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Medical Physiology > Exam #1: Physiology of the ANS I > Flashcards

Exam #1: Physiology of the ANS I Flashcards

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USMLE® Step 1 flashcards
1
Q

What is the ANS?

A

Portion of the nervous system that controls most visceral functions & accommodates coordinated responses to external stimuli.

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2
Q

What are the components of the CNS?

A
  • Brain

- Spinal cord

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3
Q

What are the components of the PNS?

A

1) Somatic Nervous System

2) Autonomic Nervous System

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4
Q

What are the three divisions of the ANS?

A

1) Sympathetic
2) Parasympathetic
3) Enteric division

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5
Q

What is the key neuron in the somatic nervous system?

A

Alpha motor neuron

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6
Q

What is the neurotransmitter in the somatic nervous system?

A

ACh

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7
Q

How does the autonomic nervous system differ from the somatic nervous system in terms of neruons?

A
  • In the somatic nervous system, there is one large neuron that synapses directly on the effect cell
  • In the ANS, there are two neurons (preganglionic & post ganglionic, with an intervening ganglia)
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8
Q

How do the sympathetic & parasympathetic nervous systems differ organization of the neurons?

A
  • Sympathetic= Short pre-ganglionic & long post-ganlgionic fiber
  • Parasympathetic= Long pre-ganglion & short post-ganglionic

*Note that the the ganglia of the PNS are clustered within the walls of visceral organs

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9
Q

What is the alternate name for the sympathetic nervous system?

A

Thoraco-lumbar division

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10
Q

What is the intermediolateral cell column?

A
  • Lateral horn of the spinal cord

- Location of the cell bodies of autonomic ganglia

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11
Q

Describe the path of sympathetic outflow.

A

1) Cell body in the intermediolateral column
2) Preganglionic axon exits the spinal cord via the ventral root w/ somatic motor neurons
3) Diverge from somatic & enter the white rami communicantes

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12
Q

What are the three modes of innervation in the SNS?

A

1) Preganglionic neuron goes to a) paravertebral ganglia or b) prevertebral ganglia, and then synapses with post-ganglionic neuron
2) Preganglionic neuron goes to a specialized ganglia, which then synapses with the target organs
3) Preganglionic neuron goes straight to the organ e.g. adrenal medulla

Specialized ganglia include: superior cervical ganglion, celiac ganglion, superior mesenteric ganglion, & inferior mesenteric ganglion

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13
Q

What is the alternate name for the PNS?

A

Cranio-Scaral Division

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14
Q

Describe cranial outflow.

A
  • Preganglionic fibers follow certain cranial nerves
  • Ganglia lie very close to target organs

Specific cranial nerves= oculumotor, fascial, glossopharyngeal, & vagus

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15
Q

Describe sacral outflow.

A
  • Parasymathetic fibers emerge from the spinal cord in a bundle known as the nervi erigentes
  • Synapse with pelvic ganglia
  • Short postganglionic fibers to target organs
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16
Q

What is the enteric nervous system?

A

Two ganglia sandwhiched between the layers of the gut:

  • Myenteric (Auerbach’s)
  • Submucosal (Meissner’s)
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17
Q

Specifically, where is the myenteric plexus located? What does the myenteric plexus control?

A
  • Between the external longitudinal & deep circular smooth muscle layers
  • Motility
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18
Q

Specifically, where is the submucosal plexus located? What does the submocosal plexus control?

A
  • Between the circular muscularis mucosae

- Ion & fluid transport

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19
Q

Where does the enteric nervous system receive input from? Can the enteric nervous system function without this input?

A

PNS & SNS

*However, the enteric nervous system can function normally without extrinsic input

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20
Q

What does dual innervation mean?

A

Most organs receive input from both SNS & PNS; thus, their action is controlled by both systems

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21
Q

What are the exceptions to dual innervation that only receive SNS innervation?

A
  • Hair follicles
  • Thermoregulatory sweat gland
  • Liver
  • Adrenal Gland
  • Kidney
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22
Q

In what organs do the SNS & PNS produce similar effects?

A

Salivary glands

*Both increase the production of saliva

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23
Q

What NT is released from all of the preganglionic fibers?

A

ACh

*Regardless of system, all preganglionic fibers release ACh

24
Q

What do the postganglionic fibers of the PNS release?

A

ACh

25
Q

What do the postganglionic fibers of the SNS release?

A

NE/Epi or DA

26
Q

What is the exception to postganglionic fibers of the SNS releasing NE/Epi or DA?

A

Thermoregulatory sweat glands, which posses muscarinic receptors & respond to ACh

27
Q

What neurotransmitter do postganglionic fibers to the renal vascular smooth muscle release?

