Exam 1 ANS Flashcards
How is the nervous system organized?
- CNS
2. PNS → SMS and ANS → sympathetic and parasympathetic
What is the somatic motor pathway in the PNS?
- contains a single neuron that releases ACh as the neurotransmitter and the receptor is a nicotinic receptor
- target is the skeletal muscles, mostly voluntary
What are the three pathways within the autonomic pathways of the PNS?
- parasympathetic
- sympathetic
- adrenal sympathetic
What is the parasympathetic pathway?
- long preganglionic neuron that releases ACh to a nicotinic receptor
- short postganglionic neuron that releases ACh to a muscarinic receptor
- ganglia is close to the post-ganglionic
What is the sympathetic pathway?
- short preganglionic neuron that releases ACh to a nicotinic receptor
- long postganglionic neuron that releases NE to alpha and beta1 receptors
- ganglia is close to CNS
What is the adrenal sympathetic pathway?
- ganglia synapses in the adrenal medulla and the release of epinephrine has to go into the circulation to go to the target organ and can interact with beta1 and beta2 receptors
What are some autonomic targets?
- smooth and cardiac muscles
- some endocrine and exocrine glands
- some adipose tissue
What are some things to know about autonomic neurons?
- regulation of the activity of smooth and cardiac muscle, glands, lymphoid and some adipose tissue
- concept of autonomic tone (involuntary) which means that the pathways tend to be active to some degree at rest
- sympathetic and parasympathetic actions are often (but not always) opposing
What are the important things to know about somatic motor neurons?
- controls skeletal muscles
2. mostly voluntary
What is the ganglia?
group of cell bodies outside of CNS
What is the first neuron in the ANS?
- termed the preganglionic neuron
- located in the CNS
- projects to the autonomic ganglia
What is the second neuron in the ANS?
- termed the postganglionic neuron
- located outside of the CNS in the autonomic ganglia
- projects to the target organ
What is the anatomy of the sympathetic nervous system?
- the preganglionic neuron is located in the middle regions of the spinal cord (thoracolumbar)
- the postganglionic neuron is long and projects to the target organ
- the sympathetic ganglia located near the spinal cord
What is the anatomy of the parasympathetic system in the ANS?
- the preganglionic neuron is located in the brainstem or outer regions of spinal cord (craniosacral)
- the postganglionic neuron is short and projects to the target organ
- parasympathetic ganglia is located in or near the target organs
What are the preganglionic neurons like in the parasympathetic system?
- long
- synapses with postganglionic neurons at or near the target organ
- releases ACh to activate nicotinic receptors on the postganglionic neurons
What are the postganglionic neurons like in the parasympathetic system?
- short
- synapses on the target organ
- releases ACh to activate muscarinic receptors on the target organ
What are the preganglionic neurons like in the sympathetic system?
- short
- synapses with postganglionic neurons near the spinal cord
- releases ACh to activate nicotinic receptors on the postganglionic neurons
What are the postganglionic neurons like in the sympathetic pathway?
- long
- synapses on the target organ
- releases NE to activate adrenergic receptors on target organs
What are the exceptions in the sympathetic nervous system?
- sweat glands
- adrenal glands
- kidneys
How are sweat glands an exception?
- postganglionic neurons involved with stress related excretion release NE → sweaty palms
- postganglionic neurons involved with thermoregulation release ACh
How are adrenal glands an exception?
- preganglionic neurons do not synapse in the paravertebral sympathetic ganglion → they synapse directly on the adrenal gland to release ACh and activate nicotinic receptors on the adrenal gland
- adrenal glands release epinephrine into systemic circulation → then to target organ
How are kidneys an exception?
- they are also affected by dopamine (endogenous) → mainly synthesized locally and not in the ANS
Most postganglionic sympathetic neurons release what neurotransmitter?
norepinephrine (NE)
What are the major points of the autonomic nervous system?
- primary transmitter of all preganglionic neurons is ACh
- the transmitter in all PSNS (parasympathetic) neurons is ACh
- transmitter in most SNS postganglionic neurons is norepinephrine (NE) → BUT sweat glands have ACh, adrenal medulla has epinephrine, and renal vasculature has dopamine
What are cholinoceptors?
- acetylcholine receptors
2. has two types: nicotinic (Nm, Nn) and muscarinic (M1, M2, M3)
What are adrenoceptors?
- norepinephrine and epinephrine receptors
2. has two types: alpha (a1, a2) and beta (beta1, beta2, beta3)
Why do we study the ANS?
- many drugs exhibit anticholinergic effects → important for treating the elderly
- ANs plays a major role in regulating BP and heart function
- there are many adrenergic drugs for BP and cardiovascular diseases
- ANS plays a large role in bronchoconstriction/dilation
- cholinergics play a role in pesticides and chemical weapons
- is the basis for the discipline of pharmacology → medication therapy management!
