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Questions and Answers
Which characteristic distinguishes electrical synapses from chemical synapses in terms of signal transmission?
Which characteristic distinguishes electrical synapses from chemical synapses in terms of signal transmission?
- Electrical synapses use neurotransmitters; chemical synapses rely on direct ion flow.
- Electrical synapses exhibit bidirectional signal transfer; chemical synapses are typically unidirectional. (correct)
- Electrical synapses have a wider synaptic cleft; chemical synapses have gap junctions.
- Electrical synapses involve a significant synaptic delay; chemical synapses are instantaneous.
What is the functional consequence of the low-resistance pathway created by gap junctions in electrical synapses?
What is the functional consequence of the low-resistance pathway created by gap junctions in electrical synapses?
- It facilitates the active transport of large molecules between cells.
- It prevents ion leakage into the extracellular space during signal transmission. (correct)
- It allows for slower, regulated neurotransmitter release.
- It increases the synaptic delay due to the need for ion channel activation.
In the context of synaptic transmission, what is the primary role of connexons in electrical synapses?
In the context of synaptic transmission, what is the primary role of connexons in electrical synapses?
- To actively transport ions against their concentration gradient.
- To bind neurotransmitters released from the presynaptic neuron.
- To form the structural framework of the synaptic cleft.
- To create pores that allow direct cytoplasmic connection between cells. (correct)
How does the structure of a chemical synapse contribute to its characteristic synaptic delay, which is absent in electrical synapses?
How does the structure of a chemical synapse contribute to its characteristic synaptic delay, which is absent in electrical synapses?
What is the significance of the close apposition of pre- and postsynaptic cell membranes at electrical synapses?
What is the significance of the close apposition of pre- and postsynaptic cell membranes at electrical synapses?
How would disruption of the alignment or function of connexons likely affect neuronal communication?
How would disruption of the alignment or function of connexons likely affect neuronal communication?
Which characteristic makes chemical synapses more adaptable than electrical synapses in the context of neural circuitry?
Which characteristic makes chemical synapses more adaptable than electrical synapses in the context of neural circuitry?
What would be the immediate consequence if all voltage-gated calcium channels at the presynaptic terminal of a chemical synapse were suddenly non-functional?
What would be the immediate consequence if all voltage-gated calcium channels at the presynaptic terminal of a chemical synapse were suddenly non-functional?
Which of the following scenarios would be LEAST affected by the differences in transmission speed between electrical and chemical synapses?
Which of the following scenarios would be LEAST affected by the differences in transmission speed between electrical and chemical synapses?
A researcher is studying a novel synapse and observes that its postsynaptic response increases significantly with repeated stimulation. Based on the information, which type of synapse is MOST likely being studied, and why?
A researcher is studying a novel synapse and observes that its postsynaptic response increases significantly with repeated stimulation. Based on the information, which type of synapse is MOST likely being studied, and why?
A drug that inhibits acetylcholinesterase is administered at the neuromuscular junction. Which of the following is the MOST likely immediate effect?
A drug that inhibits acetylcholinesterase is administered at the neuromuscular junction. Which of the following is the MOST likely immediate effect?
A patient presents with muscle weakness that worsens with activity and improves with rest. Electrophysiological studies show reduced amplitude of compound muscle action potentials with repetitive nerve stimulation. Which of the following is the MOST likely underlying mechanism?
A patient presents with muscle weakness that worsens with activity and improves with rest. Electrophysiological studies show reduced amplitude of compound muscle action potentials with repetitive nerve stimulation. Which of the following is the MOST likely underlying mechanism?
If a researcher selectively prevents the formation of new gap junctions between neurons in a mammalian brain, which of the following functions would MOST likely be impaired?
If a researcher selectively prevents the formation of new gap junctions between neurons in a mammalian brain, which of the following functions would MOST likely be impaired?
In a hypothetical scenario, a virus selectively targets and destroys voltage-gated calcium channels at the axon terminal of motor neurons. Which of the following would be the MOST immediate consequence at the neuromuscular junction?
In a hypothetical scenario, a virus selectively targets and destroys voltage-gated calcium channels at the axon terminal of motor neurons. Which of the following would be the MOST immediate consequence at the neuromuscular junction?
A scientist discovers a new neurotoxin that selectively disrupts the function of connexons. Which of the following processes would be MOST directly affected by this neurotoxin?
A scientist discovers a new neurotoxin that selectively disrupts the function of connexons. Which of the following processes would be MOST directly affected by this neurotoxin?
A researcher is comparing signal transmission in two different neuronal pathways. Pathway A uses electrical synapses, while pathway B uses chemical synapses. Considering the inherent properties of each synapse type, which of the following statements is MOST likely to be true?
A researcher is comparing signal transmission in two different neuronal pathways. Pathway A uses electrical synapses, while pathway B uses chemical synapses. Considering the inherent properties of each synapse type, which of the following statements is MOST likely to be true?
Which of the following best explains why women with myasthenia gravis (MG) can have children without necessarily passing on the condition?
