Autonomic Nervous System ( ANS) Part 1

1. Autonomic Nervous System ( ANS)Part 1 Dr TahaSadig Ahmed Physiology Department , College of Medicine , King Saud University , Riyadh

2. Nervous System • Central Nervous System (II) Peripheral Nervous • System • (I) Central Nervous System (CNS) • Consists of Brain & Spinal Cord • Brain • (1)Forebrain: Cerebrum, Diencephalon (Thalamus, Metathalamus, Epithalamus, Hypothalamus and subthalamus • (2)Mid brain • (3) Hind brain: Pons, Medulla , Cerebellum • B/Spinal cord

3. (II) Peripheral Nervous System: • Consists of cranial nerves (arising from brain) and spinal nerves (arising from spinal cord) • The Nervous System can also be classified into : • Somatic ( voluntary) Nervous System : For organs • under voluntary control (namely skeletal muscles) (II) Autonomic (involuntary,visceral) Nervous System: • Not under voluntary control. • It regulates internal organs’ visceral functions and homeostasis • Effectors include cardiac muscles , smooth muscles and glands • The Autonomic Nervous System ( ANS) helps to adjust & maintain the internal environment ( homeostasis); and helps the body to adapt to to changes in the external environment ,

4. ANS is controlled activated by centers located in the spinal cord, brain stem, hypothalamus and also cerebral cortex especially the limbic cortex • The hypothalamus is very important in this regard : • Posterior hypothalamus controls Sympathetic NS , & • Anterior hypothalamus controls Parasympathetic NS

5. Parasympathetic system activities is related to the relaxed state , rest and anabolism  It promotes vegetative functions ( nutritive , body-building , restorative functions & tissue repair ) Increased secretion of endocrine & exocrine glands . Parasympathetic NS Sympathetic NS 5

6. COMPARISON OF AUTONOMIC AND SOMATIC SYSTEMS Somatic system • One motor neuron extends from the CNS to skeletal muscle • Axons are well myelinated • Conduct impulses rapidly

7. THE AUTONOMIC NERVOUS SYSTEM Sympathetic and parasympathetic systems are consists of myelinated pre-ganglionic fibers which make synaptic connections with un-myelinated postganglionic fibers and then innervate the effector organ These synapses usually occur in clusters called ganglia.

8. COMPARISON OF AUTONOMIC AND SOMATIC MOTOR SYSTEMS Autonomic nervous system • Chain of two motor neurons in series • Preganglionic neuron ( have myelinated axons) • Postganglionic neuron ( have unmyelinated , thin axons ) • Conduction is slower than in Somatic due to presence of thin , un-myelinated postganglionic axons Pre-ganglionic Post-ganglionic Ganglion

9. The Autonomic Outflow consists 2 Neurons neurons arranged in series: • (A) Preganglionic nerves: • (1) Are myelinated • (2) In case of sympathetic NS  arise from spinal cord • In case of Parasympathetic NS  arise from Brainstem + spinal cord • .(B) Postganglionic nerves : arise from ganglia . • (1) Are unmywelinated • (2) arise from ganglia . 9

10. COMPARISON OF AUTONOMIC AND SOMATIC MOTOR SYSTEMS

11. THE AUTONOMIC NERVOUS SYSTEM • 2 neurons in the efferent pathway. • 1st neuron has its cell body in gray matter of brain or spinal cord. • Preganglionic neuron. • Synapses with 2nd neuron within an autonomic ganglion. • Postganglionic neuron. • Autonomic ganglion has axon which extends to synapse with target tissue.

12. THE AUTONOMIC NERVOUS SYSTEM Sympathetic and parasympathetic systems are consists of myelinated pre-ganglionic fibers which make synaptic connections with un-myelinated postganglionic fibers and then innervate the effector organ These synapses usually occur in clusters called ganglia.

13. Preganglionic neuron: • Cell body in brain or spinal cord • Axon is myelinated type fiber that extends to autonomic ganglion • Postganglionic neuron: • Cell body lies outside the CNS in an autonomic ganglion • Axon is unmyelinated type fiber that terminates in a visceral effector

14. DIFFERENCES IN SYMPATHETIC AND PARASYMPATHETIC DIVISIONS • Length of postganglionic fibers • Sympathetic  long postganglionic fibers • Parasympathetic  short postganglionic fibers • Therefore , in sympathetic Preganglionic fibers are shorter than Postganglionic ones • And in parasympathetic Preganglionic fibers are longer than Postganglionic ones . • Branching of axons • Sympathetic axons – highly branched • Parasympathetic axons – few branches

15. DIFFERENCES IN SYMPATHETIC AND PARASYMPATHETIC DIVISIONS

18. Preganglionic Sympathetic nerves • exit the CNS from the thoracic + lumbar • segments of the spinal cord • Therefore , the sympathetic system is • also called : “ Thoraco-lumbar Outflow “ • Preganglionic Parasympathetic nerves • exit the CNS from the Cranium ( skull ) +sacral • segments of the spinal cord • Therefore , the Parasympathetic system • is called : “ Craniosacral Outflow “ • Hence , in the Sympathtic system , • Preganglionic fibers are myelinated and • shorter than the unmyelinated Postganglionic • fibers • In Parasympathetic system , Preganglionic • fibers are also myelinated but longer than the • unmyelinated Postganglionic fibers .

19. Origin of ANS fibers Sympathetic: Originate in the thoracic and lumbar regions of the spinal cord (Thoracolumbar) Parasympathetic: Originate from cranial nerves (3rd, 7th, 9th, 10th), and sacral spinal nerves (craniosacral)

20. In the Parasympathetic NS , there is little divergence  the ratio of pre- to postgaglionic fibers is 1/3 . • This little divergence implies more specific , localized actions . • On the other hand , in the Sympathetic NS there is greater divergence . The ratio (pre/post) being = 1/10 ; • This divergence implies diffuse ( generalized ) actions . 20

21. THE AUTONOMIC NERVOUS SYSTEM