mC test 2
1) The autonomic nervous system innervates all the following effector organs and tissues except ________. A) skeletal muscles B) cardiac muscles C) endocrine glands D) adipose tissues E) exocrine glands Diff: 3 Page Ref: 303
Answer: A
27) Binding of norepinephrine to what type of receptor will trigger the activation of phospholipase C? A) 1 B) 2 C) 1 D) 2 E) muscarinic Diff: 5 Page Ref: 309
Answer: A
29) Activation of which class of adrenergic receptor will result in calcium release from intracellular stores? A) alpha1 only B) alpha2 only C) beta1 only D) beta2 only E) alpha1, alpha2, and beta1 Diff: 6 Page Ref: 309
Answer: A
35) What are swellings of postganglionic autonomic axons from which neurotransmitters are released called? A) Varicosities B) Neuromuscular junctions C) Sympathetic trunks D) Parasympathetic chains E) Ganglia Diff: 3 Page Ref: 310
Answer: A
37) What type of channels that are present within the varicosities of autonomic neurons are absent from the axon terminal of other neurons? A) Voltage-gated Na+ and K+ channels B) Voltage-gated Ca2+ and Na+ channels C) Voltage-gated Na+ channels, exclusively D) Voltage-gated Ca2+ channels, exclusively E) Voltage-gated K+ channels, exclusively Diff: 5 Page Ref: 310
Answer: A
44) Where are most of the autonomic nervous system control centers located? A) brainstem B) frontal lobe C) thalamus D) limbic system E) spinal cord Diff: 5 Page Ref: 312
Answer: A
56) How does latroxin, the venom of the black widow spider, cause muscle spasms and rigidity. A) It stimulates acetylcholine release from motor neurons. B) It stimulates acetylcholine release from autonomic preganglionic neurons. C) It inhibits acetylcholine release from motor neurons. D) It inhibits the degradation of acetylcholine at all synapses. E) It blocks nicotinic cholinergic receptors.
Answer: A
9) Which of the following structures of an autonomic neuron is NOT located within the ganglion? A) the cell body of preganglionic neurons B) the terminal axon of preganglionic neurons C) the intrinsic neurons D) the cell body of postganglionic neurons E) the dendrites of postganglionic neurons Diff: 4 Page Ref: 304
Answer: A
13) Which of the following endocrine glands is innervated by sympathetic preganglionic neurons? A) adrenal cortex B) adrenal medulla C) thyroid gland D) anterior pituitary E) pancreas
Answer: B
2) Dual innervation of organs by the autonomic nervous system refers to the observation that ________. A) two postganglionic sympathetic neurons innervate each target organ B) both sympathetic and parasympathetic neurons innervate most organs C) autonomic innervation involves preganglionic and postganglionic neurons D) autonomic and somatic neurons innervate all organs E) autonomic neurons that innervate each target organ originate from two ganglia Diff: 3 Page Ref: 303
Answer: B
21) Which of the following cranial nerves does NOT include parasympathetic nerves? A) III - oculomotor nerve B) V - trigeminal nerve C) VII - facial nerve D) IX - glossopharyngeal nerve E) X - vagus nerve Diff: 8 Page Ref: 307
Answer: B
23) Parasympathetic postganglionic neurons release the neurotransmitter ________; sympathetic postganglionic neurons release the neurotransmitter ________. A) epinephrine : norepinephrine B) acetylcholine : norepinephrine C) norepinephrine : acetylcholine D) acetylcholine : acetylcholine E) norepinephrine : norepinephrine Diff: 3 Page Ref: 208
Answer: B
30) Activation of which class of adrenergic receptor decreases the cytosolic levels of cAMP? A) alpha1 only B) alpha2 only C) beta1 only D) beta2 only E) both beta1 and beta2 Diff: 6 Page Ref: 310
Answer: B
38) What enzyme degrades the neurotransmitter released from varicosities of parasympathetic postganglionic neurons? A) catechol-O-methyltransferase only B) acetylcholinesterase C) monoamine oxidase only D) choline acetyl transferase E) catechol-O-methyltransferase and monoamine oxidase Diff: 4 Page Ref: 310
Answer: B
