ANS 1

Question 1

Compare the sympathetic & parasympathetic branches of the ANS with respect to: (a) spinal cord division of origin

Answer 1

SNS (fight or flight) = thoracolumbar division

Parasympathetic Nervous System (rest & digest) = craniosacral division. 70% of PNS activity is carried out by the Vagus N.

Question 2

Compare the sympathetic & parasympathetic branches of the ANS with respect to: (b) length of pre- and post- ganglionic neurons

Answer 2

MNEMONIC: SPeS
Sympathetic:
preganglionic fibers are typically short
postganglionic fibers are typically long

Parasympathetic:
preganglionic fibers are typically long
postganglionic fibers are typically short and lie within or very close to their target tissues

Question 3

Compare the sympathetic & parasympathetic branches of the ANS with respect to: (c) major transmitters at ganglionic and target organ synapses

Answer 3

SNS = adrenergic = noradrenaline (norepinephrine)

PNS = cholinergic = acetylcholine

In both the parasympathetic and sympathetic divisions, the preganglionic neuron releases ACh, which binds to N2 nicotinic cholinergic receptors on the postsynaptic membrane of the postganglionic neuron.

In postganglionic parasympathetic neurons, the transmitter is ACh, but the postsynaptic receptor is muscarinic cholinergic.

In most postganglionic sympathetic neurons, the transmitter is norepinephrine. The postsynaptic receptor is an adrenergic receptor

Question 4

Compare the sympathetic & parasympathetic branches of the ANS with respect to: (d) receptor types at ganglionic and target organ synapses

Answer 4

The cell bodies of the preganglionic neurons lie within the CNS in columns in the brain stem and spinal cord. Their axons exit the CNS and make synapses with postganglionic neurons in peripheral ganglia that project to target tissues

Question 5

Describe the functional effects of SNS activation, including differences between norepinephrine and epinephrine actions in distinct target tissues

Answer 5

SNS target tissues express distinct adrenergic receptor subtypes w diff affinities for epi & norepi, sometimes use muscarinic cholinergic receptors (sweat glands*), & are broadly activated by epi/norepi from the adrenal medulla.

Question 6

Parasympathetic control of the heart

Answer 6

parasympathetic activation decreases heart rate (negative chronotropic effect) via activation of muscarinic cholinergic receptors @ SA & AV nodes. 2 negatives!

Also, strong vagal stimulation mildly decreases contractility of the atria* (negative inotropic effect).

Question 7

Sympathetic control of the heart

Answer 7

sympathetic activation increases both the heart rate (positive chronotropic effect) @ SA & AV nodes, and force of contraction of the ventricles* (positive inotropic effect) primarily via activation of B1-adrenergic receptors. 2 positives!

Thus, B1-adrenergic receptor antagonists such as propranolol are used to treat hypertension and tachycardias.

Question 8

Define agonist & antagonist

Answer 8

Agonist = activator

Antagonist = inhibitor

Question 9

What does the SA node do?

Answer 9

The sinoatrial node is the impulse-generating (pacemaker) tissue located in the right atrium of the heart, and thus the generator of normal sinus rhythm. PNS & SNS exert control over the heart @ the SA node & decrease & increase HR respectively.

Question 10

Describe SNS & PNS divergence (number of postganglionic neurons to preganglionics)

Answer 10

The average preganglionic axon in the SNS contacts an estimated 100 postganglionic neurons by collateral branching, thus contributing to a diffuse output pattern. This property of divergence enables the SNS to generate widespread responses of numerous effectors when physiologically necessary.

The PNS exhibits more discrete innervation of target tissues. It is estimated that one preganglionic neuron synapses with 15-20 postganglionic neurons.

Question 11

Discuss SNS innervation of the adrenal medulla

Answer 11

The SNS directly innervates the chromaffin cells of adrenal medulla which releases primarily epinephrine (80%) & some norepinephrine (20%). These ‘hormones’ are carried by the blood and broadly effect multiple tissues of the body.

The effects are similar to direct sympathetic stimulation, but last ~5-10 times longer because the hormones are inactivated more slowly.

Also, they reach tissues that do not receive sympathetic innervation (e.g., epi increases metabolic rate in almost all cell types).

