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Neuro Science > Synaptic Transmission & Neurotransmitters > Flashcards

Synaptic Transmission & Neurotransmitters Flashcards

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1
Q

Axodendritic synapse

A

between the axon of a presynaptic neuron and a dendrite of a postsynaptic cell

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2
Q

Axosomatic synapse

A

between the axon of a presynaptic neuron and the cell body of a postsynaptic cell

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3
Q

Axoaxonic synapse

A

between the axon of a presynaptic neuron and the axon of a postsynaptic cell

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4
Q

Electrical potentials at synapses

A
  • If the synapse is neuromuscular, axosomatic, or axodendritic, the flux of ions in the postsynaptic membrane generates a local postsynaptic potential.
  • Axoaxonic synapse modulates the membrane potential of the postsynaptic cell (Presynaptic facilitation and inhibition)
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5
Q

Presynaptic Inhibition and Facilitation

A
  • release of neurotransmitters from an axon terminal can be facilitated or inhibited by the chemical action at an axoaxonic synapse
  • Axoaxonic synapses mediate presynaptic inhibition and facilitation
  • Interneurons (as axoaxonic) regulate the ability of the presynaptic neurons to release neurotransmitters by changing the amount of Ca++ influx to the presynaptic neurons
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6
Q

Interneurons can…

A
  • hyperpolarize or depolarize the presynaptic neurons
  • This changes the amount of Ca influx to the presynaptic neurons.
  • As a result, the ability of the presynaptic neurons to release neurotransmitters is modified.
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7
Q

Presynaptic Inhibition

A
  1. Interneuron releases neurotransmitters
  2. Neurotransmitters bind to presynaptic neuron, reduce Ca++ influx
  3. Presynaptic neuron releases less neurotransmitters when an AP arrives at its terminal

interneuron -> presynaptic neuron -> postsynaptic neuron

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8
Q

Presynaptic Facilitation

A
  1. Interneuron releases neurotransmitters
  2. Neurotransmitters bind to presynaptic neuron, increase Ca++ influx
  3. Presynaptic neuron releases more neurotransmitters when an action potential arrives

interneuron -> presynaptic neuron -> postsynaptic neuron

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9
Q

What is a Neurotransmitter?

A
  • synthesized in the neuron
  • transported to the presynaptic terminal
  • released in amounts sufficient to exert an action on the postsynaptic neuron or effector organ
  • removed from the synaptic cleft by a specific mechanism
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10
Q

Function of neurotransmitters

A
  • excite or inhibit the postsynaptic neuron, depending on the molecule released & the receptors present on the postsynaptic membrane
  • those that act directly are classified as fast acting, because their effects are extremely short
  • those that act indirectly are classified as slow-acting, because their transmission requires 100 milliseconds to minutes
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11
Q

Direct activation of ion channels: ligand-gated ion channels

A
  • Neurotransmitters bind to receptors that are part of the ligand-gated ion channels and directly open the ion channels.
  • Ex: Na influx
  • Fast acting
  • Rapid/brief opening of membrane channels occurs when a neurotransmitter binds to the receptor site of the membrane channel
  • Ion channel receptors act like a lock & key
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12
Q

Indirect activation of ion channels: G-proteins

A
  • Neurotransmitters bind to receptors that are separated from the ion channels, & indirectly open the ion channels by activating the G-protein.
  • involves changes in the metabolism of the cell.
  • Slow acting
  • activation of the G-protein elicits cellular events that develop slowly and last longer than the effects of ligand-gated channels
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13
Q

G-protein

A

can also cause persistent opening of membrane channels

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14
Q

What is a Neuromodulator?

A
  • Act at a distance away from the synapse
  • Modulate activity of many neurons at the same time
  • Released into extracellular fluid
  • Effects last minutes to days
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15
Q

Co-transmission of a neurotransmitter and a neuromodulator

A

Depolarization of the presynaptic terminal membrane -> events that result in the simultaneous release of neuromodulator (substance P) into the extracellular space & neurotransmitter (Glutamate) into the synaptic cleft

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16
Q

Neurotransmitters and Neuromodulators can be released…

A

at the same time

17
Q

Medications/Drugs

A

When administered “exogenously” in reasonable concentration, medications mimic the action of the endogenously released neurotransmitters or neuromodulators exactly

18
Q

Category: Amino Acid
Transmitter:
y-aminobutryric acid (GABA)
Glutamate (Glu)

