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What are the 2 parts of the peripheral nervous system?

Somatic NS- voluntary movement

Autonomic NS- involuntary


What are some similarities between Somatic and Autonomic NS?

both part of PNS

signals received from higher brain levels

integrative neurons provide stimulation/inhibition of both sysytems


What are some differences between Somatic and Autonomic NS?

somatic efferents go directly to their effector; neurons reach all the way to nueromuscular junction

autonomic efferents must synapse in a ganglion
neurons leaving the CNS- preganglionic
neuron that leaves the ganglion- postganglionic


What are integrative neurons?

complexes of neurons of the CNS, they recieve sensory input from multiple locations and throughout time

capable of processing this informatiion and determining the appropriate response

either stim/inhibt the somatic or preganglionic


2 components of the ANS:

sympathetic- fight/flight

parasympathetic- rest/digest


Where do fibers of the sympathetic nervous sysytem originate/terminate?

originate from the thoracic and lumbar spinal cord

enter the paravertebral chain of sympathetic ganglia

some will pass through to join ganglia elsewhere in the body


Give and example of sympathetic nerve fiber and its path:

Adrenal medulla

pregang fibers leave the T/L spinal segments, travel through the paravertebral chain synapse in the adrenal medulla

the cells of the medulla are considered the "post ganglionic" cells and release epinephrine


Post ganglionic symp fibers are LONG/SHORT the distance from ganglia is SHORT/FAR




What is meant by the the statement "the sympathetic is extremely reactive, and acts via mass discharge"

Extremely reactive: response to sympathetic stimulation is rapid and can vary moment to moment

Mass discharge: capable of mass action affecting virtually all sympathetic organs at once


Where do parasympathetic neurons orginate?

from nuclei in the midbrain, medulla, and sacral spinal cord

cranial nerves 3, 7, 9 10


Describe pre/post gang fibers of parasymp NS

preganglionic are long, synapse on/within effectors

therefore the post are short


Describe the effect of the sympathetic NS on the Heart

increased heart rate


Describe the effect of the sympathetic NS on the Peripheral Vasculature

constriction- decreases blood flow


Describe the effect of the sympathetic NS on the Skeletal Muscle/organ vascualture

Alpha 1- constriction
Beta 2- dialtion


Describe the effect of the sympathetic NS on the GI

Relaxation of smooth muscle
constriction of sphincter muscles
decreases secretions


Describe the effect of the sympathetic NS on the Bronchioles



Describe the effect of the sympathetic NS on the Urinary Bladder

Beta 2/3 relaxation of bladder body
alpha contraction of bladder trunk and internal sphincter


Describe the effect of the parasympathetic NS on the Heart

decreased heart rate
decreased contractile force
decreased conduction velocity


Describe the effect of the parasympathetic NS on the peripheral vascualture

dilation increases blood flow


Describe the effect of the parasympathetic NS on the skeletal muscle and organ vasculature



Describe the effect of the parasympathetic NS on the GI

increases peristalsis
relaxation of sphincter muscles
decreased conduction velocity


Describe the effect of the parasympathetic NS on the bronchioles



Describe the effect of the parasympathetic NS on the urinary bladder

contraction of bladder body
relaxation of trunk and internal sphincter


What are cholinergic receptors?

activated by acetylcholine


What are the 2 types of cholinergic receptors?




What are nicotinic receptors and where are they found?

Nicotinic Ach receptors (nAchr) – stimulated by nicotine in addition to Ach

acitvate an Ion Gated Channel

Found at synapse of preganglionic neurons onto the ganglia

Found at synapse of somatic neurons onto effectors


What are muscarinic receptors and where are they found?

Muscarinic Ach receptors (mAchr) – stimulated by muscarine, bethanechol, and pilocarpine in addition to Ach

Found at post ganglionic synapse of parasympathetic fibers onto effectors

G-coupled protein receptor


What are adrenergic receptors and where are they found?

