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NEUR 301 > Neuronal Structure and Conduction: Module 2.1-2.2 > Flashcards

Neuronal Structure and Conduction: Module 2.1-2.2 Flashcards

1
Q

What are the four morphogically defined regions of the neuron?

A
  1. Dendrites: main apparatus for receiving incoming signals from othe nerve cells.
  2. Soma: Metabolic Center. It tappers to form the axon hillock.
  3. Axon: It to carry signals to many taget neurons. An axon can convey electrical signals ranging from 0.1mm to 1m. Action potentials, are intiated at a specialized trigger region near the origin of the axon, the intial segment, from which the action potentials propagate down the axon without failure or distortion at speeds of 1 to 100m/s.
  4. Presynpatic Terminals: makes “contact” with target cells.
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2
Q

Information is recieved primarily by the ____ and ____, but synaptic inputs can also be found at the ____ and ____.

A

Information is received primarily by the dendrites and soma, but synaptic inputs can also be found in axons and axon terminals.

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3
Q

What is the integrating center of a neuron.

A

Neuronal Soma

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4
Q

Where is the “decision” made of whether an action potential will fire?

A

Axon Hillock

Due to summation of graded potentials

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5
Q

What does the firing pattern of a neuron depend on?

A

Ion channels expressed in the axon.

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6
Q

What is the function of Ankyrin G in the axon initial segment?

A

It anchors voltage gated channels to microtubules (cytoskeleton).

It anchors AIS-specific membrane proteins such as Nav and Kv channels, two-cell adhesion molecules (CAMs).
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7
Q

What is the central component of the AIS scaffold?

A

Ankyrin G

Specifically Ankyrin-G carboxy terminal side.

Connects submembrane scaffold to microtubule associated proteins.

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8
Q

What is the function of Spectrin in Axon Initial Segment?

A

Anchors ankyrin to actin rings.

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9
Q

In peripheral neurons, ankyrin-G is recruited to the nodes of Ranvier by ____, which is produced by ____, an accumulates in the ______.

A

In peripheral neurons, ankyrin‐G is recruited to the nodes of Ranvier by gliomedin, which is produced by Schwann cells and accumulates in the perinodal extracellular matrix.

Gliomedin causes the nodal clustering of Ankryin-G which in turn recruits to the nodal plasma membrane an ankyrin-G protein network consisting of Nav, K, and B4 Spectrin.

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10
Q

Does Ankyrin-G localization to the AIS depend on the extracellular cue gliomedin?

A

No

Only at Nodes

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11
Q

Where does an EPSP attenuate?

A

Between the dentrites and the soma.

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12
Q

Where does summation occur?

A

Axon Hillock

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13
Q

What regions have high thresholds?

A

Regions that have few Nav channels.

Threshold falls steeply at Axon Hillock and AIS.

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14
Q

What regions have the highest densities of Nav channels?

A

Initial Segment and Each Node of Ranvier

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15
Q

What are regenerative signals?

A

Action Potentials (All or Nothing)

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16
Q

What are Non-Regenerative Signals(Passive Responses)?

A

Subthreshold potentials (graded potentials( that spread for short distances along cell membranes. Receptor potentials are generated during the transduction of sensory stimuli and postsynaptic potentials are generated by the opening of agonist-activated channels.

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17
Q

What does the spread of electrical current depend on?

A
  • Geometry
  • Resistance (of Aq sol and Cell membrane)
  • Membrance Capicitance.
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18
Q

What is the difference between passive responses and active responses?

A

Passive responses decay with distance, but active responses do not.

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19
Q

What are is another name for Graded Potentials?

A

Postsynaptic Potentials (PSP)

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20
Q

What are the 2 types of PSP?

A

Excitatory (EPSP) - Depolarizing
Inhibitory (IPSP) - Hyperpolarizaiton

If Strong enough an EPSP can fire an action potential at the trigger zone

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21
Q

What are two ways PSP’s lose strength as they travel?

A
  • Current Leak
  • Cytoplasmic Resistance
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22
Q

What are two types of summation?

A
  1. Spatial Summation: EPSPs arriving from different dendrites.
  2. Temporal Summation: EPSPs arrive rapidly in succession
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23
Q

How would you describe as axon as an equivalent circuit model?

A
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24
Q

Explain the process of how local current helps travel a depolarizing signal.

A

1) A signal causes a transient Vm change

2) The cytosol has a slight excess of positive
charge compared with the adjacent inactive
regions of the cytosol, which have a slight
excess of negative charge.

3) The charge imbalance causes currents to
flow from the excited region to adjacent
regions of the cytoplasm.

