Autonomic nervous system Flashcards
Function of autonomic nervous system
Regulates functions with little or no voluntary control via a pair of opposing systems - parasympathetic (comfort) vs sympathetic (crisis)
Tissues that can be innervated: smooth muscle, cardiac muscle, exocrine glands, endocrine glands, fat cells
Function of parasympathetic nervous system
- Constricts pupils
- Stimulates salivary glands
- Decreases heart rate
- No effect on arterioles
- Constricts bronchi
- Stimulates peristalsis
- Stimulates contraction of bladder
- No effect on sweat glands
Function of sympathetic nervous system
- Dilates pupils
- Inhibits salivary glands
- Increases heart rate
- Constricts arterioles
- Dilates bronchi via adrenaline
- Inhibits peristalsis
- Inhibits bladder contraction
- Stimulates sweat glands via ACh receptors
Which areas of the body does the sympathetic nervous system innervate?
T1-L2
Which areas of the body does the parasympathetic nervous system innervate?
S2, S3, S4
Cranial nerves 3,7,9,10
Characteristics of parasympathetic pathway
2 neurones - long pre-ganglionic and short post-ganglionic
Ganglia close to final destination
Vagus nerve 0 autonomic functions and motor and sensory output to larynx/pharynx for speech and airways
Characteristics of sympathetic pathway
- 2 neuron pathway - short pre-ganglionic and long post-ganglionic
- Ganglia mostly in sympathetic chain (ascends to supply head, descends to supply pelvis)
- Also directly innervates adrenal medulla - directly from pre-ganglionic neuron and releases adrenaline
Symptoms of Horner’s syndrome
Constricted pupil
Eyelid droops
Dry eyes
What will be the first neurotransmitter in either nervous system?
ACh which binds to nAChR
Which neurotransmitter affects sweat glands in the sympathetic nervous system?
ACh
Parasympathetic acting distally in organ
- Ganglion - ACh: nictinic
- Terminal synapse - ACh: muscarinic
- Nicotinic: ligand-gated ion channel (Na+), e.g. neural and muscle
- Muscarinic: G-protein couples, e.g. M1, M2, M3, M4, M5, some Gi and Gq
- ACh is recycling mechanism - broken down to clear synaptic cleft
What is the neurotransmitter in all parasympathetic mAChR receptors?
ACh
Sympathetic neurotransmitters acting distally in organ
- Ganglion - ACh: nicotinic
- Terminal synapse - NA (ACh for sweating)
- Adrenoreceptors: all G protein coupled
- A1 receptor: Gq sub-type, activates phospholipase C
- B1 receptor: Gs sub type, activates adenylate cyclase
- Noradrenaline is primarily post-ganglionic transmitter
- Adrenaline is primarily released from adrenal medulla
What class of drug would help to pass urine?
- Drugs can either stimulate a receptor (agonist) or inhibit the receptor (antagonist)
What classes of drug would be used to increase heart rate?
B1 agonist or muscarinic antagonist
- The anti-muscarinic drug atropine is usually used for bradycardia
- Alternatively, isoprenaline or adrenaline can be used, acting via stimulation of B1 receptors
What type of receptor stimulates an increase in sweating?
Cholinergic muscarinic
- Sweating mediated by sympathetic cholinergic fibres
- Hyperhidrosis can be treated by botox injections locally, which reduces synaptic ACh release
What is the likely mechanism of action to constrict pupil?
Muscarinic agonist
- Pilocarpine (selective M3 agonist) treats glaucoma by constricting pupil
- A1 blockers can have similar action although rarely used to treat glaucoma
What are the main actions you would want from the ideal drug to treat an anaphylactic reaction?
A1 agonist and B2 agonist
- Anaphylaxis results in profound histamine-induced hypotension and/or bronchospasm
- Adrenaline is drug of choice, by stimulating A1 and B2
