The Post Synaptic Terminal

Question 1

What are dendritic spines?

Answer 1

spines are made up of a head and neck and exist as bumps on the dendrite

Question 2

What are the functions of dendritic spines?

Answer 2

Increased surface area to optimise packing of synapses
Serve as separate electrical units, modulating the synaptic signals
Provide biochemical compartments that restrict the mobility of molecules

Question 3

How do the sizes of dendritic spines vary and what does size mean for their function?

Answer 3

The dendritic spines vary a lot in size, smaller spines have a smaller amplitude of responses.

Question 4

How does the morphology of the dendritic spine affect its electrical resistance?

Answer 4

If the neck is smaller, or longer in length then there will be a greater electrical resistance .

R=pL/CSA

Question 5

How does the morphology of the dendritic spine affect its chemical resistance?

Answer 5

Longer or narrower neck = more resistance.

Question 6

How can you compare the electrical resistance of a dendritic spine, and its morphology?

Answer 6

FRAP can be used; dye injected then photobleached in the head and neck, then fluorescence recovery measures time taken for dye to return to head; this measurement is then compared to the neck width and length.

Question 7

How can you compare the chemical resistance of a dendritic spine to its morphology?

Answer 7

Caged glutamate becomes freed when exposed to laser light; use this on varying dendritic spines and see how signal produced is affected by morphology

Question 8

What does FRAP stand for?

Answer 8

Fluorescence recovery after photobleaching

Question 9

What are the two types of glutamate receptors?

Answer 9

AMPA and NMDA

Question 10

What are nanocoloumns

Answer 10

Arrangements of neurotransmitters so that they are directly opposed from the active zone by scaffold proteins keeping them at the synaptic cleft by a trans-synaptic adhesion complex.

Question 11

Describe the architecture of the scaffolding of NMDARs

Answer 11

(primary and secondary scaffolding)

Attached to PSD-95 (post-synaptic density protein 95) on PDZ domain, which anchors it to the actin frame.

Question 12

Describe the architecture of the scaffolding of AMPARs

Answer 12

AMPA - TARP - PSD95 - Actin frame

PSD-95 has a PDZ domain that helps it interact with NMDAs directly, but in this case AMPA uses TARP to attach to PSD-95

TARP = transmembrane AMPAR regulatory protein
PSD-95 = post synaptic density protein 95

Question 13

Describe the structure of an ACh receptor

Answer 13

Pentamer

Monomers have 4 transmembrane domains, which twist when ACh binds, opening the pore

Question 14

What is an ionotropic receptor?

Answer 14

Ligand gated ion channels

Question 15

Describe the structure of a glutamate receptor

Answer 15

Tetramer with 3 transmembrane domains.

Question 16

Describe how the glutamate receptor opens

Answer 16

Transmembrane domains are pulled apart and then begin to relax until they are closed even when glutamate bound (desensitised state).

Question 17

What ions can pass through glutamate receptors?

Answer 17

Mostly Na+ and K+

Question 18

What is the electrical effect of glutamate binding to its receptor?

Answer 18

Causes inward current called EPSC (excitatory post synaptic current), which causes a transient depolarisation in the post synaptic neuron (EPSP)

Question 19

Which glutamate receptor is the fast one and which is the slow one?

Answer 19

AMPA = fast
NMDA = slow

Question 20

What happens when glutamate binds to an AMPA receptor?

Answer 20

Ligand binds, k+ and Na+ (and sometimes Ca2+) pass through fast acting

Question 21

What happens when glutamate binds to an NMDA receptor?

Answer 21

Ligand binds and depolarisation needed as well for Mg+ plug to be removed, Na and Ca can pass through, slower acting

Question 22

Where on the dendrite are inhibitory/excitatory synapses found?

Answer 22

inhibitory = main body of dendrite
Excitatory = dendrite spines

Question 23

What is the structure of a GABA receptor

Answer 23

Pentamer (2a, 2b, y), GABA binds in between a and b subunits.

Question 24

What is the function of the GABA receptor

Answer 24

GABA receptors move Cl- ions into the neuron which causes hyperpolarisation of the post synaptic neuron, making it more difficult exceed the threshold required for an action potential to take place therefore having an inhibitory effect on the firing of the neuron