9.4 Homeostasis and the Autonomic Nervous System

• All autonomic nerves are motor nerves that regulate organs without conscious control

• Motor nerves lead to muscles that are controlled by conscious control

• The autonomic nervous system maintains homeostasis by adapting your body to the external environment

• Composed of two distinct units:

1. Sympathetic Nervous System

2. Parasympathetic Nervous System

Sympathetic system

• Prepares the body for stress

Parasympathetic system• Restores normal body condions

Sympathetic Nerves:• Come from the

thoracic vertebrae, and lumbar vertebrae

Parasympathetic Nerves:

• Exit directly from the brain, or either the cervical, or caudal sections of the spinal cord

Vagus nerve• major cranial

nerve

• parasympathetic

• Branches of the vagus nerve regulate the heart, bronchi, liver, pancreas, and digestive tract

Organ Sympathetic Parasympathetic

Heart Increase heart rate Decrease heart rate

Digestive Decrease peristalsis Increase peristalsis

Liver Increases the release of glucose

Stores glucose

Eyes Dilates pupils Constricts pupils

Bladder Relaxes sphincter Contracts sphincter

Skin Increases blood flow Decreases blood flow

Adrenal gland Causes the release of epinephrine

No effect

Some Effects of the Autonomic Nervous System

Natural Painkillers

• Pain is interpreted in the substantia gelatinosa (SG) – grey matter in the dorsal spinal cord

• Upon stimulation, the SG produes a neurotransmitter that “informs” the injured tissue or organ of the damage

• The greater the amount of the pain neurotransmitter attached to the organ, the greater the perception of pain

• Endorphins and Enkephalins attach to receptor sites in the SG

Endorphins They are produced by the pituitary gland and the hypothalamus during strenuous exercise, excitement, pain, death, and orgasm,

they resemble the opiates in their abilities to produce analgesia and a sense of well-being.

Endorphins work as "natural pain relievers", whose effects may be enhanced by other medications.

Endorphins

• Natural painkillers produced by the brain

• They work by occupying sites in the substantia gelatinosa (SG) of the brain, which are normally used by pain-signalling chemicals. The endorphins block the sites, reducing the intensity of the pain.

Endorphins• endorphins ("endogenous morphine") are one

of several morphine-like substances (opioids) that occur within our brains. Their molecular structure is very similar to morphine but with different chemical properties.

• Endorphins are polypeptides containing 30 amino acid units. They are manufactured by the body to reduce stress and relieve pain.

• Usually produced during periods of extreme stress, endorphins naturally block pain signals produced by the nervous system.

• The human body produces at least 20 different endorphins

• Beta- endorphin appears to be the endorphin that seems to have the strongest affect on the brain and body during exercise.

• Prolonged, continuous exercise like running, long-distance swimming, aerobics, cycling or cross-country skiing appears to contribute to an increased production and release of endorphins. This results in a sense of euphoria that has been popularly labeled the "runner's high."

• Chocolate is by far the most popular endorphin-producing food on Earth.

• In addition to sugar, caffeine and fat, chocolate contains more than 300 different constituent compounds, including anandamide, a chemical that mimics marijuana's soothing effects on the brain.

• It also contains chemical compounds such as flavanoids (which are also found in wine) that have antioxident properties and reduce serum cholesterol.

• Although the combined psychochemical effects of these compounds on the central nervous system are poorly understood, the production of endorphins are believed to contribute to the renowned "inner glow" experienced by dedicated chocolate lovers.

• endorphins are believed to produce four key effects on the body/mind:

–they enhance the immune system,

–they relieve pain,

–they reduce stress,

–they postpone the aging process.

–Scientists also have found that beta-endorphins can activate human NK (Natural Killer) cells and boost the immune system against diseases and kill cancer cells.

Artificial Painkillers

• Opiates – i.e. heroin, codeine, and morphine, also attach to the SG neurons, preventing production and release of Pain neurotransmitters

• Often produce feelings of tranquality

• Intake of opiates can reduce the production of the body’s natural pain killers

Depressants

i.e. Valium and Librium• Enhance the action of

inhibitory synapses• Synthesis of inhibitory

neurotransmitters often increase in the presence of depressants

• Alcohol, however, is different, it does not act directly on the synapse