Final: Synaptic transmission I and II

What are the 2 general types of synapses?

1. Electrical(gap junctions)

2. Chemical

What protein families form gap junctions in vertebrates?

Connexins and Pannexins.

Which proteins can form gap junctions?

Connexins and innexins

What is the primary protein class that forms gap junctions in invertebrates?

Innexins.

What characterizes a 'rectifying' electrical synapse?

It preferentially transmits current in one direction over the other.

Give 2 examples of a rectifying synapse.

Lateral giant axon and motor giant axon in crayfish tail

What is the molecular basis for recification in electrical synapses(Phelan)

heterotypic gap-junction channels are asymmetrically gated by voltage, which underlies rectification.

The chick ciliary ganglion is a physiological example of what combined synaptic structure?

A combined electrical and chemical synapse.

What did Otto Loewi's vagus nerve stimulation experiment prove?

The existence of chemical transmission.

Order the 4 classes of synaptic vesicles from smallest to largest.

Small dense core, light core spherical=light core ovoidal, large core vesicles

What kind of chemical synapses are directly mediated synaptic potentials mediated by?

Transmitter-gated ion channels, where the neurotransmitter receptor and ion channel are parts of the same protein.

Functionally, an 'excitatory' synapse is defined as one that _____ the likelihood of firing action potentials.

increases

What produces a postsynaptic potential (PSP) in chemical synaptic transmission?

Movement of current through the ligand gated ion channel

What determines whether an EPSP or IPSP is produced?

The type of receptors present in the postsynaptic membrane

What does α-latrotoxin (from black widow venom) do?

Causes massive transmitter release from presynaptic terminals.

Name two substances that block nicotinic ACh receptors at the vertebrate neuromuscular junction.

Curare and alpha-bungarotoxin.

Sarin and VX are 'nerve agents' that exert their effects by blocking which enzyme?

Acetylcholinesterase (AChE).

The depolarizing postsynaptic potential generated locally at the neuromuscular junction.

End-plate potential (EPP).

In vertebrates, all EPPs are _______. In invertebrates, they can be _____.

Excitatory; both excitatory and inhibitory

What drugs inhibit acetylcholinesterase?

eserine and prostygmine

Treating a neuromuscular junction with curare resulted in a dose-

dependent reduction of ________.

EPP amplitude.

EPP amplitude decays with:

Distance

Where are EEPs/synaptic current generated?

Near the end plate.

What toxin can be used to label acetylcholine receptors?

Alpha bungarotoxin

Blocking AMPA receptors leaves ____ NMDA currents intact.

Slow

Blocking NMDA receptors leaves ____ AMPA currents intact.

Fast

A decrease in cell excitability caused by increased Cl- conductance that 'short-circuits' other excitatory currents.

Shunting inhibition

When electrical potential(delta V) decreases, membrane conductance ______(increases/decreases), and channels _____(open/close).

Increases;open

When electrical potential(delta V) increases, membrane conductance ______(increases/decreases), and channels _____(open/close).

decreases; close

Which receptor type involves direct transmitter action where the receptor itself contains an ion channel?

Ionotropic receptor

Which receptor type mediates indirect transmitter action through second messenger systems?

Metabotropic receptor

Indirectly mediated synaptic potentials act through:

G protein coupled receptors

G-proteins are heterotrimers consisting of which three subunits?

Alpha, beta, gamma

Examples of transmitter receptors that mediate indirect transmission:

Muscarinic acetylcholine, adrenergic, dopamine

How do directly-mediated synaptic potentials affect membrane conductance?

They always increase conductance (open channels).

How do indirectly-mediated synaptic potentials affect membrane conductance?

It can either increase or decrease conductance potentials

How are G proteins grouped into classes?

according to the 1st known targets of their α-subunits

What is the function of GTP analogs?

They activate G coupled proteins irreversibly

What is the function of GDP analogs?

It inactivates G-proteins and inhibits their mediated responses.

