1 ANS Intro Flashcards
The peripheral nervous system is divided into what two major subdivisions?
Autonomic and Somatic
The _______ division is independent of conscious thought or control
Autonomic
Autonomic pathways originate in the:
Brain or Spinal Cord
Autonomic pathways involve a __________ nerve and a ___________ nerve, connected in series by a ___________.
A PREGANGLIONIC nerve and POSTGANGLIONIC nerve connected by a GANGLION
In the __________ system, there is no peripheral ganglia.
Somatic nervous system
A single motor neuron projects from the CNS directly to the skeletal muscle
The ANS is subdivided into:
The PARASYMPATHETIC, or craniosacral division, and
the SYMPATHETIC, or thoracolumbar division
The parasympathetic nerves leave the spinal cord with…
With the cranial and sacral nerves (hence the “craniosacral” name)
The sympathetic pathways leave the CNS…
From the spinal cord at thoracic and lumbar levels (hence the “thoracolumbar” name)
ANS fibers leaving the brain stem or spinal cord terminate in ___________.
Autonomic ganglia
Autonomic ganglia contain the nerve endings of ____________ fibers and the cell bodies of __________ fibers.
Pre-ganglionic, post-ganglionic
All pre-ganglionic fibers release the neurotransmitter ____________ onto ____________ receptors in the autonomic ganglia.
Acetylcholine, nicotinic receptors
Describe the pathway of parasympathetic innervation
Pre-ganglionic fibers leave the CNS with the CRANIAL nerves and the third and fourth SACRAL spinal roots.
The pre-ganglionic fibers may terminate on ganglia located in the wall of an innervated organ, on diffuse ganglia, or on autonomic ganglia outside the innervated organ.
Postganglionic parasympathic fibers are very ______ compared to those in the sympathetic system.
Short
Both pre- and post-ganglionic neurons in the parasympathetic system release ….
Acetylcholine
Describe the pathway of sympathetic innervation
Pre-ganglionic fibers leave the CNS with THORACIC and LUMBAR spinal nerves. Cell bodies are in the LATERAL horn of the gray matter in the thoracic and lumbar spinal cord.
Most of the pre-ganglionic fibers terminate in ganglia in the PARAVERTEBRAL chains, which run alongside the spinal column.
Broad interconnections provided by the paravertebral chains allow the whole sympathetic system to …
Activate in a coordinated discharge
Post-ganglionic sympathetic fibers project to various tissues and are ________ than those in the parasympathetic system.
Longer
The majority of post-ganglionic fibers release _________, except for ….
Most release norepinephrine (NE) except:
Sweat glands release acetylcholine (ACh)
Renal vasculature releases dopamine
Adrenal medulla releases epinephrine
The main neurotransmitters involved in the autonomic nervous system:
Acetylcholine (ACh), norepinephrine (NE) and dopamine (DA)
All pre-ganglionic fibers of both the parasympathetic and sympathetic systems are _________.
Cholinergic, i.e. they release ACh, which acts on nicotinic receptors in the ganglion.
Post-ganglionic fibers of the parasympathetic system are _____________, releasing _________, which acts on ___________ receptors.
Cholinergic —> release ACh —> act on muscarinic receptors.
Post-ganglionic fibers in the sympathetic system are primarily ______________, and release ______, which acts on ____________ receptors
Noradrenergic —> release NE —> acts on alpha and beta receptors
The sympathetic post-ganglionic innervation of ___________ is cholinergic, with ACh stimulating muscarinic receptors, even though these neurons are considered sympathetic.
Sweat glands
Sympathetic neurons to the _____________ release dopamine
Renal vascular smooth muscle
Innervation to the adrenal medulla from the spinal cord is ___________, with ______ acting on a __________ receptor to cause release of _____________.
Cholinergic —> ACh acts on nicotinic receptor —> releases Epinephrine
____________ released from the adrenal medulla circulates in the body and acts on both alpha and beta receptors.
Epinephrine (Epi)
Motor neurons to the skeletal muscle are ____________, with ________ acting on ________ receptors
Cholinergic —> ACh acts on nicotinic receptors
Blood vessels receive _________ innervation but not __________.
Sympathetic but not parasympathetic.
Blood vessel tone is predominantly sympathetic.
The _____________ are innervated by neurons from the sympathetic chain that release _________.
Sweat glands, ACh
The parasympathetic system has been called __________, meaning it facilitates growth
Trophotropic
It’s the “rest and digest” system.
Parasympathetic stimulation causes:
Slowing of the heart
Increased secretion of saliva and gastric acid
Increased GI activity, promoting digestion
Relaxation of sphincters, promoting elimination
Pupils and ciliary muscles both contract —> accommodation
The sympathetic system is designed so that it can…
Fire all at once
In the sympathetic system, there is a nearly ______ ratio of pre- to post-ganglionic innervation
1:20 —> allowing for massive activation of the whole system at once.
The sympathetic system is referred to as ________, meaning facilitating energy expenditure.
