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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
With chemical synapses the cells are
Not in direct contact
26
With chemical synapses, action potential may or may not be propagated to postsynaptic cell, depending on:
Amount of neurotransmitter released | Sensitivity of postsynaptic cell (near or far from threshold)
27
There are two classes of neurotransmitters
Excitatory neurotransmitters and inhibitory neurotransmitters
28
Excitatory neurotransmitters cause
Depolarisation of postsynaptic membranes and promote action potentials
29
Inhibitory neurotransmitters cause
Hyper polarisation of postsynaptic membranes and suppress action potentials
30
The effect of a neurotransmitter on a postsynaptic membrane depends on
The receptor not on the neurotransmitter
31
Cholinergic synapses release
ACh
32
Cholonergic synpase is any synapse that releases ACh (most widespread neurotransmitter) at:
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
CHOLINergic synapses are so named because the neurotransmitter involved is
AcetylCHOLINe
34
Events at a cholinergic synapse include
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
What is step 1 in the sequence of events at a typical cholinergic synapse?
An arriving action potential depolarises the synaptic terminal
36
What is step 2 in the sequence of events at a typical cholinergic synapse?
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
What is step 3 in the sequence of events at a typical cholinergic synapse?
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
What is step 4 in the sequence of events at a typical cholinergic synapse?
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
A synaptic delay of 0.2-0.5 msec occurs between
Arrival of action potential at synaptic terminal and effect on postsynaptic membrane
40
With synaptic delay, fewer synapses means
Faster response
41
Synaptic fatigue occurs when
Neurotransmitter cannot recycle fast enough to meet demands of intense stimuli Synapse inactive until ACh is replenished
42
There is at least 50 neurotransmitters other than
ACh
43
Major categories of neurotransmitters include:
Biogenic amines Amino acids Neuropeptides Dissolved gases
44
Important neurotransmitters, other than ACh:
Norepinephrine Dopamine Serotonin Gamma aminobutyric acid (GABA)
45
Norepinephrine (NE) is released by
Adrenergic synapses Has excitatory and depolarising effect Widely distributed in brain and portions of ANS
46
Dopamine is a
CNS neurotransmitter May be excitatory or inhibitory Involved in Parkinson's disease and cocaine use
47
Serotonin is a
CNS neurotransmitter and affects attention and emotional states
48
Gamma aminobutyric acid (GABA) has an
Inhibitory effect and functions in CNS | Roughly 20 percent of the synapses in the brain release GABA, but it functions remain incompletely understood
49
Chemical synapse: the nervous system relies on a
Complex form of chemical communication
50
With chemical synapse, each neuron is continuously exposed to a variety of neurotransmitters. Some usually have excitatory effects,
While others usually have inhibitory effects
51
Chemical synapse: yet in all cases
The effects depend on the nature of the receptor rather than the structure of the neurotransmitter
52
Many drugs affect the nervous system
By stimulating receptors that respond to neurotransmitters and can have complex effects on perception, motor control and emotional states
53
Neuromodulators are other chemicals
Released by synaptic terminal
54
Neuromodulators have a similar
Function to neurotransmitters
55
Characteristics of neuromodulators
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
Neuropeptides are
Neuromodulators that bind to receptors and activate enzymes
57
Opioids are
Neuromodulators in the CNS Bind to the same receptors as opium or morphine Relieve pain
58
Four classes of opioids
1. Endorphins 2. Enkephalins 3. Endomorphins 4. Dynorphins
59
How neurotransmitters and neuromodulators work
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
Direct effects because
These neurotransmitters alter ion movement across the membrane, they are said to have ionotropic effects Open/close gated ion channels
61
Indirect effects- G proteins
- 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
Indirect effects- intracellular receptors
Lipid soluble gases (NO, CO) Bind to enzymes in brain cells
63
What is the relationship between myelin and the propagation speed of action potentials?
The presence of myelin greatly increases the propagation speed of action potentials
64
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?
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
Describe the general structure of a synapse?
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
If a synapse involves direct physical contact between cells,
It is termed electrical
67
If the synapse involves a neurotransmitter
It is termed chemical
68
What effect would blocking voltage-gated calcium channels at a cholinergic synapse have on synaptic communication?
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
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?
Because of synaptic delay, the pathway with fewer neurons (in this case, three) will transmit impulses more rapidly
70
Differentiate between a neurotransmitter and a neuromodulators
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
Identify the three functional groups into which neurotransmitters and nueromodulators fall
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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