Neurons in Synapses Flashcards
1
Q
Synapses:
A
Cellular junction where info is transmitted from one neuron to another
2
Q
Types of synapses:
A
- electrical
- chemical
3
Q
Electrical synapses:
A
- ions passed directly from one cell to another through gap junctions (in heart tissue and smooth muscle)
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
5
Q
Axondendritic area:
A
dendrite and axon terminal
6
Q
Synaptic transmission:
A
passage of info at synapse
7
Q
Axosomatic area:
A
soma and axon terminal
8
Q
Axoaxonic area:
A
axon and axon terminal
9
Q
Neuromuscular junction (NMJ):
A
skeletal muscle and axon terminal
10
Q
Synapse en passant area:
A
smooth muscle and axon terminal
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
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
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+]
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
15
Q
Monoamine oxidase (MAO):
A
breaks down norepinephrine
16
Q
For CNS, glial cells…
A
reuptake and breakdown neurotransmitters
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
18
Q
Synaptic delay:
A
time required to diffuse across cleft
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
20
Q
Active region on membrane has receptors that are:
A
specific for neurotransmitters
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
22
Q
Step 3 in mechanism of signal transmission at chemical signal at post synaptic membrane: activation of _____ and _____
A
cAMP and cGMP
23
Q
Step 4 in mechanism of signal transmission at chemical signal at post synaptic membrane: activation of one or more ______
A
intracellular enzymes
24
Q
Step 5 in mechanism of signal transmission at chemical signal at post synaptic membrane: activation of gene _______
A
transcription
25
Neurons have post synaptic potential:
- 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
26
Unitary post synaptic potential:
- in neuron
- one vesicle causes flow of current
- not enough to make AP in post synaptic neuron
27
Excitatory post synaptic potential (EPSP):
- in neurons
- occurs with increased influx of positive ions (Na+)
- depolarizes membrane, which increases the chances of AP
28
Inhibitory post synaptic potential (IPSP):
- 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
29
T/F: at skeletal muscle junction (NMJ), each axon terminal synapses with multiple skeletal muscles
F, they only synapse with one skeletal muscle
30
NMJ has end plate potential (EPP):
- is excitatory post synaptic potential
- single release of neurotransmitter makes large EPP
- depolarizes sarcalemma above AP threshold
- will produce spike potential to create contraction
31
Function of catabolic enzymes
- 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
32
Types of coupling mechanisms on post synaptic cell:
- can affect speed of transmission
- ionotropic
- metabotropic
33
Ionotropic:
- 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
Metabotropic:
- 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
Steps of metabotropic mechanism:
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
Types of receptors in endocrine:
- catalytic receptors
- linked transcription factors
- cytosolic/nuclear receptors (lipid soluble substances use these)
37
Two patterns of response inside post synaptic cell:
- agonist
| - antagonist
38
Agonist:
- substrate binds to receptor and promotes change in cell function
- some directly gate ion channels
39
Antagonist:
- substrate binds to receptor and prevents effect
40
What are the three subunits of a G protein?
- alpha
- beta
- gamma
41
Mechanism of G protein at metabotropic pathway:
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
T/F: inactive from of G protein has GTP molecule bound to the alpha subunit
F, has GDP molecule bound to alpha subunit
43
Examples of cascade effects from dissociated alpha subunit:
- open/close of ion channel
| - activate/inhibit enzymes and promoters of DNA transcription
44
Gs protein:
- associated with stimulus receptor
| - activates adenylate cyclase
45
G proteins regulate _________ messengers
secondary
46
Mechanism of Gs protein:
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
Gi protein:
- associated with inhibitory receptor
| - inactivates adenylyl cyclase
48
Gp protein:
regulates activity of enzyme phospholipase C
49
Mechanism of Gp protein:
1. phospholipase C cleaves PiP2
2. forms 2nd messengers (IP3, DAG, and Ca2+)
3. cascade effect (know what each messenger does)
50
IP3
- inositol-1,4,5-triphosphate
- activates LG Ca2+ channels on ER
- releases Ca2+ into cytosol
51
DAG
- diacylglycerol
- stays in membrane
- activates protein kinase C (PKC)
52
Ca2+
- binds to calmodulin (cytosolic protein)
- forms complex that activates calmodulin dependent protein kinases
- activates PKC
53
How is G protein inactivated?
- by intrinsic GTPase activity, which hydrolyses GTP
| - eventually returns G protein to inactive state
54
Two types of neurotransmitters:
- low molecular weight
- peptide
- both react with specific receptor
55
Low molecular weight neurotransmitters (LMW):
- small and rapid acting molecule
- found in all somatic motor and preganglionic neurons of autonomic NS
- ex: acetylcholine, amino acids, biogenic amines
56
Acetylcholine (ACh)
- most important LMW neurotransmitter
| - usually excitatory (produce EPSP), but can be inhibitory (produce (IPSP)
57
What makes and releases acetylcholine?
cholinergic neurons
- choline-acetyltransferase: creates enzyme
- substrates: acetyl coenzyme A and choline
58
Acetylcholinesterase:
- degrades acetylcholine
- bound outside postsynaptic membrane
- produces acetate (diffuses away) and choline (reuptaken at presynaptic terminal by Na+ symporter)
59
2 main receptor types for acetylcholine in CNS and PNS:
- nicotinic (N)
| - muscarinic (M1-5)
60
Nicotinic receptor:
- ionotropic receptor that has ion channel at core
| - allows rapid influx of Na+
61
Muscarinic receptor:
- metabotropic receptor associated with G protein
| - activation of M2
62
Activation of M1 receptor leads to...
- decreases K+ conductance b/c of activation of phospholipase C
- depolarizes membrane
- used in bronchioles
63
Activation of M2 receptor leads to...
- increases K+ conductance b/c of inhibition of adenylyl cyclase
- hyperpolarizes membrane
- used in SA node
64
Amino acids:
- LMW neurotransmitters
- glutamate: excitatory transmitter in brain, spinal cord, and eye (ionotropic receptors)
- gamma-aminobutyrate (GABA): inhibitor used in brain
65
Major inhibitor role of GABA in ______ and _______
basal ganglia and cerebellar Purkinje cells
66
GABA can be ionotropic or metabotropic:
- 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
Biogenic amines:
- LMW neurotransmitter
- made from amino acids
- have NH2 group
- ex: serotonin and catecholamines
68
Serotonin:
- 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
Functions of serotonin:
- 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
Serotonin is broken down by:
- MOA in presynaptic neurons
71
Catecholamines:
- biogenic amine
- made from tyrosine
- ex: dopamine, norepi, epi
72
Dopamine:
- type of catecholamine
- mainly inhibitory
- found in brain stem nuclei
- coke: inhibits reuptake
- amphetamines: increase release
73
Functions of dopamine:
- helps in controlling complex movements and moods
74
Adrenergic neurons:
- release norepi and epi to brain and effector tissues of ANS
- main excitatory neurotransmitters of sympathetic neurons
75
Norepinephrine:
- 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
How does norepi provide feedback inhibition?
hyperpolarizes axon terminal by opening K+ channels
77
What happens to norepinephrine after signal is produced?
- 80% reuptaken into presynaptic cell
- degraded in terminal by MAO
- remainder degraded by COMT in synaptic cleft
78
Epinephrine:
- biogenic amine
- some made from sympathetic neurons
- most come from adrenal medulla
- will bind to both alpha and beta (preferred)
79
LMW are synthesized in...
presynaptic axon terminals
80
Central role of acetycholine is in the:
- basal ganglia
| - ANS
