1. Autonomic Nervous System
4th year MBChB tutorial

2. Introduction The body’s nervous system is divided in 2
The Central Nervous System (CNS)
The Peripheral Nervous System (PNS)
The PERIPHERAL nervous system consists of 2 divisions:
SOMATIC
AUTONOMIC

3. Somatic NS
Innervates and controls the motor functions of the body (joints and muscles)
Axons from the brain and spinal cord terminate at the neuromuscular junction and innervate the effector skeletal muscle
The neurotransmitter is Acetylcholine (Ach)

4. The Autonomic NS
Responsible for the involuntary control of automatic body functions
How does this work? What does this mean?
It works in the same way: nervous system with messages going to and from the brain
Each organ system has autonomic control working all the time
We are not in control of this
We are oblivious to its functioning

5. Divisions of the ANS Sympathetic (Σ) Parasympathetic (paraΣ)
Each viscus or blood vessel MUST have both types of innervation

6. Anatomy of the Sympathetic NS
The Preganglionic fibres arise from the lateral horn of the spinal cord
Synapse in the sympathetic chain ganglia
2 paravertebral chains lying alongside the spinal column
Thoracolumbar T1-L3
The Postganglionic fibres have long chains that terminate in the end organs
Usually running alongside the blood supply for each organ
ADRENAL MEDULLA – exception to the rule!

7. The Adrenal Medulla
Specialised sympathetic ganglion with no postganglionic fibres
Postganglionic fibres are secretory cells
The medulla secretes hormones when stimulated
Noradrenaline (NA) – 70%
Adrenaline (Adr)
Dopamine (DA) – small amounts

8. Anatomy of the Parasympathetic NS
CRANIOSACRAL origin
Cranial nerves: 3, 7, 9 and 10
Sacral S2-4
Preganglionic fibres are very long
Arise in the brainstem
Parasympathetic Ganglia are near or in the viscus
Postganglionic fibres are usually very short

9. Similarities between Σ and paraΣ
Both the parasympathetic and the sympathetic NS have autonomic ganglia
Both sets of postganglionic fibres will eventually terminate in one of 2 types of receptors
ADRENERGIC
CHOLINERGIC

10. What is the point of 2 divisions?
ANS innervates the heart, blood vessels, endocrine glands, viscera and smooth muscle
It controls the internal environment automatically, uninfluenced by volition
Sympathetic – “FIGHT or FLIGHT”
Temperature, glucose, vascular responsiveness, ventilation, cardiac output and GIT
Stress response
Parasympathetic – RESTORATIVE or HOMEOSTATIC
Maintains normal physiological functioning and energy levels
Digestions and Metabolism

11. The Stress Response
Series of Neurohumoral responses to optimise the bodily defence mechanisms for short-term survival “fight or flight”
Neural: HAEMODYNAMIC
Increased sympathetic outflow
Blood flow
Increased: heart, lungs, brain and muscle (β)
Decreased: GIT, kidney, liver (splanchnic circulation) and skin (α)
Humoral: HORMONAL
Defence of blood volume
Increased: aldosterone and ADH - salt and water retention
Mobilisation of glucose stores to supply vital organs with energy
Insulin inhibited

12. Organisation of the ANS

13. Organisation of the ANS
Both parasympathetic and sympathetic innervate each organ system in the body
The 2 different supplies are balanced
Relative dominance in each organ
Example: Heart - sympathetic dominance at the sino-atrial node, the denervated transplanted heart always runs at a tachycardia of 100 – 120 bpm

14. Organs Eye Glands: Sweat & Salivary Heart Lung Stomach & GIT
Liver & Gallbladder
Bladder

15. Neurotransmitters Acetylcholine (Ach) Noradrenaline (NA)
2 types of receptors:
cholinergic
adrenergic

16. Cholinergic Receptors
All autonomic ganglia (including the adrenal medulla)
All paraΣ postganglionic nerve terminals
Σ postganglionic nerve terminals in sweat glands
Somatic NS - neuromuscular junction

17. 2 types of cholinergic receptors
NICOTINIC
At skeletal NMJ and ALL autonomic ganglia (incl adrenal medulla)
Stimulated: nicotine
Inhibited: Neuromuscular blocking agents and ganglion blockers
MUSCARINIC
At paraΣ postganglionic fibres
Stimulated: muscarine
Inhibited: atropine, glycopyrrolate

18. B’s of the Parasympathetic NS
Blind
Bronchial secretions
Bronchospasm
Bradycardias
Beristalsis (peristalsis)
Bile secretion
Bladder contraction

19. Adrenergic Receptors
Only found at the sympathetic postganglionic nerve terminals
Alpha
α1: post-synaptic – smooth muscle vasoconstriction
Increases the BP ± reflex bradycardia
α2: pre-synaptic – inhibits further NA release
Beta
β1: increased contractility, HR, AV node conduction, refractory period, renin secretion and lipolysis
β2: increased skeletal muscle vessel dilatation, bronchial relaxation, uterine relaxation, bladder relaxation, glycogenolysis

20. Pharmacology of the ANS

21. To create effect, we can block one side of the autonomic system or stimulate the other
Eg: to increase heart rate – stimulate sympathetic OR block parasympathetic

22. GANGLIA Blockers – trimetaphan (competitive) vasodilation
s/e: reflex tachycardia, pulm oedema and bronchospasm, urinary retention, ileus
Stimulants – neostigmine (↑ Ach)
↑ BP, peristalsis, n+v, bronchoconstriction

23. PARASYMPATHETIC Remember postganglionic R are muscarinic (Ach)
Stimulate – muscarinic agonist (choline or muscarine alkaloid) or anticholinesterases (neostigmine, edrophonium, organophosphates)
Blockade - atropine

24. SYMPATHETIC Stimulate – direct or indirect stimulation adrenoreceptor
Antagonists

25. “Sympathomimetics” Direct acting
Epinephrine (adrenaline) and Norepinephrine
Isoprenaline
Dobutamine and Dopamine (higher doses)
Indirect
Ephedrine – releases NA from Σ terminals as well as direct αβ effect

26. Receptor specific agents
α agonists
Phenylephrine – α1 – vasoconstrictor
Clonidine – α1 and 2 – sedative and vasoconstrictor
Dexmeditomidine – α2
β agonists
Isoprenaline β1 and 2
Salbutamol β2

27. Antagonists - α
Occasionally used as antihypertensives but are agents of choice in phaeocromocytoma
Phentolamine – α1 and 2
Phenoxybenzamine - α1 (noncompetitive)
Prazosin and Doxazosin - α1

28. α and β antagonists
Labetalol – racemic mixture but predominantly a βblocker

29. β blockers All competitive with varying β1 or β2 effects
Bradycardia, antiarrythmics, sedative, lower BP
Decrease cardiac mortality
Bronchospasm in asthmatics
Inhibit gluconeogenesis in liver and lipolysis