Peripheral Nervous System Flashcards
What are the two primary divisions of the peripheral nervous system?
somatic (sensory and motor) and autonomic (sympathetic and parasympathetic)
The somatic nervous system send motor or _______ impulses to skeletal muscle. Somatic sensory nerves carry impulses (or ________) that are perceived, such as touch, pressure, pain, and temperature.
efferent; afferent
What is the predominant neurotransmitter in the periphery?
acetylcholine
What is the difference in preganglionic and post ganglionic nerves in the parasympathetic neurons vs the sympathetic neurons?
sympathetic preganglionic nerves tend to have short lengths and postganglionic tend to be longer; parasympathetic has the OPPOSITE— long pre, short post
In regards to pre and post ganglionic nerves… what is different about the adrenal medulla?
the adrenal medulla does not have post ganglionic fibers… only PRE…. so there is a direct release of the hormones (EPI, NE)
What is the primary neurotransmitter found in the pre and post ganglionic neuron of the sympathetic nervous system?
PRE: AcH
POST: NE
What is the primary neurotransmitter in the pre and post ganglionic neuron of the parasympathetic nervous system?
PRE: AcH
POST: AcH
Acetylcholine is the neurotransmitter released from somatic ______ nerves, ________ sympathetic nerves, ________ parasympathetic nerves, and _______ parasympathetic nerves.
Acetylcholine is the neurotransmitter released from somatic motor nerves, preganglionic sympathetic nerves, preganglionic parasympathetic nerves, and postganglionic parasympathetic nerves.
With one exception, norepinephrine is released from ALL sympathetic postganglionic nerves. The exception is _______.
sweat glands; AcH, not NE is released to sweat glands from sympathetic postganglionic nerves
What neurotransmitter released from the sympathetic neurons is responsible for triggering the release of hormones from the adrenal medulla?
acetylcholine….. BECAUSE the adrenal medulla is innervated by sympathetic PREGANGLIONIC neurons
What receptors are found on tissues innervated by the parasympathetic nervous system?
muscarinic receptors (cholinergic)
What receptors are found on tissue innervated by the sympathetic nervous system? The exception is the ______ ______.
adrenergic receptors; exception is the sweat glands…. where acetylcholine is released from the sympathetic postganglionic neuron to muscarinic receptors.
Where can nicotinic receptors be found?
found at the autonomic ganglia, on cells of the adrenal medulla, and at the motor-end plate of skeletal muscle
What receptor is responsible for possible bradycardia after the administration of succinylcholine?
muscarinic receptors on SA node
Alpha 1, alpha 2, and beta 1 are all examples of ______ receptors.
adrenergic
Does norepinephrine stimulate beta 2 receptors?
NO….. beta 2 is stimulated by epinephrine
Acetylcholine binds to nicotinic receptors except for the postganglionic neurons of the ________ nervous system.
parasympathetic; at the tissues of the PNS postganglionic…. but AcH still binds to nicotinic receptors in the PRE ganglionic parasympathetic neurons.
Where are nicotinic receptors found?
peripherally in the motor end plate of skeletal muscle and in cell bodies of both sympathetic and parasympathetic postganglionic neurons; nicotinic receptors respond to ACh or ACh agonists (sux) in a biphasic fashion
Nicotinic receptors respond to ACh or ACh agonists (sux) in a biphasic fashion. What does this mean in regards to dose?
in small doses, ACh stimulates nicotinic receptors of postganglionic sympathetic and parasympathetic neurons as well as nicotinic receptors of skeletal muscle end plate to cause depolarization; BUT IN HIGH DOSES or PROLONGED EXPOSURE, the nicotinic receptors become desensitized to succinylcholine and the postsynaptic membrane becomes inexcitable; this is called a PHASE II block
What are the 2 major subtypes of cholinergic receptors?
nicotinic and muscarinic
Cholinergic is the abbreviated term referring to __________.
acetylcholine; acetylcholine receptors are nicotinic and muscarinic
A substance (or ligand) is ________ if it is capable of producing, altering, or releasing acetylcholine (“indirect-acting”) or mimicking its behaviour at one or more of the body’s acetylcholine receptor types (“direct-acting”).
cholinergic
List the “fiber types” in order from largest to smallest diameter.
