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1H06A > 05 - Neurotransmission & Nerve Conduction > Flashcards

05 - Neurotransmission & Nerve Conduction Flashcards

1
Q

What is the transmission of nerve impulses across a synapse?

A

Neurotransmission

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2
Q

What is the movement of nerve impulses down neurons?

A

Nerve conduction

  • This is sometimes called the propagation of nervous impulses
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3
Q

What is a neuron consist of?

A

Dendrites, cell body, axon & axon terminal

Nucleus
Lots of mitochondria
Smooth ER
Rough ER
Neurofilaments and microtubules
Synaptic vesicles

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4
Q

What is full of neurofilaments and microtubules?

A

Axon

  • Help to give it a bit of structural strength to stay straight
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5
Q

What are the 3 types of synapses for nerve conduction?

A

Axosomatic synapses
Axodendritic synapses
Axoaxonic synapses

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6
Q

What are nerve impulses sent as?

A

Electrical messages

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7
Q

How do axons send signals?

A

In an axon, this potential difference is exploited to send a signal

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8
Q

Where does the wave of depolarization start in an axon?

A

Axon hillock

  • A small area in the cell where the axon meets the soma
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9
Q

What is the process of the wave of depolarization along the axon?

A
  1. Stimulus (an increase in voltage) triggers an action potential which depolarizes the local membrane
  2. The inside of the axon membrane becomes briefly positive. This increase in voltage triggers the next area of membrane to become positive because of opening of voltage sensitive Na+ channels in the membrane
  3. The voltage increase is terminated shortly after it begins (by closure of the Na channels and opening of the K channels) such that only a short section of axon is depolarized at any one time but the action potential moves along the axon. The area behind the depolarized membrane is in its refractory period so reverse conduction will not occur.
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10
Q

What happens to the area behind the place getting depolarized?

A

As the front gets depolarized, the area behind is repolarizing

  • In the refractory period
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11
Q

How to reestablish the membrane potential?

A
  • Na+ rush into the cell, voltage increases
    • Na+ channels open which causes K+ channels to open shortly after
  • K+ channels opens
  • K+ rush out and make the outside of the cell negative again
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12
Q

What are the 3 purposes of the refractory period?

A

Assures that transmission is a one-way event

Assures that the APs are separate events

Allows the cell to recover to the resting state

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13
Q

How does the refractory period make sure that a transmission is a one-way event?

A

The voltage-sensitive channels on the axon just respond to voltage changes so the message could go both ways but with refractory periods, it make sure it is a one-way event

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14
Q

How does the refractory period make sure that APs are separate events?

A

Each AP becomes a distinct and discrete signal so coding of the message is possible

  • We can not understand the messages if we do not have a break
  • Refractory period is that break that we have to make that change in the potential to make sense
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15
Q

How can APs encode different things/messages?

A

Stimulus strength is coded for by the frequency of discharges (APs) not the amplitude since all APs are the same

  • AP is just one message but its frequency can change
  • It’s the spread b/w the APs that’s coding everything
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16
Q

Why is it important to allow the cell to recover to the resting state?

A

This is particularly important for keeping the neurons from running down due to loss of ions and energy shortages brought about by the use of large quantities energy to shift ions to re-establish the RMP

  • Bring back to the normal level of Na+ and K+
    • Using the sodium-potassium pump
  • The Na+ and K+ channels were opened thus we have to close it and bring back the normal amount of Na+ and K+ first before the next message
    • W/out bring back the normal level of Na+ and K+ it would mess up the cell
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17
Q

How does saltatory conduction work?

A

There are myelin sheaths around the axon with node of Ranvier (area of polarity reversal) in between each sheath

  • Depolarizes one space (the node of Ranvier) then the next, etc
  • Instead of depolarizing the whole membrane, it’s depolarizing section by section
    • Determines how fast you react to pain
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18
Q

What does saltatory mean?

A

To jump

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19
Q

How much does saltatory conduction speed up depolarization?

A

Increase the speed by around 15 times

Myelinated axons can conduct messages at an absolute maximum of about 150 m/sec compared to unmyelinated which are never more than 10 m/s.

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20
Q

How does myelin speed up the process of depolarization?

A

Myelin speeds up the process because only a short section of axon has to be depolarized then the wave of depolarization jumps to the next node.

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21
Q

What are the 2 ways to speed up the process of depolarization?

A

Saltatory conduction with myelin

Thicker axons

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22
Q

How does thick axons speed up the process of depolarization?

A

Thick axons speed this process up too because there is less resistance to current flow with a large membrane

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23
Q

What is covering the membrane of the axon (saltatory conduction)?

A

Myelin sheath

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24
Q

Steps in saltatory conduction

A
  1. Stimulus (an increase in voltage) triggers an action potential which depolarizes the local membrane
  2. The inside of the axon membrane becomes briefly positive. This increase in voltage triggers the next area of exposed membrane to become positive. The action potential thus leaps from one Node of Ranvier to the next.

The AP hop across the nodes

25
Q

What is very important in saltatory conduction?

A

Myelin sheath
Nodes of Ranvier
Distance between the nodes

26
Q

What is the synapse called between an axon to the soma (the body of the cell)?

A

Axosomatic synapses

27
Q

What is the synapse called between an axon to the dendrites?

A

Axodendritic synapses

28
Q

What is the synapse called between an axon to another axon?

A

Axoaxonic synapses

29
Q

How are electrical signals transmitted across electrical synapses?

A

By inducing ionic movement in the adjacent cell

30
Q

How does electrical synapses work?

A

Send messages directly w/out any gaps in between them

eg. between 2 adjacent muscle cells

31
Q

What does electrical synapse allow?

