ANS: Key Concepts

1. ANS: Key Concepts • ANS (under the direction of the brain/spinal cord) regulates the involuntary activities of our internal organs ANATOMICAL DISTINCTIONS • Two motor neurons between CNS and effector • Neurons synapse in (autonomic) ganglia • These synapses allow for increased communication/control in the ANS via divergence or convergence • Effectors: • Cardiac muscle, smooth muscle, glands • 2 divisions • Sympathetic (SD) • Parasympathetic (PD)

2. Comparison of Somatic and Autonomic Nervous Systems

3. Components of the Autonomic Nervous System

4. Reference Slide:Two-Neuron Chain in ANS • The first neuron in the ANS pathway is the preganglionic neuron. Its cell body is in the brain or spinal cord. • A preganglionic axon extends to the second cell body housed within an autonomic ganglion in the peripheral nervous system. • The second neuron in the pathway is called a ganglionic neuron. • A postganglionic axon extends from its cell body to effector (target) cells.

5. Comparison of Somatic and Autonomic Motor Nervous Systems

6. Divisions of AutonomicNervous System • Parasympathetic Division--conservation of energy and replenishment of nutrient stores (“rest and digest”). • Sympathetic Division--preparation of body for energy expenditure/physical activity. Increased activity of this division results in increased alertness and metabolic activity.

7. CNS Origins of PD and SD PD – cranial & sacral SD – thoracic & lumbar

8. Distinction between neurons:PD v. SD Long pre-ganglionic neruon. Ganglia in or on target organ/tissue Short pre-ganglionic neruon. Ganglia near spine

9. Comparison of Sympathetic and Parasympathetic Divisions

10. SD v. PD neurons & epinephrine

11. Fig. 9.7 Neurotransmitters of ANS NE=norepinephrine

12. Parasympathetic Division • Termed craniosacral division because preganglionic neurons are housed within nuclei of in the brainstem and within lateral gray regions of the S2 -S4 spinal cord segments. • Ganglionic neurons are found in or on the effector organ(s)

13. Overview of Parasympathetic Pathways

14. PD Overview • Craniosacral • Homeostasis • Energy replenishment (rest and digest) • P=peaceful • Preganglionic neurons: • Long • Cranial nerves • III (occulomotor); VII (facial); IX (glossopharyngeal), X (vagus)—80% of PD fibers • S2-4 • Pelvic splanchnic nerves • Ach is released • Ganglia • In or on the effector organ • short post ganglionic fibers • Release ACh • Lacks extensive divergence

15. Sympathetic Division • Also termed thoracolumbar division because preganglionic neuron cell bodies are housed in lateral horn between first thoracic (T1) and second lumbar (L2) spinal segments. • Preganglionic axons travel with somatic motor neuron axons to exit the spinal cord and enter the anterior roots and then the T1-L2 spinal nerves.

16. Overview of Sympathetic Pathways Sympathetic chain/trunk (paravertebral ganglia) Prevertebral ganglia

17. Right and Left Sympathetic Trunks • Sympathetic trunks are located anterior to spinal nerves and immediately lateral to vertebral column. • Sympathetic trunk ganglia (paravertebral or chain ganglia) house sympathetic ganglionic neuron cell bodies.

18. Sympathetic Trunk w/ chain (paravertebral) ganglia)

19. Sympathetic Trunk

22. Rami Communicantes • Connect sympathetic trunk to each spinal nerve. • Preganglionic sympathetic axons of T1-L2 spinal nerves are carried by white rami communicantes (or white rami).

23. Rami Communicantes • Postganglionic sympathetic axons are carried from the sympathetic trunk to the spinal nerve by gray rami communicantes (or gray rami). Gray rami connect to all spinal nerves including cervical, sacral and coccygeal spinal nerves. • Preganglionic axons of white rami are myelinated and postganglionic axons of gray rami are unmyelinated.

24. Spinal Nerve Pathway:innervates skin and many blood vessels

25. Postganglionic Sympathetic Nerve Pathway: innervates many thoracic organs (e.g., heart, lungs, esophagus)

26. Splanchnic Nerve Pathway:innervates many abdominopelvic organs

27. Prevertebral (or Collateral) Ganglia • Splanchnic nerves typically terminate in prevertebral ganglia. • Ganglia are unpaired and immediately anterior to the vertebral column on the surface of the aorta in the abdominopelvic cavity. • Sympathetic postganglionic axons extend away from the ganglionic neuron cell bodies in the ganglia and innervate many of the abdominal organs.

28. SplanchnicNerves = bundle of pregangionic axons leading to prevertebral ganglia • preganglionic sympathetic axons that did not synapse in a sympathetic trunk ganglion. • Pass anteriorly from sympathetic trunk to much of abdominal viscera. • Splanchnic nerves typically terminate in prevertebral ganglia. • Ganglia are unpaired and immediately anterior to the vertebral column on the anterolateral surface of the aorta in the abdominopelvic cavity.

29. Adrenal Medulla Pathway: innervates adrenal medulla

30. SD and Adrenal Medulla • Preganglionic fibers directly innervate adrenal medulla (i.e., there is only one neurons and no synapses between the spinal cord and adrenal medulla). • Causes release of epinephrine (and norepinephrine) • Hormones, enter blood • Cause prolonged SD effects and effects on cells that are not directly innervated

31. From Spinal Nerves to SD Pathways • spinal nerves  sympathetic trunk • White rami • Preganglionic fibers • Sympathetic trunk  spinal nerve • Gray rami • Postganglionic fibers • Location of Synapses • Chain ganglia • Postganglionic fibers to effectors via sympathetic nerves (thoracic organs and BV’s) • Postganglionic fibers to effectors via spinal nerves (e.g., skin) • Prevertebral ganglia • Preganglionic fibers arive through splanchnic nerves (abdominal and pelvic organs) • Thoracic (greater, lesser, least), lumbar splanchnic nerves

32. SD Overview • Thoracolumbar • Maintains homeostasis • Prepararing body for energy expenditure • S=stress (physical acitivity, physical and/or emotional stress) • Preganglionic neuron location: • Lateral horns T1-L2 • Ganglia • Sympathetic Trunk (paravertebral or chain ganglia) • on both sides of the spine • White ramus into trunk, gray ramus from trunk to spinal nerve • Prevertebral (collateral) • Anterior to spine or aorta • Splanchnic nerves • Short preganglionic fibers, long post ganglionic fibers • Extensive divergence (1 axion > 20 cell bodies)

33. Dual Innervation (see image on following slide) • Many visceral effectors have dual innervation with innervation by postganglionic axons from both ANS divisions. • The actions of the divisions usually oppose each other (antagonistic effects).

34. sympathetic parasympathetic