Adrenergic receptors – activated by catecholamines such as norepinephrine or epinephrine

Found at post ganglionic synapse of sympathetic fibers onto effectors

A class of 7 transmembrane receptors who, when bound by agonist, will activate an enzyme cascade, starting with activation of a G protein


What are non-adrenergic, non-choline receptors?

Non-adrenergic, non-cholinergic receptors

Purinergic receptors – stimulated by purines

Found dispersed throughout body – i.e. urinary bladder


Facts about acetylcholine (Ach)

Acetylcholine (Ach)

oCreated by multiple enzymes in a long process

Choline-acetyltransferase is the rate limiting enzyme; the activity of this enzyme will determine the availability of Ach to be released into the synapse

o Acetylcholinesterase digests Ach in the synapse

 Breaks it down and transports metabolites back into presynaptic cell for recycling
oExcess Ach exposure can be treated with a cholinergic receptor antagonist OR acetylcholinesterase stimulant


Facts about Norepinephrine (NE):

Norepinephrine (NE)
o Classified as a catecholamine

o Tyrosine -> DOPA -> Dopamine -> Norepinephrine

Due to the relation between dopamine and NE, it is not unlikely that a dopamine agonist will likely also stimulate adrenergic receptors that bind NE


Facts about Epinephrine

Epinephrine (Epi)

o NOT identical to NE, thus will have a different effect on adrenergic receptors

o More resilient in blood stream – less susceptible to degradation in bloodstream


Alpha-1 Receptors:

Present on vascular smooth muscle for vessels feeding the skin, kidney, viscera, and skeletal muscle

When bound by agonist (i.e. NE):
- Vasoconstriction

*Note, in some locations alpha 1 will be outnumbered by beta 2 receptors; therefore stimulation with agonists of both will result in beta 2 activity


Alpha 2 receptors:

Pre-synaptic ganglia; When activated these will work to auto-inhibit NE release.


Beta 1 receptors:

Present on the SA note, Atria, and Ventricles of the heart

Agonist will induce:

-Increased contractility (contraction strength), heart rate, and conduction velocity

-Overall stimulation of the heart


Beta-2 receptors

Found in a variety of locations:

1.Pulmonary airway smooth muscle – bronchioles
a. Leads to dilation of airways – bronchodilation

2.Vasculature feeding skeletal muscle
a. Vasodilation
b. So, if there are more Beta 2 receptors than alpha 1 on a vessel feeding a skeletal muscle, then stimulation by agonist will result in vasodilation

3.Presynaptic neurons – within the membrane
a. Leads to auto-stimulation; presynaptic neuron releases NE, then that NE stimulates it to release more NE


What effects do norepinephrine/epinephrine have on the different receptor types?

-Epinephrine (Epi) is an agonist for all 4 subtypes of adrenergic receptors

-Norepinephrine (NE) is only agonistic for alpha 1,2 and beta 1

o So stimulation of Beta 2 is limited to circulating Epi


What are the 3 most common catecholamines we talked about?





Clinical application of Epi/NE/Isoproterol in local anesthetic:

1. Keep it at the location you give it bc local vasoconstriction via activation of alpha-1 receptors

2. Constriction of vasculature,

3. HOWEVER- caution, decreased peripheral blood pressure could activate baroreflex, leading to bradycardia

4. Also caustion giving in poorly perfused areas- ischemia


Clinical application of Epi/NE/Isoproterol as a hemostatic:

Constriction to stop blood flow


Clinical application of Epi/NE/Isoproterol in cardiac arrest/AV blocl

a. Beta one receptor EPI to jump start the heart

b. Complicated system


Clinical application of Epi/NE/Isoproterol inAnaphylactic Shock

a. EPI-Pen, allergic reactions
b. If you stab you finger w/ epi, need alpha one antagonist, Phentolamine most common


Clinical application of Epi/NE/Isoproterol in Bronchial asthma

Mild doses of catecholamines will provide continuous bronchodilation to counteract constant threat of airways closing due to allergens


