synaptic transmissions Flashcards
What is the structure of a synapse?
A synapse is a junction between two neurons or between a neuron and an effector cell (e.g., muscle or gland).
Key parts of a synapse include:
Presynaptic neuron: The neuron sending the signal.
Synaptic vesicles: Contain neurotransmitters (e.g., acetylcholine).
Synaptic cleft: The gap between the two neurons (or neuron and effector cell).
Postsynaptic membrane: Contains receptors for neurotransmitters.
Mitochondria: Provide energy for neurotransmitter release.
What is the process of synaptic transmission?
An action potential arrives at the presynaptic terminal.
This causes calcium ion channels to open, and calcium ions enter the presynaptic neuron.
The influx of calcium ions causes synaptic vesicles to fuse with the presynaptic membrane.
Neurotransmitters (e.g., acetylcholine) are released into the synaptic cleft by exocytosis.
Neurotransmitters bind to receptors on the postsynaptic membrane, triggering a response in the postsynaptic cell (e.g., depolarization).
The neurotransmitters are broken down by enzymes (e.g., acetylcholinesterase) or taken back into the presynaptic neuron by reuptake.
What is the role of calcium ions in synaptic transmission?
Calcium ions play a crucial role in neurotransmitter release:
The action potential causes the opening of voltage-gated calcium channels in the presynaptic membrane.
Calcium ions flow into the presynaptic neuron.
The increase in calcium concentration triggers the fusion of synaptic vesicles with the presynaptic membrane.
This fusion releases neurotransmitters into the synaptic cleft through exocytosis.
What are excitatory and inhibitory neurotransmitters?
Excitatory neurotransmitters: Increase the likelihood of an action potential in the postsynaptic cell.
Example: Acetylcholine (in skeletal muscle), glutamate (in the brain).
Inhibitory neurotransmitters: Decrease the likelihood of an action potential in the postsynaptic cell.
How does acetylcholine function in synaptic transmission?
Acetylcholine (ACh) is an excitatory neurotransmitter released at cholinergic synapses.
It binds to nicotinic receptors on the postsynaptic membrane.
This opens sodium ion channels, causing depolarization and potentially initiating an action potential.
ACh is broken down by the enzyme acetylcholinesterase in the synaptic cleft, and its products are reabsorbed by the presynaptic neuron.
What is synaptic integration?
Synaptic integration is the process by which a neuron combines multiple signals from different synapses:
Temporal summation: Multiple signals from one synapse in quick succession.
Spatial summation: Multiple signals from different synapses at the same time.
This results in either depolarization (excitation) or hyperpolarization (inhibition) of the postsynaptic membrane.
How does the reuptake of neurotransmitters occur in synaptic transmission?
After neurotransmitters have carried out their action, they are removed from the synaptic cleft to prevent continuous stimulation:
Reuptake: Neurotransmitters (e.g., serotonin, dopamine) are taken back into the presynaptic neuron by specific transport proteins.
Enzyme breakdown: Some neurotransmitters, like acetylcholine, are broken down by enzymes (e.g., acetylcholinesterase) into inactive products.
Exam Question:
Describe the process of synaptic transmission, including the role of calcium ions and neurotransmitters.
An action potential arrives at the presynaptic terminal.
Calcium ions enter the presynaptic neuron through voltage-gated calcium channels.
The influx of calcium ions causes synaptic vesicles to fuse with the presynaptic membrane, releasing neurotransmitters (e.g., acetylcholine) into the synaptic cleft by exocytosis.
Neurotransmitters bind to receptors on the postsynaptic membrane, causing ion channels to open and leading to depolarization of the postsynaptic membrane.
The neurotransmitter is either broken down by enzymes (e.g., acetylcholinesterase for acetylcholine) or taken back into the presynaptic neuron by reuptake mechanisms.
Exam Question:
How do drugs such as antidepressants affect synaptic transmission?
Selective serotonin reuptake inhibitors (SSRIs) block the reuptake of serotonin in the synaptic cleft, increasing serotonin levels in the brain.
This enhances the action of serotonin on postsynaptic receptors, improving mood and alleviating symptoms of depression.
Cocaine inhibits the reuptake of dopamine, leading to prolonged stimulation of dopamine receptors, which contributes to its stimulant effects.
Explain the role of inhibitory neurotransmitters in the nervous system.
Inhibitory neurotransmitters, reduce the likelihood of an action potential being generated in the postsynaptic cell.
They achieve this by opening chloride ion channels, leading to hyperpolarization of the postsynaptic membrane.
This makes it more difficult for the postsynaptic neuron to reach the threshold potential required to initiate an action potential.
Exam Question:
Describe how synaptic transmission at the neuromuscular junction leads to muscle contraction.
An action potential travels down the motor neuron and reaches the neuromuscular junction.
The neurotransmitter acetylcholine is released into the synaptic cleft.
Acetylcholine binds to nicotinic receptors on the muscle cell membrane, causing an influx of sodium ions.
This depolarizes the muscle cell membrane and triggers an action potential.
The action potential travels through T-tubules, stimulating the release of calcium ions from the sarcoplasmic reticulum, leading to muscle contraction.
