Chapter 7- Life span development of the brain and behavior

Question 1

After birth, during what period does the brain grow dramatically?

Answer 1

The brain dramatically grows from birth to 5 years old- results in kids being able to do many different things by the time they’re 5

Question 2

The organization of the nervous system is the result of (3)

Answer 2

1. Genes- instruction manual leading to the different characteristics of our brains
2. Environment and experience- experience can influence gene expression. Example- a famine could result in someone being shorter even if their genes code for them being tall.
3. Interaction of two

Question 3

3 cells layers of an emerging embryo

Answer 3

1. Ectoderm
2. Mesoderm
3. Endoderm

Question 4

Neurulation

Answer 4

The process of the ectoderm forming the neural plate, which will eventually develop into the nervous system. The ectoderm is also responsible for forming the skin

Question 5

Mesoderm function

Answer 5

Forms the skeleton and muscles

Question 6

Endoderm function

Answer 6

Forms the internal organs

Question 7

Neural groove

Answer 7

The neural plate is formed by the ectoderm as it flattens, and the midline of the neural plate is called the neural groove. The uneven rates of cell division in the neural plate causes the formation of the neural groove. The ridges of the neural groove join together to form the neural tube, which will develop into the brain and spinal cord. Cells lining the neural tube will be progenitors for entire CNS.

Question 8

Neural crest

Answer 8

Cells that were pinched off the side of the neural tube, forms the peripheral nervous system. Neural crest cells are progenitors for entire PNS.

Question 9

What structures will the neural tube form?

Answer 9

On day 22, the head end of the neural tube begins to divide into the forebrain, midbrain, and hindbrain. The interior of the neural tube will become the cerebral ventricles, the central canal of the spinal cord, and the passages that connect them. This is a rapid period of development for the brain- by this time the head is half the total size of the embryo.

Question 10

Brain plate

Answer 10

The cranial end of the neural tube forks out to form the brain plate, which is the rudimentary beginning of the brain. This is the result of neurogenesis.

Question 11

Forebrain (forms 3 regions)

Answer 11

Regions that form the hippocampus, hypothalamus, basal ganglia

Question 12

Midbrain

Answer 12

Forms the substantia nigra

Question 13

Hindbrain (forms 3 structures)

Answer 13

Forms the brainstem structures- pons, medulla, cerebellum

Question 14

First trimester nervous system development

Answer 14

Most of the macro structures of the brain develop during the first trimester- this is when the brain is most at risk of complications from certain environmental factors

Question 15

The telencephalon forms the (3)

Answer 15

Cerebral cortex, limbic system, and basal ganglia

Question 16

The diencephalon forms the (2)

Answer 16

Thalamus and hypothalamus

Question 17

Second and third trimester nervous system development

Answer 17

The brain gets a lot bigger during this time and looks more like an adult brain (has all regions and gyri and sulci). The different structures of the brain continue to develop, since they are underdeveloped after the first trimester even though they’ve been formed.

Question 18

6 stages of neural development

Answer 18

1. Neurogenesis
2. Cell migration
3. Differentiation
4. Synaptogenesis
5. Neuronal cell death
6. Synapse rearrangement

Question 19

Which stages of neural development can happen in glia as well?

Answer 19

The first 3- neurogenesis, cell migration, and differentiation

Question 20

Embryo

Answer 20

Considered an embryo for the first 10 weeks after fertilization, then called a fetus afterward. At 18 days, the embryo begins to implant in the uterine wall and consists of the 3 layers of cells.

Question 21

Genotype

Answer 21

The sum of all genetic information an individual has inherited is called their genotype- it is determined at fertilization and does not change.

Question 22

Phenotype

Answer 22

A phenotype is the sum of all physical characteristics that make up an individual- the phenotype changes constantly, and even changes in a small way every second. Individuals who have identical genotypes do not have identical phenotypes, since they won’t have identical experiences. Their nervous system phenotypes will be somewhat different, so they won’t behave exactly the same in the future.

