L10-12: ANS Physiology I-III

Question 1

Characteristics of SNS: describe location of cell bodies, in what region of spinal cord are these fibers found, three routes/modes of innervation, divergence of fibers, length of fibers, NTs involved and receptors they act on

Answer 1

• Cell bodes: intermediolateral cell column (lateral horn) of spinal cord
• Region: thoracolumbar region (and some CNs)
• Routes:
  1. ) PreG fiber from cell body to paravertebral ganglia where it synapses with PostG fiber to target
  2. ) PreG fiber from cell body to specialized prevertebral ganglia (celiac, mesenterics etc.) where it synpases with PostG fiber and runs to target
  3. ) PreG fiber goes straight to organ (adrenal medulla) and synapses with modified PostG fibers (chromaffin cells)
• Divergence: highly divergent (1 PreG fiber to many Post G fibers)
• Length of fibers: Short PreG fibers, Long PostG fibers
• NTs involved: ACh released from PreG fibers act on nicotinic, cholinergic receptors. ACh, DA and NE/Epi released from PostG fibers and act on muscarinic cholinergic, dopaminergic and adrenergic receptors respectively.
• Via M3 receptors on sweat glands (only SNS), lacrimal and salivary glands. These are the only areas in SNS where muscarinic receptors are seen, all PostG targets are onto dopaminergic or primarily adrenergic receptors

Question 2

Characteristics of PSNS: describe location of cell bodies, in what region of spinal cord are these fibers found, two routes/modes of innervation, divergence of fibers, length of fibers, NTs involved and receptors they act on

Answer 2

• Cell bodes: specific nuclei in brainstem, spinal cord
• Region: craniosacral (cranium and sacrum)
• Routes:
  1. ) Cranial outflow: PreG fibers in CNs III, VII, IX, X to ganglia located close to target organs, PostG fibers to organ
  2. ) Sacral outflow: PreG fibers to scattered pelvic ganglia located close to target organs, PostG fibers to organ with sympathetics
• Divergence: 1 PreG fiber to 1 PostG fiber
• Length of fibers: Long PreG fibers, Short PostG fibers
• NTs involved: ACh released from PreG fibers and acts on nicotinic, cholinergic receptors. ACh released from PostG fibers and acts on muscarinic cholinergic receptors.

Question 3

What is the enteric nervous system? Describe anatomical location and function of divisions

Answer 3

• collection of nerve plexuses surrounding GI tract including pancreas and biliary system
• Myenteric (Auerbach’s) lies between external longitudinal and deeper circular SM layer: controls GI motility
• Submucosal (Meissner’s) lies between circular muscular mucosae: controls ion and fluid transport

Question 4

ANS dually innervates all organs except

Answer 4

• Hair follicles (arrector pili muscles), sweat glands, liver, adrenals, kidneys, BVs (some PSNS fibers in some vascular beds) – all only sympathetically innervated

Question 5

Effect of SNS and PSNS activation in the salivary glands

Answer 5

• Saliva production

Question 6

Describe cholinergic neurotransmission including synthesis, storage, release and termination of action

Answer 6

1. ) Synthesis: Choline transported from ECF into neuron via CHT (choline transporter – sodium dependent) and together with acetyl-CoA (synthesized in mitochondria), ChAT (choline acetyltransferase) synthesizes ACh
2. ) Storage: ACh transported by VAT (vesicle-associated transporter) into storage vesicle, also containing peptides, ATP and proteoglycan. Vesicle-associated membrane proteins (VAMPs) on vesicles associate with synaptosome-associated proteins (SNAPs) at nerve terminal adjacent to synapse
3. ) Release: AP reaches terminal triggering opening of CA VG channels causing influx of Ca, which interacts with calmodulin. Ca-Calmodulin complex interacts with VAMP synaptotagmin and triggers fusion of vesicle to membrane and vesicle content release via exocytosis.
4. ) Termination of action:
   - ACh terminated by AChE (acetylcholinesterase), which splits it into choline and acetate.
   - Choline re-uptake into terminals
   - Diffusion
   - Autoreceptor:NT interaction decreases release

Question 7

In terms of cholinergic neurotransmission, describe points of pharmacological intervention

