PNS anatomy and physiology - french 8/18

Question 1

Homeostasis is primarily mediated by the ____ nervous system, and these functions are required for life. The _____ ns is responsible for the flight/flight.

Answer 1

parasympathetic,sympathetic

Question 2

Discuss the concept of “tone” and explain the consequences of the fact that parasympathetic tone predominates at most organs and tissues (exception: sympathetic control of blood vessels).

Answer 2

Most organs have an intrinsic level of activity (“tone”) that is determined by the dominant branch.
Predominant control is almost always exerted by the parasympathetic branch. An important exception is control of vasculature tone by the sympathetic branch.

Question 3

Parasympathetic neurons originate in ____ and _____.

Answer 3

cranial nerve nuclei (tectal region of brain stem)

sacral segments (S2-S4) of spinal cord

Question 4

Sympathetic neurons originate in the ___ and ___.

Answer 4

thoracic (T1-T12)

lumbar (L1-L5) segments of spinal cord

Question 5

Parasympathetic ganglia (most) are located in the ____

Answer 5

innervated organs

Question 6

Sympathetic ganglia are located in ___ or ___

Answer 6

two paravertebral chains along spinal cord (most) or in prevertebral ganglia in the abdomen (some)

**The adrenal medulla is embryologically and functionally a sympathetic ganglion; innervated by typical sympathetic preganglionic neurons

Question 7

Length of pre- and post-ganglionic neurons: preganglionic parasympathetic neurons are ___ and preganglionic sympathetic are __.

Answer 7

long; short

Question 8

Ratio of pre- to post-ganglionic neurons: In the PNS, the ratio is usually ___. In the SNS, the ratio is usually ____

Answer 8

1: 1, so parasympathetic are localized action
1: 20- 50, thus sympathetic can function in a diffuse or widespread manner

Question 9

In the peripheral nervous system, acetylcholine interacts with ____ receptors (name 2 subtypes) and norepinephrine (and epinephrine from the adrenal gland) interacts with _____ (2 subtypes)

Answer 9

cholinergic receptors (nicotinic [N] and muscarinic [M] subtypes)

adrenergic receptors (alpha [α] and beta [β] subtypes)

Question 10

At the neuromuscular junction, what is the receptor, neurotransmitter combination involved in signal transmission?

Answer 10

Somatic transmission from efferent neurons is via Ach at the nicotinic cholinergic receptor on voluntary skeletal muscle.

Question 11

In the parasympathetic nervous system, which neurotransmitter/receptor combinations are involved in the preganglionic neurons? Postganglionic?

Answer 11

Preganglionic: Ach, nicotinic cholinergic (same as somatic)

Postganglionic: Ach, muscarinic cholinergic

Question 12

In the sympathetic nervous system, which neurotransmitter/receptor combinations are involved in the preganglionic neurons? Postganglionic? (Hint: Effector, Sweat, Renal vasculature).

Answer 12

Preganglionic sympathetic [at the ganglia and in the adrenal medulla]: Ach, nicotinic cholinergic

Postgangionic: Target dependent.
Effector organs–> α1-adrenergic and β-adrenergic
Sweat glands –>Acetylcholine, muscarinic cholinergic (M)
Renal vascular smooth muscle–> dopamine, dopamine D1 receptors

Question 13

Most organs have dual innervation (parasympathetic and sympathetic). What is the notable exception?

Answer 13

Blood vessels receive only sympathetic input.

They only possess non-innervated muscarinic cholinergic receptors on resistance vessels (activated by muscarinic agonists but NOT by activation of the parasympathetic nervous system.

NOTE: These muscarinic receptors are NOT innervated and activation of the PNS does NOT result in vasodilation])

Question 14

What is the physiologic effect of muscarinic cholinergic activation? Remember that the postgangionic fibers of the PANS terminate at the effector organ. Consider:

Heart (HR, AV node conductivity, contractility)
Vasculature
Lungs
GI (salivation, int. motility)
GU (sphincters, detrusor)
Eye (pupil, lens, aqeuous humor)

Answer 14

Heart - decreased HR, decreased AV node conductivity, reduced contractility.
Vasculature - Vasodilation (indirect via NO)
Lungs - bronchoconstriction
GI - increased salivation, increased intestinal motility
GU - relax sphincters, contract detrusor
Eye - Miosis (pupil constriction via contraction of circular muscle), accommodation (ciliary body focuses lens for near vision), outflow of aqueous humor (tension on trabecular meshwork widens angle and increases flow into Canal of Schlemm)

Question 15

Effect of stimulation of the nicotinic receptor at the NMJ?

