Synaptic Transmission Flashcards
What is the junction between neurons over which a signal is transferred?
A synapse
What is the junction between a neuron and a muscle over which as signal is transferred?
Neuromuscular junction
What is the specialised junction between a neuron and a gland over which a signal is transferred?
Neuroglandular junction
What are the two types of synapse?
- Chemical synapse
2. Electrical synapse
Is a chemical synapse what is the message carried by across the synapse?
A neurotransmitter
In an electrical synapse how is the message carried?
By flow of a current through a low resistance electrical junction
What is the more common synapse in mammals?
Chemical
What is the neurotransmitter and the neuromuscular junction?
Acetylcholine
What is an agonist of acetylcholine at the neuromuscular junction? What receptors do they both bind two?
Nicotine is an agonist at acetylcholine nictonic receptors
What is an antagonist of aetylchloine at nictotinic receptors?
Curare (tubocurraine)(competitve reversible)
What is the effect of curare (tubocurraine)
It blocks the transmission at the neuromuscular junction and causes paralysis
How would you reverse the effect of curare (tubocurraine) at the NMJ?
Use a drug (eserine, neostigmine) that inhibits the drug acetylcholinesterase that breaks down acetylcholine so inhibiting it will increase the concentration of Ach and reverse the effect of the antagonist
Where do 95% of all synapses take place?
Between an axon terminal (releases neurotransmitter) and a dendrite
What is the axon terminal known as when its taking place in a synapse?
The presynaptic element
What is the dendrite known as when its taking part in a synapse?
The post synaptic element
What does it mean when you say the synaptic elements are discontinuous?
It means there is a synaptic cleft between the two elements
What is the synaptic delay?
The time it takes for the neurotransmitter to be released from the axon terminal in a vesicle via exocytosis and diffuse across the synaptic cleft
How long is the synaptic delay?
0.5ms
What kind of structure is present at the post synaptic element?
A dense structure of proteins and receptors
What are the two actions of the chemical synapses?
- Excitation
2. Inhibition
What kind of neurotransmitters cause depolarisation of the postsynaptic membrane? What effect do they have?
Excitatory neurotransmitters make the post synaptic element more positive
What are the depolarisations of the post synaptic membrane by an excitatory neurotransmitters called?
Excitatory postsynaptic potentials (EPSPs)
What does the sum of the EPSPs have to reach in order for an action potential to fire?
The threshold
What is temporal summation?
When several EPSPs are generated in rapid succession by one synapse
What is spatial summation?
When several synapses generate EPSPs simulataneously
What kind of neurotransmitters cause hyperpolarisation of the post synaptic membranes? What effect do they have?
Inhibitory neurotransmitters - they make the post synapic element more negative
What are the hyperpolarisation of the post synaptic membrane by the inhibitory neurotransmitters called?
Inhibitory postsynaptic potentials (IPSPs)
How does hyperpolarisation lead to imhibition?
Because the output of the neuron is coverned by the sum of EPSPs and IPSPs so hyperpolarisation by lots of IPSPs means the neurone wont reach threshold to fire an action potential
Where are inhibitory synapses located?
On the cell body or around the axon hillock
What are excitatory synapses located?
On the dendrites
What is presynaptic inhibition?
Special type of inhibition that occurs in the brain and the spinal chord
What are inhibitory synapses formed between two axon terminals called?
Axo-axonic synapses
What are the axon terminals of the axo-axonic synapses known as?
The post and pre synaptic terminals
How do axo-axonic inhibitory synapses work?
They reduce the amount of neurotransmitter released from the postsynaptic terminal so inhibit it
How could you demonstrate the existence of electrical synapses?
By injecting depolarising or hyperpolarising current into one neuron and recording from another neuron
What is recorded that shows the prescence of a electrical synapse?
Small positive or negative potentials with no synaptic delay
How could you use dyes to show the prescense of an electrical synapse?
Using dyes with a molecular weight
What are the substrates of electrical synapses?
Gap junctions
What are responsible for the communication across gap junctions if they do not have vesicles but still have a small gap?
Connexons or an array of tubes
What is the reason electrical synapses operate very quickly?
No synaptic delay
Name two properties the animals that have evolved electrical synapses have evolved?
- Escape mechanism as shown in the crayfish tail flip
2. Synchronising neuronal activity e.g. burster neurons in pond snails generate rhymic activity