Which of the following best explains why women with myasthenia gravis (MG) can have children without necessarily passing on the condition?
A patient is diagnosed with Myasthenia Gravis (MG) after presenting with ptosis and muscle weakness. An initial blood test is negative for acetylcholine receptor (AChR) antibodies. Which of the following diagnostic steps would be the MOST appropriate next step in confirming the diagnosis?
A patient is diagnosed with Myasthenia Gravis (MG) after presenting with ptosis and muscle weakness. An initial blood test is negative for acetylcholine receptor (AChR) antibodies. Which of the following diagnostic steps would be the MOST appropriate next step in confirming the diagnosis?
Why is the absence of a true refractory period significant in smooth muscle action potentials, contrasting with skeletal and cardiac muscle?
Why is the absence of a true refractory period significant in smooth muscle action potentials, contrasting with skeletal and cardiac muscle?
In the treatment of Myasthenia Gravis (MG), immunosuppressant medications like azathioprine and mycophenolate mofetil are often prescribed. What is the primary rationale behind using these drugs in MG management?
In the treatment of Myasthenia Gravis (MG), immunosuppressant medications like azathioprine and mycophenolate mofetil are often prescribed. What is the primary rationale behind using these drugs in MG management?
Which of the following explains the most critical distinction in the repolarization phase between cardiac and skeletal muscle action potentials?
Which of the following explains the most critical distinction in the repolarization phase between cardiac and skeletal muscle action potentials?
A researcher is studying the effects of a novel drug on smooth muscle contraction. They observe that the drug inhibits the opening of voltage-gated $Ca^{2+}$ channels in smooth muscle cells. What effect would this drug likely have on smooth muscle contraction?
A researcher is studying the effects of a novel drug on smooth muscle contraction. They observe that the drug inhibits the opening of voltage-gated $Ca^{2+}$ channels in smooth muscle cells. What effect would this drug likely have on smooth muscle contraction?
If a drug selectively blocked voltage-gated $K^+$ channels in skeletal muscle cells, what would be the MOST likely effect on the skeletal muscle action potential?
If a drug selectively blocked voltage-gated $K^+$ channels in skeletal muscle cells, what would be the MOST likely effect on the skeletal muscle action potential?
How do cholinesterase inhibitors alleviate symptoms of Myasthenia Gravis (MG)?
How do cholinesterase inhibitors alleviate symptoms of Myasthenia Gravis (MG)?
Flashcards
Electrical Synapse
Electrical Synapse
Direct signal transmission through gap junctions.
Chemical Synapse
Chemical Synapse
Indirect signal via neurotransmitters across a synaptic cleft.
Signal direction in Electrical Synapse
Signal direction in Electrical Synapse
Bidirectional; signal can travel in both directions.
Signal direction in Chemical Synapse
Signal direction in Chemical Synapse
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Energy and Electrical Synapses
Energy and Electrical Synapses
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Energy and Chemical Synapses
Energy and Chemical Synapses
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Myasthenia Gravis (MG)
Myasthenia Gravis (MG)
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MG Symptoms
MG Symptoms
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What is a Synapse?
What is a Synapse?
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What is the function of a Synapse?
What is the function of a Synapse?
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What are the two main types of Synapses?
What are the two main types of Synapses?
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What characterizes an Electrical Synapse?
What characterizes an Electrical Synapse?
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What characterizes Chemical Synapse?
What characterizes Chemical Synapse?
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How does information flow in Electrical Synapses?
How does information flow in Electrical Synapses?
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What is the structure of Electrical Synapses regarding membranes?
What is the structure of Electrical Synapses regarding membranes?
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How fast is the transfer in Electrical Synapses?
How fast is the transfer in Electrical Synapses?
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What is Ptosis?
What is Ptosis?
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What causes Myasthenia Gravis (MG)?
What causes Myasthenia Gravis (MG)?
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Action potential's role in skeletal muscle
Action potential's role in skeletal muscle
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Resting membrane potential in skeletal muscle
Resting membrane potential in skeletal muscle
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Depolarization in skeletal muscle
Depolarization in skeletal muscle
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Repolarization in skeletal muscle
Repolarization in skeletal muscle
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What causes the plateau phase in cardiac muscle?
What causes the plateau phase in cardiac muscle?
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Smooth muscle action potential
Smooth muscle action potential
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Study Notes
- Synapses are the junctions between two neurons or a neuron and an effector cell (like a muscle or gland).
- Synapses facilitate communication within the nervous system.
- This communication enables the transmission of signals that regulate body functions, sensory processing, and coordination of responses to stimuli.
Types of Synapses
- Electrical synapses transmit electrical signals directly via gap junctions.
- Chemical synapses transmit signals indirectly using neurotransmitters across a synaptic cleft.
- Both electrical and chemical synapses relay information through distinct mechanisms.
- Chemical synapses are better understood than electrical synapses.
Electrical Synapses
- Information transfer can be bidirectional or unidirectional.
- Pre- and postsynaptic cell membranes are very close, separated by gap junctions.
