Chapter 9 section 1

Question 1

A fertilized egg is totipotent. What does this mean?

Answer 1

The cell has the ability to develop into any class of cell in the body (e.g., bone, skin, neuron, or heart cells).

Question 2

After about 4 days of embryonic development, newly created cells lose their ________ and begin to specialize. At this stage, developing cells have the ability to develop into many, but not all, classes of body cells and are said to be _______.

Answer 2

Totipotency,

Pluripotent.

Question 3

As the embryo develops, new cells are said to become more and more specialized. Eventually, new cells can develop into different cells of only one class (e.g., different kinds of bloods cells). These new cells are said to be ________.

Answer 3

Multipotent

Question 4

Most developing cells will eventually become ______; they can develop into only one type of cell (e.g., bipolar neurons).

Answer 4

Unipotent

Question 5

Three weeks after conception, the tissue that is destined to develop into the human nervous system becomes recognizable as the _______– a small patch of ectodermal tissue on the dorsal surface of the developing embryo.

Answer 5

Neural plate

Question 6

The ______ is the outer most of the three layers of embryonic cells. What are the three layers of embryonic cells?

Answer 6

Ectoderm

1-ectoderm
2-mesoderm
3-endoderm

Question 7

The development of the _______ is the first major stage of neurodevelopment in all vertebrates.

Answer 7

Neural plate

Question 8

The development of the neural plate is induced by ________ from an area of the underlying ________- an area consequently referred to as an ________.

Answer 8

Chemical signals,
Mesoderm layer,
Organizer.

Question 9

Tissue taken from the _______ of one embryo (i.e., the donor) and implanted beneath the ventral _______ of another embryo (i.e., the host) induces the development of an extra _______ on the ventral surface of the host.

Answer 9

Dorsal mesoderm,
Ectoderm,
Neural plate

Question 10

The cells of the neural plate are often referred to as _________.

Answer 10

Embryonic stem cells.

Question 11

Stem cells are cells that meet two specific criteria:

Answer 11

(1) they have an almost unlimited capacity for self-renewal if maintained in an appropriate cell culture.
(2) they are pluripotent.

(However, as the neural plate develops into the neural tube, the fates of many of its new cells become more specified)

Question 12

The growing neural plate folds to form the ______, and then the lips of the neural fuse to form the ______.

Answer 12

Neural groove,

Neural tube.

Question 13

The inside of the neural tube eventually becomes the _______ and _______. By 40 days after conception, three dwellings are visible at the anterior end of the human neural tube; these swellings ultimate develop into the ______, ______, and ______.

Answer 13

Cerebral ventricles,
Spinal canal,
Forebrain,
Midbrain,
Hindbrain.

Question 14

Once the lips of the neural groove have fused to create the neural tube, the cells of the tube begin to _______. This _______ does not occur simultaneously or equally in all parts of the tube. Most cell division in the neural tube occurs in the _______– the region adjacent to the ventricle (the fluid-filled center of the tube).

Answer 14

Proliferate,
Neural proliferation,
Ventricular-zone.

Question 15

In each species, the cells in different parts of the neural tube proliferate in a particular sequence that is responsible for the pattern of _______ and ______ that gives the brain its characteristic shape. The complex pattern of proliferation is in part controlled by chemical signals from two organizer areas in the neural tube: the _______, which runs alone the midline of the _______ surface of the tube, and the ______, which runs along the midline of the ______ surface of the tube.

Answer 15

Swelling,
Folding,
Floor plate,
Ventral,
Roof plate,
Dorsal.

Question 16

Once cells have been created through cell division in the _______ of the neural tube, they _______ to the appropriate target location. During this period of migration, the cells are still in an ______ form, lacking the processes (axons and dendrites) that characterize mature neurons.

Answer 16

Ventricular zone,
Migrate,
Immature.

Question 17

Two major factors govern migration in the neural tube:

Answer 17

Time and location.

In a given region of the tube, subtypes of neurons arise on a precise and predictable schedule and then migrate together to their prescribed destinations.

Question 18

Cell migration in the developing neural tube is considered to be of two kinds:

Answer 18

Radial migration- proceeds from the ventricular zone in a straight line outward toward the outer wall of the tube.

Tangential migration- occurs at a right angle to radial migration– that is, parallel to the tube’s walls.

Question 19

Most cells engage in both ______ and _______ migration to get from their point of origin in the _______ to their target location.

Answer 19

Radial,
Tangential,
Ventricular zone.

Question 20

There are two methods by which developing cells migrate:

Answer 20

Somal translocation

Glia-mediated migration

Question 21

Describe somal translocation.

Answer 21

In somal translocation, an extension grows from the developing cell in the direction of the migration; the extension seems to explore the immediate environment for attractive and repulsive cues as it grows. Then, the cell body itself moves into and along the extending process, and trailing processes are retracted.

Question 22

Describe glia-mediated migration.

Answer 22

Once the period of neural proliferation is underway and the walls of the neural tube are thickening, a temporary network of glial cells, called radial glial cells, appears in the developing neural tube. At this point, most cells engaging in radial migration do so by moving along the radial glial network.

Question 23

Radial glial cells

Answer 23

Glial cells that exist in the neural tube only during the period of neural migration and that form a network along which radial migration occurs.

