Peripheral Nervous System Flashcards
What are the 2 divisions of the peripheral nervous system?
- Somatic
2. Autonomic - Parasympathetic & Sympathetic
Where do the autonomic preganglionic neurons synapse with the postganglionic neurons?
At the autonomic ganglia
How is the adrenal medulla innervated?
Preganglionic sympathetic neurons - nictoninc - Ach - Epi, NE
What is the predominant NT of the periphery?
Ach
Name the receptor & NT that is released:
Preganglionic parasympathetic
Postganglionic parasympathetic
Preganglionic sympathetic
Postganglionic sympathetic
Preganglionic sympathetic to adrenal medulla
Postganglionic sympathetic to sweat glands - muscarinic, Ach
Motor neuron
Preganglionic parasympathetic - nicotinic, Ach
Postganglionic parasympathetic - muscarinic, Ach
Preganglionic sympathetic - nicotinic, Ach
Postganglionic sympathetic - adrenergic, NE
Preganglionic sympathetic to adrenal medulla - nicotinic, Ach
Postganglionic sympathetic to sweat glands - muscarinic, Ach
Somatic motor neuron - nicotinic, Ach
Name 3 places nicotinic receptors are found.
- Autonomic ganglia
- Cells of the adrenal medulla
- Motor end-plate of skeletal muscle
Name the 2 types of cholinergic receptors.
- Muscarinic
2. Nicotinic
List the fiber types from LARGEST diameter to SMALLEST diameter (FASTEST to SLOWEST).
A-alpha A-beta A-gamma A-delta B sC dC
Which fibers are myelinated? Unmyelinated?
Myelinated: A-alpha, A-beta, A-gamma, A-delta, B
Unmyelinated: sC, dC
A-alpha Fibers
Motor & Sensory
Muscle length & force
Proprioception
Somatic motor neurons
A-beta Fibers
Motor & Sensory
Touch & pressure
Proprioception
A-gamma Fibers
Motor only
Skeletal muscle tone
A-delta Fibers
Sensory only
Pain, temp, & touch
B Fibers
Preganglionic autonomic neurons
sC Fibers
Postganglionic sympathetic neurons
dC Fibers
Sensory only
Pain, temp, & touch
The sympathetic, or __________, nervous system outflow arises from what segments?
Thoracolumbar
T1 to L2or3
Where dos most preganglionic sympathetic neurons synapse with postganglionic neurons?
Paravertebral ganglia
The stellate ganglion is formed by what to ganglia?
Inferior cervical ganglia
First thoracic ganglia
*In 80% of people, these 2 ganglia are fused
If you block — Horner’s syndrome - miosis, ptosis, anhydrosis on the IPSILATERAL side
Interscalene or supraclavicular blocks
Sympathetic preganglionic neurons arise in the ___________ and pass out of the spinal cord via the ___________ root.
Intermediolateral horn of the spinal cord Anterior root (SNS stimulation = efferent/motor)
Describe the fate of sympathetic preganglionic neurons arising in the intermediolateral horn of the spinal cord.
Start: Intermediolateral horn of the spinal cord
Exit: anterior root
ALL PREganglionic neurons pass through the WHITE rami on their way to the paravertebral ganglia
3 fates:
1. Synapse in the paravertebral ganglia…then the POSTganglionic neurons pass through the GRAY rami to reach the spinal nerve
2. Ascend or descend prior to synapse
3. Synapse in the peripheral ganglia
Preganglionic white rami are distributed to spinal nerves arising from ____. Postganglionic gray rami are distributed to ___ spinal nerves from the ganglia.
T1-L2
ALL
*Gray rami allow coordinated, mass discharge of the SNS.
What happens when presynaptic alpha-2 receptors are stimulated by NE or any other drug with alpha-2 receptor agonist activity?
The synthesis and release of NE is DECREASED
Negative feedback
Describe the formation of NE and Epi.
