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67 Cards in this Set
- Front
- Back
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3 Major functions accomplished by nervous regulation of circulaton:
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1. Global functions like redestribution of blood to the body
2. Alteration of the heart's pumping activity 3. Rapid control of systemic arterial pressure |
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Most important component of ANS regulating circulation:
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Sympathetics
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Main function of Parasympathetics in circulation:
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Regulating heart function
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What do Sympathetic nerves innervate?
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-Internal viscera
-Heart -Vasculature |
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What Blood vessels are innervated by sympathetic nerves?
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All but microarterioles, capillaries, or precapillary sphincters.
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What effect do sympathetic nerves have on small arteries and arterioles?
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Increase Resistance
Decrease rate of bloodflow |
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What effect do sympathetic nerves have on Large veins?
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Decreased Volume to push blood into the heart (increase venous return).
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What is the function of the Parasympathetics?
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Control of the heartrate via the Vagus Nerve.
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How specifically does Sympathetic innervation affect the heart?
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Via Norepinephrine on Muscarinic receptors, it has 2 effects:
1. Increased contractility 2. Increased heartrate |
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What are the principle nerve fibers carried by the Sympathetic nerves to vessels?
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-Vasoconstrictor fibers
(Few Vasodilator fibers) |
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Where i the sympathetic vasoconstrictor effect most powerful?
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-Kidneys
-Intestines -Spleen -Skin |
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Where is the sympathetic vasoconstrictor effect least powerful?
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-Muscle
-Brain |
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What controls the Vasoconstrictor system?
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The vasomotor center in the brain
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Wher in the brain is the Vasomotor Center?
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Bilaterally - in the lower 1/3 of the pons, and reticular substance of medulla.
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What types of signals are transmitted from the Vasomotor center in the brain?
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-Parasymp outflow via Vagus to the heart
-Symp outflow via spinal cord and peripheral nerves to all vessels except tiny ones. |
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For sympathetic heart innervatn:
-Neurotransmitter -Receptors -Effect |
NT = NE
Rec = Beta1 Effect = Incr HR + Incr contractility |
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3 Distinct Areas identified in the Vasomotor Center:
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1. Vasoconstrictor (C1)
2. Vasodilator (A1) 3. Sensory area (A2) |
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Where is the Vasoconstrictor area? What is its output?
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Anterolateral Upper Medulla - gives Sympathetic output
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Where is the Vasodilator area?
What is its output? |
Anterolateral Lower Medulla
Inhibits Vasoconstrictor |
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Where is the Sensory area?
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In the NTS - Nucleus tractus solitarii
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What is the NTS function?
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Recieves sensory signals from Vagus and Glossopharyngeal nerves from baroreceptors and Controls areas C1 and A1
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What is the function of the Cardiac center?
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Control of heart rate and contractility
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3 Important areas of the brain important in nervous reg of circulation:
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1. Reticular substance
2. Hypothalamus 3. Motor cortex |
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What is the normal state of blood vessels?
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Partially contracted - via Vasomotor Tone
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What is responsible for Vasomotor Tone?
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Continual firing of Sympathetic Vasoconstrictor Tone from the Vasoconstrictor Center.
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What happens if you give an animal total spinal anesthesia?
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Their blood pressure drops dramatically due to loss of vasomotor tone.
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What happens if you inject Norepinephrine in that animal a few minutes later?
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This being the principle NT responsible for vasomotor tone, arterial pressure rose for 1-3 minutes until all NE diffused.
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What portion of the Vasomotor center sends symp impulses to the HEART?
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Lateral portions
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What portion of the Vasomotor center sends signals to the heart for decreased heart pumping?
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MEDIAL portions - signal adjacent dorsal motor nuclei of the VAGUS nerves.
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On what receptors does NE act to cause vasoconstriction?
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Alpha-1
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What are the 2 principle controllers of Mean Arterial Pressure?
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MAP = TPR x CO
-Total peripheral resistance -Cardiac output |
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How can you change MAP? 3 ways:
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1. Increase TPR by constricting arterioles
2. Constricting Veins to increase venous return 3. Change CO by increasing HR and contractility |
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What is the most important thing to remember about nervous control of BP?
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IT is by far the most rapidly responding controller of BP - both positive and negatively.
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What is the most important feedback mechanism for controlling BP w/ the ANS?
