· 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).