Lecture 7: ANS Flashcards
what is the center of the central autonomic network
hypothalamus
what is the hypothalamus responsible for and what nucleus is central to this function
role in metabolism and reproduction
paraventricular nucleus is the center
SADPOX
extra-hypothalamus portion of the central autonomic network
limbic system as the higher level control system (orbitofrontal cortex, amygdala) = open loop
visceral sensory through brainstem nuclei/SC = closed loop
boundaries of the hypothalamus
superior = hypothalamus sulcus (end of sulcus limitans)
posterior (and inferior) = mammillary bodies
inferior = infundibulum
rostral = anterior commissure, lamina terminalis, and optic chiasm
functional zones of hypothalamus
anteromedially = parasympathetic/enteric
laterocaudally = cardiovascular/sympathetic
describe the descending tracts of the central auntonomic network
tracts are bilateral but ipsilaterally dominant- there are MULTIPLE DECUSSATIONS
3 tracts = major tract, medial forebrain bundle (MFB), and mammillotegmental tract
number of tracts and decussations means that ANS is seldom compromised after a brain injury
what is the major tract
the principal pathway or the dorsal longitudinal fasciculus (DLF)
originates in region of paraventricular nucleus of thalamus
what is the medial forebrain bundle
descending tract coming from higher control centers like the amygdala, OFC, etc
what is the mammillotegmental tract
descending tracts of the central autonomic network
mainly in tegmentum of brainstem
describe a somatic peripheral motor system
1 cell system = LMNs in ventral horn
target skeletal mm
synapse at NMJ
descrube a visceral peripheral motor system
2 cell system
1st cell for parasympathetic = preganglionic neuron in brainstem or SC (S2-S4)
1st cell for sympathetic = preganglionic neuron in SC (T1-L2)
2nd cell = ganglionic neuron in ganglia/LMN
target = smooth mm/cardiac mm/glands
synapses are bead like along axon terminals
what is divergence in a ganglia
one preganglionic axon synapses with multiple second cells
what is convergence in a ganglia
multiple preganglionic axons synapse with the same 2nd cell
characteristics of synapses of the visceral motor system
beadlike synapses with target organ/cell
within the target organ = gap junctions and synchronized mobility (allows mm to share the same depolarization at same time and avoid incoordination like arrhythmias)
where is the first/preganglionic neuron for the sympathetic arm of the peripheral ANS
lateral (aka intermediolateral) horn of SC from T1-L2
located in lamina VII
what is a paravertebral ganglia
aka sympathetic ganglia
somata of the 2nd cells
connected to SC and each other
go almost the whole length of the SC
location of synapsis of preganglionic axons with the second neuron
can be at the same segment or ascend/descend to different segments to form the sympathetic chain/trunk
what is a prevertebral ganglia
somata of 2nd cell for splanchnic nerve
continuous to the ganglion anterior to the aorta
3 cervical ganglia involved in sympathetic innervation of the head and neck
superior
middle (may not exist in some people)
inferior/stellate
how does sympathetic innervation travel in the neck
merge into spinal nerves
hike arteries
how does sympathetic innervation travel in the head
hike the carotid artery
then hike CN V division branches
Horner’s system can be causes by what
compression of sympathetic trunk around the neck
i.e. pancoast tumor in the cupula of the lungs
S&S of horner’s syndrome
partial ptosis - due to compromised superior tarsal mm
constriction of pupil - b/c sphincter pupillae (controlled by CN III) still works
red face w/o sweating (paradoxical signs)
- dilation of blood vessels
- lost sweat gland control
for the parasympathetic nervous system arm of the peripheral ANS, where are the 1st and 2nd cells
1st/preganglionic neuron = in brainstem AND sacral SC
2nd/ganglionic neuron = closing or directly in target organ
what are the 4 ganglia that can act as 2nd cells for the parasympathetic arm of the peripheral ANS in the head
CN III = ciliary ganglia
CN VII = pterygopalantine/submandibular ganglia
CN IX = otic ganglion
where is the 2nd neuron for the vagus nerve
neck, thoracic to midgut visceral organs
where is the 2nd neuron for the pelvic splanchnic nerve (S2-S4)
hindgut and pelvis
clinically, where is the general location of the sympathetic and parasympathetic arms of the ANS
parasympathetic in brainstem
sympathetic in SC
shown in mice
independent visceral sensory pathway
CN IX: carotid body and sinus
blood vessels controlled by parasympathetic nn
carotid body and sinus by CN IX; control O2 lvls and BP
arch of aorta by CN X; control BP
aside from the visceral sensory of the neck that is independent, where do the rest of the visceral sensory pathways travel
they follow visceral motor
some follow CN X from midgut to the caudal solitary nucleus where they synapse and ascend
others follow based on specific spinal cord level
- splanchnic nn for organs in the abdominal/peliv cavity
- spinal nn for thoracic organs, somatic walls, and extremities
what is the spinohypothalamic pathway
center of visceral motor control
diffuse pain??