What is the clinical application of dopamine?

i. In low doses will act as a DA receptor agonist

ii. In higher doses will act as a beta adrenergic agonist (remember the similarity between DA and NE)

iii. In veterinary field had been used to treat acute renal failure

1.Reasoning being high doses mimicking NE would lead to vasodilation, increasing perfusion to kidneys

2.However, not used anymore due to uncertain efficacy


What are the clinical applications of Dobutamine?

i.Most likely a beta 1 agonist

1. Had been used to treat low output congestive heart failure

2. Beta 1 agonist would stimulate the heart, acting as a positive ionotrope


What is ephedrine?

i. Closely related to pseudoephedrine

ii. Used for alpha and beta agonistic properties

iii. Historically had been used in dietary supplements (i.e. Hydroxycut) to induce beta receptor mediated lipolysis and thermogenesis

1. 2004, the FDA banned their use due to dangerous side effects

iv.Vet met uses:
1. Urinary incontinence – not very effective
2. Rarely used to combat hypotension


WHat is Phenylephrine?

i.Alpha agonist

1. Used for pupillary dilation during an ophthalmic exam

2. Combats hypotension and hypovolemic shock
a. Alpha stimulation leading to vasoconstriction to increase blood pressure


What are some common Beta 2 agonists?

i.Albuterol – found in inhalers; fast acting beta 2 agonist (good for emergency use)

ii.Clenbuterol – commonly used to treat Chronic Obstructive Pulmonary Disease (COPD)

1. This is a banned substance in horses

2. Illegal use in horse racing to stimulate bronchodilation (higher oxygen intake) and potential beta 3 stimulation (lipolysis and increase energy availability)

iii. Terbutaline – Long lasting beta 2 agonist; takes longer to take effect than albuterol


What are anti-adrenergic drugs used for?

a. Beta blockers – in veterinary medicine used to decrease blood pressure
Alpha blockers: used to reduce muscle tone in urinary sphincter


What is propanolol

1. Beta antagonist
2. Negative risk of also blocking beta 2 receptors and inducing bronchoconstriction


What is Atenolol?

1. Beta 1 receptor specific
2. Used frequently for high blood pressure in cats
3. Anti-anxiety medication for humans


How often do we use alpha blockers in Vet MEd?



What is Phenobenzamine?

1. Both an alpha 1 and 2 antagonist
2. Veterinary use:
a. Decreases urethral sphincter tone – ideal for inappropriate urine retention cases
b. Laminitis – known that laminitis is caused by circulatory problems to the hoof; alpha 1 antagonists would lead to vasodilation of peripheral vessels, leading to increased blood flow to the hoof


What is phentolamine?

1. Alpha 1 and 2 antagonist
2. Veterinary use:
a. To save fingers accidentally injected with Epi
i. Epi is agonistic to alpha 1,2 receptors, causing vasoconstriction
ii. Vasoconstriction in a digit can be so severe as to completely cut off blood supply
iii. Antagonizing these receptors will allow for restoration of blood supply to the digit
b. Treats pheochromocytomas (neoplasia of the adrenal medulla leading to excess Epi secretion) – exposure of body to an alpha 1,2 antagonist will minimize the negative effects of excess Epi


What are the 2 types of Ach receptors?

nAchR- nicotinic
Ion channels,
Ligand-gated ion channels

mAchR- muscarinic
G-protein coupled receptor
Metabolic receptors
7 Transmembrane protein



What are the 3 types of muscarinic receptors and where are they found?

Type 1 – found primarily throughout the GI tract; stimulation leads to increases in digestion, secretion, and peristalsis

Type 2 – Primarily cardiovascular; stimulation results in vasodilation and cardiac relaxation (decreased rate, contractile strength and conduction velocity)

Type 3 – Less known; Found anywhere parasympathetic system works besides GI and cardiovascular systems
i. Eye, urinary bladder, etc.


