5. + 6. Neural communication Pt 2 - Neuronal learning

Chapter 5

Neurotransmitters

___________ - chemical with an excitatory or inhibitory effect when released by a neuron onto a target— sent over synapses

• Outside the nervous system, like in the bloodstream, these are considered hormones

A __________itself is NOT what determines inhibitory and exhibitory EFFECT.

• The inhibitory or excitatory effect depends on the receptor site for it on the target.

Hormones

____________ - chemical that circulates in the bloodstream outside the CNS— much slower than neurotransmitters

• Controlled by the hypothalamus

• Uses bloodstream to impact organs throughout body

• In the CNS, these are considered neurotransmitters

Neuron communication

_____________- occurs across the synapse and is largely chemical, spurred by electrical action potentials.

• Synapse

Acetycholine (ACh)

Neurotransmitters (chemicals)

______________ - anything we need to move— activates skeletal muscles in the SNS and either excites or inhibits internal organs in the ANS

• First neurotransmitter discovered in the PNS and CNS by Otto Loewi

• The chemical messenger that is associated with slowed heartbeat in diving bradycardia (a protective physiological reflex where the heart rate slows significantly when a person holds their breath and submerges their face in water)

Epinephrine (EP)

Neurotransmitters (chemicals)

______________ -  acts as a neurotransmitter in CNS + hormone to mobilize the body in fight or flight

• AKA adrenaline

Norepinephrine (NE)

Neurotransmitters (chemicals)

______________ - accelerates heart rate in mammals— found in the brain and sypathetic (fight or flight) division of the ANS

• AKA noreadrenaline

Parkinson’s disease

Neurotransmitters (chemicals - dopamine) + CNS’ 4 activating systems (Cho, Dope, Nora, Sero) → nigrostriatal pathways

____________ - disorder of the motor system correlated w/ a loss of dopamine from the substantia nigra

• Characterized by: tremors, muscle rigidity, reduction of voluntary movement

• Less dopamine by about 10% in the basal ganglia

Dopamine (DA)

Neurotransmitters (chemicals)

______________ - amine neurotransmitter involved w/ coordinating movement, attention, learning, and reinforcing behaviours

• Parkinson’s disease

Synaptic vesicles

Structure of synapses (chemical synapses)

___________ - membranous compartment that encloses a fixed number (AKA a quantum) of neurotransmitter molecules

• A round granule that contains neurotransmitters

Structure of synapses

Synapse

___________ - contains multiple parts:

• Synaptic vesicles

• Microtubule

• Mitochondion

• Storage granule

• Presynaptic membrane

• Synaptic cleft

• Postsynaptic membrane

• Postsynaptic receptor

Synapse

__________ - spatial junction between one neuron and another— forms the info transfer site between neurons.

• Structure of synapse

• Chemical synapse

• Types of synaptic transmission (anterograde, retrograde)

Microtubule

Structure of synapses (chemical synapses)

___________ - transport molecule that carries substances to the axon terminal

Mitochondrion

Structure of synapses (chemical synapses)

___________ - organelle that provides cell w/ energy

Storage granule

Structure of synapses (chemical synapses)

___________ - large compartment that holds synaptic vesicles, containing neurotransmitters

• On the presynaptic side

Postsynaptic receptor

Structure of synapses (chemical synapses)

___________ - site to which a neurotransmitter molecule binds

• On the postsynaptic side

Postsynaptic membrane (dendritic spine)

Structure of synapses (chemical synapses)

___________ - contains receptor molecules that recieve chemical messages

• Once a neurotransmitter is expelled into the synaptic cleft and crosses it, it binds to receptor proteins here in the _________. 

