Autonomic Nervous System (4) Flashcards
What are the two main sections of the autonomic nervous system?
- Sympathetic
- Parasympathetic
What are the roles of the Autonomic nervous system?
- Important for regulating:
- Heart rate, bp, body temp
- Co-ordination body’s response to exercise and stress
- Outside of voluntary control
- Exerts control over:
- Smooth muscle, exocrine secretion, rate and force of heart contraction
What is the origin of the sympathetic NS?
- Thoraco-lumbar origin
- Preganglionic neurones arise from T1 - L2/3
Where are the majority of synapses with postganglionic nerves situated?
- Paravertebral chain of ganglia
Give examples of prevertebral ganglia.
- Coeliac
- Superior/inferior mesenteric
What does the pre and post ganglia look like in the sympathetic NS?
- Same length
What is the origin of the parasympathetic NS?
- Cranio-sacral origin
- Cranial nerves (III, VII, IX and X)
- Sacral outflow S2-S4
What do the pre and post ganglia look like in the Parasympathetic NS?
- Pre is significantly longer
- Post is v. short and close to the target tissue
What are the neurotransmitters used in the sympathetic NS?
- Pre: Ach (Acetylcholine)
- Post: NA (Noradrenaline)
What neurotransmitters used in the parasympathetic NS?
- Acetylcholine in both pre and post ganglions.
What are the different types of adrenoreceptors?
- Alpha 1
- Alpha 2
- Beta 1
- Beta 2
Why do different tissues have different subtypes?
- Allows for diversity of action
- Selectivity of drug action
Outline the use of neurotransmitters in Parasympathetic NS.
- Use Ach
- Acts at muscarinic receptors of effector cells
- G protein coupled receptors M1/2/3
- No integral ion channel
What is the general role of the parasympathetic and sympathetic NS?
- Parasympathetic: more dominant under basal conditions
- Sympathetic: Increases activity under stress
Which nerve supplies parasympathetic impulses to the heart?
- Vagus
- 10th X cranial nerve
How does the parasympathetic NS feed impulses to the heart?
- Postganglionic cells on epicardial surface
- Or within walls of heart at SAN/AVN
What do parasympathetic cells release? To what and what effect in the heart?
- Ach
- M2 receptors
- Decreases heart rate
- Decreases AVN conduction velocity
Where does the sympathetic input arise from?
- Sympathetic trunk
What does the sympathetic NS innervates?
- SAN
- AVN
- Myocardium
What does the sympathetic NS release? To what and what effect?
- Noradrenaline
- Acts on B1 adrenoreceptors
- Increases heart rate and force of contraction
What effect does the sympathetic NS have on the pacemaker potential?
- Increases rate of depolarisation
- B1 receptors
- Increase in cAMP speeds up pacemaker potential
What effect does the parasympathetic NS have on pacemaker potential?
- Decreases rate of pacemaker potential
- M2 receptors
- Inhibits adenylate cyclise
- Decreases cAMP
- Increases K conductance
How does noradrenaline increase the force of contraction?
- NA acting on B1 receptors in myocardium causes an increase in cAMP
- Phosphorylation of Ca channels
- Increases Ca entry during AP
- Increases uptake of Ca in SR
- Increases sensitivity of contractile machinery to Ca
- Increases force of contraction
What is vasomotor tone?
- The state that blood vessels take if the sympathetic output isn’t higher or lower than normal
- So there’s no vasodilation or vasoconstriction
Which types of cells have A1 and B2 receptors?
- Skeletal muscle
- Myocardium
- Liver
What are B2 receptors sensitive to?
- Circulating adrenaline
If you activate the B2 adrenoreceptor what does this cause?
- Vasodialtion
- Increases cAMP
- Which opens K channel which leads to relaxation of smooth muscle
If you activate the A1 adrenoreceptor what does this cause in VSM?
- Vasoconstriction
- Increased Ca
- Contraction of smooth muscle
What does an increase in local metabolites cause?
- Has a strong vasodilator effect
- Ensures adequate perfusion of skeletal and coronary muscle
- Then activation of B2
How are changes in the state of the system communicated to the brain?
- Via afferent nerves
- Baroreceptors - stretch receptors to increased arterial pressure
- Arterial receptors
- Alters activity of efferent nerves
What are the 3 main types of drugs that effect the autonomic NS?
- Sympathomimetics
- Adrenoreceptor antagonists
- Cholinergics (muscarinic agonists and antagonists)