Answer 15

contraction

Question 16

Stimulation of the nicotinic receptors in the autonomic ganglia will result in…?
Cardiovascular
GU/GI

Answer 16

Cardiovascular - sympathetic effects (tachy, vasoconstriction, increase BP)

GU/GI - parasympathetic effects (nausea, urination, puke)

**SO, ganglionic blockers (if they still existed) would have the opposite effect.

Question 17

α1 adrenergic receptors cause _____ in vascular tissue

Answer 17

vasoconstriction (respond to sympathetic stimulation)

Question 18

β2 adrenergic receptors cause ____ in vascular tissue

Answer 18

vasodilation (respond to sympathetic stimulation)

Question 19

What are three tissue types in which one might expect to find α1 adrenergic receptors?

Answer 19

cutaneous, mucous membranes, and splanchnic vasculature

Question 21

What receptors are found in skeletal muscle?

Answer 21

Either α1 or β2.
β2 receptor activation (as with pharmacological levels of epinephrine) results in increased blood flow to muscle and an overall decrease in total peripheral resistance.

Question 21

What is the contribution of each of the following receptor types to BP?
α1
β1
β2
α2

Answer 21

α1: Vasoconstriction increases TPR and BP (reflex bradycardia occurs)
β1: Increased heart rate and increased force of contraction increases CO and BP
β2: Vasodilation decreases TPR and BP (reflex tachycardia occurs)
α2: Decrease in SNS outflow (via action in CNS) decreases BP

Question 22

What receptors are present in the heart, and what is the end effect of stimulation at each receptor location (SA, AV, contractility?

Answer 22

Direct effects on the heart are largely mediated by β1 receptors
SA node: Increase in heart rate (positive chronotropy)
AV node: Increase in conduction velocity; refractory period decreased
Atrial and ventricular cardiac muscle: Increase in force of contraction (positive inotropy)

**(some β2 and α1 effects also)

Question 23

Describe the postural baroreflex arx. What will happen under conditions of higher arterial pressure? Lower pressure?

Answer 23

Activation of the baroreceptor - stretched by increased vessel tension due to increased arterial pressure - inhibits sympathetic discharge from medulla resulting in vasodilation and decreased heart rate (reflex bradycardia) decreased arterial pressure - vagus nerve activity also increased

Relaxation of baroreceptor – due to a decrease in arterial pressure - “disinhibits” tonic sympathetic discharge and results in SANS-mediated release of norepinephrine at the heart (β1 receptors reflex tachycardia) and blood vessels (α1 receptors vasoconstriction) that produces an increase in arterial blood pressure

Question 24

What receptor is present in the juxtaglomerular cells of the kidney, and what would stimulation of this receptor cause (ie what would the effect on the RAAS axis be)? What neurotransmitter is involved?

Answer 24

increased release of renin via NE acting on β1 receptors on juxtoglomerular cells, ultimately resulting in vasoconstriction, fluid retention (via aldosterone) and increased BP.

Question 25

What receptor is present in the juxtaglomerular cells of the kidney, and what would stimulation of this receptor cause (ie what would the effect on the RAAS axis be)? What neurotransmitter is involved?

Answer 25

The JGA contains B1 receptors. NE action on these cells will ultimately lead to increased release of renin– >aldosterone secretion –> and subsequent increase in BP

increased release of renin via NE acting on β1 receptors on juxtoglomerular cells, ultimately resulting in vasoconstriction, fluid retention (via aldosterone) and increased BP.

Question 26

What type of receptors are in the radial pupillary dilator muscle, and what would stimulation of these receptors cause?

Answer 26

a1 adrenergic receptors. Stimulation would cause constriction (mydriasis [dilation])

Question 27

What type of receptors are in the radial pupillary dilator muscle, and what would stimulation of these receptors cause?

Answer 27

a1 adrenergic receptors. Stimulation would cause contraction (mydriasis [dilation])

Question 28

The volume of aqueous humor is moderated by b2 and a1 adrenergic receptors. Adrenergic stimulation will have what major effect on the production of humor? Which of the receptors modulates this?

Answer 28

Major effect: Increased production via β2 receptors (↑ IOP) DILATED GOOGLEY EYED BASTARDS!

Minor effect: Increased outflow via α1 receptors vasoconstriction (↓ IOP)

Question 29

Genitourinary Tract: state the effect of adrenergic stimulation to each tissue, and the receptor responsible

1) Uterine smooth muscle
2) Uretal sphincter, bladder base, prostate
3) Bladder wall musculature
4) Ejaculation (vas deferens, seminal vesicle, prostate)

Answer 29

1) Uterine smooth muscle: β2 = relaxation
2) Uretal sphincter, bladder base, prostate: α1 = continence
3) Bladder wall musculature: β3 = continence
4) Ejaculation: α1