A

Allow cells to stay synchronized in their actions

  • They want to work at the same time
32
Q

What’s often found between smooth muscle cells? Think in terms of electrical synapse

A

Gap junctions

33
Q

Where do you find electrical synapses?

A
  • Heart muscle (myocardium)
  • Uterus
34
Q

What is a gap junction?

A

A tiny hole between two adjacent cells and allows for electrical synapses

35
Q

What can pass gap junctions?

A

Electrical signals and most everything else can pass between the two cells

36
Q

Steps in signal transmission across an electrical synapse

A
  1. Stimulus (an increase in voltage) triggers an action potential which depolarizes the local membrane
  2. The inside of the axon membrane becomes briefly positive. This increase in voltage triggers the next area of membrane to become positive
  3. The wave of depolarization meets the axon terminal and the positive ions flow through the ion channels causing the postsynaptic membrane to depolarize. The signal is thus propagated across the synapse
37
Q

What are the 2 types of postsynaptic potentials (PSPs)?

A

Excitatory postsynaptic potential (EPSP)

Inhibitory postsynaptic potential (IPSP)

38
Q

What increases the voltage? How? Think in terms of postsynaptic potentials

A

Excitatory postsynaptic potential (EPSP) increase in voltage (brings the cell closer to threshold)

Often due to Na+ channels opening (Na+ enters the cell)

39
Q

What decreases the voltage? How? Think in terms of postsynaptic potentials

A

Inhibitory postsynaptic potential (IPSP) decrease in voltage (brings the cell further from the threshold)

Often due to K+ channels opening (K+ moves out of the cell)

40
Q

What are the 4 summations of potentials?

A

Subthreshold - no summation

Temporal summation

Spatial summation

Spatial summation of EPSP and IPSP - just constantly firing

41
Q

If enough potentials are added up spatially and temporally and the threshold is reached what is triggered?

A

An action potential in a muscle or in the axon hillock of a neuron is triggered

42
Q

What is a substance that transmits signals across the synapse?

A

Neurotransmitter

43
Q

Where are neurotransmitters released from?

A

Axons (the presynaptic membrane)

Infrequently from the postsynaptic membrane

44
Q

Can a hormone act as a neurotransmitter?

A

Yes

45
Q

How do neurotransmitters work?

A

Some neurotransmitters change the membrane voltage as in the generation of EPSPs and IPSPs

Some alter cell function in some other way

46
Q

What is the neurotransmitter at all ganglia of the autonomic nervous system and neuromuscular junctions?

A

Acetylcholine (ACh)

47
Q

What are 3 important neurotransmitters under catecholamines?

A
  • Dopamine (important in the gut & brain)
  • Norepinephrine (aka noradrenaline)
  • Epinephrine (aka adrenaline)
48
Q

Where are norepinephrine/noradrenalin released into?

A

Released into the blood from the adrenals and also released at synapses

49
Q

What kind of neurotransmitter is epinephrine/adrenalin?

A

Sympathetic, postganglionic neurotransmitter

50
Q

How can 1 neurotransmitter control so many things?

A

B/c the neurotransmitter is found in different areas of the body

It all depends on where the neurotransmitter is to figure out what it is going to control

eg. the area in the brain that controls nausea and vomiting is different than the area that controls mood
- But in both areas, serotonin is found
- Thus serotonin controls all of those

51
Q

What is the process of catecholamines synthesis?

A
  1. Tyrosine
    - Tyrosine hydroxylase (to get to the next stage) –> O2 input
  2. L-Dopa
    - Dopa decarboxylase (to get to the next stage) –> CO2 removed
  3. Dopamine (neurotransmitter)
    - Dopamine B-hydroxylase
  4. Norepinephrine (neurotransmitter)
    - Phenylethanolamine N-methyltransferase
  5. Epinephrine (neurotransmitter)
52
Q

What are the enzymes used for catecholamine synthesis?

A

Tyrosine hydroxylase
Dopa decarboxylase
Dopamine B-hydroxylase
Phyenlethanolamine N-methyltransferase

53
Q

What are the 2 methods of neurotransmitter removal?

A

Inactivation and reuptake

54
Q

How does inactivation (neurotransmitter removal) work?

A

Usually some specific enzyme breaks down the neurotransmitter in the synapse

e.g., MAO (monoamine oxidase) converts epinephrine into an aldehyde (also converts norepinephrine and dopamine into inactive forms)

  • Many neurotransmitters are taken back up without being broken down
55
Q

How does reuptake (neurotransmitter removal) work?

A

The dominant removal method for some neurotransmitters is reuptake into the presynaptic neuron

eg. all of the catecholamines are taken back up and it is the major mechanism for removal

  • The reuptake is specific for the neurotransmitter (it is a type of active transport)
56
Q

Can reuptake (neurotransmitter removal) be blocked?

A

Yes

Examples:
Selective serotonin reuptake inhibitors (SSRIs)
- Fluoxetine (PROZAC) inhibits the reuptake of serotonin from the synapse and can be used as an antidepressant since increased serotonin is associated with increased affective tone (mood)

Norepinephrine/dopamine reuptake inhibitors (NDRIs)
- Buproprion (WELLBUTRIN)

Cocaine
- Acts to block epinephrine reuptake which leads to high synaptic levels of epinephrine and the manic feeling associated with cocaine use

57
Q

What is drug therapy based on?

A

Drug therapy is based on manipulating the actions of natural neurotransmitters and hormones

  • Many drugs are based on natural products from bacteria, fungi, plants as well as vertebrates
58
Q

How do drugs work?

A

Drugs work by inhibiting receptors and affecting neurotransmitters

1H06A (8 decks)

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