Nervous Coordination- Synaptic Transmission Flashcards
What is a synapse?
The junction between a neurone and another neurone, or between a neurone and an effector cell
What is the synaptic cleft?
The tiny gap between cells at a synapse
What is the synaptic knob?
Swelling at the end of the presynaptic neurone that contains synaptic vesicles filled with chemicals called neurotransmitters
What happens when an action potential reaches the end of a neurone?
Causes neurotransmitters to be released into the synaptic cleft and diffuse across the postsynaptic membrane and bind to specific receptors
What happens when neurotransmitters bind to receptors?
Trigger an action potential, cause muscle contraction, or causes a hormone to be secreted
Why are receptors unidirectional?
Receptors only on postsynaptic membranes
Why are neurotransmitters removed from the cleft?
So the response doesn’t keep happening
What are cholinergic synapses?
Synapses that use acetylcholine
What is the first step of a nerve impulse being transmitted across cholinergic synapses?
An action potential arrives at the synaptic knob of the presynaptic neurone
What does the action potential arriving at the synaptic knob stimulate?
Voltage-gated calcium ion channels in the presynaptic neurone to open
How do the calcium ions move into the synaptic knob?
Diffuse in
What does the influx of calcium ions cause?
Synaptic vesicles in the synaptic knob to fuse with the presynaptic membrane
What is the role of the vesicles?
Release neurotransmitter acetylcholine into the synaptic cleft (exocytosis)
What does ACh do once released?
Diffuses across synaptic cleft and binds to specific cholinergic receptors on postsynaptic membrane causing sodium ion channels to open
What does the influx of sodium ions cause?
Depolarisation
Why is ACh removed from the synaptic cleft?
So the response doesn’t keep happening
How is ACh removed from the synaptic cleft?
Broken down by acetylcholinesterase and products reabsorbed by presynaptic neurone
What is the role of excitatory neurotransmitters?
Depolarise the postsynaptic membrane, making it fire an action potential if the threshold is reached
What is the role of inhibitory neurotransmitters?
Hyperpolarise the postsynaptic membrane, preventing it from firing an action potential
What is spatial summation?
Many neurones connect to one neurone, small amount of neurotransmitter released from each neurone can be altogether enough to reach threshold and trigger an action potential