Synaptic cleft

Structure of synapses (chemical synapses)

___________ - small space seperating presynaptic terminal and postsynaptic dendritic spine

• Neurotransmitter expels into here by exocytosis, leading it to bind to the postsynaptic membrane

• AKA space between axon terminal and dendritic spine

Presynaptic membrane (axon terminal)

Structure of synapses (chemical synapses)

___________ - encloses molecules that transmit chemical messages

• After being released by the storage granule, vesicles w/ neurotransmitters in them travel here for release

Exocytosis

Structure of synapses (chemical synapses)

___________ - this is how a neurotransmitter gets from the presynaptic membrane to the synaptic cleft— process where a cell releases large molecules out of the cell by having it fuse with the plasma membrane

Tripartite synapse

Structure of synapses (chemical synapses)

___________ - functional integreation + physical proximity of the presynaptic membrane, postsynaptic membrane, and their intimate association w/ surrounding astrocytes

• Integration + closeness of the axon terminal and dendritic spine, and their association w/ surrounding astrocytes

Dendritic spine

Structure of synapses (chemical synapses)

___________ - The postsynaptic membrane is also known as…

Axon terminal

Structure of synapses (chemical synapses)

___________ - The presynaptic membrane is also known as…

space between the axon terminal + dendritic spine

Structure of synapses (chemical synapses)

___________ - The synaptic cleft is also known as the….

Chemical synapse

Synapse

___________ - junction at which messenger molecules are released when

• Diagram explains it

Anterograde synaptic transmission

_____________- process that occurs when a neurotransmitter is released from a presynaptic neuron and binds to a receptor on the postsynaptic neuron

• (From the axon terminal to the dendritic spine)

• Five easy steps!

Like a recipe, doing it step-by-step- is a precise science— if you don’t do it right the first time, it won’t come out right

Five easy steps to anterograde synaptic transmission

Anterograde synaptic transmission

_____________ - five steps which include…

1. Neurotransmitter is synthesized somewhere inside the neuron

2. It is packaged + stored within vesicles at the axon terminal (presynaptic membrane)

3. It’s transported to the presynaptic membrane + released into the cleft in response to an action potential

4. It binds to + activates receptors on the postsynaptic membrane (dendritic spine)

5. It is degraded or removed so it doesn’t continue to interact w/ a receptor and work indefinitely.

Step 1) Neurotransmitter is synthesized somewhere in neuron

Anterograde synaptic transmission (5 easy steps)

_______________ - done in two general ways— either synthesizes in the axon terminal or cell body:

1. Axon terminal: building blocks from food are pumped into the cell via transporters, embedding protein molecules in cell membrane

2. Cell body: according to instructions in DNA for peptide transmitters, while transported on microtubules to axon terminal

Transporters

Anterograde synaptic transmission (5 easy steps) → step 1+ 2: synthesis, packaging + storage

_______________ - protein molecules that pump substances across a membrane— responsible for packaging some neurotransmitter classes into vesicles

Step 2) Neurotransmitter is packaging + storage

Anterograde synaptic transmission (5 easy steps)

_______________ - neurotransmitter is packaged + stored within vesicles at the axon terminal (presynaptic membrane)— packaged in 3 ways:

1. Granules

2. Attatched to microfilaments

3. Attached to presynaptic membrane

Step 3) Neurotransmitter is released

Anterograde synaptic transmission (5 easy steps)

_______________ - Neurotransmitter is transported to the presynaptic membrane + released into the cleft in response to an action potential— like a key in a lock.

1. At the terminal, the action potential opens voltage-sensitive calcium (Ca2+) channels

2. Ca2+ enters the terminal and binds to the protein calmodulin, forming a complex.

3. The complex causes some vesicles to empty their contents into the synapse and others to get ready to empty their contents.

Neurotransmitter find their specific receptors on the postsynaptic side, where binding sites activate the neurotransmitter

Step 4) Receptor-site activation

Anterograde synaptic transmission (5 easy steps)

_______________ - After release, the neurotransmitter diffuses across the synaptic cleft to activate receptors on the postsynaptic membrane

On postsynaptic side, three things can happen: EPSPs, IPSPs, or other chemical reactions.