Where are nicotinic receptors typically found?

found at ganglionic synapses of both parasympathetic and sympathetic nervous systems


What are chlinergic/cholinomemetic drugs?

drugs that produce acetylcholine effects


What are parasympathomimetic drugs?

drugs that produce Ach like effects at parasympathetic neuroeffector junctions


What are direct acting parasympathomimetic drugs?

agonists for muscarinic receptors


What are cholinesterase inhibitors?

blockers of teh Acetylcholinesterases that degrade endogenous Ach


WHat are parasympatholytic drugs?

block/inhibit Ach-like effects at parasympathetic neuroeffector juntions


What effects do cholinergic receptor agonists have on the eye?

contraction of iris sphincter/ciliary muscle, which will cause constriction of the pupil


What effects do cholinergic receptor agonists have on the heart?

general inhibitory effects- decrease rate, contractile strength, conduction velocity


What effects do cholinergic receptor agonists have on the blood vessels?

indirect dialtion


What effects do cholinergic receptor agonists have on the Lungs?

contraction of bronchial muscles

increased secretions


What effects do cholinergic receptor agonists have on the GI tract

increase motility
relax sphincters
timualte secretions


What effects do cholinergic receptor agonists have on the Urinary bladder?

contraction of detrussor
relaxation of trigone/sphincter


What effects do cholinergic receptor agonists have on the glands

Increases secretions


What are the 2 direct acting parasympathomimetic drugs that are resistant to acetylcholinesterase ?




What is carbachol?

binds both muscarinic and nicotinic Ach receptors (all types)

Therefore, at higher concentrations, can lead to nicotinic receptor stimulation = stimulation of sympathetic ganglia

Catecholamine release from adrenal medulla

Skeletal muscle fasiculations


What is bethanecol?

binds ONLY muscarinic receptors; so will particularly get parasympathetic agonist response

sometimes used form bladder stimulation


What is pilocarpine?

Cholinomimetic alkaloid

• Used to treat keratoconjunctivitis and glaucoma

• Causes miosis (pupil constriction) and enhanced aqueous humor flow

• Binds muscarinic receptors


What are the toxic effects of cholinergic stimulation?

Slowing of heart rate and AV block (due to decreased conduction velocity)

Increased airway resistance  Dyspnea

Constriction of bronchioles

Increased secretions

Hypotension (due to vasodilation)

SLUD syndrome


What does SLUD stand for?



What are Indirect acting parasympathomimetic drugs ?

aka cholinesterase inhibitors – block acetylcholinesterase that degrades endogenous Ach

Indirectly attains the activity of Ach by preventing the digestion of Ach; allows Ach to act for a longer period of time within the synapse

Acetylcholinesterase terminates the action of endogenous Ach at just about every site where Ach is released

Including autonomic ganglia, parasympathetic neuroeffector junctions, somatic neuromuscular junctions, adrenal medulla, CNS


What are Edrophonium and Pyridostigme?

Reversible Drugs:
used for treatment of Myasthenia Gravis

•Myasthenia Gravis – hereditary condition in which postsynaptic cells lack appropriate numbers of cholinergic receptors

•Requires excessive amounts of Ach to create a normal response in the postsynaptic cell

•Use of cholinesterase inhibitors prevents digestion of Ach, allowing for the needed increase in Ach concentration


What are organophpsphates?

o Irreversible drugs  Organophosphates
 Malathion, Parathion, Dichlorvos – pesticides that use to be in flea collars; pretty much not in use anymore
 Sarin, Tabun, Soman – Nerve gas used in bio warfare
• Mild exposure leads to: pupillary constriction (miosis), tightness in the chest, wheezing
• Severe exposure: Diarrhea, Urination, miosis, bronchoconstriction, salivation, sweating, excitation of skeletal muscle and CNS


What are Parasympatholytic agens... what is the most important one we will use as vets most likely?

