ANS

Autonomic Nervous System (ANS)

Introduction to the ANS
Somatic nervous system (SNS) + ANS  peripheral nervous system (PNS)ANSNot under conscious control Is regulated by hypothalamus, brainstemThe ANS supplies nerves to visceraSmooth muscle (stomach, blood vessels)Cardiac muscle (heart)Glands (sweat and digestive glands)

Comparison: SNS vs ANS

SNS Controls skeletal muscle Conscious, voluntary control Motor pathway: one neuron from CNS to effector sensory neurons (from skin, skeletal muscles, and special sense organs) All release the neurotransmitter ACh
ANS Controls viscera: smooth and cardiac muscle, and glands Unconscious, involuntary Motor pathway: series of two neurons from CNS to effector sensory neurons (monitors viscera) Two divisions: sympathetic, parasympathetic Release either ACh or NE

Somatic Nervous System

ANS Motor Pathways
Autonomic motor pathway includes two motor neurons Preganglionic neuron from CNS to neuron in autonomic ganglion Postganglionic neuron from cell body in ganglion to effector

ANS Motor Pathways

Divisions of the ANS

Sympathetic (S) division + parasympathetic (P) divisionMost viscera supplied with nerves of both S and P divisions: dual innervationS and P have opposite (antagonistic) effectsHeart rate: S stimulates, P inhibits Digestive organs: S inhibit, P stimulateS: “fight or flight” P: “rest and digest”Some viscera receive only S (not P) nerves:Sweat glands, many blood vessels, hair muscles

Sympathetic (S) Division

Sympathetic preganglionic neuronsHave cell bodies located in lateral gray of spinal cord segments T1-T12 + L1-L2So S division is called “thoracolumbar”Axons pass through ventral roots of spinal nervesMay branch many timesMay ascend or descend to many levels of S trunk ganglia (from cervical to sacral)Can synapse with 20 or more postganglionic neuron cell bodiesResults: widespread S effects (viscera respond “in sympathy with one another”)

Sympathetic (S) Division

Sympathetic postganglionic neuronsS postganglionic neurons cell bodies locatedIn S “trunk ganglia” (2 long chains lateral to vertebrae)From cervical to sacral regions  widespread S effectsMany axons from these cell bodies pass back into spinal nerves to reach viscera in skin (sweat glands, hair muscles, blood vessels)In S “prevertebral ganglia” anterior to 3 large abdominal arteriesNamed celiac, superior and inferior mesenteric gangliaSupply abdominal viscera: stomach, intestine, kidneys, liver, spleenAxons pass from ganglia to viscera in S nerves

Sympathetic (S) Division

Parasympathetic (P) Division
P preganglionic neuronsCell bodies located in brainstem + in spinal cord segments S2-S4Therefore P division is called “craniosacral”Axons in cranial nerves III, VII, IX and X and in pelvic nerves from S2-S4Vagus nerves (cranial nerves X) carry 80% of all P nerve impulses. Vagus nerves carry both motor and sensory neurons to/from viscera within the thorax and most of the abdominal cavity.P preganglionic axons do not branch or pass though S trunk ganglia but pass directly almost to viscera

Parasympathetic (P) Division

P postganglionic neurons Cell bodies lie in terminal ganglia Located within or near the innervated organ So P nerves cause precise, localized (not widespread) effects Because of anatomical arrangement, S nerves supply all viscera but P nerves do not reach some viscera. These include sweat glands, arrector pili muscles of hairs in skin, kidneys, spleen, adrenal medullae, and the walls of most blood vessels. Axons pass from ganglia to viscera in P nerves

Parasympathetic (P) Division

ANS Neurotransmitters: Comparison

Acetylcholine (ACh) ACh more common; released by: All S and P preganglionic axons All P postganglionic axons Some S postganglionic axons (to sweat glands) ACh destroyed by enzyme ACh-ase so short-lived response
Norepinephrine (NE) NE less common; released by: Almost all S postganglionic axons NE has longer lasting effects enhanced by epinephrine + NE from adrenal medullae

Sympathetic Effects

“Fight-or-flight” activitiesIncrease heart rate and contraction, and blood pressure (BP)Dilate pupilsDilate airwaysDilate vessels to skeletal muscles, heart, liver and adipose tissueConstrict blood vessels to nonessential organs: skin, GI tract, kidneysMobilize nutrients for energy: glucose and fats

Organ/Tissue

Activity
Effect
Eye
Pupil dilation
increased
Heart
Heart rate & force
increased
Blood
Pressure
increased
Lungs
Airway dilation
increased
Kidney
Blood vessel diameter;urine production
decreased
GI tract
Blood vessel diameterSphincter
decreasedcontracted
Skeletal muscle
Blood vessel diameter
increased
Adipose tissue
Blood vessel diameterBreakdown of TGs and FAs
increased
Liver
Blood vessel diameterRelease of bile acids
increased
Skin
sweat gland activity
increased
Pancreas
Glucagon secretion
increased
Pancreas
Insulin/Digestive enzyme secretion
decreased
Pituitary gland (post.)
ADH hormone secretion
increased
Urinary bladder
Muscle wall & diameter of sphincter
relaxation & decrease
Skin
Smooth muscles of hair follicles
contract ("goose bumps")
Uterus
Smooth muscles of uterine wall
contract (pregnant)relax (non-pregnant)
Sex organs
Muscles for ejaculation of semen (man)
contract
Mouth
Salivary gland secretion
decreased


Parasympathetic Effects
Rest-and-digest activities SLUDD Salivation Lacrimation Urination Digestion Defecation Decrease heart rate, airway diameter, pupil diameter

Organ/Tissue

Activity
Effect
Eye
Radial muscle/Pupil dilation
n.e.
Heart
Heart rate & force
decreased
Blood
Pressure
decreased
Lungs
Airway narrowing (bronchoconstriction)
increased
Kidney
Blood vessel diameter;urine production
n.e.
GI tract
Blood vessel diameter, motilitySphincter
increasedrelaxed
Skeletal muscle
Blood vessel diameter
n.e.
Adipose tissue
Blood vessel diameterTG, FA build-up


Liver
Blood vessel diameterStorage of bile
decreasedincreased
Skin
sweat gland activity
n.e.
Pancreas
Secretion of digestive enzymes & insulin
increased
Pituitary gland (post.)
ADH hormone secretion
n.e.
Urinary bladder
Muscle wall & diameter of sphincter
contraction & increase
Skin
Smooth muscles of hair follicles
n.e.
Uterus
Smooth muscles of uterine wall
minimal effect
Sex organs
Erection of penis and clitoris
increased
Mouth
Salivary gland secretion
increased
Activities of the parasympathetic division of the ANS (Generally: "SLUDD responses")


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