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neuron
fundamental building blocks of nervous system
glial cells
also comprise nervous system, 1:10 ratio with neurons
brain circut
nuclei communicating with each other
brain nucleus
collection of neurons
grey matter
cell bodies ie cerebrum
white matter
axons traveling to different regions
importance of stains
the brain is opaque, so stains are needed to identify anatomy
goals of neuroanatomy
region specificity
connectivity
function in human and animal studies
comparative neuroanatomy
region specificity
distinctions between and within regions
connectivity
anterograde: tracing IN direction of info flow (body to axon term.)
retrograde: tracing in REVERSE of info flow (axon term. to cell body)
function: human studies
led to the identification of Broca and Wernicke’s area while studying stroke patients
function: animal models
stimulation studies in rats are the basis of deep brain stimulation
comparative neuroanatomy
differences between species
Neurons
building blocks of the nervous system
Parts of a neuron and their functions
dendrites: receive info
cell body/soma: process info
axon: transmit info
With neuroanatomy, we look to understand...
1. Regional specificity: distinctions between regions of the brain, and within regions of the brain
2. Connectivity: how one brain region is connected to another
3. Function: what are the roles of these brain connections, and how do they play into our actions
Standard MRI Imaging
- Allows you to look at brain STRUCTURE
- MRI scanners, best resolution = about 1 mm
- Provides snapshot of what brain anatomy looks like
-Easy to examine changes over time (ex: see how much atrophy has occurred over 12 months)ike
FMRI (Functional MRI)
- Allows you to see changes in ACTIVITY in brain based on changes in blood flow
- Shows which part of brain is stimulated the most
- FMRI scanner, best resolution = about 2 mm
dMRI (Diffusion MRI)
- analyzes water movement within axons
- if water is pushed easily, then it is going with the direction of the axon
- if not able to be pushed, it is hitting the barrier of the axon
- goal is to map CONNECTIONS within the human brain
- uses water molecules and neurons filled with salt solution
Human Connectome Project
a large-scale, multi-university effort to map all connections in the human brain within all brain regions (Harvard, USC, UMN, Washington U)
Different neuronal structure =
different neuronal function
objective of neurons
transmit information from dendrites to the end of the axon through electricity
4 key elements for electrical communication in neurons:
- sodium, chloride, potassium, calcium
- become charged when dissolved (NA+, K+, Cl-, Ca^2+)
role of neuronal membrane
charge separation (separates intracellular fluid from extracellular space, and they contain different ion solutions)
Electrical signaling is due to
-Sodium and Potassium separation
- Na is restricted to OUTSIDE neuron
- K restricted to INSIDE neuron
- Ion pumps create this
neuron resting conditions
inside of neuron is more negative than outside, rests at -80 mv
action potential
-fundamental electrical signal in brain, brief change in charge
- happens once inside of neuron has more POSITIVE charge than outside
- ALL OR NONE: they either fire or they don't
- spike = NA+ IN (more positive)
- drop = K+ OUT (more negative)
neural code
neurons communicate through timing and number of action potentials
myelin sheath
made out of glial cells, covers axon terminal, allows action potentials to travel faster down the axon
ion pumps in neuronal membrane
maintain/restore charge separation, CONTINUOUSLY ACTIVE! (channels are only active during the action potential)
Where does an action potential start?
at "decision point" between cell body and axon
presynaptic side
axon terminal
synapse
space between two neurons
postsynaptic side
dendrite of another neuron
how do action potentials start?
- when multiple excitatory (positive) graded potentials happen at in rapid progression, threshold voltage level (-50) is exceeded and sodium channels open, which starts the action potential.
- potassium rushes out = hyperpolarization = more negative = drop
how are graded potentials and action potentials different?
graded potentials can have different levels of inhibition/excitation, action potentials have all or none responses
how are graded potentials formed?
when a neurotransmitter binds to its receptor, a certain type of channel will open in the membrane. depending on the type of channel, membrane will become more positive (excitation/depolarization) or more negative (inhibition/hyperpolarization)
neurotransmitters
chemical signals of the nervous system
neurotransmitters act to either:
- induce graded potentials that excite (depolarize) post-synaptic neurons
- inhibit (hyperpolarize) the post-synaptic neuron
Dopamine imbalances linked to:
Schizophrenia (too much dope), Parkinson's Disease (too little)
Serotonin imbalances linked to:
depression, OCD
Acetylcholine imbalances linked to:
Alzheimer's Disease
GABA imbalances linked to:
anxiety
Glutamate imbalances linked to:
epilepsy, Schizophrenia
Is dopamine excitatory or inhibitory?
both
Is serotonin excitatory or inhibitory?
both
Is acetylcholine excitatory or inhibitory?
both
Is GABA excitatory or inhibitory?
inhibitory: produces hyperpolarization
Is glutamate excitatory or inhibitory?
excitatory: produces depolarization
synaptic vesicle
spherical sac containing neurotransmitters
steps of synaptic transmission
1. synthesis
2. storage
3. release
4. receptor activation
5. inactivation
synthesis:
neurotransmitter manufactured in cell
storage:
neurotransmitter stored in vesicles for protection
release
action potential arriving at axon terminal will cause vesicles to move to membrane and release neurotransmitter into the synapse
receptor activation
neurotransmitters in the synapse can freely move about it. if they interact with a receptor (bind to it), they can activate the receptor to stimulate electrical charges in the postsynaptic neuron. receptor will hyperpolarize or depolarize
inactivation
neurotransmitters in the synapse (that didn't bind to receptors) are either A. altered into active substances or B. recycled (reuptake) back into presynaptic vesicles (vesicles in the axon)
what causes the release of a neurotransmitter?
calcium triggers vesicles to migrate to the end of axon and fuse with the membrane. more action potentials = more entry of calcium = more vesicles fusing with membrane = more neurotransmitters released