What is adrenergic pharmacology?
the pharmacology of sympathetic mechanisms involving norepinephrine and epinephrine and their receptors
What is cholinergic pharmacology?
the pharmacology of parasympathetic mechanisms involving acetylcholine and its receptors
What are the neurotransmitters of the parasympathetic system (cholinergic)?
acetylcholine (endogenous), muscarine (exogenous), and nicotine (exogenous)
What are the neurotransmitters in the sympathetic system (adrenergic)?
norepinephrine (endogenous) and epinephrine (endogenous)
What is acetylcholinesterase?
membrane bound enzyme that is specific for the cholinergic receptor in which acetylcholine can bind to
What are nicotinic receptors?
- has 5 subunits and is an ionotropic open ligand gated Na channel
- acetylcholine is the ion which leads to the depolarization of the membrane → leads to the opening of the voltage gated sodium channels to produce an action potential
- selectively activated by nicotine
What are muscarinic receptors?
- 7 transmembrane domain G-protein coupled receptors (GPCRs)
What pathway does the M1, M3, and M5 muscarinic receptors signal through?
Gq pathway → IP3 mobilizes Ca2+ from intracellular stores and DAG activates PKC (protein kinase C)
What pathway does the M2 and M4 muscarinic receptors signal through?
Gi pathway → K+ channel opening causes hyperpolarization and counteract beta1 receptors which result in reduced cAMP dependent protein kinase activity
What are the agonists for muscarinic receptors?
endogenous acetylcholine or muscarine (exogenous)
What pathway do alpha1 adrenergic receptors signal through?
Gq pathway → IP3 mobilizes Ca2+ from intracellular stores and DAG activates PKC (protein kinase C)
Alpha1 adrenergic receptors are found where?
- vascular smooth muscle
- genitourinary smooth muscle
- intestinal smooth muscle
- heart
- liver
What is the main effect of alpha1 adrenergic receptors?
mediates vasoconstriction
What pathway do alpha2 adrenergic receptors signal through?
Gi pathway → inhibits adenylyl cyclase, reduced cAMP dependent protein kinase activity, activates certain K+ channels
Where are alpha2 adrenergic receptors most commonly found?
found pre-synaptically and function as autoreceptors to inhibit sympathetic output → results in decreased transmitter release → many alpha2 adrenergic receptors need CNS access to function
What pathway do beta1, beta2, and beta3 adrenergic receptors signal through?
Gs pathway → activates adenylyl cyclase, increased cAMP leading to protein kinase activation → results in phosphorylation of ion channels and other proteins (basically opposes Gi pathway)
Rate and force of contraction of the heart can be increased by stimulating what receptors?
beta1 and beta2 receptors (more beta1 than beta2 though)
Rate and force of contraction of the heart can be decreased by stimulating what receptors?
M2 receptors (since they stimulate the Gi pathway)
Vasoconstriction of most arteries is stimulated by what receptors?
alpha1 receptors
Vasoconstriction of the veins is stimulated by which receptors?
alpha1 and alpha2 receptors
Vasodilation of the skeletal muscle is stimulated by which receptor?
beta2 receptors
The release of EDRF by the endothelium is stimulated by which receptors?
M3 receptors
Bronchodilation of the bronchiolar smooth muscle is stimulated by which receptors?
beta2 receptors
Bronchoconstriction of the bronchiolar smooth muscle is stimulated by which receptors?
M2 and M3 receptors
The relaxation and contraction of the bladder wall is stimulated by which receptors?
relaxation → beta2 receptors
contraction → M3 receptors
The contraction and relaxation of the ureter is stimulated by which receptors?
contraction → alpha1 receptors
relaxation → M3 receptors
The contraction and relaxation of the sphincter is stimulated by which receptors?
contraction → alpha1 receptors
relaxation → M3 receptors
The relaxation and contraction of the pregnant uterus is stimulated by which receptors?
relaxation → beta2 receptors
contraction → alpha1 receptors
The ejaculation and erection of the penis/vas deferens is stimulated by which receptors?
ejaculation → alpha1 receptors
erection → M3 receptors
Increased secretion of the salivary glands is stimulated by which receptors?
alpha1 and M3 receptors
The relaxation and contraction of the smooth muscle walls is stimulated by which receptors?
relaxation → alpha2 and beta2 receptors
contraction → M3 receptors
The relaxation and contraction of the smooth muscle sphincters is stimulated by which receptors?
contraction → alpha1 receptors
relaxation → M3 receptors
What receptor stimulates inhibition of secretion of the GI tract?
alpha2 receptors
What receptor stimulates increased secretion of the GI tract?
M3 receptors
The contraction of hair follicles is stimulated by which receptors?
alpha1 receptors
Increased secretion of the thermoregulation sweat glands is stimulated by which receptor?
M3 receptors
Increased secretion of the apocrine (stress) sweat glands is stimulated by which receptor?
alpha1 receptors
What receptor is stimulated to contract the radial muscle of the iris?
alpha1 receptors
What receptor is stimulated to contract the circular muscle of the iris?
