synapses I and II

Question 1

What are the two major categories of synapses? Briefly describe each.

Answer 1

Electrical: communication via gap junctions

Chemical: indirect communication via neurotransmitter release and post-synaptic receptor use

Question 2

Describe the anatomical and physiological characteristics of gap junctions and
explain the features of electrical signaling

Answer 2

Presynaptic neuron and post synaptic membrane are connected via gap junctions. Vesicles and neurotransmitters are not needed, and ions can flow through the junction to propagate the electrical signal

Question 3

What is the major benefit of electrical signaling? What is this major downside?

Answer 3

They’re fast, but they can’t propagate far

Question 4

Describe the anatomical and physiological characteristics of chemical synapses.

Answer 4

A presynaptic and postsynaptic neuron are separated by a synaptic cleft. Neurotransmitters are released from the presynaptic neuron and bind to receptors on the post synaptic membrane. this influences channels that will impact ion channels in the post synaptic cell

Question 5

what are the two major chemical receptor types?

Answer 5

Ionotropic: ligand gated ion channels

Metabotropic: alter metabolism in the postsynaptic cell via G protein signaling pathways

Question 6

Describe the steps of synaptic transmission (chemical)

Answer 6

-AP invades the presynaptic terminal

-Depolarization of presynaptic terminal causes voltage gated calcium channels to open and influx of calcium into the bouton

-Calcium causes vesicles to fuse with presynaptic membrane
-Neurotransmitter is released into the synaptic cleft

-Postsynaptic channels open/close, and excitatory or inhibitory postsynaptic potential occurs

-Astrocytes/enzymatic degradation remove neurotransmitter

Question 7

What is syntaxin?

Answer 7

A protein in the presynaptic membrane important for bringing the vesicle closer to the presynaptic membrane

Question 8

What is synaptobrevin?

Answer 8

A protein in the vesicle important for bringing the vesicle closer to the presynaptic membrane

Question 9

What is SNAP-25?

Answer 9

A protein in the vesicle important for bringing the vesicle closer to the presynaptic membrane

Question 10

Describe how botulinum toxin impacts the successful synapse of neurotransmitters

Answer 10

Proteases that cleave the vesicle/membrane associated anchoring proteins, blocking the ability for calcium to allow fusion of the vesicle. Because of this, the neurotransmitter isn’t released. Primarily target Ach, limiting skeletal muscle movement

Question 11

Describe how tetanus toxin impacts the successful synapse of neurotransmitters

Answer 11

Protease that cleaves synaptobrevin to prevent vesicle docking and priming; tends to impact inhibitory neurons in the spinal cord and causes uncontrolled skeletal muscle contraction

Question 12

Describe how latrotoxin impacts the successful synapse of neurotransmitters

Answer 12

Binds to vesicle proteins and causes calcium independent vesicle fusion and neurotransmitter release

Question 13

What is Lambert-Eaton syndrome?

Answer 13

Muscle weakness caused by auto-antibodies binding to calcium channels on motor axons

Question 14

What is NMDA encephalitis?

Answer 14

Auto-antibodies binding to Glu1; associated with hallucination

Question 15

What is the major excitatory neurotransmitter in the brain? What ion channels does it use?

Answer 15

Glutamate; sodium, potassium, and calcium

Question 16

What is the major inhibitory neurotransmitter in the brain? What ion channels does it use?

Answer 16

GABA; chloride

Question 17

Where are type I glutamate synapses found? what is their post-synaptic density?

Answer 17

Dendritic spines; they have prominent post-synaptic density

Question 18

Where are type II GABA synapses found? what is their post-synaptic density?

Answer 18

The dendritic shafts, soma, or axon. They have small post-synaptic density

Question 19

GABAa is a(n) ___ receptor, while GABAb is a(n) ___ receptor

Answer 19

ionotropic, metabotropic

Question 20

Describe AMPA receptors

Answer 20

Ionotropic glutamate receptors. Fast kinetics and low calcium permeability; require high concentration of glutamate to be activated

Question 21

Describe NMDA receptors

Answer 21

Ionotropic glutamate receptors. Slow kinetics and high calcium permeability; they require glycine in addition to glutamate for activation

Question 22

Describe the cycle of moving glutamate between neurons and glia/other neurons

Answer 22

-Glutamine converts to glutamate in a presynaptic neuron

-Glutamate gets packaged into VGLUT transport vesicles, when is then released via exocytosis

-Transporters take up extracellular glutamate in the synaptic cleft

-Glutamine synthetase breaks glutamate to glutamine, which then gets shuttled between glia and neurons by SN1/SAT2

Question 23

Describe GCPR receptors

Answer 23

Metabotropic glutamate receptors that activate intracellular signaling pathways.

