Lecture 2 Flashcards
List the basic brain facts (except grey and white matter)
Human brain facts
* The brain is the size of our two fists put together
* 2-3% of body weight, ~3lbs
* Consumes ~20% of your energy! (15% of all your blood, 20% of oxygen, 25% of glucose dedicated to the brain)
* Slightly larger in men than women
* Huge individual variation
* Composed of neurons, glia, stem cells, blood vessels
* <100 billion neurons (hard to say), more than half of which are cerebellum (dense with neurons!)
* Consistency of soft tofu (yum)
* Convoluted (wrinkled) (to fit more brain in your brain, more cortex, hence folding it to fit)
These convolutions were evolved to be this way because it helped cram more cortex into our brains, whose skulls were limited in size due to the fact that it had to be able to be fit through the birthing canal
* Cells are not replaced
discussion
What is Neurogenesis? Discuss the conversation around adult neurogenesis
neurogenesis= birth of new neurons
Most neurogenesis happens in early postnatal life—at 1 years old, you already have most of the neurons you’ll have for life
If adult neurogenesis happens, it’s in such small amounts that it’s hard to detect and would mostly occur in the hippocampus
Earlier evidence of neurogenesis from the 70s and 80s was stronger for rodents and birds, but weak for humans. But recent studies found neurogenesis in 13-year-olds but not in individuals older than 17.
This means that your current neurons you have are all that you’ve got
What are Grey and White Matter?
Gray matter: is made up of mostly cell bodies and unmyelinated interneurons
White matter: is made up of mostly myelinated axons that connect different brain regions
The myelin is what gives white matter its glossy white sheen
What are the two general types of cells within the nervous system? Name and describe
1. Neurons
Dendrites→ soma (cell body)→ axon (output)→ terminals
Input—-flow of signal→ output
Neurons are located all over the body, but mainly are organized in two nervous systems:
The* CNS (central nervous system)* which are in charge of the brain and spinal cord
The PNS (peripheral nervous system) which is in charge of the rest of the body
3 types of physical forms:
Pyramidal cells: pyramid shape but the same basic design; the largest neuron cells, and are found mostly in the cortex, many dendrites converge to one axon.
Stellate cells: subcortical area, star-shaped, a mess, but still the same design, interneuron
Purkinje cells: the cerebellum, lots of dendrites, still the same design, they mainly release neurotransmitters that inhibit and block other neurons from firing off.
2 types of functions of neurons:
Projection neurons: a kind of neuron that has axons which connects local parts of the CNS to distant parts of the CNS. Like a wire that connects two distinct regions—it has a LONG axon that projects to a different brain areas.
Interneurons: a type of neuron that has axons which connect neurons within a single, local region of the CNS. They have short axons that project locally.
Synapses/junctions are sites of modifiers –> In charge of controlling the intensity or timing of signals for sensory-motor neurons.
2. Glia
4 major types of glial cells (3 are large gila, macro gila) (1 is micro gila)
Macroglia are good for faster action potential, bc they have better conduction and signal.
1. Schwann cells
Found outside of the brain and spinal cord, in the PNS (peripheral nervous system), wraps the entire cell body on the axon and only myelinates a signal axon
2. Oligodendrocyte
They myelinate several axons within the brain and spinal cord, or in the CNS (central nervous system). These two above do essentially the same thing, just in different amounts.
3. Astrocytes
These make up half of our blood-brain barrier
Of all the oxygen, amino acids, and glucose—it mediates all the nutrition your brain cells and neurons need, may buffer in or out sodium and potassium
Most abundant CNS neuroglia
Astrocytes are a part of a glial network
They are operating as a coordinated network through Gap junctions (which create pores from one astrocyte to another)
Sometimes found in Interneurons (some neurons have gap junctions as well)
Not passive, very active
**Microglia **
Microglia are like the brain’s version of white blood cells.
The blood-brain barrier keeps most immune cells out, so microglia take on the job of fighting off infections and foreign stuff.
They are inactive until they sense signals from viruses or bacteria.
Once activated, microglia move, engulf, and digest pathogens.
Limitations:
They might miss some pathogens, not seeing them as threats. As we age, microglia can become dysfunctional and become less effective at doing their job.
What is the tripartite synapse?
a conversation of three
synapse = junction/space between two cells
3 parts: Presynaptic side (the axon, output of neurotransmitters) —> synapse —> postsynaptic side (the dendrite or cell body, receptors, input of neurotransmitters)
Process includes neurotransmission and gliotransmission (like thru astrocytes) in the synapse
Wrapped around the synapse are astrocytes—they have their own receptors and can modify communication between neurons (EX. like by intensifying the signal of wakefulness or arousal)
- Research on astrocytes are limited to the last 20 years
Describe the central dogma of molecular biology
**The central dogma of molecular biology: **the theory that genetic material flows one way only from DNA —> RNA —> to protein, or RNA —> to protein
DNA replication
DNA transcription to RNA
RNA can reverse transcription to DNA
RNA translation protein
What is the Soma? What is the Mitochondria?
Soma = cell body
Mitochrondria = ATP-producing organelles that is important for powering all cellular functions
Mitochrondria:
Has own DNA—which suggests that long ago they were different cells (our ancestors ate something and got it, and they just stuck around)
They produce ATP, the major currency we perform all major actions (we break down ATP which allows us to function)
The byproduct of the ATP-making process is CO2. Sugar + oxygen —> ATP —> CO2.
Mitochondria is very important, especially to our nervous system as it affects oxygen levels
What are the 6 types of Synapses
The Synapse
Where two neurons meet—the site of neural communication
Harder to understand than the diagrams with dendrites, cell bodies and astrocytes at play
1. Axosecretory axon terminal secretes directly into bloodstream
2. Axoaxonic axon terminal secretes into another axon
**3. Axodendrite **axon terminal ends on a dendrite spine
4. Axoextracellular axon with no connection secretes into extracellular fluid
5. Axosomatic axon terminal ends on soma
6. Axosynaptic axon terminal ends on another axon terminal
Describe the relationship between dendrites and some common brain dysfunctions.
Post-synaptic side, branches
Two types of dendrites:
Smooth neurons: non-spiny neurons, often refers to gaba neurons
**Spiny neurons: ** bumpy neurons that release neurotransmitters, are glutamate neurons exclusively
You are your synapses:
Any change in your dendritic spines, density and shape will impact your personality
Early in life, you have a lot of dendritic spines,
“your prefrontal cortex is still developing” —> you’re pruning your dendrite spines
Brain Dysfunctions Related to Dendrites:
Autism: An insufficient pruning process during brain development may result in retaining too many dendritic spines, leading to excessive connectivity. This overabundance of synapses can contribute to conditions like autism, where neural communication may become overloaded or imprecise.
Schizophrenia: While schizophrenia is typically diagnosed in adulthood, its emergence is related to improper neural development earlier in life. Dysregulation in dendritic spine pruning during adolescence may lead to impaired synaptic connectivity, which contributes to the cognitive and perceptual disturbances associated with the disorder.
**Alzheimer’s Disease: **In contrast to autism, over-pruning—the elimination of too many dendritic spines—can result in conditions like Alzheimer’s. As dendritic spines are lost, synaptic connections deteriorate, leading to memory loss and cognitive decline, which are hallmark symptoms of dementia.
