Chapter 6 Flashcards
What sensors are involved with regulating blood pressure, blood volume, blood chemistry, and plasma osmolarity?
Blood pressure- baroreceptors, blood volume-volume receptors , blood chemistry(chemoreceptors), and plasma osmolarity-osmoreceptors
What is the general role of peripheral and central receptors?
Peripheral and central sensors work together with the neurohumoral mechanisms to ensure that arterial blood pressure is adequate for perfusing organs. Peripheral sensors such as baroreceptors have afferent nerve fibers that travel to the CNS where their activity is monitored and compared against a set-point for pressure.
What is a “set point”?
An optimal point which if deviated from requires action by select neurohumoral controls
What are the primary regions of the central nervous system involved in cardiovascular regulation?
Medulla oblongata (within brainstem), hypothalamus and the cortical regions work together to regulate autonomic function
From what region of the brain do the parasympathetic vagal fibers innervating the heart originate
from?
The medulla contains the cell bodies for the parasympathetic (vagal) and sympathetic efferent nerves that control the heart and vasculature.
What is the dorsal vagal nucleus and the nucleus ambiguus?
The parasympathetic vagal fibers innervating the heart originate from cell bodies located within the medulla of the brainstem. These cell bodies are found in collections of neurons located here
What is the effect of increased activity of these nuclei?
Reduces SA nodal firing (neg. chronotropy) and slows AV nodal conduction (neg. dromotropy)
What is meant by the term “vagal tone”?
Tonically active, resulting in the resting heart rates being significantly below the intrinsic firing rate of the SA nodal pacemaker
What is meant by the term “intrinsic firing rate”?
How often the SA node spontaneously fires
Describe the anatomy, innervation, and effects of efferent vagal nerve fibers.
Efferent vagal fibers exit the medulla as the tenth cranial nerve and travel to the heart within the left and right vagus nerves. Branches from these nerves innervate specific regions within the heart such as the SA and AV nodes, conduction pathways, atrial myocytes, and the coronary vasculature. The preganglionic efferent fibers synapse within or near the target tissue and form small ganglia, from which short postganglionic fibers innervate specific tissue sites.
What are postganglionic fibers and what role do they play in tissue innervation?
Postganglionic fibers innervate specific tissue sites.
Which vagal nerve primarily innervates the SA node?
Right vagus
Which vagal nerve primarily innervates the AV node?
Left vagus
How do efferent parasympathetic fibers cause direct vasodilation?
Direct vasodilation by parasympathetic activation in some tissues is achieved through the release of Ach, which binds to muscarinic receptors on the vascular endothelium to cause vasodilation through the subsequent formation of nitric oxide
How do efferent parasympathetic fibers cause indirect vasodilation?
Parasympathetic stimulation causes indirect vasodilation in some organs by stimulating nonvascular tissue to produce vasodilator substances such as bradykinin, which then binds to vascular receptors to cause vasodilation
Do parasympathetic nerves primarily regulate blood flow within specific organs, regulate systemic vascular resistance, or regulate arterial blood pressure?
Any existing parasympathetic nerves primarily serve to regulate blood flow within specific organs and do not play a significant role in the regulation of systemic vascular resistance and arterial blood pressure
Draw a schematic representation of autonomic sympathetic and vagal interconnections within the central nervous system.
A
Where does sympathetic adrenergic control of the heart originate from?
Neurons found within the medulla, the most important of which are located in the rostral ventrolateral medulla (RVLM)
What are the effects of increased stimulation of sympathetic neurons originating from the medulla (and the rostral ventrolateral medulla)?
Produces cardiac stimulation and systemic vasoconstriction. Sympathetic neurons within the RVLM have spontaneous AP activity, which results in tonic stimulation of the heart and vasculature
What would occur with sympathetic denervation of the heart and vasculature?
Acute sympathetic denervation of the heart and systemic blood vessels usual results in cardiac slowing and systemic vasodilation
At lower heart rates, what are the differences in sympathetic tone in the heart versus the vasculature?
At low resting heart rates, the effects of sympathetic denervation on the heart rate are relatively small because the heart is under a high level of vagal tone and relatively weak sympathetic tone. In contrast, sympathetic vascular tone is relatively high in most organ circulations, therefore, sudden removal of sympathetic tone produces significant vasodilation and hypotension.
Describe the anatomical path of sympathetic nerve axons that leave the medulla.
Axons from sympathetic neurons leave the medulla and travel down the spinal cord and synapse within the intermediolateral cell column of the spinal cord, and then exit at specific thoracolumbar levels (T1-L2)
Draw a schematic representation of sympathetic and vagal innervation of the heart and circulation.
