T2: Heart Innervation Flashcards
What is an animals resting heart rate dependent on?
- body size
- metabolic rate
- autonomic balance
- species characteristics
Why does data on heart rates differ?
due to the differing environmental conditions
Where does the innervation of the heart primarily arise from?
AUTONOMIC NERVOUS SYSTEM:
- sympathetic nerves
- parasympathetic nerves (vagus nerve)
What does the autonomic nervous system innervate? Why?
- atria and ventricles
- to modulate their function and coordination
What sympathetic nerves positively impact heart actions?
- chronotropic (rate of contraction)
- inotropic (force of contraction)
- bathmotropic (increase in excitability)
- dromotropic (rate of conductivity)
What do chronotropic nerves impact?
rate of contractions
What do inotropic nerves impact?
force of contraction
What do bathmotropic nerves impact?
increase in excitability
What do dromotropic nerves impact?
rate of conductivity
What is the function of sympathetic stimulation?
- increases the SA node discharge
- increases AV conduction
- increases atrial and ventricular contractility
What does sympathetic stimulation do to: contractility, frequency, conduction velocity and irritability?
increases!!
What cellular mechanisms exist for sympathetic (SNS) nervous system actions?
- catecholamine norepinephrine
Explain the functioning of norepinephrine.
- catecholamine norepinephrin released
- norepinephrin binds to adrenergic receptors (alpha/beta(main))
- adenylyl cyclase is activated
- enhancement of SA node ion channels rhythmicity
What are the major types of adrenergetic receptors in cardiac tissue?
- alpha
alpha 1
alpha 2 - beta (predominates):
beta 1
beta 2
What is the function of beta 1 adrenergic receptors?
- inotropic responses
- chronotropic responses
What is the function of beta 2 adrenergic receptors?
mediate:
- glycogenolysis
- vasodilation
What is the function of alpha 1 adrenergic receptors?
minor role (small density)
What is the function of alpha 2 adrenergic receptors?
- inotropic responses
What ions, specifically, depolarize and hyperpolarize the SA node?
depolarization: Ca2+
hyperpolarization: K+
Explain the parasympathetic NS control of the heart.
right and left vagus nerves differentially innervate the SA node!
What happens when the right vagus nerve is stimulated?
- decreases firing rate of the SA node
- decreases heart rate!
- negative inotropic effects excerted in the atria
What happens when the left vagus nerve is stimulated?
- inhibits AV conduction
- produces AV block
negative chronotropic, negative inotropic and negative dromotropic action
What does vagal stimulation cause?
- slows discharge rate of the SA node
- slows/blocks AV conduction
- decreases atrial contractability
- decreases ventricular contractability
What do vagus nerves do at rest?
exert a continuous/tonic restraint on the heart
What happens to the heart rate when the vagus nerves are cut or cooled?
heart rate becomes greatly accelerated
What alters vagal activity?
physiological and pathological conditions
What nervous system controls the heart?
autonomic nervous system
Do the sympathetic and parasympathetic nervous systens oppose each other or work together?
OPPOSE EACH OTHER!
What is the overall action of the sympathetic vs parasympathetic activation?
sympathetic- increases heart rate
parasympathetic- decreases heart rate
What happens when you apply pressure on the eyeball? (oculocardiac reflex)
slows the heart rate
What happens when you inhale irritating vapours (eg. anasthetics)?
reflex inhibition of the heart
- extrasystole
- bradycardia
What is the function of baroreceptors?
detect changes in blood pressure at:
- the aortic arch
- the carotid sinus
What is the relation of pulse with arterial blood pressure?
INVERSELY PROPORTIONAL!
- a rise in pressure causes a decrease of heart rate
- a fall in pressure causes an increase in heart rate
What happens to heart rate when pressure is increased in the carotid sinus/aortic arch?
heart rate is reduced with an increase in pressure!
What is the reflex called which explains the inverse relationship of heart rate with arterial blood pressure?
baroreflex
Explain the movement of ions in the sodium potassium pump.
- 3 Na+ out
- 2 K+ in
What type of feedback response does the baroreflex have?
negative feedback response
Where are chemoreceptors located?
next to baroreceptors in:
- carotid bodies
- aortic bodies
When do chemoreceptors send signals to the cardiovascular center?
- low O2 hypoxia
- high CO2 hypercapnia
- high H+ acidosis
What is the “chemoreflex”?
heart rate altering by arterial blood gases
What does the chemoreflex activation do to respiratory rate and depth?
- elevate respiratory rate
- elevate respiratory depth
State examples of hormones affecting the heart.
- epinephrine
- norepinephrin
- glucagon
- mineralocorticoids
- ACTH
- vasopressin
- angiotensin I
- angiotensin II
- thyroxine
What type of effect (direct or indirect) does oxygen, carbon dioxide and pH have on the cardiorespiratory system? How?
- both! (direct and indirect)
- via actions on the carotid body and central chemoreceptors
How does hypoxia and hypercapnia affect cardiac contractibility?
depresses cardiac contractability
hypoxia- too little oxygen
hypercapnia- too much carbon dioxide