39) In what class of neuron and within what organelle is the enzyme monoamine oxidase located? A) synaptic vesicles of sympathetic postganglionic neurons B) mitochondria of sympathetic postganglionic neurons C) lysosomes of sympathetic preganglionic neurons D) smooth ER of parasympathetic postganglionic neurons E) Golgi apparatus of parasympathetic postganglionic neurons Diff: 4 Page Ref: 310
Answer: B
4) Which of the following physiological responses are associated with an elevation in parasympathetic nervous system activity? A) shifting blood flow away from the gastrointestinal tract B) enhanced absorption of nutrients C) increased heart rate D) increased contractile force of the heart E) enhanced mobilization of energy stores Diff: 4 Page Ref: 303
Answer: B
43) Which of the following is NOT a visceral reflex? A) pupillary light reflex B) withdrawal reflex C) vomiting D) urination E) swallowing
Answer: B
5) At rest, what is the relative contribution of the sympathetic and parasympathetic nervous systems to the regulation of homeostasis? A) Only the sympathetic system is active. B) Both systems are active but the parasympathetic predominates. C) Only the parasympathetic system is active. D) Both systems are active but the sympathetic predominates. E) Neither system is active. Diff: 4 Page Ref: 303
Answer: B
51) Where on skeletal muscle is the highest density of nicotinic receptors? A) terminal bouton B) motor end plate C) motor unit D) dendrites E) axon hillock Diff: 3 Page Ref: 316
Answer: B
53) What is the graded change in membrane potential that occurs at the motor end plate of skeletal muscle called? A) Inhibitory postsynaptic potential B) End-plate potential C) Muscarinic potential D) Adrenergic potential E) Action potential Diff: 4 Page Ref: 316
Answer: B
55) Which of the following statements is TRUE of communication across the neuromuscular junction? A) Acetylcholine released from a motor neuron binds to muscarinic cholinergic receptors. B) The end-plate potential is always of sufficient magnitude to depolarize the muscle cell to threshold to initiate an action potential. C) Acetylcholinesterase located in the cytosol of the motor neuron degrades acetylcholine to acetate and choline. D) Acetylcholinesterase located in mitochondria of the motor neuron degrades acetylcholine to acetate and choline. E) Synaptic communication to the muscle cell can be excitatory or inhibitory. Diff: 5 Page Ref: 316
Answer: B
57) The steps of synaptic transmission at the motor end plate are listed below, out of order. Choose the correct order. 1. Acetylcholine binds to postsynaptic receptors. 2. Acetylcholine is released by exocytosis. 3. A graded depolarization is produced. 4. An action potential is produced on the muscle cell membrane. 5. Channels for both sodium and potassium are opened. 6. Voltage-dependent calcium channels on the plasma membrane open. 7. An action potential arrives at the axon terminal. A) 7521346 B) 7621534 C) 5231746 D) 2153674 E) 4357261
Answer: B
11) Sympathetic preganglionic neurons exit the spinal nerve via the ________ before they enter the ________. A) white ramus : effector organ B) gray ramus : effector organ C) gray ramus : ganglion of the sympathetic trunk D) ventral root : ganglion of the sympathetic trunk E) white ramus : ganglion of the sympathetic trunk Diff: 5 Page Ref: 305
Answer: E
12) Which of the following contributes to the ability of the sympathetic nervous system to produce widespread responses within the body? A) multiple preganglionic neurons innervate each ganglion, sending out individual postganglionic neurons B) one postganglionic neuron branches into many collaterals that affect multiple organs C) one preganglionic neuron sends collaterals to multiple ganglia, affecting multiple postganglionic neurons D) one preganglionic neuron can activate only one postganglionic neuron E) several preganglionic neurons activate a single postganglionic neuron Diff: 4 Page Ref: 305
Answer: C
24) Which of the following neurons of the efferent branch of the peripheral nervous system does NOT release acetylcholine? A) sympathetic preganglionic neuron B) parasympathetic preganglionic neuron C) sympathetic postganglionic neuron D) parasympathetic postganglionic neuron E) motor neuron Diff: 4 Page Ref: 208