A
Are sympathetic preganglionic nerve fibers typically shorter or longer than parasympathetic preganglionic nerve fibers?
Sympathetic preganglionic nerve fibers are short compared to preganglionic parasympathetic fibers
What are paravertebral ganglia and vertebral ganglia?
Paravertebral ganglia (cervical, stellate, and thoracolumbar sympathetic chain) are located on either side of the spinal cord Prevertebral ganglia are located within the abdomen (celiac, superior mesenteric, and inferior mesenteric ganglia)
Are sympathetic postganglionic nerve fibers typically shorter or longer than parasympathetic postganglionic nerve fibers?
Postganglionic sympathetic fibers are long compared to postganglionic parasympathetic fibers
Do postganglionic sympathetic fibers innervate arteries? Veins? Capillaries?
Innervate arteries and veins while capillaries are not innervated
When postganglionic sympathetic fibers innervate vessels, in what tunic of the vessel do they connect with the vessel?
Small branches of these efferent nerves are found in the adventitia layer of the blood vessels
What are varicosities?
Small enlargements along the sympathetic nerve fibers, provide the site of neurotransmitter release
What components of the cardiovascular system do postganglionic sympathetic fibers innervate?
SA and AV nodes, conduction system, cardiac myocytes and coronary vasculature
What will activation of postganglionic sympathetic fibers do to chronotropy, dromotropy, and inotropy?
Sympathetic activation increases chronotropy, dromotropy, and inotropy
Does sympathetic activation cause vasodilation or vasoconstriction in the coronary vasculature?
Why is this a paradox?
Vasoconstriction. It is a paradox because increases cardiac activity produces metabolic coronary vasodilation that overrides that direct sympathetic vasoconstrictor effects on the coronary vesseles
In the body organs, what does sympathetic activation of resistance vessels do to vascular tone?
Contributes to the vascular tone
What happens to blood flow when an α- adrenoceptor drug is administered?
Blood flow increases, the amount of which depends upon the degree of sympathetic tone and the strength of local autoregulatory mechanisms that will attempt to maintain constant blood flow.
Explain how standing up serves as an example of sympathetic and vagal reciprocity.
Baroreceptor reflexes cause the RVLM to increase sympathetic outflow to stimulate the heart (increase HR and inotropy) and to constrict the systemic vasculature
At rest, which division of the central nervous system (vagal or sympathetic) is more dominant in the heart?
Vagal influences are dominant over sympathetic influences in the heart
What is the flight-or-fight response?
Coordinated responses including sympathetic mediated tachycardia, increased inotropy, catecholamine releases and systemic vasoconstriction. Hypothalamic activation of sympathetic neurons within the RVLM and inhibition of vagal nuclei
What are the effects of sudden fear, strong emotion, fear, and anxiety on the cardiovascular system?
Can sometimes cause vagal activation leading to bradycardia, withdrawal of sympathetic vascular tone and fainting
What is vasovagal syncope?
fainting
What neurotransmitter is released from sympathetic efferent nerves to the heart?
Norepinephrine
What postjunctional receptors for this neurotransmitter are located on the heart?
What postjunctional receptors for this neurotransmitter are located on the heart?
List the order of functional importance for the three postjunctional adrenoceptors in the heart.
B1>B2>A1
What are the effects of sympathetic stimulation on cardiac chronotropy, dromotropy, and inotropy?
Increase inotropy, chronotropy, and dromotropy
What prejunctional receptors can bind to this neurotransmitter?
A2-adrenoceptors
What are the effects of this neurotransmitter binding to prejunctional receptors?
inhibit NE release through a negative feedback mechanism
What neurotransmitter is released from parasympathetic (vagal) efferent nerves to the heart?
ACh
What postjunctional receptors for this neurotransmitter are located on the heart?
M2, muscarinic, principally in the nodal tissue and in the atrial myocardium
What are the effects of vagal stimulation on cardiac chronotropy, dromotropy, and inotropy?
Decreased inotropy, chrontropy, and dromotropy
What prejunctional receptors can bind to this neurotransmitter?
M2, muscarinic
What are the effects of this neurotransmitter binding to prejunctional receptors?
Inhibit release of NE
What signal transduction pathways are activated by adrenergic and muscarinic receptor stimulation?
Gi-protein/cAMP
What neurotransmitter is released from sympathetic efferent nerves to the blood vessels?
NE
What postjunctional receptors for this neurotransmitter are located on the blood vessels?
A1
List the order of functional importance for the three postjunctional adrenoceptors in blood vessels.
A1>A2>B2