Lecture 3: Brain Basics Flashcards
Human brain facts
- 2 - 3% of body weight, around 3lbs (probably less on average)
- Consumes roughly 20% of your energy
- Slightly larger in men than in women (size does not correlate to intelligence)
- Huge individual variation
- Composed of neurons, glia (support/structure), stem cells (proliferate into different cell types), blood vessels
- More than 10 billion, less than 100 billion neurons (hard to say), more of half (70%) of which are in the cerebellum - only 10% of the brains volume
- Consistency of soft tofu
- Convoluted (wrinkled): increasing the amount of cortex, that can fit inside our skull - flattened, cortex is much bigger than the other brain regions
- Cells are not replaced: neurons you have at 1 years old, you will have the same amount for the rest of your live - neurogenesis does not count for much
It’s not the size that counts
- Bigger animals have bigger brains
- Above the line of best fit, disproportionately large brain compared to the size of the body - humans, the most
- Below the line of best fit, disproportionately small brain compared to body size
- Still doesn’t give us a mechanism, though - the link
Chimpanzee 450 Human 1,350 Bottlenose Dolphin 1,600 African Elephant 6,075 Fin Whale 7,200 Sperm Whale 9,200
Brain cell density
- Intelligence also correlates with sophistication of cellular connections (i.e. wiring)
- African Bush Elephant’s brain is much larger, double the size - although a Human’s brain has almost 3 times the neurons
- More neurons means more intelligence - seem to be a predictor - disproportionately dense brain (humans the most dense)
Human African Bush Elephant
Primate Non-primate
1232 g 2,848 g
16.3 billion neurons 5.5 billion neurons
Two basic cell types
Neuron
Glia
Neuron
o Type of cell in our nervous system
o Main communicating cells
o Release chemical messengers; chemicals received by other neurons
o Able to communicate really really quickly
o Axon/axon terminals - carries axon potential
o Communicate with things really far away, goes to a specific location - very targeted, very fast (whale, giraffe)
Glia
o (Long undervalued within neuroscience)
o Latin word for glue
o Structural support role - especially in development
o Variety of active roles - the way in which brains communicate
The neuron
• Many types, but similar design
• Dendrite - soma - axon - terminals
o Dendrite: « input layer » information comes from other cells, converge onto a cell body (soma)
o Soma: from the soma, emerges a single axon
o Axon: input travels down the axon
- Terminals: input/neurotransmitters
1 - pyramidal
2 - stellate
3 - purkinje
Pyramidal
o Common in cerebral cortex
o Dendrites reaching to different layers
Apical dendrites
Basal dendrites
Stellate
o Common in subcortical regions
o Mess, different branches converges on the cell body
Purkinje
o Common in cerebellum
o Dense with dendrites - tens and tens and tens of thousands
o Only ever one axon coming out of the cell (axon can branch - axon collateral )
Two basic types of neurons
Projection neurons
Interneurons
Projection neurons
o Interesting shapes (often)
o Axon is long, projects to different parts of the brain (far away)
Interneurons
o Typically star shapes
o Short axons, project locally
Neuron (more info)
- Big long wire, with some interruptions
- No reason why the axon has to stop - can be very very long
- Synapse - is not a physical limitation - every synapse, provides an opportunity to modify the signal
- Surrounding these 2 projection neurons, there are these interneurons - receiving inputs by other interneurons/projection neurons - using that information to modify/modulate the signal
- Interneurons: synchronizing and timing (motor task, moving together in an intelligent way); suppressing (sleeping; blocking sensory information from coming into your brain)
Glial cells
- Support cells
- Variety of interesting goals
- Majority = macroglia (larger)
- Microglia
- Schwann cell
- oligodendrocyte
- astrocytes
Microglia
o Small
o Act as the “immune system” in the brain - walled off, carefully guarded from bacteria/viruses in blood (devastating effects on the brain)
o Detecting; sense debris/cells damages/protein related to bacteria - primed state/become active, searching for bacteria - if found, enlarged to an enormous size, engulf the foreign body & digest it
Myelinated glia
• (Schwann cell & oligodendrocyte)
o Wrap around the axon, creating an insulated sheathe
o Fatty substance
o Myelinate the axon - signal travels much faster
Schwann cell
o Found in the peripheral nervous system (outside the brain/spinal cord)
o Myelinate only a single axon* wraps its whole body around
Oligodendrocyte
o Found in the central nervous system (brain/spinal cord)
o Oligo-: “several or a few”
o Myelinate several different axons
Astrocytes
o Blood brain barrier: wrapping around our capillaries
o Provides nutrition to neurons (oxygen/glucose) mediated by astrocytes
From the blood, to the astrocytes, down to the neuron
o Wrapped around neuron and often the synapse - control over that environment - help to maintain the environment around the area
Too much potassium - buffer away; too little potassium - bring some extra in)
o Release their own chemicals
o Gliosis: need scarring in the brain, astrocytes do this through gliosis
Ripped from the headlines
- Glia play a key role in brain function, and we will hardly talk about them throughout this course
- Not just support cells
- “Key role in regulating motivation for drug and heroin addictions”
- “Glial cells are critical players in brain’s response to social stress”
The tripartite system
- A conversation of 3
- Glia have receptors, transmitters
- Glia shape conditions at the synapse
- Axon terminal = pre-synaptic
- Dendrites = post synaptic
• Astrocyte:
o Can release their own transmitters (glio-transmitters); bind to either the pre-synaptic axon or post-synaptic dendrite
o Receive signals: have receptors; can change processes (ex. Bringing in more glucose/oxygen)
Grey matter
o Where you find the cell bodies of neurons
o Where you find unmyelinated axons
White matter
o Where you find myelinated axons
o Connecting two areas of grey matter
