Autonomic Nervous System Flashcards
Where are all neuronal cell bodies found and why?
In the CNS or near it (none in arms and legs): better protected
Define Neurolemma
The nuclei and cytoplasm of Schwann cells wrapped around the outside of the myelin sheath
Define Ganglia, nuclei, nerves, and tracts (and the difference between them)
Ganglia: collection of nerve cell bodies in the PNS
-Nerves: collection of axons in the PNS
Nuclei: collection of nerve cell bodies in the CNS
-Tracts: collection of axons in the CNS
Dorsal Roots
Contains sensory information (afferent impulses)
-posterior part of spinal cord
Ventral Roots
-Motor (efferent nerves)
-Anterior part of spinal cord
-Gray matter of spinal cord (cell bodies)
-white matter is axons
Nervous System divisions
CNS
-brain
-spinal cord
PNS
-Cranial Nerves
-Spinal Nerves
-somatic
-ANS
PNS divisions
somatic (voluntary): carries info to the skeletal muscles
Autonomic (visceral, involuntary): supplies smooth muscles, glands, and conducting system of the heart
Somatic vs ANS (how many neurons transmit messages?)
Somatic efferent impulses utilize a single neuron to transmit info from CNS to skeletal muscle
symp and parasymp efferent information is transmitted through 2 neurons
-Preganglionic and postganglionic (very specific to ANS)
Somatic sensory info:
touch, pain, temp, proprioception
motor fibers: innervate muscle fibers, controls VOLUNTARY movement
Where are cell bodies located for preganglionic and postganglionic neurons?
Preganglionic: CNS
Postganglionic: autonomic ganglion (ends at target organ)
-whether parasympathetic or sympathetic, preganglionic neuron originates in CNS
-where it ends depends on symp or parasymp
Where along the spine do sympethetic preganglionic neurons originate?
Lateral!! horn of thoracolumbar!! spinal cord (T1-L3)
Through where do preganglionic axons exit the spinal cord?
Ventral (anterior) roots
Preganglionic and postganglionic neuron lengths: sympathetic vs parasympathetic
Sympathetic: pre = short, post = long
-pregang neurons go to the paravertebral ganglia chain (22 pairs)
parasympathetic: pre = long, post = short
-Preganglionic neurons go to ganglions located on or near target organs
sympathetic preganglionic fibers: routes to synapse with postganglionic neuron (paravertebral ganglionic chain)
1: enter and immediately synapse with postgang in paravert ganglion at its respective vertebral level
2: pass through and ascend before synapsing
3: pass through and descend before synapsing
4: pass through the paravertebral ganglia without synapsing and continue via splanchnic nerves to the PREvertebral ganglia anterior to the AORTA and synapse there
-celiac, superior/inferior ganglia
Prevertebral aortic ganglia
-Just know this is an option of where neurons could go, not all will go to ganglionic chain
-A MAJORITY of sympathetic preganglionic neurons are SHORT and go to the paravertebral area
Sympathetic postganglionic neurons
-enter the gray rami and re-enter and travel along the spinal nerves to the target organ
-gray rami: essentially houses pre and postganglionic neurons I guess
Which cranial nerves have preganglionic cell bodies from the parasympathetic system? Where on the vertebrae?
-CN III, VII, X, IX
-S2-S4 (craniosacral!!!)
-innervate pelvic viscera and some abdominal structures
-innervate smooth muscle in the eye (CN III), salivary glands and lacrimal glands (CN VII)
-Vagus nerve carries 80% of parasympathetic nerves
-Gray matter of brainstem
Clarification: This slide is describing where parasympathetic neurons originate, being in the brain as well as sacral region of the vertebrae (Vagus literally innervates most major organs involved in parasympathetic responses involved in important processes of homeostasis)
Which nerves have their parasympathetic ganglia located directly in their target organs?
Vagus nerve: heart, lungs, liver, esophagus, most of GI tract up to transverse colon
pelvic splanchnic nerves (S2, S3, S4): reproductive organs and bladder
CN III, CN VII, CN IX (not X)
-Synapse in cranial ganglia near target organ
-oculomotor: Ganglia located behind the eyes, innervating pupil
-Facial: innervates the sublingual and submandibular salivary glands, lacrimal glands, and glands in nasal cavity
-Glossopharyngeal: innervating the parotid salivary gland
Which neurotransmitter is released by ALL preganglionic neurons?
Ach (Cholinergic)
-cholinergic:
-nicotinic
-muscarinic
Acetylcholine binds to what receptors on ALL postganglionic cell bodies?
Nicotinic
-this opens ion channels allowing Na+ and Ca2+ to enter the neuron and activate the postganglionic neuron
Most postganglionic neurons release what at a SYMPATHETIC synapse?
