PSYCHOLOGY the
DOC. KEVIN MOISES MW(3:30-4:30PM)
Brain Development
Maturation of the Vertebrate Brain
The human CNS begins to form when the embryo is about 2 weeks old
The dorsal surface thickens, long thin lips rise, curl and merge forming a neural tube that surrounds a fluid
filled cavity
As the tube sinks under the surface, the forward end enlarges to form the hindbrain, midbrain and
forebrain. The rest becomes the spinal cord
At birth, the brain usually weighs 350g, by age 1yo it weighs 1000g close to the adult brain weight of
1200-1400 grams
Growth and Development of Neurons
Proliferation - refers to the production of new cells
Early in development, the cells lining the ventricles of the brain divide. Some cells remain as they are (stem
cells), continuining to divide.
The others become primitive neurons and glia migrating to different locations
Migration - after cells have differentiated as neurons or glia, they move.
Some neurons move radially from the inside of the brain to outside, some move tangentially along the
surface of the brain.
Differentiation - a process wherein a neuron grows its axons and dendrites
The axon grows first as it migrates to its desired location. After the migrating neuron reaches its destination,
dendrites begin to form.
Myelination - the process by which glia produces the insulating fatty sheaths that accelarate transmission
of many vertebrate axons
Synaptogenesis - the final stage is the formation of the synapses
This process begins before birth and continues throughout life, as neurons form new synapses and discard
old ones
New Neurons Later in life
The traditional belief is that vertebrate brains formed all their neurons in embryological development or
early infancy. Neurons could modify their shape, but the brain could not develop new neurons.
More recent research found that new neurons form in adults, at the olfactory receptors, neurons in the
hippocampus
Evidently, the human brain forms few or no new neurons in the cerebral cortex after birth
, Determinants of Axon Survival
Initially the sympathetic nervous system forms far more neurons than it needs. When one of its neurons
forms a synapse on to a muscle, that muscle delivers a protein called nerve growth factor (NGF) that
promotes survival and growth of its axon.
An axon that does not receive NGF degenerates, and its cell body dies
If its axon does not make contact with an appropriate post synaptic cell by a certain age, the neuron kills
itself through a process called apoptosis
In addition to NGF, the nervous system responds to BDNF (brain-derived neurotrophic factor) and several
other neurotrophins
When neurons release neurotransmitters, they also release neurotrophins
Experience and Dendritic Branching
Because of the unpredictability of life, our brains have evolved the ability to remodel themselves (within
limits) in response to experiences.
Axons and dendrites continue to modify their structure throughout life.
The gain or loss of spine means a turnover of synapses, which probably relates to learning.
About 6% of dendritic spines appear / disappear within a month (Xu, Pan, Young, Gan, 2007)
As animals grow older, they continue altering the anatomy of their neurons at a slower pace.
Laboratory animal studies suggest:
A rat in a more stimulating environment developed a thicker cortex, more dendritic branching and
improved learning.
The advice to exercise for your brain's sake is particularly important for older people
On the average, the thickness of the cerebral cortex declines with advancing age, beginning age 30 and
accelerating in later years
Neurons become less active partly because of decreased blood flow.
Brain volume and activity decline somewhat less in people who remain mentally active (Schooler, 2007) and
much less in people who remain physically active (Colcombe, et.al, 2003)
Neuroplasticity
Can neurons be repaired? For decades, we thought not
Now, as we begin to understand neuroplasticity, hope grows
The promise and controversy of stem cells
Plasticity of the nervous system
fundamental for learning and relearning - rehabilitation interventions
evolving in parallel with basic and clinical neuroscience
Plasticity – the ability to be moulded /shaped (from Greek ”plastos” )
Almost all survivors of brain damage show partial behavioral recovery and in some cases, it is substantial.
Some of the mechanisms rely on the growth of new branches of axons and dendrites.
Understanding the process may lead to better therapies for people with brain damage and to insights into the
functioning of a healthy brain.
