Lecture 21 Major Senses

1. Lecture 21Major Senses

2. Sensory Perception • Thesensory nervous systemtells the central nervous system what’s happenin’! • Sensory receptors • Specialized sensory cells that detect changes inside and outside the body • Sensory organs • Complex sensory receptors • Eyes, ears, taste buds

3. The path of sensory information • Stimulation • Physical stimulus activates a sensory receptor • Transduction • Converting the stimulus into an action potential • Stimulus-gated ion channels in sensory neuron are opened or closed • An action potential is generated • Transmission • Nerve impulse is conducted to the CNS • Two main types of sensory receptors • Extroreceptors sense stimuli in external environment • Introreceptors sense stimuli in internal environment

4. Sensing the Internal Environment • Vertebrates use many different sensory receptors to respond to changes in internal environment • Temperature Change • Two nerve endings in the skin • One stimulated by cold, the other by warmth • Blood chemistry • Receptors in arteries sense blood CO2 levels • Pain • Special nerve endings within tissues near the surface

5. Muscle contraction Sensory receptors called proprioceptors embedded within muscle & tendons sense stretch of muscle Touch Pressure receptors buried below skin Blood pressure Neurons called baroreceptors in major arteries Sensing Pressure & Strectch

6. Sensing Chemicals: Taste • Taste • Taste budsarelocated in raised areas called papillae • Food chemicals dissolve in saliva and contact the taste cells

7. Sensing Chemicals: Smell • Smell • Olfactoryreceptor cellsare embedded in the epithelium of the nasal passage • These are far more sensitive in dogs than in humans

8. Evolution of Balance & Hearing • Lateral Line and the fish’s sense of hearing • Fish are able to sense objects that reflect pressure waves and low-frequency vibrations • The system consists of canals running the length of the fish’s body under the skin • Canals have sensory structures containing hair cells projecting into a gelatinous cupula • Vibrations produce movements of the cupula • Hair cells bend and depolarize associated sensory neurons

9. Human Sensation of Gravity and Motion • Receptors in the ear inform the brain where the body is in three dimensions • Balance • Gravity is detected byshifting ofotolith sensory receptors • These are located in a gelatin-like matrix in the utricle and saccule chambers of the inner ear • Motion • Motion is detected by the deflection of hair cells by fluid in a direction opposite to that of motion • These hair cells are found in the cupula,tent-like assemblies in the three semicircular canals

10. Properties of Sound • Sound is: • A pressure disturbance (alternating areas of high and low pressure) originating from a vibrating object • Composed of areas of rarefaction and compression • Represented by a sine wave in wavelength, frequency, and amplitude • Frequency – the number of waves that pass a given point in a given time • Pitch – perception of different frequencies (we hear from 20–20,000 Hz) • Amplitude – intensity of a sound measured in decibels (dB) • Loudness – subjective interpretation of sound intensity

11. Sensing Sounds: Hearing • When a sound is heard, air vibration is detected • Eardrummembrane is pushed in and out by waves of air pressure • Three small bones (ossicles) located on other side of eardrum increase the vibration force • Amplified vibration is transferred to fluid within the inner ear • Inner ear chamber is shaped like a tightly coiled snail shell and is called cochlea

12. Cochlea are hair cells that rest on a membrane running up and down the chamber They are covered by another membrane Sound waves entering the cochlea cause this membrane “sandwich” to vibrate Bent hair cells send nerve impulses to brain Pitch is determined by different frequencies causing different parts of the membrane to vibrate Different sensory neurons are fired Sound intensity is determined by how often the neurons fire Sensing Sounds: Hearing PLAY Transduction of Sound Waves

13. The Evolution of Vision • Vision begins with the capture of light energy by photoreceptors • Many invertebrates have simple visual systems • Photoreceptors are clustered in an eyespot • Perceive light direction but not a visual image • Members of four phyla have evolved well-developed, image-forming eyes • Annelids • Mollusks • Arthropods • Vertebrates • The eyes are strikingly similar in structure but are believed to have evolved independently

14. Eyes in Three Phyla of Animals

15. Structure of the Vertebrate Eye • The vertebrate eye works like a lens-focused camera • Cornea – Transparent covering that focuses light • Lens – Completes the focusing • Ciliary muscles – Change the shape of the lens • Iris – Shutter that controls amount of light • Pupil – Transparent zone • Retina – The back surface of the eye • Contains two types of photoreceptors: rodsandcones • Fovea– Center of retina • Produces the sharpest image

16. How Rods and Cones Work • Rodsare extremely sensitive to dimlight • Cannot distinguish colors • Do not detect edges • Produce poorly defined images • Cones can detect color • Detect edges well • Produce sharp images

17. Pigmentin rods and conesare made from carotenoids cis-retinalis attached to a protein called opsin This light-gathering complex is called rhodopsin How Light is Converted to a Nerve Impulse • When light is absorbed by cis-retinal, it changes shape to trans-retinal • This induces a change in the shape of the opsin protein • A signal-transduction pathway is initiated leading to generation of a nerve impulse

18. Color Vision • Three kinds of cone cells exist, each with its own opsin type • Differences in opsin shape, affect the flexibility of the attached cis-retinal • This shifts the wavelength at which it absorbs light • 420 nm – Blue • 530 nm – Green • 560 nm – Red

19. Colorblindness • Colorblindnessis a condition in which a person cannot see all three colors • Caused by a lack of one or more types of cones • It is inherited as a sex-linked trait and is more likely to affect males

20. Conveying the Light Information to the Brain • Rods and cones are at the rear of the retina, not front! • Light passes through four types of cells before it reaches them • Photoreceptor activation stimulates bipolar cells, and then ganglion cells • Nerve impulse travels through the optic nerve to the cerebral cortex

21. Focusing the Eye • Focusing for Distant Vision: • Light from a distance needs little adjustment for proper focusing • Far point of vision – the distance beyond which the lens does not need to change shape to focus (20 ft.) • Focusing for Close Vision: • Accommodation – changing the lens shape by ciliary muscles to increase refractory power • Constriction – the pupillary reflex constricts the pupils to prevent divergent light rays from entering the eye • Convergence – medial rotation of the eyeballs toward the object being viewed

22. Problems of Refraction • Normal eye (Emmetropic) – with light focused properly • Nearsighted (Myopic) – the focal point is in front of the retina • Corrected with a concave lens • Farsighted (Hyperopic) – the focal point is behind the retina • Corrected with a convex lens

23. Muscles That Move the Eye • Six strap-like extrinsic eye muscles • Enable the eye to follow moving objects • Maintain the shape of the eyeball • Four rectus muscles originate from the annular ring • Two oblique muscles move the eye in the vertical plane

24. Binocular Vision • Primates and most predators have eyes on front of the head • The two fields of vision overlap allowing the perception of 3-D images and depth • Prey animals generally have eyes located on sides of the head • This prevents binocular vision but enlarges the perceptive field

25. Lacrimal Apparatus • Consists of the lacrimal gland and associated ducts • Lacrimal glands secrete tears • Tears • Contain mucus, antibodies, and lysozyme • Enter the eye via lacrimal excretory ducts • Exit the eye medially via the lacrimal punctum & lacrimal canal • Drain into the nasolacrimal duct

26. Other Types of Sensory Reception Heat • Pit vipers can locate warm prey, using infrared radiation • Heat-detecting pit organs Electricity • Used by aquatic vertebrates to locate prey and mates Magnetism • Eels, sharks and many birds orient themselves in relation to the Earth’s magnetic field