OPTION A: NEUROBIOLOGY AND BEHAVIOUR
A.1 Neural Development
• Neurulation: folding process that develops the neural plate into
the neural tube, occurring in the first month of human life
o Cells located in the ectoderm (outer layer) differentiate to Ectoderm
form a neural plate
o The neural plate then folds inwards forming a neural
groove (initiated by signals from the notochord)
o The lateral edges join to form a tube-like structure
o The neural tube fuses together & elongates as the embryo
Ectoderm
develops to form the central nervous system (brain &
spinal cord)
▪ Anterior part develops into brain, whilst the rest
thickens to form the spinal cord
o Cells of the neural crest differentiate to form the
peripheral nervous system
• The process of neurulation can be
studied using Xenopus laevis (African
clawed frog) embryos as they are
transparent, robust, develop rapidly
& are fertilised externally
o It is hard to perform
experiments on humans due
to ethical reasons, and
therefore researchers
frequently work with other species even if they are investigating human development
• Spina Bifida: a birth defect caused by incomplete closure of the embryonic neural tube
o It most commonly occurs in the lower back and varies in severity from mild to
debilitating
▪ E.g. spina bifida occulta rarely causes symptoms as splits in vertebrae are so
small that spinal cord does not protrude
o It can cause spinal nerves to protrude, leaving them exposed to damage
o Not having enough folate in the diet during pregnancy is believed to play a significant
role in causing spina bifida
• Neurons are initially produced by differentiation in the neural tube
o Two types of cells develop from the neural tube: neurons and glial cells (provide
physical and nutritional support for neurons)
▪ Differentiation produces many types of functioning neurons (e.g. motor,
sensory, relay)
o Cell proliferation through mitosis continues as the CNS develops into the brain and
spinal cord
o Most neurons survive for the lifetime of the individual and do not proliferate following
embryogenesis
▪ Certain brain regions may be capable of adult neurogenesis, but most of the
nervous system is incapable of regeneration
, • Some immature neurons migrate from where they are produced to a final location. Migration
occurs via either:
o Glial guidance: Glial cells may provide a scaffolding network along which an immature
neuron can be directed to its final location
o Somal Translocation: neuron may form an extension and then translocate its soma
along this length
• An immature neuron consists of a cell body (soma) containing a nucleus and cytoplasm
o Axons and dendrites grow from each immature neuron in response to chemical signals
from surrounding cells
▪ Chemical stimuli control when & how a neuron differentiates and in what
direction it grows
o Some axons may be quite short (within CNS), compared to axons in the PNS
▪ Axons need to carry impulses to effector cells (e.g. muscle and gland cells),
which extends beyond the neural tube
▪ It is possible for damaged axons to regrow if the cell body remains intact
o When a growing axon reaches its target cell, a synapse develops between the neuron
and the cell
▪ Most neurons will develop multiple synapses with their target cell
• Neural pruning involves the loss of unused neurons (by removing excess axons and eliminating
their synaptic connections)
o As an organism matures some synapses are used more frequently and these connections
are strengthened
o Other synapses which are not used as often weaken and do not persist
o Infants brains generally form many more synaptic connections (haven’t undergone
neural pruning yet)
• Plasticity is the ability of the nervous system to change in structure and function as it develops
with experience
o E.g. you may grow to like food, you did not like when you were younger
• Strokes occur when blood supply to the brain is disrupted (can be due to arterial blood clot or
rupture of blood vessel)
o The high-energy demand of the brain means it needs a constant supply of oxygen and
glucose to respire
o If respiration ceases, neurons begin to be damaged beyond repair and die – with some
strokes being fatal
o The neural connections that have been destroyed cannot always be rebuilt, but the
brain can reorganise itself to restore function (healthy areas may adopt functions of
damaged regions)
▪ Stroke patients sometimes have to relearn key skills (e.g. speech & writing)
o The areas of the brain damaged by strokes cannot rebuild new axons due to scar tissue
▪ However, research into the growth of nerve tissue for spinal cord injury patients
