Target tissues: smooth muscle, glandular tissues, and cardiac muscle

Anatomically distinct from the somatic motor system.

Composed of sympathetic and parasympathetic nervous systems

1) Control visceral systems to maintain homeostasis in response to changes in the external and internal environment

2) Adaptive reponses to environmental stimuli: miosis (cons) vs mydriasis (dil) of pupil, vasodilation/contstiction in response to heat, and fight or flight response to stress

series of rapid adjustments that allow an individual to meet the metabolic demands of severe physical exertion

-increase heart rate and force of contraction

-dilated pupils

-pallor (blood goes to muscles)

-goose pimpling

-cold sweat

-dry mouth

these changes can occur with in seconds

1) Speed of onset: changes can occur with in seconds

2) Tonic activity: continuously firing low frequency bursts of action potentials, sets baseline and permits activity to be increased or decreased

3) Reflex regulated:can be altered by emotion

-Thoraco-lumbar T1-L3: preganglionic cell body lies in the spinal cord lateral gray, axons leave via the white ramus to enter the sympathetic chain

-can innervate the cervical, lumbar, and sacral sympathetic ganglia

-axons from T5-L3 can go straight to one of three prevertebral ganlgia (celiac, superior mesenteric, inferior mesenteric) to supply the visceral organs

-preganglionic fibers can also pass through the verterbral ganglia and the celiac ganglion and go to the chromaffin cells in the adrenal medulla

Sympathetic Nervous System: thoracolumbar outflow, short preganglionic axon, distinct ganglionic system, long postganglionic axon

Parasympathetic Nervous System: cranial sacral outflow, long preganglionic axon, little divergence, ganglion (if present) located at or near the target organ, short postganglionic axon

-Come from cranial nerves III, VII, IX, and X and S2-4

-preganglionic axon goes to the effector organ

-little divergence: ratio of pre-post ganglionic neuron is 1:1 or 1:2

-post galglionic neuron lies close to the effector organ

-Varicosities: present on the postganglionic terminals and contain neurotransmitter

-receptors are scattered widely through out the effector organ so the distance between the nerve terminal and membrane of the effector cell varies

-receptors on effector cells are g-protein coupled and can have inhibitory or excitatory effects

Sympathetic: diffusely distributed, involved in fight or flight

Parasympathetic: regulates activity involved in replinishment (feed and breed), discrete and selective

-All pregalionic cells release acetylcholine

-Parasympathetic postganglionic nerves release acetylcholine

-Sympathetic post-ganglionic nerves release norepinephrine except for sweat glands which use acetylcholine

Acetylcholine is broken down by acetylcholinesterase

Norepinephrine is taken back up into the varicosities by a sodium-dependent membrane pump and then stored or metabolized

Receptors on postganglionic neurons are nicotinic receptors

The parasympathetic receptors are muscarinic.  They have an excitatory effect on smooth muscle and an inhibitory effect on the heart

The sympathetic nervous system has alpha and beta receptors except for general sweating which is muscarinic

Overactive muscarinic receptors results in SLUDE

Salivation, Lacrimation, Urination, Defecation, and Emesis as well as wheezing and bradycardia

atropine blocks muscarinic receptors (muscarinic antagonist) and therefore produces opposing effects-

dry, tachycardia, loss of pupillary light reflex, cyclopegia (inability to focus for near vision)

- alpha 1 found on smooth muscle

-activation is always excitatory

-EPI is more effective, but at physiological condition only NE has high enough concentration to be effective

-alpha1 excitation involves IP3 production and Ca release from the SR to cause contraction

alpha 2 is found on nerve terminals and inhibit transmitter release (ex. postganglionic parasympathetic nerves innervating the GI tract- this is how the SNS inhibits GI function)

much more sensitive than alphas

Beta 1: excitation on the heart

Beta 2: relaxation/inhibition of smooth muscle (low dose epi causes vasodilation, but high dose kicks in alpha and causes vasoconstriction)

more sensitive to EPI than NE

coupled with adenlate cyclase and generate cAMP which activates protein kinase A and the phosphorylation of proteins

Dilator or radial require sympathetic innervation and dilate the pupil/mydriasis

The sphincter/circular muscles require innervation by the parasympathetic system.  Responsible for pupilary light reflex.  Stimulation can cause myosis (pinpoint pupils).