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Micro-neuroanatomy - Coggle Diagram
Micro-neuroanatomy
Brain structure
Cell types
- Neurons: nerve cells, 10-100B, highly interconnected
- Glial cells: nutrients & structural support
Structure of neuron
- Dendrites: receive info
- Cell body: where processing occurs
- Nucleus: contains DNA
- Axon hillock: graded potential
- Axon: transmits electrical signal from cell body
- Myelin: covers axon to insulate
- Nodes of Ranvier: uncovered, boosts signal
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- Synapse: gap between terminal button & dendrites, where chemicals released
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Structural classification
- Unipolar: 1 projection - axon or dendrite (none in adults)
- Bipolar: 2 projections (visual)
- Multipolar: many projections (most common)
- Pseduo-unipolar: axon & dendron (motor sensory, brain -> motor)
Functional classification
- Sensory: from sensory receptors -> brain (afferent)
- Motor: from brain -> muscles & organs (efferent)
- Inter: between neurons - most common
White vs grey matter
- White matter: myelinated axons = info transmission (e.g. corpus callosum, spinal cord)
- Grey matter: cell bodies & dendrites = processing (e.g. cortex)
Chemistry
Ions: electrically charged molecule
- Cation = positive
- Anion = negative
Ion movement
- Passive process -> dynamic action
- Diffusion: move from high -> low concentration
- Electrostatic pressure: attraction of opposite charge, repulsion of same charge
Cell membrane
- Semi-permeable: some things can move between
- Ion channels: open and close by electrical stimulation
- Membrane potential: charge inside neuron relative to outside
** Intracellular: -ve
** Extracellular: +ve
* Resting potential = -70mV*
Potentials
- Ion channels open/close -> change relative concentration ions -> change membrane potential
- Excitatory: depolarise - less polar - cations in, e.g. -66mV
- Inhibitory: hyperpolarise - more polar cations out, e.g. -76mV
- Graded potential: vary in magnitude of conduction of signal
- Can cancel out
Step B - Axon Hillock -> Terminal Button
Steps
- If summed potentials > threshold of excitation -> action potential (neuron fires)
- If summed potentials < threshold -> nothing happens
- Action potential at axon hillock & nodes of Ranvier
- Transmit signal down axon via saltatory communication
Action potential
- Starts at -70mV
- If reach excitation threshold of -65 to -55MV
- Depolarisation
- Repolarisation
- Hyperpolarisation: refractory period - cannot open -> one-way
Saltatory communication
- Passively conducted under myelin
-> new action potential at nodes of Ranvier (boosted)
- Passive conduction saves resources
Neurotransmitters
Psychotropics
- Chemical substances that affect affect, behaviour & cognition
- Increase or decrease neurotransmitter & networks
Psychotropic actions
- Amt of nt produced (Tryptophan, PD)
- Amt of nt released (MDMA)
- Rate of nt uptake (SSRI)
- Rate of nt breakdown (MAO inhibitors - reduce)
- No. post-synaptic receptors (down regulation - reduce)
- Impersonate neurotransmitter
** Act like them & activate (agonists, e.g. cocaine)
** Block receptor sites (antagonists, e.g. naloxone, schiz)
Types
- Glumate: excitatory (seizures, memory)
- GABA: inhibitory (alcohol, anti-anxiety meds - Xanax, Valium, anaesthesia) (gamma-aminobuteric acid)
- Dopamine (DA): reward pathways + emotion, motivation, arousal, movement (addiction, meth/coke, schizo - high, Parkinson's - low)
- Serotonin (5-HT): sleep, mood, arousal, empathy/emotion (depression, ecstasy)
- Acetylcholine (ACh): learning, memory, movement/coordination (Alzheimer's)
- Endorphins: pain management, mood (morphine, heroin, runner's high)
Step C - Terminal Button -> Dendrite at Synapse
Steps
Pre-synaptic neuron
- Terminal button receives action potential
- Vesicles release neurotransmitters into synapse
Synapse
- Neurotransmitters move passively
Post-synaptic
- Bind to receptors in dendrites, if free & appropriate (lock & key principle)
-> open ion channel -> ions move -> create EPSP/IPSP
Neurotransmitters
Start
- In neuron, stored in vesicles
- Specialised: usually release one type of neurotransmitter
Stop
- Bind to receptors in pre-synaptic neuron
** Reuptake
** Feedback loop to stop releasing neurotransmitter
- Excess degraded by enzymes in synapse
Step A - Dendrite -> Axon Hillock
Steps
- Adjacent neurons send electrical signals to dendrites or cell bodies
- Changes membrane permeability
- Causes excitatory or inhibitory potentials
- Graded potentials summed at axon hillock -> whether neuron fires (continue transmitting info to next neuron)
** Excitatory (EPSP) = yes
** Inhibitory (IPSP) = no