1. Chapter 8 Special Senses

2. Sensory system Sensory system serves as a protective mechanism for an organism by Sensory system serves as a protective mechanism for an organism by detecting changes in the environment detecting changes in the environment An environmental change becomes a stimulus and An environmental change becomes a stimulus and initiates nerve impulse to CNS by sensory neurons. initiates nerve impulse to CNS by sensory neurons. The stimulus is then interpreted by cerebral cortex The stimulus is then interpreted by cerebral cortex Senses are classified according to the distribution of the receptors as Senses are classified according to the distribution of the receptors as somatic (general) senses: touch, pain, pressure, temperature somatic (general) senses: touch, pain, pressure, temperature special senses :vision, taste, smell, hearing and balance special senses :vision, taste, smell, hearing and balance

3. A special sense is located in a special sense organ e.g. A special sense is located in a special sense organ e.g. Chemoreceptors: two types Chemoreceptors: two types Taste : receptors on tongue Taste : receptors on tongue Smell : receptors in the upper nasal cavity Smell : receptors in the upper nasal cavity Photoreceptors : Photoreceptors : Vision : receptors of eye Vision : receptors of eye Mechanoreceptors: Mechanoreceptors: Hearing and Equilibrium: receptors of internal ear Hearing and Equilibrium: receptors of internal ear

4. Chemical Senses – Taste and Smell Both senses use chemoreceptors Both senses use chemoreceptors Stimulated by chemicals in solution Stimulated by chemicals in solution Taste has four types of receptors Taste has four types of receptors Smell can differentiate a large range of chemicals Smell can differentiate a large range of chemicals Both senses complement each other and respond to many of the same stimuli Both senses complement each other and respond to many of the same stimuli

5. Sense of Smell: or olfaction Sense of Smell: or olfaction occurs in response to odors occurs in response to odors The special nasal epithelium of nasal cavity is called olfactory epithelium The special nasal epithelium of nasal cavity is called olfactory epithelium Airborne molecules enter nasal cavity and Airborne molecules enter nasal cavity and stimulate chemo receptors present in olfactory epithelium stimulate chemo receptors present in olfactory epithelium

6. Stimulation creates action potential sending impulses to brain Stimulation creates action potential sending impulses to brain through olfactory nerve (I) to cerebral cortex through olfactory nerve (I) to cerebral cortex Between frontal and temporal lobe above hypothalamus Between frontal and temporal lobe above hypothalamus These receptors degenerate with age These receptors degenerate with age Sense of Smell: or olfaction

7. During common cold, nasal mucous producing cells is inflammated During common cold, nasal mucous producing cells is inflammated preventing the odor from reaching the olfactory neurons of nose and preventing the odor from reaching the olfactory neurons of nose and thus preventing the sense of smell thus preventing the sense of smell Sense of Smell: or olfaction

8. Sense of Taste The sense structures that detect gustatory or taste stimuli are called taste buds The sense structures that detect gustatory or taste stimuli are called taste buds Taste buds are oval structures embedded in the epithelium of tongue and mouth Taste buds are oval structures embedded in the epithelium of tongue and mouth Known as papillae Known as papillae

9. Food particles dissolved in saliva stimulate taste buds Food particles dissolved in saliva stimulate taste buds And send impulse to brain through And send impulse to brain through Medulla by Medulla by facial nerve (VII) facial nerve (VII) glassopharyngeal nerve (IX) glassopharyngeal nerve (IX) vagus (X). vagus (X). Sense of Taste

10. There are four primary taste sensations detected by taste buds: There are four primary taste sensations detected by taste buds: a. Bitter: e.g. coffee. Taste buds are at the back of the tongue a. Bitter: e.g. coffee. Taste buds are at the back of the tongue b. Sour: due to acids. Taste buds are on either side of tongue c. Salty : salts like NaCl. Taste buds are on the sides and front of tongue d. Sweet : Sugars give sweet taste. Taste buds are in front of the tongue Sense of Taste

11. 70% of all sensory receptors are in the eyes 70% of all sensory receptors are in the eyes Each eye has over a million nerve fibers Each eye has over a million nerve fibers Protection for the eye Protection for the eye Most of the eye is enclosed in a bony orbit Most of the eye is enclosed in a bony orbit A cushion of fat surrounds most of the eye A cushion of fat surrounds most of the eye The Eye and Vision

12. Eyelids and eyelashes Eyelids and eyelashes Conjunctiva Conjunctiva Lacrimal apparatus Lacrimal apparatus Extrinsic eye muscles Extrinsic eye muscles Accessory Structures of the Eye

