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What is the primary neurotransmitter released by all preganglionic neurons in the autonomic nervous system?
What is the primary neurotransmitter released by all preganglionic neurons in the autonomic nervous system?
Which type of receptors do preganglionic neurons activate on postganglionic neurons?
Which type of receptors do preganglionic neurons activate on postganglionic neurons?
What structural characteristic do nicotinic receptors possess?
What structural characteristic do nicotinic receptors possess?
What benefit does the 'en passant' synapse arrangement provide to autonomic axons?
What benefit does the 'en passant' synapse arrangement provide to autonomic axons?
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What distinguishes the molecular subtype of nicotinic receptors found on postganglionic neurons from the type found at the neuromuscular junction?
What distinguishes the molecular subtype of nicotinic receptors found on postganglionic neurons from the type found at the neuromuscular junction?
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In the autonomic nervous system, synaptic transmission between preganglionic and postganglionic neurons occurs in which type of location?
In the autonomic nervous system, synaptic transmission between preganglionic and postganglionic neurons occurs in which type of location?
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What type of channel are nicotinic receptors classified as?
What type of channel are nicotinic receptors classified as?
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Which statement is true regarding varicosities in postganglionic neurons?
Which statement is true regarding varicosities in postganglionic neurons?
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What is the primary effect of the sympathetic division on the heart rate?
What is the primary effect of the sympathetic division on the heart rate?
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Which autonomic division typically stimulates peristalsis in the gut?
Which autonomic division typically stimulates peristalsis in the gut?
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Which of the following organs receives input solely from the sympathetic division?
Which of the following organs receives input solely from the sympathetic division?
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What is a distinguishing feature of postganglionic autonomic neurons?
What is a distinguishing feature of postganglionic autonomic neurons?
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How do antagonistic effects of the sympathetic and parasympathetic divisions generally function?
How do antagonistic effects of the sympathetic and parasympathetic divisions generally function?
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What misconception was previously held about the release of neurotransmitters in the autonomic nervous system?
What misconception was previously held about the release of neurotransmitters in the autonomic nervous system?
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In which situation would the sympathetic division typically be active?
In which situation would the sympathetic division typically be active?
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Which statement about the salivary glands is correct?
Which statement about the salivary glands is correct?
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What role does the third cytoplasmic loop of muscarinic receptors play?
What role does the third cytoplasmic loop of muscarinic receptors play?
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Which muscarinic receptors couple preferentially to Gαq and phospholipase C?
Which muscarinic receptors couple preferentially to Gαq and phospholipase C?
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What is typically released by most postganglionic sympathetic neurons?
What is typically released by most postganglionic sympathetic neurons?
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What type of receptors are adrenergic receptors categorized under?
What type of receptors are adrenergic receptors categorized under?
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Which adrenergic receptor subtype is primarily linked to activating Gs and stimulating adenylyl cyclase in the heart?
Which adrenergic receptor subtype is primarily linked to activating Gs and stimulating adenylyl cyclase in the heart?
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Which of the following statements about sweat glands is true?
Which of the following statements about sweat glands is true?
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How many major types of adrenergic receptors are recognized?
How many major types of adrenergic receptors are recognized?
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What is a result of Gαi or Gαo coupling in muscarinic receptors?
What is a result of Gαi or Gαo coupling in muscarinic receptors?
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What neurotransmitter is primarily released by sympathetic preganglionic neurons?
What neurotransmitter is primarily released by sympathetic preganglionic neurons?
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Which type of receptor is mainly found on postganglionic parasympathetic neurons?
Which type of receptor is mainly found on postganglionic parasympathetic neurons?
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How do N1 and N2 receptors primarily differ regarding drug sensitivity?
How do N1 and N2 receptors primarily differ regarding drug sensitivity?
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Which of the following statements about autonomic neurotransmission is true?
Which of the following statements about autonomic neurotransmission is true?
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Which neurotransmitter is released by parasympathetic postganglionic neurons?
Which neurotransmitter is released by parasympathetic postganglionic neurons?
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What is the role of preganglionic neurons in autonomic transmission?
What is the role of preganglionic neurons in autonomic transmission?
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Where are the cell bodies of sympathetic preganglionic neurons located?
Where are the cell bodies of sympathetic preganglionic neurons located?
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What type of receptors do sympathetic postganglionic neurons predominantly use?
What type of receptors do sympathetic postganglionic neurons predominantly use?
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What type of neurotransmission do nicotinic receptors mediate?
What type of neurotransmission do nicotinic receptors mediate?
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Which receptor type is responsible for a slower electrical response that can be either inhibitory or excitatory?
