Networks- Holman Flashcards by Nina Soto

2 primary categories of dendrites

apical (in) and basal (out)

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3 categories of neurons based on number of processes

unipolar/pseudounipolar (spinal cord), bipolar(early development), multipolar (CNS)

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Majority of neurons in the body are

multipolar

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3 types of multipolar cells

motor neuron (spinal cord)
pyramidal cell (hippocampus)
purkinjee cell (cerebellum)

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Are all dendrites equal?

No, they differ in frequency, symmetry, thickness etc

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2 shapes of a dendritic tree

pyramidal

stellate

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2 categories of neurons based on length of axons

projection neuron with intracortical collaterals: long axons

interneurons/intrinsic neurons: short axons

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3 main basic cells of the neocortex

Pyramidal
Spiny non-pyramidal
Aspiny non-pyramidal

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Features of pyramidal cells

Glutamatergic /excitatory
Projection neuron(long axons)
70-80% of total population

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Features of spiny non-pyramidal cells

Glutamatergic /excitatory
Spiny interneurons(short axons)
Mainly in Layer IV

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Features of aspiny non-pyramidal cells

GABAergic/inhibitory
Smooth interneurons: (mostly) local axons
15-30% of total population (primate>rodent)
Morphologically diverse

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Examples of aspiny non-pyramidal cells

basket cells
chandelier cells
bouquet cells

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Differences between symmetric and asymmetric synapses

Asymmetric: excitatory due to depolarization, both ends are curved boutons (convex/concave), thick post synaptic density

Symmetric: inhibitory due to hyperpolarization, closer to the soma, both ends are flat(no boutons)

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3 types of axonal target cells/conncections

Axo-dendritic cells
Axo-somatodendritic cells (variable preferences)
Axo-axonic cells (only cell type exclusive for pyramids)

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Two parts of an excitatory microcircuit

SOURCE=Presynaptic partner (fires AP)

TARGET=Postsynaptic Partner (synaptic potentials)

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Define electrical coupling and state 2 major roles it plays

2 neurons connected by a tight junction, allows ions to diffuse through a connexin pore

Roles:

Signal to noise enhancement
Synchronization due to instant activation

Describe synaptic divergence (fan out of outputs)

multiple outputs from a single source(one source cell synapses on many target cells)
One output (AP) can generate synaptic potentials in many target cells.
example: sensory afferents in the thalamus

Advantages:
Amplification: one axon activates several postsynaptic cells
Synchronization: precise timing of inputs to different cells
Retention of sign: usually, divergent boutons from one axon are either excitatory or inhibitory
Release Probability/Safety Factors

Describe synaptic convergence (fan in of inputs)

Multiple cells synapse on one hence summation of inputs

Advantages:
Temporal Summation
Spatial Summation
Quantal vs. Graded Actions
Nonlinear summation

Define feedforward excitation

input pathways connect to excitatory interneurons, which provide a feedforward relay to the output neurons of that region
eg DG to CA3 or CA3 to CA1

Define feedback excitation

Reexcitation or recurrent excitation; usually without excitatory interneuron hence lead to subsequent reactivation after the input signal
eg CA3 to CA3

Main role of feedback excitation in learning

Pattern completion, pattern separation based on previously strengthened recurrent connections

2 types of inhibitory microcircuits

Feed forward inhibition

Feedback inhibition

Features of feedforward inhibition

Mono- or disynaptic
Creates enhanced temporal precision eg during activity changes
(Change -> Burst & Steady state -> Periodic firing)

Pre-synaptic inhibition turns off an input without directly affecting the target cell

Define feedback inhibition

Excitation of one Neuron leads to the inhibition of that Neuron or a neighbouring Neuron
eg in oscillations (on/off)

Define lateral contrast enhancement

occurs when the activity of one cell (strong) suppresses the activity of a nearby cell (weak). This increases the contrast and sharpness eg in visual response (mammalian retina) In the dark, a small light stimulus will enhance the different photoreceptors (rod cells). ... This contrast between the light and dark creates a sharper image.

Name 4 distinct regions of the hippocampus/hippocampal formation

(1) the dentate gyrus (DG) (2) the hippocampus proper(CA1,CA2,CA3) (3) the subiculum, (4) the entorhinal cortex

Which pathway connects the entorhinal cortex to the dentate gyrus?

Perforant path

Which pathway connects CA3 pyramidal cells to CA1 pyramidal cells?

Schaffer collaterals

Which pathway connects the dentate gyrus to CA3?

Mossy fibre pathway

Name 6 layers of the neocortex

``` Layer I Molecular Layer Layer II External Granular Layer Layer III External Pyramidal Layer Layer IV Internal Granular Layer Layer V Internal Pyramidal Layer Layer VI Multiform Layer ```

2 main intralayer projections

Layer IV to layer II/III (short range) | Layer II//III to layer V/VI (long range)

What do you call groups of neurons with identical receptive fields?

Columns