Answer 7

1. ) Choline carrier blocker: eg. Hemicholiniums – prevent re-uptake of choline at CHTs
2. ) ACh carrier blocker: eg. Vesamicol – prevents transports of ACh into vesicles by VAT
3. ) Presynaptic toxins: eg. Botulinum toxin – prevents VAMPs/SNAPs interaction and fusion of ACh containing vesicles and therefore blocks ACh release
4. ) Anticholinesterases: eg. Neostigmine – prevents action of AChE and allows ACh concentration to remain high at synapse
5. ) Neuromuscular blocking agent: eg. Tubocurarine – inhibitor of cholinoceptors
6. ) Cholinoceptor and nicotinic receptor agonists – activate cholinoceptors

Question 8

Effect of hemicholiniums

Answer 8

1.) prevent re-uptake of choline at CHTs

Question 9

Effect of vesamicol

Answer 9

• prevents transports of ACh into vesicles by VAT

Question 10

Effect of botulinum toxin

Answer 10

• prevents VAMPs/SNAPs interaction and fusion of ACh containing vesicles and therefore blocks ACh release

Question 11

Effect of neostigmine

Answer 11

• prevents action of AChE and allows ACh concentration to remain high at synapse

Question 12

Effect of tubocurarine

Answer 12

• inhibitor of cholinoceptors

Question 13

Types of cholinergic receptors. Describe each in terms of downstream actions upon activation of the receptors

Answer 13

1. ) Muscarinic: 5 subtypes M1-M5
   - G-protein linked with effect differing based on type of G-protein
   - M1, M3 are Gq linked: activation = PLC cleaves PIP2 into IP3 and DAG. IP3 = increase in [Ca], DAG = increase in PKC
   - M2 are Gi/0 (inhibitory) linked: activation = inhibition of adenylyl cyclase = decrease in [cAMP] and PKA
2. ) Nicotinic: 2 subtypes Nn (neuronal) and Nm (muscle) with many variations of receptor subunits
   - These are ion channels and are permeable to Na and K, more so to Na. Activation of channel leads to EPP, depolarizes membrane and leads to AP

Question 14

Location of nicotinic receptors and response when these receptors are stimulated

Answer 14

• Nn (neuronal) located in adrenal medulla and leads to secretion of NE and Epi
• Nn (neuronal) also located in autonomic ganglia and stimulation depends on SNS/PSNS innervation and dominance of receptors at target
• Nm (muscle) located on muscle and stimulation leads to muscle contraction (twitch, hyperactivity)

Question 15

Location, types and effects of muscarinic receptor activation

Answer 15

1. ) Eye:
   - Sphincter/constrictor muscle = M3 = miosis (contraction)
   - Ciliary muscle = M3 = accommodation for near vision (fatter lens)
2. ) Heart
   - SA node = M2 = decrease in HR
   - AV node = M2 = decrease in conduction velocity
   - Atrial cardiac muscle = decrease in atrial contraction
   - * weak or no ventricular effects
3. ) Lungs
   - Bronchioles = M3 = contraction
   - Glands = M3 = secretion
4. ) GI tract
   - Stomach = M3 = contraction
   - Glands = M1 = secretion
   - Intestines = M3 = contraction
5. ) Bladder
   - M3 = contraction (detrusor muscle) and relaxation (trigone/sphincter)
6. ) Sphincters
   - M3 = relaxation except for lower esophageal sphincter, which contracts
7. ) Glands
   - M3 = secretion (salivation, lacrimation, sweat)
8. ) Blood vessels
   - M3 on endothelium and causes dilation via EDRF (endothelium-derived relaxing factor) released from endothelium, which acts on SM cells
   - M3 are located on vascular smooth muscle, implicated in pathologies where endothelium becomes damaged and counter effect by endothelium is absent, leading to vasoconstriction

Question 16

Describe adrenergic neurotransmission including synthesis, storage, release and termination of action

Answer 16

1. ) Synthesis: two pathways for synthesis both starting with the amino acid tyrosine. Main pathway uses tyrosine hydroxylase, which converts tyrosine into Dopa (rate-limiting step). Dopa → dopamine. Dopamine → NE and epinine (two diff ezs). Epinine → Epi. NE → Epi (only in adrenal medulla inside vesicles). Other pathway is: tyrosine → tyramine → octopamine → NE.
2. ) Storage: Catecholamines transported by VMAT (vesicle monamine transporter) into storage vesicle. Vesicle-associated membrane proteins (VAMPs) on vesicles associate with synaptosome-associated proteins (SNAPs) at nerve terminal adjacent to synapse
3. ) Release: AP reaches terminal triggering opening of CA VG channels causing influx of Ca, which interacts with calmodulin. Ca-Calmodulin complex interacts with VAMP synaptotagmin and triggers fusion of vesicle to membrane and vesicle content release via exocytosis.
4. ) Termination of action
   - Catecholamine re-uptake by carriers. NET1 (NE transporter) carries NE back into the cell where MAO (mitochondrial monoamine oxidase) degrades it
   - Diffusion – metabolized in liver by catechol-O-methyltransferase (COMT)
   - Autoreceptor:NT interaction decreases release