Cholera toxin increases the production of what second messenger?

cAMP

What does pertussis toxin prevent?

The inhibition of cAMP

ACh activates K+ channels in cardiac muscle and inhibits Ca2+ through which type of ACh receptor?

Muscarinic Ach

Which experimental preparation can discriminate between direct G-protein effects and second messenger systems because it lacks cytoplasmic components?

Inside-out patch

In frog sympathetic ganglia, norepinephrine (NE) inhibits presynaptic release by reducing the influx of which ion?

Ca2+

2nd messenger-coupled systems alter the activity of ion channels via what process? What amino acids are affected?

Phosphorylation; serine and threonine

What second messenger activates β-Adrenergic receptors?

cAMP

The ability of synaptic or hormonal stimuli to alter the active electrical behavior of neurons via intracellular biochemical changes.

Neuromodulation

What are the three general neuronal properties affected by neuromodulation?

AP shape(amplitude, duration), spontaneous discharge, and synaptic efficacy

Increasing amplitudes of back-propagated APs can have what effect?

Can produce large increases in associated Ca++ influx, which can enhance synaptic plasticity

Increasing action potential duration in axon terminals has what effect on neurotransmitter release?

Increases amount of neurotransmitter released

How does broader action potential duration affect propagation at axonal branch points?

It allows spikes to pass branch points and invade fine terminals more readily.

What are 2 ways you can shorten AP duration in DRG?

Increase conductance of K+, decrease conductance of Ca2+

How does AP narrowing occur?

A decrease is Ca2+ current

What substances can block a spike narrowing effect?

GDP analogs, pertussis toxin?

What are enkephalins? What effect does it have on APs?

Endogenous opioids that inhibit pain pathways in the CNS. Narrowing of APs.

What effect does stimulation of β-adrenergic receptors have on cardiac muscle APs? Why?

prolongs cardiac muscle APs. It increases current of Ca2+.

Neurons that exhibit clusters of action potentials separated by silent periods are described as _____ neurons.

Bursting

What 2 factors is the firing pattern of a neuron in the CNS determined by?

1. Intrinsic membrane properties

2. synaptic input from other cells

Give 2 examples of spontaneous electrical activity:

1. continuous repetitive firing at a fixed frequency

2. endogenous "bursting" activity

True or false: neuromodulators can convert a cell from a silent one to a spontaneously active one

True

Action potentials in bursting neurons occur during the _____ phase of rhythmic membrane oscillations.

Depolarized

What behaviors are endogenous bursting used for?

To drive rhythmic behaviors and facilitate the release of peptide transmitters

What is APLYSIA's R15?

An endogenous burster that regulates water balance in some fuckass molusk

What neuromodulator enhances both the depolarizing and hyperpolarizing phases of bursting pacemaker activity?

Serotonin

Serotonin (5-HT) increases the amplitude and duration of interburst hyperpolarization in R15 by increasing which K+ current?

Inward rectifying

Serotonin increases the action potential frequency and depolarization during R15 bursts by enhancing which current?

Ca2+ current

What effect does noradrenaline have on hippocampal pyramidal cells?

inhibits a calcium-activated K+ current (IK(Ca)) that produces a post-spike slow afterhyperpolarization (AHP).

How does noradrenaline (NA) affect spike accommodation in hippocampal pyramidal neurons?

It decreases accommodation (increases the number of spikes).

What is spike accomadation?

a decreasing spike frequency over time during a maintained, depolarizing stimulus

Noradrendaline _______(increases/decreases) hippocampal cell excitability. What mediates this effect?

Increases. Beta adrenergic receptors

What neurotransmitter produces a similar effect as noradrenaline. except in cortical pyramidal neurons?

Serotonin(5-HT)

Serotonin (5-HT) enables the expression of _______ potentials in spinal motor neurons by reducing a __________ current.

Plateau; calcium activated potassium current.

What are plateau potentials?

long-lasting depolarizations that can occur in response to brief depolarizing inputs,