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Physiology > Neurons in Synapses > Flashcards

Neurons in Synapses Flashcards

1
Q

Synapses:

A

Cellular junction where info is transmitted from one neuron to another

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2
Q

Types of synapses:

A
  • electrical

- chemical

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3
Q

Electrical synapses:

A
  • ions passed directly from one cell to another through gap junctions (in heart tissue and smooth muscle)
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4
Q

Chemical synapses:

A
  • majority of synapses in body
  • has two cells (pre and post cells)
  • also has synaptic cleft w/ ICF between cells
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5
Q

Axondendritic area:

A

dendrite and axon terminal

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6
Q

Synaptic transmission:

A

passage of info at synapse

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7
Q

Axosomatic area:

A

soma and axon terminal

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8
Q

Axoaxonic area:

A

axon and axon terminal

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9
Q

Neuromuscular junction (NMJ):

A

skeletal muscle and axon terminal

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10
Q

Synapse en passant area:

A

smooth muscle and axon terminal

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11
Q

Step 1 in mechanism of signal transmission at chemical signal at presynaptic neuron: terminal ends of axons enlarged

A
  • has neurotransmitter in membrane bound vesicles

- vesicle has set # of neurotransmitters

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12
Q

Step 2 in mechanism of signal transmission at chemical signal at presynaptic neuron: depolarization of axon

A
  • leads to depolarization of axon terminal

- VG Ca2+ channels open

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13
Q

Step 3 in mechanism of signal transmission at chemical signal at presynaptic neuron: Ca2+ enters from ISF down electrochemical gradient

A
  • increase of [Ca2+] inside cell
  • helps fuse vesicle to presynaptic membrane, which leads to exocytosis of neurotransmitters
  • # of vesicles released is directly proportionate to ICF [Ca2+]
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14
Q

Step 4 in mechanism of signal transmission at chemical signal at presynaptic neuron: end of conduction of impulses

A
  • free intracellular Ca2+ removed from axon terminal by Na+/Ca2+ antiporter pumps
  • Na+/K+ ATPase restores membrane potential
  • neurotransmitters in cleft are removed and broken down on post synaptic membrane by catabolic enzymes
  • reuptake pumps: in presynaptic membrane and recycle/degrade neurotransmitters
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15
Q

Monoamine oxidase (MAO):

A

breaks down norepinephrine

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16
Q

For CNS, glial cells…

A

reuptake and breakdown neurotransmitters

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17
Q

Mechanism of signal transmission at chemical signal at synaptic cleft

A
  • physical gap
  • has ISF
  • neurotransmitter diffuses across b/c of large [ ] diffused from release site to receptor site
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18
Q

Synaptic delay:

A

time required to diffuse across cleft

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19
Q

Step 1 in mechanism of signal transmission at chemical signal at post synaptic membrane: neurotransmitters bind to receptor

A
  • on neuron/effector tissues
  • receptor changes shape and activates coupling mechanism
  • activation leads to message to the rest of the post synaptic cell
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20
Q

Active region on membrane has receptors that are:

A

specific for neurotransmitters

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21
Q

Step 2 in mechanism of signal transmission at chemical signal at post synaptic membrane: signal transduction pathway

A
  • temporarily opens ion channels directly/indirectly

- ions will leave/enter cell, just depends on which channels are open and the electrochemical gradient

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22
Q

Step 3 in mechanism of signal transmission at chemical signal at post synaptic membrane: activation of _____ and _____

A

cAMP and cGMP

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23
Q

Step 4 in mechanism of signal transmission at chemical signal at post synaptic membrane: activation of one or more ______

A

intracellular enzymes

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24
Q

Step 5 in mechanism of signal transmission at chemical signal at post synaptic membrane: activation of gene _______

A

transcription

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25
Q

Neurons have post synaptic potential:

A
  • ionic flow that creates localized voltage change
  • magnitude is based on # of ion channels opened
  • are graded and nonpropagated, which causes ion current to flow toward axon hillock
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26
Q

Unitary post synaptic potential:

A
  • in neuron
  • one vesicle causes flow of current
  • not enough to make AP in post synaptic neuron
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27
Q

Excitatory post synaptic potential (EPSP):

A
  • in neurons
  • occurs with increased influx of positive ions (Na+)
  • depolarizes membrane, which increases the chances of AP
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28
Q

Inhibitory post synaptic potential (IPSP):