Answer: C
25) Binding of acetylcholine to ________ receptors causes a ________ by opening channels that permit both sodium and potassium to permeate the membrane. A) muscarinic : depolarization B) muscarinic : hyperpolarization C) nicotinic : depolarization D) nicotinic : hyperpolarization E) nicotinic : no change in membrane potential Diff: 5 Page Ref: 309
Answer: C
48) The somatic nervous system regulates the activity of ________. A) endocrine organs B) many organs C) skeletal muscle D) the kidneys E) the cardiovascular system
Answer: C
49) With respect to their innervation, individual skeletal muscle fibers (cells) are innervated by ________. A) a single motor neuron B) multiple motor neurons C) a single motor neuron and autonomic neuron D) multiple motor neurons and autonomic neurons E) a single motor neuron and multiple autonomic neurons Answer: A Diff: 4 Page Ref: 314 50) What is the neurotransmitter released from motor neurons? A) Epinephrine B) Norepinephrine C) Acetylcholine D) Dopamine E) GABA Diff: 3 Page Ref: 316
Answer: C
52) Which of the following is located between the invaginations of the motor end plate of a neuromuscular junction? A) 2 receptors B) 3 receptors C) Acetylcholinesterase D) Muscarinic receptors E) Nicotinic receptors Diff: 5 Page Ref: 316
Answer: C
7) Which of the following best describes the general arrangement of the efferent limb of the autonomic nervous system? A) one neuron B) two neurons in parallel C) two neurons in series D) three neurons in series E) three neurons in parallel Diff: 3 Page Ref: 303
Answer: C
10) Where do the preganglionic neurons of the sympathetic nervous system emerge from the spinal cord? A) thoracic region only B) sacral region only C) lumbar region only D) thoracic and lumbar regions E) lumbar and sacral regions Diff: 4 Page Ref: 305
Answer: D
15) Which of the following are indicative of the relative release of catecholamines from the adrenal medulla? A) 80% epinephrine : 20% dopamine B) 80% norepinephrine : 20% dopamine C) 80% norepinephrine : 20% epinephrine D) 80% epinephrine : 20% norepinephrine E) 100% acetylcholine Diff: 3 Page Ref: 305
Answer: D
22) Parasympathetic preganglionic neurons release the neurotransmitter ________; sympathetic preganglionic neurons release the neurotransmitter ________. A) epinephrine : norepinephrine B) acetylcholine : norepinephrine C) norepinephrine : acetylcholine D) acetylcholine : acetylcholine E) norepinephrine : norepinephrine Diff: 3 Page Ref: 307
Answer: D
3) Which of the following physiological responses are associated with elevated sympathetic nervous system activity? A) enhanced digestion B) enhanced absorption of nutrients C) decreased heart rate D) increased contractile force of the heart E) inhibition of cardiovascular function Diff: 4 Page Ref: 303
Answer: D
33) Which of the following does NOT have nicotinic cholinergic receptors? A) skeletal muscle cells B) parasympathetic postganglionic neuron cell bodies C) sympathetic postganglionic neuron cell bodies D) effector organs for the parasympathetic nervous system E) chromaffin cells Diff: 5 Page Ref: 308
Answer: D
36) The presence of ________ within varicosities mediate the release of neurotransmitter. A) mechanically-gated Na+ channels B) mechanically-gated Ca2+ channels C) voltage-gated Na+ channels D) voltage-gated Ca2+ channels E) voltage-gated K+ channels Diff: 4 Page Ref: 310
Answer: D
41) Which of the regions of the brain listed below is NOT involved in the control of the autonomic nervous system? A) hypothalamus B) pons C) medulla oblongata D) cerebellum E) limbic system Diff: 5 Page Ref: 312
Answer: D
45) Which of the following descriptions is TRUE for the parasympathetic nervous system, but NOT the sympathetic nervous system? A) Some preganglionic neurons originate in the spinal cord. B) Some ganglia are connected together in a chain. C) Preganglionic fibers release acetylcholine. D) Postganglionic fibers release acetylcholine. E) Receptors on effector organs are nicotinic cholinergic. Diff: 6 Page Ref: 307
Answer: D
