What are the transmitters and receptors at the synapse between pre & post ganglionic cells in the Sympathetic System?
Acetylcholine is the transmitter and nicotinic are the receptors
What are the transmitters and receptors at the synapse between pre & post ganglionic cells in the Parasympathetic System?
In the parasympathetic system the synapses between post-ganglionic cells and their targets use what kind of receptors?
Whats different about post-ganglionic cells in the adrenal medulle?
Theyre part of the sympathetic system but unlike normal ones they:
- have no axons
- Release Adrenaline & Noradrenaline directly into the blood –> So activate lots of adrenergic receptors contributing to mass activation
What type of receptors do adrenaline & noradrenaline act on?
Adrenergic receptors, specifically the alpha & beta receptor subtypes of adrenergic receptors
What effect does the sympathetic system have on the eye?
- Relaxation of ciliary muscle –> So the lens tightens and focusses further away
- Contraction of dilator pupillae (Alpha 1 receptors)
What receptors do eye drops that dilate the eye act on?
Activate the Alpha1 receptor in dilator pupillae (alpha1 agonist)
Block activation of muscarinic receptor in constrictor pupillae (Muscarinic antagonist)
What effect does parasympathetic activation have on the heart?
Releases acetylcholine to activate muscarinic receptors causing:
- Decrease in HR
- has little to no effect on stroke volume (vagal fibres dont reach the ventricles)
What effect does the sympathetic system have on blood vessels?
- Peripheral vasoconstriction (alpha 1 receptors)
- Vasodilation in cardiac muscle & skeletal muscle (Beta 2 receptors)
What effect does the sympathetic system have on the lungs?
- Relaxation of smooth muscle to reduce airway resistance
Describe the anatomy and synapses of the Sympathetic system?
- Outflow is thoraco lumbar (T1-L5)
- Synapses in the Paravertebral ganglia (sympathetic trunk) using ACh on Nicotinic Receptors
- Postganglionic cells synapse at their target organ releasing noradrenaline
- Post ganglionic sympathetic cells at the adrenal medulla directly release adrenaline into the blood
- Some post-ganglionic sympathetic fibres release acetylcholine triggering sweating
Is the ANS a branch of the Afferent or Efferent and PNS or CNS?
ANS is a branch of the Efferent PNS
Describe the types and actions of adrenergic receptors:
Alpha 1 and beta 1 -> stimulatory responses
Alpha 2 , beta 2 & beta 3 -> inhibitory responses
- Dilator Pupillae
- GI & Urinary Sphincters
- Cardiac Pacemaker (increases HR)
- Myocardium (Increases contraction strength
- Salivary Gland (Secretomotor)
- GI Tract (Inhibits motility)
- Urinary Bladder (Decreases muscle tone allowing greater filling)
- Vasodilation (In coronary and skeletal muscle arteries)
- Dilation of bronchial tree (Asthma treatment)
Describe the anatomy & synapses of the Parasympathetic System?
Outflow is from cranial and sacral nerves
Synapse in Terminal or Intramural ganglia (near or in their target organs) using ACh on Nicotinic Receptors
Post-ganglionic fibres synapse in target organ using ACh on Muscarinic Receptors
What do Alpha 1 Adrenergic receptors do?
- Dilator Pupillae
- Tightens up urinary & GI sphincters
What do beta 1 adrenergic receptors do?
- Increases HR (Cardiac Pacemaker) and contraction strength (Myocardium)
- Secretomotor to salivary glands plus causes absorption of water in ducts creating a more viscous saliva
What do beta 2 adrenergic receptors do?
- Vasodilation in skeletal muscle and coronary arteries
- Relaxes muscle of bronchial tree
- Reduces GI motility
- Decreases muscle tone in urinary bladder
How is the sympathetic system involved in regulating blood pressure?
It helps regulate short term blood pressure, through the baroreflex.
Remember this is purely for short term irregularities in BP not long term management
How does the baroreflex work?
Mechanoreceptors known as baroreceptors sit in the wall of some blood vessels e.g. aortic arch & Carotid Sinus
They have a resting rate of APs:
- Higher BP -> More stretch -> More APs
- Lower BP -> Less Stretch -> Less APs
Signals travel up the Glossopharyngeal Nerve (From carotid Sinus) and Vagus Nerve (from Aortic Arch) to Vital centres in the Medulla
Return signals come down:
1) The Vagus nerve to the Heart
- > Changes in HR & Contraction Strength
- > Alters cardiac output to raise or lower BP
2) Spinal Sympathetic fibres to arterioles
- -> Alters sympathetic tone to alpha 1 Adrenergic receptors to alter Total Peripheral Resistance and so influence BP