Neuroplasticity - an umbrella term describing lasting change to the brain throughout the person's life
DOC. KEVIN MOISES MW(3:30-4:30PM)
Brain Development
Maturation of the Vertebrate Brain
The human CNS begins to form when the embryo is about 2 weeks old
The dorsal surface thickens, long thin lips rise, curl and merge forming a neural tube that surrounds a fluid
filled cavity
As the tube sinks under the surface, the forward end enlarges to form the hindbrain, midbrain and
forebrain. The rest becomes the spinal cord
At birth, the brain usually weighs 350g, by age 1yo it weighs 1000g close to the adult brain weight of
1200-1400 grams
Growth and Development of Neurons
Proliferation - refers to the production of new cells
Early in development, the cells lining the ventricles of the brain divide. Some cells remain as they are (stem
cells), continuining to divide.
The others become primitive neurons and glia migrating to different locations
Migration - after cells have differentiated as neurons or glia, they move.
Some neurons move radially from the inside of the brain to outside, some move tangentially along the
surface of the brain.
Differentiation - a process wherein a neuron grows its axons and dendrites
The axon grows first as it migrates to its desired location. After the migrating neuron reaches its destination,
dendrites begin to form.
Myelination - the process by which glia produces the insulating fatty sheaths that accelarate transmission
of many vertebrate axons
Synaptogenesis - the final stage is the formation of the synapses
This process begins before birth and continues throughout life, as neurons form new synapses and discard
old ones
New Neurons Later in life
The traditional belief is that vertebrate brains formed all their neurons in embryological development or
early infancy. Neurons could modify their shape, but the brain could not develop new neurons.
More recent research found that new neurons form in adults, at the olfactory receptors, neurons in the
hippocampus
Evidently, the human brain forms few or no new neurons in the cerebral cortex after birth
, Determinants of Axon Survival
Initially the sympathetic nervous system forms far more neurons than it needs. When one of its neurons
forms a synapse on to a muscle, that muscle delivers a protein called nerve growth factor (NGF) that
promotes survival and growth of its axon.
An axon that does not receive NGF degenerates, and its cell body dies
If its axon does not make contact with an appropriate post synaptic cell by a certain age, the neuron kills
itself through a process called apoptosis
In addition to NGF, the nervous system responds to BDNF (brain-derived neurotrophic factor) and several
other neurotrophins
When neurons release neurotransmitters, they also release neurotrophins
Experience and Dendritic Branching
Because of the unpredictability of life, our brains have evolved the ability to remodel themselves (within
limits) in response to experiences.
Axons and dendrites continue to modify their structure throughout life.
The gain or loss of spine means a turnover of synapses, which probably relates to learning.
About 6% of dendritic spines appear / disappear within a month (Xu, Pan, Young, Gan, 2007)
As animals grow older, they continue altering the anatomy of their neurons at a slower pace.
Laboratory animal studies suggest:
A rat in a more stimulating environment developed a thicker cortex, more dendritic branching and
improved learning.
The advice to exercise for your brain's sake is particularly important for older people
On the average, the thickness of the cerebral cortex declines with advancing age, beginning age 30 and
accelerating in later years
Neurons become less active partly because of decreased blood flow.
Brain volume and activity decline somewhat less in people who remain mentally active (Schooler, 2007) and
much less in people who remain physically active (Colcombe, et.al, 2003)
Neuroplasticity
Can neurons be repaired? For decades, we thought not
Now, as we begin to understand neuroplasticity, hope grows
The promise and controversy of stem cells
Plasticity of the nervous system
fundamental for learning and relearning - rehabilitation interventions
evolving in parallel with basic and clinical neuroscience
Plasticity – the ability to be moulded /shaped (from Greek ”plastos” )
Almost all survivors of brain damage show partial behavioral recovery and in some cases, it is substantial.
Some of the mechanisms rely on the growth of new branches of axons and dendrites.
Understanding the process may lead to better therapies for people with brain damage and to insights into the
functioning of a healthy brain.
Neuroplasticity - an umbrella term describing lasting change to the brain throughout the person's life