Norepinephrine (NE)
-adrenergic neurons
In sympathetic synapses, what is the 1 case without NE/adrenergic
Sweat glands (cholinergic [Ach], muscarinic)
In the sympathetic pathway, adrenergic receptors can be divided into:
alpha (1,2) and beta (1,2,3)
-reminder: exception of sweat glands and first synapse from CNS which use cholinergic receptors
Side note:
If you hear in pharm that a med interacts with alpha or beta receptor, think sympathetic
Sympathetic cholinergic receptors (ONLY at first synapse and sweat glands)
Nicotinic: Ach receptor at postganglionic cell body
Muscarinic: Ach receptor on target organ
Sympathetic Adrenergic receptors
alpha and beta
-G-couple proteins, G protein is activated and causes changes in the cell
Catecholamines:
NE and E
What is the only neurotransmitter in the parasympathetic system
Ach
-nicotinic receptor on postgang
-muscarinic receptor on target cell
-G-protein couple receptors
T or F: Parasympathetic has no control over contractility of the heart
T: sympathetic controls contractility of heart and diameter of vessels
-(!!) it is through the suppression of sympathetic involvement that certain (NOT all) parasympathetic goals can be accomplished
-while the sympathetic response causes vasoconstriction and dilation to various parts of the body, parasympathetic merely removes the sympathetic control so that all vessels dilate and blood can flow freely and regularly throughout the body
What organs are not controlled by parasympathetic?
Blood vessels
Sweat glands
Other neurotransmitters: Dopamine, Epinephrine, Cotransmitter
Dopamine: important transmitter in the CNS and may be released by some peripheral sympathetic fibers
Epinephrine: released with NE by Adrenal medullary cells (think endocrine)
Cotransmitter: (ATP, Nitric Oxide, GABA)
To reiterate:
Sympathetic uses NE receptors!!
Cocaine:
blocks the re-uptake of NE, which would normally be recycled, thus increasing heart rate significantly (sympathetic overdrive)
Main goals of Sympathetic system:
Increase cardiac output and divert bloodflow to organs in need
-active at all times at low levels
Alpha receptors are usually associated with what?
Vascular smooth muscle
Alpha and Beta blockers
Sympathetic: mostly adrenergic receptors
-blocking one of these (Alpha or Beta) will suppress sympathetic symptoms)
-beta-blockers decrease heart rate (see pwpt), contractility
-effect could be bronchoconstriction/short breath because of common receptor type
-aka don’t give beta blocker for heart to an asthmatic
baroreceptors
-pressure or stretch
-sense blood pressure
Two types of baroreceptors
-Arterial
-cardiopulmonary
arterial baroreceptors
Found on the carotid sinus and aortic arch
-not to be mistaken with body
Aortic arch: join to form part of CN X
Carotid sinus: join to form CN IX (glosso)
where do arterial baroreceptors synapse?
-at the nucleus tractus solitarius of the medulla (brainstem)
-which then relays the info to the cardiovascular centers (found in pons and medulla)
What are the two main Cardiovascular centers?
Vasomotor: vessels
Cardiac control: heart
-autonomic control of cardiac and vascular function
Cardiac Control Center
Cardiac Accelerator Center
-increases HR and contractility via sympathetic Outflow Tract
Cardiac Decelerator
-Decreases HR via parasympathetic Outflow Tract
Baroreceptor Reflex
-sympathetic controls diameter of blood vessels and contractility
-parasympathetic and sympathetic control heart rate
When BP is high, what is the body’s response?
Inhibit sympathetic stimulation, so arterioles and veins dilate
-blood then pools in periphery and less blood is returned to the heart
-HR decreased from sympathetic inhibition and parasympathetic stimulation
-less contractility of heart form inhibition of sympathetic system
-altogether decreases BP
what is renin?
an enzyme
Where are cardiopulmonary baroreceptors and why?
Embedded in the walls of the right atrium, right ventricle, pulmonary artery and veins
These are low pressure areas, so stretch mainly depends on blood VOLUME
Why would the body increase heart rate when we have a high volume?
Can remove volume more quickly by increasing blood flow to kidneys
Kidneys will respond by excreting more Na+ and water to decrease the volume
If blood volume is high…(vagus nerve)
The vagus nerve will send a signal to the hypothalamus to decrease production of ADH
(ADH is responsible for water reabsorption in the kidney)
If blood volume is high, Cardiopulmonary baroreceptors stimulate the secretion of what hormone
ANP (causes renal arterioles to dilate allowing kidneys to receive and filter more blood)
-ANP also inhibits Na and water reabsorption
If blood volume is low:
increase ADH production
less ANP production
Less sympathetic stimulation, so heart rate slows (decreasing blood flow to kidneys)
All of this results in less water and Na secretion which will help increase blood volume
Note: Blood volume is primarily regulated through controlling blood flow to the KIDNEYS
The Vagus nerve (CN X) and the pelvic splanchnic nerves (S2, S3, S4) have their parasympathetic ganglia located where?
