L12 Neurophysiology and Neurosecretion Flashcards Preview

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Flashcards in L12 Neurophysiology and Neurosecretion Deck (41)
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1
Q

Where do the axons arise from?

A

Axons arise from the axon hillock

2
Q

What are telodendria?

A

The branches at the end of axons.

3
Q

What are presynaptic terminals (boutons)?

A

Small swellings which indicate the termination of telodenrias.

Presynaptic terminals contain small vesicles which contain neurotransmitters.

4
Q

Which statement(s) about resting membrane potentials are correct?

1) When there is a low [Na] and a high [K] outside the cell, K flows out of the cell
2) When there is a low [Na] inside the cell, K flows into the cell
3) When there is a high [Na] and a low [K] outside the cell, K flows out of the cell
4) When there is a high [Na] inside the cell, K flows into the cell

A

2) When there is a low [Na] inside the cell, K flows into the cell
3) When there is a high [Na] and a low [K] outside the cell, K flows out of the cell

5
Q

What are the key components of a resting membrane potential?

A

Inside the cell has a negative potential.

Na/K pump

6
Q

How is an electrical gradient created in a nerve cell?

A

It has a high concentration of K inside the cell and a high concentration of Na outside the cell, producing an electrical gradient

7
Q

True or false: Nerve cell membranes are permeable to sodium

A

False. The membranes are impermeable to sodium ions and require voltage gated channels for the movement of the ions.

8
Q

True or false: Nerve cell membranes are permeable to potassium

A

True. Potassium moves down an electrical gradient and a concentration gradient.

9
Q

The resting membrane potential is maintained at:

A

-70 to -90mV

10
Q

In the Nernst Equation, what do the letters represent?

V = (RT/ZF).ln(C0/C1)

A

V = equilibrium potential

C0 and C1 = outside and inside concentrations of potassium

R = gas constant

T = absolute temperature

F = Faradays constant

Z = charge of the ion

11
Q

What happens during an action potential?

A

Na channels open, Na enters the cell = depolarisation.

The Na/K pump opposes it by opening voltage gated K channels = 3Na out, 2K in.

12
Q

Function of intrinsic (local) currents:

A

Open downstream voltage gated Na channels = initiates another action potential

13
Q

A period of A.P inactivation is known as:

A

Refractory period. This prevents the back flow of excitation

14
Q

Function of myelinated sheaths:

A

Increases conduction of the axon, which increases the intrinsic currents and the conduction velocity

15
Q

Where are myelin sheaths formed?

A

In Schwann cells

16
Q

What are nodes of Ranvier?

A

Short unmyelinated stretches along the axon

17
Q

True or false: Local anaesthetics have a high affinity for open sodium ion channels

A

True.

Local anaesthetics target voltage gated channels - especially open sodium ion channels (the more channels open, the greater the effect of the anaesthetic).

The LA maintains ion channel in inactivated state and so the cell cannot be re-stimulated.

18
Q

What is the difference between an electrical and chemical synapse?

A
  • Electrical synapse: Very quick as sends transmissions via pores (i.e. gap junctions). Found in smooth and cardiac muscle.

Chemical synapse: AP causes pre-synaptic membrane to release neurotransmitters which diffuse across the synaptic cleft and bind to receptors on the pots-synaptic membrane. This causes ligand-gated Na channels to OPEN, allowing the AP to continue its journey.

19
Q

What are the 3 amino acid neurotransmitters?

A

Glutamate, GABA and Glycine.

20
Q

What are the 6 monoamine neurotransmitters?

A

Ach, Dopamine, NA, adrenaline, serotonin (5-HT), histamine.

21
Q

What are the 2 purine neurotransmitters?

A

Adenosine and ATP

22
Q

What are the 6 peptide neurotransmitters?

A

Substance P

Vasoactive intestinal peptide

Somatostatin

Cholecystokinin

B-endorphin

Met-enkephalin

23
Q

What are the 3 gas neurotransmitters?