Question 17

In terms of adrenergic neurotransmission, describe points of pharmacological intervention

Answer 17

1. ) Synthesis: inhibition of tyrosine hydroxylase via metyrosine (tyrosine analog)
2. ) Storage: reserpine inhibits VMAT preventing storage of catecholamines
3. ) Release: bretylium inhibits VAMPs from interacting with SNAPs and therefore blocks release of NTs
4. ) Neuronal reuptake: re-uptake carrier NET is inhibited by cocaine and TCA, resulting in increase in NT activity at cleft
5. ) Degradation after re-uptake: MAOIs for depression inhibit MAO activity, which normally degrades catecholamines
6. ) Extraneuronal uptake: NET2/ENT inhibitors (corticosteroids) inhibit extraneuronal uptake of catecholamines

Question 18

Effect of metyrosine

Answer 18

• Inhibition of tyrosine hydroxylase on converting tyrosine into Dopa, net reduction in NE and Epi

Question 19

Effect of reserpine

Answer 19

• Inhibits VMAT and prevents storage of catecholamines in vesicles, therefore leading to a reduction in release

Question 20

Effect of bretylium

Answer 20

• Inhibits VAMPs/SNAPs interactions and blocks release of catecholamines

Question 21

Effect of cocaine from adrenergic transmission perspective

Answer 21

• Prevents re-uptake of NE by NET, resulting in increase in NT activity at cleft

Question 22

Effect of TCAs (tricyclic antidepressants) from adrenergic transmission perspective

Answer 22

• Prevents re-uptake of NE by NET, resulting in increase in NT activity at cleft

Question 23

Effect of MAOIs in terms of adrenergic transmission

Answer 23

• Inhibits MAO activity in catecholamine producing cells, leading to higher levels of NE availability

Question 24

Effect of corticosteroids in terms of adrenergic transmission

Answer 24

• Inhibits NET2/ENT inhibiting extraneuronal uptake of catecholamines

Question 25

Types of adrenergic receptors. Describe each in terms of downstream actions upon activation of the receptors

Answer 25

• All receptors are G-protein-coupled and activity is dependent on type of G-protein each is associated with
  1. ) Alpha-1: Gq-coupled
  2. ) Alpha-2: Gi/0 (inhibitory)-coupled
  3. ) Beta-1/2: Gs (stimulatory)-coupled
• Gq: activation = PLC cleaves PIP2 into IP3 and DAG. IP3 = increase in [Ca], DAG = increase in PKC
• Gi/0: activation = inhibition of adenylyl cyclase = decrease in [cAMP] and PKA
• Gs: activation = activation of adenylyl cyclase = increase in [cAMP] and PKA

Question 26

Which cholinergic, adrenergic, dopaminergic, histaminic and vanilloid receptors are associated with the Gq, Gs, Gi G-proteins?

Answer 26

• Mnemonic: KISS and KICK til you’re SICK of SEX (QISS and QIQ til you’re SIQ of SQS)
  1. ) QISS (adrenergic)
• alpha-1 = Q
• alpha-2 = I
• beta-1 = S
• beta-2 = S

2. ) QIQ (cholinergic, muscarinic)
   - M1 = Q
   - M2 = I
   - M3 = Q
3. ) SIQ SQS (in alphabetical order: dopaminergic, histaminic, vanilloid)
   - D1 = S
   - D2 = I
   - H1 = Q
   - H2 = S
   - V1 = Q
   - V2 = S

Question 27

What are the downstream cellular responses in activating Gq, Gs and Gi G-proteins?

