Chapter 18 ( nervous regulation of the circulation and rapid control of arterial pressure) Flashcards Preview

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Flashcards in Chapter 18 ( nervous regulation of the circulation and rapid control of arterial pressure) Deck (33)
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How is the sympathetic nervous system distributed?

thoracic nerves and first one or two lumbar nerves


how does the sympathetic nervous system enter circulatoin?

1. via specific nerves that innervate vasculature of internal viscera and heart
2. via peripheral portions of spinal nerves in peripheral areas


what is the only vessel that is not innervated by sympathetic NS?



what does sympathetic stimulation do to small arteries and arterioles?

increase resistance which decreases blood flow to tissues.


what does sympathetic stimulation to large vessels like veins do?

these vessels decrease in volume which pumps more blood to the heart


parasympathetic innervation of heart

Vagus nerve which decreases heart rate and contractility


Where is the vasomotor center?

reticular substance in brain and lower 1/3 of pons


where is the vasodilator area ?

anterolateral part of lower medula. These project upward and inhibit the vasoconstrictor area


Where is the vasoconstricor area?

anterolateral part of upper medula


sympathetic vasoconstrictor tone

continuous firing of vasoconstrictors. ~1-2 per second. They maintain a partial state of contraction


vasomotor center affect on heart

lateral portion of vasomotor center on heart transmits excitatory impulses through sympathetic fibers to the heart and increases heart rate and contractility. Medial portion of vasomotor area sends signals to adjacent dorsal motor nuclei of vagus nerves which transmit parasympathetic impulses to slow the heart.


control of vasomotor center by higher nervous centers

reticular substance of pons, mesencephalon, and diencephalon can excite or inhibit vasomotor area. In general the neurons in the lateral and superior portions of the reticular substance cause excitation. The more medial and inferior cause inhibition.


hypothalamus role on vasomotor center

Causes both powerful excitatory or inhibitory effects on vasomotor center. The posterolateral portions cause excitation and the anterior portion causes mild excitation or inhibition


cerebral cortex role on vasomotor center

many parts can either excite or inhibit vasomotor center



secreted out of vasoconstrictor nerves which acts on alpha adrenergic receptors of vascular smooth muscle( in some tissues it causes vasodilation)
adrenal medullae- these secrete the epinephrine and norepinephrine into the blood.


emotional fainting( vasovagal syncope)

vagus nerve slows heart and vasodilation occurs which causes the fainting.


3 ways to increase arterial pressure

arterioles are constricted, large vessels like veins constrict which causes the heart to pump harder, direct stimulation by autonomic nervous system


rapidity of arterial pressure

can increase pressure 2 times in 5- 10 seconds and decrease pressure by ½ in 10-40 seconds. It is the fastest way of controlling arterial pressure


Baroreceptor arterial pressure control system-

s initiated by stretch receptors called either baroreceptors or pressoreceptors which are located at specific points in walls of several large systemic arteries. A rise in arterial pressure causes them to stretch and send feedback signals through the ANS to reduce arterial pressure.


carotid baroreceptors pathway

via herings nerve, glossopharyngeal nerve, tractus solitarius in medulla


aortic baroreceptors pathway

via vagus nerve, tractus solitarius of medulla.


carotid sinus baroreceptors stimulation

get stimulated at 60 mm Hg and maximize at 180 mm Hg


what causes baroreceptors to respond quicker

a rising pressure


control of arterial pressure by carotid and aortic chemoreceptors

sensative to Oxygen lack, Co2 excess, and hydrogen excess. They excite nerve fibers along the baroreceptor fibers which pass through herings nerves and vagus nerves to vasomotor nerve. They decrease parasympathetic stimulation and increase sympathetic stimulation which increases heart rate and constricts the vessels. ( probably to try and get blood to the tissue thats lacking O2)


when are chemoreceptors most powerfull?

below 80 mm Hg


atrial and pulmonary reflexes

contain low pressure receptors that act like baroreceptors(if 300 ml was inserted into a dogs atria, the atria pressure rises only 15 mmHg. With the arterial baroreceptors removed it rises to 40 mm Hg and with the low pressure receptors removed in rises to 100 mm Hg)


atrial reflex that activates the kidney (volume reflex)

an increase in atrial pressure increases the heart rate as much as 75%. ( 15% from increase in atrial volume and 40-60 % from bainbridge reflex)


what is the bainbridge reflex?

when the atrial stretch receptors stretch and send a signal via vagus nerves to the medulla. Signals are sent back via vagus and sympathetic nerves to increase heart rate and strength of heart contraction


CNS ischemic response

most powerful of all activators of sympathetic vasoconstrictor response. It is only activated when arterial pressure is below 60 mmHg and works its best at 15-20 mm Hg. Its an emergency pressure control system that acts rapidly and very powerfully to prevent further decrease in arterial pressure whenever blood flow to the brain decreases dangerously close to lethal level. Often called the last ditch stand


cushing reaction

CNS ischemic response is initiated when CSF fluid is higher that arterial pressure in the brain. High CSF pressure can squish the brain and its arteries so the response acts as a cushion.