• Transmitter-activated receptors

• Ionotropic receptors

• Metabotropic receptors

• Autoreceptors

• Quantum (pl. quanta)

EPSPs

Anterograde synaptic transmission (5 easy steps) → step 4: receptor-site activation

_______________ - on postsynaptic side, an excitatory action or depolatrization of the postsynaptic membrane can happen

IPSPs

Anterograde synaptic transmission (5 easy steps) → step 4: receptor-site activation

_______________ - on postsynaptic side, an inhibiatory action or hyperpolarization of the postsynaptic membrane can happen

Transmitter-activated receptors

Anterograde synaptic transmission (5 easy steps) → step 4: receptor-site activation

_______________ - protein that has a binding site for a specific neurotransmitter and is embedded in the cell membrane

Ionotrophic receptors

Anterograde synaptic transmission (5 easy steps) → step 4: receptor-site activation

_______________ - embedded membrane protein— acts as a binding site for a neurotransmitter AND a pore that regulates ion flow to directly + rapidly change membrane voltage

• Associated w/ a pore that can open to allow ions to pass through it— two ways:

  • Allowing Na+ to enter = depolarization → leads to an excitatory effect on postsynaptic membrane

  • Allow K+ to leave neuron, or Cl- to enter = hyperpolarization → leads to inhibatory effect on postsynaptic membrane

Metabotrophic receptor

Anterograde synaptic transmission (5 easy steps) → step 4: receptor-site activation

_______________ - embedded membrane protein w/ a binding site for a neurotransmitter linked to a G protein— can affect other receptors or act w/ second messangers to affect other cellular processes, like opening a pore

Autoreceptors

Anterograde synaptic transmission (5 easy steps) → step 4: receptor-site activation

_______________ - AKA self-receptors — responds to the same transmitter released by the neuron. Part of negative feedback loop allowing neuron to adjust its output

• Serve critical function for this loop, provides info about adjustments to synaptic communication

Can fo in a loop from presynaptic to postsynaptic— have a modulatory role.

Quantum (pl. quanta)

Anterograde synaptic transmission (5 easy steps) → step 4: receptor-site activation

_______________ - no. of neurotransmitter molecules— equivalent to the content of a SINGLE synaptic vesicle— that provides a just-observable change in postsynaptic electric potential

• Producing a postsynaptic potential large enough to cause a postsynaptic action potential needs the simulatenous release of MANY ______ from the presynaptic cell

• No. of_____ in response to an AP depends on:

  • 1) Amount of Ca+ that enters axon terminal in response to AP

  • 2) No. of vesicles docked @ membrane, waiting to be released

Step 5) Neurotransmitter inactivation

Anterograde synaptic transmission (5 easy steps)

_______________ - neurotransmitter needs to end to not occupy other messahes— this flexibility is needed to allow the synapse to respond to the frequency of its own use.

• Four ways: Double' D’s Re-Up!!!!!!

  • Diffusion

  • Degradation

  • Reuptake

  • Astrocyte reuptake

Diffusion, degradation, reuptake, astrocyte uptake (Double D’s Re-Up)

Anterograde synaptic transmission (5 easy steps) → step 5: inactivation

_______________ - 4 ways of anterograde synaptic transmission — inactivation are…

• Name the four ways and the weird acronym

1) Diffusion

Anterograde synaptic transmission (5 easy steps) → step 5: inactivation (Double D’s Re-Up!!)

_______________ - some of the neurotransmitter simply diffuses away from the cleft and is no longer available to bind to receptors

• Cannot bind after this

2) Degradation

Anterograde synaptic transmission (5 easy steps) → step 5: inactivation (Double D’s Re-Up!!)

_______________ - enzymes in synaptic cleft break down the neurotransmitter

• If it doesn’t diffuse on its own, an enzyme breaks it down so it no longer has the same structure and therefore, can’t bind

3) Reuptake

Anterograde synaptic transmission (5 easy steps) → step 5: inactivation (Double D’s Re-Up!!)