Question 23

What signals do cells in the nervous system rely on for development?

Answer 23

No matter what genes you inherit, whether and when cells usually use those genes during neural development is controlled by environmental influences, including experience. A cell is said to express a gene when it actually transcribes the gene and starts making the protein it encodes.

Question 24

Cell differentiation definition

Answer 24

Cell differentiation is the process by which a given cell expresses a particular subset of genes and becomes a very specific type of cell. This is the transformation of precursor cells into neurons and glia.

Question 25

Where do neurons and glial cells originate?

Answer 25

The cells that give rise to neurons begin as a single layer of cells along the inner surface of the neural tube, and they divide through mitosis. They eventually form a closely packed layer of cells called the ventricular zone. Neurons and glial cells are derived from cells that originate from this ventricular mitosis- cells will leave the ventricular zone and begin transforming into either neurons or glial cells. We can predict at roughly which day of embryonic development that the precursor cells of each group of neurons will stop dividing.

Question 26

When will most neurons form?

Answer 26

Most neurons generated before birth, some during childhood

Question 27

Why does the weight of the brain increase after birth? (5)

Answer 27

After birth, the weight of the brain increases due to growth in the size of neurons, branching of dendrites, elaboration of synapses, increase in myelin, and addition of glial cells.

Question 28

Precursor/progenitor cells

Answer 28

Cells that divide symmetrically to expand the ventricular zone- located in the lining of the central canal. Neurons and glial cells will be derived from this mitosis.

Question 29

Asymmetric division during neurogenesis

Answer 29

Precursor/progenitor cells will no longer sit in the lining of the central canal and will begin to migrate outwards. Cell division switches to asymmetric division- one daughter cell migrates out radially, while the other continues to divide. It will migrate to the marginal zone, which will become the brain tissue.

Question 30

Cell migration definition

Answer 30

Cell migration is when nerve cells move away from the ventricular layer after mitotic division. In primates, almost all future neurons have completed their migration by the time of birth. What brain region a cell ends up in is dictated by where (and when) it was born in the ventricular zone. At this point, the cells are not neurons yet.

Question 31

Which cells act as guides during cell migration?

Answer 31

Radial glial cells act as guides. These cells connect the ventricular zone with a particular spot in the marginal zone- they form “train tracks” from the neural tube to the edge of the brain. Cells pull themselves along to form the different parts of the brain

Question 32

Cell adhesion molecules definition

Answer 32

Molecules that guide migrating cells and growing axons- these molecules are laid down by cells along the path, which is an example of cell-cell interaction guiding neural development.

Question 33

How are the layers of the cerebral cortex formed during migration?

Answer 33

The cells of the cerebral cortex arrive in waves during fetal development, and each successive wave forms a new outer layer, forming the six layers of the adult cortex. As neurons migrate, they push past previous neurons to populate the outermost part of the cortical plate- the layers are formed in an inside out manner. Layer 6 is the innermost layer and is formed first, then cells push through layer 6 to form layer 5, and the layers are build outward

Question 34

When does cellular differentiation occur?

Answer 34

Once cells reach their destination, they begin to express particular genes. The cells transcribe a certain set of genes to make the specific proteins it needs. This process of cell differentiation reflects the genes that are expressed by shaping the cell into the specific form and function of the neurons found in that particular brain region. They take on a specific final morphology (glia, neurons, and particular subtypes of each)

Question 35

What controls what a cell will differentiate into? (2)

Answer 35

1. Intrinsic factors- internal genetic/molecular signals
2. Extrinsic factors- molecular/chemical influences around cell- differentiation appears to be strongly influenced by the local environment.

Question 36

Sonic hedgehog

Answer 36

The notochord releases sonic hedgehog into ventral developing spinal cord, producing motor neurons. The cells it signals to will become motor neurons- if you don’t have it, the neuron becomes a sensory neuron. This is an example of an extrinsic factor.

