4 - Synaptic and Neuromuscular Transmission

What are the 3 neuron structural types?

1. multipolar

2. bipolar

3. unipolar

With an electrical synapse, the current flows between cells via _____

gap junctions

Gap between presynaptic and postsynaptic cells

synaptic cleft

The following are associated with a(n) [electrical/chemical] synapse:

1. AP in presynaptic cell causes voltage-gated Ca2+ channels to open

2. Ca2+ influx causes release of neurotransmitter from presynaptic terminal

3. Neurotransmitter binds ligand-gated Na+ channel on postsynaptic cell, leading to depolarization (can be excitatory or inhibitory)

chemical

Neurons are arranged in _____ where input cells synapse on output cells

circuits

Output cell may or may not fire an action potential depending on amount of excitation provided by the _____

input cells

_____ synapses:

-Neuromuscular junction

-Single AP in motoneuron causes single AP in muscle fiber

one-to-one

_____ synapses:

-Found in some motoneurons of spinalcord

-Single AP in motoneurons causes many APs in postsynaptic cells

one-to-many

_____ synapses:

-Many presynaptic cells converge on a postsynaptic cell

-Common

many-to-one

Postsynaptic potentials commonly use _____ synapse arrangement

many-to-one

The following are associated with [excitatory/inhibitory] postsynaptic potentials:

-Pre-synaptic neuron depolarizes post-synaptic neuron, brings neuron's membrane potential to threshold, opens Na and K channels

-Ach, NE, Epi, dopamine, glutamate, serotonin are excitatory neurotransmitters

excitatory

The following are associated with [excitatory/inhibitory] postsynaptic potentials:

-Pre-synaptic neuron hyperpolarizes post-synaptic neuron and membrane potential moves away from threshold, opens Cl channels

-GABA, glycine are inhibitory neurotransmitters

inhibitory

What are the 3 ways synaptic inputs get integrated?

1. spatial summation

2. temporal summation

3. synaptic fatigue

Two or more inputs arrive at postsynaptic cell simultaneously

spatial summation

Two inputs arrive at postsynaptic cell in rapid succession

temporal summation

Repeated stimulation yields a

smaller than expected response

synaptic fatigue

-Ligand-gated ion channels that usually open in response to binding of neurotransmitter

-Usually located along dendrites or cell bodies and receive incoming information from other neurons

ionotropic receptors

A post-synaptic neuron may be excited due to _____ influx causing depolarization

Na

A post synaptic neuron may be inhibited due to either _____ efflux or _____ influx causing hyperpolarization

K; chloride

What are the 4 neurotransmitters that activate ionotropic receptors?

1. glutamate

2. acetylcholine

3. glycine

4. GABA

-Neurotransmitter that activates ionotropic receptors

-Primary excitatory neurotransmitters in the CNS

glutamate

-Neurotransmitter that activates ionotropic receptors

-Only neurotransmitter used at neuromuscular junction

-Also used by autonomic nervous system (PSNS and SNS)

acetylcholine

-Neurotransmitters that activate ionotropic receptors

-Both neurotransmitters are used

in the CNS and both are chloride

channels

-Binding of these causes inhibition,

since increase in Cl permeability is

inhibitorys

glycine & GABA

-Located along dendrites or cell bodies, receive incoming information, slower than ionotropic receptors

-Can use G-protein-coupled receptors (GPCR)

metabotropic receptors

-Neurotransmitter that activates G-protein-coupled receptors

-Uses alpha- or beta-adrenergic receptors

norepinephrine (NE)

-Neurotransmitter that activates G-protein-coupled receptors

-Metabotropic receptor

-Acts on post-synaptic sites in CNS

-Modulates cell excitability and

synaptic transmission via second

messenger pathways

-3 groups

glutamate

-Neurotransmitter that activates G-protein-coupled receptors

-Found in CNS and autonomicdivision of peripheral nervoussystem

GABA

Synthesized and packaged innerve cell body instead of axon terminal

neuropeptides

-May act on pre-synaptic cell to alter amount of neurotransmitter released

-May be co-secreted with neurotransmitter to alter response of post-synaptic cell

neuromodulators

Released from neurons into blood

neurohormones

The different neuron structure types are based on the # of processes that extend from the _____

cell body

Neuron structure - 3 or more processes extending from the cell body

multipolar

What is the major neuron type in the CNS and efferent PNS?

multipolar

Neuron structure - 2 processes extending from cell body in opposite directions - dendrite & axon

bipolar

Where will we find bipolar neurons?

retina & olfactory system

- Neuron structure - single short process from the cell body, branching into 2 or more

-peripheral process associated with sensory perception

-central process goes toward the CNS

unipolar

Where will we find unipolar neurons?

afferent PNS

[Electrical/chemical] synapse:

-Fast & has ability to stimulate cells simultaneously

-Found in cardiac tissue

-Found in some smooth muscle

electrical

AP moves from the presynaptic to postsynaptic cell through a _____ synapse

chemical

[Electrical/chemical] synapse is slower

chemical

What is the goal with chemical synapse?

get neurotransmitter released from the presynaptic cell and get it to the postsynaptic cell

