Neurotransmitters

Question 1

Where does integration of the signals coming down the dendrites occur?

Answer 1

In the soma

Question 2

What is the width of a synaptic cleft?

Answer 2

20-100 nm

Question 3

Describe the process of synaptic transmission.

Answer 3

The vesicles dock on the pre-synaptic membrane and await a signal before the contents of the vesicles are expelled into the synaptic cleft.

Question 4

What are the three classes of neurotransmitter?

Answer 4

Amino acids
Amines
Neuropeptides

Question 5

What allows the vesicles to dock stably?

Answer 5

Interaction between the vesicle membrane proteins and pre-synaptic membrane proteins.

Question 6

What triggers the vesicle exocytosis?

Answer 6

There is a high concentration of calcium channels at the area where the vesicle docks. An influx of calcium causes vesicle exocytosis.

Question 7

State three toxins that target vesicle proteins and the effects that they have.

Answer 7

Tetanus - causes spastic paralysis (zinc dependent endopeptidase)
Botulinum - causes flacid paralysis
Alpha-latrotoxin - prevents recycling of the vesicles and hence releases the transmitter to total depletion

Question 8

What are the two types of receptor and what is the most important difference in their properties?

Answer 8

Ion Channel Receptor - FAST

G-protein linked receptor – SLOW

Question 9

What is the effect of glutamate on the post-synaptic membrane?

Answer 9

Glutamate is excitatory - causes influx of Na+

Question 10

What is the effect of GABA on the post-synaptic membrane?

Answer 10

GABA is inhibitory - causes influx of Cl-

Question 11

What are the two main types of glutamate receptor? State some properties.

Answer 11

AMPA - rapid acting - responsible for the majority of fast excitatory synapses
NMDA - slower acting (despite still being excitatory and fast) - requires two conditions for activation = depolarisation of membrane + glutamate binding
NMDA lets in Na+ and Ca2+

Question 12

Where is glutamate formed?

Answer 12

Glutamate is a product of intermediary metabolism (e.g. glycolysis and TCA cycle)

Question 13

Which transporter takes glutamate up into glial cells on the pre-synaptic membrane?

Answer 13

Excitatory Amino Acid Transporter 2 (EAAT 2)

Question 14

How is glutamate inactivated in the glial cells?

Answer 14

Glutamate is converted to glutamine by GLUTAMINE SYNTHETASE

Question 15

What causes epilepsy?

Answer 15

Increased release of glutamate causing hyperexcitability

Question 16

Describe the structure of GABA and state how it is produced.

Answer 16

GABA has the same structure as Glutamate but with the carboxyl group removed. So GABA is produced from glutamate by the action of GLUTAMIC ACID DECARBOXYLASE (GAD).

Question 17

What transporter takes GABA up into the glial cells?

Answer 17

GABA Transporter (GAT)

Question 18

Describe the inactivation of GABA in the glial cells.

Answer 18

GABA is converted to SUCCINATE SEMIALDEHYDE by GABA Transaminase

Question 19

Describe how the GABA receptor can be manipulated to create treatments for epilepsy.

Answer 19

There are binding sites on the pentameric GABA receptor for benzodiazepines, steroids, barbiturates etc. so these sites can be manipulated to facilitate the activity of GABA and produce antiepileptic drugs.