Synapses Flashcards
What problems do synapses help overcome?
Transmission of an electrical signal across a high resistance membrane and intercellular gap
What is a synapse?
A specialised junction between two neurons?
What do the presynaptic and postsynaptic neurons do and what is between them?
- Presynaptic neuron: sending the information
- Postsynaptic neuron: receiving the information
- Synaptic cleft of varying length is between them for the signal to cross
What causes a postsynaptic potential?
Action potential in the presynaptic neuron
What does it mean that the direction of transmission is rectifying?
It is one way
What is another name for electrical synapses?
Gap junctions
What do electrical synapses do?
Directly transfer ions and small molecules between cells
What does it mean that the electrical synapses are bidirectional?
Current can pass in both directions
Is there a synaptic delay with electrical synapses?
No - there is fast transmission
Is there action potential: action potential transmission of the signal with electrical synapses?
No - in the postsynaptic cell you will see an attenuated signal compared to the presynaptic cell
What do gap junctions allow?
direct cytoplasmic communication between cells
What are electrical synapses made up of?
many gap junction ‘channels’/pores. Each channel is made up of two connexons and each connexon unit is made up of six connexin subunits. You can got homotopic and heterotopic connexons depending on whether all the connexin subunits are the same of not
Give a summary of electrical synapses
- They are fast
- Many be two-way (non rectifying)
- Can give one-to-one transmission but signal often attenuated
- Allow exchange of other chemicals
- Used by invertebrates, lower vertebrates and mammals
- Much less common than chemical synapses
- Used in fast pathways e.g. escape/ defence
- Used to promote synchronous activity within a network
- Electrical synapses are fast and reliable but are capable of only limited plasticity (contrasts chemical synapses)
Talk about the electrical synapse and the fly
- Electrical synapses are used for a fly to get away from a predator
- First the eyes and so optical lobes are shadowed by a predator
- The giant fibres take the signal down through the neck to the thoracic mass which is where the wings and legs are activating the jump muscle and flight muscle
- If fluorescent dye is injected into giant fibre we find that injecting one neuron stains the entire circuit of the jump and flight muscles: this proves the whole circuit is connected by gap junctions.
- Evidence: They found a mutation you can squash and the fly won’t jump – this mutation coded for a gap junction
Which type of synapses are plastic?
Chemical synapses