Chapter 4: Brain Development, Damage & Neuroplasticity Flashcards
what factors does brain development depend on
- Maturation
- learning
the human nervous system starts developing during
it forms when the embryo is approximately 2 weeks old
the dorsal surface thickness and different parts like the midbrain, forebrain, and hindbrain start forming
Cerebrospinal fluid
It is a fluid that exists in the central canal of the spinal fluid and the ventricles of the brain provide nourishment and removes waste
Brain weight
just born: 350g
1 year: 1000g
adult human brain weight: 1200 to 1400g
process of the development of neurons
- proliferation
- migration
- differentiation
- myelination
- synaptogenesis
Proliferation: development of neurons
is the production of new cells\ neurons in the brain in the early stages of life
after the production, some cells become stem cells that continue to divide and others remain where they are or become neurons or glia that migrate to other locations.
Migration: development of neurons
the movement of newly formed neurons and glia to their eventual location some don’t reach their location until adulthood chemicals like immunoglobulin and chemokines guide neuron migration
Differentiation: development of neurons
is the forming of axons and dendrites that give the neuron its distinctive shape the axon forms during the migration or when it reaches its destination and it is followed by the development of dendrites
Myelination: development of neurons
the process where glia produce the fatty sheet that covers the axons of some neurons
myeline protects the neuron and speeds up the transmission of impulses myelination first occurs in the spinal cord and then the hindbrain and then the midbrain and then the forebrain it occurs gradually
Synaptogenesis: development of the neuron
The final stage of neural development –
the formation of the synapses between
neurons
– Occurs throughout life as neurons are
constantly forming new connections and
discarding old ones
– Slows significantly later in the lifetime
what is life span of new neurons
it was believed in the past that no new neurons were formed after the early stages but later research showed otherwise
Stem cells
Stem cells: undifferentiated cells found in the interior of the brain that generates “daughter cells” that can transform into glia or neurons
how often do olfactory receptors replace dying ones
New olfactory receptors also continually replace dying ones
where does the development of neurons occur in brain regions
Development of new neurons also occurs in other brain regions
Example: songbirds have a steady replacement of new neurons in the singing area of the brain
* Stem cells differentiate into new neurons in the adult hippocampus of mammals and facilitate learning
Life Span of Neurons: skin cells
Different cells have a different average life
spans
* Skin cells are the newest; most are under
a year old
Life Span of Neurons: Heart cells
- Heart cells, on the other hand, tend to be
as old as the person
Life Span of Neurons: mammalian cerebral cortex
- Mammalian cerebral cortexes form few or
no new neurons after birth
What is Pathfinding by Axons
Axons must travel great distances across
the brain to form the correct connections
it is the process by which neurons send out axons to reach their correct targets.
How do axons get to their targeted area
to reach their correct targets. Axons often follow very precise paths in the nervous system following the chemical trail to reach their appropriate target.
Growing axons reach their target area by
following a gradient of chemicals in which
they are attracted by some chemicals and
repelled by others
Competition among axons as a general principle
When axons initially reach their targets, they form synapses with several cells
* Postsynaptic cells strengthen the connection with some cells and eliminate connections with others
The formation or elimination of these connections depend on the pattern of input from incoming axons
Neural Darwinism
Some theorists refer to the idea of the selection process of neural connections as neural Darwinism
synaptic connections competition
In this competition among synaptic connections, we initially form more connections than we need
The most successful axon connections and combinations survive while the others fail to sustain active synapses
Determinants of Neuronal Survival
chemicals called neurotrophins such as NGF are responsible for the survival of the neurons
Nerve growth factor (NGF) is a type of protein released by muscles that promote the survival and growth of axons
Neurotrophins
Chemicals that promote the survival and
activity of neurons (i.e., NGF)
Axons that are not exposed to neurotrophins
after making connections undergo apoptosis –
a preprogrammed mechanism of cell death
– Therefore, the healthy adult nervous system
contains no neurons that failed to make
appropriate connection
What happens if axons are not exposed to neuro tropins
Axons that are not exposed to neurotrophins after making connections undergo apoptosis –a preprogrammed mechanism of cell death
Therefore, the healthy adult nervous system contains no neurons that failed to make the appropriate connection
apoptosis
Apoptosis is a form of programmed cell death that occurs in multicellular organisms.
