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Neurobiology > Neurotransmitters > Flashcards

Neurotransmitters Flashcards

1
Q

What are the 4 points that define a neurotransmitter?

A

Presence: must be produced and stored in the presynaptic terminal

Release: must be released from terminal upon pre-synaptic stimulation

Postsynaptic receptors: receptors that it can bind should be present on the post-synaptic membrane

Inactivation

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2
Q

Can you outline the steps from Neurotransmitter production and release beginning with synthesis?

A

Presynaptic:

  • Synthesis of NT
  • Storage
  • Release of NT

Post-synaptic:

  • NT interacts with receptor on post-synaptic membrane
  • Removal of NT from synapse
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3
Q

Synthesis: Small-Molecule Neurotransmitters

A
  • Small molecule NT are synthesized in the presynaptic terminal
  • Enzymes to produce the NT are made in the cell body and transported down to the axon (slow)
  • Precursors for NT are taken up in the terminal
  • Occurs with small, clear vesicles
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4
Q
A
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5
Q

Synthesis: Neuropeptides

A

Synthesized on the rough ER located in the cell body

Precursor peptides are packaged in vesicle then transported by terminals via fast axonal transport

Mature peptides are synthesized by enzymes at the axon terminal–> cleave off into the active peptide portions

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6
Q

Storage: Types of Vesicles

A

Small Synaptic Vesicles:

  • Classical NT’s
  • Ach, Glutamate, GABA, Glycine

Large Dense Core Vessicles:

  • Neuropeptides (generally)
  • Dopamine, Norepinephrine
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7
Q

T of F: A single neuron can have both large dense core vesicles and small synaptic vesicles in the same neuron

A

True

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8
Q

Outline of NT production and release

A
  1. Synthesis and storage of NT
  2. AP arrives in terminal–> NA+ ion channels let Na+ in–> membrane potential changes
  3. Voltage gated CA2+ channels open–> allows Ca2+ inside–> mobilization of vesicles
  4. Increase of Ca2+ triggers the fusion of vesicles with presynaptic membrane
  5. NT released via exocytosis across synaptic cleft
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9
Q

Compare and contrast synthesis and storage of small molecule neurotransmitters and neuropeptides.

A

Neuropeptides:

  • Synthesized on the rough ER located in the cell body
  • Precursor peptides are packaged in vesicle then transported by terminals via fast axonal transport
  • Mature peptides are synthesized by enzymes at the axon terminal–> cleave off into the active peptide portions

Small molecule NT:

  • Small molecule NT are synthesized in the presynaptic terminal
  • Enzymes to produce the NT are made in the cell body and transported down to the axon (slow)
  • Precursors for NT are taken up in the terminal
  • Occurs with small, clear vesicles
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10
Q

What are the two types of storage vesicles?

A

Small synaptic vesicles

  • Ach, glutamate, GABA, glycine

Large dense core vesicles

  • Neuropeptides, dopamine, NE

BOTH can be found in the same cell, AP determines if one or both are released

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11
Q

Release of Vesicles:

How do the vesicles differ with respect to the mechanism which stimulates them to dump their product?

A

Small Vesicles:

  • Released with low stimulation
  • Local increases in Ca2+ cause them to be released
  • Preferential release due to low-frequency stimulation

Dense core vesicles:

  • Released with high-frequency stimulation
  • Dependent on general calcium levels
  • High would ultimately cause the release of both

Large amount of Ca2+ = both vesicles released

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12
Q

Name 2 different types of receptors on the post synaptic membrane that a NT could bind to cause an effect.

How do they differ?

A

Ionotropic Receptors:

  • Very fast
  • Each receptor (multiple subunits) contains an ion channel @ center
  • At rest= channel is closed
  • NT binds = channel opens
  • When the ligand leaves, the channel quickly closes

Metabotropic Receptors:

  • Works more slowly than ionotropic receptors
  • Long lasting
  • DO NOT possess a channel or pore
  • Have an NT binding site
  • Causes a G-protein to be activated which signals a cascade, opening an ion channel or a second messenger
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13
Q

What are 3 ways that a neurotransmitter can be removed from a synapse?

A

Glial cells: Can reuptake the NT via transporters

Enzymatic degradation = in synapse & presynaptic terminal

(Binds to receptors, falls off and enzymes work to degrade the NT so the effect is not long lasting)

Pre-synaptic reuptake by transporters

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14
Q

How Is acetylcholine made?

What 2 components are used?

