Chapter 13: The Peripheral Nervous System and Reflex Activity

                The peripheral nervous system contains all the neural structures outside the brain and spinal cord. This includes the sensory receptors, peripheral nerves, associated ganglia, and motor endings. The peripheral nervous system provides links to and from the external environment.

                Sensory receptors are a big portion of the peripheral nervous system; they are special structures to respond to stimuli. The activation of sensory receptors results in the depolarization that triggers impulses to the CNS. The understanding of these stimuli, sensation and perception all occur in the brain. It is important to remember with sensory receptors is that is isn’t necessarily important where the information is coming from, but more so where the input goes in the brain is what is important. All the receptors can be classified by their type of stimulus.

a. Mechanoreceptors-  respond to touch, pressure, vibrations, stretch, and itch

b. Thermoreceptors- responds to change in temperature

c. Photoreceptors- responds to light energy, for example the retina

d. Chemoreceptors- responds to chemicals, for example, smells, taste, and also changes in blood chemistry

e. Nociceptors- sensitive to pain-causing stimuli

Not only can receptors be classified by stimulus type, but they can also be categorized by their location.

1.       Exteroceptors (outside the body)- these type of receptors respond to stimuli arising outside the body, these are usually found near the body’s surface. They are sensitive to touch, pressure, pain, and temperature, this classification includes the special sense organs.

2.       Interoceptors (within the body)- these receptors are found in internal viscera and blood vessels. These are sensitive to chemical changes, stretch, and temperature changes.

3.       Proprioceptors- these receptors respond to degree of stretch of the organs that they occupy. These are found in the skeletal muscles, tendons, joints, ligaments, and connective tissue coverings of bones and muscles. It helps to think of these receptors as “advising” the brain of one’s movement. Because of these receptors, is why you know where your legs or arms are for example without even looking at them. But on the other hand, you make “know” where certain organs are in your body because you have studied diagrams but your brain can’t really distinguish exactly where they are.

Check back next week for a book review on "The Spirit Catches You and You Fall Down" by Anne Fadiman and also key points of chapter 14 in your anatomy book!

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