Networks- Holman

Question 1

2 primary categories of dendrites

Answer 1

apical (in) and basal (out)

Question 2

3 categories of neurons based on number of processes

Answer 2

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

Question 3

Majority of neurons in the body are

Answer 3

multipolar

Question 4

3 types of multipolar cells

Answer 4

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

Question 5

Are all dendrites equal?

Answer 5

No, they differ in frequency, symmetry, thickness etc

Question 6

2 shapes of a dendritic tree

Answer 6

pyramidal

stellate

Question 7

2 categories of neurons based on length of axons

Answer 7

projection neuron with intracortical collaterals: long axons

interneurons/intrinsic neurons: short axons

Question 8

3 main basic cells of the neocortex

Answer 8

Pyramidal
Spiny non-pyramidal
Aspiny non-pyramidal

Question 9

Features of pyramidal cells

Answer 9

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

Question 10

Features of spiny non-pyramidal cells

Answer 10

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

Question 11

Features of aspiny non-pyramidal cells

Answer 11

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

Question 12

Examples of aspiny non-pyramidal cells

Answer 12

basket cells
chandelier cells
bouquet cells

Question 13

Differences between symmetric and asymmetric synapses

Answer 13

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)

Question 14

3 types of axonal target cells/conncections

Answer 14

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

Question 15

Two parts of an excitatory microcircuit

Answer 15

SOURCE=Presynaptic partner (fires AP)

TARGET=Postsynaptic Partner (synaptic potentials)

Question 16

Define electrical coupling and state 2 major roles it plays

Answer 16

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

Roles:

1. Signal to noise enhancement
2. Synchronization due to instant activation

Question 17

Describe synaptic divergence (fan out of outputs)

Answer 17

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

Question 18

Describe synaptic convergence (fan in of inputs)

Answer 18

Multiple cells synapse on one hence summation of inputs

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

Question 19

Define feedforward excitation

Answer 19

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

Question 20

Define feedback excitation

Answer 20

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

Question 21

Main role of feedback excitation in learning

Answer 21

Pattern completion, pattern separation based on previously strengthened recurrent connections

Question 22

2 types of inhibitory microcircuits

Answer 22

Feed forward inhibition

Feedback inhibition

Question 23

Features of feedforward inhibition

Answer 23

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

Question 24

Define feedback inhibition

Answer 24

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

Question 25

Define lateral contrast enhancement

Answer 25

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.

Question 26

Name 4 distinct regions of the hippocampus/hippocampal formation

Answer 26

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

Question 27

Which pathway connects the entorhinal cortex to the dentate gyrus?

Answer 27

Perforant path

Question 28

Which pathway connects CA3 pyramidal cells to CA1 pyramidal cells?

Answer 28

Schaffer collaterals

Question 29

Which pathway connects the dentate gyrus to CA3?

Answer 29

Mossy fibre pathway

Question 30

Name 6 layers of the neocortex

Answer 30

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

Question 31

2 main intralayer projections

Answer 31

Layer IV to layer II/III (short range)

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

Question 32

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

Answer 32

Columns