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Anatomy > Neurotransmission > Flashcards

Neurotransmission Flashcards

1
Q

Axon diameter and propagation speed: ion movement is related to

A

Cytoplasm concentration

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2
Q

Axon diameter affects

A

Action potential speed

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3
Q

The larger the axon diameter,

A

The lower the resistance

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4
Q

“Information” travels within the nervous system as

A

Propagated electrical signals (action potentials)

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5
Q

The most important information (vision, balance, motor commands) is carried by

A

Large-diameter, myelinated axons

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6
Q

There are three groups of axons

A
  1. Type A fibres
  2. Type B fibres
  3. Type C fibres
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7
Q

These three groups of axons are classified by?

A

Diameter
Myelination
Speed of action potentials

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8
Q

Type A fibres have a high speed (140m/sec) and have

A

Large, Myelinated axons, with large diameters (4-20 um)
Carry rapid information to/from CNS
For example, position, balance, touch and motor impulses

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9
Q

Type B fibres, medium speed (18m/sec) and have

A

Smaller, myelinated axon with diameters 2-4um
Carry intermediate signals
For example, sensory information, peripheral effectors

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10
Q

Type c fibres, slow speed (1m/sec) and have

A

Unmyelinated and less than 2 um in diameter
Carry slower information
For example, involuntary muscle, gland controls

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11
Q

Neurons are the basic functional units of

A

The nervous system

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12
Q

There are 100,000 billion neurons in human brain and

A

10,000 different types

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13
Q

Neurons must communicate with other neurons and tissues to produce

A

Coordinated behavioural responses

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14
Q

Communication occurs at specialised sites known as

A

Synapses

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15
Q

One neuron may have between several thousand and 150 thousand synapses

A

Acting on the cell

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16
Q

Synaptic activity: action potentials (nerve impulses) are transmitted from

A

Presynaptic neuron to postsynaptic neuron (or other postsynaptic cell) across a synapse

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17
Q

What are the two types of synapse?

A

Electrical synapse and chemical synapse

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18
Q

Electrical synapses involve

A

Direct physical contact between cells

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19
Q

With electrical synapses, pre and post synaptic membranes are locked together at gap junctions called

A

Connexons

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20
Q

Connexons allow ions to

A

Pass between cells

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21
Q

Electrical synapses produce continuous

A

Local current and action potential propagation

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22
Q

Electrical synapses are found in

A

Areas of brain, eye and ciliary ganglia and are common in invertebrates and embryos

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23
Q

Chemical synapses involve a

A

Signal transmitted across a gap by chemical neurotransmitters

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24
Q

Chemical synapses are found in

A

Most synapses between neurons and all synapses between neurons and other cells

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25
Q

With chemical synapses the cells are

A

Not in direct contact

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26
Q

With chemical synapses, action potential may or may not be propagated to postsynaptic cell, depending on:

A

Amount of neurotransmitter released

Sensitivity of postsynaptic cell (near or far from threshold)

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27
Q

There are two classes of neurotransmitters

A

Excitatory neurotransmitters and inhibitory neurotransmitters

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28
Q

Excitatory neurotransmitters cause

A

Depolarisation of postsynaptic membranes and promote action potentials

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29
Q

Inhibitory neurotransmitters cause

A

Hyper polarisation of postsynaptic membranes and suppress action potentials

30
Q

The effect of a neurotransmitter on a postsynaptic membrane depends on

A

The receptor not on the neurotransmitter

31
Q

Cholinergic synapses release

A

ACh

32
Q

Cholonergic synpase is any synapse that releases ACh (most widespread neurotransmitter) at:

A
  1. All neuromuscular junctions with skeletal muscle fibres
  2. Many synapses in CNS
  3. All neuron-to-neuron synapses in PNS
  4. All neuromuscular and neuroglandular junctions of ANS parasympathetic division
33
Q

CHOLINergic synapses are so named because the neurotransmitter involved is

A

AcetylCHOLINe

34
Q

Events at a cholinergic synapse include

A
  1. Action potential arrives, depolarises synaptic terminal
  2. Calcium ions enter synaptic terminal, trigger exocytosis of ACh
  3. ACh binds to receptors, depolarises postsynaptic membrane
  4. ACh removed by AChE - AChE breaks ACh into acetate and choline
35
Q

What is step 1 in the sequence of events at a typical cholinergic synapse?

A

An arriving action potential depolarises the synaptic terminal

36
Q

What is step 2 in the sequence of events at a typical cholinergic synapse?

A

Calcium ions enter the cytoplasm of the synaptic terminal
ACh is released through exocytosis of synaptic vesicles
ACh release ceases because calcium ions are removed from the cytoplasm of the synaptic terminal

37
Q

What is step 3 in the sequence of events at a typical cholinergic synapse?

A

ACh diffuses across the synaptic cleft and binds to receptors on the postsynaptic membrane
Chemically gated sodium channels on the postsynaptic membrane open, producing a graded depolarisation

38
Q

What is step 4 in the sequence of events at a typical cholinergic synapse?

