Cellular Anatomy + Neural Signaling Flashcards
Neurons =
excitable cells transmitting APs to neurons via synapse (=axon terminal, dendritic process of target cell, glial cell process)
Anatomy ~ neurons =
STABLE (no regeneration, no 1° neoplasia)
Gray Matter =
Unmyelinated Tissue (somas + dendrites)
White Matter =
Myelinated Tissue (somas + dendrites + white-l lipid in myelin)
Neurite =
process, such as dendrite or axon; # processes used to classify neuron
Multipolar Neurons: Define
most abundant neuron in CNS (pyramidal, Purkinje, motor) - Multiple dendrites branching from soma; single axon from axon hillock
Pseudounipolar Neurons: Define
sensory neurons in spinal ganglion - Single dendritic axon (sensory) to spinal cord, bypassing cell body (no processing)
Bipolar Neurons: Define
found in retina and olfactory epithelium
- Dendrite —> cell body (processing!) —> retina/olfactory epithelium
Axodendritic Synapse: Define
MC type; dendritic tree receives thousands of synapses = AP
Sum of signals depends on architecture of dendritic tree (Temperospatial Summation)
Axosomatic Synapses: Define
less common; ↑powerful signal b/c close to axon hillock
Axoaxonic Synapses: Define
↑powerful b/c close to axon hillock (↑/inhibit previous AP)
Dendrodendritic Synapse: Define
coordinated firing of neurons (phrenic nucleus neuron)
Principal Cells: Define
projection neurons b/c integrate info and send to other brain areas ~ long axon; aka Golgi Type I Cells
Interneuron: Define
local circuit neurons; local brain areas; Chandelier, basket, double bouqet cells ~ short/no axon; aka Golgi Type II
Glia (“Glue”) ~ what are they?
non-excitable (no AP generated); 50% of brain volume (10 glia/1 neuron)
Astroglia: fibrous (white matter), protoplasmic (gray matter), Muller Cells (retina)
Functions:
recycle/transfer neuroTx, ion homeostasis (via end-feet lining vessels of BBB), component of tripartite synapse
Oligodendroglia: Define
myelinating cells of CNS; wrap axons via cell processes = trophic support, protection, organize ion channels
Schwann Cells: Define
myelinating cells of PNS; one Schwann cell myelinates ONE axon (ONE internode)
Microglia: Define
monocyte/macrophage derived immune cells (phagocytose/APCs)
Polydendrocyte: Define
stem cells for both neurons + glial cells
Ependymal Cells: Define
ciliated/microvilli cuboid/columnar epithelium separates CSF from neuropil
Satellite Cell: Define
cuboidal cells from neural crest (modified Schwann/Oligo); act as ANS Astrocyte
Blood Brain Barrier (BBB)
Two Components:
a) Endothelium of Vessels: tight junc, ↓pinocytosis, BM
b) Astrocyte Processes (End-Feet): line vessel from neuropil side
Blood Brain Barrier (BBB)
Transport:
a) Diffusion: (passive) of lipophilic + gas + H2O
b) Active: all else
Nernst Equation: Used?
used to determine the equilibrium potential
Note the potential of K is negative because ions move in —> out
Goldmann Equation:
estimates the resting membrane potential
Action Potential Summary:
APs must be unidirectional (refractory), fast (↓capacitance/resistance), efficient (@ nodes only), simple (all/none)
Electrical Synapses:
charge/ion move via connexon (gap junction)
- 6 Connexins per cell —> connexon x 2 —> Gap Junction
- RAPID (no delay), bidirectional, pre-/post cells must match - Areas where neurons req sync
Chemical Synapse:
no charge/ion movement; neuroTx
Chemical Synapse: - Excitatory =
Gray’s Type I / asymmetric (post-syn density)
Chemical Synapse: - Inhibitory =
Gray’s Type II / symmetric (pre/post = density)
- DELAYED (Δsignal), unidirectional
Excititory Post-synaptic potential (EPSP): caused by?
- Na Channel —> generates EPSP brining membrane potential closer to threshold (adds + into cell)
Inhibitory Post-synaptic Potential (IPSP): caused by?