Ergotropic - it allows for “fight or flight”
Sympathetic stimulation causes:
Heart to beat more rapidly and CO increases
Blood vessels supplying skeletal muscles relax, allowing for more blood flow to muscles
Blood vessels to the skin constrict, reducing bleeding in response to energy
Bronchioles dilate, allowing for easier breathing
GI system less active, sphincters contract
Pupils dilate, ciliary muscles relax (distance vision)
Glycogenolysis and gluconeogensis are stimulated, lipolysis occurs and renin released from kidney
Acetylcholine is formed from …
Cholinergic and acetyl CoA by the enzyme choline acetyltransferase (ChAT)
ACh is stored in _______ within the nerve terminal
Synaptic vesicles
The action of ACh within the synaptic cleft is rapidly terminated via …
Hydrolysis by acetylcholinesterase (AChE), which converts ACh back into choline and acetate
What happens to choline after ACh is broken down by AChE?
It is taken back up into the nerve terminals and recycled back into ACh.
Besides AChE, what else can affect circulating ACh?
Pseudo holiness erase can also inactivate circulating ACh
ACh binds to _______ receptors, which are located either on the postsynaptic cell or on presynaptic terminals
Cholinergic
What are the two subgroups of cholinergic receptors?
Muscarinic and nicotinic
M1 muscarinic receptors are found…
In the CNS and in sweat glands
Gq protein linked —> activate phospholipids C —> IP3 and DAG —> Ca2+ release and activation of protein kinases
M2 muscarinic receptors are found
In the heart, some smooth muscle, and presynaptically on neurons
Gi protein linked, INHIBIT adenylyl cyclase, open K+ channels, hyperpolarizing neurons
M3 muscarinic receptors are found…
In exocrine glands, smooth muscle, and endothelium
Gq protein linked, same mechanism as M1
What are the two kinds of nicotinic receptors?
Nn are found on postganglionic neurons and presynaptic terminals
Nm are found at NMJs of skeletal muscles
For both, binding of ACh opens Na+ channels, depolarizing the cell
Parasympathetic innervation of the heart
The vagus nerve projects to the atrium of the heart
M2 receptors slow the heart by decreasing SA node activity, AV conduction, directly and by inhibiting release of NE from incoming sympathetic neurons
Parasympathetic innervation of the lungs
M2 receptors cause bronchoconstriction and increase mucous secretion in the lungs
Secretions from the salivary and lacrimal glands are increased by both _____ and _____ receptor activation
M1 and M3 (parasympathetic)
M3 receptors cause _______ and ________ in the eye
Mitosis (constricting pupil)
Accommodation of the lends for near vision
In the stomach, M3 receptor activation increases…
Gastric acid secretion
M3 receptors stimulate the GI tract by
Stimulating the GI tract wall, increasing motility
Relaxing the sphincters, allowing for defecation
Contract the bladder wall, increasing the urge to urinate, as well as relaxing the base of the bladder and urinary sphincter
In men, M3 receptors do what to the penis?
Promote erection
“Point”
How do the nicotinic receptors at NMJs differ from the muscarinic/nicotinic receptors of the parasympathetic system?
The nicotinic receptor is an ion channel, and which ACh binds, it opens, allowing Na+ to enter the cell, resulting in depolarization, leading to an action potential (some K+ also leaves the cell)
______ is hydroxylated to become I-dopa, which is then decarboxylated to dopamine (DA)
Tyrosine
DA is a neurotransmitter on its own, but what else can happen to it?
In noradrenergic neurons, DA is hydroxylated to form NE in the synaptic vesicles
NE is converted to epinephrine in the adrenal medulla.
NE is stored in vesicles and released when?
When the cell depolarizers, the vesicles fuses with the presynaptic membrane and NE is released
Drugs such as _______ and ______ cause release of NE from the pre-synaptic terminal and will have effect only if noradrenergic terminals are intact
Tyramine and amphetamine
What is the main mechanism for the termination of action of NE in the synaptic cleft?
Reputable into the presynaptic terminal
Reputable of NE into the presynaptic terminal is blocked by drugs such as …
Antidepressants and cocaine
NE is metabolized by what two enzymes?
monoamine oxidase (MAO) and catechol-0-methyl transferase (COMT)
The end product, measured as a diagnostic marker, is vanilla-Mandela’s acid (VMA)
Alpha1 receptors are found in….
Smooth muscle
Gq protein linked —> activation of PLC increases IP3 and DAG —> Ca2+ increases and cell depolarizes
Alpha2 receptors are found …
On presynaptic terminals, in platelets, lipocytes, and some smooth muscle
Gi protein linked, inhibits adenylyl cyclase
Beta1 receptors are found
On many pre- and post-synaptic sites, most specifically in the HEART
Beta2 receptors are found…
On some smooth mucscle, specially the bronchioles (and the heart)
Beta3 receptors are found…
On lipocytes, causing lipolysis
In the urinary bladder, causing relaxation
All beta receptors are _____ protein linked
Gs - stimulate adenylyl cyclase to increase cAMP
Dopamine receptors are found in ….