47) Mismatches between vestibular, visual, and proprioceptive sensory inputs activate the autonomic nervous system, leading to symptoms that are characteristic of ________. A) the accommodation reflex B) the vomiting reflex C) fainting D) motion sickness E) the pupillary light reflex Diff: 3 Page Ref: 313
Answer: D
54) The opening of a cation channel that allows both Na+ and K+ to move through will cause the membrane to ________ because of the ________. A) hyperpolarize : greater K+ electrochemical gradient as compared with Na+ B) hyperpolarize : greater Na+ electrochemical gradient as compared with K+ C) depolarize : greater K+ electrochemical gradient as compared with Na+ D) depolarize : greater Na+ electrochemical gradient as compared with K+ E) not change : same electrochemical gradient for K+ and Na+ Diff: 5 Page Ref: 316
Answer: D
6) When the body is stressed, what is the relative contribution of the sympathetic and parasympathetic nervous systems to the regulation of homeostasis? A) Only the sympathetic system is active. B) Both systems are active but the parasympathetic predominates. C) Only the parasympathetic system is active. D) Both systems are active but the sympathetic predominates. E) Neither system is active. Diff: 3 Page Ref: 303
Answer: D
14) What cells of the adrenal medulla release epinephrine? A) alpha cells B) beta cells C) delta cells D) adrenergic cells E) chromaffin cells Diff: 4 Page Ref: 305
Answer: E
16) Which of the following descriptions of collateral ganglia is true? A) Collateral ganglia are part of the somatic nervous system, located where the motor neuron leaves the ventral horn. B) Collateral ganglia are part of the somatosensory system, located off of the afferent neuron just prior to entering the spinal cord dorsal horn. C) Collateral ganglia are located within the effector organs and are the sites of communication between parasympathetic preganglionic neurons and postganglionic neurons. D) Collateral ganglia are located within a chain just outside the spinal cord and are the sites of communication between sympathetic preganglionic neurons and postganglionic neurons. E) Collateral ganglia are in the sympathetic nervous system but distinct from the sympathetic chain, and they function as a site of communication between sympathetic preganglionic neurons and postganglionic neurons. Diff: 5 Page Ref: 305
Answer: E
18) Where in the central nervous system do the preganglionic neurons of the parasympathetic nervous system originate? A) thoracic region of the spinal cord only B) sacral region of the spinal cord only C) lumbar region of the spinal cord only D) thoracic and lumbar regions of the spinal cord E) brainstem and sacral region of the spinal cord Diff: 4 Page Ref: 307
Answer: E
19) Parasympathetic preganglionic neurons travel in what nerves? A) cranial nerves only B) spinal nerves only C) pelvic nerves only D) cranial and spinal nerves E) cranial and pelvic nerves Diff: 5 Page Ref: 307
Answer: E
20) Parasympathetic neurons from which cranial nerve innervate most of the viscera in the thoracic and abdominal cavities? A) I B) III C) VII D) IX E) X Diff: 7 Page Ref: 307
Answer: E
26) What cholinergic receptors are coupled to G proteins? A) alpha1 B) alpha2 C) beta2 D) nicotinic E) muscarinic Diff: 4 Page Ref: 309
Answer: E
28) Compared to norepinephrine, epinephrine has a greater affinity for what type of receptor? A) nicotinic B) muscarinic C) alpha1 D) beta1 E) beta2 Diff: 4 Page Ref: 310
Answer: E
31) What class of adrenergic receptor activates the enzyme adenylate cyclase? A) alpha1 only B) alpha1 and alpha2 C) beta2 only D) beta1 and beta2 E) beta1, beta2, and beta3 Diff: 7 Page Ref: 310
Answer: E
32) Actions at which class of adrenergic receptor generally have excitatory effects? A) alpha1 and alpha2 B) beta1 and beta3 C) beta1, beta2, and beta3 D) alpha1 and beta1 E) alpha1, alpha2, beta1, and beta3 Diff: 7 Page Ref: 310
Answer: E
34) What type of receptor agonists are used to treat people suffering from asthma or nasal congestion? A) muscarinic B) nicotinic C) 2 D) 3 E) 2 Diff: 5 Page Ref: 310
Answer: E
