Autonomic Nervous System (ANS)

Introduction to the ANS Somatic nervous system (SNS) + ANS  peripheral nervous system (PNS) ANS Not under conscious control Is regulated by hypothalamus, brainstem The ANS supplies nerves to viscera Smooth muscle (stomach, blood vessels) Cardiac muscle (heart) Glands (sweat and digestive glands)

Comparison: SNS vs ANS SNS ANS 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) division Most viscera supplied with nerves of both S and P divisions: dual innervation S and P have opposite (antagonistic) effects Heart rate: S stimulates, P inhibits Digestive organs: S inhibit, P stimulate S: “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 neurons Have cell bodies located in lateral gray of spinal cord segments T1-T12 + L1-L2 So S division is called “thoracolumbar” Axons pass through ventral roots of spinal nerves May branch many times May ascend or descend to many levels of S trunk ganglia (from cervical to sacral) Can synapse with 20 or more postganglionic neuron cell bodies Results: widespread S effects (viscera respond “in sympathy with one another”)

Sympathetic (S) Division Sympathetic postganglionic neurons S postganglionic neurons cell bodies located In S “trunk ganglia” (2 long chains lateral to vertebrae) From cervical to sacral regions  widespread S effects Many 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 arteries Named celiac, superior and inferior mesenteric ganglia Supply abdominal viscera: stomach, intestine, kidneys, liver, spleen Axons pass from ganglia to viscera in S nerves

Sympathetic (S) Division

Parasympathetic (P) Division P preganglionic neurons Cell bodies located in brainstem + in spinal cord segments S2-S4 Therefore P division is called “craniosacral” Axons in cranial nerves III, VII, IX and X and in pelvic nerves from S2-S4 Vagus 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” activities Increase heart rate and contraction, and blood pressure (BP) Dilate pupils Dilate airways Dilate vessels to skeletal muscles, heart, liver and adipose tissue Constrict blood vessels to nonessential organs: skin, GI tract, kidneys Mobilize nutrients for energy: glucose and fats

Activities of the sympathetic division of the ANS (Generally: "Fight-or-flight responses") Organ/Tissue Activity Effect Eye Pupil dilation increased Heart Heart rate & force Blood Pressure Lungs Airway dilation Kidney Blood vessel diameter; urine production decreased GI tract Blood vessel diameter Sphincter decreased contracted Skeletal muscle Blood vessel diameter Adipose tissue Blood vessel diameter Breakdown of TGs and FAs Liver Blood vessel diameter Release of bile acids Skin sweat gland activity Pancreas Glucagon secretion Insulin/Digestive enzyme secretion Pituitary gland (post.) ADH hormone secretion Urinary bladder Muscle wall & diameter of sphincter relaxation & decrease 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

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

Activities of the parasympathetic division of the ANS (Generally: "SLUDD responses") Organ/Tissue Activity Effect Eye Radial muscle/Pupil dilation n.e. Heart Heart rate & force decreased Blood Pressure Lungs Airway narrowing (bronchoconstriction) increased Kidney Blood vessel diameter; urine production GI tract Blood vessel diameter, motility Sphincter increased relaxed Skeletal muscle Blood vessel diameter Adipose tissue Blood vessel diameter TG, FA build-up n.e.   Liver Blood vessel diameter Storage of bile decreased increased Skin sweat gland activity Pancreas Secretion of digestive enzymes & insulin Pituitary gland (post.) ADH hormone secretion Urinary bladder Muscle wall & diameter of sphincter contraction & increase Smooth muscles of hair follicles Uterus Smooth muscles of uterine wall minimal effect Sex organs Erection of penis and clitoris Mouth Salivary gland secretion

THANKS