1. Dr Farah Nabil Abbas MBChB, MSc, PhD Chair Dept. of Physiology
Autonomic Nervous System
Dr Farah Nabil Abbas
MBChB, MSc, PhD
Chair Dept. of Physiology

3. The Autonomic Nervous System
The Autonomic Nervous System (ANS) is that portion of the nervous system that controls the visceral functions of the body e.g. arterial pressure, GI motility, secretion, urinary bladder emptying, sweating, & body temperature.
One of the most striking characteristics of the autonomic nervous system is the rapidity and intensity with which it can change visceral functions. For instance, within 3 to 5 seconds it can increase the heart rate to twice normal, and within 10 to 15 seconds the arterial pressure can be doubled; or, at the other extreme, the arterial pressure can be decreased low enough within 10 to 15 seconds to cause fainting. Sweating can begin within seconds, and the urinary bladder may empty involuntarily, also within seconds

7. General Organization of the Autonomic Nervous System
The autonomic nervous system is activated mainly by centers located in the spinal cord, brain stem, and hypothalamus. Also, portions of the cerebral cortex, especially of the limbic cortex, can transmit signals to the lower centers and in this way influence autonomic control. The autonomic nervous system also often operates by means of visceral reflexes. That is, subconscious sensory signals from a visceral organ can enter the autonomic ganglia, the brain stem, or the hypothalamus and then return subconscious reflex responses directly back to the visceral organ to control its activities.
General Organization of the Autonomic Nervous System

8. ANS has 2 subdivisions: Sympathetic: fight or flight.
Parasympathetic: vegetative functions.

10. Physiological Anatomy: Sympathetic Nervous System
CNS – Spinal cord – T1-L2
Intermediolateral horn  (preganglionic)  Anterior horn  white ramus  (Ganglia) in the sympathetic chain (paravertebral)  postganglionic  gray ramus  spinal nerve
Fate of Preganglionic Fibers:
1. Synapse at the ganglia.
2. Goes up or down, then synapse in a ganglia.
3. Synapse at an outlying sympathetic ganglia.

11. Parasympathetic Nervous System
1. CNS – Cranial outflow
X vagus – 75% of parasympathetic outflow  thoracic
III oculomotor: sphincter of pupils ciliary muscle
VII facial: lacrimal, nasal, sub maxillary glands.
IX glossopharyngeal: parotid gland.
2.Sacral outflow –
nervi egents – lower GI - bladder
Preganglionic: long, ganglia, outlying in the wall of the organ
Postganglionic: short, 1mm

12. Neurotransmitters of the ANS:
Cholinergic fibers secrete acetyl choline. Adrenergic fibers secrete norepinephrine (noradrenalin). Non-adrenergic non-cholinergic (NANC) 1. All preganglionic neurons (sympathetic & parasympathetic)  cholinergic 2. Postganglionic parasympathetic  cholinergic 3. Postganglionic sympathetic  adrenergic except: postganglionic sympathetic to sweat glands and few blood vessels  cholinergic

13. Mechanism of secretion of Ach & NE:
Action potential  depolarization  increased permeability to Ca+2  secretion of neurotransmitter
Synthesis of Ach & Its Destruction:
Synthesis:
Acetyl-CoA + choline Cholineacetyl transferase Ach
Axoplasm to vesicle
Destruction:
Ach Acetylcholine esterase Choline + acetate
Present in terminal nerve ending
receptor organ (tissue acetylcholine esterase)
serum acetylcholine
destruction in seconds

18. Autonomic Effects on Various Organs of the Body

23. Functions of the adrenal
Sympathetic stimulation – large quantities of epinephrine (80%) & norepinephrine (20%) 1. Epinephrine & norepinephrine have similar effects, but with the following differences: 2. Epinephrine has greater effects on the heart 3. Epinephrine has a weak constriction on blood vessels of muscles NE increase total peripheral resistance Increase blood pressure 4. Epinephrine causes a greater increase in BMR (basal metabolic rate) The effects of adrenal medulla stimulation are more prolonged and widely distributed in the body.