L3: Synapses and the Role of Neurotransmitters Flashcards
What is the primary role of a synapse?
A synapse is the contact point between neurons or between a neuron and another cell, enabling communication between them
What is the significance of the resting membrane potential in neurons?
The resting membrane potential, typically around -65 to -70 mV, is the baseline electrical charge of a neuron, essential for the generation of action potentials
What is an action potential threshold, and why is it important?
The action potential threshold is the critical level of depolarisation a neuron must reach to initiate an action potential, enabling neural communication
Describe the term “hyperpolarisation” and its effect on neurons
Hyperpolarisation occurs when the inside of a neuron becomes more negative, making it less likely to fire an action potential, thus inhibiting the neuron
What is a synaptic vesicle, and what role does it play in neurotransmission?
Synaptic vesicles store neurotransmitters and release them into the synaptic cleft upon fusion with the presynaptic membrane during exocytosis
Define “exocytosis” in the context of neurotransmission
Exocytosis is the process by which synaptic vesicles fuse with the presynaptic membrane to release neurotransmitters into the synaptic cleft
What is synaptic cleft, and what occurs there during neurotransmission?
The synaptic cleft is the small gap between the presynaptic and postsynaptic cells where neurotransmitters are released and bind to receptors
Name the two types of synapses and how they differ
- Chemical synapses (use neurotransmitters to communicate and are unidirectional)
- Electrical synapses (use gap junctions for direct ion flow and allow bidirectional communication)
What is the difference between excitatory and inhibitory neurotransmitters?
Excitatory neurotransmitters increase the likelihood of an action potential in the postsynaptic neuron, while inhibitory neurotransmitters decrease it
What are the two main signalling mechanisms for neurotransmitters at the synapse?
- Ionotropic receptors (fast, involve direct ion flow)
- Metabotropic receptors (slower, use G-proteins to indirectly affect cell excitability).
What are ionotropic receptors, and how do they function?
Ionotropic receptors are ligand-gated ion channels that open quickly upon binding a neurotransmitter, allowing ions to flow directly into the postsynaptic cell
How does a metabotropic receptor differ from an ionotropic receptor?
Metabotropic receptors use G-protein-coupled mechanisms to trigger intracellular signalling cascades, resulting in slower but longer-lasting effects than ionotropic receptors
What are G-protein-coupled receptors (GPCRs), and how do they function in neurons?
GPCRs are metabotropic receptors that activate intracellular G-proteins when bound to a neurotransmitter, leading to various cellular responses
What is an action potential and how does it propagate?
An action potential is a rapid change in membrane potential that travels along the axon, initiated by depolarization due to sodium ion influx
Describe the term “neurotransmitter receptors” and their role
Neurotransmitter receptors are proteins on the postsynaptic membrane that bind neurotransmitters, triggering changes in the postsynaptic cell’s excitability
How are neurotransmitter signals terminated at the synapse?
- Reuptake into the presynaptic neuron
- Enzyme degradation
- Diffusion away from the synapse
Define neurotransmitter reuptake and its importance
Neurotransmitter reuptake is the process by which neurotransmitters are absorbed back into the presynaptic neuron, terminating the signal and recycling the neurotransmitter
What are glial cells and what roles do they play?
Glial cells support neurons by providing structural scaffolding, metabolic support, insulation, and facilitating some signalling processes
Describe the structure of a typical neuron
A neuron has a cell body (soma), dendrites for receiving input, an axon for transmitting impulses, and an axon terminal that connects to other cells
What is the function of the axon hillock?
The axon hillock is where action potentials are initiated, as it integrates incoming signals and determines whether the neuron will reach threshold to initiate an action potential
Describe the term “axon” and its function
The axon is a long projection from the neuron’s cell body that conducts action potentials to the axon terminals, enabling communication with other cells
Define the term “axon terminal” and its function
The axon terminal is the end of an axon where neurotransmitters are stored and released to communicate with other neurons or cells
What neurotransmitter is primarily excitatory in the central nervous system?
Glutamate is the major excitatory neurotransmitter in the CNS
What is the main inhibitory neurotransmitter in the central nervous system?
GABA (gamma-aminobutyric acid) is the primary inhibitory neurotransmitter in the CNS
What is a GABA receptor and what effect does it have?
A GABA receptor binds gamma-aminobutyric acid (GABA) and typically causes an inhibitory effect by allowing chloride ions to enter, hyperpolarizing the cell
How does calcium influence neurotransmitter release at the synapse?