A-alpha (largest and fastest), A-beta, A-gamma, A-delta, B, sC, dC (smallest and slowest)
What fiber types are myelinated?
ALL of the A fibers (alpha, beta, gamma, delta) & B; sC, dC are UNMYELINATED
Which fibers carry sensations of sharp, prickling pain and temperature?
A-delta (sensory-afferent)
Which fibers carry sensations of throbbing pain and temperature?
dC fibers (sensory afferent)….. they are smaller so you get a slow throbbing pain
What is the function of A-alpha fibers?
motor (efferent) and sensory (afferent) to skeletal muscle and joints; muscle length, muscle force, proprioception
What two fibers are responsible for proprioception?
A-alpha and A-beta sensory fibers
Sympathetic and parasympathetic (both autonomic) preganglionic neurons are _____ fibers.
B fibers
Postganglionic sympathetic neurons are ____ fibers.
C fibers (sC)
________ nerves conduct action potentials at greater velocities than ______ nerves. (myelinated vs unmy.)
myelinated faster than unmyelinated
Do larger…. or smaller fibers conduct action potentials at a greater velocity?
larger
Where do the cardiac accelerator fibers arise from?
T1-T4
What is another name for the sympathetic outflow?
thoracolumbar outflow; arises from segments T1-L2 or T1-L3
The _______ _______ is formed by the inferior cervical and first thoracic ganglia.
stellate ganglion
Notes: The stellate ganglion (or cervicothoracic ganglion) is a sympathetic ganglion formed by the fusion of the inferior cervical ganglion and the first thoracic ganglion, which exists in 80% of cases. Stellate ganglion is located at the level of C7 (7th cervical vertebrae), anterior to the transverse process of C7, superior to the neck of the first rib, and just below the subclavian artery.
The clinical significance of these ganglia is that they may be cut in order to decrease the symptoms exhibited by Raynaud’s phenomenon and hyperhydrosis (extreme sweating) of the hands. Injection of local anesthetics near the stellate ganglion can sometimes mitigate the symptoms of sympathetically mediated pain such as complex regional pain syndrome type I (reflex sympathetic dystrophy). Injection is often given near the Chassaignac’s Tubercle (anterior tubercle of transverse process of C6) due to this being an important landmark lateral to the cricoid cartilage. It is thought that anesthetic is spread along the paravertebral muscles to the stellate ganglion.
What are some s\s of Horner’s syndrome? What causes this?
stellate ganglion blockade; The symptoms are: IPSILATERAL (meaning one-sided) miosis, ptosis, enophthalamos, flushing, increased skin temp, anhydrosis (no sweat), and nasal congestion.
How long does it take for the autonomic nervous system to mature in the neonate? What will you see in the place of bradycardia?
~6 mos; no bradycardia…. will see desaturation
All sympathetic preganglionic fibers pass through _______ (white or gray) rami while some, but not all, sympathetic postganglionic fibers pass through ______ (white or gray) rami.
PRE=WHITE, POST=GRAY; gray rami are distributed to ALL spinal nerves, while white rami are distributed to spinal nerves arising from T1-L2.
________ (WHITE or GRAY) rami allow coordinated, mass discharge of the sympathetic nervous system.
GRAY
What happens when alpha-2 receptors are stimulated?
When presynaptic alpha-2 receptors are stimulated by norepinephrine or any other drug with alpha-2 receptor agonist activity, the SYNTHESIS and RELEASE of NOREPINEPHRINE is DECREASED==== THIS IS NEGATIVE FEEDBACK
What are some common alpha-2 agonist drugs?
clonidine (catapres), precedex (dexmetatomadine)– 200:1
List out the synthesis of norepinephrine.
