1. The Autonomic Nervous System
Chapter 14

2. Introduction
The stability of our internal environment depends largely on the autonomic nervous system
Autonomic nervous system(ANS) receives signals from visceral organs
The ANS makes adjustments as necessary to ensure optical support for body system

3. Overview of the ANS The autonomic nervous system differs in it’s
Effectors
Efferent pathways
Target organs

4. Effectors of ANS
The somatic nervous system stimulates skeletal muscles
The ANS innervates cardiac and smooth muscles and glands

5. Efferent Pathways and Ganglia
In the somatic system
Cell bodies are within the central nervous system
Axons extend to the muscles they serve
Somatic motor fibers are thick, heavily myelinated Type A fibers that conduct impulses very rapidly

6. Efferent Pathways and Ganglia
In the autonomic nervous system
The motor unit is a two neuron chain
The cell body of the first neuron, the preganglionic neuron, resides in the brain or spinal cord
Its axon, the preganglionic axon, synapses with the second motor neuron, the post- ganglionic neuron, in an autonomic ganglion outside the central nervous system
The postganglionic axon then extends to the effector organ

7. Efferent Pathways and Ganglia
Axons of most preganglionic neurons run from the CNS to synapse in a peripheral autonomic ganglion with a postganglionic neuron

8. Efferent Pathways and Ganglia
Axons of postganglionic neurons run from the ganglion to the effectors (cardiac and smooth muscle fibers and glands)

9. Efferent Pathways and Ganglia
Preganglionic axons are lightly myelinated thin fibers
Postganglionic axons are even thinner and are unmyelinated
Conduction though the autonomic chain is slower than through the somatic motor
Many pre and postganglionic fibers are incorporated into spinal or cranial nerves for most of their course

10. Efferent Pathways and Ganglia
Remember that autonomic ganglion are motor ganglia, containing the cell bodies of motor neurons
They are sites of synapse and information transmission from pre to postganglionic neurons
Also note that the somatic motor division lacks ganglia entirely

11. Neurotransmitter Effects
All somatic motor neurons release acetylcholine at their synapses with their effectors, skeletal muscle fibers
The effect is always excitatory, and if stimulation reaches threshold, the skeletal muscle fibers contacts

12. Neurotransmitter Effects
Neurotransmitters released onto visceral effector organs by postganglionic autonomic fibers include
Norepinephrine secreted by most sympathetic fibers
Acetylcholine released by parasympathetic fibers
Depending on the receptors present on the target organ, its response to these neuro- transmitters may be either excitation or inhibition

13. Overlap of Somatic & Autonomic
Higher brain centers regulate and coordinate both somatic and visceral motor activities
Nearly spinal nerves and many cranial nerves contain both somatic and autonomic fibers
Most of the body’s adaptations to changing internal and external conditions involve both skeletal activity and enhanced response of visceral organs

14. Divisions of ANS There are two division of the ANS
Parasympathetic
Sympathetic
Generally the two divisions serve the same visceral organs but cause essentially opposite effects
If one division stimulates certain smooth muscle to contract or a gland to secrete, the other division inhibits that action
Through this process of duel innervation the two systems counterbalance each other

15. Divisions of ANS
The sympathetic part mobilizes the body during extreme situations (such as fear, exercise or rage)
The parasympathetic division allows us to unwind as it performs maintenance activities and conserves body energy

16. Role of Parasympathetic Division
The parasympathetic division is most effective in non-stressful situations
This division is chiefly concerned with keeping body energy use as low as possible, even as it directs body processes such as digestion and elimination
Resting and digesting division

17. Role of Sympathetic Division
Its activity is evident when we are excited or find ourselves in emergency or threatening situations (frightened)
Pounding heart; rapid, deep breathing; cold, sweaty skin; and dilated eyes are signs
Also changes in brain wave patterns
Its function is to provide the optimal conditions for an appropriate response to some threat (run / see / think)

18. Role of Sympathetic Division
During exercise the sympathetic division also promotes physiological adjustments
Visceral blood supply is diminished
Blood is shunted to working musculature
Bronchioles of the lungs dilate to increase ventilation
Liver releases more sugar into blood stream to support metabolism