- Ions flow through gap junctions, creating a low-resistance pathway for ion flow between cells without leakage into the extracellular space.
- This transfer is instantaneous and fast, occurring in less than 0.3 milliseconds.
Chemical Synapses
- Chemical synapses use indirect chemical signals
- Synaptic delay occurs, in around 0.5ms or more.
- Signal amplification can occur via receptor activation
- High plasticity is present
- Common in the central and peripheral nervous system
Electrical vs Chemical Synapses
| Feature | Electrical Synapse | Chemical Synapse |
|---|---|---|
| Mode of Signal Transmission | Direct electrical signal via gap junctions | Indirect chemical signal via neurotransmitters |
| Speed of Transmission | Very fast | Relatively slower |
| Direction of Signal | Usually bidirectional | Unidirectional |
| Structure | Gap junctions with connexons | Synaptic cleft and vesicles with neurotransmitters |
| Energy Requirement | Minimal (passive transmission) | Requires energy for neurotransmitter release |
| Signal Amplification | No amplification | Can amplify signals via receptor activation |
| Plasticity (Learning/Memory) | Limited plasticity | High plasticity |
| Occurrence | Found in reflex pathways, heart, and retina | Common in the central and peripheral nervous system |
| Type of Signal | Electrical impulses (ion flow) | Chemical signals (neurotransmitters) |
| Delay | Virtually no delay | Synaptic delay (~0.5 ms or more) |
Neuromuscular Transmission
- Action potential travels down neuron to the terminal
- This causes an influx of Ca2+ via voltage-gated calcium channels
- Vesicles containing Acetylcholine (ACh) fuse with the presynaptic membrane
- ACh is released and diffuses across to the other side of the cleft
- ACh then binds to acetylcholine receptors on the muscle membrane
- Na+ and K+ channels then open, which leads to the muscle cell to depolarize
Action Potential in Skeletal Muscle Cell
- The action potential first arrives at the neuromuscular junction.
- Acetylcholine (ACh) is then released into the synaptic cleft.
- ACh binds to receptors, causing Na+ influx and the opening of voltage-gated Na+ channels leading to membrane depolarization,
- The process goes through T-tubules, which activates Ca2+ release from the sarcoplasmic reticulum.
Skeletal Muscle Action Potential Features
- Resting membrane potential is ~ -90 mV.
- Depolarization: Voltage-gated Na+ channels open, resulting in rapid Na+ influx.
- Repolarization: Voltage-gated K+ channels open that cause K+ efflux.
- There is no plateau phase during short duration (2-5 ms).
Action Potential in Cardiac Muscle
- Key Features:
- Resting membrane potential of ~ -85 mV.
- Rapid depolarization occurs due to Na+ influx through voltage-gated Na+ channels.
- Plateau phase: Slow Ca2+ influx through L-type Ca2+ channels leads to prolonged depolarization.
- Repolarization: K+ efflux through voltage-gated K+ channels.
- Prolonged duration of approximately 200-400ms which prevents tetany.
Action Potential in Smooth Muscle Cells
- Resting membrane potential varies between -50 to -60 mV.
- Depolarization occurs mainly due to Ca2+ influx via voltage-gated Ca2+ channels, and isn't due to Na+.
- Repolarization is due to K+ efflux.
- Slow-wave potentials - Oscillations in membrane potential can result in the triggering of action potentials.
- No true refractory period exists.
Comparison of Muscle Cell Action Potentials
| Feature | Skeletal Muscle | Cardiac Muscle | Smooth Muscle |
|---|---|---|---|
| Resting Potential | ~ -90 mV | ~ -85 mV | ~ -50 to -60 mV |
| Depolarizing Ion | Na+ | Na+, Ca2+ | Ca2+ |
| Plateau Phase | No | Yes | No |
| Duration (ms) | 2-5 | 200-400 | Variable |
| Refractory Period | Short | Long (prevents tetany) | Minimal/none |
Myasthenia Gravis (MG)
- Chronic autoimmune neuromuscular disease with long term effects.
- Occurs among any ethnic group, and commonly in women under 40 and men under 60.
- Newborns can have neonatal MG if their mothers have the disease; symptoms disappear after 3 months and MG itself isn't inherited or contagious.
- Symptoms include affecting muscles that control swallowing, facial expression, and eye movement.
- Can lead to blurred or double vision, weakness in limbs and facial expression changes and difficulty breathing if breathing muscles are impacted.
- Cause is unknown and may linked to a thymus gland tumour (Thymoma)
- Diagnosed through medical history, physical exams, blood tests for acetylcholine receptor antibodies, CT or MRI scans, and nerve conduction studies.
- Treatment involves avoiding stress, medications like prednisone, Azathioprine, Cyclosporin, mycophenulate, Mofetil, and Tracrolimus.
- These medications all suppress the immune system, thymectomy (Neostigmine, Physostigmine, Pyridostigmine -Cholinesterase inhibitors) and plasma replacement
- Prognosis: With proper treatment, signs and symptoms could reduce, and it doesn't affect life expectancy and women with MG can have children.
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