Chapter 6 Neurotransmitter Systems

Question 1

Cholinergic Neurons

Answer 1

Acetylcholine (ACh) is the neurotransmitter at the neuromuscular
junction and is therefore synthesized by all the motor neurons in the
spinal cord and brain stem. Requires ChAT (what are only in cholinergic neurons, good marker)
-memory, arousal, analgesia (kiputunnottomuus)
-

Question 2

Synthesis and degradation of ACh

Answer 2

synthesis: Acetyl CoA + Choline

Degradation : By AchE -> Acetic acid + Choline (in the cleft).

Question 3

The lilfe cycle of ACh

Answer 3

ACh released-> Choline and acetic acid produced-> Cholines influx to the cell via a transporter that requires Na+ to power to movement. ->choline limits how much ACh is synthesized (transport of choline to neuron is said to be rate-limiting step in ACh synthesis)-> ACh synthesized by Acetyl CoA and choline and up to vesicles by ACh transporter.

Question 4

What else do cholinergic neurons manufacture?

Answer 4

ACh degradative enzyme acetylcholinesterase (AChE). AChE degrades ACh into choline and acetic acid. ->Inhibition of AChE prevents the breakdown of ACh.

Question 5

Catecholaminergic Neurons

Answer 5

Three different amine neurotransmitters are collectively called catehcholamines.
-dopamine (DA) , norepinephrine (NE), and epinephrine, also called adrenaline

-Found in nervous system involved in the regulation of movement, mood, attention, and visceral function

Question 6

Catecholaminergic neurons all contain? What are the steps of catecholamines synthesis?

Answer 6

They all contain the ezyme tyrosine hydroxylase (TH) which catalyzes -> conversion of tyrosine to dopa.

• > Dopa is converted into the neurotransmitter DA by the enzyme dopa decarboxylase(the amount of DA synthesized depends primarily on the amount of dopa available. )
• > Neurons that use NE as a neurotransmitter contain, in addition to TH and dopa decarboxylase, the enzyme dopamine -hydroxylase (DBH) , which converts DA to NE. ( DBH is not found in the cytosol but instead is located within the synaptic vesicles.-> DA made into NE in vesicles)
• > The last in the line of catecholamine neurotransmitters is epinephrine (adrenaline). Adrenergic neurons contain the enzyme phentolamine N -methyltransferase (PNMT), which converts NE to epinephrine. (made in cytosol->back to vesicle to be relesed)

Question 7

How are catcholamines recycled or degraded?

Answer 7

he catecholamine systems have no fast extracellular degradative enzyme. Instead, the actions of catecholamines in the synaptic cleft are terminated by selective uptake of the neurotransmitters back into the axon terminal via Na -dependent transporters.
Once inside the axon terminal, the catecholamines may be reloaded into synaptic vesicles for reuse, or they may be enzymatically destroyed by the action of monoamine oxidase (MAO) , an enzyme found on the outer membrane of mitochondria.

Question 8

end-product inhibition

Answer 8

Regulation: For example, decreased catecholamine release by the axon terminal causes the catecholamine concentration in the cytosol to rise, thereby inhibiting TH.

Question 9

Synthesis of serotonin

Answer 9

Tryptophan-> (5-HTP) by the enzyme tryptophan hydroxylase.

• > The 5-HTP is then converted to 5-HT by the enzyme 5-HTP decarboxylase
• Serotonin synthesis appears to be limited by the availability of tryptophan in the extracellular fluid bathing neurons.( The source of brain tryptophan is the blood, and the source of blood tryptophan is the diet (grains, meat, dairy products, and chocolate are particularly rich in tryptophan). )

Question 10

How is serotonin (5-HT) removed from synaptoc cleft?

Answer 10

by the action of a specific transporter.
->Once it is back in the cytosol of the serotonergic axon terminal, the transmitter is either reloaded into synaptic vesicles or degraded by MAO.

Question 11

Glutamate and glycine synthesis?

Answer 11

from glucose and other precursors by the action of enzymes that exist in all cells.

Question 12

GABA synthesis?

Answer 12

not one of the 20 amino acids used to construct proteins, it is synthesized in large quantities only by the neurons that use it as a neurotransmitter.

->The precursor for GABA is glutamate. Synthesised by GAD.

Question 13

How are to synaptic actions of the amino acid neurotransmitters terminated?

Answer 13

By selective uptake into the presynaptic terminals and glia, once again via specific Na -dependent transporters. Inside the terminal or glial cell, GABA is metabolized by the enzyme GABA transaminase .

Question 14

Structure of receptors, nicotinic ACh receptors, GABA A and glycine, glutamate, ATP:

Answer 14

Nicotinic ACh receptor, GABA A, glycine:
-two alfa subunits, and one each of beta, ypsilon and sigma.=five protein subunits
-four separate segments that will coil into alpha helices
Glutamate: four sub unit
purineric ATP: three subunits

Question 15

Importance of Ca2+:

Answer 15

trigger presynaptic neurotransmitter release, activate many enzymes, regulate the opening of a variety of channels, and affect gene expression; in excessive amounts, Ca+2 can even trigger the death of a cell

Question 16

Most G-proteins have the same basic mode of operation:

Answer 16

1. 3 subunits, alfa, beta, ypsilon. In the resting state, a guanosine diphosphate (GDP) molecule is bound to the G subunit, and the whole complex floats around on the inner surface of the membrane.
2. .When activated by a G-protein-coupled receptor, the GDP is exchanged for GTP.
3. .The activated GTP-bound G-protein splits into two parts: the G _alfa (GTP) and the G_beta,ypsiloncomplex. Both can then move on to influence various effector proteins.

54The G_alfa subunit is itself an enzyme that eventually breaks down GTP into GDP. Therefore, G eventually terminates its own activity by converting the bound GTP to GDP.

5.The G _alfa and G _beta,ypsilonsubunits come back together, allowing the cycle to begin again.

Question 17

It is called ?? When action potentials skip from node to node resulting quick propagation.

Answer 17

Saltatory conduction

Question 18

It is called ?? When action potentials are in the direction from the soma to the axon terminal.

Answer 18

Orthodromic conduction

Question 19

It is called ?? When action potential are in direction from action terminal to soma

Answer 19

Antidromic conduction

Question 20

Second messenger cascade

Answer 20

Activation of an enzyme by G-protein that triggers a series of biomedical reactions, activating of other downstream enzymes that alter neuronal functions.

Question 21

Properties of amino acid- gated channels

Answer 21

They mediate most of the fast synaptic transmission in the CNS. Their properties:

1. Pharmacology of the binding sites: which transmitters affect them
2. Kinetics of the transmitter binding process and channel gating: duration of effect
3. Selectivity of ion channels: whether they produce excitation or inhibition, whether Ca2+ enters the cell in significant amounts
4. Conductance of open channels: magnitude of the channels’ effects

Question 22

What is special in GABA_A receptor?

Answer 22

Has several other sides where chemicals can dramatically modulate its functions for unknown reasons, like drugs.
-GABAA have a similar structure than nicotinic ACh receptors

Question 23

For what are GABA_A, GABA_B and Glysine nd glutamate receptors permeable to?

Answer 23

GABA_A= Cl-
GABA_B=K+
Glysine=Cl-
Glutamate: Na2+,K+,Ca2+(NMDA)

Question 24

Which channels cause EPSP?

Answer 24

Activation of ACh and glutamate-gated channels

Question 25

Which neurotransmitterchannels cause IPSP?

Answer 25

Avtivation of GABA and glycine-gated ion channels