9-Development of the Nervous System (copy)

Plastic

changeable

Brain

It is a plastic (changeable),

living organ that continuously changes in response

to its genetic programs and environment.

Zygote

single cell formed by

the amalgamation of an ovum and a sperm.

1. Induction of neural plate

2. Neural proliferation

3. Migration and aggregation

4. Axon growth and synapse formation

5. Neuron death and synapse rearrangement

Phases of neurodevelopment

Totipotent

A fertilized egg is -, that is, the cell has the ability

to develop into any class of cell in the body (e.g., bone,

skin, neuron, or heart cells).

Pluripotent

At this stage, developing cells have the ability to develop

into many, but not all, classes of body cells and are said to be -

Multipotent

As the embryo develops, new cells become more

and more specialized. Eventually, new cells can develop into

different cells of only one class (e.g., different kinds of blood

cells).

Unipotent

Most developing

cells will eventually become -: they can

develop into only one type of cell

Neural plate

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.

Three weeks after conception

How long after conception does the neural plate develop?

Ectoderm, mesoderm, endoderm

Layers of the embryonic cells

Ectoderm

outermost embryonic layer

development of the neural plate

The - is the first major

stage of neurodevelopment in all vertebrates.

mesoderm

The development of the neural plate is induced by

chemical signals from an area of the underlying - layer

mesoderm

an area consequently referred to as an organizer

embryonic stem cells

The cells of the neural plate are often referred to

as -

Stem cells

They have an almost unlimited capacity for

self- renewal if maintained in an appropriate cell culture

Stem cells

they have the ability to develop into many different

kinds of cells—they are either totipotent, pluripotent,

or multipotent

neural groove

Neural plate folds to form the - , which then fuses to form the neural tube

neural tube

the lips of the neural

groove fuse to form the -

neural tube defects

which develop into severe

birth defects of the CNS, can result from errors

in this folding process

cerebral ventricles and spinal canal

The

inside of the neural tube eventually becomes the -

1. forebrain

2. midbrain

3. hindbrain

By 40 days after conception,

three swellings are visible at the anterior end of the human

neural tube:

proliferate

Once the lips of the neural groove have fused to create the

neural tube, the cells of the tube begin to -, or increase greatly in number

neural proliferation

does

not occur simultaneously or equally in all

parts of the tube.

ventricular zone

Most cell division in the

neural tube occurs in the -

1. floor plate

2. roof plate

The complex pattern of proliferation is in

part controlled by chemical signals from two organizer

areas in the neural tube:

Floor plate

which runs along

the midline of the ventral surface of the tube

Roof plate

which runs along the midline!of the dorsal surface of

the tube

Migration

Once cells have been created through cell division

in the ventricular zone of the neural tube, they migrate

to the appropriate target location

Migration

During this period, the cells are still in an immature

form, lacking the processes (i.e., axons and dendrites)

that characterize mature neurons

1. Time

2. Location

Two

major factors govern migration in the developing neural

tube:

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

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

Glia-mediated migration

Once the period of neural proliferation

is under way and the walls of the neural tube

are thickening, a network of glial cells, appears in the developing neural tube.

At this point, many cells engaging in radial

migration do so by moving along the radial

glial network

radial glial cells

thickening, a network of glial cells

Somal translocation

an extension develops that leads migration, cell body follows

Glial-mediated migration

cell moves along a radial glial network

inside-out pattern

Because each wave of cortical cells migrates

through the already formed lower

layers of cortex before reaching its destination,

this radial pattern of cortical development

is referred to as an

Neural crest

A structure dorsal to the neural tube and formed from neural tube cells

Neural crest

develop into the neurons and glial cells

of the peripheral nervous system as well as many other

cell types in the body

Aggregation

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

cell-adhesion molecules (CAMs)

Both migration and aggregation are thought to be

mediated by -, which

are located on the surfaces of neurons and other cells

cell-adhesion molecules (CAMs)

have the ability

to recognize molecules on other cells and adhere to them.

Gap junctions

play a role

in migration and aggregation and other aspects of neurodevelopment

Axon growth

Once neurons have migrated to their appropriate

positions and aggregated into neural structures, axons

and dendrites begin to grow from them.