Answer 27

• Gq: activation = PLC cleaves PIP2 into IP3 and DAG. IP3 = increase in [Ca], DAG = increase in PKC
• Gi/0: activation = inhibition of adenylyl cyclase = decrease in [cAMP] and PKA
• Gs: activation = activation of adenylyl cyclase = increase in [cAMP] and PKA

Question 28

Location of alpha-1 receptors and effects from activation

Answer 28

1. ) Eye
   - Contraction of radial/dilator muscle = mydriasis (dilation)
2. ) Arterioles
   - Contraction = increase TPR, increase DBP, increase afterload
3. ) Veins
   - Contraction = increase venous return, increase preload
4. ) Bladder trigone/sphincter
   - Contraction = retention of urine
5. ) Vas deferens
   - Contraction = ejaculation
6. ) Liver
   - increase glycogenolysis
7. ) Kidney
   - decrease in renin release

Question 29

Location of alpha-2 receptors and effects from activation

Answer 29

1. ) prejunctional nerve terminal (incl. walls of GI as heteroreceptors, postG SNS fibers as autoreceptors)
   - decrease transmitter release and NE synthesis
2. ) platelets
   - aggregation
3. ) pancreas
   - decrease insulin secretion

Question 30

Location and beta-1 receptors and effects from activation

Answer 30

1. ) Heart
   - SA node: increase HR
   - AV node: increase conduction velocity
   - Atrial/ventricular muscle: increase FOC, conduction velocity, CO and o2 consumption
   - His-Purkinje: increase automaticity and conduction velocity
2. ) Kidney
   - increase in renin release

Question 31

Location of beta-2 receptors and effects from activation

Answer 31

1. ) Blood vessels
   - Vasodilation – decreases TPR, diastolic BP and afterload
2. ) Eye
   - Ciliary muscle – relaxation
3. ) Uterus
   - Relaxation
4. ) Bronchioles
   - Dilation
5. ) Skeletal muscle
   - increase glycogenolysis and contractility (tremors)
6. ) Liver
   - increase glycogenolysis
7. ) Pancreas
   - increase insulin secretion

Question 32

Location of D1 receptors and effects from activation

Answer 32

• In renal, mesenteric and coronary vascular beds. Activation leads to vasodilation. In kidney this results in increased GFR, RBF (renal blood flow) and Na+ excretion

Question 33

Compare and contrast homotropic vs heterotropic interactions

Answer 33

• Homotropic interaction: nerve terminals contain presynaptic receptors known as autoreceptors, which bind to the same NT the nerve terminal releases. This is an autoinhibitory feedback system.
• Heterotropic interaction: nerve terminals contain presynaptic receptors known as heteroreceptors, which binds to a different NT than the nerve terminal releases. In this manner, SNS NT can inhibit the release of PSNS NT from a nearby nerve terminal.

Question 34

What is denervation supersensitivity? Mechanism responsible for this? Clinical relevance?

Answer 34

• Aka withdrawal rebound hyperactivity, aka disuse hyperactivity
• If nerve is cut (or transmission is blocked another way), structure/downstream target becomes supersensitive to the transmitter when later seen again. Eg. Skeletal muscle undergoes contraction to ACh in large dose. After denervation; however, contraction of muscle occurs to much smaller amounts of ACh.
• Mechanism: a.) proliferation of receptors, b.) loss of mechanisms for transmitter removal
• Clinical relevance: 1.) Withdrawal rebound from use and then halting of certain medications. 2.) Diagnosis of autonomic failure through positive response to low-dose stimulatory medication.

Question 35

What is cotransmission?

Answer 35

• Neurons typically release multiple substances that interact with specific receptors and produce effect at both the pre- and post-synpatic levels.
• NTs have their effect on the downstream target receptors. Other transmitters/neuromodulators can have effect (inhibitory or excitatory) on pre-synaptic nerve terminal and also on the same target receptors as the NTs.

Question 36

Describe the effect of the autonomic nervous system in production and flow of aqueous humor

Answer 36

• Ciliary epithelium produces aqueous humor. Production of aqueous humor is under control via activation of beta-receptors (1 and 2) found on the ciliary epithelium. Alpha-2 inhibits production of aqueous humor
• Constrictor/sphincter muscle state can determine the angle between the cornea and the iris and therefore flow of aqueous fluid from the posterior chamber to the anterior chamber (into Canal of Schlemm). This muscle has M3 receptors and when activated creates a wider angle and increases flow

Question 37

What class of medication could be used to treat patient with glaucoma?

