1. INTRODUCTION
The autonomic nervous system (ANS) operates via reflex arcs.
Operation of the ANS to maintain homeostasis, however, depends on a continual flow of sensory afferent input, from receptors in organs, and efferent motor output to the same effector organs.
Structurally, the ANS includes autonomic sensory neurons, integrating centers in the CNS, and autonomic motor neurons.
Functionally, the ANS usually operates without conscious control.
The ANS is regulated by the hypothalamus and brain stem.

2. Chapter 15 The Autonomic Nervous System
Regulate activity of smooth muscle, cardiac muscle & certain glands
Structures involved
general visceral afferent neurons
general visceral efferent neurons
integration center within the brain
Receives input from limbic system and other regions of the cerebrum

3. SOMATIC AND AUTONOMIC NERVOUS SYSTEMS
The somatic nervous system contains both sensory and motor neurons.
The somatic sensory neurons receive input from receptors of the special and somatic senses.
These sensations are consciously perceived.
Somatic motor neurons innervate skeletal muscle to produce conscious, voluntary movements.
The effect of a motor neuron is always excitation.

4. SOMATIC AND AUTONOMIC NERVOUS SYSTEMS
The autonomic nervous system contains both autonomic sensory and motor neurons.
Autonomic sensory neurons are associated with interoceptors.
Autonomic sensory input is not consciously perceived.
The ANS also receives sensory input from somatic senses and special sensory neurons.
The autonomic motor neurons regulate visceral activities by either increasing (exciting) or decreasing (inhibiting) ongoing activities of cardiac muscle, smooth muscle, and glands.
Most autonomic responses can not be consciously altered or suppressed.

5. SOMATIC vs AUTONOMIC NERVOUS SYSTEMS
All somatic motor pathways consist of a single motor neuron
Autonomic motor pathways consists of two motor neurons in series
The first autonomic neuron motor has its cell body in the CNS and its myelinated axon extends to an autonomic ganglion.
It may extend to the adrenal medullae rather than an autonomic ganglion
The second autonomic motor neuron has its cell body in an autonomic ganglion; its nonmyelinated axon extends to an effector.

6. AUTONOMIC NERVOUS SYSTEM
The output (efferent) part of the ANS is divided into two principal parts:
the sympathetic division
the parasympathetic division
Organs that receive impulses from both sympathetic and parasympathetic fibers are said to have dual innervation.
Table 15.1 summarizes the similarities and differences between the somatic and autonomic nervous systems.

7. Sympathetic Ganglia
These ganglia include the sympathetic trunk or vertebral chain or paravertebral ganglia that lie in a vertical row on either side of the vertebral column (Figures 15.2).
Other sympathetic ganglia are the prevertebral or collateral ganglia that lie anterior to the spinal column and close to large abdominal arteries.
celiac
superior mesenteric
inferior mesenteric ganglia
(Figures 15.2 and 15.4).

8. Dual Innervation, Autonomic Ganglia
Sympathetic (thoracolumbar) division
preganglionic cell bodies in thoracic and first 2 lumbar segments of spinal cord
Ganglia
trunk (chain) ganglia near vertebral bodies
prevertebral ganglia near large blood vessel in gut (celiac, superior mesenteric, inferior mesenteric)
Parasympathetic (craniosacral) division
preganglionic cell bodies in nuclei of 4 cranial nerves and the sacral spinal cord
Ganglia
terminal ganglia in wall of organ

9. Autonomic Plexuses
These are tangled networks of sympathetic and parasympathetic neurons (Figure 15.4) which lie along major arteries.
Major autonomic plexuses include
cardiac,
pulmonary,
celiac,
superior mesenteric,
inferior mesenteric,
renal and
hypogastric

10. Structures of Sympathetic NS
Preganglionic cell bodies at T1 to L2
Rami communicantes
white ramus = myelinated = preganglionic fibers
gray ramus = unmyelinated = postganglionic fibers
Postganglionic cell bodies
sympathetic chain ganglia along the spinal column
prevertebral ganglia at a distance from spinal cord
celiac ganglion
superior mesenteric ganglion
inferior mesenteric ganglion

11. Postganglionic Neurons: Sympathetic vs. Parasympathetic
Sympathetic preganglionic neurons pass to the sympathetic trunk. They may connect to postganglionic neurons in the following ways. (Figure 17.5).
May synapse with postganglionic neurons in the ganglion it first reaches.
May ascend or descend to a higher of lower ganglion before synapsing with postganglionic neurons.
May continue, without synapsing, through the sympathetic trunk ganglion to a prevertebral ganglion where it synapses with the postganglionic neuron.
Parasympathetic preganglionic neurons synapse with postganglionic neurons in terminal ganglia (Figure 17.3).

12. Organs Innervated by Sympathetic NS
Structures innervated by each spinal nerve
sweat glands, arrector pili mm., blood vessels to skin & skeletal mm.
Thoracic & cranial plexuses supply:
heart, lungs, esophagus & thoracic blood vessels
plexus around carotid artery to head structures
Splanchnic nerves to prevertebral ganglia supply:
GI tract from stomach to rectum, urinary & reproductive organs

13. Circuitry of Sympathetic NS
Divergence = each preganglionic cell synapses on many postganglionic cells
Mass activation due to divergence
multiple target organs
fight or flight response explained
Adrenal gland
modified cluster of postganglionic cell bodies that release epinephrine & norepinephrine into blood