- Cl Channel —> generates IPSP taking membrane potential away from threshold (adds - into cell)
NMJ:
anatomically specialized end plate for ↑safety/quanta via ↑release sites, ↑quantal content, ↑receptors
CNS (Central Synapses):
much simpler synapse, but more diverse neuroTx; ↓quantal content, ↓safety, post synaptic potentials (PSP) are small, requiring summation for AP
Temporospatial Stimulation:
AP are all/nothing, but PSPs are graded; EPSPs can be “added” to reach threshold if nearby and in occur similar time (det by RC time constant)
Receptors: neuroTx bind ionotropic
binding opens ion channel
Receptors: neuroTx bind metabotropic
activates G-Protein —> Δion flow directly/via 2nd messenger
- G protein effects are neuromodulatory; do not Δpolarization directly but Δsignaling, excitability, function
Glutamate: synthesized/function
synthesized from glutamine by astrocytes (recycle); released glutamate +/- shuttled into Krebs Cycle
Glutamate: Ionotropic Receptors:
NMDA + AMPA + Kainate —> binding of glutamate causes influx of cations —> EXCITATORY
NMDA: unique b/c constantly blocked by Mg when unbound; when glutamate binds, all cations (Na + Ca) flow in
Glutamate: Metabotropic Receptors:
mGluRs (metabotropic glutamate receptors) —> EXCITATORY
GABA + Glycine:
MC INHIBITORY neuroTx
Glycine (Spinal Cord):
binds to ionotropic receptor —> Cl- Influx —> INHIBITORY
GABA (CNS) Ionotropic:
GABA_a + GABA_c —> Cl- Influx —> INHIBITORY
GABA (CNS) Metabotropic:
GABA_b —> ↑K+ Influx but ↓Ca2+ efflux —> NET INHIBITORY
AcH: found/function
found in CNS (forebrain) and PNS (ganglionic transmission + NMJ); no reuptake but AcHesterase inactivates AcH
AcH: Ionotropic
Nicotinic: ionotropic receptors coupled to non-specific cation channel
AcH: Metabotropic
Muscarinic: metabotropic receptors coupled to G-proteins (M1/M3 = Gq; M2 = Gi)
Dopamine: receptor type?
metabotropic receptors (D1 = Gs, Excitatory, D2 = Gi, Inhibitory) involved in emotion, reward and motivation
Nor/Epi: receptor types?
metabotropic (ɑ1 = Gq, ɑ2 = Gi, β1 = Gs, β2 = Gs, all excitatory) involved in wakefullness and attention
Recall: synth from Tyrosine —> L-Dopa —> Dopa —> NorEpi —> Epi —(inactivated)—> reuptake / COMT + MAO
Histamine: receptor type?
metabotropic (H1 = Gq, H2 = Gs, all excitatory) involved in wakefullness
Serotonin: receptor type? synthesized?
many metabotrobic, one ionotropic (excitatory); metabotropic are both excitatory/inhibitory
Recall: synth from Tryptophan —> 5-Hydroxytryptophan —> 5-Hydroxytryptamine (5-HT = Serotonin)
ATP ~ Cotransmitter + Neuromodulator
(b/c released with other neuroTx) + (b/c actions ↑ or ↓ action of other neuroTx)
ATP P2X:
ionotropic receptors - excitatory (ATP —> Adenosine [purine])
ATP P2Y:
metabotropic receptors - both
P-Lipid Membrane ~ RC Circuit ~
Battery (membrane potential E_k) + Resistor (Ion Channels) in series + Capacitor (Membrane) in ||
Resistance:
limits flow of charge (ion flow) = 1/g (1/conductance)
Capacitance:
element that stores charge ~ two conductors w/separating insulator (↓insulation = ↑charge storage = ↓active current)
Current =
I_m (total membrane current) = I_c (capacitative current) + I_i (ionic current)
Consequence of RC Circuitry:
signal propagation will decay exponentially w/↑distance 1/e of the max every time constant (ƛ)
