Physiology > Module 12: Synapses > Flashcards

Module 12: Synapses Flashcards

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1
Q

Synapse

A

Junction between two neurons or neuron & effector: axon terminal (synaptic knobs; synaptic terminals) of neuron almost touch cell membrane of the next cell

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2
Q

Function of Synapses

A

Sites of neuron communication; new synapse formation occurs in the cerebral cortex during the process of learning, so new synapse ≈ memory

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3
Q

Electrical Synapse

A

Gap junctions (connexons) between neurons allow direct ICF to ICF communication

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4
Q

Characteristics of Electrical Synapse

A

Rapid transmission, direct current flow; common in embryo, relatively rare in adults

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5
Q

Chemical Synapse

A

Most common type of synapse; includes true synapse (neuron/neuron), neuroeffector, neuromuscular, and neuroglandular junctions.

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6
Q

True Synapse

A

Type of chemical synapse between neurons

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7
Q

Neuromuscular Junction (NMJ)

A

Type of neuroeffector junction between neuron and muscle fiber

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8
Q

Neuroglandular Junction

A

Type of junction between neuron and gland

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9
Q

Axon terminal

A

Swelling at the end of an axon

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10
Q

Synaptic vesicles

A

Membrane-bounds sacs within the axon terminal which contain neurotransmitters

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11
Q

Presynaptic neuron

A

Sends impulse across synapse (pitcher); stores neurotransmitter and releases a neurotransmitter (NT, the ball)

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12
Q

Postsynaptic neuron

A

Receives NT from synapse (catcher)

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13
Q

Transmission across the chemical synapse goes in which direction?

A

unidirectional; one-way

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14
Q

What is a synaptic cleft?

A

the space between two neurons or between a neuron and a muscle or gland cell, where neurotransmitters are released.

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15
Q

Why can’t action potentials jump across the synaptic cleft?

A

they are electrical signals that require a direct connection; instead, chemical messengers (neurotransmitters) bridge the gap.

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16
Q

What happens when an action potential reaches the axon terminal of a presynaptic neuron?

A

it opens voltage-gated calcium (Ca²⁺) channels, allowing calcium ions to enter the neuron.

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17
Q

What is the role of calcium ions in neurotransmitter release?

A

Calcium ions (Ca²⁺) entering the presynaptic neuron trigger exocytosis, leading to the release of neurotransmitters into the synaptic cleft.

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18
Q

What are some examples of neurotransmitters?

A

acetylcholine (ACh), GABA, epinephrine, and norepinephrine.

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19
Q

What occurs after neurotransmitters diffuse across the synaptic cleft?

A

They bind to receptors on the postsynaptic neuron, leading to a response in that neuron.

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20
Q

What happens when a neurotransmitter binds to protein receptors on the postsynaptic neuron?

A

It often opens ligand-gated ion channels, causing graded membrane potential.

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21
Q

fast ionotropic receptor

A

The name for a ligand-gated ion channel

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22
Q

What is an EPSP?

A

Excitatory postsynaptic potential; it occurs when a neurotransmitter binds to a ligand-gated Na+ channel, causing depolarization and excitation of the postsynaptic neuron.

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23
Q

What is the result if an EPSP reaches the threshold?

A

It will cause an action potential (AP) if threshold is reached

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24
Q

What is an IPSP?

A

Inhibitory postsynaptic potential; it occurs when a neurotransmitter binds to a ligand-gated K+ channel, resulting in hyperpolarization and inhibition of the postsynaptic neuron.

