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Neuroscience > Ch 3. Synapses and Synaptic Transmission > Flashcards

Ch 3. Synapses and Synaptic Transmission Flashcards

1
Q

Where does neural communication occur?

A

at synapses

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2
Q

What can be interfered with in diseases that disrupt synaptic communication?

A

neural function

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3
Q

Where do most drugs that affect the CNS act at?

A

the synapse

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4
Q

What is a synapse?

A

A specialized site where a neuron communicates with another neuron or effector cell

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5
Q

What 2 cells are involved in synapses?

A

presynaptic

postsynaptic

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6
Q

What are presynaptic cells?

A

The neuron conducting the electrical signal toward the synapse

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7
Q

What are presynaptic terminals?

A

Located at the end of the axon of the presynaptic cell

Vesicles containing neurotransmitters are located here

Site of neurotransmitters release

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8
Q

What are postsynaptic cells?

A

The cell which receives the signal from the presynaptic cell

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9
Q

What is a postsynaptic terminal?

A

The membrane region of the postsynaptic cell (the receiving cell) that contains receptors for neurotransmitters

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10
Q

What is the synaptic cleft (gap)?

A

A narrow space filled with interstitial fluid that separates presynaptic cell and postsynaptic cell

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11
Q

What is the neuromuscular junction?

A

A synapse between a neuron and a muscle cell

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12
Q

What is a Neuroglandular Junction?

A

A synapse between a neuron and a gland

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13
Q

What are the steps of events that occur at the synapse?

A
  1. An AP reaches presynaptic terminal
  2. Presynaptic terminal depolarizes causing voltage-gated Ca+ channels in presynaptic terminal to open
  3. Ca+ enter presynaptic terminal
  4. Ca+ triggers movement of synaptic vesicles, containing neurotransmitters, toward a release site in the presynaptic terminal
  5. Synaptic vesicles fuse with presynaptic membrane and release neurotransmitter into the synaptic cleft
  6. The neurotransmitter crosses the synaptic cleft
  7. The neurotransmitter binds to its specific receptor on a membrane protein which contains a chemical-gated ion channel in the postsynaptic membrane
  8. The membrane protein changes shape which will either:
    a. Open the ion channel associated with the membrane protein receptor, or
    b. Activate intracellular messengers associated with the membrane receptor
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14
Q

Does the binding of a neurotransmitter on the Postsynaptic Receptor open an ion channel directly or indirectly?

A

either

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15
Q

What can binding of a neurotransmitter on the Postsynaptic Receptor activate?

A

intracellular messengers associated with

the membrane receptor

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16
Q

What are the types of synapses based on?

A

which parts of the pre- and post-synaptic membrane form the synapse

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17
Q

What is an axodendritic synapse?

A

connection between axon to dendrite

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18
Q

What is an axosomatic synapse?

A

connection between axon to cell body

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19
Q

What is an axoaxonic synapse?

A

connection between axon to axon

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20
Q

How many synaptic inputs can a single neuron have?

A

A single neuron can have multiple synaptic inputs in each region

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21
Q

What 3 things are postsynaptic cells affected by?

A

The total number of action potentials reaching the presynaptic axon terminal

Strength of the stimulus to the presynaptic cell

Duration of the stimulus to the presynaptic cell

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22
Q

What is postsynaptic potential?

A

An electrical change in the postsynaptic membrane

It is a graded, nonpropagated electrical signal

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23
Q

What is postsynaptic potential the result of?

A

Local changes in ion concentration across the postsynaptic membrane

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24
Q

The effect of the stimulus in terms of postsynaptic potential can either do what?

A

Depolarization of the postsynaptic membrane: An Excitatory Postsynaptic Potential (EPSP)

Hyperpolarization of the postsynaptic membrane: An Inhibitory Postsynaptic Potential (IPSP)

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25
Q

Is a neurotransmitter that

depolarizes the Postsynaptic Membrane excitatory or inhibitory?

A

Excitatory because it brings the membrane potential closer to the threshold for generating an action potential

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26
Q

Is a neurotransmitter that

hyperpolarizes the Postsynaptic Membrane excitatory or inhibitory?

