Neuronal Control BP Flashcards
What neuronal system is important in BP
How it is different from hormonal
Function
Orthostatic hypotension
- Provides moment to moment regulation
- Vital for the maintenance of blood pressure after haemorrhage
- Orthostatic hypotension: blood would pool in the legs, less goes to the brain and leads to dizziness or faint
Neural control
Baroreceptor system
What process neural control of BP uses
What the sensors do
Where baroreceptors are found, why there are two places
What baroreceptors do
How blood flow in the brain is regulated
- Neural control of blood pressure is a fast homeostatic process controlled by negative feedback
- All negative feedback systems have sensors to monitor the controlled variable
- Baroreceptors are found mainly in:
a. carotid sinus in the internal carotid artery just above the bifurcation of the carotid arteries (detects BP in the internal carotid)
b. aortic sinus at the base of the aortic valve (detects BP at the start of the aorta,relay information to the CN when there is a change in BP)
- Brainstem vasomotor centre uses these two pressures to compute flow in the internal carotids and thus blood flow in the anterior circulation to the brain.
- Brain blood flow is autoregulated and doesn’t change over a wide range of systemic blood pressures - Baroreceptors are important in detecting and relaying information to the brain that involves in the changes in the BP
- Baroreceptors respond to stretch: increase stretching -> increase in BP
Baroreceptor system
What process is and how it works
- Receptor senses a variable
- Control centre compares the actual variable value with a desired reference value
- Activates effector system to drive the variable back to the reference level
Why is high BP bad
They can lead to several condition such as:
1. Aneurysm
2. Bulging regions of blood vessels
3. Kidney failure
4. Weakening of arteries
5. Artery modification
6. Increase risk of cardiovascular disease: stroke
Carotid sinus
What does the short sinus nerve join
Afferent fibres
action potential with systole and diastole
- Nerve endings in the carotid sinus give rise to the short sinus nerve
- This nerve joins the glossopharyngeal nerve and/or the vagus nerve (travels in either or both )
- Afferent fibres from the sinus nerve travel in these cranial nerves and synapse in the brainstem (picking up signals)
- Electrical recordings of sinus nerve activity show that a continuous train of action potentials is present in the nerve fibres, which increase in frequency during systole and decreases during diastole
- Senses blood pressure
Carotid body
name of special receptors
which nerve fibre it travels
what it sense
- contains carotid chemoreceptors: sensitive to the oxygen level in the blood
- sensory nerve fibres from the carotid body also travel in the IX or X cranial nerve
- senses hypoxia
Glossopharngeal nerve
What it contains
Where each travels from to
- IX cranial nerve
- Mixed cranial nerve primarily sensory: containing afferents from tongue, pharynx, larynx and the carotid sinus
- secretomotor output (parasympathetic) to parotid gland
- stylopharngeus: motor output to a single muscle
Vagus nerve
- X cranial nerve
- Large mixed (motor and sensory) cranial nerve
- Motor output
- (visceral) sensory afferent nerve fibres from lungs and gut, pharnx and larynx
Nerve and receptors from organs
Vessel
Heart (RA)
carotid
aorta
- Carotid baroreceptors, carotid sinus nerve
- Aortic depressor nerve, aortic baroreceptors
- Sympathetic vasomotor
- Cardiac parasympathetic (vagal), cardiac sympathetic
- Medullary cardiovascular center
Where do afferent fibres from the sinus nerve enter and terminate?
- Enter the brainstem in the vagus or glossopharyngeal nerve
- Terminate in the nucleus of the solitary tract (NTS) in the medulla, the lowest part of brainstem
Role of the NTS in regulating BP
- Low blood pressure:
a. Low BP activates the vasomotor centre
b. this activates stimulates sympathetic outflow to the heart via reticulospinal tract
c. vasoconstriction in the vessels and at the heart
d. Increase in BP - High blood pressure
a. High BP picked up by carotid sinus
b. Relayed through the sinus via the glossopharagyneal nerve at medulla
c. Activates NTS
d. This stimulates parasympathetic outflow to the heart via vagus nerve
e. Drop in contractability and blood pressure (vagus nerve has both sensory and motor components)
Lateral reticulospinal tract
What it is
Where it is found
Where the synapse runs
How it affects BP (preganglionic and postganglionic neurons)
- Vasomotor centre activates reticulospinal tract axons
- Preganglionic neruons synapse on postganglionic sympathetic neurons which project to smooth muscle in arterioles
- Activates post-ganglionic sympathetic fibres which release noradrenaline on arteriolar blood vessels
- This contract via an action on alpha 1 adrenoreceptors
Lateral reticulospinal tract:
a. A group of axons in the dorsolateral spinal cord
b. Arises from cells in the reticular formation of the medulla of the brain stem
c. Synapse on sympathetic pre-ganglionic neurons in the intermediate part of the lumbar (IML) and thoracic ventral horn
What happens in low BP
From baroreceptors
Relevance to equation
how SNS affects BP (2 ways)
- Input from the baroreceptors too low (rate of action potential firing)
- Vasomotor centre activates sympathetic nervous system
- SNS results in a constriction of peripheral arterioles (increases venous return and preload-> raised stroke volume and cardiac output)
- This raises total peripheral resistance (TPR)
- RIse in TPR increase BP
(assuming cardiac output, the outflow in litres/min from the heart, stays constant)
Cardiac output x Total peripheral resistance (TPR)= Mean arterial pressure (MAP)
Heart rate x Stroke volume=Cardiac output (increased sympathetic outflow -> sends signals to SAN-> increase the frequency of firing->increase in HR)
What happens in high BP
From baroreceptors
Relevance to equation
How SNS and PNS works
- Input from the baroreceptors too high
- Vasomotor centre is inhibited
- Parasympathetic nervous system is activated via nucleus ambiguous
- This stimulates vagus nerve
- Vagus acts at the sinoatrial node of the heart
- Reduced sympathetic outflow
- Relaxation of arterioles
- Lowered HR
- Reduction of CO and TPR
- Reduction BP
Heart rate x Stroke volume=Cardiac output
Cardiac output x TPR = Mean arterial pressure