A

Amine– but not derived from an amino acid

Synthesis: Choline + Acetyl coA

Effect on Postsynaptic Cell:

  • Found in neuromuscular junctions so ALWAYS excitatory

Ionotropic Receptors: Nicotinic are found in muscle (specifically skeleton)

Muscarinic: Found in the heart, smooth muscles of the brain

Brain- binds to metabotropic receptors in CNS

PNS: binds to ionotropic receptor

Removal: degradation by enzymes

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15
Q

For all 3 of these catecholamine neurotransmitters, name the two ways by which they are recycled (broadly speaking, not all the details, they are taken up by _____ and by ______)

A

Norepinephrine, dopamine, epinephrine

Synthesis requires tyrosine (rate limiting step is the supply of tyrosine and tyrosine hydroxylase to create the precursor for the NT)

Removal Is done by two enzymes (COMT, MAO)

COMT: Catechol-O-Methyltransferase

MAO: Monamine oxidase

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16
Q

Norepinephrine

A

Synthesis:

Tyrosine hydroxylase pre-cursor –> Dopamine–>

Dopa decarboxylase–> Dopamine–>

Dopamine beta-hydroxylase–> NE

Effects on postsynaptic cell: EPSP

Acts on metabotropic receptors (G-protein coupled)

Removal:

  1. Re-uptake via NET transporter
  2. Reuptake into presynaptic cell or surrounding glial cells via NET transporter
  3. Degraded by momoamine oxidase (MAO) or COMT inside cell –> repackaged into synaptic vesicles

Then diffusion into vascular system around neuron

17
Q

Dopamine:

A

Synthesis:

Tyrosine hydroxylase pre-cursor –> Dopamine

Dopa Decarboxylase –> Dopamine

Effects on postsynaptic cell: EPSP

Acts on metabotropic receptors (G-protein coupled)

Removal:

  1. Re-uptake via DAT transporter
  2. Reuptake into presynaptic cell or surrounding glial cells via NET transporter
  3. Degraded by momoamine oxidase (MAO) or COMT inside cell –> repackaged into synaptic vesicles

Then diffusion into vascular system around neuron

18
Q

Name 2 Amino acid neurotransmitters.

What is their general removal mechanism?

What is that?

How does that relate to action potentials?

A

Glutamate:

  • Primary excitatory AA NT in CNS
  • Found widely in CNS
  • Synthesized from glutamine
  • Major excitatory, binding to at least 4 receptors (metabotropic/ionotropic)
  • Uptake by glia and the presynaptic terminal
  • Reconverted to glutamine
  • Returned to Neuron
19
Q

Name 2 Amino acid neurotransmitters.

What is their general removal mechanism?

What is that?

How does that relate to action potentials?

A

GABA = hyperpolarization of post-synaptic cell

  • Primary inhibitory NT of CNS- shuts things down
  • Synthesized from glucose
  • Converted to glutamate
  • Widely distributed
  • Removal is take up by glia OR degraded by enzymes

AP Relationship: Generates IPSPs in the post-synaptic cell

Fast chemical synaptic transmission:

  • GABAa receptor is ionotropic (ligand-gated)
  • Cl- channel, leading to a hyperpolarization of the post-synaptic cell
  • Chlorine enters the cell

Slow chemical synaptic transmission:

  • GABAb receptor, g-protein receptor linked to K+ channels (no second messenger involvement)
  • Increases K+ conductance and hyper polarizes the post-synaptic cell
20
Q

Where are neuropeptides synthesized?

A

Rough ER

21
Q

Maturation of Neuropeptides

A

Occurs after packing into vesicles

22
Q

T or F:

Multiple types of neuropeptides are released by a single vesicle

A

True

Can also be released by the same neuron with small molecule NT’s

Can act like hormones- released- drift into bloodstream- can effect a post-synaptic neuron far away

Initiate their effects by binding metabotropic receptors

Removal: broken down into AA’s by peptidases

Need relatively low concentrations to act on receptor

23
Q

Small clear vesicles can be released by:

A. Relatively high levels of Ca2+

B. Relatively low levels of Ca2+

C. Inhibitory NT’s

D. Excitatory NT’s

A

Both:

A. Relatively high levels of Ca2+

B. Relatively low levels of Ca2+ (localizaed)

24
Q

After a NT is released it:

A. Can be recycled by the glial cells

B. Can be removed by diffusion

C. Can be removed by enzymes

D. All of the above

E. A & C are correct

A

A. Can be recycled by the glial cells

B. Can be removed by diffusion

C. Can be removed by enzymes

25
Q

T or F: Acetylcholine always acts rapidly

A

False- can act on ionotropic and metabotropic receptors

Acts rapidly in the muscle- ionotropic nicotinic receptors

26
Q

Mature neuropeptides are made:

A. from precursors that are taken into the terminal

B. In the cell body

C. In the vesicles at the neuron terminal

D. In the axons of the neuron

A

C. In the vesicles at the neuron terminal

27
Q

When an NT binds to a metabotropic receptor:

A. The receptor is found on an ion channel that immediately opens

B. The response of the receptor is relatively fast

C. The receptor activates 2nd messenger cascade to open an ion channel

D. It always causes an IPSP or inhibitory response

A

C. The receptor activates 2nd messenger cascade to open an ion channel

Neurobiology (7 decks)

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