1. Nervous System III Anatomy and Physiology
Notes Ch. 12b
Nervous System III
Anatomy and Physiology

2. General Senses
This senses have widespread sensory receptors that are related to the skin, muscles, joints, and viscera. There are 3 groups:
Exteroreceptive senses – Anything associated with changes at the body surface – this would include senses of touch, pressure, temperature, and pain.
Interoreceptive senses – associated with changes in blood pressure stretching blood vessels, an ingested meal stimulating pH receptors in the small intestine and things like that (viscera).
Proprioceptive senses – associated with changes in the muscles and tendons and in body position.

3. Touch and Pressure Senses
There are 3 types of touch and pressure senses:
Free nerve endings – found in epithelial tissues, responsible for the feeling of itching.
Tacticle (Meissner’s) corpuscles – found in connective tissue, mainly in hairless areas of the skin – lips, fingertips, palms, soles, nipples, and external genital organs. They provide fine touch.
Lamellated (Pacinian) corpuscles – Found in deeper dermal tissues of the hands, feet, urethra, breasts, and synovial joints. They detect vibrations in tissues.

4. Temperature Senses
There are 2 groups of free nerve endings in the skin for temperature receptors. One group responds to warm receptors and the other responds to cold receptors.
Warm receptors are sensitive to temps above 25˚C and become unresponsive at temps above 45˚C.
Cold receptors are sensitive to temps between 10˚C and 20˚C.

5. Senses of Pain
Pain receptors are found throughout the skin and internal tissues, except in the nervous tissue of the brain.
Pain receptors protect because they are stimulated when tissues are damaged and prevent further damage.
Most signals are unpleasant so the person will remove the source of the pain.
There are pain receptors that respond to mechanical damage, while others to temperature, other to chemicals, lack of oxygen.

6. Visceral Pain
Pain receptors in the viscera respond differently then those on the surface tissue.
Example – damage to the intestinal tissue during surgery may not activate pain sensations. But if the intestinal tissue is stretched or when smooth muscle in the intestinal walls spasms there may be a strong pain sensation.

7. Referred pain is when you have visceral pain that feels as if it is coming from some part of the body other than the part being stimulated.
Example – pain the starts in the heart may feel like left shoulder or upper limb pain.
This may come from common nerve pathways that send impulses from the skin and the internal organs (they use the same pathway).

8. Pain Pathways
There are 2 types of pain fibers – fast pain fibers and slow pain fibers.
Fast pain fibers are myelinated. They move impulses rapidly. This gives the sensation of sharp pain.
Slow pain fibers are unmylelinated. They cause a delayed, dull, aching pain that is hard to pinpoint.
Most of the time pain receptors are stimulated you stimulate both types of fibers.

9. Regulation of Pain Pathways
Sensation of pain occurs when pain impulses reach the thalamus.
The cerebral cortex judges the intensity of the pain and locates the source. It also is responsible for emotional and mechanical responses to pain.
Enkephalins suppress acute and chronic pain impulses – this is like morphine and other opiate drugs.
Endorphins also suppress pain.

10. Proprioception
Proprioceptors are mechanoreceptors that send information to the CNS about body position and the length and tension of skeletal muscles. The main proprioceptors are lamellated corpuscles, and stretch receptors made of muscle spindles and Golgi tendon organs.
Muscles spindles are located in skeletal muscles.
Golgi tendon organs are in tendons close to where they attach to muscles.

11. Visceral Senses
These are receptors in internal organs that give information like a sense of fullness, discomfort of intestinal gas, and the pain that signals a heart attack.