A
  • in neurons
  • two ways: by increasing efflux of positive ions or by increasing influx of negative ions
  • hyperpolarizes membrane, which lowers the chances of AP
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29
Q

T/F: at skeletal muscle junction (NMJ), each axon terminal synapses with multiple skeletal muscles

A

F, they only synapse with one skeletal muscle

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30
Q

NMJ has end plate potential (EPP):

A
  • is excitatory post synaptic potential
  • single release of neurotransmitter makes large EPP
  • depolarizes sarcalemma above AP threshold
  • will produce spike potential to create contraction
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31
Q

Function of catabolic enzymes

A
  • inactivates/breaksdown neurotransmitters
  • are on surface of post synaptic membrane (ACHE, COMT), pre synaptic membrane (MAO), and glial cells (glutamate to glutamine)
  • prevents continual stimulation of post synaptic cell
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32
Q

Types of coupling mechanisms on post synaptic cell:

A
  • can affect speed of transmission
  • ionotropic
  • metabotropic
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33
Q

Ionotropic:

A
  • fast chemical transmission
  • neurotransmitters released from small synaptic vesicles near pre synaptic release site
  • binding with post synaptic receptor directly activates LGC, which alters membrane conductance of ion
    and the post synaptic membrane potential
34
Q

Metabotropic:

A
  • slow chemical transmission
  • neurotransmitters released from larger vesicles are more distant from synaptic cleft
  • a specific membrane receptor indirectly opens/closes ion channels
  • associated with G proteins
35
Q

Steps of metabotropic mechanism:

A
  1. receptor is coupled to G protein
  2. amplification of signal through generation of 2nd messengers
  3. activates multiple pathways and regulates multiple cell functions, which can form kinases and phosphotases
36
Q

Types of receptors in endocrine:

A
  • catalytic receptors
  • linked transcription factors
  • cytosolic/nuclear receptors (lipid soluble substances use these)
37
Q

Two patterns of response inside post synaptic cell:

A
  • agonist

- antagonist

38
Q

Agonist:

A
  • substrate binds to receptor and promotes change in cell function
  • some directly gate ion channels
39
Q

Antagonist:

A
  • substrate binds to receptor and prevents effect
40
Q

What are the three subunits of a G protein?

A
  • alpha
  • beta
  • gamma
41
Q

Mechanism of G protein at metabotropic pathway:

A
  1. neurotransmitter binds to receptor, which activates G protein
  2. GDP dissociates and binding site opens
  3. GTP binds to alpha subunit
  4. alpha subunit dissociates from rest of G protein, which activates many intracellular proteins
42
Q

T/F: inactive from of G protein has GTP molecule bound to the alpha subunit

A

F, has GDP molecule bound to alpha subunit

43
Q

Examples of cascade effects from dissociated alpha subunit:

A
  • open/close of ion channel

- activate/inhibit enzymes and promoters of DNA transcription

44
Q

Gs protein:

A
  • associated with stimulus receptor

- activates adenylate cyclase

45
Q

G proteins regulate _________ messengers

A

secondary

46
Q

Mechanism of Gs protein:

A
  1. adenylate cyclase is activated
  2. ATP converts to cAMP (2nd messenger)
  3. activates protein kinase a (PKA), which phosphorylates proteins
  4. increases Ca2+ influx through membrane channels
47
Q

Gi protein:

A
  • associated with inhibitory receptor

- inactivates adenylyl cyclase

48
Q

Gp protein:

A

regulates activity of enzyme phospholipase C

49
Q

Mechanism of Gp protein:

A
  1. phospholipase C cleaves PiP2
  2. forms 2nd messengers (IP3, DAG, and Ca2+)
  3. cascade effect (know what each messenger does)
50
Q

IP3

A
  • inositol-1,4,5-triphosphate
  • activates LG Ca2+ channels on ER
  • releases Ca2+ into cytosol
51
Q

DAG

A
  • diacylglycerol
  • stays in membrane
  • activates protein kinase C (PKC)
52
Q

Ca2+

A
  • binds to calmodulin (cytosolic protein)
  • forms complex that activates calmodulin dependent protein kinases
  • activates PKC
53
Q

How is G protein inactivated?

A
  • by intrinsic GTPase activity, which hydrolyses GTP

- eventually returns G protein to inactive state

54
Q

Two types of neurotransmitters:

A
  • low molecular weight
  • peptide
  • both react with specific receptor
55
Q

Low molecular weight neurotransmitters (LMW):

A
  • small and rapid acting molecule
  • found in all somatic motor and preganglionic neurons of autonomic NS
  • ex: acetylcholine, amino acids, biogenic amines
56
Q

Acetylcholine (ACh)

A
  • most important LMW neurotransmitter

- usually excitatory (produce EPSP), but can be inhibitory (produce (IPSP)

57
Q

What makes and releases acetylcholine?

