The Autonomic Nervous System II Flashcards
Includes a receptor (e.g. chemoceptors and baroceptors), afferent neurons to the CNS, usually one or more CNS interneurons, and pre- and post-ganglionic ANS efferents
An autonomic reflex
Autonomic reflexes control several vital functions such as detecting changes in
Blood gases, BP, and volume status
The electrical activity of the heart is regulated by the
ANS
What are the effects on heart rate of
- ) Elevated SNS tone
- ) Elevated PSNS activity
- ) Heart rate increases
2. ) Heart rate decreases
The PSNS controls resting heart rate. What effect would down regulation of PSNS activity have?
Increase resting heart rate
SNS innervation is abundant in the heart, where as PSNS innervation is sequestered to the
SA and AV nodal tissues
The Nucleus of tractus solitarius (NTS), nucleus ambiguous (NA), and dorsal motror nucleus of the vagus (DMV) are specific nuclei in the medulla that are the origin of ANS control of
Cardiac Function
The DMV and NA are subdivided into three key centers that control
HR and vasomotor function
The DMV and NA are subdivided into three key centers that control HR and vasomotor function, these are the
- ) Cardioacceleratory center
- ) Cardioinhibitory center
- ) Vasomotor center
To increase SNS tone, which neurotransmitters activity is increased within the SNS regions of vasomotor and cardioacceleratory centers?
Glutamine and Substance P
When glutamine and substance P are activated in the SNS cardioacceleratory and vasomotor centers, which neurotransmitter is activated in the PSNS cardioinhibitory centers?
The inhibitor GABA
The result of this coordinated action is an
- ) Increase in SNS tone
2. ) Decrease in PSNS tone
What would we expect to see if we wanted to decrease HR and BP?
GABA and Substance P are upregulated in SNS cardioinhibitory and vasomotor centers respectively
Glutamine is upregulated in PSNS cardioacceleratory centers
Within the heart, there are two specific regions of cardiac neuromuscular electrogenic tissue. What are they and where are they located?
- ) SA node: in the right atrium
2. ) AV node: Junction between right and left atria and ventricles
The SA node is expressed by
Type β1 adrenoreceptors and CM2
The fundamental circuitry is as follows: ANS vagal efferents innervate the
SA node
SA nodal activity controls
AV nodal activity
AV nodal activity in turn initiates the depolarization of main conduction tracts (bundle of His and Purkinje fibers) that are coupled to
Ventricular myocytes
Decreased blood volume induces a change in BP. BP drops below approximately 60 mm Hg. This is detected by the
Low pressure baroreceptors within the atria
In response to the low BP, afferent (sensory) vagal fibers signal the ANS centers within the
C1 area of the medulla (cardioacceleratory center)
Medullary fibers release excitatory neurotransmitters that then activate
SNS efferent
Preganglionic SNS efferents form polysynaptic connections with post-ganglionic SNS efferents. These synapses are located within the
Nucleus of Tractus Solitarius, a part of C1
Activation of cholinergic-nicotinic receptors within the post-synaptic membrane induces activation of
Ligand gated Na+ channels
AP reaches the postganglionic nerve terminus and causes Ca2+-dependent release-coupling of vesicles containing
Norepinephrine
Norepi binds and activates which two things?
- ) a1 adrenoreceptors in vascular smooth muscle
2. ) B1 adrenoreceptors in cardiac nodal and muscle tissue
The ensuing combination of accelerated heart rate (chronotropy), increased cardiac contractile force (inotropy), and vasoconstriction will
Increase BP
If high pressure baroreceptors are activated, sensory vagal and glossopharyngeal tracts running from the carotid sinus and aortic arch are activated. These fibers
innervate
Inhibitory interneurons within the medulla (C1) region
These inhibitory fibers suppress activity of the
SNS efferents
Without SNS tone, there is an alleviation of
a1 vasoconstricitive response
Concomitantly, populations of stimulatory interneurons induce activation of
PSNS preganglionic efferents
Then post-ganglionic vagal efferents are activated; these fibers innervate cardiac SA nodal tissue; the result is a
Decrease in HR
A rare catecholamine-secreting neuroendocrine tumor which arises from the adrenal medulla
Pheochromocytoma
Usually secrete both epi and norepi in an episodic manner
Pheochromocytomas
What are the effects of excessive
- ) Norepinephrine
- ) Epinephrine
- ) Hypertension
2. ) Tachyarrhythmias
What can we measure to test for pheochromocytomas?
- ) Plasma and urine catecholamines
- ) Urinary metanephrines
- ) Urine vanillylmandelic acid
- ) Plasma-free metanephrines
The level of plasma fractionated free metanephrines (normetanephrine and metanephrine) is the most sensitive test for
Secretory Pheochromocytomas
Once identified and localized using MRI or CT scan, a
pheochromocytoma can often be surgically removed using
Laparascopy