42) What area of the brain initiates the fight-or-flight response by producing widespread activation of the sympathetic nervous system? A) brainstem B) cerebellum C) amygdala D) limbic system E) hypothalamus Diff: 5 Page Ref: 312
Answer: E
46) Which class of autonomic nervous system receptors is ionotropic? A) all alpha adrenergic B) all beta adrenergic C) some beta adrenergic but no alpha adrenergic D) muscarinic cholinergic E) nicotinic cholinergic Diff: 5 Page Ref: 308
Answer: E
8) Within the autonomic ganglia, what are the cells that modulate the flow of information to the target organ called? A) intraganglionic neurons B) ganglionic neurons C) preganglionic neurons D) postganglionic neurons E) intrinsic neurons Diff: 5 Page Ref: 304
Answer: E
12) Binding of a ligand to the 1 adrenergic receptor activates Gi, thereby inhibiting the synthesis of cAMP. Diff: 4 Page Ref: 309
Answer: FALSE
13) Atropine, first derived from the Atropa belladonna plant, is a nicotinic receptor antagonist. Diff: 5 Page Ref: 310
Answer: FALSE
14) The somatic nervous system provides both excitatory and inhibitory signals to skeletal muscle. Diff: 4 Page Ref: 316
Answer: FALSE
15) A motor unit consists of a skeletal muscle fiber (cell) and all of the motor neurons that innervate that skeletal muscle fiber. Diff: 4 Page Ref: 314
Answer: FALSE
2) Physiological stressors will cause parasympathetic nervous system activity to increase. Diff: 3 Page Ref: 303
Answer: FALSE
6) The primary hormone released from the adrenal medulla is norepinephrine. Diff: 4 Page Ref: 305
Answer: FALSE
8) All autonomic nerves contain only efferent fibers. Diff: 4 Page Ref: 307
Answer: FALSE
5) Describe the anatomical arrangement of the somatic nervous system, including the concept of motor units.
Answer: In the somatic nervous system, a single efferent neuron runs from the central nervous system to the skeletal muscle. These motor neurons originate in the ventral horn of the spinal cord and receive input from multiple sources, including afferent neurons. A single motor neuron innervates multiple muscle fibers but each muscle is innervated by a single neuron. A motor unit describes a single motor neuron and all of the skeletal muscle fibers innervated by that neuron. Thus, when a motor neuron is activated, all of the muscle fibers innervated by that motor neuron are stimulated to contract simultaneously. Diff: 4 Page Ref: 314
4) Norepinephrine is one of the more important neurotransmitters of the peripheral nervous system. Identify the branches of the peripheral nervous system for which norepinephrine is the neurotransmitter and describe the receptors responsible for responding to norepinephrine. Include the mechanisms whereby these receptors transduce the response to norepinephrine.
Answer: Neurons that release norepinephrine are referred to as adrenergic neurons. Norepinephrine is the neurotransmitter for most postganglionic sympathetic neurons (except sympathetic neurons that innervate sweat glands). The end organ receptors for norepinephrine are classified into two majors groups: and receptors. Within each of these classes are several subclasses of receptors with different sensitivities to catecholmines (norepinephrine and epinephrine) and different links to second messenger cascades. Each of the adrenergic receptors are metabotropic and are coupled to a G protein, but the particular G protein can be different (Gs vs Gi). The 1 adrenergic receptor subtype is coupled to activation of phospholipase C for the synthesis of inositol triphosphate, while the 2 adrenergic receptor subtype acts through Gi to suppress the synthesis of cAMP. All three of the receptors are stimulatory, linked through Gs, and are involved in the activation of cAMP. Diff: 6 Page Ref: 309
3) Acetylcholine is one of the most common neurotransmitters in the peripheral nervous system. Identify the branches of the peripheral nervous system for which acetylcholine is the neurotransmitter and describe the receptors responsible for responding to acetylcholine. Include the mechanisms whereby these receptors transduce the response to acetylcholine.
