Chapter 2 - Synaptic Transmitters and Neurotransmitters

Question 1

How do you identify the axon from the dendrite under a microscope?

Answer 1

Look for synaptic vesicles.

Question 2

Describe the steps involved in synaptic transmission briefly

Answer 2

Release of neurotransmitters from presynaptic axon terminal –> Detection of neurotransmitters by receptors in the postsynaptic dendrite, binding of receptors to specific neurotransmitters –> Destruction of leftover neurotransmitters or reuptake

Question 3

When are neurotransmitters released from the presynaptic neuron?

Answer 3

Neurotransmitters are released to the synaptic cleft after an action potential reaches the presynaptic axonal terminal.

Question 4

What are 2 types of receptors present at the postsynaptic dendritic spine?

Answer 4

1) Ligand-gated ion channels

2) Metabotropic Receptor

Question 5

What are ligand-gated ion channels/ionotropic receptors?

Answer 5

They are receptors that are themselves ion channels.

Question 6

How do ionotropic receptors work?

Answer 6

Once a neurotransmitter binds to the receptor, it changes configuration, which opens the channel.

Rather similar to voltage-gated ion channels, except that rather than opening with changes in voltage, they open when a specific chemical (a neurotransmitter) binds to it.

They exert their effect directly through the passage of ions.

Question 7

How do metabotropic receptors work?

Answer 7

They open ion channels indirectly, through the action of intracellular processes.

when a neurotransmitter binds to this receptor, it evokes biochemical changes in molecules inside the cell, and these molecules then diffuse and open the ion channels in the vicinity.

also known as G-protein-coupled receptor because the key protein that interacts with them is known as G-protein.

Question 8

What causes depolarization to occur in the cell?

Answer 8

Opening of ion channels

Caused by receptors binding to specific neurotransmitters, which then opens ion channels and cause depolarization.

Question 9

What happens to leftover neurotransmitters?

Answer 9

They are either destroyed in the synaptic cleft or are reabsorbed by the presynaptic neuron or by the glia surrounding the synapse (aka reuptake)

Question 10

______ and __________ increase the release of dopamine.

Answer 10

amphetamines and cocaine.

Question 11

What blocks the reuptake of dopamine?

Answer 11

amphetamines, cocaine and ritalin.

Question 12

Why is Ritalin used as a drug to treat ADHD, whereas cocaine is seen as a dangerous addictive drug?

Answer 12

Because cocaine is delivered in high concentrations and for a short period, while Ritalin is delivered in small doses over an extended period of time.

Note: The faster dopamine levels go up, the greater the potential for abuse.

Both the increase of dopamine release and the decrease in reuptake means that a lot more dopamine is swimming in the synaptic cleft and this lasts for a lot longer.

Question 13

What does spatial summation mean?

Answer 13

When the postsynaptic neuron is summing inputs in different locations.

Question 14

How does spatial summation occur?

Answer 14

3 different inputs

When all 3 presynaptic neurons are active simultaneously, this allows the postsynaptic neuron to cross the threshold and fire an action potential.

Question 15

What does temporal summation mean?

Answer 15

When the postsynaptic neuron is summing inputs from the SAME SOURCE over time to cross the threshold

Question 16

There are 3 presynaptic neurons, but only 1 is active.

a) Will this allow the postsynaptic neuron to cross the threshold?
b) Suppose this one neuron starts firing at a higher rate. Will the postsynaptic neuron still fire an action potential?

Answer 16

a) no

b) yes.

Question 17

How does propagation of voltage occur in the membrane?

Answer 17

diffusion of ions

Question 18

Dendrites propagate changes in the membrane potential via the activation of voltage-gated channels.
True or false?

Answer 18

False. There are no voltage-gated channels in dendrites.

The way they propagate changes in the membrane potential acts similarly to diffusion of ions.

The depolarization caused at one point in the membrane will diffuse passively along in the membrane. Unlike the action potential, at the dendrite, the voltage will move symmetrically in both directions, since there are no inactivated channels causing a refractory period.