A

Inhibitory because it brings the membrane potential away from the threshold for generating an action potential

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27
Q

What is an Inhibitory Postsynaptic Potential (IPSP)?

A

a local neurotransmitter that hyperpolarizes the Postsynaptic Membrane

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28
Q

What is an Excitatory Postsynaptic Potential (EPSP)?

A

a local neurotransmitter that depolarizes the Postsynaptic Membrane

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29
Q

When does an EPSP occur?

A

when neurotransmitters bind to postsynaptic membrane receptors that open chemical-gated ion channels

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30
Q

In an EPSP when a chemical-gated ion channels open what happens next?

A

Leads to an influx of positively charged ions into the cell

This depolarizes the postsynaptic cell membrane

Creates an EPSP

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31
Q

What occurs in a summation of EPSPs vs an individual EPSP?

A

An individual EPSP has only a small effect on membrane potential

Summation of EPSPs can lead to generation of an action potential

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32
Q

When does an IPSP occur?

A

when neurotransmitters bind to postsynaptic membrane receptors that open chemical-gated ion channels

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33
Q

In an IPSP when a chemical-gated ion channels open what happens next?

A

Leads to the flow of Cl– into or K+ out of the postsynaptic membrane

This hyperpolarizes (more negative) the postsynaptic cell membrane and creates an IPSP

This can inhibit the generation of an action potential

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34
Q

What happens if EPSPs coincide with IPSPs?

A

Summation of EPSPs and IPSPs determines whether the postsynaptic membrane is Depolarized (Excited) or
Hyperpolarized (Inhibited)

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35
Q

An AP will occur only when what is sufficient?

A

Only if depolarization is sufficient to reach membrane threshold

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36
Q

What occurs in spatial summation of ESPSs and IPSPs?

A

changes in membrane potential can cancel each other out

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37
Q

What are presynaptic facilitation and inhibition?

A

synaptic mechanisms by which neurons may affect the activity of other neurons

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38
Q

What is the function of presynaptic facilitation and inhibition?

A

Regulate the ability of the presynaptic cell to release neurotransmitters

Can either increase (facilitate) or decrease (inhibit) the rate of neurotransmitter release at the presynaptic membrane

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39
Q

What structures are involved in presynaptic facilitation and inhibition?

A

3 Neurons

An Axoaxonic Synapse

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40
Q

What does an interneuron do?

A

Releases neurotransmitters that bind to receptors on the axon terminal of the presynaptic neuron

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41
Q

What are the two possible actions of the binding of the neurotransmitter released from interneurons?

A

Increase (facilitate) the amount of Ca2+ that enters the presynaptic terminal

Decrease (inhibit) the amount of Ca2+ that enters the presynaptic terminal

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42
Q

When neurotransmitters from interneurons increase the amount of Ca2+ entering the presynaptic terminal what will this lead to?

A

This will lead to an increase in the amount of neurotransmitter that will be released by the presynaptic neuron

Results in increased stimulation (facilitated) of postsynaptic neuron

Increasing both the Degree of Depolarization and Likelihood of an Action Potential

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43
Q

When neurotransmitters from interneurons decrease the amount of Ca2+ entering the presynaptic terminal what will this lead to?

A

This will lead to a decrease in the amount of neurotransmitter that will be released by the presynaptic neuron

Results in decreased stimulation (inhibited) of postsynaptic neuron

Decreasing both the Degree of Depolarization and Likelihood of an Action Potential

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44
Q

What are the steps in Presynaptic Facilitation?

A
  1. AP arrives in interneuron
  2. serotonin release at interneuron
  3. activation of calcium channels at presynaptic terminal
  4. AP arrives at presynaptic terminal
  5. More calcium enters presynaptic terminal
  6. More neurotransmitter released at presynaptic terminal
  7. increased effect on postsynaptic membrane
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45
Q

What are the steps in Presynaptic Inhibition?

A
  1. AP arrives in interneuron
  2. GABA release at interneuron
  3. inactivation of calcium channels at presynaptic terminal
  4. AP arrives at presynaptic terminal
  5. Less calcium enters presynaptic terminal
  6. Less neurotransmitter released at presynaptic terminal
  7. Reduced effect on postsynaptic membrane
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46
Q

What are the four major categories of neurotransmitters?

