Networks- Holman Flashcards
2 primary categories of dendrites
apical (in) and basal (out)
3 categories of neurons based on number of processes
unipolar/pseudounipolar (spinal cord), bipolar(early development), multipolar (CNS)
Majority of neurons in the body are
multipolar
3 types of multipolar cells
motor neuron (spinal cord) pyramidal cell (hippocampus) purkinjee cell (cerebellum)
Are all dendrites equal?
No, they differ in frequency, symmetry, thickness etc
2 shapes of a dendritic tree
pyramidal
stellate
2 categories of neurons based on length of axons
projection neuron with intracortical collaterals: long axons
interneurons/intrinsic neurons: short axons
3 main basic cells of the neocortex
Pyramidal
Spiny non-pyramidal
Aspiny non-pyramidal
Features of pyramidal cells
Glutamatergic /excitatory
Projection neuron(long axons)
70-80% of total population
Features of spiny non-pyramidal cells
Glutamatergic /excitatory
Spiny interneurons(short axons)
Mainly in Layer IV
Features of aspiny non-pyramidal cells
GABAergic/inhibitory
Smooth interneurons: (mostly) local axons
15-30% of total population (primate>rodent)
Morphologically diverse
Examples of aspiny non-pyramidal cells
basket cells
chandelier cells
bouquet cells
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)
3 types of axonal target cells/conncections
Axo-dendritic cells
Axo-somatodendritic cells (variable preferences)
Axo-axonic cells (only cell type exclusive for pyramids)
Two parts of an excitatory microcircuit
SOURCE=Presynaptic partner (fires AP)
TARGET=Postsynaptic Partner (synaptic potentials)
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
