Autonomic Nervous system
Medical Physiology
2nd Module
2020
Items to be discussed
• Introduction.
• Integration of Sympathetic and parasympathetic
functions
• Sympathetic and Parasympathetic tone.
• Control of autonomic nervous system.
Introduction
Integration of Sympathetic and
parasympathetic functions
Sympathetic and Parasympathetic
tone
• Definition:
The
sympathetic
and
parasympathetic
systems are continually active, and the basal rates of
activity are known, respectively, as sympathetic tone and
parasympathetic tone.
• Value: it allows a single nervous system both to increase
and to decrease the activity of a stimulated organ.
Sympathetic tone
• Example: The sympathetic tone keep most of blood
vessels partially constricted and this maintains ABP.
• Loss of sympathetic tone → drop of blood pressure and
shock.
Parasympathetic tone
• Example: The parasympathetic tone
1. Maintains smooth muscle tone of intestine
2.
keep resting HR 70- 80 bpm to ↓ inherited rhythm of SAN
(vagal tone)
• Cut of parasympathetic vagus nerve to the heart→
the heart beats by its intrinsic rate (100 bpm)
Control of the ANS
• (A)Reflex control of autonomic functions.
• (B)Higher control of autonomic function
(a)Reflex control of autonomic function.
1. Spinal autonomic reflex:
Produce responses by stimulating the spinal autonomic centers
(LHCs) e.g.(The micturition and defecation reflexes).
2. Brain stem autonomic reflexes: Produce responses by stimulating
the cranial parasympathetic centers in brain stem, e.g:
I.Reflex salivary, gastric and pancreatic secretion.
II.Reflex pupilloconstriction.
(B)Higher control of autonomic functions
• (1)The reticular formation.
• (2)The hypothalamus.
• (3)The cerebral cortex.
Thank You