19. Anatomy of ANS
The sympathetic and parasympathetic divisions are distinguished by
Unique sites of origin
Different lengths of their fibers
Location of their ganglia

20. Anatomy of ANS Unique origin sites
Parasympathetic fibers emerge from the brain and spinal cord at the sacral level
Sympathetic fibers originate from the thoracic and lumbar regions of the spinal cord

21. Anatomy of ANS Different Lengths of their Fibers
Parasympathetic division has long preganglionic and short postganglionic fibers
Sympathetic is the opposite with short preganglionic and long postganglionic fibers

22. Anatomy of ANS Length of their Ganglia
Most parasympathetic ganglia are located in the visceral effector organs
Sympathetic ganglia lie close to the spinal cord

23. Parasympathetic Division
The parasympathetic emerge from opposite ends of the central nervous system
The preganglionic axons extend from the CNS nearly all the way to the structures to be innervated

24. Parasympathetic Division
The preganglionic neurons synapse with the ganglionic neurons located in terminal ganglia
Very short post ganglionic axons issue from the terminal ganglia and synapse with effector cells in their immediate area

25. Parasympathetic Division
Several cranial nerves contain outflow of the parasympathetic
Preganglionic fibers run in the oculomotor, facial, glossopharyngeal, and vagus nerve

26. Cranial Outflow Oculomotor nerve III
The parasympathetic fibers of the oculomotor nerves innervate smooth muscles of the eye
Constrictor muscles of iris cause pupil to constrict
Ciliary muscle within the orbits of the eye controls lense shape for visual focusing
Allow the eye to focus on close objects in the visual field

28. Cranial Outflow Facial Nerves VII
The parasympathetic fibers of the facial nerves stimulate the secretory activity of many large glands of the head
The pathway activates the nasal glands and the lacrimal glands of the eyes
The preganglionic fibers then run to synapse with ganglionic neurons in the pterygopalatine ganglia stimulating the submandibular and sublingual salivary glands

30. Cranial Outflow Glossopharyngeal (IX)
The parasympathetic nerves originate in the medulla and activate the parotid salivary gland

31. Cranial Outflow Vagus nerves (X)
The major portion of the parasympathetic cranial outflow is via the vagus nerves
The two vagus nerves account for an estimated 90% of all preganglionic parasympathetic fibers in the body
They provide fibers to the neck and contribute to nerve plexuses that serve virtually every organ in the thoracic and abdominal cavity

32. Cranial Outflow
The vagus nerve fibers arise from the dorsal motor of the medulla and terminate by synapsing in terminal ganglia that are usually located in the walls of the target organ

33. Cranial Outflow
Most of the terminal ganglia are not individually named; instead they are collectively called intramural ganglia, literally ganglia “within the walls”
As the vagus nerves passes into the thorax, they send branches to autonomic plexuses
Cardiac plexuses
Pulmonary plexuses
Esophageal plexuses

34. Cranial Outflow
When the vagus nerves reach the esophagus, their fibers intermingle to form the anterior and posterior vagal trunks
Each trunk carries fibers from both vargus nerves

35. Cranial Outflow
The vagal trunks ride the esophagus down to enter the abdominal cavity
They send fibers to form the aortic plexuses (formed by the celiac, superior mesenteric and hypogastric)

36. Cranial Outflow
Abdominal organs which receive vagal innervation include the liver, gallbladder, stomach, small intestine, kidneys, pancreas, and the proximal half of the large intestine
The rest of the cavity are innervated by the sacral outflow

37. Sacral Outflow
The sacral outflow arises from neurons located in the lateral horn of the spinal cord at S2 - S4
The axons of these neurons run in the ventral roots of the spinal nerves to the ventral rami

38. Sacral Outflow
From the ventral rami the neurons branch to form the pelvic splanchnic nerves
Most neurons synapse in the intramural ganglia located in the walls of the distal large intestine, urinary bladder and reproductive organs

39. Sympathetic Division The sympathetic division innervates more organs
It supplies not only the visceral organs in the internal body cavities, but also the visceral structures in the superficial part of the body
Sweat glands
Arrector pili
Arteries and veins

