4 - Regulation of Cardiac Function Flashcards
What are the key neural regions for cardiovascular function?
- Reticular Formation - Ventrolateral Medulla / Lower 1/3 Pons
- Hypothalamus - integrates responses
- Cerebral Cortex - Emotion, Anger, Sprinters before race
What area of the cerebral cortex recuits muscles for specific activities–and how is it related to regulation of CV response?
Somatomotor Central Command Center
Functions as a “feed-forward” center to regulatory centers of the medulla
What areas of the medulla/pons function in cooridinated fashio for CV regulation?
- Nucleus Tractus Solitarius (NTS) - sensory area of medulla; receives CN IX / X ; Baroreceptors and Chemoreceptors
- Rostral Ventrolateral Medulla (RVLM) - helps control sympathetic output to heart / blood vessels
What two areas of the NTS project excitatory neurons to?
What type of neurons are the target?
Dorsal Vagal Nucleus, Nucleus Ambiguus
Parasympathetic Neurons
What is the location of the NTS?
What stimulates (+) the NTS?
What are the two targets for the NTS?
How do these targets affect the heart, and vessels?
Medulla
Receptor Afferents (Baro/Chemo Receptors)
NTS Targets:
(+) Vagal (Dorsal Vagal Nucleus/Nucleus Ambiguus)
(-) Sympathetic (RVLM)
Vagal (Dorsal Vagal/Nucleus Ambiguus)
(-) Heart
(-) Sympathetic (RVLM)
Sympathetic (RVLM):
(-) Vagal (Dorsal Vagal / Nucleus Ambiguus)
(+) Vessels
(+) Heart
In what state are neurons controlling sympathetic output to the heart?
How can these be controlled?
What does inhibition result in?
Tonically Active
Controlled via inhibitory neurons from the Nucleus Tractus Solitarius (NTS), in response to afferent receptors (Baro/Chemo)
Inhibition results in vasodilation
What does stimulation of the Dorsal Vagal Nucleus and Nucleus Ambiguus result in?
What is this termed?
What is the normal resting state of these neurons? Why is this the case?
Bradycardia – HR slows
Cardioinhibitory Center
Tonically Active, the heart rate is normally well below its maximum value
Where are cell bodies of parasympathetic which innervate the heart located?
Dorsal Vagal Nucleus
Nucleus Ambiguus
Both in medulla
What is the topographical distribution of the vagus nerve (parasympathetics) to the heart?
Nodes
Myocardium
Right Vagus - Inhibits SA Node (Right Atrium!)
Left Vagus - Inhibits AV Node (more left)
Atrial Muscle innervated by vagal efferents, ventricular myocardium has sparse vagal innervation
What is the main neurotransmitter for parasympathetic action on the heart?
Why don’t these stick around too long at the heart?
Acetylcholine (ACh)
Rapid decay from high concentration of cholinesterase at the SA and AV nodes
Stimulation of what area will induce tachycardia and vasoconstriction?
What is the topographical representation of their effect on the heart?
How does their decay rate compare to parasympathetics?
How are vasoconstrictor effects accomplished?
Rostral Ventrolateral Medulla (RVLM)
SA , AV Nodes
Conduction Pathways
Myocardium
Decay rate is slower than vagal stimulation
Vasoconstrictor effect of sympathetic nerves are mediated by noradrenergic fibers (fibers that release norepinephrine)
Positive vs Negative Chronotropy
Positive vs Negative Dromotropy
Positive vs Negative Inotropy
+ Increases HR
- Decreases HR
- -
+ Increases Conduction Velocity
- Decreases Conduction Velocity
- -
+ Increases Force of Contraction
- Decreases Force of Contraction
How does sympathetics affect:
Chronotropic
Inotropic
Dromotropic
+ , + , +
What is the most important adrenergiv receptor for regulation cardiac function?
How does it compare to other receptors present?
B1 Receptor
B1>B2>a1
What does ACh bind to in the heart?
How does it (parasympathetics) affect:
Chronotropic
Inotropic
Dromotropic
M2 Muscarinic Receptors
Chronotropic - Negative
Inotropic - modest Negative (atria)
Dromotropic - Negative
What determines the intrinsic rate of the heart and what is it?
What is the most important regulator of this?
What is the predominating influence on this in healthy people like yourself?
SA Node, 100 BPM
Autonoic Nervous System
Well think, that’s high. So parasympathetics is the predominating influence
What will impact the heart more, a block of M2 receptors, or a block of B receptors?
M2 (ACh) - Parasympathetics usually keep the HR down from instrinsic 100 BPM
B (Ne) - Sympathetics don’t play as large a role in regulating normal resting HR
What type of receptors are baroreceptors?
Where are they found and how are they stimulated?
Where are they highly focused?
How are these transmitted to the CNS?
What chamber of the heart are these monitoring?
Stretch receptors
Heart and blood vessels, stimulated by distension
Carotid Sinus / Aortic Arch
Gloosopharyngeal Nerve (Carotid Sinus)
Vagus Nerve (Aortic Arch)
Atrial Pressure
How will baroreceptor firing change with blood pressure?
What centers of the medulla are activated by an increase in arterial pressure, and what is the result at the level of the heart?
Clinical: You’re laying down, and suddenly pop up
Direct relationship, increase firing with increase in blood pressure and vise versa
Increase in transmission to Nucleus Tractus Solitarius (NTS)
Inhibit vasoconstrictor center (symp) and activate vagal parasympathetic center–vasodilation of peripheral vessels and decrease in rate of cardiac contraction
- - -
Baroreceptors sense decreased atrial pressure, low firing, decrease NTS activity, sympathetic activity kicks in, HR/Inotropy/Vasoconstriction increase, you don’t pass out
How does temperature affect HR?
How does the thyroid hormone affect HR?
Temperature = direct, increase increase, decrease decrease
Excess thyoid increses cardiac function, decreased thyroid diminishes cardiac function
