Lecture 18 - Circuit Construction II Flashcards

1
Q

What is John Langley known for studying?

A

He’s known for studying the sympathetic pathways associated with the “fight or flight” response, like pupil dilation and blood vessel constriction. He studied through working with the superior cervical ganglion (anterior-most sympathetic ganglion).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What happened when Langley stimulated the T1 and T4 preganglionic fibers?

A

Stimulation of T1 (thoracic level 1) preganglionic fibers coming from the spinal cord activate postganglionic neurons that cause pupil dilation in the eye. Simulation of T4 (thoracic level 4) preganglionic fibers activate postganglionic neurons that cause constriction of blood vessels of the ear.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Axons from T1 and T4 run together in the same bundle to the ganglion. What does this indicate?

A

This indicates that there is an organization of connections in the ganglion that allows for specific behaviour effects.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What did Langley find would happen when the cervical sympathetic trunk was cut?

A

He found that the injured sympathetic nervous system could regenerate following this cut. Behaviour responses would be lost upon cutting but could be re-established within a few weeks despite the ganglion having a mixed population of postganglionic targets.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Despite the superior cervica ganglion having a mixed population of postganglionic cell targets, selective responses could be re-established within a few weeks after injury (cervical sympathetic trunk cut). What does this indicate?

A

This suggested that neurons make selective choices for their partners and connections.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What layers of cells (in order) must light pass through in order to reach the photoreceptors in the retina?

A

Light must pass through ganglion cells, amacrine cells, bipolar cells, and horizontal cells.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

How do sidekick 1 and 2 proteins contribute to synaptic organization in the inner plexiform layer of the retina?

A

Cells on each side of the IPL (from ganglion cell layer and inner nuclear layer) meet up in different layers of the IPL depending on which proteins they are expressing. For example, sdk-1 expressing cells meet in layer S4.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Suppose you take a SP+ INL cell and cause it to also express sdk-1. What type of GCL cell will it connect with, and in which IPL layer?

A

The cell will connect with a normal sdk-1+ cell in the S4 layer (normal layer for two sdk-1+ cells).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Which 4 CAMs are involved in homophilic adhesion in the retina IPL?

A

Sidekick-1, Sidekick-2, DscamL, and Dscam

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What are basket cells?

A

Basket cells are inhibitory interneurons that form basket synapses near the axon initial segment of Purkinje neurons.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What would happen in a mutant with ankyrinG knocked out?

A

The basket cells would not form inhibitory synpases at the AIS of Purkinje cells.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Where is ankyrinG most concentrated?

A

AIS of Purkinje Cells

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is used for synapse targeting of basket neuron axons to Purkinje neurons of the cerebellum?

A

Targeting is mediated by oligomeres of neurofascin with ankyrinG.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What are the two options for an axon once it settles on a target?

A

It can form a synapse or retract/degenerate.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is a motor unit composed of?

A

A motor unit is composed of a motor neuron and the muscle fibers it innervates.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What makes the neuromuscular junction a good system to study synapse formation?

A

It is a good system because it is large, relatively simple, and accessible. It also has good tools such as the electric organ of Torpedo californica, the original source for many NMJ-related proteins.

17
Q

True or False?:

The electric organ of Torpedo californica contains muscle-related electrolytes which are heavily innervated by motor terminals

A

True

18
Q

Where on the muscle fibre are AChRs found?

A

Synaptic Basal Lamina

19
Q

How many subunits are AChRs made up of?

A

5

20
Q

How many ACh molecules does each AChR bind?

A

2

21
Q

True or False?:

AChRs are ligand-gated potassium channels with some permeability to calcium.

A

False

AChRs are ligand-gated sodium channels with some permeability to calcium.

22
Q

What is often used to label AChRs (since it blocks ACh binding sites)?

A

The snake venom toxin alpha-bungarotoxin is used for labelling the AChRs.

23
Q

The muscle contains AChRs and VGSC (voltage-gated sodium channels) at the NMJ. In the below diagram of the NMJ, which channels are found in the red and which are found in the green?

A

Green - AChRs

Red - VGSC

24
Q

What happens during AChR organization during NMJ development?

A

AChRs are clustered early on, but undergo aggregation and reorganization during synaptogenesis and maturation.

25
Q

Cultured myotubes express AChRs that are distributed evenly across the cell surface. What happens if extracts from the synaptic basal lamina of Torpedo are placed on these myotubes? What does this mean?

A

The extracts induce AChR aggregation. This means something in the synaptic basal lamina causes aggregation. It was found that this aggregation was caused by agrin.

26
Q

What does local application of agrin on muscle fibres do?

A

It induces AChR aggregation without neuronal innervation.

27
Q

What secretes agrin?

A

Agrin is secreted from neurons and muscle (but in much lower concentrations from the muscle).

28
Q

What happens to muscles in agrin-deficient mutants?

A

They have small AChR clusters, decreased density of clusters, and less organized NMJs.

29
Q

What happens to the NMJ in agrin-/- knockout mice?

A

There are still clusters of AChRs, but they are much smaller. The axons will extend to the clusters and then extend along the muscle looking for more AChRs.

30
Q

How are NMJs formed during development?

A

The motor axon approaches a newly formed muscle cell. A nerve terminal is developed through the release of agrin. The muscle then forms a complex postsynaptic apparatus where AChRs are enriched at the surface.

31
Q

What are the two counter-balancing forces in AChR stabilization?

A

The scheer force of the action potential reaching the NMJ and ACh transmission creates a force that destabilizes AChRs. This force is counter-balanced by stabilization through agrin activity.

32
Q

True or False?:

ACh transmission destabilizes AChR clusters on muscle membrane. Agrin released from neuron stabilizes AChR clusters on muscle membrane.

A

True

33
Q

Why are AChR clusters large in mutant mice without motor neurons?

A

They are large because while there is no agrin, there is also no destabilizing force from ACh transmission.

34
Q

You are a doctor and see a 38 year old female patient come in with progressive fatigue and weakness. What disease may she have?

A

She may have myasthenia gravis.

35
Q

What happens in myasthenia gravis?

A

In it, your body develop antibodies against AChRs and musk, causing the NMJ to be much smaller and damaged. When there is a sequence of signals transmitted, the muscle gets fatigued because the antibodies have inhibited the NMJ.

36
Q

What is Lambert-Eaton syndrome?

A

It is a autoimmune disease that usually occurs with cancer. In it, antibodies are raised against presynaptic calcium channels. When multiple signals are transmitted, there is an action potential fatigue leading to inefficient/weak transmission. As such, the disease causes progressive fatigue and weakness.