_______________ - transmitter is brought back into the presynaptic axon terminal— RECYCLE

• By-products of degradation can also be recycled

4) Astrocyte reuptake

Anterograde synaptic transmission (5 easy steps) → step 5: inactivation (Double D’s Re-Up!!)

_______________ - nearby astrocytes take up the neurotransmitter, and can also store these transmitters for re-export to the axon terminal— repurpose them

Varieties of synapses

Synapse

___________ - anterograde synaptic transmission are genertic chemical synapses, but there is more diversity as synapses vary widely in the nervous system, specializing in specific locations, structurs, functions, and targets

Wide connections make synapses = versatile

• 7 types

Dendrodentritic

Varieties of synapses

____________ - dendrites send messages to other dendrites

Axodendritic

Varieties of synapses

____________ - Axon terminal of one neuron synapses on dendritic spine of another

Axoextracellular

Varieties of synapses

____________ - terminal with no specific target– secretes transmitter into extracellular fluid

Axosomatic

Varieties of synapses

____________ - axon terminal ends on cell body

Axosynaptic

Varieties of synapses

____________ - axon terminal ends on another terminal

• Synapses can exert precise control over another neurons input to a cell

Axoaxonic

Varieties of synapses

____________ - Axon terminal ends on another axon

Axosecretory

Varieties of synapses

____________ - axon terminal ends on tiny blood vessels and secretes transmitter directly into blood

Electrical synapses/gap junction

Synapse

____________ - Very fast. Fused presynaptic and postsynaptic membrane that allows an action potential to pass directly from one neuron to the next

• ___________  is found in interneurons to exchange certain substances between neurons and glial cells, or synchronize their behaviour

Area of contact between adjacent cells where connexin proteins in each cell form connection hemichannels, that when open, allow ions to pass thru the two cells.

• A diff way of getting messages cell to cell— this is why crayfish flick their tail so efficiently

While chemical synapses are most common, these are another type…

Excitatory synapse

Synapse

____________ - Makes neuron MORE LIKELY to fire an AP— usually located on dendrites. Round vesicles, dense material on membranes, wide cleft— large active zone (receptors cover more area)

• If enough inhibition, the axon hillock can stop the flow – if net excitatory and inhibition doesn’t stop the AP, then it’s a go.

• “Open the gate” strat = excitation NEEDS inhibition to lift, to allow neuron to fire

  • Like a racehorse ready to run the track, the inhibatory starting gate must be removed

Inhibitory synapse

Synapse

____________ - Makes neuron LESS LIKELY to fire an AP— usually located on cell body— flat vesicles, sparse material on membrane, narrow cleft, smaller active zone (receptors cover sparse area)

• Closer to where the APs start (soma or axon hillock)

• “Cut em off at the pass” start = inhibition stops excitation at the soma — blocking signal early

  • Better to stop it at the soma close to the initial segment/axon hillock

Chemical vs electrical synapses

Synapse

_____________ - some major differences:

1. Chemical synapse: relied on more— more flexible and show plasticity (learning)

   1. Can amplify or diminish signal sent form one neuron to the next

   2. can change with experience to alter signals AKA, LEARN

2. Electrical synapse: less relied on due to no plasticity, but way quicker

   1. Don’t show plasticity, but build for speed + efficient communication

Evolution of complex neurotransmission systems

____________ - Chemical transmission may have had its origins in the feeding behavior of single-celled creatures

• Digestive juices are secreted onto prey via exocytosis (release of neurotransmitter)

• Prey is captured via endocytosis

This process parallels the use of neurotransmitters for communication

chemical synapses; gap junction/electrical synapses

5-1 Review Questions

1. In mammals, the principal form of communcation between neurons occurs via _________, even though this structure is slower and more complex than the fused ________.

experience; learning

5-1 Review Questions

2. The principal benefit of chemical synapses over electrical synapses is that they can change with__________ to alter their signals and therefore, mediate (show) __________.

dendrite; cell body/soma

5-1 Review Questions

4. Excitatory synapses are usually lcoated on a(n) ____________, while inhibatory synapses are usually located on a(n) ___________.