Question 37

Extrinsic factors

Answer 37

Molecular and chemical signals around the cell. Give specificity- tell neurons whether they will become motor neurons, sensory neurons, neuron that makes serotonin, and so on.

Question 38

When do most synapses form?

Answer 38

Most synapses form after birth. Within a few months, babies learn how to do things very quickly- can sit up, grab things, etc.- learning is encoded in the formation of synapses. An explosion of synapses occurs and it continues to adolescence

Question 39

Growth cones

Answer 39

At the tips of axons and dendrites, there are specialized swellings called growth cones. Growth cones have fine extensions called filopodia, which adhere to CAMs laid down by other cells, and then contract to pull the growth cone in a particular direction. The axon or dendrite attached to the growth cone will follow. They mediate the changes in dendrites that occur with experience.

Question 40

Where are CAMs released?

Answer 40

The CAMs that guide growth cones are released by the target nerve cells or other tissues, like muscles. The axon growth cone responds to the concentration gradients of these chemicals that provide directional guidance.

Question 41

Types of CAMs

Answer 41

CAMs that attract certain growth cones are called chemoattractants, while chemicals that repel growth cones are chemorepellents. The same secreted protein may act as a chemoattractant to some growth cones and a chemorepellent to others- some axons must remain on one side of the body, while others must cross over.

Question 42

Why is cell death important for development?

Answer 42

Cell death (apoptosis) is like a sculpting process for emerging tissues. Most young neurons actually die during prenatal development, which is necessary to prevent the brain from becoming too large for the skull. The cells are essentially committing suicide, rather than dying due to a defect.

Question 43

How does apoptosis occur?

Answer 43

The chromosomes carry death genes, which are only expressed when a cell undergoes apoptosis. For example, caspases are a family of proteases that will cut up proteins and nuclear DNA. Apoptosis begins with a sudden influx of calcium ions that cause the mitochondria to release a protein called Diablo.

Question 44

Diablo function

Answer 44

Diablo binds to a family of proteins called inhibitors of apoptosis proteins (IAPs), which normally inhibit the caspases. Once the IAPs are bound, the caspases are free to dismantle the cell.

Question 45

BcI-2

Answer 45

A protein that blocks apoptosis by preventing Diablo release from the mitochondria, creating a system of checks and balances.

Question 46

Two structures that should be connected share

Answer 46

A common chemical substrate that lays down the pathway between them- neurotrophic factors

Question 47

What do neurons need to survive? (2)

Answer 47

1. Adequate synapses- reducing synaptic targets will result in cell death
2. Neurotrophic factors

Question 48

Neurotrophic factors

Answer 48

Chemicals released by the target structure in a synapse- they “feed” neurons to help them survive. Without neurotrophic factors, cell death will occur

Question 49

Why is selective elimination of synapses necessary?

Answer 49

Initial synaptogenesis overproduces synapses. Selective elimination is pruning of the extra, unnecessary synapses. For example, babies refine the set of sounds they make based on the language of their primary caregivers

Question 50

Why is the formation of new synapses necessary?

Answer 50

Formation of new synapses continues for life. New synapses are how we learn and remember

Question 51

How is the formation/elimination of synapses regulated?

Answer 51

Regulated by neuronal activity (action potentials). Synapses receiving less action potentials might be eliminated since they aren’t used as much

Question 52

Until what age does the brain continue to mature?

Answer 52

Into our 20s

Question 53

How does the brain change as it matures?

Answer 53

Gradual drop in gray matter cells- this includes the number of synapses as they are refined. Myelination (white matter) increases, especially in the prefrontal cortex.

Question 54

How does myelination in the prefrontal cortex influence behavior?

Answer 54

The prefrontal cortex is responsible for decision making and impulse control. Children have a small connection between the prefrontal cortex and the brain- this is why children have trouble controlling their emotions. During adolescence, the connection gets stronger and improves into adulthood

Question 55

Growth cones

Answer 55

Specialized part of the neuron that develops into the dendritic spine and the axon terminal