1. The Autonomic Nervous System

2. The Autonomic Nervous System
Objectives:
Understand the chief function of the ANS
Understand the anatomy of the ANS
Learn the two divisions of the ANS and their functions
Learn the Neurotransmitters involved in the function of the ANS

3. The Autonomic Nervous System
What is the Autonomic Nervous System?
The chief function of the ANS is to control the function of smooth muscle, cardiac muscle, and glands, oh my!
The ANS maintains homeostasis by increasing or decreasing the activity of these organs in response to environmental changes
The ANS does NOT make an organ function! It controls the function!
It doesn't make the truck run, it controls how fast or how slow it runs.

4. The Autonomic Nervous System
Organization of the ANS:
Neuroeffector tissues:
Cardiac Muscle – ANS controls the rate of contraction (chronotropy) and force of contraction (inotropy)
Smooth Muscle – Lines the intestines, sphincters, walls of blood vessels, and bronchioles
Glandular Epithelium – secretion is controlled by the ANS

5. The Autonomic Nervous System
Principles of the ANS:
All of the neurons in the ANS synapse in ganglions
A ganglion is a collection of neuron cell bodies outside of the CNS
In the ANS, there are two types of neurons;
Pre-ganglionic
Post-ganglionic
All ANS neurons are GVE fibers

6. The Autonomic Nervous System
Pre-ganglionic vs. Post-ganglionic:

7. The SNS vs. PsNS They SNS is the Fight or Flight division of the ANS
Resides in the lateral horn cells of the spinal cord gray matter
Between T1-L2
Impulses reach the body globally by way of the paravertebral ganglia

8. The SNS vs. PsNS The PsNS is the Rest and Relax portion of the ANS
AKA ”craniosacral” division
Resides in the cranial nerves and sacral nerves
CN's 3, 7, 9, 10
Sacral nerves S2-S4

9. The SNS vs. PsNS Parasympathetic: Sympathetic:
Has long pre-ganglionic neurons and short post- ganglionic neurons
Only affects a select number of structures
Chief Neurotransmitter is Acetylcholine
Most neurons do NOT travel in spinal nerves
Sympathetic:
Has short pre-ganglionic neurons and long post- ganglionic neurons
Globally affects the body
Chief Neurotransmitters are Epinephrine and Norepinephrine
Most neurons travel in spinal nerves

10. The SNS vs. PsNS

11. The Sympathetic Nervous System
Travels through the body via the paravertebral sympathetic chain ganglia
Course of a typical sympathetic neuron:
Myelinated GVE axons leave the spinal cord from the ventral root
The GVE neurons travel through the spinal nerve, then exit the spinal nerve via the white rami communicantes to enter the paravertebral ganglia
Then 1 of 4 things will happen...

12. The Sympathetic Nervous System
The fibers synapse in the chain at the level of entrance
Ascend or descend the chain and synapse with the postganglionic neuron cell body
Pass through the chain in the thoracic portion of the trunk without synapsing, form the splanchnic nerves
Pass through the sympathetic chain and synapse directly in the adrenal medulla

13. The Sympathetic Nervous System
Spinal origin of preganglionic neurons and the tissues they innervate:
T1-T2: Head
T3-T4: Heart and Lungs
T3-T6: Upper Limbs
T4-T9: Abdominal Viscera
T10-T11: Adrenal Glands
T12-L2: Reproductive organs
T7-L1: Lower Limbs
Why would the SNS innervate the limbs?

14. The Sympathetic Nervous System
Receptors of the Sympathetic nervous system:
ALL preganglionic receptors in the ANS are Cholinergic Nicotinic receptors
These receptors respond to acetylcholine (ACH)
Postganglionic receptors in the SNS are Adrenergic; these respond to Epinephrine and Norepinephrine
Alpha 1
Alpha 2
Beta 1
Beta 2

15. Adrenergic Receptors Alpha 2 locations and functions:
Blood vessels - VasoCONSTRICTION
Sphincters - constriction
Diffusely in other tissues – general stimulation
Alpha 2 locations and functions:
Postganglionic adrenergic axons – autoinhibition
”Shuts off” the SNS – Adrenal Fatigue?
Stimulation of Alpha 2 receptors by norepi will stop the release of more norepi; Negative feedback loop

16. Adrenergic Receptors Beta 1 locations and functions:
Heart - +inotropy, +chronotropy
Kidneys – Renin secretion
Adipose tissue - Lipolysis
Beta 2 locations and functions:
Lungs – relaxation, bronchodilation
Walls of blood vessels – Relaxation, vasoDILATION

17. The Sympathetic Nervous System
NEUROTRANSMITTERS:
Acetylcholine (ACH)
Acts on Cholinergic receptors
Nicotinic receptors or Muscarinic receptors
Present in ALL preganglionic synapses
Also present in the neuronal endplate of skeletal muscle
Epinephrine and Norepinephrine
Released by the Adrenal Medulla 80/20
Acts on Adrenergic receptors (Alpha and Beta)

18. The Sympathetic Nervous System
Actions of the SNS:
Mydriasis (Dilation)
+ Inotropy
+ Chronotropy
Increased blood glucose
Bronchodilation
Increase in blood flow to skeletal muscles
Cutaneous vasoconstriction
Pilo Erection
Diaphoresis (sweating)
Ejaculation

19. The Sympathetic Nervous System
The Big Picture:
The Sympathetic Nervous System keeps you alive during a crisis, like being chased by a bear.
It is not designed to be ”on” all the time.
When we are stressed, our sympathetic nervous system turns on. Until we mellow out, we stay in sympathetic mode.
Source of disease?

20. The Parasympathetic Nervous System
Origin:
The Brain Stem, Carried in CN's 3, 7, 9, 10
Carried in the pelvic splanchnic nerves, S2-S4
The ”Craniosacral Nervous System”
Preganglionic neurons synapse close to the neuroeffector tissue
ONLY neurotransmitter involved is ACH
Responsible for resting and relaxing. Designed to be ”on” all the time
Stress shuts off the PsNS, turns on the SNS

21. The Parasympathetic Nervous System
GVE cell columns in the brain stem contain four nuclei that give rise to GVE PsNS fiber:
Edinger-Westphal Nucleus – CN 3 (Miosis)
Superior Salivatory Nucleus – CN 7 (Lacrimation, Salivation)
Inferior Salivatory Nucleus – CN 9 (Salivation)
Dorsal Motor Nucleus – CN 10 (Thoracic and Abdominal Viscera)

22. The Parasympathetic Nervous System
Sacral segments give rise to parasympathetic GVE Neurons – S2, S3, S4
These are known as pelvic splanchnic nerves – AKA, nervi erigentes
These nerves innervate...
The descending colon
The sigmoid colon
The urinary bladder
The reproductive organs

23. The Parasympathetic Nervous System
Receptors of the PsNS:
ALL of the receptors of the PsNS are Cholinergic
ALL cholinergic receptors respond to ACH
Cholinergic receptors are either Nicotinic or Muscarinic
Nicotinic receptors are present in ALL synaptic ganglia in ALL the ANS; Sympathetic and Parasympathetic
Muscarinic receptors are present ONLY in the neuroeffector tissue innervated by the PsNS

24. The Parasympathetic Nervous System
Receptors of the PsNS:
Muscarinic receptors are found in...
Smooth muscles of the eye (miosis)
The lacrimal and salivary glands
The heart, lungs, and abdominal viscera
The reproductive organs, colon, bladder

25. The Parasympathetic Nervous System
Functions of the PsNS:
- Inotropy
- Chronotropy
Miosis
Increased gut motility
Bronchoconstriction
Erection
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