·         Autonomic Nervous System (ANS)

·         Nerves supplying organs, glands and blood vessels

·         Function automatically, unconsciously

·         Help maintain the internal milieu of body, meeting its moment to moment needs

·         AKA “visceral nervous system”


·         Sympathetic Division - arouses body in response to stress/increased demands

·         Increase HR & BP

·         Increase respiration

·         Dilate blood vessels to heart

·         Increase blood flow to muscles

·         Release adrenaline

·         Release stored energy (glycogen)

·         Dilate pupils

·         Sweat to cool body

·         Decrease blood to skin

·         GI tract slows down; mouth dry


·         Parasympathetic Division - serves non-emergency, body maintenance functions, conserving & replenishing body reserves

·         Decreases HR & BP

·         Slows breathing

·         Lubricates mouth, eyes

·         Stimulates digestion and storing energy

·         Constricts pupil

·         Responsible for elimination


·         Sending an autonomic message requires a 2 neuron sequence


·         Sympathetic Nerves

·         leave CNS at thoracic or lumbar levels  (“thoracolumbar system”)

·         preganglionic neurons are SHORT, traveling to just outside the spinal column to a “chain” or “trunk” of sympathetic ganglia.

·         postganglionic neurons are long, traveling rest of the way to body organs, glands, & vessels.

·          almost all release NE as their transmitter (except those to sweat glands)

·         Sympathetic nerves usually respond in unison.



·         Parasympathetic Division

·         leave CNS from the brain or from sacral cord (“craniosacral”).

·         preganglionic neurons are LONG and go all the way out to body organs to reach ganglia.

·         postganglionic neurons are short, going from those ganglia to nearby organ/gland cells.

·         All release ACh.

·         Parasympathetic nerves tend to operate individually, as needed.


·         Parasympathetic ganglia are near to organs and are not all interconnected.


·         CNS-ANS Interaction

·         The hypothalamus, brainstem reflex centers, & even frontal lobe centers help to coordinate & control ANS activity.

·         Some autonomic reflexes are spinal reflexes & can function independent of the brain.

·         Spinal injuries can damage:

·         descending voluntary control pathways (ANS “UMNs”)

·         damage the “LMNs” of the ANS, causing loss of reflex responses


·         Autonomic Dysreflexia
(can occur after spinal shock wears off)

·         Cervical or upper thoracic spinal injury disrupts normal feedback between sympathetic & parasympathetic nerves.

·         Bladder/bowel distension/irritation, skin irritation, uterine contractions, or air temperature changes can provoke uninhibited autonomic discharges (sym. below injury, parasym. above) with dangerous hypertension.

·         Signs: intense headache, sweating


·         Raynaud’s Disease

·         Over-reaction of sympathetic nerves to peripheral blood vessels to cold causing intense vasoconstriction, pallor, cyanosis and pain in fingers.


·         Raynaud’s Induced Gangrene


·         Spinal Shock

·         Immediately following a spinal injury the cord below injury may “go into shock” and show little or no function for a period of time. As the shock wears off, reflex functions (and perhaps some degree of other functions) will return.


·         ANS Afferents

·         Autonomic nerves also carry sensory fibers from organs to CNS

·         These play a role in autonomic reflexes as well as our conscious awareness of some bodily functions

·         Localization of autonomic sensations is imprecise (e.g. referred pain phenomena)


·         Drug Manipulation of ANS

·         Drugs which act like NE or make NE more available will produce sympathetic effects (asthma inhalers, amphetamine, cocaine are some “sympathomimetics”).

·         Drugs which block NE receptors will decrease sympathetic function ( e.g. alpha or beta “blockers”).

·         Drug Manipulation

·         Drugs which act like ACh can be used to stimulate parasympathetic function.

·         Drugs which block ACh receptors will decrease parasympathetic function (e.g. atropine, tricylic antidepressants).