Week 4 (How does the nervous system develop) Flashcards
How are the development of the brain and behaviour studied?
- Does the emerging brain structure correlate with an emerging behaviour (myelination of the motor cortex and increased complexity in grasping)
- Does the emerging behaviour correlate with changes in the brain structure (increased complexity of language and the thickening of cortical areas)
- Are there factors that influence both brain and behaviour development. (injury)
What are the 3 stages of prenatal development?
- Germinal Stage (Conception - 3 weeks)
- Embryonic Stage (3 weeks - 9 weeks)
- Foetal stage (9 weeks - birth)
What happens in the Germinal stage?
From conception until implantationin the wall of the uterus.
0-2 weeks from conception:zygotetravels down fallopian tube to uterus
Cells multiply rapidly: from 2 cells at 36hours post-fertilisation to 76-90 cells 5days later
Cells differentiate as they multiply…
What happens in the Embryonic stage?
Period of rapid cell division and differentiation, during which embryo takes on recognisably human shape
Three key structures emerge from fertilised egg:
Amniotic sac
Placenta
Umbilical cord
Organism divides into 3 layers:
Ectoderm: hair, teeth, outerskin layer, NS
Mesoderm: inner skin layer,skeleton, muscles….
Endoderm: vital organs,glands, gastrointestinal tract….
What happens in the Foetal stage?
Period of continuous growth formajor structures and systems,culminating in birth
Major feature = brain development (not complete at birth)
How does nervous system develop in the first 3 weeks?
The ectoderm thickens and becomes the neural plate by day 18 of gestation. The sphere of dividing cells flatten and the outer layers thicken lengthways.
The neural plate then folds to form the neural groove, which then closes over to form a fluid-filled cylinder- the neural tube
A defect of the neural tube can be Anencephaly:
-The neural tube fails to completely close over
-Underdeveloped skull and brain : life-limiting condition, 5/10,000 births
How does the nervous system develop from 4 weeks onwards?
By week 4, the main divisions of the CNS are formed.
-forebrian
-midbrain
-hindbrain
-spinal cord
By mid-pregnancy, the cerebral hemispheres have expanded to cover the rest of the brain.
By 6 months, cell proliferation –> infolding –> sulci and gyro on surface of cortex . Lobes can be differentiated.
What is the first stage of nervous system development?
- Cell birth: Neurogenesis
Single layer of cells along inner surface of neural tube –> ventricular zone
All neuron and glial cells come from here
(Non-neuronal cells divide by mitosis to produce neurons)
What is the second stage of nervous system development?
- Cell Migration
-newly formed cells move from the ventricular zone to the correct destination in the nervous system
-Travel along radial glial cells which act as guides
What is the third stage of the nervous system development?
- Cell differentiation
Cells reach their destinations and start to express particular genes
Cell-cell interaction coordinates development – ensures right type of neuron for that part of the brain
What is the fourth stage of the nervous system development?
- Cell Maturation: Dendrite and axon growth
What is the fifth stage of the nervous system development?
- Synaptogenesis: Formation of synapses
(Synapotgensis continues after birth)
What if the sixth stage of the nervous system development?
- Cell death (apoptosis) and cell pruning
‘use it or lose it’: synaptic connections that do not become part of a functional neural network are lost
synaptic pruning/rearrangement and maturity proceed at different rates in different brain areas
What if the seventh stage of the nervous system development?
- Myelination: axons become wrapped in a fatty sheath
speeds the conduction of electrical signals
Some prenatally; rapid shortly after birth; continues into adulthood
What are intrinsic factors
Factors originating within the developing organism, e.g. genes