Question 19

Describe the ripple effect in spatial summation

Answer 19

Small depolarization occurs at synapse because the release of neurotransmitters is detected by postsynaptic neuron. This in turn opens up ion channels which then causes a small depolarization.

Diffusion of ions occurs in both directions, towards and away from the soma. Therefore, depolarization also occurs at areas adjacent to the synapse, but of a smaller magnitude.

A few microseconds later, the ion channels in the synapse close, so membrane returns to resting state. Diffusion of ions still occurs but the effects are getting smaller and smaller.

Question 20

Describe how spatial summation can elicit an action potential in a neuron.

Eg: 4 inputs

Answer 20

Time 0: First input is activated.

Time 1: Second input is activated. Decayed potential from first input and high potential from second synapse compound and add up, evoking a large depolarization.

Time 2: Third input activated. High potential from 3rd input and decayed potential from first and second overlap –> larger depolarization.

Time 3: 4th input activated. High potential from 4th input. Evokes a very large depolarization, which is the sum of all 4 effects combined.

Time 4: No more inputs that are active at this point. However, the depolarization spreads to the soma, and reaches the axon hillock, where there are many voltage-gated channels. The depolarization is enough to cross the threshold, and this results in the firing of an action potential.

Question 21

If the order of inputs is reversed, would it still result in an action potential?

Answer 21

No because summation would occur in the opposite direction. The large depolarization would never reach the soma.

Question 22

What does information mean?

Answer 22

The reduction of uncertainty

Question 23

Glutamate usually acts as an ____________ neurotransmitter, while GABA acts as an ___________ one.

Answer 23

excitatory

inhibitory

Question 24

Why is it that glutamate is not always an excitatory neurotransmitter?

Answer 24

the specific effect of a neurotransmitter will depend on the specific ion channels opened by the neurotransmitter and the specific ionic balance of the neuron.

Question 25

What kind of effects do GABA and Glutamate exert on the postsynaptic cell?

Answer 25

ionotropic effect

Question 26

What kind of effects do neuromodulators exert on the postsynaptic cell?

Answer 26

metabotropic effect.
Influence larger groups of neurons in a more diffused manner and for a longer period of time. They are not reabsorbed so quickly, and affect a larger area.

Question 27

Which part of the brain produces noradrenaline?

Answer 27

Small nucleus in the pons, which is part of the hindbrain, called the locus coeruleus.

Question 28

What is the function of norepinephrine?

Answer 28

thought to increase attention and arousal

Question 29

Which part of the brain produces dopamine?

Answer 29

substantia nigra and ventral tegmental area.

distributed in large parts of the brain, including cortex and basal ganglia.

Question 30

What is the function of dopamine?

Answer 30

generally thought to be important for the reward system, motor system and cognition.

Question 31

Which part of the brain releases serotonin?

Answer 31

Raphe nuclei, a small nuclei in the brainstem –> project serotonin to large areas of the brain.

Question 32

What is the function of serotonin?

Answer 32

regulation of mood and sleep

Question 33

How do SSRIs act as an antidepressant?

Answer 33

Blocks the reuptake of serotonin, which in effect, increases its concentration and duration in the brain.

Question 34

Where is acetylcholine produced?

Answer 34

Produced in small clusters of neurons, in the basal forebrain and pons. Also project to multiple areas in the CNS

Question 35

List 4 functions related to acetylcholine.

Answer 35

learning
memory
reward
arousal.

Question 36

Describe the projection from these ascending modulatory systems.

Answer 36

1) used to coordinate large parts of the brain to accomplish something
2) projection is usually diffuse and long-range
3) but this also means they are not very specific.
4) to complicate things further, neuromodulatory systems modulate each other.

Question 37

Which neurons do neuropeptides affect?

Answer 37

released through dendrites, soma, and axon. mostly from dendrites. Unlike other neurotransmitters released exclusively at axon terminals. Released by repeated depolarisation, not a single action potential.

Question 38

What are hormones?

Answer 38

refer to neurotransmitters released into the blood stream and affect every tissue around the body with appropriate receptors. Particularly useful for coordinating long lasting changes in multiple parts of body.