Tyrosine from bloodstream to nerve terminal - Dopa - Dopamine - presynaptic vesicle - NE - adrenal medulla - Epi
*Adrenal medulla pool - 80% Epi, 20% NE
Detail the termination of NE.
1st step is diffusion away from the receptors
80% reuptake into the presynaptic nerve terminal
MAO found in the synaptic cleft
COMT found in the bloodstream
Where are alpha-2 receptors found? What are their actions at these 3 sites?
- Sympathetic postganglionic, presynaptic nerve varicosities - inhibition of NE synthesis and release
- Sympathetic postganglionic, postsynaptic receptors in the brainstem - inhibition of SNS outflow
- Sympathetic postganglionic, postsynaptic receptors in the substantia gelatinosa - analgesia
Beta-2 receptor stimulation is inhibitory in what 2 places?
- Lungs
- Uterus
* Stimulation of beta-2 receptors in smooth muscle is INHIBITORY
What 2 side effects of beta-2 receptor stimulation should you consider?
- Glycogenolysis and gluconeogenesis - BG will increase
2. Na-K pump stimulation - K is driven into cell, HYPOkalemia results
________ receptor stimulation increases renin release and _______ receptor stimulation decreases renin release.
Increases renin release - Beta-1
Decreases renin release - Alpha-1
_______ receptor stimulation increase insulin secretion and ________ receptor stimulation decreases insulin secretion.
Increases insulin secretion - Beta-2
Decreases insulin secretion - Alpha-2
85% of the resting BP is controlled by _________.
Renin
Enzyme release from juxtaglomerular cells of the afferent arteriole
Converts angiotensinogen to angiotensin I
What 2 things does angiotensin II promote?
- Vasoconstriction
2. Aldosterone release
Name 2 important stimuli for aldosterone release.
- Angiotensin II
- HYPERkalemia
*Less potent stimuli include ACTH & HYPOnatremia
What 2 things does aldosterone promote?
- Secretion of K
2. Retention of Na
Name the receptors that the following drugs work on. Epi NE Dopamine Ephedrine Dobutamine
Epi - alpha-1,2 + beta-1,2
NE - alpha-1,2 + beta-1 (NO beta-2!)
Dopamine - alpha-1,2 + beta-1 + dopamine
Ephedrine - alpha-1,2 + beta-1,2 (basically a weak Epi!)
Dobutamine - beta-1
Would you notice an increase or decrease in HR with a NE infusion?
Decrease in HR - baroreceptor reflex
Would you notice an increase or decrease in DBP with a low-dose Epi infusion?
Decrease in DBP - beta-2-mediated vasodilation
*Beta receptors are MORE sensitive than alpha
Are beta or alpha receptors MORE sensitive to agonist?
Beta!
Would you notice an increase or decrease in DBP with an infusion of isoproterenol?
Decrease in DBP - beta-2 mediated vasodilation (no alpha-1 activity)
Rebound HTN is a problem with clonidine is suddenly withdrawn. Rebound HTN is mediated by what 3 things?
- Catecholamines
- Renin
- Angiotensin II
Name 2 nonselective alpha-2 blockers.
Name 1 selective alpha-1 blocker.
Nonselective alpha-2 blockers 1. Phenoxybenzamine - pheo! 2. Phentolamine Selective alpha-1 blocker Prazosin
Name 2 selective beta-1 blockers.
*side notes on metabolism/elimination
- Metoprolol
- Atenolol (eliminated by kidneys, others BB liver)
?Esmolol (metabolized by non-selective esterases)
Labetolol blocks what receptors?
Alpha-1, Beta-1,2
- same as Carvedilol
- alpha to beta block is 1:7 - stronger beta!
Caution with nonselective beta blockers in what patients?
Irritable airways (bronchoconstriction)
Diabetics (hypoglycemia w/o warning signs)
*Also could have HYPERkalemia
Reversal of beta blockade.