drugs that act as antagonists for muscarinic receptors
1. Atropine – prototypical muscarinic antagonist
a. Used to minimize the effects of nerve gas
b. Effects:
i. Tachycardia
ii. Relax GI musculature and decrease secretion
iii. Bronchodilation and decreased airway secretion
iv. Dry oral mucosa


What is the parasympathetic innervation to the bladder?

a.Preganglionic fibers originate in sacral spinal cord

b.Course through the pelvic nerve

c.Join ganglion adjacent to the bladder

d. Postganglionic fibers innervate the bladder wall musculature

i.Muscarinic receptors (M3) found along body of bladder – stimulation leads to contraction of musculature – inducing urination


What is the sympathetic innervation to the bladder?

a.Preganglionic fibers originate in T/L spinal cord

b.Immediately form ganglia adjacent to spinal cord

c.Postganglionic fibers extend toward bladder – innervate bladder wall musculature, internal sphincter, AND parasympathetic ganglia

i.Alpha 1 adrenergic receptors found at base/neck of bladder – stimulation leads to contraction of musculature – inhibiting urination

ii.Beta 2/3 adrenergic receptors found on body – stimulation leads to relaxation of musculature – inhibiting urination


What is the somatic innervation to the bladder?

a. Pudendal nerve

b. Innervates the external sphincter – skeletal muscle under voluntary control


What are the stages of bladder filling?

a. Primarily Sympathetic Activity
i. Internal sphincter contracted
ii. Neck of bladder contracted
iii. Body of bladder relaxed
iv. Inhibits parasympathetic ganglia activity


What are the stages of micturition?

(bladder emptying dumb ass)

a. Primarily Parasympathetic Activity
i. Body of bladder contracts
b. Somatic activity – decision made to urinate allows for external sphincter relaxation


What are common causes of urinary incontinence?

o Hormonal deficiencies
o Neurologic dysfunction – trauma to neurons or CNS involved in micturition
o Ectopic ureters – ureter links directly to the urethra, bypassing the bladder
 Results in a dripping incontinence
 20x more common in females
o Obstructions – urolith, stenosis, irregular sphincters


What type of incontinence cn pharmalogical interventions help to cure

o Hormone responsive incontinence – most commonly due to estrogen dependence
 In an unknown manner, estrogen interacts with bladder neck and internal sphincter to prevent inappropriate urination
 Animals that are recently spayed have sudden decrease in estrogen; in these cases, hormone therapy resolves the problem


What 2 drugs can be used to alleviate hormonal incontinence?

Oral Diethylstilbestrol (DES)
– had been used as an estrogen replacement in humans but was discovered to be a carcinogen and/or teratogen
• Used in vet med but should be avoided by pregnant women

Phenylpropanolamine (PPA)
– alpha receptor agonist, potentially inducing the production of estrogen


What is urge incontinence?

overstimulation of muscarinic receptors resulting in frequent urge to urinate


What 2 drugs can be used to treat urge incontinence?

Oxybutynin – M3 antagonist
• Blocks the muscarinic receptors that are being overly activated
• However, has unwanted side effect of dry mouth – most humans will prefer the incontinence over dry mouth

Tolterodine – same activity and side effects of oxybutynin
• However, there is a wider margin of dose providing relief of incontinence and causing dry mouth


T/F Most organs are innervated by BOTH the sympathetic and parasympathetic systems

TRUE; What receptors predominate determines what has action on it


T/F The adrenal gland originates from neuronal tissue

TRUE; this is why it has direct sympathetic action act on it. It is basically a synapse without post-ganglionic fibers


What would it look like if acetylcholinesterases were damaged?

It would look like PS activity; excess ACh would sit around in the synapse.


Where is nor epinephrine transformed to epinephrine?

Adrenal gland


What is more stable in the blood stream epinephrine or norepinephrine?



Phentolamine is a:

alpha blocker; keep your fingers


Propanalol and atenalol are:

Beta blockers



alpha agonist


What 2 different types of drugs would be beneficial to control urinary incontinence?

Alpha agonists or mAChR antagonists