Answer: Peripheral neurons that release the neurotransmitter acetylcholine are classified as cholinergic. Acetylcholine is released by all autonomic preganglionic fibers, postganglionic fibers of the parasympathetic nervous system, and the somatic branch of the efferent nervous system. One exception is that acetylcholine is a postganglionic sympathetic neurotransmitter for sweat glands. The two classes of cholinergic receptors are termed nicotinic (based upon the binding of this receptor to nicotine) and muscarinic (based upon the binding of this receptor to a toxic chemical in mushrooms). Nicotinic receptors are ionotropic receptors (receptor and ion channel are within the same protein) that are always excitatory. Thus, the binding of acetylcholine increases the number of open non-selective cation channels that are permeable to both sodium and potassium. The greater electrochemical gradient for sodium means that activating a nicotinic receptor will result in a depolarization of the membrane (i.e., more sodium moves in than potassium moves out). Nicotinic receptors are found on all autonomic postganglionic fibers and the end organ of the somatic nervous system (skeletal muscle). Muscarinic receptors are coupled to G proteins. Thus, these metabotropic receptors can be either inhibitory or excitatory, depending upon the target cell and the signal transduction pathway. Muscarinic receptors are found on the effector organs of the parasympathetic nervous system. Diff: 6 Page Ref: 307
2) The nature of a response from the parasympathetic nervous system is determined by the anatomy of this system. Describe the anatomy of the parasympathetic nervous system and how that differs from the sympathetic nervous system.
Answer: Preganglionic neurons from the parasympathetic nervous system originate from the brainstem and the sacral region of the spinal cord (craniosacral region). The parasympathetic nerves that leave the spinal cord do not join with the spinal nerve as occurs in the sympathetic nervous system. Instead, they join with other parasympathetic preganglionic fibers to form pelvic nerves. Generally speaking, preganglionic parasympathetic nerves are long (compared with the postganglionic nerves), traveling to a ganglion that is located near the effector organ. This arrangement is quite different from the sympathetic nervous system, where most preganglionic nerves are short and enter ganglia within the sympathetic trunk. Thus, the parasympathetic nervous system is able to exert more discrete effects than the sympathetic nervous system due to the lack of interconnection between ganglia. Four parasympathetic preganglionic neurons originate from cranial nerve nuclei located within the brainstem, which explains why some preganglionic parasympathetic nerves travel within cranial nerves. The vagus nerve (X) is one of the more important parasympathetic nerves, innervating the lungs, heart, stomach, etc. The other cranial nerves that contain preganglionic parasympathetic axons are the oculomotor (III), facial (VII), and glossopharyngeal nerves (IX). Diff: 5 Page Ref: 307
1) The autonomic nervous system is also known as the involuntary nervous system. Diff: 2 Page Ref: 303
Answer: TRUE
10) Acetylcholine binding to nicotinic cholinergic receptors always excites the postsynaptic cell. Diff: 4 Page Ref: 309
Answer: TRUE
16) Some visceral reflexes are spinal reflexes. Diff: 4 Page Ref: 312
Answer: TRUE
17) According to the theory of dual innervation, the two branches of the autonomic nervous system innervate the same effector organs, but tend to have opposite effects on those organs. Diff: 3 Page Ref: 303
Answer: TRUE
3) The autonomic nervous system consists of efferent pathways with two peripheral neurons that travel in series from the central nervous system to the effector organ. Diff: 3 Page Ref: 303
Answer: TRUE
4) Sympathetic preganglionic neurons traveling to collateral ganglia travel through ganglia of the sympathetic trunk without making synaptic communication. Diff: 5 Page Ref: 305
Answer: TRUE
5) The preganglionic neurons of the sympathetic nervous system originate in the spinal cord from a region of gray matter called the intermediolateral cell column. Diff: 4 Page Ref: 305
Answer: TRUE
7) The parasympathetic nervous system exerts more discrete effects on effector organs than the sympathetic nervous system due to the independence of parasympathetic ganglia. Diff: 4 Page Ref: 307
Answer: TRUE
9) The most abundant neurotransmitter in the peripheral nervous system is acetylcholine. Diff: 3 Page Ref: 307
Answer: TRUE
1) The nature of a response from the sympathetic nervous system is determined by the anatomy of this system. Describe the general structure of the sympathetic nervous system, including the three anatomical configurations and how they contribute to the overall sympathetic response.
