lecture 14- brain development Flashcards
The adult human brain
-Most complex system of which we know
-Human brain and CNS consist of trillions of highly specialised cells that work in synchrony
Chemical signals
Electrical signals
Larger and more
complex than brains
of other mammals
The first and second brains
-Human brain makes up about 2/3 of the neuronal mass of the body and contains almost ¾ of all of our synapses (neural junctions through which cells communicate to each other)
-Enteric nervous system (gut) consists of sheaths of neurons embedded in the walls of the gut
It contains ~100 million neurons (more than the spinal cord or the peripheral NS)
Brain outsources the digestion process to this NS
90% of fibers in the vagus nerve carry information from the gut to the brain
ENS uses more than 30 neurotransmitters
95% of the body’s serotonin is found in the bowels
Neurogastroenterology field
brain growth
The brain grows at an astounding rate early in life
At birth, it weighs 25% of adult weight
By age 2, it weights 75% of adult weight
Between the 7th prenatal month and the 1st birthday, the brain increases in weight by ~1.7 grams per day
“Brain growth spurt” - last 3 months prenatally and first 2 years after birth
Central nervous system (CNS):
Brain and spinal cord
Peripheral nervous system:
Nerves attached to the CNS that lie outside of the CNS
soma
The cell body of a neuron, which contains the nucleus
synapse
A junction between the terminal of the axon and the membrane of another neuron
axon
Long thin cylindrical structure that conveys information from the soma of a neuron to its terminal
multipolar neuron
: A neuron with one axon and many dendrites attached to its soma
neurotransmitter
A chemical released by the nerve terminal that has an excitatory or inhibitory effect on another neuron
types of neurons
Basic unit of the brain Three basic types Sensory neurons Motor neurons Interneurons
all neurons have
Cell body - (soma), which contains all the information needed to keep the cell functioning
Dendrites - fibres that receive information from other cells and conduct that information towards the cell body in the form of electrical impulses
Axon - the fibre, anyway from a few micrometers to over a meter in length, that conducts electrical signals away from the cell body to connections with other neurons
Neurons
Basic units of the brain and central nervous system (CNS)
Receive and transmit neural impulses across the synapses
Product of the neural tube of the developing embryo
Neurons migrate along pathways laid down by a network of guiding cells to form the major parts of the brain
The vast majority of neurons a person will ever have has already been formed by the end of the second trimester of pregnancy.
Scientists have recently established that formations of new neurons occur in the hippocampus (an area of the brain important for learning and memory) and these new neurons occur throughout life.
Neuron specialisation
Neurons assume specialised functions depending on where they migrate
Any neuron has the potential to serve any neural purpose (pluripotency)
If a neuron that would normally migrate to the visual area of the brain is instead transplanted to the hearing area of the brain, it will change to become an auditory neuron instead of a visual neuron.
Glial cells
Glial cells are the brain’s white matter, and they make up nearly half the human brain outnumbering neurons 10 to 1
They perform a variety of critical functions including the formation of the myelin sheath around the axons of the neurons
Glial cells also play a role in communication within the brain by
influencing the formation and strengthening of synapses
communicating among themselves in a network separate from the neural network
It is thought that people with schizophrenia or bipolar disorder may have a defect in a gene that regulates the production of myelin