A

The depolarisation ends as ACh is broken down into acetate and choline by AChE
The synaptic terminal reabsorbs choline from the synaptic cleft and uses it to resynthesise ACh

39
Q

A synaptic delay of 0.2-0.5 msec occurs between

A

Arrival of action potential at synaptic terminal and effect on postsynaptic membrane

40
Q

With synaptic delay, fewer synapses means

A

Faster response

41
Q

Synaptic fatigue occurs when

A

Neurotransmitter cannot recycle fast enough to meet demands of intense stimuli
Synapse inactive until ACh is replenished

42
Q

There is at least 50 neurotransmitters other than

A

ACh

43
Q

Major categories of neurotransmitters include:

A

Biogenic amines
Amino acids
Neuropeptides
Dissolved gases

44
Q

Important neurotransmitters, other than ACh:

A

Norepinephrine
Dopamine
Serotonin
Gamma aminobutyric acid (GABA)

45
Q

Norepinephrine (NE) is released by

A

Adrenergic synapses
Has excitatory and depolarising effect
Widely distributed in brain and portions of ANS

46
Q

Dopamine is a

A

CNS neurotransmitter
May be excitatory or inhibitory
Involved in Parkinson’s disease and cocaine use

47
Q

Serotonin is a

A

CNS neurotransmitter and affects attention and emotional states

48
Q

Gamma aminobutyric acid (GABA) has an

A

Inhibitory effect and functions in CNS

Roughly 20 percent of the synapses in the brain release GABA, but it functions remain incompletely understood

49
Q

Chemical synapse: the nervous system relies on a

A

Complex form of chemical communication

50
Q

With chemical synapse, each neuron is continuously exposed to a variety of neurotransmitters. Some usually have excitatory effects,

A

While others usually have inhibitory effects

51
Q

Chemical synapse: yet in all cases

A

The effects depend on the nature of the receptor rather than the structure of the neurotransmitter

52
Q

Many drugs affect the nervous system

A

By stimulating receptors that respond to neurotransmitters and can have complex effects on perception, motor control and emotional states

53
Q

Neuromodulators are other chemicals

A

Released by synaptic terminal

54
Q

Neuromodulators have a similar

A

Function to neurotransmitters

55
Q

Characteristics of neuromodulators

A

Effects are long term, slow to appear
Responses involve multiple steps, intermediary compounds
Affect presynaptic membrane, postsynaptic membrane, or both
Released alone or with a neurotransmitter

56
Q

Neuropeptides are

A

Neuromodulators that bind to receptors and activate enzymes

57
Q

Opioids are

A

Neuromodulators in the CNS
Bind to the same receptors as opium or morphine
Relieve pain

58
Q

Four classes of opioids

A
  1. Endorphins
  2. Enkephalins
  3. Endomorphins
  4. Dynorphins
59
Q

How neurotransmitters and neuromodulators work

A

Direct effects on membrane channels e.g ACh, glycine, aspartate

Indirect effects via G proteins e.g E, NE, dopamine, histamine, GABA

Indirect effects via intracellular enzymes e.g lipid-soluble gases (NO, CO)

60
Q

Direct effects because

A

These neurotransmitters alter ion movement across the membrane, they are said to have ionotropic effects
Open/close gated ion channels

61
Q

Indirect effects- G proteins

A
  • Work through second messengers
  • Enzyme complex that binds GTP
  • Link between neurotransmitter (first messenger) and second messenger
  • Activate enzyme adenylyl cyclase- which produces second messenger cyclic-AMP (cAMP)
62
Q

Indirect effects- intracellular receptors

A

Lipid soluble gases (NO, CO)

Bind to enzymes in brain cells

63
Q

What is the relationship between myelin and the propagation speed of action potentials?

A

The presence of myelin greatly increases the propagation speed of action potentials

64
Q

Which of the following axons is myelinated: one that propagates action potentials at 50 metres per second, or one that carries them at 1 meter per second?

A

Action potentials travel along myelinated axons at much higher speeds (by saltatory propagation); the axon with a propagation speed of 50 metres per second must be the myelinated axon

65
Q

Describe the general structure of a synapse?

A

The major structural components of a synapse, the site where a neuron communicates with another cell, are a presynaptic cell and a postsynaptic cell, whose plasma membrane are separated by a narrow synaptic cleft

66
Q

If a synapse involves direct physical contact between cells,

A

It is termed electrical

67
Q

If the synapse involves a neurotransmitter

A

It is termed chemical

68
Q

What effect would blocking voltage-gated calcium channels at a cholinergic synapse have on synaptic communication?

A

If the voltage-gated calcium channels at a cholinergic synapse were blocked, Ca2 could not enter the presynaptic terminal and trigger the release of ACh into the synapse, so no communication would take place across the synapse

69
Q

One pathway in the central nervous system consists of three neurons , another of five neurons. If the neurons in the two pathways are indentical, which pathway will transmit impulses more rapidly?

A

Because of synaptic delay, the pathway with fewer neurons (in this case, three) will transmit impulses more rapidly

70
Q

Differentiate between a neurotransmitter and a neuromodulators

A

Both neurotransmitters and neuromodulators are compounds that are released by one neuron and that affect another neuron. Neurotransmitters alters the transmembrane potential of the other neuron, whereas a neuromodulator alters the other neurons response to specific neurotransmitters

71
Q

Identify the three functional groups into which neurotransmitters and nueromodulators fall

A

They are either

  • compounds that have a direct effect on membrane potential
  • have an indirect effect on membrane potential
  • lipid-soluble gases that exert their effects inside the cell

Anatomy (8 decks)

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