CNS control Lecture 1 Flashcards
Describe the central neural control of the cardiovascular system reflexes
Involves reflex responses to specific stimuli
Reflex responses are superimposed on local influences by Heart, arterioles, capillaries, veins
Afferent input by spinal nerves or cranial nerves. Sympathetic nerve fibres supplying the heart are on the way out. Also parasympathetic never supply that supply the heart.
Cortical influences- emotion
Complex reflex patterns originate in nuclei in the brain- exercise, feeding/satiety, alerting, thermoregulation, reproduction
Simple reflexes originate from the medulla (barorecptor reflex and volume recptor reflex)
Reflexes also influence catecholamines, vasopressin, renin I angiotensin system
Describe the autonomic supply of the CVS
Rostral ventrolateral medulla (RVLM)- nucleus, organotopically organised- descending excitatory activity to T1➡ L1-2- increases HR via beta1 receptors, stimulates adrenaline secretion, and vasoconstriction
Vagus- decreases HR via muscarinic receptors
Parasympthetic never firbres go the heart, Ach acting on muscarinic recpetors - if parasympathetic increases, heart rate goes down
Describe the baroreceptor reflex pathway
Homeostatically regulates ABP. When presrue goes/up down it brings it back to normal levels.
Found in carotid sinus and arch of aorta. Strech receptors which when the pressure goes up, increases afferent activty- responding to resting levels in blood pressure. Afferent activty goes up to the nucleus tractus solitarius (NTS).
Individual barorecptors have different thresholds -respond to magnitude of strech and rate of change of stretch.
Mechainsm when Baroreceptor detects a drop in ABP and signals to CNS which:
Increases sympathetic activity
-Constricts arterioles which increases TPR and decreases capillary hydrostatic pressure (which increases EDV, increasing stroke vol by Starling’s Law)
Increases venous constriction
-Increases EDV
Increases contractility
-Decreases ESV, increasing SV which increases CO
Decreases parasympathetic activity
-This increases HR which increases CO
Increased TPR and CO = increased ABP
How it works in the CNS:
Decrease ABP, decrease baroreceptors firing Input from CN 9&10 to nucleus tractus solitarius ➡ inhibit nucleus ambiguus less ➡ inhibit RVLM less, Increase HR and vasoconstriction ➡ inhibit SON and PVN (normally inhibit ADH release) ➡ inhibit pituitary less➡ ADH release
Rhythmicity in sympathetic nerve acctivity is mainly caused by baroreceptor reflex. When ABP is low - less activity from barorecptors and sympathetic activity goes up. When ABP is high, more activty from barorecptors and sympathetic activity goes down.
How do different organs react to decreased ABP?
- Reflex vasoconstriction in GI tract and skeletal muscle
- Kidney shows myogenic dilatation in small ABP decreases
- Cerebral circulation shows myogenic dilation to keep CBF
- Coronary circulation shows functional hyperaemia in response to increased cardiac work
What are the functions of the baroreceptor reflex
Continuously buffers changes in ABP
Increase during exercise, coughs, sneezes
Decrease during standing up, dehydration or haemorrhage , digestion, thermoregulation in high temperature
How can you quantify the baroreceptor reflex and how can it change?
Set point = Resting level of ABP
Gain = How much change for a given change in blood pressure
During aging, baroreceptor reflex becomes slower but barely any change in set point and gain
In hypertension set point is raised. Cardiac baroreflex gain is blunted (because cardio-vagal neural activity is reduced in Hypertensive patients) but vascular gain is unchanged
Describe the atrial stretch receptor reflex
Volume receptors are strech recptors found in the right arum, project into NTS. Affected by canges in CVP (distension of veins - affected by sitting/standing). Also affected by ral changes in blood volume and by changes in distribution of blood volume.
Atrial stretch receptors funciton to correct your blood volume and therefore correct the pressure.
Decrease blood volume- decrease afferent activity to NTS➡ paraventricular nuclei➡ increase sympathetic activity to kidney via a pathway that by bypasses RVLM and via renal nerves from the RVLM➡ increases renal vasoconstriction➡ decrease GFR by decreased renal perfusion➡increase renin release➡ angiotensin I/II release➡ ADH from posterior pituitary➡ increase blood volume and decrease urine flow
When an increase in blood volume - has the opposite effects o kidney. Bainbridge reflex increase sympathetic activty to the heart, increasing HR
When are artial strech receptors used
VOlume receptors continously monitor blood volume
Used when in decreased distnesion of atrium - in standing position - haemorrhage, dehydration
INcreased distnesion of atrium - in supine postiion, large fluid intake by mouth or over-transfusion.
Bringing the reflexes together
Baroreceptors and volume receptors contiinousl monitor and adjust ABP and CVP to indivduals own set points
Baroreceptor effects on ABP are much faster than volume receptor reflex on blood volume
The reflexes keep ABP and BV
Sensitivty and/or set point of baroreceptor reflex can be changed eg in hypertentsion
