Autonomic Nervous System

Sympathetic

Thoracolumbar region of the spinal cord

Effectors

• The effectors of the SNS are skeletal muscles. • The effectors of the ANS are cardiac muscle, smooth muscle, and glands.

Referred Pain

- Pain stimuli arising from the viscera are perceived as somatic in origin. - This may be due to the fact that visceral pain afferents travel along the same pathways as somatic pain fibers.

Neurotransmitter Effects: All somatic motor neurons release Acetylcholine (ACh), which has an excitatory effect. In the ANS:

- Preganglionic fibers release Ach. - Postganglionic fibers release norepinephrine or ACh and the effect is either stimulatory or inhibitory. - ANS effect on the target organ is dependent upon the neurotransmitter released and the receptor type of the effector.

ANS divisions: sympathetic and parasympathetic.

- The sympathetic mobilizes the body during extreme situations. - The parasympathetic performs maintenance activities and conserves body energy. - The two divisions counterbalance each other.

Parasympathetic

Brain and Sacral spinal cord or CranioSacral

Cooperative Effects

• ANS cooperation is best seen in control of the external genitalia. • Parasympathetic fibers cause vasodilation and are responsible for erection of the penis and clitoris. • Sympathetic fibers cause ejaculation of semen in males and reflex peristalsis in females.

Role of the Parasympathetic Division

• Concerned with keeping body energy use low. • Involves the D activities - digestion, defecation, and diuresis. • Its activity is illustrated in a person who relaxes after a meal; • Blood pressure, heart rate, and respiratory rates are low. • Gastrointestinal tract activity is high. • The skin is warm and the pupils are constricted.

Efferent Pathways

• Heavily myelinated axons of the somatic motor neurons extend from the CNS to the effector.

Interactions of the Autonomic Divisions

• Most visceral organs are innervated by both sympathetic and parasympathetic fibers. • Sympathetic fibers increase heart and respiratory rates, and inhibit digestion and elimination. • Parasympathetic fibers decrease heart and respiratory rates, and allow for digestion and the discarding of wastes.

Parasympathetic - "Relaxation"

• Pupils constrict. Pin Point Pupils • He is drooling because of increased secretions. • Blood sent to abdominal organs. • Blood glucose levels drop to normal. • Heart beats sluggishly because GI hogs the energy. • Airways (bronchioles) constrict so he needs Oxygen. • He is defecating and urinating AND has an erection. - Saliva=watery -Point=erection

Sympathetic "fight or flight"

• Pupils dilate. • Decreased pulmonary secretions and • Bronchodilation increases blood circulation. • Increased HR and contractility improves Cardiac Output. • Blood sent to muscles, heart, liver - away from GI. • Ejaculation occurs. - Shoot=ejaculation • Liver makes glucose from glycogen. Blood glucose levels rise. • GI motility and secretions decrease and urine is retained -Saliva=Less water, dry

Unique Roles of the Sympathetic Division

• Regulates many functions not subject to parasympathetic influence. • Includes the activity of the adrenal medulla, sweat glands, arrector pili muscles, kidneys, and most blood vessels. • The sympathetic division controls: • Thermoregulatory responses to heat. • Release of renin from the kidneys.

Parasympathetic Tone

• Slows the heart. • Dictates normal activity levels of the digestive and urinary systems. • The sympathetic division can override these effects during times of stress. • Drugs that block parasympathetic responses increase heart rate and block fecal and urinary retention.

Levels of ANS Control

• The hypothalamus is the main integration center of ANS activity. • Subconscious cerebral input via limbic lobe connections influences hypothalamic function. • Other controls come from the cerebral cortex, the reticular formation, and the spinal cord.

Localized Versus Diffuse Effects

• The parasympathetic division exerts short-lived, highly localized control. • The sympathetic division exerts long-lasting, diffuse effects.

Axons of the ANS are a two-neuron chain;

• The preganglionic (first) neuron has a lightly myelinated axon. • The ganglionic (second) neuron extends to an effector organ.

Sympathetic Tone

• The sympathetic division controls blood pressure and keeps the blood vessels in a continual state of partial constriction. • This sympathetic tone (vasomotor tone): • Constricts blood vessels and causes blood pressure to rise as needed. • Prompts vessels to dilate if blood pressure is to be decreased.

Metabolic Effects

• The sympathetic division promotes metabolic effects that are not reversed by the parasympathetic division. • Increases the metabolic rate of body cells. • Raises blood glucose levels. • Mobilizes fat as a food source. • Stimulates the reticular activating system (RAS) of the brain, increasing mental alertness.

Effects of Sympathetic Activation

• is long-lasting because NE: • Is inactivated more slowly than Ach. • Is an indirectly acting neurotransmitter, using a second-messenger system. • And epinephrine are released into the blood and remain there until destroyed by the liver.

Role of the Sympathetic Division

• is the "fight-or-flight" system. • Involves E activities - exercise, excitement, emergency, and embarrassment. • Promotes adjustments during exercise - blood flow to organs is reduced, flow to muscles is increased. • Its activity is illustrated by a person who is threatened; heart rate increases, and breathing is rapid and deep. • The skin is cold and sweaty, and the pupils dilate.