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25
What alternative channel can some inhibitory synapses use instead of K+ channels?
Chloride (Cl-) channels.
26
How is epilepsy related to neurotransmitter function?
Epilepsy is a condition where neurons fire action potentials abnormally and inappropriately; it is often treated with drugs that hyperpolarize neurons.
27
What is the difference between ionotropic and metabotropic receptors?
Ionotropic receptors are fast and directly open ion channels, while metabotropic receptors are slower and use G-protein receptors to indirectly cause ion channel opening, which can lead to depolarization or hyperpolarization of the cell.
28
What is the effect of a neurotransmitter binding to a ligand-gated K+ channel?
It causes hyperpolarization and inhibition of the postsynaptic neuron.
29
What is the role of ligand-gated ion channels in synaptic transmission?
They facilitate the rapid changes in membrane potential in response to neurotransmitter binding.
30
What is the clinical significance of hyperpolarizing drugs in treating epilepsy?
They help to stabilize neuronal firing and prevent abnormal action potentials.
31
Common mechanisms of removing neurotransmitters (4)
diffuses away, reuptake, enzyme breakdown, astrocytes
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NT Diffusion
A mechanism of removing neurotransmitters where NT diffuses away from the synapse.
33
What is reuptake and what NT's is this most common for?
The whole NT is taken back into the axon terminal of the presynaptic cell; common for dopamine, serotonin, norepinephrine at many synapses.
34
NT Enzymatic Breakdown
A mechanism where an enzyme breaks down the neurotransmitter; sometimes the breakdown product is reuptaken into the presynaptic cell.
35
Acetylcholinesterase
An enzyme that degrades acetylcholine at many synapses.
36
Monoamine Oxidase
An enzyme that degrades norepinephrine (NE), epinephrine (E), and dopamine at some synapses.
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Astrocytes
Glial cells that remove neurotransmitter from the synaptic cleft.
38
Neural Integration
The brain's process of combining sensory input to coordinate responses
39
What are the three neural integration principles?
Convergence, divergence, and 'all-or-none' principle.
40
Convergence
Multiple presynaptic cells communicating with one postsynaptic cell; allows many sources to influence a cell's activity.
41
Divergence
A single presynaptic cell communicating with multiple postsynaptic cells; allows information source to affect lots of other cells.
42
All or none principle
The axon hillock of the post-synaptic cell sums (integrates) all of the inhibitory and excitatory impulses. If threshold is achieved, an AP follows. If not, no AP follows.
43
When do new synapses form?
during sleep
44
What are the two types of summation?
temporal and spatial
45
What is summation in the context of postsynaptic activation?
Summation refers to the process where multiple action potentials (APs) in the presynaptic neuron are required to release enough neurotransmitter to open enough chemical-gated Na+ channels to reach threshold in the postsynaptic neuron.
46
What is the typical synaptic delay time?
The synaptic delay typically ranges from 0.2 to 5.0 milliseconds.
47
What is temporal summation?
the postsynaptic cell is stimulated again before the first EPSP has died away, adding to the number of open ion channels and bringing the cell closer to threshold.
48
What is spatial summation?
Stimulation of the postsynaptic cell simultaneously with two EPSPs from two different excitatory synapses, requiring convergence.
49
How can drugs modify synaptic transmission?
interfering with the synthesis/release of neurotransmitters, their removal or binding to receptors.
50
What are MAOIs, SSRIs, and SNRIs?
types of drugs that interfere with the removal of neurotransmitters.
51
What is the role of agonist drugs?
produce a response similar to the normal activation of the receptor; for example, nicotine is an acetylcholine agonist.
52
What is the function of antagonist drugs?
the drug occupies the receptor without activating a normal response; examples include caffeine and tetrodotoxin from pufferfish.
53
What are neurotransmitters?
Chemicals (ligands) used for communication within the nervous system
54
How many neurotransmitters have been identified?
Approximately 60 neurotransmitters.
55
What is the molecular weight characteristic of most neurotransmitters?
Most are small (low molecular weight).
56
How do neurotransmitters act?
They are fast-acting and bind to receptors to start EPSP (excitatory) or IPSP (inhibitory) responses.
57
What determines the response to a neurotransmitter?
The response is tissue-specific and dependent on the receptor.
58
How are neurotransmitters and receptors often discovered?
The impact of a drug is often known before the receptor or the neurotransmitter is discovered.
59
What is an example of a drug that was used before its receptor was identified?
Opium was used for thousands of years before opioid receptors or endorphins were understood.
60
How are receptors named?
Receptors can be named after the drug (e.g., opioid receptors) or the endogenous chemical (e.g., GABA-ergic receptors).
61
What is the relationship between GABA and its receptors?