A

Nitric oxide

Hydrogen sulphide

Carbon monoxide

24
Q

What causes the release of neurotransmitters?

A

AP at the synaptic bouton opens Ca channels, so Ca enters.

Synaptotagmin detects the Ca ions, which promotes the formation of SNARE complex between synaptobrevin (embedded in the vesicle membrane) and the SNARE proteins (syntaxin and SNAP-25, in the pre-synaptic membrane).

The vesicle and pre-synaptic membrane fuse and the neurotransmitter is released into synapse.

25
Q

How are neuropeptides released?

A

They are released from any location of the terminal membrane.
More than one can be released from a single synapse.
It requires a higher concentration of Ca ions.

26
Q

What is the function of autoreceptors?

A

Monitor self secretion. - Part of localised negative feedback system

27
Q

Function of heteroreceptors:

A

Monitor transmissions from other synapses. - Part of negative feedback system

28
Q

When neurotransmitters released at a single synapse are too small to trigger a full action potential they are known as:

1) Threshold potential
2) Sub-threshold potential

A

Sub-threshold potential.

These can be Excitatory post-synaptic potentials (EPSPs) or inhibitory post-synaptic potentials (IPSPs)

29
Q

How does a neurotransmitter become inactivated?

A

1) Reuptake: secondary active transport
2) Enzymes: acetylcholinesterase breaks Ach down into acetate and choline
3) Diffusion: neurotransmitters diffuse away slowly, prolonging effects

30
Q

What is a resting membrane potential?

A

The inside of a nerve cells is less positively charged than the extracellular fluid.

Maintained because sodium is actively pumped out of the cell and cannot reenter across the membrane. Potassium is pumped into the cell but can diffuse back out across the cell membrane (to balance K+ concentrations) and so effect is that the outside has both Na+ and K+, inside only has K+ making the inside more -ve.

31
Q

Sodium channels in a nerve cell membrane are normally closed. How can they be opened?

A

Localised changes in resting-membrane potential (voltage-gated), or by neurotransmitter activation (ligand-gated).

32
Q

What is a ‘polarised nerve cell’?

A

When the resting membrane potential is maintained in balance.

33
Q

What is a ‘depolarised nerve cell’?

A

When sodium channels are activated (by local change in resting membrane potential or a neurotransmitter) and an influx of Na+ causes the inside of the cell to becomes more positively charged.

34
Q

What is a refractory period and why is it important?

A

Following cell depolarisation the voltage-gated sodium channel goes through a period of inactivation while the cell re-polarises. This prevents back flow of excitation to maintain a unidirectional propagation of the action potential.

35
Q

What is a node of Ranvier?

A

A gap in the myelin sheath between two Schwann cells.

36
Q

What is ‘saltatory conduction’?

A

Conduction of an action potential between nodes of Ranvier.

37
Q

Which protein is embedded in the membrane of a vesicle?

a) Syntaxin
b) SNAP-25
c) Synaptobrevin
d) Synaptotagmin

A

c) Synaptobrevin

This protein binds to the SNARE receptors in the presynaptic membrane to allow fusion of the vesicle and membrane and ultimately the dispersal of a neurotransmitter into the synapse.

38
Q

Which protein is embedded in a presynaptic membrane?

a) Syntaxin
b) SNAP-25
c) Synaptobrevin
d) Synaptotagmin

A

both a and b

a) Syntaxin
b) SNAP-25

These are known as SNARE proteins (SNAP-receptor proteins) and allow the vesicle to fuse with the presynaptic membrane to facilitate the release of a neurotransmitter into a synapse.

The vesicle membrane protein is synaptobrevin.

39
Q

What types of receptor do neurotransmitters bind to?

A

Type 1 (ionotropic) and type 2 (metabotropic, G protein-coupled)

40
Q

True or false: Neuropeptide release requires high concentrations of calcium?

A

True.

41
Q

What does co-transmission mean for neuropeptides?

A

More than one neuropeptide can be released from a single synapse

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