A

Biogenic amines (monoamines)

Amino acids

Neuropeptides

Dissolved Gases

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47
Q

Name the Biogenic Amines (Monoamines)

A

Catecholamines

  • Epinephrine
  • Norepinephrine
  • Dopamine

Serotonin(5-hydroxytryptamine; 5-HT)

Histamine(Only recognized in the CNS as a neurotransmitter)

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48
Q

Name the Amino Acids

A

Glutamate

Aspartate

GABA

Glycine

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49
Q

Name the Neuropeptides

A

Substance P

OpioidPeptides

  • Endorphins
  • Enkephalins
  • Dynorphin
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50
Q

Name the dissolved gases

A

Carbon Monoxide

Nitric Oxide

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51
Q

Define neurotransmitter

A

chemicals released by synaptic terminals for the purpose of transmitting information from the presynaptic cell to a postsynaptic cell

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52
Q

What is Neurotransmitter Synthesis?

A

Some neurotransmitters are synthesized in the:

  • Neuron cell body and transported to the axon terminal (e.g., neuropeptides such as Substance P)
  • Axon terminal (e.g., ACh)
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53
Q

Where are neurotransmitters released from?

A

the axon terminal of a presynaptic neuron

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54
Q

What happens with neurotransmitters at the postsynaptic cell?

A

Bind onto receptors located on the membrane of a postsynaptic cell to cause a direct response in the postsynaptic cell

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55
Q

An excitatory or inhibitory response by a neurotransmitter on the postsynaptic membrane depends on what?

A

Specific neurotransmitter

Receptor on the postsynaptic membrane

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56
Q

How do neurotransmitters directly affect the postsynaptic cell?

A

By binding to an Ionotropic Receptor and directly activating a membrane channel

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57
Q

How do neurotransmitters indirectly affect the postsynaptic cell?

A

By binding to a Metabotropic Receptor and activating proteins inside the postsynaptic cell that stimulate

  • The opening of a membrane channel or
  • Changes inside the cell
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58
Q

What are Neuromodulators?

A

Signaling compounds that are released from axon terminals and are capable of modulating (enhance or suppress) synaptic transmission by modulating effects of neurotransmitters at the synapse

Can affect the response of a neuron to other neurotransmitters

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59
Q

How do neuromodulators react with presynaptic receptors?

A

They bind to receptors on a presynaptic neuron and can alter the rate of neurotransmitter release by a presynaptic neuron

60
Q

How do neuromodulators react with postsynaptic receptors?

A

They bind to receptors on a postsynaptic neuron and can change the postsynaptic cell’s response to the neurotransmitter

They can producing slower or longer lasting changes in membrane excitability

61
Q

Neuromodulators resulting in either excitatory or inhibitory actions depends on what?

A

the postsynaptic receptor

62
Q

Which major category of neurotransmitters are neuromodulators typically fall into?

A

neuropeptides

63
Q

Can chemicals be both a Neurotransmitter and Neuromodulator?

A

yes

64
Q

How do the effects of neuromodulators compare with those of neurotransmitters?

A

Neuromodulator effects manifest slower than those of neurotransmitters

Neuromodulators effects usually last longer than those of neurotransmitters

65
Q

What is the span of release for Neuromodulators?

A

May be:

  • Local
  • Widespread: Can diffuse throughout an area and act at distance from the site of release so they can affect groups of neurons or effector cells
66
Q

What are Neuropeptides?

A

a distinct class of chemical signaling molecules

67
Q

Where are neuropeptides synthesized and subsequently transported to?

A

synthesized in the neuron cell body and transported to the axon terminal

68
Q

What do neuropeptides function as?

A

Neurotransmitters

Neurohormones (e.g., ADH, Oxytocin)

Neuromodulators

69
Q

Name the 2 neuropeptides

A

Substance P: Acts as a neurotransmitter and neuromodulator

OpioidPeptides

  • Endorphins
  • Enkephalins
  • Dynorphin
70
Q

What is Acetylcholine (ACh)?