4 criteria for identifying neurotransmitters

____________ - are used to figure out “hey this chemical might be a neurotransmitter!”

1. Transmitter must be synthesized or present in neuron

2. When released, transmitter must produce a response in target cell (essentially it must have a job (exhibitory, inhibitory, or signal to proteins)

3. Same receptor action must be obtained when transmitter is experimentally placed on receptor– you can replicate that job/action/response in an artificial way or elicit the same response on the receptor side

4. There must be a mechanism for removal after the transmitter’s work is done.

1) Transmitter must be synthesized in the neuron or be present

4 criteria for identifying a neurotransmitter

_______________ - step 1

2) When neuron is active, transmitter must be released + produce a response in a target

4 criteria for identifying a neurotransmitter

_______________ - step 2

3) Same response must be obtained when the transmitter is placed on target

4 criteria for identifying a neurotransmitter

_______________ - step 3

4) Mechanism must exist for removing neurotransmitter from site when done working

4 criteria for identifying a neurotransmitter

_______________ - step 4

Renshaw loop

____________ - these cells are inhibitory interneurons found in the gray matter of spinal cord, associated w/ an alpha motor neuron

Neurotransmitters

___________ - applies to chemcials that carry a message from the presynaptic membrane of one meuron to another by influencing postsynaptic membrane voltage, changes the structure of a synapse, communicate by sending messages in opposite direction.

• Retrograde messages: influence release of reuptake of transmitters on presynaptic side

Reuptake

Neurotransmitters

___________ - inactivation of a neurotransmitter when the membrane transporter proteins bring the transmitter back into the presynaptic axon terminal for reuse

Retrograde messages

Neurotransmitters

___________ - reverse direction messages that influence reuptake of transmitters on the presynaptic side

• Neurotransmitters communicate by sending messages in the opposite direction/doing this

SPL-GI: Small-molecule, peptide, lipid, gaseous, ion,

________________ - these are the 5 classes of neurotransmitters.

5 classes of neurotransmitters (SPL-GI)

___________ - include…

1. Small-molecule transmitters

2. Peptide transmitters

3. Lipid transmitters

4. Gaseuous transmitters

5. Ion transmitters

1) Small-molecule transmitters

Classes of neurotransmitters

____________ - quick-acting neurotransmitter made in the axon terminal from products in your diet

• ACh, DA, Glu

Acetycholine (ACh) synthesis

Classes of neurotransmitters (small-molecule transmitters)

____________ - Assembled @ axon, released @ terminal— what you eat can influence the abundance/activity of these:

• Choline (egg yolk, salmon, avocado)

• Acetate (lemom juice, vinegar)

For the breakdown of these…

• Enzyme: acetycholinesterase (AChE)

Types of synthesis include…

• Amine synthesis

• Serotonin synthesis

• Amino acid synthesis

• Purines

Chemistry of ACh

Classes of neurotransmitters (small-molecule transmitters) → ACh synthesis

_______________ - two enzymes combine the dietary precursors of ACh in the cell, while a third breaks them down in the synapse for reuptake

1. Acetyl CoA carries acetate to the transmitter synthesis site

2. ChAT transfers acetate to choline to form ACh

3. Breakdown products can be taken back up into the cell and reused

4. In synaptic cleft AchE detaches acetate from choline

Amine (DA, NE, EP) synthesis

Classes of neurotransmitters (small-molecule transmitters)

____________ - precursor chemical comes from food (like cheese)

• Enzyme: Tyrosine hydroxylase changes tyrosine to L-Dopa

  • This is limited, and so is production of DA, NE, EP.

  • Orally taking L-Dopa bypasses the rate-limiting factor

In movement disorders like Parkinson’s– we can’t just give them dopamine. L-dopa is admistered as it can cross the blood-brain barrer, while dopamine will not do anything good. L-dopa can be a precursor for dopamine development.