Neuronal Death and its benefits
The elimination of massive cell death is part of normal development and maturation
After maturity, the apoptotic mechanisms become dormant
describe how is brain vulnerable during the early stages of development
The early stages of brain development are critical for normal development later in life
A mutation in one gene can lead to many defects
Chemical distortions in the brain during early development can cause significant impairment and developmental problems
what is Fetal Alcohol Syndrome
A condition that children are born with if the mother drinks heavily during pregnancy
and it causes to the child do the following
what are the effects of fetal Alcohol Syndrome on children
it causes to the child do the following
Hyperactivity and impulsiveness
– Difficulty maintaining attention
– Varying degrees of mental retardation
– Motor problems and heart defects
– Facial abnormalities
How are the neurons of children who are born with fetal alcohol syndrome different?
The dendrites of children born with fetal alcohol syndrome are short with few branches
* Exposure to alcohol in the fetus brain
suppresses glutamate and enhances the
release of GABA
* Many neurons consequently receive less
excitation and exposure to neurotrophins
than usual and undergo apoptosis
How are the neurons of children who are born with fetal alcohol syndrome different?
The dendrites of children born with fetal alcohol syndrome are short with few branches
* Exposure to alcohol in the fetus brain
suppresses glutamate and enhances the
release of GABA
* Many neurons consequently receive less
excitation and exposure to neurotrophins
than usual and undergo apoptosis
explain how fetal alcohol syndrome affects neurons: the process
Exposure to alcohol in the fetus’s brain suppresses glutamate and enhances the release of GABA
Many neurons consequently receive less excitation and exposure to neurotrophins than usual and undergo apoptosis
explain how neurons differ according to their location
Neurons in different parts of the brain differ from one another in their shape and chemical components
– Immature neurons transplanted to a
developing part of the cortex develop the
properties of the new location
– Neurons transplanted at a later stage of
development develop some new properties
but retain some old properties
* Example: ferret experimen
what happens if the immature neuron is transplanter in a new location: early stages
Immature neurons transplanted to a developing part of the cortex develop the properties of the new location
what happens if the neuron is transplanter in a new location: later stages
Neurons transplanted at a later stage of development develop some new properties but retain some old properties
Example: ferret experiment
Brain Adaptations> deaf people
People who are deaf from an early age become more responsive to touch and vision.
Touch and vision come to activate what would be the auditory cortex in deaf people
Effects of Special Experiences> blind people how their brains adapt
Blind people improve their attention to touch and sound, based on practice
Touch information activated this occipital cortex area, which is ordinarily devoted to vision alone
- The occipital lobe is normally dedicated to processing visual information and adapts to also, process tactile and verbal information
differences between the brains of musicians and non-musician
MRI studies reveal the following: The temporal lobe of professional musicians in the right hemisphere is 30% larger than
non-musicians
Thicker gray matter in the part of the brain responsible for hand control and vision of professional keyboard players
Results suggest that practicing a skill reorganizes the brain to maximize the performance of that skill
adulthood experiences affect on the brain
Adult experiences can also modify the brain anatomy however research is needed to determine if the changes can be observed by fMRI
what happens when Brain Reorganization Goes Too Far?
The fingers of musicians who practice extensively become clumsy, fatigue easily, and make involuntary movements
This condition is a result of the extensive reorganization of the sensory thalamus and cortex so that touch responses to one finger overlap those of another
Brain Development and Behavioral Development> adolescents
Adolescents tend to be more impulsive than adults
Adolescents are not equally impulsive in
all situations
The prefrontal cortex of adolescents is
relatively inactive in certain situations, but
this may or may not be the cause of
impulsivity
When do people claim that adolescents make risky decisions because of a lack of inhibition, which brain area do they point to as being responsible for inhibition?
The prefrontal cortex of adolescents is relatively inactive in certain situations, but this may or may not be the cause of impulsivity
how being older compensates for neural loss?
Some neurons lose their synapses, and the remaining synapses change more slowly than before in response to experiences Brain structures begin to lose volume
Older people have a greater base of knowledge and experience, and many find ways to compensate for losses
Plasticity
The brain’s special capacity for change
Plasticity after Brain Damage
Almost all survivors of brain damage show behavioral recovery to some degree Some recovery relies on the growth of new
branches of axons and dendrites.