A

The most prevalent fast-acting neurotransmitters are Glutamate (excitatory) and GABA (inhibitory).
(ligand-gated ion channels)

19
Q

Amino acid: Glutamate (Glu)

A
  • MAJOR Fast-acting excitatory neurotransmitter found in the CNS
  • Involved in learning and memory
  • Glutamate is present in a wide variety of foods, e.g. MSG
  • Over-activity of glutamate may cause seizures
  • Excitotoxicity: Excessive glutamate may produce neuronal damage or death, e.g. TBI or CVA
20
Q

Amino acid: GABA

A
  • MAJOR Fast-acting inhibitory neurotransmitter found in the CNS (e.g. inhibitory interneurons in spinal cord)
  • Prevents excessive neural activity.
  • Barbiturates mimics the action of GABA and are used for sedation or anticonvulsants.
  • Baclofen, a muscle relaxant to control muscle spasticity, increases presynaptic release of GABA.
21
Q

Cholinergic: Acetylcholine (ACh)

A
  • MAJOR neurotransmitter in PNS, ANS, CNS
  • Fast-acting effect: act at neuromuscular junction: Nicotinic receptors
  • Slow-acting effect: regulate HR, ANS: Muscarinic receptors
  • ACh has excitatory actions at the neuromuscular junction, at autonomic ganglion, at certain glandular tissues, and in the CNS.
  • It has inhibitory actions at certain smooth muscles and at cardiac muscle
22
Q

ACh receptors

A

-The structural difference between the nicotinic and muscarinic receptors

23
Q

Nicotinic receptor

A

activation causes the opening of the postsynaptic receptor channel.
This increases the Na+ movement into the target cell, leading to depolarization and generation of the action potential (EPSP).

24
Q

Muscarinic receptor

A

activation of postsynaptic cells can be either excitatory or inhibitory & is always slow in onset and long in duration

25
Q

Nicotinic (summarized)

A
  • Bind nicotine
  • Linked to ion channels
  • Fast and brief response
  • Located at neuromuscular junctions, autonomic ganglia, and some CNS
  • Mediate excitation
26
Q

Muscarinic (summarized)

A
  • Bind muscarine
  • Liked to 2nd messenger system through G protein
  • Slow and prolonged response
  • Found on myocardial muscle, certain smooth muscle, in some CNS regions
  • Mediate inhibition and excitation
27
Q

Acetylcholine (ACh) functions as….

A

-a neuromodulator in CNS
–Controls…
Locomotion
Arousal
–Facilitate attention, memory, learning

28
Q

Amines: Dopamine (DA)

A
  • Produced in substantia nigra pars compacta of basal ganglia
  • Primarily an inhibitory effect in the CNS
  • All DA receptors are 2nd messenger systems to suppress the activity of Ca++ channels.
  • Affects motor activity, motivation/reward behavior, and cognition
29
Q

Dopamine Projecting System

A
  • BG: movement
  • Limbic: reward/wanting addiction
  • Prefrontal: working memeory and attention
30
Q

Neurologic Conditions: Dopamine

A
  • PD:↓DA in basal ganglia
  • Lack of motivated behaviors
  • Depression/cognitive: ↓DA in forebrain
  • Schizophrenia: too much DA
  • Drug addiction: block the DA reuptake into the presynaptic neurons, allowing DA to activate receptors repetitively
31
Q

Schizophrenia

A
  • Pts w/ schizophrenia exhibit a variety of abnormalities of thought including delusions, hallucinations, disorganized, tangential speech; flat affect, & occasionally, a profound decrease in spontaneous activity called catatonia.
  • Cognition, particularly working memory, is also often affected.
  • Abnormalities in the limbic system, frontal lobes, and BG
  • symptoms improve with antidopaminergic agents
32
Q

Peptides: Substance P

A

-Neuromodulator
-Neuromodulator function in chronic pain syndrome
–increase pain perception
-Also released from some of the presynaptic sensory neurons
-Neurotransmitter function in the nociceptive pathway
stimulates free nerve endings at the site of injury & transmit pain signals from the periphery to the CNS

33
Q

Peptides: Endogenous opioids (endorphin, enkephalin, dynorphin)

A
  • Body’s natural pain killers
  • Inhibit CNS neurons involved in the perception of pain
  • Exercise increases endogenous opioids

Neuro Science (10 decks)

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