40. Sympathetic Division
All preganglionic fibers in the sympathetic division arise from cell bodies of preganglionic neurons located in spinal cord segments from T1 through L2
It is also called the thoracolumbar

41. Sympathetic Division
After leaving the cord via the ventral root, the preganglionic sympathetic fibers pass through a white ramus communicans to enter the adjoining chain (paravertebral) ganglion forming part of the sympathetic trunk or chain

42. Sympathetic Division
The sympathetic trunks flank each side of the vertebral column and appear as strands of white beads

43. Sympathetic Division
Although the sympathetic trunks extend from the neck to the pelvis, sympathetic fibers arise only from the thoracic and lumbar spinal cord segments

44. Sympathetic Division
The ganglia vary in size, position, and number, but there are typically 23 ganglia in each sympathetic chain…
3 cervical
11 thoracic
4 lumbar
4 sacral
1 coccygeal

45. Sympathetic Division
Once a preganglionic axon reaches a paravertebral ganglion one of three things can happen to it

46. Sympathetic Division
Once a preganglionic axon reaches a paravertebral ganglion one of three things can happen to it…
1. It can synapse with a ganglionic neuron within the same chain ganglion

47. Sympathetic Division
Once a preganglionic axon reaches a paravertebral ganglion one of three things can happen to it…
2. It can ascend or descend the sympathetic chain to synapse in another chain ganglion

48. Sympathetic Division
Once a preganglionic axon reaches a paravertebral ganglion one of three things can happen to it…
3. It can pass through the chain ganglion and emerge from the sympathetic chain without synapsing

49. Sympathetic Division
Preganglionic fibers which emerge from the sympathetic chain without synapsing help to form the splanchnic nerves which synapse with prevertebral or collateral ganglia

50. Sympathetic Division
The prevertebral ganglia are located anterior to the vertebral column

51. Sympathetic Division
Unlike the paravertebral ganglia the prevertebral ganglia . . .
Are neither paired nor segmentally arranged
They occur only in the abdomen and pelvis

52. Sympathetic Division Note:
Regardless of where the synapse occurs, all sympathetic ganglia lie close to the spinal cord
The postganglionic fibers which run from the ganglion to the organs are typically much long than the preganglionic fibers

53. Visceral Reflexes
The visceral sensory neurons are the first link in the autonomic reflexes
These neurons send information concerning chemical changes, stretch, and irritation of the viscera

54. Visceral Reflexes
Visceral reflex arcs have essentially the same components as somatic reflex arcs
Receptor
Sensory neuron
Integration center
Motor neuron
Effector

55. Visceral Reflexes
Visceral reflex arcs differ in that they have a two-neuron chain

56. Visceral Reflexes
Nearly all sympathetic and parasympathetic fibers are accompanied by afferent fibers conducting sensory impulses from glands or muscular structures
Thus, peripheral processes of visceral sensory neurons are found in cranial nerves, VII, IX, and X, the splanchnic nerves, and the sympathetic trunk, as well as the spinal nerves

57. Visceral Reflexes
Like sensory neurons serving somatic structures (skeletal muscles and skin)
The cell bodies of visceral sensory neurons are located in the sensory ganglia of associated cranial nerves or in the dorsal root ganglia of the spinal cord

58. Visceral Reflexes
Visceral sensory reflexes are also found within sympathetic ganglia where synapses with preganglionic neurons occur
Complete three-neuron reflex arcs (sensory, motor, and intrinsic neurons) exist within the walls of the gastro-intestinal tract
Enteric nervous system
Controls gastrointestinal activity

59. Visceral Reflexes
The fact that visceral pain travels along the same pathways as somatic pain fibers helps to explain the phenomenon of referred pain in which pain stimuli arising in the viscera is perceived as somatic in origin

60. Visceral Reflexes
A heart attach may produce a sensation of pain that radiates to the superior thoracic wall and along the medial aspect of the left arm

61. Visceral Reflexes
Since the same spinal segments (T1-T5) innervate both the heart and the regions to which pain signals from heart tissue are referred, the brain interprets most such inputs as coming from the somatic pathway

62. Visceral Reflexes
Additional cutaneous areas to which visceral pain is referred

63. Chapter 14
This concludes the material for which you will be responsible