Answer 37

• Beta-blocker would decrease production of aqueous humor, leading to a decrease in IOP
• Alpha-agonist would also decrease production of aqueous humor
• M3 agonist increases iris/corneal angle and increases aqueous humor outflow

Question 38

Describe distribution of autonomic receptors in the heart and their effects

Answer 38

1. ) SNS (all via beta-1)
   - SA node: increase HR
   - AV node: increase conduction velocity
   - Atrial/ventricular muscle: increase FOC, conduction velocity, CO and o2 consumption
   - His-Purkinje: increase automaticity and conduction velocity
2. ) PSNS
   - SA node = M2 = decrease in HR
   - AV node = M2 = decrease in conduction velocity
   - Atrial cardiac muscle = decrease in atrial contraction
   - * weak or no ventricular effects

Question 39

Describe distribution of autonomic receptors in blood vessels. Describe input on smooth muscle and the difference between visceral and vascular smooth muscle? What are the effects of shear stress?

Answer 39

• Vascular smooth muscle receives dual input when controlling luminal diameter: 1.) neural (directly onto smooth muscle) and 2.) endothelial input (from endothelial cells onto smooth muscle). Visceral blood vessels only receives neural input (directly onto smooth muscle).
  1. ) PSNS: M3 receptors are present on both endothelium and on vascular smooth muscle. When endothelium is intact and their M3 receptors are stimulated, endothelium derived relaxing factor (NO) is released and leads to vasodilation. When endothelium is damaged, direct effect of M3 activation on vascular smooth muscle leads to vasoconstriction as no un-opposing effects by EDRF (NO).
  2. ) SNS: beta-2 receptors are present in vascular smooth muscle in muscle and activation leads to vasodilation. Alpha-1 receptors located in vascular smooth muscle of skin and splanchnic regions, with activation leading to vasoconstriction.
• Shear stress of blood vessels leads to endothelial cell activation and production of EDRF, leading to vasodilation of the vessels.

Question 40

Concern for giving asthmatic patient M3 agonists

Answer 40

• M3 receptors are located in bronchi/bronchioles and lead to contraction when activated. They are also located in bronchiolar submucosal glands and lead to glandular secretion when activated. These effects exacerbate asthmatic conditions

Question 41

What is the autonomic action of Angel’s Trumpet flower?

Answer 41

• It is a PSNS antagonist

Question 42

How can fermented cheese cause increased production of NE?

Answer 42

• Tyramine is the starting substrate to a second biosynthetic pathway for NE. Tyramine is contained in many fermented foods

Question 43

Describe autonomic receptor distribution in eye and the effects of their activation

Answer 43

• Radial/dilator muscle: alpha-1 – mydriasis (dilation)
• Sphincter/contractor muscle: M3 – miosis (constriction)
• Ciliary muscle: beta-2 – relaxation, accommodation of lens (flattened) for far-sight, M3 – contraction, accommodation of lens (fatten) for near-sight
• Ciliary epithelium: beta-1/2 – production of aqueous humor, alpha-2 receptor activation inhibits production of aqueous humor

Question 44

Function of ANS

Answer 44

1. ) Assist body in maintaining constant internal environment (homeostasis)
2. ) Accommodate coordinated responses to external stimuli

Question 45

Describe autonomic feedback loop that controls MAP (mean arterial blood pressure)

Answer 45

• Increase in BP (MAP = TPR.HR.SV) is detected via baroreceptors, which increase their discharge upon detected. This is detected by vasomotor center in brainstem and output is as follows to counter increased BP

1. ) SNS tone decreases
   - decrease vasoconstriction via decreased input to alpha-1 (on arterioles, veins)
   - decrease cardiac FOC (atria and ventricles) via decreased input to beta-1 (atria, ventricles)
   - decrease HR via decreased input to beta-1 (SA, AV and His-Purkinjes)
   - what about effect on beta-2?
2. ) PSNS tone (vagal tone) increases
   - decrease HR via input to M2 (predominant effect)
   - * also decrease in atrial/ventricular contraction, but weak/insignificant effect. What about effect of increased vagal tone on M3 receptors in blood vessels?

Question 46

Describe hormonal feedback loop that controls MAP

Answer 46

• Drop in BP = decrease in RBF = increase in renin production = increase in angiotensin (potent vasoconstrictor = increase in TPR) = increase in aldosterone = increased retention of Na (and therefore H20) in kidneys = increase in blood volume = increase in CO = increase in BP