Glucagon 1-10 mg IV followed by 5 mg/hr IV
Should a patient with a pheochromocytoma be alpha or beta blocked first?
Block ALPHA prior to beta
Anesthetics & Beta Blockers
List from LEAST favorable to MOST favorable: opioids, halothane, enflurane, ketamine, isoflurane
Ketamine - least favorable Enflurane Halothane Opioids Isoflurane - most favorable
Explain down-regulation.
Chronic exposure to AGONIST
DECREASED # of receptors
Ex: CHF - high SNS discharge results in down regulation of beta-1 receptors
Explain up-regulation.
Chronic exposure to ANTAGONIST (competitive)
INCREASED # of receptors
Ex: beta-blocked patient - abruptly d/c meds = exaggerated response
The parasympathetic, or __________ nervous system outflow arises from what?
Craniosacral
CN 3, 7, 9, 10 (midbrain, pons, medulla)
S2-4
What CN transmits 3/4ths of the traffic of the parasympathetic NS?
CN X - 10 - Vagus
Parasympathetic NS stimulation - contraction or relaxation of the detrusor muscle?
Contraction of the detrusor muscle (bladder)
What is Pilocarpine?
Parasympathomimetic used to treat narrow-angle glaucoma
Drainage of aqueous humor is facilitated by miosis
*Another drug in this class: Bethanechol - used to treat ileus and urinary retention
Name 5 cholinesterase inhibitors.
- Edrophonium
- Neostigmine
- Pyridostigmine
- Physostigmine
- Echothiophate
Avoid Sux and Mivacurium with which cholinesterase inhibitors?
Neostigmine Pyridostigmine Echothiophate *Cholinesterase inhibitors inhibit both true acetylcholinesterase and plasma cholinesterase Indirectly stimulate nicotinic receptors
Which cholinesterase inhibitor is a tertiary NOT quaternary ammonium compound and crosses the BBB?
Physostigmine
*Used to treat anticholinergic syndrome
Which cholinesterase inhibitor is used in the treatment of glaucoma? It is a longer acting agent.
Echothiophate
Which 2 cholinesterase inhibitors are used in the treatment of myasthenia gravis?
- Neostigmine
2. Pyridostigmine
What receptors are involved in mediating the responses to reversal agents?
Nicotinic and muscarinic receptors
How will excessive doses of acetylcholinesterase inhibitors affect NDMR? Sux?
Potentiate NDMR
Prolong Sux
Cholinergic Antagonists
Anticholinergic vs. Antimuscarinic
Anticholinergic: antagnoize Ach
Antimuscarinic: antagonize muscarinic receptors
Name 3 anticholinergics.
- Atropine
- Scopolamine
- Glyco
Which antimuscarinic least crosses the BBB and why?
Glyco
Has a charged quaternary ammonium group
Which cholinesterase inhibitor is used to treat anticholinergic syndrome?
Physostigmine
*Tertiary ammonium compound, non-ionized, readily crosses BBB
The probability of esophageal reflux __________ when the patient is given an antimuscarinic drug.
INCREASES
How do phosphodiesterase inhibitors such as aminophylline work?
Block the breakdown of cAMP and thus promote bronchodilation as cAMP accumulates
List the 4 second messengers working in the bronchial smooth muscle cell.
- cAMP
- cGMP
- Ca
- IP3
When clonidine is given to the patient, there is a decreased in MAC of____%.
15-50%
What higher center regulates the SNS?
Hypothalamus
List 3 drugs that block nicotinic receptors at the autonomic ganglia.
- Trimethaphan
- d-Tubocurarine
- Metocurine
* Blocks transmission of sympathetic impulses - hypotension
Why does tachyphylaxis result from ephedrine use?
Depletion of NE from sympathetic postganglionic nerve terminals
How does phentolamine produce tachycardia?
Tachycardia reflects release of NE from sympathetic post-ganglionic nerve terminals owing to alpha-2 blockade