Question 24

It is now clear that many radial glial cells eventually develop into _______.

Answer 24

Neurons

Question 25

Inside-out pattern

Answer 25

The pattern of cortical development in which orderly waves of tangential migrations progress systematically from deeper to more superficial layers.

Question 26

The _______ is a structure situated just dorsal to the neural tube.

Answer 26

Neural crest

Question 27

The ______ is formed from cells that break off from the neural tube as it is being formed. _______ cells develop into the neurons and glial cells of the peripheral nervous system, and thus many must migrate over considerable distances.

Answer 27

Neural crest,

Neural crest

Question 28

Numerous _______ guide various classes of migrating neurons by either _______ or _______ them. These guidance molecules play a critical role in neurodevelopment because the brain cannot function normally unless each class of developing neurons arrives at the correct location.

Answer 28

Chemicals,
Attracting,
Repelling.

Question 29

Describe the process of aggregation.

Answer 29

Once developing neurons have migrated, they must align themselves with other developing neurons that have migrated to the same area to form the structures of the nervous system.

Question 30

Both migration and aggregation are thought to be mediated by ________, which are located on the surfaces of ________ and other cells.

Answer 30

Cell-adhesion molecules (CAMs),

Neurons.

Question 31

__________ have the ability to recognize molecules on other cells and adhere to them. Elimination of just one kind of ________ in a knockout mouse has been shown to have a devastation effect on _________.

Answer 31

Cell adhesion molecules (CAMs),
CAM,
Brain development.

Question 32

________ between adjacent cells have been found to be particularly prevalent during brain development.

Answer 32

Gap junctions

Question 33

There is increasing evidence that ________ play a role in migration and aggregation and other aspects of neurodevelopment.

Answer 33

Gap junctions

Question 34

Once neurons have migrated to their appropriate positions and aggregate into neural structures, ______ and ______ begin to grow from them.

Answer 34

Axons,

Dendrites.

Question 35

At each growing tip of an axon or dendrite is an amoebalike structure called a _______, which extends and retracts fingerlike cytoplasmic extensions called _______, as if searching for the correct route.

Answer 35

Growth cone,

Filopodia.

Question 36

What is the chemoaffinity hypothesis of axonal development?

Answer 36

The hypothesis that growing axons are attracted to the correct targets by different chemicals released by the target sites.

Question 37

The chemoaffinity hypothesis fails to account for:

Answer 37

The discovery that some growing axons follow the same circuitous route to reach their target in every member of a species, rather than growing directly to it. This led to a revised theory, in where is was hypothesized that a growing axon is not attracted to its target by a single specific attractant released by the target, but influenced by a series of chemical signals along the route.

Question 38

Guidance molecules are not the only signals that guide growing axons to their targets. Other signals come from ______.

Answer 38

Adjacent growing axons.

Question 39

________- the first growth cones to travel along a particular route in a developing nervous system- are presumed to follow the correct trail by interacting with guidance molecules along the route. Then, subsequent growth cones embarking on the same journey follow the routes blazed by the _______. The tendency of developing axons to grow along the paths established by preceding axons is called ________.

Answer 39

Pioneer growth cones,
Pioneers,
Fasciculation.

Question 40

What is fasciculation?

Answer 40

The tendency of developing axons to grow along the paths established by preceding axons.

Question 41

In most species, the synaptic connections between the retina and optic tectum are established ______ either reaches full size. Then, as the retinas and optic tectum grow at different rates, the initial synaptic connections shift to other tectal neurons so that each retina is precisely mapped onto the ______, regardless of their _________.

Answer 41

Long before,
Tectum,
Relative size.

Question 42

What is the topographic gradient hypothesis?

Answer 42

Hypothetically, axons growing from one topographic surface (the retina) to another (the optic tectum) are guided to specific targets that are arranged on the terminal surface in the same way as the axons’ cell bodies are arranged on the surface. The key part of this hypothesis is that the growing axons are guided to their destinations by two intersecting signal gradients (e.g., an anterior-posterior gradient and a medial-lateral gradient).

Question 43

A single neuron can grow an _______ of its own, but it takes coordinated activity in at least two neurons to create a _______ between them.

Answer 43

Axons,

Synapse.

Question 44

Perhaps the most exciting recent discovery about _______ (the formation of new synapses) is that is depends on the presence of _______, particularly ________.

Answer 44

Synaptogenesis,
Glial cells,
Astrocytes.

Question 45

Many more neurons – about _____ more – are produced than required, and large scale ______ occurs in waves in various parts of the brain throughout development.

Answer 45

50%,

Neuron death.

Question 46

Passive cell death is called ______; active cell death is called ______.

Answer 46

Necrosis,

Apoptosis.

Question 47

Which is safer, apoptosis or necrosis?

Answer 47

Apoptosis

Question 48

_______ cells break apart and spill their contents into extracellular fluid, and the consequence is potentially harmful inflammation.

Answer 48

Necrotic

Question 49

_______ removes excess neurons in a safe, near, and orderly way.

Answer 49

Apoptosis.

Question 50

Several life-preserving chemicals that are supplied to developing neurons by their targets have been identified. The most prominent class of these chemicals is the _______. _______ was the first ______ to be isolated.

Answer 50

Neurotrophins,
Nerve growth factor (NGF),
Neurotrophin.