ANATOMY & PHYSIOLOGY OF THE SENSES

1. ANATOMY & PHYSIOLOGY OF THE SENSES ANATOMY & PHYSIOLOGY 2013-2014

3. Are There Additional Human Senses? • Proprioception = sense of body position (i.e. what is your body doing right now) • Equilibrium = balance • Acceleration • Nociception = sense of pain • Temperature • Satiety • Thirst • Micturition • Amount of CO2 and Na in blood

4. Senses • Means by which an organism obtains information for perception • Sensation is part of the Somatic Division of the Peripheral Nervous System • However integration and perception require the Central Nervous System • Five major senses • Opthalamoception • Gustaoception • Audioception • Olfacaoception • Tactioception

5. Sensory Transduction • All of our senses receive input with specialized cells/nerves called transducers • The transducers convert stimuli into action potentials • Action potentials (APs) are electro-chemical messages that are conveyed along nerves • These messages are ultimately received and “understood” by the various cortices of the brain

6. Examples of Transduction Audition = convert kinetic energy of sound waves into action potentials Gustation = generate action potentials from binding of proteins to specific receptors Opthalamoception= convert radiant energy into action potentials

7. Anatomy of the Eye

8. Changing Views About the Physiology of the Eye • Platonic view: Extramission (light emanates from the eye) • Aristotelian view: Intramission (light enters the eye) • Galen: Optical pneuma flows from the brain into the eye via hollow optical nerves • Kepler: first to suggest the centrality of the retina (over a crystalline lens) in vision

9. Ophthalmoception (Sight) • GOAL: Light stimuli transduced into an Action Potential (AP) • HOW: Our eyes act as converging lenses, focusing this light to their transducing structures • When light strikes the transducers, the photosensitive proteins rhodopsin & photopsinchange 3D shape • This conformational change in shape triggers an AP which then travels to the occipital lobe of the brain via the optic nerve

10. Phototranducers • RODS • Concentrated on periphery of retina • 125 million cells in retina • Most sensitive to light • Scotopic (night) vision • CONES • Responsible for color vision • Work best in more intense light • 4.5-6 million in retina

11. Hermann Grid Illusion • Lateral Inhibition: Stimulation of adjacent rods causes rods at vertices to be shut off

12. Color Afterimages • opponencyprocess =The optic nerve encodes color in three separate channels; one for intensity of lightandtwo for color. • photopsin may take as long as 45 minutes for it to change back to its original form. During that period of time, the photopsin is said to be photobleached and it sends a constant stimulus to the brain. • Eventually, the brain becomes desensitized to the constant stimulation from that color photoreceptor and the brain does not see that color. • However, due to the opponency process, the complimentarycolor appears as an “afterimage”.

13. Colorblindness • “Normal” color vision is trichromatic: red, blue, green color receptors (cones). • Color “blindness” or deficiency comes from a lack or absence of one or more of these types of cones

14. Audioception (Hearing)

15. Audioception(transduction of sound) • Mechanical stimuli transduced into an Action Potential • Our ears funnel and relay vibrations, directing these compression (sound) waves to their transducing structures, the cilia • The sloshing of the cochlear fluid causes cilia to deflect (fold over) • Deflection triggers an AP directed to the temporal lobe of the brainvia the auditory nerve

16. McGurk Effect Explanation • Processing of audition is highly reliant upon visual input as well as auditory input • However, as auditory processing is 5x faster than visual processing, there can be a “disconnect” between the two senses

18. Shepard Rissert Tone: Explained • Overlapping tones at octaves produce vibrations in the inner ear that are the same sine wave and hence sound like the same tone

19. Conductive Hearing Loss • Conductivehearingloss (CHL) is usually the result of some disturbance in the outer or middle ear structures • It is often due to fluid buildup in the middle ear from colds, allergies (serous otitis media), a perforated eardrum, or earwax (cerumen) that has partially blocked the auditory canal • This type of hearing loss can usually be treated with antibiotics or simple as it is a mechanical blockage of the sound waves

20. Sensorineural Hearing Loss • Sensorineuralhearingloss (SNHL) is the result of damage to the inner ear (cochlea)or nerve pathways (auditory nerve) from the ear to the brain • Causes: age, severe head trauma, genetic or hereditary deformations, or drugs that are toxic to hearing. • Much more difficult to correct than CHL as it is an issue with transduction—cochlear implants may restore hearing to some

21. Anatomy of the Skin

22. Tactioception (touch) • Mechanical/Temp/Pain stimuli transduced into AP • Transducing structures are specialized nerves • mechanoreceptors: Detect pressure, vibrations& texture • thermoreceptors: Detect hot/cold • nocireceptors: Detect pain • proprioreceptors: Detect spatial awareness • This triggers an AP which then travels to various locations in the brain via the somatosensory nerves

23. Density of Different Receptors

24. Density and Distribution of Different Receptors

25. Anatomy of the Nasopharygeal & Buccal Cavities

26. Gustaoception (taste) & Olfacaoception (smell) • Chemical stimuli transduced into AP • Sensitive regions in our tongues & noses respond to chemicals, processing them in their transducing structures • Taste buds: Detect sweet (OH-), sour (H+), salt (metal ions), and bitter (N-rich alkaloids) in food • Cilia: Detect odorants in the air • Each transducer is specialized to interpret a particular chemical (taste or smell) • This triggers an AP which then travels to the temporal lobes of the brain via gustatory & olfactory nerves

27. Olfactory & Gustatory Illusions • Similar to afterimages, once a molecule has bound to a receptor, it will continue to send action potentials • However, eventually the neuron will enter a refractory period during which it cannot send a message