A

An excitatory neurotransmitter

71
Q

Where do neurons release Acetylcholine (ACh)?

A

In the Autonomic Nervous System

At the skeletal neuromuscular junction

In the brain

72
Q

What is Glutamate?

A

An excitatory neurotransmitter in the CNS

Important in Learning and Memory

73
Q

What happens if there is excessive release of glutamate and when would this occur?

A

May contribute to neuron death following CNS damage (e.g., stroke)

74
Q

Name the amino acid neurotransmitters

A

Glutamate

Aspartate

GABA

Glycine

75
Q

What is glycine?

A

Mainly acts as an inhibitory neurotransmitter primarily in the Brainstem and Spinal Cord

Inhibits the postsynaptic membrane

76
Q

What is GABA (Gamma-aminobutyric Acid)?

A

The major inhibitory neurotransmitter in the CNS particularly with interneurons in the spinal cord

77
Q

What is GABA essential for?

A

the overall balance between neuronal excitation and inhibition that is vital to normal brain function

78
Q

What are low levels of GABA associated with?

A

seizures

79
Q

Name the catecholamines

A

Epinephrine

Norepinephrine

Dopamine

80
Q

What is dopamine?

A

Usually an inhibitory neurotransmitter

Can be excitatory neurotransmitter

81
Q

Where is dopamine produced?

A

Produced by neurons in the substantia nigra (midbrain)

82
Q

What are the functions of dopamine?

A

Plays an essential role in the control of movement

Cognition

Behavior

Affects the ability to experience pleasure and reward (therefore, affects behavior)

83
Q

What are low levels of dopamine associated with?

A

Depression

Loss of motor control (Parkinson’s Disease)

84
Q

What are elevated levels of dopamine associated with?

A

Schizophrenia

Anxiety

85
Q

Which drugs affect dopamine and how?

A

-cocaine and amphetamines: inhibit the re-uptake ofdopamine into the presynaptic neuron which prolongs dopamine activity, by allowing it to continueto bind and activate receptors-
Leads to the euphoria associated with cocaine use

-Amphetamines: Increase the release of dopamine and block dopamine and NE reuptake

86
Q

What is norepinephrine?

A

Usually an excitatory neurotransmitter

Can be inhibitory neurotransmitter

87
Q

Where is norepinephrine released in the CNS and PNS?

A

CNS

  • Brainstem
  • Thalamus
  • Hypothalamus

PNS

  • Postganglionic Sympathetic Fibers
  • Adrenal Medullae
88
Q

What are the functions of norepinephrine?

A

Involved in the “fight-or-flight” response

Increased arousal and alertness

Increased blood pressure

Increased heart rate

Breakdown of glycogen

89
Q

What are elevated levels of norepinephrine associated with?

A

Fear and panic

Increased sympathetic nervous system activity

Increased panic attacks and stress in individuals with PTSD

90
Q

What are low levels of norepinephrine associated with?

A

Fatigue

Depression

ADHD

Decreased sympathetic nervous system activity

91
Q

Is Serotonin excitatory or inhibitory?

A

Mainly acts as an inhibitory neurotransmitter

92
Q

What is serotonin released by?

A

Neurons in the CNS

Neurons in the enteric nervous system

Enterochromaffin cells of the gastrointestinal mucosa

93
Q

What are the functions of serotonin?

A

Improved Mood

Pain Regulation

Decreased Appetite

Sleep

Inhibits Gastric Acid Secretion

Modulation of GI Motility

94
Q

What are low levels of serotonin associated with?

A

Depression

Suicidal Behavior

95
Q

What are elevated levels of serotonin associated with?

A

Agitation

Rapid Heart Rate

96
Q

What is histamine?

A

A compound released from Mast Cells and Basophils

Recognized as an Excitatory and Inhibitory neurotransmitter only in the CNS

97
Q

Where are histamine released from?

A

from neurons with cell bodies in the hypothalamus

98
Q

What roles do histamine play in the CNS?

A

Learning and Memory

Sleep-wake Cycle

99
Q

Name the neuropeptides

A

Substance P

OpioidPeptides

  • Endorphins
  • Enkephalins
  • Dynorphin
100
Q

What does substance P act as?