- tyrosine transported into nerve terminal from bloodstream
- tyrosine converted to dopa
- dopa converted to dopamine
- dopamine transported into presynaptic vesicle
- dopamine converted to norepinephrine
- NE stored in presynaptic vesicles (in adrenal medulla, NE is converted to epinephrine; normally in adrenal medulla, NE comprises 20% and EPI comprises 80%)
What happens to norepinephrine after it diffuses away from the receptor it attached to? (3 things)
it is removed from the synaptic cleft by:
1) reuptake (80%)
2) metabolism by MAO in the synaptic cleft
3) diffusion into the plasma where metabolism by COMT occurs (catechol-O-methyl-transferase)
How do most indirect acting sympathomimetics work? What is a common drug of this class used in the OR?
work in part by displacing NE from sympathetic nerve terminals; Ephedrine is commonly used; ephedrine also stimulates adrenergic receptors directly, so it is also a direct acting agent.
What are TWO drugs that should be AVOIDED in patients taking MAO inhibitors?
indirect acting sympathomimetics (EPHEDRINE) and one opioid, meperidine (DEMEROL); meperedine, like ephedrine, triggers release of NE; when either are administered to patients taking MAO inhibitors, the release of excess amounts of norepinephrine may cause a hypertensive crisis; generally more severe when giving meperidine than ephedrine.
What are some physiologic changes seen when the sympathetic nervous system is activated?
increased HR, CO, BP, blood glucose concentration; shunting of blood away from intestines and other viscera to better supply skeletal muscles; DILATION of bronchial tree
Where are alpha-1 receptors found and what happens when they are activated?
found peripherally in a variety of tissues (vascular smooth muscle, glands) innervated by sympathetic postganglionic neurons
excitatory response: arterial (increases SVR) and venous vasoconstriction (increases venous return, increases SV, increases CO)–> increased systemic arterial blood pressure
Where are alpha-2 receptors found and what happens when they are activated?
found on presynaptic nerve terminals of sympathetic postganglionic neurons, but also in tissues on postsynaptic membranes in the brainstem
stimulation on post-ganglionic, pre-synaptic nerve varicosities produce: inhibition of NE synthesis and release (negative feedback)
stimulation on postsynaptic alpha-2 in brainstem inhibits outflow of sympathetic nervous system
stimulation in substantia gelatinosa of spinal cord promotes analgesia (unrelated to SNS function)
Where are beta-1 receptors found and what happens when they are activated?
found in heart, kidney, and adipose tissue
stimulation is excitatory: increased HR and myocardial contractility–> increase CO–> increase arterial BP
Where are beta-2 receptors found and what happens when they are activated?
found in smooth muscle and in glandular tissue
stimulation if inhibitory: blood vessels of skeletal muscle dilate (small decrease in SVR, but overshadowed by beta-1), bronchodilation and relaxation of pregnant uterus
STIMULATES hepatocytes–> glycogenolysis and gluconeogenesis–> increasing blood glucose levels
What SNS receptors are found in the SA node, AV node, and muscle fibers?
beta-1
What receptor stimulation is responsible for dilation of the pupils (mydriasis)?
alpha-1
What receptor is responsible for vasodilation of skeletal muscles?
beta-2
What receptor is responsible for vasoconstriction of arterial and most systemic vessels?
alpha-1
What receptor stimulation is responsible for increased renin release in the kidneys?
beta-1
What receptor stimulation is responsible for decreased renin release in the kidneys?
alpha-1
An increase in blood glucose by glycogenolysis (breakdown of glycogen to glucose) and gluconeogenesis (formation of new glucose from non-carbohydrate sources, namely from amino acids) is the result of stimulation of what receptor?
beta-2
What receptor stimulation causes an increase in insulin secretion by the pancreas? decrease?
beta-2, alpha-2
What receptor causes a stimulation in the Na-K pump, thereby decreasing plasma K+?