4) Current always flows in a complete circuit along pathways of least resistance and spreads:

a) longitudinally from positive to negative regions along the cytoplasm
b) across membrane conductance pathways (“leak channels”)
c) along the extracellular medium back to the site of origin, thereby
closing the current loop.

5) Because of this flow of current the region of membrane immediately
adjacent to the active region becomes more depolarized.

25
Q

What is represented by λ?

A

Space constant: Determines the spread of voltage changes in space

The Distance over which Voltage decays to 37%.

26
Q

What is the equation to describe λ?

A
27
Q

Does a signal spread farther in a thinner or thicker dentrite?

A

Thicker

28
Q

Given that dendtrites attenuate synaptic potentials:

What are 2 strategies dendrites employ to avoid signal loss?

A

a) Increase Rm x cable radius(a)
b) expression of voltage-gated channels

Some dendrites have voltage-gated ion channels that can modulate signal strength. In certain cases, these channels can help to either amplify or attenuate signals. For example, dendrites might reduce the impact of incoming signals by selectively regulating which ion channels open or close in response to a signal. This selective response can prevent weaker or distant signals from having too much influence on the neuron’s overall activity.

29
Q

What is the usual voltage channel composition of a dentrite?

A

Low Density of Nav and Kv Channels
Have V-gated Ca channels that boost signal

30
Q

What are Calcium Spikes?

A

Ca-Dentritic Spikes

Ca spikes can porpagate into the soma but not down the Axon.

31
Q

What volume of the brain do glial cells constitute?

A

Half

Outnumber Neurons

32
Q

What are the different types of Glia?

A

CNS (CENTRAL NERVOUS SYSTEM)
* Astrocytes (strength-support, promote Blood-Brain Barrier, in embryo
regulate growth-migration-interconnection, scavengers of K+ and
neurotransmitters)
* Oligodendrocytes (CNS myelin sheath)
* Microglia (phagocytes, immune cells, big role in pathological conditions)
* Ependymal cells (epithelia, line the ventricle and canal of spinal cord;
production and circulation of cerebrospinal fluid)

PNS (PERIPHERAL NERVOUS SYSTEM)
* Schwann cells (PNS myelin sheath)
* Satellite cells (surround cell bodies of neurons, regulate exchange of
materials)
* Enteric glia (Schwan cell-like, no myelination)

33
Q

What is Myelination?

A

The process by which a fatty substance called myelin forms a sheath around the axons of neurons.

Sheath acts as an insulating layer.

34
Q

What Cells form Myelin?

A
One Oligodendrocyte - Many axons Multiple Schwan cells - One axon
35
Q

What is white matter?

A

Regions of the brain that are dominated by myelinated tracts.

36
Q

Do unmyelinated axons have no schwaan cells associated with them?

A

No

Still with schwaan cells however cells dont form myelin sheaths.

37
Q

Explain the differences in the regrowth of neurons in the different nervous systems?

A

CNS neurons do not regrow after being severed.

PNS neurons regenerate after being severed.

38
Q

Myelin Sheath formation not completely understood in Oligodendrocytes

What are the stages of myelination in Schwann cells?

A

1) The Schwann cell surrounds the axon.

2) The outer aspects of the plasma membrane have become tightly apposed in one area (membrane fusion).

3) Several Layers of the Schwann cell cytoplasm around the axon.

4) A mature myelin sheath has formed; much of cytoplasm has been squeezed out of the innermost loop.

When Schwann Cell touches itself again after engulfing axon (2) it initiates rotation of cell.
39
Q

How do schwann cells know where to wrap on the axon?

A

Neuregulin-1 Family Proteins

NRG1-1 and NRG1-2 are paracrine signals. NRG1-3 -Remains Associated with Membrane - Serves as Anchor MP - Metaloproteinase - Cleaves
40
Q

What is the axon theshold diameter?

A

The minimum diameter at which an axon can be activated by an external electric field.

(>0.2 - 0.4um)

41
Q

What is the g ratio?

A

The optimal myelin thickness.

It is reached when the ratio between the axon cylinder diameter and that of the myelinated axon is close to 0.68

42
Q

What protein helps schwann cells “sense” axon size (make correct number of wraps).

A

NRG1-3 (Anchor)

43
Q

Explain the regulation of Schwann cell differentiation.

A
44
Q

What are characteristics of the Paranodes.

A

Ends of the sheaths attached.

Paranodal Loops contatin cytoplasm and are not compacted.

High Density of NRG1-3 - Attaches to ErbB2Rs

45
Q

What are the characteristics of paranodal axoglial junctions?

