Lecture 18 - The Baroceptor Reflex Flashcards
What is arterial blood pressure controlled by
Cardiac output, total peripheral resistance and blood volume
How is arterial blood pressure regulated short term
Neuronal mechanisms
How is arterial blood pressure regulated long term
Hormonal mechanisms
Baroreceptors found where monitor arterial pressure
The aortic arch and carotid sinus
Where do baroreceptors project nerve fibres to
The cardiovascular centre in the brain stem
Is the baroreceptor reflex neuronal or hormonal
Neuronal
What does the baroreceptor reflex consist of
A detector, afferent neural pathways, a coordinating centre, efferent neural pathways and effectors
What is the function of the afferent neural pathways
Conway information to the CNS
What is the coordinating centre and where is it
It compares signals detected in the periphery and compare them to a set-point and generates an error message. It is found in the CNS
What is the function of efferent neural pathways
They relay the output of the coordinating centre to the periphery
What is the function of the effectors
The execute an appropriate response and alter the controlled variable, correcting the deviation from the set-point
What does increase mean arterial pressure cause
Vasodilation and bradycardia
What does decreased mean arterial blood pressure cause
Vasoconstriction and tachycardia
What does blood flow to the brain through
The carotid arteries
What type of receptors are baroreceptors
Mechanoreceptors
How are baroreceptors activated in vessels
By stretch, not directly by pressure
What nerve do the carotid sinus afferents travel on
The sinus nerve
What cranial nerve do carotid sinus afferent end up on
The glossopharyngeal
What part of the brain stem is the cardiovascular centre found
In the medulla
What nerve do the aortic arch afferents travel in
The vagus nerve
What are baroreceptors the terminals of
Myelinated and unmyelinated sensory fibres
What do myelinated and unmyelinated sensory fibres express
Cation-selective ion channels activated by stretch
When the cation-selective ion channels are open what do they generate
A graded receptor potential that causes an action potential generation with both static and dynamic qualities
What is dynamic in relation to pressure
When the pressure is changing
What is static, in relation to pressure
When the pressure is constant
When does baroreceptor activity stop
At very low pressures (40-60 mmHg)
How is central coordination of the baroreceptor reflex accomplished
By a complex of medullary nuclei collectively termed the cardiovascular centre
What is the most important transmitter within bulbospinal neurones
Glutamate
Bulbospinal neurones synapse with preganglionic sympathetic neurones between what levels of the spinal cord
T1 and L3
When preganglionic neurones excite post ganglionic neurones through the sympathetic nervous system what does it cause
Vasodilation, increased heart rate and force of contraction
How do preganglionic neurones excite adrenomedullary chromaffin cells
Via the release of ACh and activation of nicotinic receptors causing the release of adrenaline and noradrenaline
When preganglionic neurones excite post ganglionic neurones through the parasympathetic nervous system what does it cause
A decreased heart rate and limited vasodilation
What are the reflex effects of baroreceptor unloading
Increased sympathetic activity, decreased vagal parasympathetic activity so this causes increased HR and contractility so increases CO, arteriolar vasoconstriction so increased TPR and venoconstriction which supports central venous pressure and stroke volume