Functional plasticity refers to the brain’s ability to heal itself after injury. To achieve this, healthy regions of the brain adapt to take over certain functions that the damaged parts of the brain used to perform.
how does recovery take place after brain damage
Some of the mechanisms of recovery include those similar to the mechanisms of brain development such as the new branching of axons and dendrites
Possible causes of brain damage
Tumors
– Infections
– Exposure to toxic substances or radiation
– Degenerative diseases
– Closed head injuries
what is a closed head injury
refers to a sharp blow to the head that does not puncture the
brain
what is a stroke or cerebrovascular accident
is a temporary loss of blood flow to the brain
A common cause of brain damage in elderly
what is a common cause of brain dame in elderly and young adults?
A common cause of brain damage in the elderly is a stroke
closed head injury is the main cause of brain damage in young adults
Types of Strokes
Ischemia
Hemorrhage
apoptosis
a preprogrammed mechanism of cell death
what happens if the brain of a fetus was exposed to an alcohol
Exposure to alcohol in the fetus’s brain suppresses glutamate and enhances the release of GABA
Many neurons consequently receive less excitation and exposure to neurotrophins than usual and undergo apoptosis
Effects of Ischemia and hemorrhage strokes
they cause Edema: the accumulation of fluid in the brain resulting in increased pressure on the brain and increasing the probability of further strokes
Disruption of the sodium-potassium pump leading to the accumulation of sodium ions inside neurons
Effects of Ischemia and hemorrhage strokes 2
- The overstimulation of neurons leads to
sodium and other ions entering the neuron
in excessive amounts - Excess positive ions in the neuron block
metabolism in the mitochondria and kill the
neuro
Treatments of stroke
A drug called tissue plasminogen activator (tPA) breaks up blood clots and can reduce the effects of ischemic strokes
Research has begun to attempt to save neurons from death by blocking:
– Glutamate synapses
– Calcium entry
Also cooling the brain helps with after-ischemia it prevents the brain from overstimulation apoptosis and inflammation
and the Cannabinoids have been shown to minimize cell loss after brain stroke.
Later Mechanisms of Recovery from Brain Damage
after a brain damage is survived areas reorganize or increase their activity
as well as stimulate drugs are used to stimulate activity in
healthy regions of the brain after a stroke
Diaschisis
decreased activity of surviving neurons after damage to other neurons
Because activity in one area stimulates other areas, damage to the brain disrupts patterns of normal stimulation
regeneration of cell bodies after they die: how does that happen
Destroyed cell bodies cannot be replaced, but damaged axons do grow back under certain circumstances
If an axon in the peripheral nervous system is crushed, it follows its myelin sheath back to the target and grows back toward the
periphery at a rate of about 1 mm per day
Regrowth of Axons: what is the process
Damaged axons do not readily regenerate in a mature mammalian brain or spinal cord
– Scar tissue makes a mechanical barrier to
axon growth
– Neurons on the two sides of the cut pull apart
– Glia cells that react to CNS damage release
chemicals that inhibit axon growth
Axon Sprouting
Collateral sprouts are new branches formed by other non-damaged axons that attach to vacant receptors
- Cells that have lost their source of innervation releases neurotrophins that induce axons to form collateral sprouts
- Over several months, the sprouts fill in most vacated synapses and can be useful, neutral, or harmful
What is a phantom limb
the continuation of the sensation of an amputated body part
a phantom limb can lead to the feeling of sensations in the amputated part of the body when other parts of the body are
stimulated
what helps with phantom limb
Use of an artificial limb can reduce the likelihood of experiencing phantom limb
Deafferentated limb
limbs that have lost their afferent sensory input
Can still be used but are often not because
use of other mechanisms to carry out the
behavior is easier
– Has led to the development of therapy techniques to improve the functioning of the brain damaged people
What happens when neurons in the brain die
you can’t regenerate neurons but you can regenerate the growth of axons and dendrites
What is Denervation supersensitivity
is the heightened sensitivity to a transmitter after the destruction of an incoming axon it can result to a chronic pain
What chemicals help the migration process
Immunoglobulins and chemokines
What is the function of myleine sheet?
myleine speeds up the transmission of neural impulses
what is the life span of neurons
what is life span of new neurons
it was believed in the past that no new neurons were formed after the early stages but later research showed otherwise
