Autonomic Nervous System Effects on Circulation

Question 1

Sympathetic Innervation in Blood Vessels

Answer 1

Innervate ALL vessels EXCEPT capillaries, precapillary sphincters, and metarterioles

Vasocontrictor nerve fibers (especially effective in the kidneys, gut spleen and skin

Release Norepinephrine that activate alpha-adrenergic recpetors on smooth muscle cells

This impulse ALSO signals the adrenal medulla to produce more norepinephrine and epinephrine

Question 2

Parasymapthetic Innervation

Answer 2

VERY SMALL

Decrease heart rate
decrease contractility slightly in heart muscle

Question 3

Sympathetic Innervation…

Answer 3

increases Arterial P (Cardiac Output x Peripheral Resistance) by:

1) constricting almost all arterioles in the body = inc in preripheral reisitance (alpha receptors)
2) Constricitng large veins = inc in venous return = inc in cardiac output AND dec compliance (alpha receptors)
3) stimulating heart to increase heart rate and contractility = inc in cardiac output (beta receptors)

Question 4

Vasomotor Center

Answer 4

Collection of cell bodies in the medulla oblongata the controls innervation of the heart

Importatn areas = vasoconstrictor region, cardiac region, and sensory region

Question 5

Vasoconstrictor Region of the Vasomotor Center

Answer 5

Continuous signal transmitted to sympathetic nerve fibers = impulse firing continuously = sympathetic tone

impulses maintain partial state of contraction = in smooth muscle cells contracting = vasomotor tone

Question 6

Cardiac Centers

Answer 6

Cardiac Accelerator Areas = transmits signal to regulate sympathetic Nerves ( Norepinephrine activating beta adrenergic receptors)

Cardioinhibitory Area = dorsal motor nuclei of vagus nerve (transmits parasympathetic impulses to heart through the vagus nerve; acetylcholine activating muscarinic receptors

Question 7

Sensory Area of the Vasomotor Center

Answer 7

located in the nucleus tactus solitarius (NTS)

Receives sensory information from the baroreceptors

Motor output is then achieved through the Vasoconstrictor region, and the cardiac centers producing relfex mechanims for circulation

Question 8

Reflex mechanisms for maintaining arterial P

Answer 8

Baroreceptor reflex, chemoreceptor reflex, atrial and pulmonary reflex, central nervous system ischemic response

Question 9

Baroreceptors

Answer 9

stretch receptors located in the carotid sinus and aortic arch

sensory afferents (back to CNS)

terminate in NTS

Question 10

Barorectptor Reflex

Answer 10

Senses P change = sends signal to CNS = Sympathetic and parasympathetic impulses bring P back to set point

Buffer function (reduces changes from moment to moment and NOT LONG-TERM)

Question 11

What happens to arterial P and what is the body’s response when a dog is hit by a car and hemorrhaging

Answer 11

Arterial pressure decreases due to decrease of blood volume

Body’s repsponse = Baroreceptors signal = excitement of vasoconstrictor areas of the medulla and inhibition of the vagal parasympathetic center:

1) vasoconstriction of veins and arterioles throughout the peripheral circulation in order to increase resistance
2) Increase in rate of heart and strength of contraction to increase cardiac output

INCREASES ARTERIAL P

Question 12

Increase in Arterial P = ?

Answer 12

Baroreceptors respond = send signal to NTS = inhibition of vagoconstrictor areas and excitement of the vagal parasympathetic center:

1) Vasodilation of veins and arteriole throughout the peripheral circulation in order to decrease resistance
2) Decrease in heart rate and strength of contraction to decrease cardiac output

Question 13

Lying down to standing up = ?

Answer 13

Decrease in arterial P

Question 14

Carotid and Aortic Chemoreceptors

Answer 14

Chemosensitive Cells in carotid bodies and aortic arch detect decrease in O2, excess of CO2 and for the H+ ions excess and are stimulated when P falls below 80 mmHg

Sensory afferents (to CNS)

Causes excitation of vasomotor center and sympathetic impulses are sent out to increase BP

Question 15

Baroreceptors are more important for… and chemoreceptors are more important for…

Answer 15

Cardiac control

Respiratory Function

Question 16

CNS Ischemic Response

Answer 16

Emergency P Control System that only turns on with a large decrease in arterial P (below 60mmHg); maximum activation occurs between 15 and 20 mmHg

1) Turns on when baroreceptors cannot balance P and is due to a decrease of blood flow to the brain’s VMC and an increase in CO2 concentrations = cardiac ischemia
2) causes a direct activation of the Vasoconstrictor and cardiacaccelerator neurons in VMC = increase in sympathetic activity = closes off blood to different organs

Greatest activator of sympathetic vasoconstrictor system

Question 17

Activation of Kidneys

Answer 17

Detected by low P receptors in atria and pulmonary arteries

minimize arterial P by detecting changes in blood volume:

1) Blood volume increases
2) Atrial Stretch increases
3) decrease in renal sympathetic activity and increase in atrial natriuretic peptide (heart’s endocrine function)
3) increase in sodium and water excretion

Question 18

Increase in atrial stretch causes…

Answer 18

Increase in kidney activity to decrease atrial P

Increase in heart rate due to inc in heart contractility due to VMC center sympathetic signals

AFFECTS HEART NOT VESSELS

Question 19

Vasovagal Syncope

Answer 19

Emotional stress = signalling from the cortext to the hypothalamus to the medulla:

1) Decreased sympathetic output = decrease in total peripheral resistance
2) Increase in vagal output = decrease in venous return and cardiac output

BOTH cause decrease in arterial P = dec in cerebral blood flow = loss of consciousness