The Autonomic Nervous System

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

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.

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

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

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

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

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

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

The SNS vs. PsNS

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...

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

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?

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

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

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

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)

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

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?

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

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)

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

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

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

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