14. Structure of the Parasympathetic Division
The cranial outflow consists of preganglionic axons that extend from the brain stem in four cranial nerves. (Figure 15.3).
The cranial outflow consists of four pairs of ganglia and the plexuses associated with the vagus (X) nerve.
The sacral parasympathetic outflow consists of preganglionic axons in the anterior roots of the second through fourth sacral nerves and they form the pelvic splanchnic nerve. (Figure15.3)

15. Parasympathetic Cranial Nerves
Oculomotor nerve
ciliary ganglion in orbit
ciliary muscle & pupillary constrictor muscle inside eyeball
Facial nerve
pterygopalatine and submandibular ganglions
supply tears, salivary & nasal secretions
Glossopharyngeal
otic ganglion supplies parotid salivary gland
Vagus nerve
many brs supply heart, pulmonary and GI tract as far as the midpoint of the colon

16. Cholinergic Neurons and Receptors
Cholinergic receptors are integral membrane proteins in the postsynaptic plasma membrane.
The two types of cholinergic receptors are nicotinic and muscarinic receptors (Figure 15.6 a , b).
Activation of nicotinic receptors causes excitation of the postsynaptic cell.
Nicotinic receptors are found on dendrites & cell bodies of autonomic NS cells (and at NMJ.)
Activation of muscarinic receptors can cause either excitation or inhibition depending on the cell that bears the receptors.
Muscarinic receptors are found on plasma membranes of all parasympathetic effectors

17. Adrenergic Neurons and Receptors
The main types of adrenergic receptors are alpha and beta receptors. These receptors are further classified into subtypes.
Alpha1 and Beta1 receptors produce excitation
Alpha2 and Beta2 receptors cause inhibition
Beta3 receptors (brown fat) increase thermogenesis
Effects triggered by adrenergic neurons typically are longer lasting than those triggered by cholinergic neurons.
Table 15.2 describes the location of the subtypes of cholinergic and adrenergic receptors and summarizes the responses that occur when each type of receptor is activated.

18. Receptor Agonists and Antagonists
An agonist is a substance that binds to and activates a receptor, mimicking the effect of a natural neurotransmitter or hormone.
An antagonist is a substance that binds to and blocks a receptor, preventing a natural neurotransmitter or hormone from exerting its effect.
Drugs can serve as agonists or antagonists to selectively activate or block ANS receptors.

19. Physiological Effects of the ANS
Most body organs receive dual innervation
innervation by both sympathetic & parasympathetic
Hypothalamus regulates balance (tone) between sympathetic and parasympathetic activity levels
Some organs have only sympathetic innervation
sweat glands, adrenal medulla, arrector pili mm & many blood vessels
controlled by regulation of the “tone” of the sympathetic system

20. Sympathetic Responses
Dominance by the sympathetic system is caused by physical or emotional stress -- “E situations”
emergency, embarrassment, excitement, exercise
Alarm reaction = flight or fight response
dilation of pupils
increase of heart rate, force of contraction & BP
decrease in blood flow to nonessential organs
increase in blood flow to skeletal & cardiac muscle
airways dilate & respiratory rate increases
blood glucose level increase
Long lasting due to lingering of NE in synaptic gap and release of norepinephrine by the adrenal gland

21. Parasympathetic Responses
Enhance “rest-and-digest” activities
Mechanisms that help conserve and restore body energy during times of rest
Normally dominate over sympathetic impulses
SLUDD type responses = salivation, lacrimation, urination, digestion & defecation and 3 “decreases”--- decreased HR, diameter of airways and diameter of pupil
Paradoxical fear when there is no escape route or no way to win
causes massive activation of parasympathetic division
loss of control over urination and defecation

22. PHYSIOLOGICAL EFFECTS OF THE ANS - Summary
The sympathetic responses prepare the body for emergency situations (the fight-or-flight responses).
The parasympathetic division regulates activities that conserve and restore body energy (energy conservation-restorative system).
Table 15.4 summarizes the responses of glands, cardiac muscle, and smooth muscle to stimulation by the ANS.

23. Autonomic or Visceral Reflexes
A visceral autonomic reflex adjusts the activity of a visceral effector, often unconsciously.
changes in blood pressure, digestive functions etc
filling & emptying of bladder or defecation
Autonomic reflexes occur over autonomic reflex arcs. Components of that reflex arc:
sensory receptor
sensory neuron
integrating center
pre & postganglionic motor neurons
visceral effectors

24. Control of Autonomic NS
Not aware of autonomic responses because control center is in lower regions of the brain
Hypothalamus is major control center
input: emotions and visceral sensory information
smell, taste, temperature, osmolarity of blood, etc
output: to nuclei in brainstem and spinal cord
posterior & lateral portions control sympathetic NS
increase heart rate, inhibition GI tract, increase temperature
anterior & medial portions control parasympathetic NS
decrease in heart rate, lower blood pressure, increased GI tract secretion and mobility

25. Autonomic versus Somatic NS - Review
Somatic nervous system
consciously perceived sensations
excitation of skeletal muscle
one neuron connects CNS to organ
Autonomic nervous system
unconsciously perceived visceral sensations
involuntary inhibition or excitation of smooth muscle, cardiac muscle or glandular secretion
two neurons needed to connect CNS to organ
preganglionic and postganglionic neurons

26. Autonomic Dysreflexia
Exaggerated response of sympathetic NS in cases of spinal cord injury above T6
Certain sensory impulses trigger mass stimulation of sympathetic nerves below the injury
Result
vasoconstriction which elevates blood pressure
parasympathetic NS tries to compensate by slowing heart rate & dilating blood vessels above the injury
pounding headaches, sweating warm skin above the injury and cool dry skin below
can cause seizures, strokes & heart attacks