Growth cone

At each growing tip of an axon or

dendrite is an amoebalike structure called a

-, which

extends and retracts fingerlike cytoplasmic

extensions

Filopodia

fingerlike cytoplasmic

extensions

chemoaffinity hypothesis

each postsynaptic

surface in the nervous system releases a specific chemical

label and that each growing axon is attracted by the label to its postsynaptic target during both neural development

and regeneration

chemoaffinity hypothesis

postsynaptic targets release a chemical that guides axonal growth, but this does not explain the often circuitous routes often observed

Synapse formation

Once axons have reached their

intended sites, they must establish an appropriate pattern

of synapses. A single neuron can grow an axon on

its own, but it takes coordinated activity in at least two

neurons to create a synapse between them

Synaptogenesis

formation of new synapses

Astrocytes

synaptogenesis

depends on the presence of glial cells, particularly -

Pioneer growth cones

– the first to travel a route, interact with guidance molecules

Fasciculation

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

Topographic gradient hypothesis

seeks to explain topographic maps

Neuron death

Neurons die due to failure to compete for chemicals provided by targets

Necrosis

passive cell death

Apoptosis

active cell death

Necrotic cells

break

apart and spill their contents into extracellular fluid, and the

consequence is potentially harmful inflammation

Apoptic cell death

DNA and other internal structures

are cleaved apart and packaged in membranes before the cell

breaks apart. These membranes contain molecules that attract

scavenger microglia and other molecules that prevent inflammation.

Apoptosis

removes excess neurons in a safe, neat,

and orderly way

Neurotrophins

promote growth and survival, guide axons, stimulate synaptogenesis

Nerve growth factor (NGF)

the first neurotrophinto be isolated

Synapse rearrangement

cell death results in

a massive rearrangement of synaptic

connections.

Prefrontal cortex

last part of the human brain to

reach maturity

synaptogenesis

There is

a general increase in - in the human cortex

shortly after birth, but there are differences among the cortical

regions.

Myelination

increases the speed of axonal conduction,

and the - of various areas of the human

brain during development roughly parallels their functional

development

sensory areas

Myelination of - occurs in the first few months

after birth,

motor areas

myelination of the - follows

soon after

Prefrontal cortex

myelination of the -

continues into adulthood

Dendritic branching

In general, the pattern of - in the cortex

duplicates the original pattern of neural migration in

the sense that - progresses from deeper

to more superficial layers.

Prefrontal cortex

displays

the most prolonged period of development

of any brain region

Prefrontal cortex

Its development is believed

to be largely responsible for the course

of human cognitive development, which occurs over the

same period

Prefrontal cortex

plays a role in working memory, planning and carrying out sequences of actions, and inhibiting inappropriate responses

Perseveration

is the tendency to continue making a formerly

correct response when it is currently incorrect.

Permissive experiences

those

that permit the information in genetic programs of brain

development to be expressed and maintained

Permissive experiences

those that are necessary for information in genetic programs to be manifested

Instructive experiences

are those that contribute to the information in

genetic programs and influence the course of development

Critical period

If it is absolutely essential for an experience to occur within a particular

interval to influence development

Sensitive period

If an experience has a great effect on development

when it occurs during a particular interval but can still

have weak effects outside the interval

sensitive periods

the vast majority of experiential effects on development

have been shown to be

Neurogenesis

growth of new neurons

subventricular zone of the lateral ventricles

New olfactory bulb and striatal neurons

are created from adult neural stem cells at certain sites in the

-

dentate gyrus

new hippocampal

cells are created near their final location in the -

of the hippocampus.

interneurons

Adult-generated olfactory

bulb and striatal neurons become -

granule cells

adult-generated hippocampal neurons become -

Pattern separation

refers to our ability to separate distinct percepts

into individual memories for storage

Myelination

increases the speed of axonal conduction.

Perseveration error

Lack of, or incomplete, schema of object performance is

referred to as a

Prefrontal cortex

Various parts of the _____ play various roles, working

memory being one of them.

instructive experiences

Experiences that contribute to the information in genetic

programs are called

Monocular deprivation

An experimental technique used by neuroscientists to

study central nervous system plasticity is called

Axons

Roe and colleagues performed a study involving

surgically altering the _____ of ferrets.

Neurons

Before the nervous system is fully developed, _____

begin to fire and begin to interact with environment

Olfactory bulbs

The output in the _____ goes primarily to the amygdala

and piriform cortex.

Sensory and cortical maps

Experience in adulthood can lead to reorganization of

Tinnitus

ringing in the ears, produces major reorganization of primary auditory cortex

Autism Spectrum Disorder (ASD)

a reduced capacity for social interaction and communication and restricted and repetitive patterns of behavior, interests,

or activities