M3 receptors
The relaxation and contraction of the ciliary muscle is stimulated by which receptors?
relaxation → beta2 receptors
contraction → M3 receptors
The increased secretion of aqueous humor of the ciliary epithelium is stimulated by which receptor?
beta2 receptors
Mucus and enzymes of the lacrimal glands are stimulated by which receptor?
alpha1 receptors
Tears or watery lacrimal glands are stimulated by which receptor?
M3 receptors
What is the role of the iris?
the iris is a ring of muscles oriented in two different ways whose activity determines the amount of light entering the eye through the pupil
What is miosis?
the pupillary constriction of the circular muscle which is constricted by the activation of parasympathetic nerves → M3 receptors are responsible for this
What is mydriasis?
the pupillary dilation of the radial muscle which is constricted by the activation of sympathetic nerves → alpha1 receptors are responsible for this
M3 agonists like pilocarpine act on what?
the ciliary muscle → the contraction facilitates the outflow of aqueous humor which decreases intraocular pressure
Alpha2 agonists like brimonidine act on what?
the ciliary body → inhibits the production and increases outflow of aqueous humor to decrease intraocular pressure
Beta antagonists like timolol act on what?
the ciliary epithelium → secretion of aqueous humor to decrease intraocular pressure
What increases the outflow of aqueous humor?
prostaglandins (PGF2 analog) like latanaprost
What is glaucoma?
is characterized by intraocular pressure which is induced by aqueous humor and decreased outflow through trabecular network and increased secretion from ciliary body epithelium
What receptors stimulate glycogenolysis in the liver?
alpha1 and beta2 receptors
What receptors stimulate lipolysis in fat cells?
alpha1, beta1, beta2, and beta3 receptors
What receptor stimulates increased renin secretion in the kidneys?
beta1 receptors
What receptor stimulates decreased insulin release in the pancreas?
alpha2 receptors
The pupil is stimulated by which receptor and what are the sympathetic and parasympathetic effects?
alpha1 receptors
sympathetic effect → dilation (mydriasis)
parasympathetic effect → constriction (miosis)
The ciliary muscle is stimulate by which receptor and what are the sympathetic and parasympathetic effects?
beta2 receptors
sympathetic effect → relaxation (far vision)
parasympathetic effect → contraction (near vision)
The AV node of the heart is stimulated by which receptor and what are the sympathetic and parasympathetic effects?
beta1 receptors
sympathetic effect → increased conduction
parasympathetic effect → slowed conduction
The myocardium of the heart is stimulated by which receptor and what are the sympathetic and parasympathetic effects?
beta1 receptors
sympathetic effect → increased force of contraction and automaticity
parasympathetic effect → decreased force of contraction
The veins are stimulated by which receptors and what is the sympathetic effect?
alpha1 and beta2 receptors
sympathetic effect → constriction, dilation
The visceral arteries are stimulated by what receptor and what is its sympathetic effect?
alpha1 receptors
sympathetic effect → constriction
Vasculature is only controlled by which system?
sympathetic nervous system (SNS)
The bronchi in the lungs is stimulated by which receptor and what are the sympathetic and parasympathetic effects?
beta2 receptors
sympathetic effect → relaxation
parasympathetic effect → contraction
The male sex organs is stimulated by which receptor and what are the sympathetic and parasympathetic effects?
alpha1 receptors
sympathetic effect → ejaculation
parasympathetic effect → erection
The male sex organs are the only organs where both systems do what?
both the parasympathetic and sympathetic nervous systems work together
What sites have a sympathetic predominant tone?
arterioles, veins (no PSNS innervation), sweat glands (muscarinic)
What sites have a parasympathetic predominant tone?
heart, iris, ciliary, GI tract, bladder, salivary
What is the uninnervated effect?
the receptor is not activated by the neurotransmitter released from the nerve → but neurotransmitter released from other cell types like immune cells and platelets activates the receptor → AN ADRENERGIC OR CHOLINERGIC EFFECT (NOT SYMPATHETIC OR PARASYMPATHETIC EFFECT) since adrenergic/cholinergic is affected by receptors and has nothing to do with the nervous system
How do drugs influence the ANS?
- mimic or block the effects of the 2 primary neurotransmitters → acetylcholine and norepinephrine/epinephrine
- drugs that mimic neurotransmitters are referred to as receptor agonists → these drugs activate the receptor
- drugs that block neurotransmitters are referred to as receptor antagonists → these drugs block the endogenous neurotransmitters from activating receptors
What are the classification of drugs that affect the parasympathetic nervous system?
- mimic acetylcholine = cholinergic = muscarinic agonists = parasympathomimetic
- blocks acetylcholine = anticholinergic = muscarinic antagonist = parasympatholytic
What are the classification of drugs affecting the sympathetic nervous system?
- mimic norepinephrine = adrenergic = adrenergic agonist = sympathomimetic
- block norepinephrine = antiadrenergic = adrenergic antagonist = sympatholytic