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Baroreceptors
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2 Sites of Baroreceptors:
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1. Carotid sinus
2. Aortic arch |
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What nerves transmit fibers from
-The carotid sinus -The aortic arch |
Carotids: Hering's nerve
Aorta: Vagus nerves |
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Where are the signals from the carotids transmitted to?
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-Glossopharyngeal nerves via Hering's nerves -> NTI
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Where are the signals in the aortic arch transmitted to?
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-Vagus nerves to NTI
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To what pressure range do Carotid baroreceptors respond? How are aortics different?
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Carotids: 60 mm Hg - 180 mm Hg
Aortics: respond to CHANGES in pressure |
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Where is the sensitivity of baroceptors highest?
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Right around where it needs to be; from 60-180
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What determines the intensity with which a baroceptor is stimulated?
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The nature of the stimulus:
-if pressure is CHANGING it will stimulate with twice as much intensity. |
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What happens when carotid baroceptors detect an increase in BP?
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It increases the rate of firing which results in:
1. Inhibiting of the vasoconstrictor center 2. Activation of the parasymp vagal center |
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What are the net effects in the from a baroceptor stimulus?
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1. Vasodilation
2. Decreased HR and contractility |
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What will happen if you take out (occlude) the carotid arteries?
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The vasomotor center will become very active and try to increase aortic arterial pressure b/c it lacks their signal.
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What happens when you remove the occlusion?
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Blood pressure returns to normal b/c it rises again in the carotids.
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In what "code language" do the baroreceptors speak?
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Intensity of stimulus = frequency of firing - the more CHANGE in BP, the stronger stim.
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What kind of a curve is generated for that 'code'?
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Change in impulse frequency
---------------------------slope Change in Blood Pressure (Plot I vs. P) |
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On the Baroreceptor impulse vs. BP plot what does the plateau mean?
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All baroreceptors are stimulated and firing; no more intensity can be achieved.
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What is the relationship between the carotid distending pressure, muscle sympathetic nerve activity, and cardiac RR interval?
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As pressure increases, sympathetic nerve activity decreases, and RR interval goes up because it's 1/HR and HR goes down.
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Why does HR go down when BP goes up?
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Because the signal is sent to the vasomotor center inhibiting sympathetics and exciting parasympathetics (vagal).
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How does baroreceptor regulation act in long-term changes in BP?
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The receptors reset themselves so that they can still do their job even if baseline BP is now 130 instead of 100 for example.
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What do Chemoreceptors sense?
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-O2 LACK
-Co2 EXCESS -H+ EXCESS |
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Where are chemoreceptors located?
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About the same place as baroreceptors.
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How is chemoreceptor stimulation related to blood pressure?
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When MAP falls O2 will lack and CO2 and H+ will be in excess.
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What is the vasomotor center response to chemoceptors?
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Stimulates Sympathetic output
Stimulates Vagal output too! |
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So what is the net effect of Vasomotor stimulation by chemoreceptors?
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An increase in MAP
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What BP detectors are in the Atria and Pulmonary artery?
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LOW-bp detectors - "low" because the atria and pulm circ are low pressure areas.
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What triggers the low BP detectors in the Atria/Pulm A?
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Increased circulation through the pulmonary system
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What is the response to low-pressure receptor stimulus?
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-Decrease secretion of ADH
-Increased GFR -Decreased Na reabsorption To get the BP to go down |
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How does stimulus of the Atria stretch receptors effect the kidneys?
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It increases dilation of the afferent glomerular arterioles
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What happens in the brain when cerebral blood flow is reduced? (ischemia)
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Buildup of CO2 which stimulates the vasomotor center to increase arterial pressure.
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What is the nature of this stimulus?
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One of the STRONGEST stimulus that will ever reach the vasomotor center - but RARE
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When is the CNS ischemic response employed?
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Only in emergency
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What is the mechanism of the CNS ischemic response?
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1. CNS ischemia
2. Increased CO2 3. Stimulates vasomotor center 4. Respond w/ increased MAP |
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What is the threshold low for activation of the CNS ischemia response?
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60 mm Hg
-Best is at 15-20 |
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What is the Cushing reaction?
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A response to high CSF pressure that is cutting of cerebral bloodflow - Cushing response is to increase MAP until it exceeds the CSF pressure and allows bloodflow.
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How does prolonged ischemia effect the vasomotor center?
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Depresses it
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