Synaptic Transmission

Question 1

What are electrical synapses?

Answer 1

Neurones are joined together by gap junction channels so that action potentials can pass from the presynaptic neurone to the postsynaptic neurone almost instantly.

Question 2

What are gap junction channels composed of?

Answer 2

made up of conexion channels, made up of connexin proteins.

Question 3

Describe the electrical synapses at the inferior olive.

Answer 3

Located at the brainstem nucleus, it governs movement as neurons form electrical synapses with each other to synchronise activity of networks.

Question 4

Describe the electrical synapses at the Astrocytes.

Answer 4

inter-connected via gap junctions to formsyncytia, uses Ca+signalling

Question 5

What are Chemical Synapses?

Answer 5

Use neurotransmitters to communicate with adjacent neurones.

Question 6

What stimulates the release of neurotransmitters?

Answer 6

Synaptic Vesicles store neurotransmitters that are triggered by the influx of calcium ions during depolarisation to fuse to the presynaptic membrane and release vesicles into the synaptic cleft by exocytosis.

Question 7

How do neurotransmitters stimulate the postsynaptic neurone.

Answer 7

Neurotransmitters bind to receptors on the postsynaptic membrane to cause depolarisation in the postsynaptic membrane. The neurotransmitters then are either broken down and recycled or diffuse out the synaptic cleft.

Question 8

How do vesicles dock and release neurotransmitters?

Answer 8

1. SNARE proteins are expressed on the membrane of the axon terminal and the surface of the vesicles and they are calcium dependent.
2. Calcium causes the activation of these proteins which allows the vesicles to fuse to each other and the presynaptic membrane.

Question 9

What research revealed the chemical synapse?

Answer 9

Otto Loewi(1921), used a perfused frog heart and stimulated the attached vagus nerve which rapidly slowed the heartbeat of the first heart but there was a delay in slowing the second the conclusion was that the chemical released into the solution inhibited heartbeat.

Question 10

What are neuromuscular junctions/motor end plates?

Answer 10

specialisedchemical synapsesformed atthe sites where theterminalbranches of the axon of amotor neuroncontact a targetmuscle fibre

Question 11

What is a motor unit?

Answer 11

agroupofmuscle fibresinnervatedby asingle neuron

Question 12

Describe the experiment that discovered end plate potentials in terms of profile and decay.

Answer 12

Fatt& Katz(1951)Stimulated motor nerve & recorded EPPof muscle fibreusingintracellular electrode found the Depolarisation largerin amplitudethan needed to initiate an actionpotential Further awayalong the musclethe intracellular electrode wasfrom the end plate thesmallerandslowerthe response Conclusion: EPPbrief surgeofcurrentinto muscle fibre locally atthe end plate that passivelyspreadsinboth directionsbecomingsmaller.

Question 13

Describe the experiment that discovered end plate potentials in terms of mapping acetylcholine sensitivity.

Answer 13

Del Castillo & Katz(1955) AppliedAChtomuscle fibrebyiontophoresis & recorded EPPof muscle fibreusingintracellular electrode EPP onlyoccurred atend plateregion. AsdistanceofACh applicationincreasedfrom the end plate thesmallerandslowertheresponse
Conclusion:ACh postsynapticreceptors onlyon muscle fibremembrane directly oppositepresynaptic terminal.

Question 14

What are Nicotinic ACh Receptors?

Answer 14

• Ionotropic
• Channelopens in response tobindingof theAChon itsextracellularside
• Allows Na+topassacross themembrane
• Results indepolarisation
• Rapidresponse

Question 15

How does botox work?

Answer 15

• Botulinum toxin
• Causesparalysisofmusclefibres
• InterfereswithSNARE proteinspreventing ACh release
• Transienteffects- weeks

Question 16

What does Eserine do?

Answer 16

Blocks acetylcholinesterase which prevents the breakdown of ACh and increases its’ action on the postsynaptic membrane.

Question 17

What does Tubocurarine do?

Answer 17

Nicotinic receptor antagonist which prevents the action of ACh.

Question 18

What are EPSPs?

Answer 18

• Principle neurotransmitter =glutamate
• Result of neurotransmitter openingchannels which allow the movement of ionswithpositive reversal potentialse.g.Na+andCa2+
• Small response(subthreshold)

Question 19

What are IPSPs?

Answer 19

• Principle neurotransmitters =GABAandglycine
• Result of neurotransmitter opening channelswhich allow the movement of ions withnegative reversal potentialspositivee.g.K+andCl-
• Small response

Question 20

What effect does the summation of EPSPs and IPSPs have?

Answer 20

Cancel each other out -> no response

Question 21

What does the synaptic arrangement tell you about the postsynaptic potential

Answer 21

Axon terminal to dendrite: - Likelyexcitatory

Axon terminal to soma: - Likelyinhibitory with a greater effect- closer tohillock

Axon terminal to axonterminal: - Presynaptic inhibition