A&P Chapter 15 - Autonomic Nervous System

Somatic Nervous System

Consciously perceived sensations

Excitation of skeletal muscle

One neuron connects CNS to organ

Autonomic Nervous System (ANS)

Unconsciously perceived visceral sensations

Involuntary inhibition or excitation of effectors

Two neurons needed to connect CNS to organ

ANS Functions

Regulates activities that are automatic or involuntary

ANS Nerve Functions

Control functions not under conscious control (cardiac, smooth muscle, glands)

ANS Concern

Striking a balance or maintaining homeostasis in the functioning of many organs of the body

ex. heart contraction, heart rate, digestion, breathing, salivation, bladder

SNS and ANS Overlap

Most body responses to changing internal and external stimuli involve both skeletal muscle activity and visceral organ responses

ANS and SNS Differ In

Effectors

Efferent pathways

Target organ responses

ANS Subdivisions (2)

Sympathetic (Thoracolumbar) Division- adrenergic: adrenaline

Parasympathetic (Craniosacral) Division- cholinergic: acetylcholine

*have opposite effects on organs they control

*output (efferent)

Parasympathetic Division Role

Concerned with keeping body energy use low

Most active in resting state

Vital "housekeeping" activities

SLUDD (Salivation, lacrimation, urination, digestion, defecation)

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

Effects of ANS on Effectors

1. Sudoriferous (Sweat) Gland = increase sweat production

2. Pupils = dilate

3. Adrenal Medulla = release norepinephrine and epinephrine

4. Heart = increases heart rate and force of contraction

Sympathetic Division Role

"fight-or-flight"

Energy-expending stressful situations

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

Unique Roles of Sympathetic Division

Regulates functions not subject to parasympathetic influence

ex. activity of adrenal medulla, sweat glands, arrector pili muscles, kidneys, blood vessels

Controls theromoregulatory responses to heat, release of renin from kidneys, and metabolic effects

Localized Versus Diffuse Effects

Parasympathetic: exerts short-lived, highly localized control over effectors

Sympathetic: exerts long-lasting, diffuse effects. interconnected to cause body-wide mobilization

Where does Sympathetic Tone occur?

Vascular System

Where does Parasympathetic Tone occur?

Digestive and Urinary Tracts

Parasympathetic and Sympathetic Interactions/Cooperative Effects

May work together to achieve a common purpose

ex. para controls vasodilation and erection of penis and clitoris while symp controls ejaculation of semen in males and reflex peristalsis in females

*best seen in control of external genitalia

Dual Innervation

Organs that receive impulses from both para and symp fibers

Referred Pain

Sensation of pain that appears to originate from site other than that of painful stimulus

Pain stimuli arising from the viscera are perceived as somatic in origin

May be due to the fact that visceral pain afferents travel along the same pathways as somatic pain fibers

ex. damage to heart causes left chest and arm pain, gallbladder causes shoulder pain