Rate-limiting factor

Classes of neurotransmitters (small-molecule transmitters) → amine synthesis

____________ - any chemical in limited supply that restricts the pace at which another chemical can be synthesized

• This can be bypassed in the oral administration of L-Dopa, which why it is a medication used in treating Parkinson’s.

In movement disorders like Parkinson’s– we can’t just give them dopamine. L-dopa is admistered as it can cross the blood-brain barrer, while dopamine will not do anything good. L-dopa can be a precursor for dopamine development.

Serotonin (5-HT) synthesis

Classes of neurotransmitters (small-molecule transmitters)

____________ - comes from L-tryptophan— found in pork, turkey, milk, bananas…

• Serotonin (5-HT)

Serotonin

Classes of neurotransmitters (small-molecule transmitters) → 5-HT synthesis

____________ - amine neurotransmitter— helps regulate mood, aggression, appetite, arousal, pain perception, respiration

Amino acid synthesis

Classes of neurotransmitters (small-molecule transmitters)

____________ - creation of the workhouses of the brain, since so many synapses use them

• Glutamate (Glu) → excitatory

• GABA → inhibatory

• Also includes histidine, which is the source of histamine (H)

Glutamate (Glu)

Classes of neurotransmitters (small-molecule transmitters) → amino acid synthesis

____________ - amino acid transmitter— typically excites neurons. Becomes neurotransmitter if appropriately packaged in vesicles in the axon terminal

• Worhouse of the brain

GABA

Classes of neurotransmitters (small-molecule transmitters) → amino acid synthesis

____________ - amino acid transmitter— typically inhibits neurons. Formed by simple modification of glutamate (Glu) molecule

• Workhouse of the brain

Histamine (H)

Classes of neurotransmitters (small-molecule transmitters) → amino acid synthesis

____________ - source is histidine (an amino acid)— _____ is a neurotransmitter which contrrols arousal, waking, causes constriction of smooth muscles— when activated in allergic reactions, constricts airway and contributes to asthma 

Purines

Classes of neurotransmitters (small-molecule transmitters)

____________ - building blocks for DNA + RNA AKA nucleotides

• Ex: ATP— removing 3 phosphate groups from ATP leaves adenosine, which promotes sleep, suppresses arousal, blood flow regulation thru vasodilation

  • Remember ATP is the main energy currency.

2) Peptide transmitters/neuropeptides

Classes of neurotransmitters

____________ - short multifunctional amino acid chain (>100)— acts as neurotransmitter, can act as a hormone— acts slow, replaced slowly.

May contribute to learning— also regulate stress + bonding hormones, eating, drinking, pleasure and pain.

• Ex: Opioids, oxytocin

• Perform a HUGE role of functions since they have such large numbers

• Can act as hormones that respond to stress, enable mother-child bonding

These leave the cell by exocytosis

• Act slower compared to small-molecule, requires instructions from DNA to create new ones

3) Lipid transmitters

Classes of neurotransmitters

____________ - newer, not as established exception to “5 easy steps”— these are retrograde. Move backwards from post-synaptic to pre-synaptic

• AKA Endocannabindoids like anandamide and 2-AG

Endocannabinoids

Classes of neurotransmitters (lipid transmitters)

____________ - class of lipid neurotransmitters including anandamide and 2-AG, synthesized @ postsynaptic membrane to act on receptors at the presynaptic— affects appetite, pain, sleep, mood, memory, anxiety + stress response

Can reduce # of small-molecule transmitter being released

• Are lipophilic AKA “Fat-loving”— not soluable in water, not stored in vesicles

• Comes from food like eggs and poultry

4) Gaseuous transmitters

Classes of neurotransmitters

____________ - newer, not as established. Not stored in synaptic vesicles or released from them— synthesized on demand, in cell as needed + easily crosses cell membrane.

