brain development Flashcards
the adult human brain
- size of the human brain is larger and more complex than other mammals.
- human brain and CNS consist of trillions of highly specialized cells that work in synchrony using chemical signals and electrical signals
brain stats
- human brain makes up 2/3 of the neurnal mass of the body and contains 3/4 of all our synapses
- enteric ns (gut) consists of sheaths of neurones embedded in the walls of the gut. contains 100 million neuorns
- brain outsources the digestion process to this nervous system
- 90% of fibers in the vagues nerve carry information the gut to the brain.
- ENS uses more than 20 neurotransmitters
- 95% of body’s serotonin is found in our bowels.
brain growth
- between the 7th prenatal month and the 1st birthday the brain increases in weight by 1.7 grams a day
- ‘brain growth spurt’ = lasts 3 months prenatally and first 2 years after birth.
Neurulation and neurogenesis
the brain starts to develop in weeks 2 and three , with the folding and fusion of the ectoderm to form the neural tube
- main development after birth is the surface area of the brain
- following on is a sequence of events that are genetically determined, and environmentally influenced via epigenetics
neurons
neurons migrate along pathways laid down by a network of guiding cells to form major parts of the brain
- peeks at the end of trimester of pregnancy.
- basic unit of the brain: three types; sensory neurons, motor neurons, interneurons
neuron types and specialization
- different types of neurons: neurons assume specialized functions depending on where they migrate
- nay neurons has the potential to serve any neural purpose
growth of dendrites
dendrites of the neurons and arborization rapidly accelerate around the 28th week of gestation onwards
glial cells
- glial perform a variety of critical functions. there are five types, glial cells play a major role in communication within the brain by influencing the formation and the strengthening of synapses, producing myelin, and communicating among themselves in a network separate from the neural network
astrocytes
- most common, mop up excess neurotransmitters emitted from synapses, feed neurons by supplying nutrients. control where and when neurons make new synapses
Oligodendrocytes
- wraps tips around the axons of neurons and extrudes myelin, creating sheaths that help speed conduction of electrical activity
Schwann cells
- these cells form a layer around the axon, helping conduct electrical impulses
- they are the main Glial cell found in the peripheral NS, so they act like oligo.
Microglia
serve as immune system in the brain
NG2+ cells
precursor cells to ologo, astrocytes and neurons.
Myelination
Myelin (80% lipid and 20% protein)
- oligodendrocytes
myelinated portions of axons are white- t/f term white matter
- sheath acts as insulator to speed up the transmission of neural impulses
- begins 7 months of gestation.
myelination (cont.)
- allows for increasingly complex movement
- different cortical areas myelinate at different rates
- an infants ability to process emotional expressions on another persons face may improve when myelination occurs
- myelination continues into early adulthood: the reticular formation and the frontal cortex are not fully myelination at puberty. these are areas of the brain that allow us to concentrate and make good descisions.
synaptogenesis
synaptogenesis: is the formation of synapse connections between neurons
- proceeds rapidly during the brain growth spurt
the peak occurs 34th week of gestation in humans at the rate of 40,000 new synapses per second
- continues in postnatal life
- timing and rate of synapse production vary across different cortical areas
synapse
a synapse is a specialized junction between two cells through which they communicate
apoptosis
the brain has evolved so that is produces excess of neurons and synapses in preparation for recieving information from the world sensory and motor stimulation
- neurons that succesfully interconnect with other neurons corwd out those that do not, so that about half of the neurons produced early in life also die.
- if neurons are not used they will die by a process called apoptosis and their connections with other neurons will die- this is called synaptic pruning.
Austin Rissen
- kept infant chipmunks in a dark room for 16 months, and their retina adapted to this situation, and the chipmunks turned blind
- if released at 7 months the damage was reversible
- this showed that if neurons are not properly stimulated they will die.
lower brain
At birth the most highly developed areas is the lower (SUBCORTICAL) brain. these areas control states of consciousness, inborn reflexes, vital biological functions such as respiration, digestion of food and elimination of waste
cerebrum and cerebral cortex
cerebrum= outer grey matter aka cerebral cortex and white matter
cerebral cortex= grey matter
- these are the areas involved in voluntary movement, perception, higher intellectual activities,
Lebel study
103 healthy subjects got their brain scanned twice or more (5-32) findings:
- white matter volume increased significantly across the age range
- grey matter decreased across the age range
- white matter increases were the offset of grey matter decreases so there was no total change in the brain mass with age
further analysis of Label findings
increase in white matter reflects myelination whilst decrease in grey matter reflects synaptic pruning and myelination,