A

DA

28
Q

What NTs are released by the adrenal medulla?

A

Epi & NE

29
Q

What receptors are present in the target organs of the PNS?

A

Muscarinic ACh

30
Q

What receptors are present in the thermoregulatory sweat glands?

A

Muscarinic ACh

31
Q

What receptors are present in the target organs of the SNS? What are the two exceptions to this?

A
  • Alpha & Beta Adrenergic

- Exceptions: 1) thermoregulatory sweat, 2) renal vasculature

32
Q

What receptors are present in the renal vasculature?

A

DA-1

33
Q

What receptors are present in skeletal muscle?

A

Nicotinic ACh

34
Q

How is ACh synthesized?

A

1) Uptake of choline from the ECF via the Na+ dependent choline transporter (CHT)
2) Conjugation by ChAT (AcetylCoA + Choline)
3) Final product: ACh

Note that acetylcholine is synthesized in BOTH the cytoplasm & in the mitochondria. ChAT= choline acteyltransferase

35
Q

What drug can block the choline transporter (CHT)?

A

Hemicholiniums

*Note that these are not used clinically.

36
Q

How is ACh stored?

A

Once ACh is synthesized, it is transported into the storage vesicle via the “vesicle assocaited transporter” (VAT)

37
Q

What drug blocks VAT?

A

Vescamicol

38
Q

How is ACh released?

A

1) Depolarization of nerve
2) Voltage-dependent Ca++ entry
3) Ca++ binds Calmodulin, activating “vesicle associated membrane proteins,” VAMPs & “synaptosome-assocaited proteins,” (SNAPs)
4) Exocytosis

39
Q

What is the function of the VAMPs & SNAPs?

A
  • Docking storage vesicles on the inner surface of the nerve terminal facing the synapse
  • Fusion of the synaptic vesicle with the neural membrane
40
Q

What does botulinum toxin block?

A

VAMPs & SNAPs

*Botulinum toxin enzymatically removes two amino acids from one or more of these fusion peptides

41
Q

How is ACh action terminated?

A

1) Rapid hydrolysis of ACh via acetylcholine esterase (AChE)
2) Choline re-uptake into terminals
3) ACh interaction with ACh autoreceptors

42
Q

What does acetylcholine esterase break ACh into?

A

Choline & Acetate

43
Q

What drug blocks Acetylcholine esterase? What happens at the synapse in response to these drugs? Give an example of an AChE inhibitor.

A
  • AChE inhibitors
  • Increase ACh concentrations & over-stimulation of receptors

*Neostigmine is an AChE inhibitor

44
Q

What are the two major types of ACh receptors?

A
  • Muscuarinic

- Nicotinic

45
Q

What are muscarinic receptors?

A

Transmembrane G-protein coupled receptors

*The type of G-protein associated with the particular receptor will result in a differential effect

46
Q

What are nicotinic receptors?

A

Transmembrane Na+ ion channel

*ACh acts as a ligand that causes the channel to undergo a conformational change & opening when bound; both Na+ & K some K+ flow down their electrochemical gradients

47
Q

How is aqueous humor produced? Describe the path that aqueous humor takes after being secreted.

A
  • By the ciliary body epithelium
  • Passes anterior to the lens
  • Drains into the canal of schlemm (deep in the angle formed by the cornea & iris)
48
Q

What increases intra-ocular pressure in glaucoma?

A
  • Increased production of aquenous humor by the ciliary body epithelium
  • Decreased drainage of aqueous humor from the Canal of Schlemm
49
Q

What are two functions of the ciliary muscle?

A

1) Contraction= near accomodation & miosis

2) Opening of the Canal of Schlemm

50
Q

What will contraction of the ciliary muscle do to intra-ocular pressure?

A

Decrease

51
Q

What two receptors are located on the ciliary muscle? What action does stimulation of each receptor produce?

A

M3= Contraction, PNS, ACh

B2= Relaxation, SNS, NE

52
Q

What type of alpha subunit is associated with M1 & M3? What does their activation ultimately lead to?

A
  • Gq
  • Increased Ca++
  • Increased PKC
53
Q

What type of alpha subunit is associated with M2? What does the activation of M2 ultimately lead to?

A
  • Gi/o
  • Decreased cAMP
  • Decreased PKA
54
Q

What muscle controls dilation of the pupil?

A

Radial (dilator) muscle

55
Q

What type of receptor controls the function of the radial muscle?

A

Alpha-1 (SNS)

56
Q

What types of receptors are associated with the ciliary epithelium? What is the effect of stimulating these receptors?

A
  • Beta-1 & Beta-2

- Increased production of aqueous humor

Medical Physiology (74 decks)

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