Parasympathetic nervous system Flashcards
Describe the synthesis of EACh in ANS Describe the metabolism of EACh released from the ANS nerves Outline the main types of cholinergic receptors, including 3 types of muscarinic receptors and their distribution target tissues Outline the PS control of the heart, eye and smooth muscle tissues - include drugs used to treat disorders in the eye Outline the PS cotransmission of ACh and vasoactive intestinal polypeptide
What are the 3 key parts of the PS division?
Known as the craniosacral division
Role in keeping the body energy use low
Inhibitory effect on many tissues and organs
What does craniosacral mean?
Cranio - head and neck region
Sacral - pelvic region
What are the 4 cranial outflows?
- Oculomotor - smooth muscles of the eye
- Facial - facial glands: salivary, lacrimal (tears)
- Glossopharyngeal - salivary glands
- Vagus nerve - heart, lungs, stomach, liver… most organs
What are the 2 sacral outflows?
- Sacral nerves from pelvic plexuses with ganglia
2. Sacral nerves innervate distal part of there large intestine, bladder and reproductive organs
Describe the PS neuroeffector pathway:
Brain -> Preganglionic neurone -> ACh bind to NICOTINIC receptors at ganglion -> Postganglionic neurone -> ACh bind to MUSCARINIC receptors at the effector
What is the neurotransmitter always used in PS pathways?
Acetylcholine ACh
Describe the synthesis of ACh:
- Acetyl CoA + Choline = choline acetyltransferase
- Choline acetyltransferase (CAT) + Cytosolic enzyme
- ACh produced
Describe the process at cholinergic synapses: (5)
- ACh is synthesised
- ACh is packaged into vesicles
- AP comes along and releases ACh vesicles to diffuse across the synaptic cleft
- ACh binds to cholinergic (nicotinic) receptors, need 2 molecules at once, this allows Na+ to go through and depolarise the junction
- Acetylcholinesterase breaks down ACh to terminate synaptic transmission - Choline and acetate - recycled
Name the 2 ACh receptors in PS:
Nicotinic and muscarinic
Where are the nicotinic receptors located and what type of receptor is it?
They are located at the ganglia in the brain and NMJ
They are inotropic receptors meaning they are an ion channel that regulates transport of Na+/K+
2 ACh are needed
Where are the muscarinic receptors located and what type of receptor is it?
They are located at autonomic target tissues and the brain
They are metabotropic - they create a 2nd messenger when activated - ion channels
What are the 4 types of muscarinic receptors?
- M1 - neuronal/gut (gastric acid secretion increased)
- M2 - cardiac/presynaptic (HR/force decreased)
- M3 - glandular (secretion inc.) smooth muscle (constriction)
- M4 - neostriatum M5 - substantiated nigra (all brain)
How does the PS control the heart?
- Post ganglionic vagal nerves release ACh which decreases heart function
SA node = decrease HR
Atrial muscle = decreased contractility
AV node = decrease rate of conduction
What muscarinic receptors are used in the heart?
M2
What drug is used for resuscitation after cardiac arrest?
Atropine - muscarinic antagonist (promotes heart function)
What muscarinic receptors are used in the eye?
M3
How does PS control effect the eye?
The nerves are activated and smooth muscle contracts - pupil constriction occurs
What is another word for pupil constriction?
MIOSIS
What is inhibition of contraction called?
Mydriasis (passive dilation) - atropine block the contraction for this to occur
How does the PS help with eyes focussing long distance?
Ciliary muscle relaxed - lens flattened, suspensory ligaments taut (DISTANT vision)
How does the PS help with eyes focussing short distance?
Ciliary muscle contracts - (ACh at M3) suspensory ligaments relax, lens gets fatter (NEAR vision)
What is the paralysis of the ciliary muscle called?
Cycloplegia
What are mydriatic drugs and what are they used for?
They are used for eye inspection and surgery
Passive dilation to keep pupil open
What are miotic drugs and what are they used for?
Glaucoma and rapid pupil close (surgery)
What is PS contransmission?
ACh + Vasoactive intestinal polypeptide (VIP)
What happens at low frequency stimulation of cotransmission?
ACh is released, increased salivary secretion from acinar cells
What happens at high frequency stimulation of cotransmission?
ACh & VIP are released
Dilation of blood vessels by VIP
VIP acts as a neuromodulator to enhance ACh effect on acinar cells
What receptor is always at the effector?
Muscarinic