Question 24

Magnesium ion can block which receptor at resting membrane potential?

Answer 24

NMDA

Question 25

Describe GABAa receptors: structure and function

Answer 25

GABAa: ionotropic. A pentameric structure surrounding an aqueous pore. The pore conducts chloride, typically entering the cell, hyperpolarizing the neuron and creating an IPSP. (The chloride can be leaving the cell via this method). Because of this, GABAa in adults is typically considered inhibitory. In infants, it is mildly stimulatory

Question 26

Describe GABAb receptors

Answer 26

G protein coupled receptors that are metabotropic. They’re highly associated with GIRK channels, using the outward flow of potassium to hyperpolarize the cell. This receptor is slower than GABAa.

Question 27

Describe how summation of IPSPs and EPSPs determines whether an action
potential is generated

Answer 27

Single EPSPs are typically subthreshold. If we stimulate multiple EPSPs closer together, we can reach action potential. This is also dependent on lower amounts of IPSPs, as those can decrease depolarization abilities of EPSP

Question 28

Describe temporal summation

Answer 28

Two stimuli occurring closer together in time, making their combined effort more likely to cause an action potential

Question 29

Describe spatial summation

Answer 29

Two stimuli occurring closer together in space, making their combined effort more likely to cause an action potential

Question 30

Describe the actions of modulatory neurotransmitters

Answer 30

The presence of modulatory neurotransmitters can increase or decrease excitability. With the same stimulus, the presence of these neurotransmitters can greatly increase or decrease the output.

Question 31

describe how excitability can be modulated presynaptically

Answer 31

Presynaptic: inhibit release calcium channels and SNARE proteins that allow for vesicle fusion and release of neurotransmitter

Question 32

describe how excitability can be modulated postsynaptically

Answer 32

Postsynaptic: opens K+ channels to reduce excitability. GABAb is a good example.

Question 33

Discuss the role of G proteins in the primary signaling pathways of neurotransmitter

Answer 33

A neurotransmitter binds to the G protein, causing the GDP on the subunit for exchange for GTP. The beta and gamma subunits then release and go on to impact signaling within the cell.

Question 34

Describe G protein signaling with Gs

Answer 34

Stimulatory; activates adenyl cyclase, which activates cAMP, which then activates PKA. Typically associated with beta adrenergic receptors (both glutamate and GABA)

Question 35

Describe G protein signaling with Gi

Answer 35

Inhibitory; deactivates adenalyl cyclase, prevents activation of PKA

Question 36

Describe G protien signaling with Gq

Answer 36

Activates phospholipase c, which activates IP3 and DAG. IP3 opens ca channels and DAG activates PKC, both of which increase stimulatory actions. Typically associated with glutamate

Question 37

describe nitric oxide as an unconventional neurotransmitter

Answer 37

generated when neuronal activity increases and calcium permeable channels are active. It can freely diffuse out of the axon and can have influence far from where it was made. It can also bind to iron heme groups (aguanyl cyclase), leading to generation of second messengers (cGMP) and activate PKG. it is a retrograde signaling method

Question 38

describe endogenous cannaboids as an unconventional neurotransmitter

Answer 38

made by the neurons and resemble THC. Receptors are found on presynaptic terminals and GABA and glutamate neurons to regulate release of neurotransmitter. It is a retrograde signaling method (made in a postsynaptic cell, and diffuse back to the presynaptic cell).

Question 39

describe acetylcholine

Answer 39

Found in septal nuclei in the brain. They use nicotinic acetylcholine receptors as well as muscarinic G protein receptors

Question 40

Describe catecholamines

Answer 40

Dopamine, NE, and epinephrine. Dopamine neurons are found in substantis nigra and ventral tegmental area. NE are found in the locus coeruleus. These bind metabotropic receptors, and their impact is dependent on specific monoamine transporters that take them back into the nerve terminal.

Question 41

Describe serotonin

Answer 41

Neurons originate in the raphe nuclei and pons. They typically bind to metabotropic receptors, but there is one type of ionotropic receptor. Their action is terminated by serotonin transporters that take it back into the neuron

Question 42

Describe peptide neurotransmitters

Answer 42

Proteins made in the nucleus that travel down the axon. Once they reach the terminal, they are cleaved to become active. They typically activate G protein coupled metabotropic receptors on presynaptic and postsynaptic membranes (they regulate excitability)