Question 12

Discuss a1 receptors

Answer 12

a1 SNS receptor causes vasoconstriction of the smooth muscle of the blood vessels

Question 13

Discuss B1 receptors

Answer 13

B1 SNS receptor is the major adrenergic receptor in the heart it controls heart-rate & force of contraction

Question 14

Discuss B2 receptors

Answer 14

B2 SNS receptors mediate dilation of the bronchi

Question 15

Discuss PNS receptors

Answer 15

5 different subtypes of PNS muscarinic receptors linked to different G-proteins

Question 16

Antagonist for N1 nicotinic Ach receptor

Answer 16

d-tubocurarine

Question 17

Antagonist for N2 nicotinic Ach receptor

Answer 17

Hexamethonium

Question 18

Antagonist for M1 - M5 muscarinic Ach receptor

Answer 18

Atropine

Question 19

Antagonist for B1 adrenergic receptor

Answer 19

Propanolol

Question 20

SNS & PNS opposing actions & intergraton

Answer 20

In many cases the SNS & PNS exert opposing actions. e.g., heart rate is increased by the SNS and decreased by the PNS, and GI motility is increased by the PNS and decreased by the SNS. However, in some cases, they act in a complimentary manner e.g., PNS activation causes penile erection (vasodilatation) and SNS activation causes ejaculation, both aiding in male reproductive function.

Question 21

a & B adrenergic receptors have what affinities for epi & norepi

Answer 21

Epinephrine (epi) has a greater affinity for B-adrenergic receptors

Whereas norepi has somewhat greater affinity for a-adrenergic receptors.

The adrenal medullary contribution of the SNS reflects this difference in different target organs. For example, epi effects are more prominent in targets where B-adrenergic receptors predominate, such as the heart, lungs, and liver

Whereas norepi effects predominate in the vasculature where a-adrenergic receptors are expressed.

Question 22

When SNS is activated, describe changes in a1 receptors

Answer 22

mydriasis (pupil dilation) & eyelid retraction

vasoconstriction (to the unnecessary rest & digest functions & organs like digestion)

increase cellular metabolism (epi from adrenal medulla) & decrease GI motility

Question 23

When SNS is activated, describe changes in B1 receptors

Answer 23

Increase in heart-rate & force of contraction

increase cellular metabolism (epi from adrenal medulla) & decrease GI motility

increase blood flow to active muscles (& skin) via vasodialation

Question 24

When SNS is activated, describe changes in B2 receptors

Answer 24

bronchial dilation

increase cellular metabolism (epi from adrenal medulla) & decrease GI motility

increase blood flow to active muscles via vasodialation

Question 25

When SNS is activated, describe changes in Muscarinic receptors

Answer 25

Sweating

Question 26

Describe the possible causes and functional effects of abnormal SNS activity in pheochromocytoma

Answer 26

Pheochromocytoma – neoplasms (tumors) of the adrenal medulla that secrete excessive amounts of norepinephrine (most common), epinephrine, or both resulting in sustained hypertension, and other effects (e.g., cold hands and feet, sweating and feeling hot) .

Rare, observed in age range 40’s - 50’s, & in both men & women.

Treatment = excise tumor. To treat the symptoms, give α1 and β1-adrenergic antagonists.

Question 27

Describe the possible causes and functional effects of abnormal SNS activity in Horner syndrome

Answer 27

Symptoms due to SNS problem = PAM is Horny. On the affected side of the face, there is ptosis (drooping eyelid), anhydrosis (dryness of face), miosis (partial constriction of pupil).

1st order lesion - brainstem lesions interrupting descending tracts e.g. stroke

2nd order lesion - preganglionic sympathetic cell bodies or fibers supplying eye synapse in superior cervical ganglion

3rd order lesion – postganglionic sympathetic cell bodies or fibers

Question 28

Adrenergic α1 receptors produce physiologic actions by stimulating the formation of

Answer 28

inositol 1,4,5 -triphosphate (IP3) and causing a subsequent increase in intracellular [Ca2+].

Question 29

Both β1 and β2 receptors act by stimulating

Answer 29

adenylate cyclase and increasing the production of cyclic adenosine monophosphate (cAMP).

Question 30

Muscarinic and nicotinic receptors are

Answer 30

cholinergic

Question 31

Preganglionic sympathetic fibers synapse on the chromaffin cells of the adrenal medulla at ______ receptors. After this, what is released?

