Synaptic Transmission

Question 1

What are the two types of synapse?

Answer 1

Electrical and chemical

Question 2

Which synapse type is more prevalent?

Answer 2

Chemical

Question 3

Which synapse type is more biologically flexible?

Answer 3

Chemical

Question 4

What is a synapse?

Answer 4

The interface between the pre-synaptic part and post-synaptic part of a neuron.

Question 5

Which type of synapse is faster?

Answer 5

Electrical are faster

Question 6

Why are chemical synapses more flexible?

Answer 6

Huge range of NTs - and different expressions of the receptors - means that there is variability as to their response.

Question 7

What is a gap junction and what is it made from?

Answer 7

A physical connection between two neurons - is made from a protein called Connexon 36. (CX36)

Question 8

How many connexin subunits for the connexon channel?

Answer 8

6

Question 9

How do gap junctions work?

Answer 9

When an AP arrives - it undergoes conformational change - allowing ions and small molecules to flow through it.

Question 10

In which type of synapse are the cells physically connected together?

Answer 10

Gap junction - electrical synapse

Question 11

What is the difference between a pre-synaptic potential and a post-synaptic potential (in terms of voltage).

Answer 11

Pre-synaptic = huge change in voltage - from -60 to approx +34/40 mV

Post-synaptic - very small change in voltage transferred from pre-synaptic - only about 1mV

Question 12

Given the difference between pre-synaptic voltage and the post-synaptic potential that is received - what does this mean for generating an AP in the post-synaptic neuron?

Answer 12

As the post-synaptic neuron only receives a small depolarisation from the pre-synaptic neuron (via the gap junction) - it means the post-synaptic neuron needs lots of depolarisations in order to generate an AP in it.

Question 13

How do multiple depolarisations happen in the post-synaptic neuron?

Answer 13

They are often innervated by multiple cells = neural integration & summation of signal.

Question 14

What do chemical synapses use to propagate a signal?

Answer 14

They use neurotransmitters

Question 15

What is the site of NT release on a neuron called?

Answer 15

The active zone

Question 16

Where are NTs stored?

Answer 16

In synaptic vesicles

Question 17

Are the cells connected in a chemical synapse?

Answer 17

No - there is a space between them (30nm wide)

Question 18

What happens when the NT crosses the synaptic cleft? How does it cause an AP?

Answer 18

NT crosses the cleft, binds to a post-synaptic receptor in the membrane - this enables the post-synaptic receptor to undergo conformational change, which allows the induction of ions into the post-synaptic neuron, causing depolarisation and generating potential required for an AP to occur.

Question 19

What is the name of a synapse between an axon and a dendrite?

Answer 19

Axodendritic synapse

Question 20

What is the name of a synapse between an axon and a soma?

Answer 20

Axosomatic synapse

Question 21

What is the name of a synapse between the axons of neurons?

Answer 21

Axoaxonic synapse

Question 22

What are the names of these synapses?

Answer 22

A). Axodendritic synapse
B). Axosomatic synapse
C). Axoaxonic synapse

Question 23

Where are NTs synthesised?

Answer 23

In neuronal main cell body (usually in the RER).

Question 24

What are NTs?

Answer 24

Molecules that cross the synaptic cleft, binding to receptor targets on the postsynaptic membrane.

Question 25

Why do NTs need to be removed from the cleft?

Answer 25

To prevent constant stimulation of the post-synaptic neuron.

Question 26

What is transport of NTs from the cell body to the synapse called?

Answer 26

Axonal transport

Question 27

How are NTs transported in the neuron?

Answer 27

In vesicles, along microtubules

Question 28

Where are NTs packaged into vesicles?

Answer 28

In the Golgi apparatus

Question 29

What is the direction of travel of NTs from cell body to synapse called? Which protein is used to facilitate this?

Answer 29

Anterograde direction Protein = Kinesin

Question 30

What is the direction of travel of NTs from the synapse to the cell body called? Which protein is used to facilitate this?

Answer 30

Retrograde direction Protein = Dynein

Question 31

What happens to NTs when an AP arrives at the pre-synaptic membrane?

Answer 31

AP arrives and depolarises the pre-synaptic neuron. This causes Ca voltage-gated ion channels in the active zone to open - allowing an influx of Ca into the neuron. The Ca influx changes proteins on vesicles & the presynaptic membrane (snaps and snares) - these changes bring about docking of the vesicle - and then the contents are released into the synapse via exocytosis.

Question 32

What is the name of the process by which NTs are released into the synaptic cleft?

Answer 32

Exocytosis

Question 33

What is the lifecycle of a vesicle in the pre-synaptic membrane?

Answer 33

Made by Golgi - contains NT Travels to pre-synaptic membrane Docking Priming AP arrives, Ca channels open - causes conformational change of snaps & snares on vesicle leading to Exocytosis The excess membrane is budded back into the cell via endocytosis The empty vesicle then joins an endosome Eventually reused and filled with NTs again

Question 34

How are docked vesicles held in position on the membrane?

Answer 34

By specialised proteins

Question 35

Name 4 ways in which NTs are removed from the synaptic cleft?

Answer 35

1). Degradation by enzymes in the cleft 2). Uptaken into glial cells nearby (and then broken down with enzymes or recycled and repackaged into vesicles) 3). Reabsorbed into the pre-synaptic cell for repackaging 4). Reabsorption into the pre-synaptic cell for degradation

Question 36

What ensures that the amount of NT released is proportional to the signal that is received by the post-synaptic neuron?

Answer 36

The removal of NTs from the cleft in a speedy manner

Question 37

By which process do glial cells absorb NTs from the cleft?

Answer 37

Via pinocytosis

Question 38

How is ACh removed from the cleft? What happens to the products?

Answer 38

It is removed by acetylcholinesterase in the cleft (broken into down into acetate and choline). Choline is then reabsorbed by the pre-synaptic neuron and used to make more ACh.

Question 39

Do motor nerves axons have single branches or multiple branches?

Answer 39

Motor nerve axons have multiple branches - when they reach skeletal muscle they branch out.

Question 40

Are motor neuron axons myelinated?

Answer 40

They are myelinated by Schwann cells until they get close to the motor end plate. Then they are myelinated very thinly by a Schwann cell but only as protection from the fluid in the area, rather than for conduct of the impulse.

Question 41

What increases the surface area in the motor end plate?

Answer 41

Subneural clefts

Question 42

What do subneural clefts do?

Answer 42

Increase the surface area upon which ACh can act.

Question 43

Which ion initiates exocytosis in the neuromuscular junction?

Answer 43

Calcium

Question 44

What is another name for the active zone?

Answer 44

The dense bar

Question 45

What type of receptor is the AChR?

Answer 45

Ligand-gated ion channel.

Question 46

How many subunits are in the AChR?

Answer 46

5 - 2 x ⍺, β, 𝛾 & 𝛅

Question 47

Which subunits does the ACh bind to?

Answer 47

The ⍺ units

Question 48

Which ions can pass through the AChR channel when it is open?

Answer 48

Large amounts of Na+ and Much smaller amounts of K+ & Ca+

Question 49

What is the polarisation of the end plate known as?

Answer 49

The end plate potential

Question 50

How does opening of the AChR channels affect the end plate potential?

Answer 50

Opening of the AChR = influx of Na+ = local depolarisation of the end plate potential - this opens the remaining Na channels and an AP is initiated.

Question 51

What happens when the end plate is depolarised and an AP is initiated?

Answer 51

Muscle contracts