A

Acts as a neurotransmitter and neuromodulator

101
Q

What are the functions of Substance P?

A

It enhances the perception of pain

In the brain it acts as a neuromodulator to produces long-duration excitation of postsynaptic cells

Can assist in the immune response

102
Q

What is the mechanism of pain involved with Substance P?

A

Tissue injury causes the release of various inflammatory mediators from the damaged tissue

  • Cytokines
  • Serotonin
  • Prostaglandins
  • Bradykinin
  • H+

These mediators can stimulate nociceptors directly

103
Q

What are nociceptors?

A

The free nerve endings of primary afferent Aδ (A Delta) and C Fibers

104
Q

What happens when nociceptors are stimulated?

A

They transmit an action potential that results in the release of Substance P from the afferent terminal endings of the neuron fibers in the

  • Dorsal Gray Horn
  • Skin
  • Muscle
  • Joints
105
Q

What happens when Nociceptor-related primary afferent fibers synapsing in the dorsal gray horn of the spinal cord
release Substance P?

A

stimulates a 2nd Order Neuron to transmit pain signals upward to the brain

106
Q

What is Peripheral Sensitization?

A

Substance P acts to reduce the activation threshold of nociceptors so less stimulation is required to trigger an action potential

107
Q

What do Endogenous Opioids

act as?

A

Neurotransmitters

Neuromodulators

108
Q

Endogenous Opioids bind to the same receptors as what?

A

exogenous opioid drugs

109
Q

What is the function of endogenous opioids?

A

Inhibit neurons in the CNS that are involved in the perception of pain

Alter the rate of neurotransmitter release by the presynaptic neuron

Change the postsynaptic cell’s response to neurotransmitters

110
Q

What are the 3 main families of endogenous opioids the body synthesizes to help control pain?

A

Endorphins

Enkephalins

Dynorphins

111
Q

What is Nitric Oxide?

A

A lipid-soluble gas that acts as a diffusible neurotransmitter

112
Q

What releases nitric oxide?

A

Released by neurons that innervate smooth muscle of blood vessels in the PNS and Brain

113
Q

What kind of receptor does nitric oxide bind to?

A

Does not require a receptor on the plasma membrane to bind for activation

Diffuses through the plasma membrane and acts on a messenger system in the postsynaptic cell

114
Q

What does nitric oxide cause?

A

vasodilation

115
Q

When neurotransmitters are released into the synaptic cleft what must happen for them to have an effect?

A

Must bind to a specific receptor

116
Q

What determines the effect of the neurotransmitter?

A

Effect is based on the receptor, not the neurotransmitter

There are numerous receptor subtypes for any neurotransmitter

117
Q

Where are neurotransmitter receptors located?

A

Presynaptic Neurons

Postsynaptic Neurons

118
Q

What are Presynaptic Neuron Receptors also known as?

A

autoreceptors

119
Q

What is the function of Presynaptic Neuron Receptors (autoreceptors)?

A

release-regulating receptors that help monitor the amount of neurotransmitter so when its being released, they monitor if there are proper levels in the synapse and when there are enough, they slow process down

120
Q

What are Presynaptic Neuron Receptors (autoreceptors) sensitive to?

A

the neuron’s own Chemical Signaling Molecules (e.g., neurotransmitters, neuromodulators, neurohormones)

121
Q

What do Presynaptic Neuron Receptors (autoreceptors) serve as?

A

A negative feedback mechanism that can inhibit the release of a neuron’s own

  • Neurotransmitter
  • Neurohormone
  • Neuromodulator
122
Q

What are the 2 ways in which Neurotransmitter Postsynaptic Receptors can be classified?

A

Ionotropic Receptors (Ligand-gated Ion Channels)

Metabotropic Receptors (G Protein-Linked Receptors)

123
Q

What do Ionotropic Receptors generally mediate in comparison to Metabotropic Receptors?

A

Ionotropic Receptors generally mediate rapid postsynaptic effects

Metabotropic Receptors typically produce much slower responses

124
Q

What is the receptor coupled with in ionotropic receptors (Ligand-gated Ion Channels)?

