Unit 2: Synapses Flashcards
What is a synapse?
the junction between two neurones.
What is the gap between two neurones called?
the synaptic cleft
Action potentials cannot cross the synaptic cleft, how is the nerve impulse continued in the next neurone?
the nerve impulses are carried to the next neurone by neurotransmitters
Where are neurotransmitters made?
the presynaptic neurone
Where are neurotransmitters stored?
in the synaptic vesicles in the synaptic knob
Which two organelles are important for the manufacture of neurotransmitters?
mitochondria and endoplasmic reticulum
What are neuroreceptors?
charge gated ion channels that are specific binding sites for the neurotransmitters
Where are neuroreceptors found?
on the post synaptic neurone
What is the name of the neurotransmitter in a cholinergic synapse?
Acetylcholine
What is acetylcholine made up of?
ethanoic acid and choline
In which two places do cholinergic synapses occur?
The central nervous system and neuromuscular junctions
What happens when an action potential reaches the presynaptic neurone?
the calcium voltage gated channels open, causing calcium to diffuse into the cell down the concentration gradient.
What does the influx of calcium ions in the presynaptic neurone cause?
the synaptic vesicles to fuse with the membrane and release acetylcholine into the synaptic cleft via exocytosis
What happens after acetylcholine diffuses across the synaptic cleft?
It binds to the receptor sites on the post synaptic neurone which causes sodium ion channels to open. Sodium diffuses into the membrane down the concentration gradient.
What happens after the sodium ion channels open in the post synaptic neurone?
It causes depolarisation of the postsynaptic cell membrane called the post synaptic potential which then generates an action potential
What is the name of the enzyme that breaks down acetylcholine?
acetylcholinesterase
What does acetylcholinesterase do?
hydrolyses the neurotransmitter into acetyl and choline.
What happens after acetylcholine has been hydrolysed in the postsynaptic cleft?
Acetyl and choline diffuse back across the synaptic cleft and are absorbed by presynaptic neurone by endocytosis
Why does acetylcholine get broken down at the postsynaptic neurone?
To prevent continuously generating an action potential
How is acetylcholine reformed in the presynaptic neurone?
ATP made by mitochondria is used to recombine acetyl and choline which is then stored in the synaptic vesicle for future use.
What are the five different types of synapses?
Excitatory ion channel synapse, Inhibitory ion channel synapse, non channel synapse, neuromuscular synapse and electrical synapse
What are the neuroreceptors for excitatory ion-channel synapses?
sodium channels
Why does the excitatory ion-channel synapse make action potentials more likely?
because positive ions diffuse in causing depolarisation
What a typical neurotransmitter for an excitatory ion-channel synapse?
acetylcholine
What is the neuroreceptor for the inhibitory ion channel synapse?
chloride channels
Why is an action potential less likely in an inhibitory ion channel synapse?
because negative ions diffuse in causing hyperpolarisation (more negative inside than usual)
What are non channel synapses?
synapses where the neuroreceptors are membrane bound enzymes, not ion channels
What type of response do non channel synapses create?
long lasting, slow responses
Which type of synapse is a junction between effectors and muscle cells
neuromuscular junctions
What is the neurotransmitter for neuromuscular junctions?
acetylcholine
Why are electrical synapses different from the other four types of synapses?
They are the only synapses to touch and share proteins. Action potentials pass directly through the neurones without a neurotransmitter
Electrical synapses are very rare, in which two places do they occur?
the heart and the eye
What is summation?
The process that produces enough neurotransmitters to trigger an action potential in the neighbouring neurone.
What are the two different types of summations?
Spatial and temporal
What is spatial summation?
where a number of different presynaptic neurones together release enough neurotransmitters to exceed threshold potential and generate an action potential
What is temporal summation?
where a single presynaptic neurone releases neurotransmitter many times over a short time period and generate enough to exceed threshold potential and produce an action potential
How does a drug that mimics a neurotransmitter affect the synapse?
Stimulates it
How does a drug that stimulates the release of neurotransmitters affect the synapse?
stimulates it
How does a drug that opens neuroreceptor channels affect the synapse?
stimulates it
How does a drug that blocks neuroreceptor channels affect the synapse
inhibits it
How does a drug that inhibits the breakdown enzyme affect the synapse?
stimulates it
What is the term that describes a drug that stimulates a synapse?
Agonists
What is the term that describes a drug that inhibits a synapse?
Antagonists