Directly in their target organs
Which organs are not controlled by the parasympathetic NS at all?
Blood vessels
sweat glands
The baroreceptors in the aortic arch join to form part of which nerve?
Vagus (CN X)
The baroreceptors in the carotid sinuses join to form part of which nerve?
Glossopharyngeal (CN IX)
What are the most important measurements taken by chemoreceptors?
Hydrogen (pH), oxygen, CO2
-chemoreceptors send info to the brain to keep cardiovascular and respiratory systems balanced
Two types of chemoreceptors?
Peripheral
Central
Where are the peripheral chemoreceptors located?
Located in aortic body and carotid body
Monitor changes in pO2 and pCO2 and pH (metabolic acids like ketones, lactic acid)
*Aortic body chemoreceptors send signals via the Vagus nerve
*The carotid body chemoreceptors send signals via the Glossopharyngeal nerve
What are the first and second most powerful stimuli for breathing?
low O2 levels (pO2 <60) or CO2 levels
Respiratory centers:
autonomic control of breathing
communicated with the cardiovascular centers
POV: you have hypoxemia, hypercapnia, and acidemia. What cardiovascular events happen next?
(low O2, high CO2, low pH)
Chemoreceptors detect these changes and send increased signals to vasomotor centers
-result is vasconstriction in arterioles that lead to peripheral/noncrucial organs, increasing PVR (peripheral vascular resistance and preserving O2 for brain and heart)
-veins constrict causing more blood return to heart
-decrease in metabolic rate to decrease CO2 production
-heart works slowly and less forcefully (which will soon be reversed by pulmonary response, for an end result of increased HR and contractility & increased blood flow to the lungs to help with gas exchange)
What respiratory events happen next?
Stimulating the diaphram causes chest wall muscles to help you breath deeper and faster, causing airways to stretch
How do pulmonary stretch receptors react to dilated airways? How does this impact the cardiovascular response?
Contraction sends signals via the Vagus nerve back to respiratory centers to slow down
also stimulate cardiac accelerator center to increase HR and contractility
Reverses the effect the chemoreceptors originally had
How do pulmonary stretch receptors react to dilated airways? How does this impact the cardiovascular response?
Contraction sends signals via the Vagus nerve back to respiratory centers to slow down
also stimulate cardiac accelerator center to increase HR and contractility
Reverses the effect the chemoreceptors originally had
QUESTION:
So to be clear, the initial cardiovascular response helps preserve O2 for vital organs and increased return to the heart, BUT it also decreases contractility of the heart. The last part is not ideal, so dilation of the airways leads to an increase in forceful breathing, which then stimulates the heart to increase its contractility, thus sending more blood to the lungs to get oxygenated. At this point, is only the HR and contractility undone by the respiratory response? Or are the other impacts also disabled?
Not this deep on the test, but this is kinda confirmed by Ruzga, it’s a matter of time and can’t stay in this state forever
Where are the central chemoreceptors found?
In the brain: clusters of neurons on the ventral surface of the medulla oblongata, near respiratory centers
-bathed in CSF (now we are looking at CSF composition, not blood)
-CSF is composed of gases that are able to pass through the BBB
Where are the central chemoreceptors found?
In the brain: clusters of neurons on the ventral surface of the medulla oblongata, near respiratory centers
-bathed in CSF (now we are looking at CSF composition, not blood)
-CSF is composed of gases that are able to pass through the BBB
peripheral vs central
Peripheral is more sensitive to low O2
Central is more sensitive to pCO2 and pH
-when pCO2 rises in the blood, the molecules rapidly diffuse across the BBB and buildup in CSF
-CSF is mostly H2O, so the CO2 molecules bind and form carbonic acid (H2CO3), which then rapidly breaks down to H+ and HCO3- ions.
-The pCO2 and the now increasing H+ or decreasing pH are picked up by central chemoreceptors which stimulates respiratory center to increase breathing
Central Chemoreceptors and blood flow in the brain
All CO2 that is produced via brain cells will not be removed and will accumulate in the CSF
Central chemoreceptors detect this and send signal to vasomotor center which will decrease blood vessels size and increase the BP
By increasing BP this will overcome the pressure in the CSF and allow blood flow to continue to the brain to remove the CO2 and correct the pH
This increased BP result from increased intracranial pressure is known as the Cushing reaction
(If there is a mass or other intracranial pressure that interferes with blood flow in/out of brain will cause ischemia to the brain)
