the LGN (with topography)?

Answer 22

1. Pathway selection
2. target selection
3. address selection

Question 23

(): growing tip of a neurite

Answer 23

Growth cone

Question 24

(): constantly probe the environment and direct the growth of the neurite towards attractive cues.

Answer 24

Filopodia

Question 25

Neurite growth occurs when a filopodium binds the () and pulls the growth cone forward

Answer 25

substrate (the surface on which it is growing)

Question 26

Filopodia bind appropriate proteins, such as laminin, in the ()

Answer 26

extracellular matrix (growing axons express integrin that binds laminin)

Question 27

(): permissive substrates bordered by repulsive ones

Answer 27

Molecular “highway”

Question 28

(): process of growing axons sticking together by cell adhesion molecules, CAMs, forming bundles of axons

Answer 28

Axonal fasiculation ## Footnote (“fascicles”) = bundles of axons

Question 29

() stretch as nervous system expands. - Guide neighbor axons to same targets

Answer 29

Pioneer axons

Question 30

Pioneer neurons grow in the correct direction by “()” (a few hundred microns long).

Answer 30

connecting the dots

Question 31

The pioneering axon concludes a segment when it arrives at an (). The interaction of the axon and the () throws a molecular switch that sends the axon onward to another ().

Answer 31

intermediate target

Question 32

Growth cones differ in terms of the molecules they express on their membranes -> Interactions of these () with guidance cues in the environment determine the direction and amount of growth

Answer 32

cell surface molecules

Question 33

diffusible molecules that act over a distance to attract growing axons toward their targets

Answer 33

Growth guidance cues

Question 33

examples of growth guidance cues

Answer 33

chemoattractant (e.g., netrin), chemorepellent (e.g., slit)

Question 34

The protein called netrin is secreted by cells in the ventral midline of the spinal cord. Axons with the appropriate netrin receptors are (attracted to/repelled from) the region of highest netrin concentration.

Answer 34

attracted to

Question 35

The protein called (1) is also secreted by midline cells. Axons that express the protein called (2), the (1) receptor, grow away from the region of highest (1) concentration

Answer 35

1. slit 2. robo ## Footnote Up-regulation of robo by axons that cross the midline ensures that they keep growing away from the midline.

Question 36

(): chemical markers on growing axons are matched with complementary chemical markers on their targets to establish precise connections

Answer 36

Chemoaffinity hypothesis

Question 37

Large-scale () in neurons and synapses during the process of refining connections (from before birth all the way through adolescence)

Answer 37

reduction

Question 38

proper development of brain function requires balance between ()

Answer 38

genesis and elimination of cells and synapses

Question 39

Autism spectrum disorder: () disorder

Answer 39

neurodevelopmental

Question 40

Cell death reflects competition for () provided by the target cells; life-sustaining substances that are provided in limited quantities

Answer 40

trophic factors

Question 41

(): identified in 1940s (released by targets of sympathetic neuronal axon) -> example of trophic factor

Answer 41

Nerve growth factor (NGF)

Question 42

* (): NT-3, NT-4, BDNF, etc. Bind to trk receptors (tyrosine kinase) altering gene expressions -> family of proteins, including NGF

Answer 42

neurotrophins

Question 43

programmed cell death; cell death genes are expressed (normally suppressed by trophic factors)

Answer 43

apoptosis

Question 44

(): the number of synapses a neuron can receive

Answer 44

Synaptic capacity

Question 45

(): change from one pattern of synaptic connections to another

Answer 45

Synaptic arrangement ## Footnote involved in critical period

Question 46

Synaptic arrangement is a consequence of (2)

Answer 46

neural activity and synaptic transmission ## Footnote both before (spontaneous activity) and after (sensory experience during childhood) birth

Question 47

* In some circuits, final refinement of synaptic connections requires ()

Answer 47

neural activity

Question 48

(): whenever a wave of retinal activity drives a postsynaptic LGN neuron to fire action potentials, the synapses between them are stabilized

Answer 48

Hebbian modification -> strengthened synapses are called Hebbian synapses

Question 49

Visual cortex has () (cat, monkey)—segregated input from each eye (by molecular cues + activity difference)

Answer 49

ocular dominance columns

Question 50

(): a period after birth when the ocular dominance columns may be modified by activity dependent plasticity (monkey: ~6 wk).

Answer 50

Critical period ## Footnote dependent on experience

Question 51

Inputs from two eyes must be combined for () -> Convergence of inputs from layer IV neurons serving the left and right eyes in layer III

Answer 51

binocular vision

Question 51

(): formed by correlated patterns of activity from two eyes as a consequence of vision (c.f., ocular dominance columns by asynchronous activity from two eyes)

Answer 51

Binocular receptive fields

Question 52

(): disrupts binocular connections, results in ocular dominance shift ## Footnote shift may occur within hours (synaptic changes without substantial remodeling of axons)

Answer 52

monocular deprivation

Question 53

(): inputs from two eyes actively compete for synaptic control of postsynaptic neurons

Answer 53

Binocular competition

Question 54

(): eyes are not perfectly aligned so that one eye is turned in a direction different from the other eye (cross-eyed or wall-eyed)

Answer 54

Strabismus

Question 55

Two rules for synaptic modification

Answer 55

– Fire together, wire together (Hebbian modifications) (pre + strong postsynaptic activation) – Fire out of sync, lose their link (pre + weak postsynaptic activation)

Question 56

A single synapse has little influence on firing rate of postsynaptic neuron -> Activity of a synapse must be () with activity of many other inputs converging on the same postsynaptic neuron for strong postsynaptic activation

Answer 56

correlated

Question 56

# Focus on two glutamate receptors 1. () receptors: glutamate-gated ion channels 2. () receptors: have unique properties

Answer 56

1. AMPA 2. NMDA

Question 57

2 unique properties of NMDA receptors

Answer 57

– Voltage-gated owing to action of Mg2+ (magnesium block) – Conducts Ca2+

Question 58

Magnitude of Ca2+ flux into axon terminal signals level of ()

Answer 58

pre- and postsynaptic coactivation