Autonomic Nervous System Flashcards
How is the nervous system organized?
CNS = brain and spinal cord
PNS = spinal and cranial nerves that carry electrical signs to the CNS (afferents) and away from the CNS (efferents)
What are the somatic and visceral portions of the efferent and afferent portions of the PNS?
EFFERENT (motor):
- somatic: to skeletal muscle
- visceral: to cardiac muscle, smooth muscle, and exocrine glands
AFFERENT (sensory):
- somatic: from skin, retina, membranous labyrinth
- visceral: from thoracic and abdominal organs, olfactory epithelium, and taste buds
What makes up the autonomic nervous system? What do they do?
visceral and afferent axons responsible for involuntary control of smooth muscle, cardiac muscle, some glands and physiological life support functions
- heart rate
- blood pressure
- digestion
What does the somatic nervous system (SoNS) innervate? How are the neurons set up?
skeletal muscle
one neuron whose cell body is located in the CNS and whose axon extends uninterrupted to the skeletal muscle
What does the autonomic nervous system (ANS) innervate? How are the neurons set up?
cardiac muscle and smooth muscle of the blood vessels, GI tract, and bladder
two peripheral neurons
1. preganglionic neuron with its cell body in the CNS and its axon innervating the postganglionic neuron
2. postganglionic neuron with its cell body in the peripheral ganglion
How does the amount of myelin compare between somatic and autonomic neurons?
SOMATIC: myelinated axons
AUTONOMIC: postganglionic neurons are slowly conducting and are unmyelinated
What 7 bodily functions does the autonomic nervous system (ANS) control?
- cardiovascular and respiratory control
- thermal regulation
- GI motility
- urinary and bowel excretory functions
- reproduction
- metabolic and endocrine physiology
- fight or flight response
What are the 2 subdivisions of the peripheral autonomic nervous system (ANS)?
- origin in the CNS - efferent
- origin not in the CNS - afferent
What are the 3 subdivisions of the autonomic nervous system (ANS)?
- sympathetic nervous system (SNS)
- parasympathetic nervous system (PSNS)
- enteric nervous system (ENS)
Where are sympathetic nervous system axons located? How do the preganglionic and postganglionic axons compare? Where do the preganglionic axons pass through?
thoracolumbar —> first thoracic through 3rd to 4th lumbar spinal nerves
- PREGANGLIONIC = short
- POSTGANGLIONIC = long
pass through the ventral root and enter the paravertebral ganglion chain, sympathetic trunk
Where are parasympathetic nervous system axons located? How do the preganglionic and postganglionic axons compare? Where do the preganglionic axons come from?
craniosacral —> brainstem and sacral spinal cord
- PREGANGLIONIC = long
- POSTGANGLIONIC = short
leaves CNS by cranial nerves III (oculomotor), VII (facial), IX (glossopharyngeal), X (vagus), and several sacral spinal nerves
Where do parasympathetic preganglionic axons synapse with postganglionic axons?
diffuse parasympathetic ganglia close to or within the intramural ganglia in pelvic viscera
What is the enteric nervous system? What is it characterized by?
extensive network of interconnected sensory and motor interneurons within the GI wall that controls gut function independently of the CNS
presence of intrinsic neural network that includes the myenteric plexus and submucosal plexus
What is the enteric nervous system innervated by? How is it influenced by the CNS?
nonadrenergic-noncholinergic (NANC) nerve fibers
sensory and motor interneurons receive input from sympathetic and parasympathetic subdivisions
What is dual ANS innervation? What does it not indicate?
organs and tissues innervated by both sympathetic and parasympathetic arms of the ANS
that the physiological function of the target is balancd to the same degree for each arm of the ANS
What 4 organs have only sympathetic innervation?
- adrenal medulla
- peripheral blood vessels
- pilomotor muscles
- sweat glands
What cells act as ganglionic neurons in the adrenal medulla? What do they do? What are they innervated by? What receptors do they contain?
chromaffin cells - synthesize and release epinephrine and norepinephrine into the blood
sympathetic preganglionic fibers
nicotinic N receptors
What is the primary neurotransmitter released from preganglionic sympathetic neurons? What does it primarily bind to?
acetylcholine (ACh)
nicotinic (neuronal) N receptors
What does acetylcholine released from sympathetic postganglionic-cholinergic fibers bind to?
muscarinic (M) receptors
What is the predominant neurotransmitter released from postganglionic sympathetic neurons? What does it bind to and activate? What are fibers that synthesize and release this NT called?
norepinephrine (noradrenaline)
α and β receptors
adrenergic fibers
Other than norepinephrine, what other neurotransmitter is sometimes released from postganglionic sympathetic neurotransmitters? Where is it most important and what does it bind to?
dopamine (D), an immediate metabolic precursor to norepinephrine
peripheral vasculature
dopaminergic (D) receptors
What neurotransmitter is released from preganglionic and postganglionic parasympathetic axons? What does it bind to?
acetylcholine (ACh)
- nicotinic neural receptors on the postganglionic parasympathetic neuron
- muscarinic receptors
ANS neurotransmitters:
What are 7 non-adrenergic and non-cholinergic neurotransmitters?