beta-2
______ receptor stimulation promotes hyperglycemia.
beta-2; glycogenolysis and gluconeogenesis
______ receptor stimulation promotes hypokalemia.
beta-2; stimulates Na-K pump
What are some side effects of the beta-2 agonist, ritodrine (Yutopar)?
hyperglycemia, hypokalemia, and tachycardia (tachy only because these drugs are known to have some beta-1 receptor activity)
What controls 85% of the resting blood pressure?
renin
Where is renin released from?
the juxtaglomerular cells of the afferent arteriole
What does renin do?
converts angiotensinogen (a protein released into circulation from the liver) to angiotensin I
What is ACE and what does it do?
angiotensin converting enzyme; found on endothelial surface of pulmonary capillaries; converts angiotensin I to angiotensin II
What are the effects of angiotensin II?
promotes vasoconstriction and aldosterone release
What are the TWO important stimuli for aldosterone release?
angiotensin II and high serum K+ levels
What is the MOST potent vasoconstrictor out of angiotensin II and ADH?
ADH (also called vasopressin) is MORE POTENT
What are the effects of aldosterone?
increases K+ secretion (and excretion) and increases Na reabsorption, which promotes Na retention—> which promotes volume expansion
What causes the release of renin?
decreased renal BP (renal artery stenosis) and increased sympathetic nervous system activity
What receptors are stimulated by Phenylephrine (Neo-synephrine)?
Alpha 1; minimal Alpha-2
What receptors are stimulated by Clonidine (Catapress)?
Alpha-2; minimal Alpha-1
What receptors are stimulated by Isoproterenol (Isuprel)?
Beta 1 and Beta 2 in almost EQUAL amount
What receptors are stimulated by Dobutamine (Dobutrex)?
Beta 1 and minimal Alpha-1
What receptors are stimulated by Terbutaline (Brethine)?
Beta-2; minimal Beta-1
What receptors are stimulated by Albuterol (Ventolin, Proventil)?
Strong Beta-2; minimal Beta-1
What receptors are stimulated by Ritodrine (Yutopar)?
Beta-2; minimal Beta-1
What receptors are stimulated by Epinephrine (Adrenalin)?
Alpha-1 (+++), Alpha-2 (+), Beta-1 (++), Beta-2 (++), dopamine-1 (+)
What receptors are stimulated by Norepinephrine (Levophed)?
Alpha-1 (++++), Alpha-2 (+++), Beta-1 (++), NO beta-2
What receptors are stimulated by Dopamine (Inotropin)?
Alpha-1 (++), Alpha-2 (++), Beta-1 (++), minimal Beta-2 (+), DA-1 (++), DA-2 (++)
What receptors are stimulated by Fenoldopam?
DA-1 (++++)
What receptors are stimulated by Metoclopramide (Reglan)?
DA-1 (+)
What receptors are stimulated by Ephedrine?
Alpha-1 (++), Alpha-2 (++), Beta-1 (+), Beta-2 (+)
What receptors are stimulated by Metarminol (Aramine)?
Alpha-1 (++), Alpha-2 (++), Beta-1 (+), Beta-2 (+); same as Ephedrine
Why is Dopamine unique is comparison to other catecholamines?
It simultaneously increases contractility, renal blood flow, GFR, sodium excretion, and urine output
What are some of the common uses for Dopamine?
to increase CO in patients with low systemic BP, increased atrial filling pressures, and in low urine output
What are some of the common uses for Dobutamine?
to increase CO in CHF, particularly if HR and SVR are increased
What is the primary use for Isoproterenol?
to treat complete heart block; chemical pacemaker; 1-5mcg/kg/min continuous infusion
Whether pertinent or not, what is a difference shown in literature of outcomes using phenylephrine vs. ephedrine in the parturient?
phenylephrine is associated with a higher umbilical artery pH and less fetal acidosis at delivery, compared to using ephedrine