Calcium enters the presynaptic neuron upon depolarization, triggering vesicles to release neurotransmitters into the synaptic cleft
What is the significance of calcium ions (Ca²⁺) in neurotransmitter release?
Calcium ions enter the presynaptic terminal during an action potential, triggering synaptic vesicles to release neurotransmitters into the synaptic cleft
What are gap junctions and where are they commonly found?
- Gap junctions are protein channels that directly connect adjacent cells
- Commonly found in cardiac tissue and during neuronal development
What is the role of gap junctions in the heart?
Gap junctions allow rapid ion exchange between cardiac cells, enabling synchronized heart contractions
What is the neocortex and its role in the brain?
The neocortex is the outer layer of the brain involved in high-order functions like thought, sensory perception, decision-making, and motor commands containing a high density of neurons
What are dendrites, and what is their primary function?
Dendrites are branched projections from a neuron’s cell body that receive input from other neurons and transmit signals toward the cell body
What are dendritic spines, and why are they important?
Dendritic spines are small protrusions on dendrites that help receive synaptic inputs and play a role in learning and memory
Describe the function of the autonomic nervous system and its branches
The autonomic nervous system controls involuntary functions with branches: sympathetic (activates fight-or-flight), parasympathetic (rest-and-digest), and enteric (gastrointestinal control)
Name two well-known neurotransmitters involved in the autonomic nervous system
- Norepinephrine (noradrenaline)
- Acetylcholine
What is norepinephrine’s role as a neurotransmitter?
Norepinephrine modulates arousal, alertness, and the body’s response to stress
Explain the function of acetylcholine in the nervous system
Acetylcholine is a neurotransmitter involved in muscle activation, autonomic nervous system function, and cognitive processes
What is an example of a neurotransmitter that can have both excitatory and inhibitory effects?
Acetylcholine can be excitatory at neuromuscular junctions but inhibitory in the heart
What is myelin, and why is it important?
Myelin is an insulating layer around axons that speeds up the transmission of electrical impulses along the neuron
Explain the role of the presynaptic and postsynaptic cells in neurotransmission
The presynaptic cell releases neurotransmitters, while the postsynaptic cell receives the signal via receptors, initiating a response
Describe the term “postsynaptic density” and its importance
Postsynaptic density is a protein-dense region in the postsynaptic membrane that anchors receptors, essential for effective neurotransmitter binding and signalling
What are Schwann cells, and what do they do?
Schwann cells are glial cells in the peripheral nervous system that form myelin around axons, aiding in rapid signal conduction
What is dopamine, and what roles does it play in the body?
Dopamine is a neurotransmitter involved in reward, motivation, motor control, and several other brain functions
What are purinergic neurotransmitters, and give an example
Purinergic neurotransmitters include molecules like ATP, which act on purinergic receptors involved in various signaling pathways
What are motor neurons, and what function do they serve?
Motor neurons transmit signals from the brain and spinal cord to muscles, causing movement
What is a pseudo-unipolar neuron, and where is it commonly found?
A pseudo-unipolar neuron has one axon that splits into two branches, typically found in sensory neurons
What are neuropeptides, and give an example.
Neuropeptides are small protein-like molecules used as neurotransmitters, such as endorphins, which modulate pain and pleasure
What is synaptic plasticity, and why is it important?
Synaptic plasticity is the ability of synapses to strengthen or weaken over time, crucial for learning and memory
How does the brain’s cortical folding relate to neuron density?
The brain’s cortical folding increases surface area, allowing for a high density of neurons in a compact space, enhancing processing power
What is the significance of neurotransmitter vesicle recycling?
Recycling neurotransmitter vesicles ensures a continuous supply of neurotransmitters for repeated signalling, essential for sustained synaptic transmission
Explain the concept of neurotransmitter specificity
Neurotransmitter specificity means each neurotransmitter binds to specific receptors, ensuring precise signalling pathways
How does serotonin affect mood and where is it commonly released?
Serotonin helps regulate mood, sleep, and appetite, and is commonly released in brain areas associated with mood regulation
What is acetylcholinesterase, and what role does it play in neurotransmission?
Acetylcholinesterase is an enzyme that breaks down acetylcholine in the synaptic cleft, terminating its action and allowing reuptake or breakdown
Explain what an interneuron is and its function in the nervous system
Interneurons connect sensory and motor neurons within the CNS, playing a critical role in reflexes and neural circuits
Explain what a “secondary messenger” is in neurotransmitter signalling
A secondary messenger transmits signals from receptors on the cell surface to target molecules inside the cell, amplifying the original signal