Which receptor type is responsible for a slower electrical response that can be either inhibitory or excitatory?
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What is the effect of muscarinic neurotransmission on the M current?
What is the effect of muscarinic neurotransmission on the M current?
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What happens to neuron excitability when the M current is inhibited by muscarine?
What happens to neuron excitability when the M current is inhibited by muscarine?
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The primary result of activating a nicotinic receptor involves which type of postsynaptic response?
The primary result of activating a nicotinic receptor involves which type of postsynaptic response?
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What characterizes the response of postganglionic neurons to ACh in autonomic ganglia?
What characterizes the response of postganglionic neurons to ACh in autonomic ganglia?
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In what way do muscarinic responses enhance autonomic nervous system function?
In what way do muscarinic responses enhance autonomic nervous system function?
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What is the role of K^+ channels relating to the M current in the baseline state?
What is the role of K^+ channels relating to the M current in the baseline state?
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What is the primary neurotransmitter associated with postganglionic sympathetic neurons?
What is the primary neurotransmitter associated with postganglionic sympathetic neurons?
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Which adrenergic receptor subtype is linked to increasing intracellular cAMP levels?
Which adrenergic receptor subtype is linked to increasing intracellular cAMP levels?
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Which receptor subtype is primarily activated by norepinephrine and epinephrine?
Which receptor subtype is primarily activated by norepinephrine and epinephrine?
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What is the main effect of agonists on the α2 adrenergic receptor?
What is the main effect of agonists on the α2 adrenergic receptor?
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Which of the following is a known antagonist for the β2 adrenergic receptor?
Which of the following is a known antagonist for the β2 adrenergic receptor?
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What second messenger is produced via activation of the M1, M3, and M5 muscarinic receptors?
What second messenger is produced via activation of the M1, M3, and M5 muscarinic receptors?
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What type of G protein is associated with both β1 and β2 adrenergic receptors?
What type of G protein is associated with both β1 and β2 adrenergic receptors?
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Which antagonist is used for the nicotinic ACh receptor subtype N2?
Which antagonist is used for the nicotinic ACh receptor subtype N2?
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Which receptor subtype is primarily responsible for vasodilation in response to epinephrine?
Which receptor subtype is primarily responsible for vasodilation in response to epinephrine?
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What signal transduction mechanism do M2 muscarinic receptors utilize?
What signal transduction mechanism do M2 muscarinic receptors utilize?
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Study Notes
Autonomic Nervous System Synaptic Physiology
- All skeletal muscle innervation is excitatory, but visceral targets receive both inhibitory and excitatory inputs from the sympathetic and parasympathetic divisions.
- In organs active during physical activity, the sympathetic division is excitatory and parasympathetic is inhibitory. For example, sympathetic input increases heart rate, while parasympathetic decreases it. The opposite is true for organs active at rest.
- Sympathetic and parasympathetic divisions generally have opposing effects, but exceptions exist. For example, salivary glands are stimulated by both, and some organs receive input from only one division (e.g., sweat glands, piloerector muscles, most peripheral blood vessels).
- Autonomic synapses are specialized with varicosities (bulbous expansions) along axons, distributing neurotransmitter release across the target organ.
- Varicosities form synapses with their targets, forming a ~50nm synaptic cleft.
- This arrangement allows a single axon branch to influence many targets, with wider distribution of autonomic output.
Preganglionic Neurons
- All preganglionic neurons (sympathetic and parasympathetic) release acetylcholine (ACh) and stimulate N2 nicotinic receptors on postganglionic neurons.
- N2 nicotinic receptors are ionotropic receptors with a pentameric structure. They are different from the N1 nicotinic receptors found at the neuromuscular junction.
Postganglionic Neurons
- Sympathetic postganglionic neurons primarily release norepinephrine onto visceral targets, acting through adrenergic receptors (with exceptions).
- Parasympathetic postganglionic neurons primarily release acetylcholine (ACh) onto visceral targets, stimulating muscarinic receptors.
- Muscarinic receptors are metabotropic receptors that can have varying effects depending on the subtype (M1 to M5) and are more variable in their effects than nicotinic receptors.
- Some postganglionic neurons have both nicotinic and muscarinic receptors.
- Muscarinic receptors lead to slower, more variable responses compared to fast nicotinic responses. This involves second-messenger activation and often has inhibitory or excitatory outcomes depending on the target.
Receptor Types
- Adrenergic receptors are a family of G-protein coupled receptors that differ in subtype and tissue distribution (a1, a2, β1, β2, and β3).
- Muscarinic receptors are G-protein coupled receptors with various subtypes (M1 through M5) that have diverse effects through second messengers, such as changes in cAMP and Ca++.
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