Answer: The efferent pathway of the sympathetic nervous system is composed of two neurons, connected in series, that provide for communication between the central nervous system and the effector organ. Those neurons communicate with one another by synapsing within autonomic ganglia. The neurons that travel from the central nervous system to the sympathetic ganglia are the preganglionic neurons, while those that travel from the ganglia to the effector organ are the postganglionic neurons. The preganglionic neurons of the sympathetic nervous system emerge from the lateral horn of the spinal cord within the thoracic and lumbar (thoracolumbar) regions, and exit from the ventral root. The dorsal and ventral roots combine to form the spinal nerve. Thereafter, the organization of the sympathetic nervous system can be described in three ways, based upon anatomical differences. First, the most common arrangement involves a short preganglionic neuron (compared to the postganglionic neuron) that leaves the spinal nerve via a branch called the white ramus and enters one of several sympathetic ganglia. These ganglia are linked together to form a structure that parallels the spinal cord within the sympathetic chain. After entering the sympathetic chain, a preganglionic neuron may branch into several collateral axons that travel up and down the sympathetic trunk to synapse with other postganglionic neurons. Each of these postganglionic neurons travels to a particular effector organ. Thus, activation of the sympathetic nervous system typically produces a response that is widespread, affecting multiple organs simultaneously. The second anatomical arrangement of the sympathetic nervous system contains a long preganglionic fiber that innervates the adrenal medulla. In this case, the chromaffin cells of the adrenal medulla act as the postganglionic neuron. When stimulated, chromaffin cells release catecholamines into the blood (80% epinephrine, 20% norepinephrine, and trace amount of dopamine). This architecture reinforces the widespread effect of the sympathetic nervous system on the body. The final anatomical arrangement contains preganglionic neurons that synapse with postganglionic fibers in collateral ganglia located outside of the sympathetic trunk. One example is a ganglion within the digestive system called the celiac ganglion, which is innervated by a long preganglionic neuron and is located outside of the sympathetic trunk. This arrangement provides for some very specific activity particular to organs, although this type of arrangement is uncommon.
6) Describe the synaptic junctions between the neurons of the autonomic and somatic nervous systems and their effector organs.
Answer: The neuroeffector junction describes the synapse between neurons of the autonomic nervous system and their effector organs. The anatomy of these structures is quite different from the typical neuron-neuron synapse. The postganglionic neuron does not have a discrete, well-defined axon terminal. Rather, those neurons contain numerous swellings along their length (varicosities). Within those varicosities, neurotransmitters (norepinephrine and acetylcholine) are synthesized and stored in vesicles, as occurs at axon terminals. However, while the swellings contain the voltage-gated calcium channels that are required for the release of neurotransmitter, they also contain the voltage-gated sodium and potassium channels that are required for the propagation of an action potential along the length of the axon. At the same time, the distance between a varicosity and the postsynaptic membrane is greater than what is observed in the synaptic cleft of other synapses. In the somatic nervous system, the synapse (neuromuscular junction) couples the motor neuron to skeletal muscle fibers. The terminal bouton of the motor neuron contains acetylcholine stored in vesicles. The motor end plate is a specialized region of the skeletal muscle that contains an invagination where nicotinic receptors are located. Surrounding this invagination are local regions of high acetylcholinesterase concentration. Diff: 7 Page Ref: 310