A

an ion channel

125
Q

What kind of effect do Neurotransmitters that bind to ionotropic receptors have?

A

Have a direct activation effect on the ion channel

126
Q

What do membrane proteins on ionotropic receptors (Ligand-gated Ion Channels) act as?

A

Receptors (Ionotropic Receptors) and

Direct-acting Ion Channels

127
Q

What are the ligand-gated channels like in the resting state?

A

they are closed which blocks the flow of ions through the channel

128
Q

What happens when a ligand binds to its specific receptor?

A

The ion channel will change shape and open to allow specific ions to pass through the channel (cross the plasma membrane into or out of the cell)

129
Q

How does the process of when a ligand binds to its specific receptor differ for Excitatory Neurotransmitters and Inhibitory Neurotransmitters?

A

The process is the same for both

130
Q

What is the receptor coupled with in Metabotropic receptors (G Protein-Linked Receptors)?

A

The receptor is not coupled to an ion channel

The receptor is coupled to a G-protein

131
Q

What kind of effect do Neurotransmitters that bind to Metabotropic Receptors (G Protein-Linked Receptors) have?

A

indirect activation of ion channels

When a neurotransmitter binds to the receptor the G-protein (an intracellular protein) can indirectly open ion channel

132
Q

What happens when a neurotransmitter (First Messenger) binds to a Metabotropic Receptor (G Protein-Linked Receptor)?

A

activates the G Protein (an intracellular protein)

133
Q

What are the two possible subsequent actions of an activated G protein?

A

Bind to a membrane ion channel causing the channel to open
or

Bind to and activate a membrane enzyme which then, through a series of steps a Second Messenger is formed. 
The a Second Messenger can:
-Activate enzymes
-Inhibit enzymes 
-Activate genes
-Modulate Ca2+ levels in the cell
134
Q

What is the general result of movement of ions across the plasma membrane?

A

Results in a change in the membrane potential

135
Q

What is hyperpolarization?

A

A change in the transmembrane potential toward a more negative value than the resting membrane potential

136
Q

What movements cause hyperpolarization?

A

Positive ions out of the cell

Negative ions into the cell

137
Q

How does hyperpolarization affect neuronal activity?

A

Can cause inhibition of neuronal activity

138
Q

How do EPSPs (excitatory postsynaptic potentials) occur in ionotropic receptors?

A

ion channels open and positive charges enter the postsynaptic neuron, causing an EPSP

139
Q

How do IPSPs (inhibitory postsynaptic potentials) occur in ionotropic receptors?

A

ion channels open and the postsynaptic neuron gains negative charges or loses positive charges, causing an IPSP

140
Q

Describe the Second Messenger System

A
  1. hormone (1st messenger) binds receptor
  2. receptor activates G protein
  3. G protein activates adenylate cyclase (enzyme)
  4. adenylate cyclase converts ATP to cAMP (2nd messenger)
  5. cAMP activates protein kinases
  6. active protein kinase triggers responses of target cell (activates enzymes, stimulates cellular secretion, opens ion channel, etc)
141
Q

Continuous activation or continuous inhibition of cell receptors can affect what?

A

Receptor Sensitivity

  • Receptor Desensitization (Inactivation)
  • Receptor Supersensitivity (Hypersensitivity)

The Number of Cell Receptors

  • Receptor Down-Regulation (Internalization)
  • Receptor Up-Regulation (increase number of receptors)
142
Q

What happens in Receptor Desensitization (Inactivation)?

A

When receptors are continuously stimulated the receptor can become less responsive (desensitized) due to modification of the receptor

The ligand-gated channel can close despite the continued presence of the ligand

143
Q

How long does Receptor Desensitization (Inactivation) last?

A

Usually for just a brief period of time

Return of normal response occurs within a few minutes after the stimulus is removed

144
Q

What is Receptor Supersensitivity (Hypersensitivity)?

A

A prolonged decrease in the stimulation of a receptor

145
Q

What could Receptor Supersensitivity (Hypersensitivity) result in?

A

an increase in receptor sensitivity

Neuroscience (3 decks)

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