Reflex Control of the Circulation Flashcards
What are the different types of sensory receptors in the CVS?
- Arterial baroreceptors – Are linked to a decrease in BP (a depressor response, reducing HR, force of contraction, causing vasodilation).
- Cardiac stretch receptors – Have mixed actions, some decrease BP, some increase BP.
- Arterial chemoreceptors – Increase BP (pressor response – switch on sympathetics).
- Muscle metaboreceptors – Increase BP (pressor response – switch on sympathetics).
What are the central pathways involved in control of the circulation?
- Medulla relay station (nucleus tractus solitaries) –> relays info from receptors to other parts of the body
- Vagal motor neurones (nucleus ambiguus)
- Pre-sympathetic neurones (RVLM)
Give examples of and describe the excitatory inputs.
Arterial chemoreceptors and muscle work receptors to the medulla which modulates the info and sends information via vagus or sympathetic nerves to control venous tone, heart rate and SV or resistance vessel tone. PRESSOR response.
Give examples of and describe the inhibitory inputs.
Arterial baroreceptors, Cardiac-pulmonary receptors
Stimulation of reflexes - Decrease cardiac output, TPR, and blood pressure DEPRESSOR response.
Why is the baroreflex important for measuring blood flow?
There are no blood flow sensors. What we do is we measure pressure (BP = CO x TPR). This is done by looking at the amount of stretch in the carotid and coronary arteries or aorta. The carotid arteries perfuse the brain so by having blood pressure sensors in the walls measuring pressure changes this info can inform the brain of these changes. We also have them in the aorta (tells brain about pressure changes in coronary circulation). These sensors detect wall stretch.
Where are the baroreceptors located?
The arterial baroreceptors are in the carotid sinus (base of internal carotid) and in the arch of the aorta. The ends of the receptors are spread out over the area of blood vessel and send info (via impulse frequency) back to the NTS.
Describe what happens to the baroreceptors once the BP increases.
The frequency of APs of the baroreceptor afferents increases (very high firing rate) and the speed of onset of this high level of firing is very quick. This is called a dynamic response and it is related to how much the BP has increased (sensitivity). This tells the brain immediately the BP is increasing. Then you get adaptation.
What does it mean when the baroreceptors undergo adaptation?
Once the BP has reached that new certain level and the baroreceptor sends less frequent rhythmic APs to tell the brain BP is still high (frequency not as high as the dynamic change). The reason you get adaptation is because your BP could be at that high level over a long time (e.g. exercise) so you don’t want to have your baroreceptors stimulated the whole time.
