Lecture 3-4 Flashcards
What are the two types of depressor reflexes?
Baroreceptors and cardiac receptors
What are the two types of excitatory reflexes?
Chemoreceptors and muscle work receptors
What is the controlled variable? In reflex control
Blood pressure
What are the two structures found within the medulla oblongata?
Nucleus ambiguous and nucleus tractus solitartius
What is the nucleus ambiguous?
Origin of the vagus nerve
What does the nucleus ambiguous do?
It has an inhibitory effect on the heart, acting on the relapse of ACH and acting on the muscarinic effectors
What is the nucleus tractus solitartius important for?
Connections to the nucleus ambiguous
What do baroreceptors do?
Give information about pressure
What do the connections in the baroreceptors do?
Have connections that go up into the brain stem to go into the nucleus tractus and simulates and fire impulses into the nucleus tractus
What is the cycle of the reflex loop?
Baroreceptors, nucleus tractus, nuelcus ambiguous, vagus nerves, release of ACh to muscarinic receptors
What is the vagus nerve part of?
Cranial nerves
Describe the vagus nerve
A nerve that originates from the brain stem region and comes out of the cranium and comes down into the rest of the body 10th cranial nerve
What number is the vagus nerve in regards to cranial nerves?
10th
What are CVLM and RVLM useful for?
Areas of the brain stem that are responsible for sympathetic outflow
Describe RVLM
Output of the sympathetic nervous system, goes to the ganglia alongside the spinal chord
What is the end goal for the sympathetic nervous system?
Increase heart rate and contractility
Describe the CVLM
Connected between the RVLM and is an inhibitory mechanism which reduces the release of adrenaline - wont get an increase heart rate or contractility.
REDUCES heart rate
Where are the majority of the baroreceptors located?
In the aortic arch
Where else are baroreceptors located?
Carotid artery
What happens to the carotid artery as it get’s higher?
Splits into two - has an external and internal carotid artery
What is found at the start of the internal artery?
Some swelling and its known as the carotid sinus
What happens at the carotid sinus?
There is high contraction of baroreceptors
How are baroreceptors connected?
Connected through to the brain by nerve connections
What are afferent fibres?
Take information into the brain
What are efferent nerve fibres?
Nerves leaving the brain and They take information to the organs
How are the carotid sinus baroreceptors connected through the cranial nerve?
By the 9th cranial nerve called glossypharyngeal nerve
What type of receptors are baroreceptors?
They are stretch receptors, and are mechanoreceptors embedded in the wall of the artery
Describe stretch receptors?
As blood pimps through the carotid sinus it stretches and that stretches the baroreceptors, stretching of wall increases firing rate
What happens if you stopped the carotid sinus from stretching?
You wont get firing as the baroreceptors no longer respond to changes in pressure
What happens if pressure increases?
You get more firing
What is the maximum sensitivity?
Change in number of impulses/ change of pressure
In regards to Pulsatile pressure, when a curve shifts to the left what does it mean?
It is more sensitive
What are baroreceptors more sensitive too?
Pulsatile changes because that is how blood flows
What do some baroreceptors have that some don’t?
Myelinated fibres
What happens if you get the sinus nerve?
There will be no connection between the baroreceptors and the brain stem - decreases blood pressure
What do increases carotid sinuses pressure lead to?
Decrease in blood pressure
What does decreases carotid sinus pressure lead to?
Increases blood pressure
Do you need both sets of baroreceptors in the aortic and carotid sinuses?
No the carotid sinus baroreceptors are probably the most important in maintaining blood pressure
What are some mechanisms that the baroreceptors use to adjust blood pressure?
Central resting, peripheral resetting and resetting in hypertension
Does the baroreceptors reflex happen all the time?
No, if it was working all the time you wouldn’t be able to do activity therefore central resetting is used to rest the baroreceptors
What is an example of resetting in baroreceptors?
When you exercise, the central resetting system known you are exercising and so it changes the way baroreceptors are responding and the sensitivity of the baroreceptors are adjusted
What happens if there is a change in blood pressure in the peripheral reset system?
If BP decreases the baroreceptors become more sensitive and causes vasodilation, if there is an increase in BP the baroreceptors become less sensitive and vasoconstriction occurs
Hypertensive =
More sensitive
Hypotension =
Less sensitive
Describe hypertension baroreceptors reset
Baroreceptors become less sensitive, and function at a less sensitive rate then with low pressure
What are baroreceptors main job?
To smooth out blood pressure and allows us to sit down and stand up at keep blood pressure at a maintained range
What happens to BP when you take baroreceptors away?
You have a much broader arterial pressure
What system do baroreceptors act as?
A buffering system - reduce the blood pressure in daily events when you change posture, respiration or excitement
What do cardiopulmonary receptors do?
Similar job to baroreceptors, but have a structural difference, they fine tune the system
What is the structural difference between cardiopulmonary receptors and baroreceptors?
Cardiopulmonary receptor have 80% afferent and have a small diameter with unmyelinated fibres
What do cardiac mechanoreceptors do?
Give information about pressure changes in the chambers of the heart itself
Where are cardiac mechanoreceptors located?
Around the right atrium and the vessels that bring blood to the heart (around the atrial tissue) and pulmonary veins
What does type A respond to?
Atrial systole
What does type B respond to?
V wave of atrial filling
What feedback to cardiac mechanoreceptors demonstrate?
Information about venous pressure and cardiac filling
What do veno-atrial stretch receptors do?
Detect changes in cardiac blood volume
Describe the brain bridge reflex
Controls heart rate in response to blood volume
What do chemoreceptors do?
Give information into the cardiovascular system about different factors that affect the system
Where are peripheral chemoreceptors found?
In the aortic and carotid bodies
What is the aortic body innervated by?
By the aortic nerve (a branch of the vagus)
What do peripheral chemoreceptors primarily regulate?
Respiration rate (PCO2)
What do peripheral chemoreceptors support?
Blood pressure when baroreceptors reflex out of range, less than 70mmHg
What are the reflex effects that peripheral chemoreceptors respond to?
Vasoconstriction of arterioles and venoconstriction, tachycardia
What do mechanoreceptors (myelinated) do?
Target the reflex effect of tachycardia and are stimulated by local pressure and muscle contraction
What are chemoreceptors (metaboreceptors, unmyelinated) activated by?
By chemicals release during exercise e.g. K+, H2PO4-. H+ and ATP
What are the reflex effects of chemoreceptors?
Increased sympathetic flow, tachycardia and increase YPT
What are mechanoreceptors and chemoreceptors both blocked by?
Local anaesthetic to muscle nerves
Describe syncope
A sudden, transient loss of consciousness and postural tone, with spontaneous recovery - sitting down to stranding up
What is the mechanism for syncope?
Transient global hypoperfusion
What generation is syncope common In?
All ages groups but particular elderly
What is nuerocardiogenic syncope?
An autonomically mediated reflex mechanisms associated with inappropriate vasodilation or bradycardia causing syncope
What is the most common type of neurocardiogenic syncope?
Vasovagal syncope
What does vasovagal syncope mechanisms involve?
Pathophysiological autonomic reflex, with triggering factors, modulating factors and afferent pathways
What are some warning signs of the vasovagal response?
Nausea, warmth and lightheadedness
What is the vasovagal response?
An inappropriate vessel dilation and bradycardia response leading to reduced cerebral perfusion and syncope