Answer 31

nicotinic cholenergic

Then epinephrine and, to a lesser extent, norepinephrine are released into the circulation.

Question 32

Discuss the role of B2 & a receptors in vasodialation

Answer 32

β2 receptors on vascular smooth muscle produce vasodilation. α receptors on vascular smooth muscle produce vasoconstriction.

Because β2 receptors are more sensitive to epinephrine than are α receptors, low doses of epinephrine produce vasodilation, and high doses produce vasoconstriction.

Question 33

Local control of the circulation predominates over neural control in which main organs?

Answer 33

The best answer for local control of blood flow is the cerebral circuit. Most other circulations listed all are under the significant sympathetic adrenergic control.

Question 34

During vigorous exercise, skeletal muscle blood flow increases tremendously. The circulatory adjustment most responsible for this change is

Answer 34

local vasodilation in skeletal muscle–The vasodilation and increased blood flow to exercising muscle is mainly via the local production of vasodilatory metabolites. Circulating epinephrine will stimulate β2 receptors to contribute to the vasodilation. There is only a small increase in stroke volume during exercise, and cardiac parasympathetic stimulation would tend to decrease cardiac output and flow to the periphery.

Question 35

During exercise, total peripheral resistance (TPR) decreases because of the effect of

Answer 35

local metabolites on skeletal muscle arterioles–During exercise, local metabolites accumulate in the exercising muscle and cause local vasodilation and decreased arteriolar resistance of the skeletal muscle. Because muscle mass is large, it contributes a large fraction of the total peripheral resistance (TPR). Therefore, the skeletal muscle vasodilation results in an overall decrease in TPR, even though there is sympathetic vasoconstriction in other vascular beds.

Question 36

Describe negative & positive inotropic effects on the heart

Answer 36

A negative inotropic effect is one that decreases myocardial contractility. Contractility is the ability to develop tension at a fixed muscle length. Factors that decrease contractility are those that decrease the intracellular [Ca2+]. Increasing heart rate increases intracellular [Ca2+] because more Ca2+ ions enter the cell during the plateau of each action potential. Sympathetic stimulation and norepinephrine increase intracellular [Ca2+] by increasing entry during the plateau and increasing the storage of Ca2+ by the sarcoplasmic reticulum (SR) [for later release]. Cardiac glycosides increase intracellular [Ca2+] by inhibiting the Na+-K+ pump, thereby inhibiting Na+-Ca2+ exchange (a mechanism that pumps Ca2+ out of the cell). Acetylcholine (ACh) has a negative inotropic effect on the atria.

Question 37

Discuss the sympathetic stimulation of the heart

Answer 37

Increased sympathetic stimulation of the heart increases heart rate, atrial contractility, and ventricular contractility and also increases norepinephrine release at the ventricular sympathetic nerve endings. It does not release acetylcholine. It does cause an increased sodium permeability of the A-V node, which increases the rate of upward drift of the membrane potential to the threshold level for self-excitation, thus increasing heart rate.

Question 38

Discuss which organ systems vasoconstrict in response to an adrenergic stimulation

Answer 38

The cutaneous and renal vessels have a more pronounced vasoconstrictor response to the stimulation of adrenergic neurons than do the vessels of skeletal muscle and the lungs. The cerebral and coronary circulatory systems are among the least sensitive systems in the body to the constrictor actions of norepinephrine.

Question 39

What are negative & positive inotropic effects?

Answer 39

decreases contractility of the atria (negative inotropic effect)

force of contraction of the ventricles (positive inotropic effect)

Question 40

What are negative & positive chronotropic effects?

Answer 40

decreases heart rate (negative chronotropic effect)

increases both the heart rate (positive chronotropic effect)

Question 41

Compare preganglionic & postgangionic fibers to skeletal fibers with respect to conducting speed & myelination.

Answer 41

In contrast to the large-diameter/fast conducting myelinated motor neurons innervating skeletal muscle: preganglionic axons are small-diameter/slower conducting myelinated fibers. Postganglionic axons are primarily small diameter/slower conducting unmyelinated fibers.

Question 42

Coordinated sympathetic nervous system activation in the “fight or flight” syndrome includes:

Answer 42

Increased sweating and piloerection via activation of muscarinic and alpha-1 adrenergic receptors, respectively.