Week 3: Synaptic Transmission & Neurotransmitters

Question 1

What are the 2 primary neurotransmitters in the nervous system?

Answer 1

Glutamate (excitatory) & GABA (inhibitory)

Question 2

How to locate axon and dendrite under a microscope?

Answer 2

Look for synaptic vesicles

Question 3

Briefly describe the sequence of chemical events at a synapse. (5 steps)
Hint: synthesise, calcium, cleft, separate, reuptake

Answer 3

1) Neuron synthesizes chemicals that serve as neurotransmitters.
2) Action potential travels down axon. At presynaptic terminal, an action potential enables calcium to enter the cell. Calcium releases neurotransmitters into synaptic cleft.
3) Neurotransmitters diffuse across cleft, attach to receptors, and alter activity of postsynaptic neuron.
4) Neurotransmitter separate from receptors.
5) May either be reabsorbed back into presynaptic neuron (reuptake) or diffuse away.

Question 4

What are 2 types of receptors at the postsynaptic neuron?

Answer 4

Ligand-gated ion channels (ionotropic receptors)

G-protein-coupled receptors (metabotropic receptors)

Question 5

Briefly describe how an ionotropic receptor works.

Answer 5

Receptor itself is an ion channel
Opens when a specific neurotransmitter binds to it
Changes configuration and channel opens.
Effect is direct where ions pass through the channel.
Effect is faster but shorter lived (eg. vision & hearing which requires rapid quick changing info)

Question 6

Briefly describe how a metabotropic receptor works.

Answer 6

opens ion channels indirectly, through the action of intracellular processes
When neurotransmitter binds to this receptor, it evokes biochemical changes in molecules inside the cell, which diffuse and open ion channels in the vicinity.
G-protein, an energy storing molecule, detaches and takes its energy elsewhere.
Exert effect through metabolic pathways (slower but longer effect) (eg. taste, smell, pain – exact timing is not so important)

Question 7

Do receptors in postsynaptic cells bind to any neurotransmitter?

Answer 7

No, they bind to specific neurotransmitters.

Question 8

After ion channels of receptors are opened, what happens to postsynaptic cell?

Answer 8

It is depolarised. Ions entering contributes to synaptic input for initial depolarization. Could take many simultaneous active synapses to reach threshold for action potential in postsynaptic cell.

Question 9

Amphetamines are used to treat ADHD, what do they do?

Answer 9

They inhibit transporters for dopamine, lowers reuptake, prolonging dopamine’s effects. Also increase the release of dopamine into the synapse. Increases the amount of dopamine in the synaptic cleft.

Question 10

What is spatial summation?

Answer 10

Summing inputs from different dendrites at different locations.

Question 11

What is temporal summation?

Answer 11

Summing inputs from the same source over time to cross the threshold.

Question 12

How is spatial summation critical to brain functioning?

Answer 12

Each neuron receives sensory input from many incoming axons. This might produce synchronised responses, exciting a neuron enough to activate it

Question 13

How do dendrites propagate changes in membrane potential?

Answer 13

Through diffusion of ions. No voltage-gated channels in dendrite, so depolarization just diffuse passively along the membrane.

Question 14

How does voltage move in dendrites? How is this different from how it moves in axons?

Answer 14

Voltage moves symmetrically in both directions (towards & away from soma) since there are no hyperpolarised segments during refractory period.

Question 15

Describe the ripple effect in spatial summation.

Answer 15

Some depolarisation occurs at location of synapse.
Ions diffuse to the sides, resulting in depolarisation in locations adjacent to synapse, but of smaller magnitude. A few microseconds later, ion channels in first synapse closes and membrane potential returns to resting state. Effects become smaller and smaller.

Question 16

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

Answer 16

When the depolarisation from the 1st input reaches the 2nd input, it overlaps with the effect of the 2nd input. They compound and add up evoking a larger depolarisation. Overlap of responses evoke a larger and larger depolarisation, summing the effects from all 4 synapses combined. Depolarization eventually spreads to soma, when it reaches axon hillock, the depolarisation is enough to cross the threshold and elicit an action potential in the postsynaptic neuron

Question 17

In spatial summation, what happens if we reverse the order of inputs from near to far?

Answer 17

The neuron depolarises much less, and does not evoke an action potential. The summation occurs in the opposite direction away from the soma, so the large depolarisation never reaches the axon hillock.

Question 18

What does the information theory measure?

Answer 18

It is a measure of the reduction of uncertainty

Question 19

GABA usually acts as an _____ neurotransmitter.

Glutamate usually acts as an _____ neurotransmitter

Answer 19

inhibitory; excitatory
Note: most of the time, but not all the time. The specific effect of a neurotransmitter depends on the specific ion channels opened by the neurotransmitter and specific ionic balance of the neuron.

Question 20

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

Answer 20

Ionotropic effect

Question 21

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

Answer 21

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 22

Where is noredrenalin/norepinephrine produced?

Answer 22

locus coeruleus (project to CNS)

Question 23

What function is norepinephrine thought to be involved in?

Answer 23

thought to increase arousal and attention

Question 24

Where is dopamine produced?

Answer 24

Substantia nigra and ventral tegmental area (project to cortical areas and basal ganglia)

Question 25

What function is dopamine thought to be important for?

Answer 25

important for reward system, motor system, and cognition. Projections are diffuse and long range in an ascending modulatory system (ie. from lower to higher brain regions)

Question 26

Where is the primary source of serotonin?

Answer 26

dorsal raphe nuclei (project to CNS)

Question 27

What is serotonin thought to be important for?

Answer 27

mood regulation and sleep

Question 28

Where is the primary source of acetylcholine?

Answer 28

Basal forebrain and pons (project to CNS)

Question 29

What is acetylcholine thought to be important for?

Answer 29

learning, memory, reward, arousal etc.

Question 30

What are neuropeptides?

Answer 30

Chains of amino acid.

Question 31

Where are neuropeptides released in neurons?

Answer 31

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 32

Which neurons do neuropeptides affect?

Answer 32

affect all nearby neurons that have appropriate receptors through diffusion. diffuse to a wide area and effects last a long time.

Question 33

What are hormones?

Answer 33

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.