describe visceral pain (fiber type & change type)
mainly through C fibers
diffuse until it touches the somatic wall and irritates a delta fibers
must be fast change, otherwise the pt would adapt to stimuli
describe referral pain
feel the pain where the visceral senses enter the CNS
internal organs do not match physical location
common clinically relevant referral patterns
gallbladder = 30-80% population’s follows the R phrenic n
pericardium and parietal pleura in mediastinum follow the phrenic nn in R bicipital groove (R atrium expands with certain heart conditions and thus pain is felt when heart pushes into lungs on R side)
compare and contrast sympathetic vs parasympathetic system
sympathetic
- increases metabolism
- fight/flight/freeze
-tonic (constant)
- 2nd cell in adrenal gland of medulla; no axons’ directly release epinephrine and norepinephrine
- unique = supply skin, kidney, blood vessels
parasympathetic
- decrease metabolism
- phasic
- rest/digest
- unique = supply ciliary body and sphincter pupillae mm
both = reproduction
how does the sympathetic system control body temp
decreases body temp via sweating
anterior nucleus of the hypothalamus (parasympathetic function) gives information to the sympathetic system for this to occur
how does the sympathetic system control circadian rhythm
when light is on
- retinal ganglion neurons activate in superchiasmic nucleus
- inhibition of sympathetic nervous system, no melatonin released, alert and aroused
when light is off
- tonic sympathetic nervous system
- activate pineal gland to release melatonin
- you get sleepy
how do neurotransmitters/receptors work in the sympathetic system
1st cell releases ACh
binds to nicotonic receptor in post synaptic membrane (ligand gated ionotropic receptors)
2nd cell releases NE as neurotransmitter
amplification occurs by activating the medulla of the adrenal gland which then releases epinephrine and norepinephrine
these then bind to adgrenergic receptors in the target cells (multiple subtypes of alpha or beta metabotropic*)
*metabotropic = diffuse/slow
how do neurotransmitters/receptors work in the parasympathetic system
1st cell releases ACh
binds to nicotonic receptor in post synaptic membrane (ligand gated ionotropic receptors)
2nd cell still releases ACh as a neurotransmitter
this then binds to muscarinic receptor in the target cells (multiple subtypes of metabotropic receptors)
what are cholinergic drugs
agonists for parasympathetic nervous system
effects of cholinergic drugs
pupillary constriction/near vision
salivation
constriction/secretion of bronchi
slow HR
gastric secretion/increased diarrhea
voiding of urine from bladder
effects of anticholinergic drugs
pupillary dilation/far vision
dry mouth
relaxation/sticky dry bronchi
acceleration of HR
constipation/reduced gastric secretion
retention of urine
things to keep in mind with pts with CAD taking cholinergic drugs
the meds slow HR but keep in mind other effects it may be having on other parts of the body
what are anticholinergic drugs
antagonists for parasympathetic nervous system
things to keep in mind with pts taking anticholinergic drugs for incontinence
inhibits detrusor mm contraction but what other systems are also being affected?
what is the enteric nervous system and how can it function independently
ANS of GI system
can function independently b/c:
- intrinsic motor/sensory neurons
- independent circuitry
- can be modulated by ANS
often still functions even in a vegetative state
neurons outnumber the number found in the SC
what is an interstitial cell
pacemaker of the enteric system
allows for rhythm/contractions per min
proximal contracts while distal relaxes; creates rhythm
describe the mechanism of peristalsis
contraction of proximal intestinal lumen
distension of bolus segment
dilation of distal intestinal lumen
why is it important to understand the enteric system and the mechanisms of peristalsis
neurotransmitters can get interfered with by pain meds and result in S&S such as constipation or abnormal emotions
describe the visceral sensory center and its functional divisions
visceral sensory center = solitary nucleus
rostral portion = relays special info about taste
caudal portion = relays all other visceral sensory info
this center cross talks with other regions to allow for reflexes to occur based on sensory input
why is the ANS so important
maintains major vitals
body temp via the intra hypothalamic nucleus
respiratory rate, HR, and BP in the brainstem
how does a normal baroreceptor reflex work
maintains BP and prevents it from becoming too high
with body position change blood pools in LE and the reflex increases HR to prevent the BP from getting too low
afferent/efferent signals with body position change related to BP
afferent (sensory) via CN IX and X from the carotid/aortic sinus
efferent (motor) via CN X for parasympathetic and IML neurons for sympathetic
CN X for visceral motor has 2 nuclei that function differently but synergistically to decrease BP
- Dorsal vagal nucleus decreases cardiac mm contraction
- nucleus ambiguous inhibits sinoatrial node to decrease HR
storage phase of bladder control
can happen with or without pintine storage descending signals
tonic sympathetic and somatic control
constant relaxation of detrusor mm and contraction of both sphincters
describe the control of the urinary bladder
bladder wall (detrusor mm/smooth mm)
- sympathetic inhibits
- parasympathetic activates
internal sphincter (visceral motor)
- sympathetic activates
- parasympathetic inhibits
external sphincter (somatic motor)
- via pudendal nn (S2-S4)
*similar control as that of anal sphincters
micturition phase of bladder control
must activate the micturition center through the reflex
phasic parasympathetic control activation through stretch
contraction of detrusor mm and relaxation of both sphincters
AD occurs at what levels
T6 and above
what happens with AD
noxious stimuli induces a reflex with pts that cannot feel below T6
blood vessel constricts below level of injury; cold/pale/goosebumps/sweaty
above injury level is red/hot/no sweat
above the level:
- there is an increase in BP (20-40 mmHg)
- pounding HA
- baroreceptor relfex activated; CN X efferent to decrease HR/cardiac contraction
- blood vessel dilation/flush/no sweat; paradoxical to below lesion