A

cholinergic neurons

  • choline-acetyltransferase: creates enzyme
  • substrates: acetyl coenzyme A and choline
58
Q

Acetylcholinesterase:

A
  • degrades acetylcholine
  • bound outside postsynaptic membrane
  • produces acetate (diffuses away) and choline (reuptaken at presynaptic terminal by Na+ symporter)
59
Q

2 main receptor types for acetylcholine in CNS and PNS:

A
  • nicotinic (N)

- muscarinic (M1-5)

60
Q

Nicotinic receptor:

A
  • ionotropic receptor that has ion channel at core

- allows rapid influx of Na+

61
Q

Muscarinic receptor:

A
  • metabotropic receptor associated with G protein

- activation of M2

62
Q

Activation of M1 receptor leads to…

A
  • decreases K+ conductance b/c of activation of phospholipase C
  • depolarizes membrane
  • used in bronchioles
63
Q

Activation of M2 receptor leads to…

A
  • increases K+ conductance b/c of inhibition of adenylyl cyclase
  • hyperpolarizes membrane
  • used in SA node
64
Q

Amino acids:

A
  • LMW neurotransmitters
  • glutamate: excitatory transmitter in brain, spinal cord, and eye (ionotropic receptors)
  • gamma-aminobutyrate (GABA): inhibitor used in brain
65
Q

Major inhibitor role of GABA in ______ and _______

A

basal ganglia and cerebellar Purkinje cells

66
Q

GABA can be ionotropic or metabotropic:

A
  • ionotropic GABAa receptor: LGC that increases Cl- conductance
  • metabotropic GABAb receptor: activates G protein, which increases K+ conductance and can act to inhibit release of neurotransmitter
67
Q

Biogenic amines:

A
  • LMW neurotransmitter
  • made from amino acids
  • have NH2 group
  • ex: serotonin and catecholamines
68
Q

Serotonin:

A
  • biogenic amine
  • made from tryptophan
  • found in brain, spinal cord, and brain stem
  • can be excitatory/inhibitory, just depends on coupling mechanism and receptor
  • 80% is reuptaken to presynaptic neuron via Na+/Cl- dependent transporter
  • rest is reuptaken into glial cells
69
Q

Functions of serotonin:

A
  • stimulates neurons in sensory perception
  • promotes learning and memory
  • controls mood
  • promotes sleep induction b/c it activates inhibitory neurons in reticular formation
  • causes reduced relay of sensory info to cortex
  • stimulates interneurons of lateral spinothalamic tract involved in inhibition of pain transmission
70
Q

Serotonin is broken down by:

A
  • MOA in presynaptic neurons
71
Q

Catecholamines:

A
  • biogenic amine
  • made from tyrosine
  • ex: dopamine, norepi, epi
72
Q

Dopamine:

A
  • type of catecholamine
  • mainly inhibitory
  • found in brain stem nuclei
  • coke: inhibits reuptake
  • amphetamines: increase release
73
Q

Functions of dopamine:

A
  • helps in controlling complex movements and moods
74
Q

Adrenergic neurons:

A
  • release norepi and epi to brain and effector tissues of ANS
  • main excitatory neurotransmitters of sympathetic neurons
75
Q

Norepinephrine:

A
  • biogenic amine
  • binds to metabotropic alpha (preferred) or beta receptors
  • alpha 1 receptors: produce EPSP
  • alpha 2 receptors: autoreceptor and produces feedback inhibition (inhibits norepi from being released)
76
Q

How does norepi provide feedback inhibition?

A

hyperpolarizes axon terminal by opening K+ channels

77
Q

What happens to norepinephrine after signal is produced?

A
  • 80% reuptaken into presynaptic cell
  • degraded in terminal by MAO
  • remainder degraded by COMT in synaptic cleft
78
Q

Epinephrine:

A
  • biogenic amine
  • some made from sympathetic neurons
  • most come from adrenal medulla
  • will bind to both alpha and beta (preferred)
79
Q

LMW are synthesized in…

A

presynaptic axon terminals

80
Q

Central role of acetycholine is in the:

A
  • basal ganglia

- ANS

Physiology (33 decks)

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