- adenosine triphosphate (ATP)
- vasoactive intestinal polypeptides (VIP)
- neuropeptide Y (NPY)
- serotonin (5-HT)
- substance P
- calcitonin gene-related peptide (CGRP)
- nitric oxide (NO)
What are cotransmitters?
molecules/substances in the ANS nerves that also play a role as a neurotransmitter released from NANC nerve endings
Where does ATP bind? What other neurotransmitter is it commonly synthesized and stored with?
purinergic receptors, adenosine P1, P2X, and P2Y receptors
norepinephrine
Where is neuropeptide Y commonly released from? What receptors does it bind?
released with norepinephrine from pre- and postganglionic sympathetic nerves
neurokinin receptors Y1 and Y2
What do parasympathetic nerves innervating the urinary bladder release as a cotransmitter? Salivary glands?
BLADDER = ATP
SALIVARY GLANDS = vasoactive intestinal polypeptide (VIP)
(stored and released with Ach, too)
In what 3 systems are cotransmitters most important? What do they do?
- cardiovascular
- urogenital
- respiratory
increase pharmacological and physiological finesse in the regulation of tissue responses
What 2 vesicles are present at cholinergic nerve terminals?
- small membrane-bound vesicles where Ach is stored
- large vesicles that contain biological substances
What 2 proteins are found in large vesicles that contain biological substances at cholinergic nerve terminals? What do they do?
- vesicle-associated membrane proteins (VAMPs) - align Ach-containing vesicles
- synaptosomal nerve-associated proteins (SNAPs) - interact with VAMPs to facilitate fusion with plasma membrane
What enzyme is typically found in the cytoplasm of cholinergic nerves? What does it do? What enzyme aids in this process?
choline acetyltransferase (ChAT) - synthesizes ACh from acetyl-CoA and choline
sodium-dependent membrane choline transporter - transports choline across the neuronal membrane from the extracellular space
How much acetylcholine is typically packaged into vesicles?
quanta - 1000 to 50000 molecules
Where is acetylcholinesterase (AChE) typically found? What does it do?
synaptic spaces, closest to synaptic clefts
hydrolyzes Achy into choline and acetate
What is the release of acetylcholine controlled by? What controls its binding to postsynaptic receptors?
the arrival of action potentials that activate voltage-gated calcium channels
acetylcholinesterase - inactivates ACh = no binding
What 3 endogenous catecholamines are most commonly synthesized by adrenergic neurons?
- norepinephrine
- epinephrine
- dopamine
What neurons commonly terminate catecholamine synthesis with dopamine? Norepinephrine?
DOPAMINE: select peripheral postganglionic sympathetic neurons
NOREPINEPHRINE: (terminal enzymatic step) post ganglionic sympathetic and CNS neurons
What 2 physiological processes control the level of catecholamines in cytoplasm?
- inactivation by the neuronal mitochodrial enzyme monoamine oxidase (MAO)
- transportation of norepinephrine into granules by vesicular. monoamine transporter
What is the primary catecholamine released from the chromaffin cells of the adrenal medulla? What initiates its release from granules?
epinephrine (80%)
- norepinephrine (20%)
arrival of an action potential (calcium-dependent)
What 2 receptors can norepinephrine bind to upon release?
- adrenergic receptors on postsynaptic cells
- presynaptic adrenergic (α2) receptors located on the postganglionic nerve terminal from which it was released, resulting in inhibition of additional release of more NE from the presynaptic neuron
How can the release of norepinephrine from postganglionic sympathetic neurons be augmented?
activation of presynaptic β2-adrenergic receptors
What 3 physiological processes control the elimination of synaptic norepinephrine and/or termination of norepinephrine synaptic activity?
- NE metabolism by catechol-O-methyltransferase (COMT)
- NE transportation back into preganglionic sympathetic nerve terminals by an active NE transporter (NET)
- NE diffuses away from the synaptic cleft and is metabolized in the plasma/liver or is excreted in the urine
In what 4 places are nicotinic (N) receptors present?
- postganglionic neurons in autonomic ganglia (intramural, prevertebral, paravertebral)
- adrenal medullary chromaffin cells - mediate neurotransmission from preganglionic sympathetic neurons
- CNS
- nonneuronal tissues - skeletal muscle
What do nicotinic muscle (NM) receptors do? What kind of receptors are they?
signal transmission at the neuromuscular junction (somatic nervous system)
ligand-gated ion channels with 5 homologous subunits
What 5 things happen upon the activation of nicotinic muscle (NM) receptors?
(ligand-gated ion channel)
1. increases cellular permeability to cations (Na+ and Ca2+)
2. cell membrane depolarization
3. excitations of postganglionic ANS neurons
4. excitation of adrenal medullary chromaffin cells
5. excitation of skeletal muscle fibers
Where are most muscarinic receptors (M1-M5) located? What kind of receptors are they?
postsynaptic target sites innervated by postganglionic parasympathetic nerves - heart, glands, urinary bladder, GI tract
G-protein-coupled receptors (GPCRs)
- M1, M3, M5 = Gq/11
- M2, M4 = Gi, G0
What are the endogenous catecholamines norepinephrine and epinephrine agonists for? Dopamine? What kind of receptors are they?
α (1a, 1b, 1d, 2a, 2b, 2c) and β (1, 2, 3) adrenergic receptors
dopaminergic (1-5) receptors
G-protein-coupled receptors (GPCRs)
ANS regulation; eye, head glands, lungs, heart:
ANS regulation; blood vessels, GI tract, urinary bladder, adrenal medulla, kidney, liver:
True or false: chromaffin cells are innervated by parasympathetic preganglionic fibers.
FALSE - sympathetic only
True or false: the adrenal medulla secretes mostly NE and relatively little EPI.
FALSE - EPI = 80%
What is the primary neurotransmitter released from preganglionic neurons at sympathetic ganglionic sites?
a. EPI
b. NE
c. ATP
d. ACh
D