1. Ch 9 Sensory System In order to maintain homeostasis (ie stable internal environment), it is necessary to detect changes in the external environment and react appropriately. Several sensory systems exist that detect external changes rapidly. These systems include: the somatosensory (touch, pressure, pain etc) system, visual system, auditory and vestibular system, olfactory (smell) system, and gustatory (taste) system. A major objective of this section is to look at how events in the outside environment are detected, converted to action potentials, travel to the brain, and become consciously perceived.

2. Sensations or senses are categorized into 2 types 1. General senses = receptors widely scattered throughout body and detect touch pressure temperature pain vibration itch proprioception (position of limbs/muscle sense

3. Sensations or senses 2. Special senses = receptors are housed in specialized organs ear = hearing & equilibrium eye = vision tongue = taste nose = olfaction (smell)

4. Sensory Receptors detect internal & external changes (stimuli) they are specialized cells or sensory neurons (dendrites or dendritic processes)

5. Sensory information from receptors are relayed to the CNS CNS interprets information & conveys a sensation or sense back to original area neurons

6. Types of Sensory Receptors Receptor types can be associated with both the general and special senses Pain receptors (nociceptors) = detect tissue damage Mechanoreceptors = detect changes in or distortions of cell membranes, respond to mechanical stimuli such as stretching or bending of receptors, or movement Touch Pressure Hearing Equilibrium

7. General Senses: Touch, pressure receptors Examples proprioceptors = tendons & muscles (muscle spindle) baroreceptors = stretch receptors

8. Touch, pressure mechanoreceptors quickly adapts Examples fine touch & pressure = Merkels & Meissner’s corpuscles deep pressure = pacinian corpuscles

9. Other Types of Sensory Receptors Thermoreceptors = detect changes in temperature (hot & cold) Photoreceptors = changes in light (vision) Chemoreceptors = changes in chemical composition (taste & smell)

10. Chemoreceptors respond to chemicals  odor molecules in blood vessels  detect blood pH, O 2 and CO 2

11. Receptor Characteristics Sensory adaptation = ability of a receptor to adapt (reduce its sensitivity) to a constant stimulus

12. Olfaction and touch adapt quickly to a constant stimuli

13. Pain common in skin, joints, bones, blood vessels, eye(s) few in deep tissue, viscera (in fact very dull) none in the brain doesn’t adapt or does so slowly!

14. Pain referred pain = the perception of pain coming from parts of body not actually stimulated −c−common with viscera pain receptors = often dull − Ex. Heart, Gallbladder, or Bladder

15. Temp. located in: − skin, eye(s), muscles, liver, hypothalamus cold receptors 3-4x more numerous quickly adapts

16. Transduction Transduction (2 viewpoints) Takes external stimuli and converts it into an electrical signals (done in the lab) Takes environmental information (environmental stimuli) from the periphery and turns it into the language the brain understands  Action Potentials

17. Environmental Stimuli

18. Primary Somatosensory Cortex Once sensory information reaches the brain through specific nerve tracts, it travels to the primary somatosensory cortex, which is located in the parietal lobe on the postcentral gyrus behind the central sulcus.

19. Homunculus Somatosensory cortex is arranged in a topographical manner on the postcentral gyrus. This area of the brain is called the somatosensory homunculus. It receives sensory information from each part of the body