A

Characterisitc Electron-Dense Transverse Bands

46
Q

How does myelin compaction occur?

A

MBP(Myelin Basic Protein) - Peripheral Membrane Protein Associate with eachother with electrostatic and hydrophobic interactions.(Stabilizes)

Neutralizes repulsive negative charges on the membranes and, given its small size, can bring two cytoplasmic leaflets into close apposition.

Needs a certain critical concentration for compaction. Cooperative association of MBPs to membrane when concentrations pass threshold level.

47
Q

What is CNP and what is its function?

A

Cyclic Nucleotide 3’ Phosphodiesterase

Maintenance of Axonal integrity. Essential factor in generating and maintaining cytoplasm within the myelin compartment.

Associates and Organizes Actin cytoskeleton - provides structure that counteracts MBP action.

48
Q

What are 2 strategies to improve conduction in mammals and non mammals?

A

Increase diameter (increase a, decrease Ri) - Squid Axon - 1mm diamter (cant do this in mammals)

Increase Rm - Myelin - Mammals

Squid Axon diameter increases conduction 10x, myelin in mammals increases conduction 1000x

49
Q

What are 3 ways myelin increases conduction?

A
  1. Increases Rm
  2. Decreases Membrane Capicitance (increases distance between charges) —>C = eA/D —-> Only capicitance at Nodes of Ranvier.
  3. Decreases Time constant increases speed of propagation. Tm = Rm x Cm —> Reduction of Cm is more significant than increased Rm = decreased Tm
50
Q

For unmyleniated axons

What is the relationship between conduction velocity and axon diameter.

A

Conduction increases with the square root of the axons diameter.

51
Q

For mylinated axons

What is the relationship between conduction velocity and axon diameter?

A

Lincear function - 6m/s per 1-um increase in outer diamter.

52
Q

A mammalian myelinated axon with an outer diameter of ____ has roughly the same impulse velocity as a squid axon wiht a diameter of ____ um.

A

A mammalian myelinated axon with an outer diameter of 4 um has roughly the same impulse velocity as a squid axon wiht a diamter of 500 um.

53
Q

What are the functions of astrocytes?

A
  • **Control the immediate environmnent of neurons - Control the Synapses
  • Brain Glycogen (energy storage), contain all the enzymes required for glucose metabolism.
  • Provide fuel to neurons in the form of lactate (from glycogen or glucose)**
  • Promotes BBB
  • Scavengers of K and NT
  • Strength Support
  • Regulate Growth-Migration-Interconnection in Embyro.
  • **Synthesis of Glutamate and GABA, provide Glutamine to Neurons.(Astrocytes carry the precursors)
  • Removal of Glutamate from synaptic cleft.
  • Astrocytes are responsible for buffering excess of extracellular K+**

Glutamate an GABA arre the exitatory and inhibitory NT of the CNS

Excess Extracellular K+ is Caused after burst activity and cause unwanted depolarizations –> Na/K pump is not fast enough to correct —> Need Astrocytes.

54
Q

What are the 2 pathways in which neurons obtain energy and glucose?

A
  • Direct Path
  • Trans-astrocyte Path
55
Q

What is the direct path to provide neurons with energy?

A

The oxidation of one glucose molecule provides 30 ATP

Normal Glucose Metabolism

56
Q

What is the Trans-astrocyte path?

A

Conversion of Glucose to 2 pyruvate and and 2 lactate and then oxidation of pyruvate and tranfer of lactate to neuron where it is oxidized yields 28
ATP.

GLUT 1 and GLUT 3 and MCT1 and MCT2 transporters.

57
Q

What type are all synapses?

A

Tripartic Synapse

Presynaptic, Postsynaptic, And Astrocyte

58
Q

Explain the Glutamate-Glutamine Cycle.

A
Most of the glutamate is generated from glutamine, which the neurons themselves cannot make. However, astrocytes take up some of the glutamate that is released at synapses (or produced by metabolism) and convert it into glutamine. The glutamine then enters the neuron, where it is converted back to glutamate. Glutamine derived from astrocytes is also important for synthesis of GABA. In neurons, the enzyme glutamic acid decarboxylase converts glutamate (generated from glutamine) to GABA.

Excitatory Amino Acid Transporter(EAATs) = Na+ Dependent high affinity Glutumate Transporters

59
Q

Explain Astrocyte K+ buffering.

A
K Influx Does not depolarize because the gap junction creates the effect of 1 giant cell --> K influx dissipates and does not cause Depolarization and decreases Extracellular Calcium around Neuron.

NEUR 301 (8 decks)

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