The goal of a chemical synapse is to get neurotransmitter released from the presynaptic cell and get it to the postsynaptic cell. In order to do that, we need an AP to occur. In order for that to happen, we need to voltage gated _____ channels to open.

calcium

When calcium rushes to the post synaptic cell, it causes the vesicles that have _____ in them to move to the cell membrane and get released, for receptor binding.

neurotransmitters

Neurotransmitters bind _____ channel on the postsynaptic cell, leading to depolarization or hyperpolarization

ligand-gated

Excitatory response = _____polarization

depolarization

Inhibitory response =_____polarization

hyperpolarization

What is the most common type of synapse?

many-to-one

With a many-to-one synapse, you are getting many inputs from many neurons, so info is coming in from multiple neurons all the time. What do we need in order to cause an AP?

need convergence of multiple input neurons to cause an AP = sum the inputs

When converging multiple input neurons to cause an AP, if our net is depolarization, that -> _____

excitation

When converging multiple input neurons to cause an AP, if our net is hyperpolarization, that -> _____

inhibition

Ach, NE, Epi, dopamine, glutamate, and serotonin are _____ neurotransmitters

excitatory

Excitatory postsynaptic potentials -> [depolarize/hyperpolarize]

depolarize

Inhibitory postsynaptic potentials -> [depolarize/hyperpolarize]

hyperpolarize

GABA and glycine are _____ neurotransmitters

inhibitory

With spatial summation, 2 or more inputs arrive at the postsynaptic cell at the same time. What happens (3)?

-both inputs could be excitatory -> summation -> depolarization

-one could be excitatory & other inhibitory -> nothing

-both inputs could be inhibitory -> hyperpolarize -> further from threshold

Both inputs could be excitatory -> summation -> _____

depolarization

Both inputs could be inhibitory -> _____ -> further from threshold

hyperpolarization

One input could be excitatory & other inhibitory -> _____

nothing/ cancel out

With temporal summation, 2 inputs arrive at the postsynaptic cell in rapid succession (get one and then the other). What happens?

effects are additive

- could have 2 excitatory, one after another

- could have 1 excitatory & 1 inhibitory, one after another

With temporal summation, the effects are _____

additive

Synaptic fatigue -> [smaller/larger] than expected response

smaller

What if there is a Ca influx from an ionotropic receptor interaction?

may or may not cause depolarization

(Ca usually associated with 2nd messenger system)

What are the 2 types of glutamate receptors?

1. AMPA

2. NMDA

Allows both Na and K to cross the membrane, but the gradient that drives Na is the strongest one -> net effect is depolarization

AMPA

AMPA allows Na and K to cross the membrane, but the gradient that drives _____ is stronger -> _____

Na; depolarization

Depends on both glutamate binding and voltage, so when you are around resting membrane potential , there is a magnesium ion that blocks the binding site/ movement of other ions -> when glutamate binds and cell depolarizes -> magnesium block is removed

NMDA

NMDA depends on both glutamate binding and voltage, so when you are around resting membrane potential , there is a _____ ion that blocks the binding site/ movement of other ions -> when glutamate binds and cell depolarizes -> _____ block is removed

magnesium; magnesium

Binding of the glycine and GABA neurotransmitters will cause _____, because of increase in Cl permeability

inhibition

GABA sub A is associated with _____

chloride

In the system associated with metabotropic receptors, when we get binding, we get a _____ protein that's activated and a G protein alpha subunit that binds to _____

G; Gdp

G protein beta subunit may activate ion channel like _____ while the alpha subunit may activate enzymes that are promoting _____

potassium; 2nd messenger synthesis

Enzymes used in the 2nd messenger systems are ______ and _____

phospholipase C; adenylyl cyclase

What is the goal when you set off cascade of the 2nd messenger system?

-activating enzymes, like protein kinases

-phosphorylate something & set off cascade of events in the cell

Beta adrenergic GPCRs = _____

initiates cAMP second messenger system

Alpha 2 adrenergic receptors = _____

suppress cAMP system

Alpha 1 adrenergic receptors = _____

activate phospholipase C second messenger system

Glutamate activates 3 groups of G-protein coupled receptors. Group 1 does what?

increase neuron excitability & activate phospholipase C pathway

Glutamate activates 3 groups of G-protein coupled receptors. Groups 2 and 3 do what?

suppress neuron excitability & inhibit adenylyl cyclase pathway

GABA _____polarizes the cell when we get an AP

hyper

We can group neurotransmitters based on their _____ properties

biochemical

Acetylcholine belongs to a group of _____, along with NE, Epi, DA, serotonin, and histamine

biogenic amines

Glutamate, glycine, and GABA are all examples of _____

amino acids

Neuropeptides are neuromodulators, which have the ability to act on the presynaptic cell to change how much of a _____ is released

neurotransmitter

Neuropeptides are neuromodulators, which have the ability to be cosecreted along with the neurotransmitter, so the action is on the _____ cell

postsynaptic

Neurohormones travel a [shorter/longer] distance

longer

VIP and Substance P are commonly acting as neuro_____

modulators