is progressing
A.1 Neural Development
• Neurulation: folding process that develops the neural plate into
the neural tube, occurring in the first month of human life
o Cells located in the ectoderm (outer layer) differentiate to Ectoderm
form a neural plate
o The neural plate then folds inwards forming a neural
groove (initiated by signals from the notochord)
o The lateral edges join to form a tube-like structure
o The neural tube fuses together & elongates as the embryo
Ectoderm
develops to form the central nervous system (brain &
spinal cord)
▪ Anterior part develops into brain, whilst the rest
thickens to form the spinal cord
o Cells of the neural crest differentiate to form the
peripheral nervous system
• The process of neurulation can be
studied using Xenopus laevis (African
clawed frog) embryos as they are
transparent, robust, develop rapidly
& are fertilised externally
o It is hard to perform
experiments on humans due
to ethical reasons, and
therefore researchers
frequently work with other species even if they are investigating human development
• Spina Bifida: a birth defect caused by incomplete closure of the embryonic neural tube
o It most commonly occurs in the lower back and varies in severity from mild to
debilitating
▪ E.g. spina bifida occulta rarely causes symptoms as splits in vertebrae are so
small that spinal cord does not protrude
o It can cause spinal nerves to protrude, leaving them exposed to damage
o Not having enough folate in the diet during pregnancy is believed to play a significant
role in causing spina bifida
• Neurons are initially produced by differentiation in the neural tube
o Two types of cells develop from the neural tube: neurons and glial cells (provide
physical and nutritional support for neurons)
▪ Differentiation produces many types of functioning neurons (e.g. motor,
sensory, relay)
o Cell proliferation through mitosis continues as the CNS develops into the brain and
spinal cord
o Most neurons survive for the lifetime of the individual and do not proliferate following
embryogenesis
▪ Certain brain regions may be capable of adult neurogenesis, but most of the
nervous system is incapable of regeneration
, • Some immature neurons migrate from where they are produced to a final location. Migration
occurs via either:
o Glial guidance: Glial cells may provide a scaffolding network along which an immature
neuron can be directed to its final location
o Somal Translocation: neuron may form an extension and then translocate its soma
along this length
• An immature neuron consists of a cell body (soma) containing a nucleus and cytoplasm
o Axons and dendrites grow from each immature neuron in response to chemical signals
from surrounding cells
▪ Chemical stimuli control when & how a neuron differentiates and in what
direction it grows
o Some axons may be quite short (within CNS), compared to axons in the PNS
▪ Axons need to carry impulses to effector cells (e.g. muscle and gland cells),
which extends beyond the neural tube
▪ It is possible for damaged axons to regrow if the cell body remains intact
o When a growing axon reaches its target cell, a synapse develops between the neuron
and the cell
▪ Most neurons will develop multiple synapses with their target cell
• Neural pruning involves the loss of unused neurons (by removing excess axons and eliminating
their synaptic connections)
o As an organism matures some synapses are used more frequently and these connections
are strengthened
o Other synapses which are not used as often weaken and do not persist
o Infants brains generally form many more synaptic connections (haven’t undergone
neural pruning yet)
• Plasticity is the ability of the nervous system to change in structure and function as it develops
with experience
o E.g. you may grow to like food, you did not like when you were younger
• Strokes occur when blood supply to the brain is disrupted (can be due to arterial blood clot or
rupture of blood vessel)
o The high-energy demand of the brain means it needs a constant supply of oxygen and
glucose to respire
o If respiration ceases, neurons begin to be damaged beyond repair and die – with some
strokes being fatal
o The neural connections that have been destroyed cannot always be rebuilt, but the
brain can reorganise itself to restore function (healthy areas may adopt functions of
damaged regions)
▪ Stroke patients sometimes have to relearn key skills (e.g. speech & writing)
o The areas of the brain damaged by strokes cannot rebuild new axons due to scar tissue
▪ However, research into the growth of nerve tissue for spinal cord injury patients
is progressing
