D6 & D7 - ANS Flashcards
Parasympathetic nervous system
- connects to the CNS via 2 cholinergic nerves - meaning they synthesise, store and release acetyl choline
- pre ganglionic nerve in the CNS from cranial or sacral nerves
- post ganglionic nerve - in the autonomic ganglion
Sympathetic nervous system
- pre ganglionic nerve is a cholinergic nerve
- post ganglionic nerves: most are adrenergic and some are cholinergic
- some nerves pass directly through the paravertebral ganglia without synapsing, and do directly to the adrenal medulla - which is stimulated to release adrenaline and noradrenaline into the blood stream which binds to adrenoceptors on cardiac, smooth muscle or exocrine glandular cells
Adrenergic nerves
release noradrenaline
- most sympathetic post ganglionic nerves
Cholinergic nerves
- release acetyl choline
- some sympathetic post ganglionic nerves
- all parasympathetic post ganglionic nerves
Cholinoceptors
2 types
- nicotinic - ion channel
- muscarinic - g protein linked coupled receptor
Muscarinic receptors
- 5 subtypes
- M2 - expressed mainly on cardiac cells, causes decrease in heart rate when activated by acetyl choline
- M3 - smooth muscle and glandular cells, smooth muscle contraction and glandular secretion
Mascarinic receptors are stimulated by
Acetyl choline
Nicotinic receptors are stimulated by
Acetyl choline
adrenergic nerves
- release noradrenaline which bind to adrenoceptors
- exist alpha and beta
alpha adrenoceptors
- Alpha ○ A1 § Vascular smooth muscle cells § Noradrenaline and adrenaline will target to promote contraction § Vasoconstriction
beta adrenoceptors
- Beta ○ B1 § Expressed on heart § Increase in heart rate § Increases force of contraction ○ B2 § Present on smooth muscle cells § Vascular smooth muscle cell relaxation - also in airways and uterus
Modulating activity of end effect
- Increase/decrease levels of neurotransmitters
- Mimic the actions of neurotransmitter - use drugs that activate receptors
- Inhibit the actions of neurotransmitter - use drugs that inhibit receptors
Adrenoceptor Agonists
- Bind to and activate adrenoceptors
- Endogenous compounds eg. adrenaline and noradrenaline - adrenoceptor agonists
- Drugs can also do this
○ Phenylephrine
○ Salbutamol - Also called Sympathomimetics/adrenomimetics - adrenoceptor agonists
- Target one or more of 5b subtypes of adrenoceptor
2 adrenoceptor agonists
adrenaline, noradrenaline
Adrenaline
○ Hormone and drug
○ Stimulate all of the adrenoceptor subtypes
○ Limitation
§ Inactive orally
□ Extensively metabolised in gut and liver by enzymes
□ Inactivate the compound - can no longer bind to and activate adrenoceptors
§ Typically given by injection in settings where blood pressure and ECG can be monitored
adrenaline local infection
§ Dose dependant
□ At low doses, adrenaline binds to high affinity B2 on vascular smooth muscle - relaxation - mostly vasodilator effect
□ Increase concentration - binds to low affinity A1 - mostly vasoconstrictive effect
□ Because it has a higher affinity for B2 than A1
§ Net effect - at high concentrations, predominantly vasoconstrictive, but at low doses - vasodilatory effect
§ No adrenaline - status quo maintained
§ Local injection
□ Delivering initially high concentration locally
® Vasoconstriction
□ As it is metabolised
® Dose decreased
® Vasodilation
adrenaline instravascular injection
§ Effects on cardiovascular system
□ When adrenaline is injected, the net effect is dependant upon
® Dose
® Rate of administration
□ Intravenous infusion
® Delivering adrenaline at a constant rate into the blood stream
® Starting
◊ Increase in heart rate
} Adrenaline will activate B1 - cause heart rate increase
◊ Associated with an increase in systolic blood pressure - also stimulated B1 receptors that cause heart muscle to constrict more strongly
◊ No change in mean arterial blood pressure
} Increase in systolic blood pressure is counteracted by a decrease in diastolic pressure
– Decrease in diastolic is because when given as IV infusion - decreases total peripheral resistance
– Because adrenaline is activating B2 receptors causing vasodilation in skeletal muscle - will override
– constriction effect in other parts of the body
adrenaline slow bolus injection
§ Large amount of adrenaline directly into blood vessels
§ Dose will decrease with time as adrenaline is metabolised and redistributed
§ Effects on heart rate and blood pressure and total peripheral resistance are more complex
§ Delivering high concentration
§ Predominant effect is alpha adrenoceptor mediated vasoconstriction
§ Associated with an increase in total peripheral resistance
□ Will cause an Increase is diastolic blood pressure
§ Increase in mean arterial blood pressure because the systolic blood pressure is also increased - because adrenaline is stimulating cells in the heart to constrict more strongly
§ Heart does not beat more quickly
□ Because Increase in mean arterial blood pressure causes reflex release of acetyl choline to decrease heart rate to counteract increase in mean arterial blood pressure
§ Lower concentrations of adrenaline over time
□ Vasodilator effect - by B2 adrenoceptors
® Decrease in TPR
® Decrease in diastolic blood pressure
® Return mean arterial blood pressure to normal
□ Direct effects of adrenaline on heart rate
® Increase
clinical uses of adrenaline
○ Related to effects on blood vessels, heart, other smooth muscle
○ Adrenaline added to local anaesthetic
§ prolong action and delay systemic absorption of local anaesthetics
§ Especially in dentistry
§ Causes constriction to localise the anaesthetic in the region
○ Used in cardiac arrest
§ Helps to restore cardiac rhythm
§ Increase TPR during resuscitation
§ In the community
□ Better to use deregulator and CPR
□ Adrenaline can only be given in a hospital situation
○ Treatment of Acute anaphylactic reaction
§ Massive release of histamine
□ Causes constriction of the airways
§ Adrenaline relaxes airways by targeting B2 receptors on smooth muscle
§ Inhibits mast cell degranulation
○ Adrenaline added to local anaesthetic
§ prolong action and delay systemic absorption of local anaesthetics
§ Especially in dentistry
§ Causes constriction to localise the anaesthetic in the region
○ Used in cardiac arrest
§ Helps to restore cardiac rhythm § Increase TPR during resuscitation § In the community □ Better to use deregulator and CPR □ Adrenaline can only be given in a hospital situation
○ Treatment of Acute anaphylactic reaction
§ Massive release of histamine
□ Causes constriction of the airways
§ Adrenaline relaxes airways by targeting B2 receptors on smooth muscle
§ Inhibits mast cell degranulation
Noradrenaline
○ Not the same as adrenaline
○ Nor is also not active orally due to extensive metabolism in the gut and liver
○ Adrenaline activates all 5 adrenoceptor subtypes
○ Nor can do most of them but not B2 adrenoceptor
○ Nor does not cause vasodilatation in (esp. in skeletal muscle vascular beds)