Sympathetic nervous system Flashcards
Describe the synthesis of noradrenaline in the ANS nerves Describe the uptake and metabolism of NA in ANS nerves Outline the main types and distribution and a and b adrenoreceptors and the role of the presynaptic receptors Outline the sympathetic control of the heart, eye and smooth muscle tissue including drugs used to treat the eye Outline sympathetic cotransmission of NA, neuropeptide Y and A-5-TP
Where do preganglionic sympathetic axons terminate? (3)
- Paravertebral sympathetic chains
- Prevertebral ganglia/plexuses - abdominal cavity: coeliac, superior mesenteric and hypogastric
- Adrenal medulla - 10th & 11th segment
Describe the sympathetic ganglionic structure:
Preganglionic fibres are SHORT, post ganglionic fibres are LONG
What is the receptor and neurotransmitter on the sympathetic prevertebral ganglion? (same as PS NS)
Receptor: Nicotinic
Neurotransmitter: ACh
Where is the preganglionic nerve located?
Thoraco-lumbar spinal cord
What is the most common receptor and neurotransmitter on the postganglionic axon to effector?
Receptor: Adrenoreceptors
Neurotransmitter: Noradrenaline
What releases noradrenaline?
Varicosities
What are the steps in noradrenaline synthesis and use? (6)
- Tyrosine
- NA synthesis (enzymes)
- MAO is released (monoamine oxidase)
- NA is packaged into vesicles
- Varicosities are evaded
- Released by exocytosis
What are the receptors on the post synaptic cell?
Alpha and Beta adrenoreceptors
What receptor causes inhibition of NA on presynaptic cell and how does it work?
Alpha 2 receptors act as a brake, recycling the NA to be reused
What are the uptakes on post and presynaptic cleft for?
They reduce levels in the synaptic cleft which stops perpetual activation
What type of receptors are a and b adrenoreceptors?
Metabotrophic receptors
What does a metabotrophic receptor do? (4)
- Attaches to a G protein
- Activates a 2nd messenger system
- Enzyme activation/ion transport
- Response (change in shape)
What receptors can be found on the post synaptic cleft?
a1, a2, b1, b2, b3
What receptors can be found on the pre synaptic cleft?
ONLY a2
What receptors are AGONISTS and what can they be used for? (3)
- a1 - decongestant, eye drops, mydriasis (constrict blood vessels)
- b2 - salbutamol (asthma inhaler) relaxes airways
- b1 - enhance cardiac muscle contraction
What receptors are ANTAGONISTS and what can they be used for? (2)
a1 - antihypertensive
b - beta blockers, can slow HR
At a synapse, how would a AGONISTIC a2 receptor affect NA?
Would reduce NA release as it would uptake more to the presynaptic cell
At a synapse, how would a ANTAGONISTIC a2 receptor affect NA?
Would increase NA release as it would lower the uptake
How does SNS control pupil diameter? (3)
- Sympathetic nerve activation
- Radial muscle contraction (ciliary) or relaxing
- Pupil dilation or pupil decreases in size
What receptor is used at the eye?
Muscarinic 3 (M3)
What can mydriatic drugs be used for?
Eye inspection and surgery - dilation
What can anti glaucoma drugs be used for?
Miosis, pupil constricts and releases pressure
What is neuropeptide Y and what does it do? (3)
Nueromodulator that:
- Prejunctional - decreases NA & ATP release
- Post junctional - increases NA action
- Acts with ATP for VASCONSTRICTION
What is adenosine 5’-triphosphate and what does it do? (3)
ATP
- Directs actions - P2 receptors
- Neuromodulator - P1 receptors
- Acts with NPY for VASOCONSTRICTION
