Download Option A A1 Neural Development

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Transcript
Option A: Neurobiology &
Behavior
A1: NEURAL DEVELOPMENT
USE THE INFO IN THE PRESENTATION TO COMPLETE A1 NOTES
GUIDE
INFORMATION TAKEN FROM:
HL BIOLOGY 2 ND EDITION DAMON, MCGONEGAL , TOSTO, AND
WARD
BIOLOGY FOR THE IB DIPLOMA PREPARATION GUIDE WALPOLE
Essential Idea: Modification of neurons starts in the earliest stages of
embryogenesis and continues to the final years of life
The study of neurogenesis in the embryonic brain has shown that
neurons are producing and responding to chemical messages.
Immature nerve cells migrate to their final locations and the brain
matures as millions of connections are formed. These connections
are reinforced by experience and remain as learning and memory.
How does the neural tube develop in an embryo?
• Embryonic chordates
Nerve cord is made along the dorsal side early in development
• In humans this happens in the 1st month in utero
•
Embryogenesis: the study of embryonic development
• Allows scientists to learn key principles of neural development using the frog as a
model of chordate development
•
•
3 distinct tissue layers develop after fertilization
• Ectoderm – outer most layer becomes the brain & spinal cord
• Endoderm – inner layer forms the lining of the gut & other organs
• Mesoderm – middle layer develops into the other systems of the body
Embryonic Tissues of Xenopus (a frog species)
You should be able to draw and
label this diagram.
You should be able to annotate the
diagram by stating the fate of each part
as it develops into the adult frog.
How are neurons produced from the neural tube?
• Cells of the neural plate form the neural tube
• Some of these cells will differentiate and become neurons, some become
glial cells (cells that do not carry messages, but provide supporting
functions to the neurons)
• Neurons continue to develop in the brain and spinal cord
• Majority of neuronal cell division stops before birth
•
Majority of new neurons are formed between the 5th week and 5th month of
development in a human
• Neuroblasts: immature neurons that are precursor cells
• Neurogenesis: the process of differentiation from neuroblasts to neurons
Neural Tube Development
1. Ectoderm cells on the dorsal surface form the neural plate region
2. This region folds inward to form a groove
3. The neural groove becomes a neural tube, growing longer as the
embryo develops
4. The neural tubes becomes separate from the rest of the embryo
The notochord develops from the mesoderm
Neural Tube Development
What if the neural tube doesn’t close?
• Incomplete closure of the embryonic neural tube can cause spinal
bifida.
How do immature neurons reach their final
destination?
• Neural migration
•
Glial cells provide a scaffolding network along which immature neurons
migrate
Cytoplasm and organelles move to one side of the cell & the whole cell
follows in that direction
During development neurons move from one side of the brain to the other
Mature neurons do not migrate
•
Axons extend from the cell body in response to chemical stimuli (CAMS)
•
•
•
•
•
•
This determines the length and direction of the axon growth
Some axon are very short, some are very long
Only one axon per cell, but they can be branched
Migration along glial cells
Neuronal Migration and CAMs
Cell Adhesion Molecules
How do synapses develop and what happens to those
not used?
• As axons and dendrites grow from developing neurons that start
making connections with other neurons
•
Motor neurons also create synapses with muscle cells
*Synapses that are not used, disappear. Synaptic transmission causes a
synapse to become stronger and be retained.
When an infant is 2 or 3 years old, they have 15000 synapses per neuron,
twice as many as in an adult brain.
What is the consequence of plasticity?
• Neural Plasticity is the ability of the nervous system to change as a
person has new experiences.
• Unused neurons are pruned (removed) and allows the nervous system to
rewire itself.
• New experiences cause new connections to form and old ones to be lost.
• Plasticity is important for neural repair.
Functional plasticity – ability of the brain to move functions from a
damaged area to an undamaged area
Structural plasticity – ability of the brain to actually change its physical
structure as a result of learning
Stroke
• Following a stroke, both functional and structural plasticity can be
observed.
• Using primate models, we have learned improvement can be made
with intervention. After a stroke resulting in weak hand
movements, monkeys that did exercises to move the hand
recovered more rapidly than those that did not exercise. The part
of the brain that improved shoulder movement took over the
movement of the hand. The brain reorganized itself in the monkeys
that received the exercise therapy.
Check your understanding
1. Describe spina bifida.
2. Outline the differentiation and migration of immature neurons
3. Explain neural pruning
4. Compare structural and functional plasticity