5- Nervous regulation of the circulation and rapid control of arterial pressure

Question 1

what happens when someone stand up quickly after lying down?

Answer 1

• cardiovascular reflexes act to maintain blood pressure

- constricting arterioles and venules and increasing heart rate and cardiac contractility

Question 2

Global cardiovascular functions of nervous system

Answer 2

1. nervous control is important in redistributing blood flow
2. nervous control is important in heart rate and pumping action of the heart
3. neural reflexes are important for the rapid control of arterial pressure

Question 3

Two important concepts to understand about neural regulation

Answer 3

1) medulla to the pons to the cortex sets a “baseline” level of sympathetic outflow to the blood vessels and heart.
This outflow and the resulting constriction it causes (sometimes referred to as “sympathetic tone” or just “tone”) sets a baseline level of blood pressure. (120/80)

2) The sympathetic outflow and thus the blood pressure is modulated around this baseline by a set of reflexes, collectively known as the baro-reflexes

Question 4

heart rate and pumping ability

Answer 4

inversely related to one another

Question 5

what neural system drives heart rate

Answer 5

parasympathetic system and the SA node

-BUT pumping of the heart has to do with contractility of the LV and sympathetic influences

so BOTH

Question 6

vasomotor center

Answer 6

• responsible for setting overall level of blood pressure
• sets sympathetic tone
• sympathetic and parasympathetic integrative center
• sympathetic outflow arises here and run in spinal column and exit through thoracic and lumbar spinal nerves

Question 7

vagus nerve and heart

Answer 7

mainly parasympathetic

Question 8

sympathetic innervation of systemic circulation

Answer 8

arteries: change total peripheral resistance (also diameter and volume on a lesser scale)
veins: change volume

sympathetic innervation activation causes constriction of smooth muscle which results in constriction and decreases in compliance

Question 9

what happens to stroke volume when you constrict the veins

Answer 9

increases stroke volume cause more blood gets pushed back to the heart

Question 10

what happens to stroke volume when you constrict the arteries

Answer 10

decreases stroke volume cause more blood gets pushed into the veins

Question 11

reticular substance and regulation of circualtion

Answer 11

• lateral and superior: excitation

- medial and inferior: inhibition

Question 12

hypothalamus and regulation of circulation

Answer 12

• posterior-lateral: mainly excitation

- anterior: mild excitation or inhibition

Question 13

motor cortex and regulation of circulation

Answer 13

-excitation or inhibition depending on region stimulated

Question 14

what happens when you block sympathetic system (CV)

Answer 14

blood pressure drops cause you’d be cutting off the sympathetic tone which requires a small amount of sympathetic stimulation

Question 15

baro-receptors

Answer 15

CV system (mainly brainstem) has regions that sense blood pressure

• main purpose is to maintain constant blood pressure on a moment to moment basis, but NOT setting long-term level of average bp (someone with denervated baroreceptors will have same average bp)
• they are stretch receptors in walls of certain blood vessels (more stretch = more activity)

-stretch receptors are rate sensitive so the impulses occur at the
beginning of the rise in pressure

-At lower pressures activity in the sympathetic sensory afferents is “entrained” to
the pulse.

Question 16

most important location of baro-receptors

Answer 16

• in carotid sinuses (at branch point of internal and external carotid artery in neck) and the aortic chest.
• send afferent nerves to the brainstem via vagus nerve (aortic) and the glossopharyngeal nerve (carotids)

Question 17

carotid sinus vs carotid body

Answer 17

carotid sinus: baro-sensitive, blood pressure
-when pressure here goes up, muscle nerve activity goes down (less constriction of arterioles and less resistance and HR decreases) which lowers bp

carotid body: chemo-sensitive, senses blood gases like O2 and CO2

-if carotids are clamped down then bp increases drastically cause they arent getting info from the body so they increase bp cause they think there is none

Question 18

x-axis: arterial bp

y-axis: number of impulses from carotid sinus nerves per second

Answer 18

• sigmoidal curve
• most sensitive when a small stretch makes a big change in bp
• firing saturates and you can no longer reach a higher level of action potentials firing
• but the system cant tell the difference b/w anything too low or too high cause the reflex can no longer control bp at that level (levels change per person)

Question 19

when mean pressure rises what happens to the number of impulses per peat?

Answer 19

it increases

Question 20

what happens when mean pressure gets VERY high?

Answer 20

number of impulses is saturated and the reflex can no longer control blood pressure above this level

Question 21

what type of interneurons are in the reflex arch of the central nervous system?

Answer 21

inhibitory