Explanation:
All autonomic preganglionic neurons release acetylcholine, which acts on nicotinic receptors in autonomic ganglia. Sweat-gland sympathetic postganglionic neurons are an important exception because they release acetylcholine, which acts on muscarinic receptors.
2. A drug selectively blocks nicotinic acetylcholine receptors in autonomic ganglia but does not block muscarinic receptors at effector organs. Which immediate effect is most likely?
A.
Enhanced parasympathetic effects with unchanged sympathetic effects
B.
Failure of transmission through both sympathetic and parasympathetic ganglia
C.
Selective failure of sympathetic transmission because only sympathetic ganglia contain nicotinic receptors
D.
Blockade of neurotransmitter release only from postganglionic neurons
Correct Answer:
Failure of transmission through both sympathetic and parasympathetic ganglia
Explanation:
Both sympathetic and parasympathetic preganglionic neurons release acetylcholine onto nicotinic receptors in their respective autonomic ganglia. Blocking these receptors interrupts transmission in both divisions before the postganglionic neuron.
3. Which pairing correctly matches a postganglionic autonomic neurotransmitter with its principal receptor type at the effector?
A.
Parasympathetic acetylcholine—muscarinic receptor
B.
Parasympathetic noradrenaline—nicotinic receptor
C.
Sympathetic acetylcholine—nicotinic receptor at cardiac muscle
D.
Sympathetic noradrenaline—muscarinic receptor at vascular smooth muscle
Explanation:
Most parasympathetic postganglionic neurons release acetylcholine, which acts on muscarinic receptors on target tissues. Nicotinic receptors are mainly present in autonomic ganglia, not as the usual receptors on parasympathetic effector cells.
4. The adrenal medulla is functionally similar to which component of an autonomic pathway, and why?
A.
A postganglionic parasympathetic neuron, because it releases acetylcholine into the bloodstream
B.
A preganglionic sympathetic neuron, because it receives acetylcholine at muscarinic receptors
C.
A sympathetic postganglionic neuron, because it releases noradrenaline directly onto smooth muscle
D.
A sympathetic postganglionic effector, because chromaffin cells release catecholamines into the blood after nicotinic stimulation
Correct Answer:
A sympathetic postganglionic effector, because chromaffin cells release catecholamines into the blood after nicotinic stimulation
Explanation:
Sympathetic preganglionic fibers release acetylcholine onto nicotinic receptors of adrenal medullary chromaffin cells. The chromaffin cells then secrete mainly adrenaline and some noradrenaline into the bloodstream, acting like modified postganglionic neurons.
5. If acetylcholinesterase activity is inhibited at a parasympathetic effector synapse, which change is most directly expected?
A.
Shortening of the action of acetylcholine at muscarinic receptors
B.
Prolongation and intensification of acetylcholine-mediated effects
C.
Conversion of acetylcholine into noradrenaline at the synapse
D.
Prevention of acetylcholine release from the preganglionic neuron
Correct Answer:
Prolongation and intensification of acetylcholine-mediated effects
Explanation:
Acetylcholinesterase normally terminates acetylcholine action by hydrolyzing it in the synaptic cleft. Inhibiting the enzyme allows acetylcholine to remain longer near muscarinic receptors, prolonging its parasympathetic effect.
6. Which statement best distinguishes neurotransmission at an autonomic ganglion from neurotransmission at most autonomic effector junctions?
A.
Ganglia use muscarinic receptors exclusively, whereas effectors use nicotinic receptors exclusively
B.
Ganglia receive noradrenaline from preganglionic neurons, whereas effectors receive acetylcholine
C.
Ganglia generally use acetylcholine acting on nicotinic receptors, whereas effectors may use acetylcholine acting on muscarinic receptors or noradrenaline acting on adrenergic receptors
D.
Ganglia contain only inhibitory synapses, whereas effectors contain only excitatory synapses
Correct Answer:
Ganglia generally use acetylcholine acting on nicotinic receptors, whereas effectors may use acetylcholine acting on muscarinic receptors or noradrenaline acting on adrenergic receptors
Explanation:
Preganglionic autonomic neurons release acetylcholine onto fast nicotinic receptors in autonomic ganglia. At effector organs, parasympathetic neurons usually release acetylcholine onto muscarinic receptors, while most sympathetic neurons release noradrenaline onto adrenergic receptors.
7. A sympathetic postganglionic neuron supplying a blood vessel is prevented from synthesizing noradrenaline. Which event would be directly impaired?
A.
Activation of nicotinic receptors on the sympathetic postganglionic neuron
B.
Release of acetylcholine by the preganglionic neuron
C.
Transmission from the spinal cord to the autonomic ganglion
D.
Activation of adrenergic receptors on the vascular smooth muscle
Correct Answer:
Activation of adrenergic receptors on the vascular smooth muscle
Explanation:
The preganglionic neuron can still release acetylcholine and activate nicotinic receptors in the ganglion. However, without noradrenaline from the postganglionic neuron, adrenergic receptors on the vascular smooth muscle cannot be normally stimulated.
8. Which combination correctly identifies the neurotransmitter and receptor at the junction between a sympathetic preganglionic neuron and a sympathetic postganglionic neuron?
A.
Noradrenaline and beta-adrenergic receptor
B.
Acetylcholine and nicotinic receptor
C.
Acetylcholine and muscarinic receptor
D.
Adrenaline and alpha-adrenergic receptor
Correct Answer:
Acetylcholine and nicotinic receptor
Explanation:
The junction within a sympathetic ganglion follows the general autonomic rule: the preganglionic neuron releases acetylcholine, and the postganglionic neuron is activated through nicotinic acetylcholine receptors.
9. Which observation most strongly indicates that a drug is acting at adrenergic receptors rather than at autonomic ganglionic nicotinic receptors?
A.
It prevents both sympathetic and parasympathetic preganglionic neurons from exciting their ganglion cells
B.
It blocks responses to noradrenaline at a sympathetic effector without preventing transmission through the autonomic ganglion
C.
It inhibits acetylcholine release from every autonomic preganglionic neuron
D.
It abolishes transmission in both autonomic divisions before the postganglionic neurons
Correct Answer:
It blocks responses to noradrenaline at a sympathetic effector without preventing transmission through the autonomic ganglion
Explanation:
Adrenergic receptors are located on many sympathetic effector tissues and respond to noradrenaline or adrenaline. Ganglionic nicotinic receptors are located on postganglionic neurons, so blocking adrenergic receptors can leave ganglionic transmission intact.
10. Why can one preganglionic autonomic neuron influence several postganglionic neurons, producing amplification of an autonomic response?
A.
A single postganglionic neuron always releases neurotransmitter into the spinal cord
B.
Preganglionic axons branch within autonomic ganglia and form synapses with multiple postganglionic neurons
C.
Postganglionic neurons release acetylcholine backward into several ganglia
D.
Adrenergic receptors automatically convert one neurotransmitter molecule into several action potentials
Correct Answer:
Preganglionic axons branch within autonomic ganglia and form synapses with multiple postganglionic neurons
Explanation:
Autonomic preganglionic axons commonly branch in their ganglia. Since each branch can release acetylcholine onto a different postganglionic neuron through nicotinic receptors, activity can diverge and affect multiple target tissues.
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