Floating in between cells as needed

• Gases include:

  • Nitric oxide (NO)

  • Carbon monoxide (CO)

  • Hydrogen sulfide (H2S)

• Water-soluable

Nitric oxide (NO)

Classes of neurotransmitters (gaseous transmitters)

____________ - gaseuous neurotransmitter that acts to dilate blood vessels, help digestion, and activate cellular metabolism

Carbon monoxide (CO)

Classes of neurotransmitters (gaseous transmitters)

____________ - gaseuous neurotransmitter that activates cellular metabolism

Hydrogen sulfide (H2S)

Classes of neurotransmitters (gaseous transmitters)

____________ - gaseuous neurotransmitter that slows cellular metabolism

5) Ion transmitter

Classes of neurotransmitters

____________ - actively transported, packaged into vesicles— usually with another transmitter like glutumate— and released into the synaptic cleft

• Zinc

Zinc

Classes of neurotransmitters (ion transmitter)

____________ - an ion transmitter that’s packaged and stored in vesicles that’s then released, and interacts w/ several receptors

After out of the synaptic cleft, it’ll cause diff change thru interacting with diff neurotransmitters.-

• Alzheimer’s disease

  • Lots of correlational evidence that behaviour or maladaptive behaviour w/ alzheimers has an association in reduction of prefrontal cortex, reduced grey matter, higher ventral sizes, and levels of zinc also correlate

  • Normal levels of zinc = normal cognitive functioning – dysregulated zinc = seen in cognitive decline, like Alzheimer's

    • unknown if zinc causes this, or if other things in Alzheimer's cause zinc to dysregulate

2 classes of receptors

___________- two kinds. One is quicker, has a pore and binding site— the other one does not have a pore, just a binding site, and is much slower.

1. Ionotrophic receptor

2. Metabotrophic receptor

1) Ionotrophic receptor

2 classes of receptors

______________ - often excitatory—  often trigger an AP. These bring rapid change in membrane voltage, which is quick.

• Two parts:

  • Binding site (for a neurotransmitter)

  • Pore or channel (for ion)

    • Pore either opens or closes when the neurotransmitter binds.

2) Metabotrophic receptor

2 classes of receptors

______________ - slower, longer-lasting with widespread effects though they do not have a pore for ions— therefore indirecetly produce changes in nearby ion channels, OR in cell’s metabolic activity

• G-protein

  • Subunits: alpha, beta, gamma

• Second messenger

G-protein

2 classes of receptors (metabotropic receptors)

______________ - key to the downstream effects of metabotrophic receptors— guanyl nucleotide-binding proteins that couples w/ a metabotropic receptor— when activated, it’ll bind to other proteins

• Subunit

  • Alpha, betam gamma

  • When a neurotransmitter binds to this metabotropic receptor, alpha subunit detatches

Second messenger

2 classes of receptors (metabotropic receptors)

______________ - detatched alpha subunit will binds to an enzyme— this enzyme turns into _________ — a chemical that starts a biochemical process when activated by a neurotransmitter (who are the first messenger)

______ can:

1. Bind to a channel & alter ion flow

2. Form new ion channels

3. Bind to DNA to alter protein production

Amplification cascade

Subunits

2 classes of receptors (metabotropic receptors) - G protein

______________ - protein molecule that assembles w/ other protein molecules

• For G-protein, these are alpha, beta, gamma

Amplification cascade

2 classes of receptors (metabotropic receptors) - G protein (second messenger)

______________ - metabotrpic receptors allow for the possibility that a single neurotransmitter’s binding can actiavte this—escalating sequence of events— a cascade effect in downstream proteins (second messengers or channels or both) being activated or deactivated

• Creates a widespread amplifying effect, not seen in ionotropic receptors

Receptor subtypes

______________ - Each neurotransmitter may interact with a number of receptor subtypes specific to that neurotransmitter.

• Each subtype has slightly different properties, which confer different activities.

• Presence or absence of binding sites for other molecules, how long a channel remains open or closed, ability to interact with intracellular signaling molecules.