GABA binds to GABA-ergic receptors, which also bind to some anti-anxiety drugs.
62
What types of potentials can neurotransmitters cause?
They can cause excitatory postsynaptic potentials (EPSP) or inhibitory postsynaptic potentials (IPSP).
63
What is the significance of receptor subtypes in neurotransmitter action?
Neurotransmitters often have more than one receptor subtype, affecting their action.
64
What is the role of endogenous chemicals in receptor binding?
Endogenous chemicals bind to receptors that may also bind to exogenous drugs.
65
What determines the response to a neurotransmitter in signal transduction pathways?
The receptors present on the target cell.
66
What type of chemical messengers activate intracellular signal transduction pathways?
Lipid-soluble chemical messengers.
67
What is the general process for lipid-soluble chemical messengers?
Gene activation.
68
What forms when a lipid-soluble chemical messenger binds to a receptor in the cytoplasm?
A ligand-receptor complex.
69
What is the end result of the ligand-receptor complex interacting with DNA?
Activation of transcription and translation of specific genes.
70
Name two examples of lipid-soluble hormones that bind to intracellular receptors.
Cortisol and estrogen.
71
What initiates signal transduction pathways for water-soluble chemical messengers?
Binding to cell membrane receptors.
72
What happens when a chemical messenger binds to ion channel receptors?
Ion channels open or close, causing a graded membrane potential.
73
What type of receptors respond to acetylcholine and are important in learning and memory?
Nicotinic cholinergic receptors.
74
Receptors that also function as enzymes
tyrosine kinase receptor
75
What is the function of tyrosine kinase receptors?
A ligand binds to a cell membrane receptor, which releases a phosphate group to a cellular protein, activating or deactivating its activity.
76
Janus kinases
intracellular tyrosine kinases that act as signal transmitter, starting the synthesis of new proteins.
77
What do G-protein coupled receptors activate?
ion channels or enzymes in the plasma membrane.
78
What is the physiological change in the cell after signal transduction? (5)
Activation of transcription, enzyme activation, secretion, cell division, or changes in membrane polarization.
79
What initiates a nerve impulse?
A local or graded potential triggered by various stimuli.
80
What occurs if a depolarizing graded potential reaches threshold?
An action potential is produced.
81
How is the magnitude of the initial stimulus conveyed to the CNS?
By the frequency of action potentials sent to the brain.
82
What is adaptation in the context of action potentials?
A decrease in the frequency of action potentials in response to a constant stimulus.
83
How do males and females differ in their capacities for adaptation?
They differ in their capacities for adaptation/accommodation to stimuli.
84
Define the receptors, function, removal, chemical class, and drugs/disorders for cholinergic neurotransmitters.
Receptors: cholinergic - nicotinic and muscarinic Function: CNS learning/ PNS moving Removal: acetylcholinesterase enzyme Chemical class: choline derivative Drugs/disorders: nicotine, curare, alzheimer's
85
Define the receptors, function, removal, chemical class, and drugs/disorders for dopaminergic neurotransmitters.
Terminology: dopaminergic Receptors: dopaminergic (D1 & D2)Function: seeking/ reward pathway Removal: reuptake or monoamine oxidase enzyme Chemical class: biogenic amine /catecholamine Drugs/disorders: addiction, Parkinson's, schizophrenia
86
Define the receptors, function, removal, chemical class, and drugs/disorders for adrenergic neurotransmitters.
Receptors: adrenergic (α, β) Function: CNS attention, PNS sympathetic NS Removal: reuptake or monoamine oxidase enzyme Chemical class: biogenic amine /catecholamine Drugs/disorders: Wellbutrin, amphetamines, ADHD
87
Define the receptors, function, removal, chemical class, and drugs/disorders for serotoninergic/5HT-ergic neurotransmitters.
Receptors: serotoninergic or 5HT-ergic Function: liking, impacts entire brain Removal: reuptake Chemical class: biogenic amine NOT catecholamine Drugs/disorders: depression, anxiety, SSRI antidepressants, hallucinogens
88
Define the receptors, function, removal, chemical class, and drugs/disorders for glutamatergic neurotransmitters.
Receptors: NMDA receptors Function: neuroplasticity Chemical class: amino acids Drugs/disorders: ADHD, PCP, ketamine
89
Define the receptors, function, removal, chemical class, and drugs/disorders for GABA-ergic neurotransmitters.
Receptors: GABA-ergic Function: anti-anxiety, chilling Chemical class: amino acids Drugs/disorders: alcohol, benzodiazepines
90
Define the receptors, function, removal, chemical class, and drugs/disorders for opioids/opiates neurotransmitters.
Receptors: opioid (Δ, Κ, μ) Function: reduce pain transmission Chemical class: neuropeptides Drugs/disorders: opioid medications and opioid addictions
91
Define the receptors, function, chemical class, and drugs/disorders for cannabinoid neurotransmitters.
Receptors: cannabinoid receptors (CB1 and CB2), Function: pain signaling; memory, eating sleeping, pleasure and food rewarding Chemical class: endocannabinoidsDrugs/disorders: THC, CBD
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