Renal vascular bed and some blood vessels
Stimulate adenylate cyclase
The “fight or flight” response of the sympathetic nervous system includes responses such as:
Increase in both heart rate and force of contraction
Dilation of blood vessels to heart and skeletal muscle
Constriction of blood vessels to skin and other areas
Dilation of bronchioles
Decrease in GI activity and constriction of GI and GU sphincters
Increases in lipolysis, glycogenolysis, and blood glucose
Increase in the release of renin
Dilation of pupils, with a slight increase in distance vision
Sympathetic innervation to the heart
Beta1 (and some B2) receptors increase heart rate, AV conduction, and contractility
Sympathetic innervation of the lungs
B2 receptors relax the bronchioles
Sympathetic innervation of the blood vessels
alpha1 receptors constrict blood vessels in the skin and skeletal muscle
Beta2 receptors relax blood vessels in the skeletal muscle
Sympathetic innervation of the glands and eyes
M3 receptors increase sweating (ACh)
Alpha1 receptors increase activity of apocrine and salivary glands
Alpha1 receptors cause dilation of pupils (mydriasis)
Alpha1 receptors cause constriction of nasal blood vessels, decreasing congestion
Sympathetic innervation of GI and GU tracts
Alpha2 and Beta2 receptors relax the walls of the GI tract
B2 receptors relax the pregnant uterus
B3 receptors relax the urinary bladder
Alpha1 receptors contract the urinary sphincter, making it harder to urinate (esp men)
Alpha1 receptors promote ejaculation
Presynaptic ____ receptors on noradrenergic nerve terminals decrease NE release
Alpha2
Presynaptic ____ receptors on cholinergic nerve terminals decrease ACh release
M2
Autoreceptors refer to…
when the presynaptic receptor is for the type of transmitter within the terminal
Heteroreceptors refer to
when the presynaptic receptor is for other types of neurotransmitters other than the type within the terminal
A decrease in receptor number (either through internalization or destruction) that occurs in response to repeated, high frequency stimulation.
Down regulation
Receptors for a neurotransmitter increasing either in number or affinity in response to inhibition or removal of an input/stimulus
Up regulation
An extreme example of up-regulation in which a total loss of input may cause a large increase in receptor number
Enervation supersensitivity
If a drug increases BP by constricting the blood vessels, the body will attempt to compensate for the increased pressure by slowing heart rate and decreasing cardiac output. This is called…
Reflex bradycardia
If a drug dilates blood vessels and drops blood pressure, the level of signal at the baroreceptrs is decreased and the brain will increase sympathetic output, so that the body can compensate by increasing heart rate. This is called…
Reflex tachycardia
The net effect of NE on the heart is an increase in peripheral resistance (diastolic pressure), but some increase in BP is moderated to some degree by…
The decrease in heart rate due to vagal stimulation (reflex bradycardia)
A blockage of ____ receptors with atropine will prevent…
The reflex bradycardia resulting from NE stimulation
Contraction of the ciliary muscle and constriction of the pupil by __________ stimulation widens the space in the trabecular meshwork and allows aqueous humor to be cleared more easily
Parasympathetic stimulation
This decreases intraocular pressure
Activation of ______ receptors by sympathetic stimulation also increases clearance of aqueous humor and decreases ocular pressure
Alpha
Stimulation of ___________ increases production of aqueous humor, increasing intraocular pressure
Beta receptors
Therefore, a blockade of beta receptors is used to decrease intraocular pressure
The size of the pupil is controlled by the …
Iris radial muscle and the circular muscle
Contraction of the radial muscle in response to ______ stimulation _______ the pupil
Sympathetic —> dilates
Contraction of the circular muscle in response to ________ stimulation causes the pupil to ________
Parasympathetic —> pupillary constriction
Contraction of the ciliary muscle relaxes tension on the suspensory ligaments, allowing the lens to…
Become more convex and shift forward, increasing accommodation for near vision
The iris circular and ciliary muscles are controlled by _________
Cholinergic inputs
Stimulation of muscarinic receptors contracts the iris sphincter and ciliary muscles —> miosis and increased accommodation for near vision
If the ciliary muscle is blocked with cholinergic antagonists, what will happen?
Cycloplegia, or loss of accommodation
Pupil dilation
___________ can be used to treat glaucoma. How?
Cholinergic agonists
Cholinergic stimulation increases removal of aqueous humor through the trabecular meshwork, decreasing intraocular pressure.
Because the iris radial muscles contract in response to alpha receptor stimulation, alpha receptor agonists can cause
Mydriasis (dilation of the pupil)
Alpha receptor agonists can also be used to treat glaucoma because…
Contraction of the radial muscle promotes drainage of intraocular fluid and can decrease pressure
___________ increase production of aqueous humor, resulting in an increase in intraocular pressure
Beta receptors
Beta receptor blockers can also be used to treat glaucoma