13. Eyelids: Eyelids protect eye from foreign objects Eyelids: Eyelids protect eye from foreign objects Tarsal glands in eyelids lubricate the eye Tarsal glands in eyelids lubricate the eye Eyebrows: prevent sweat from entering eyes and help in shading eyes Eyebrows: prevent sweat from entering eyes and help in shading eyes

14. Accessory Structures of the Eye Conjunctiva Conjunctiva Delicate membrane that lines the eyelids Delicate membrane that lines the eyelids Connects to the surface of the eye Connects to the surface of the eye Secretes mucus to lubricate the eye Secretes mucus to lubricate the eye

15. Accessory Structures of the Eye Lacrimal apparatus: Lacrimal apparatus: Consists of lacrimal gland Consists of lacrimal gland Lacrimal gland— produces lacrimal fluid, located above the lateral end of eye Lacrimal gland— produces lacrimal fluid, located above the lateral end of eye Properties of lacrimal fluid Properties of lacrimal fluid Dilute salt solution (tears) Dilute salt solution (tears) Contains antibodies and lysozyme Contains antibodies and lysozyme Protects, moistens, and lubricates the eye Protects, moistens, and lubricates the eye Empties into the nasal cavity Empties into the nasal cavity

16. Accessory Structures of the Eye Extrinsic eye muscles Extrinsic eye muscles Six muscles attach to the outer surface of the eye Six muscles attach to the outer surface of the eye Produce eye movements Produce eye movements

17. Structure of the Eye Eye is enclosed in three layers or tunics Eye is enclosed in three layers or tunics Fibrous layer Fibrous layer Outside layer Outside layer Vascular layer Vascular layer Middle layer Middle layer Sensory layer Sensory layer Inside layer Inside layer

18. Structure of the Eye: The Fibrous Layer Sclera Sclera White connective tissue layer White connective tissue layer Seen anteriorly as the “white of the eye” Seen anteriorly as the “white of the eye” Cornea Cornea Transparent, central anterior portion Transparent, central anterior portion Allows for light to pass through Allows for light to pass through Repairs itself easily Repairs itself easily The only human tissue that can be transplanted without fear of rejection The only human tissue that can be transplanted without fear of rejection

19. Structure of the Eye: Vascular Layer Choroid is a blood-rich nutritive layer in the posterior of the eye contains a dark pigment Choroid is a blood-rich nutritive layer in the posterior of the eye contains a dark pigment Light is focused by choroid pigment onto retina thus preventing scattering of the light Light is focused by choroid pigment onto retina thus preventing scattering of the light Modified anteriorly into two structures Modified anteriorly into two structures Ciliary body— smooth muscle attached to lens Ciliary body— smooth muscle attached to lens Iris— regulates amount of light entering eye Iris— regulates amount of light entering eye Pigmented layer that gives eye color Pigmented layer that gives eye color Pupil— rounded opening in the iris Pupil— rounded opening in the iris

20. Iris is regulated by: Iris is regulated by: a. sympathetic nervous system by dilating it b. parasympathetic nervous system by constricting it b. parasympathetic nervous system by constricting it Structure of the Eye: Vascular Layer

21. Structure of the Eye: Sensory Layer Retina contains two layers Retina contains two layers Outer pigmented layer Outer pigmented layer They contain photosensitive pigments They contain photosensitive pigments Involved in the conversion of light into nerve impulses Involved in the conversion of light into nerve impulses Inner neural layer Inner neural layer Contains receptor cells Contains receptor cells Biopolar cells Biopolar cells Ganglion cells Ganglion cells

22. Light sensitive pigments are Light sensitive pigments are Rods: contain rhodopsin pigment differentiates between light and darkness Rods: contain rhodopsin pigment differentiates between light and darkness Cones: detect colors (red, blue and green) of the visual light. Cones: detect colors (red, blue and green) of the visual light. Structure of the Eye: Sensory Layer

23. Cone Sensitivity There are three types of cones There are three types of cones Different cones are sensitive to different wavelengths Different cones are sensitive to different wavelengths Color blindness is the result of lack of one cone type Color blindness is the result of lack of one cone type

24. Fovea centralis: region where there are more cones Fovea centralis: region where there are more cones Blind spot: region where the optic nerve exits the eye Blind spot: region where the optic nerve exits the eye Structure of the Eye: Sensory Layer

25. o Lens is present behind the pupil o Lens focuses the light on the retina o Lens is made of transparent intercellular material o It is suspended by ligaments o Lens regulates the focusing with the help of suspensory ligaments Lens

26. o Lens divides the eye cavity into o Anterior cavity or aqueous humor o Posterior cavity or vitreous humor o It is made of water and mucoprotein. o It maintains the pressure to support retina Lens

27. Physiology of vision · Light reflected from the object enters cornea towards lens to retina. · Retina has cones, which detect colors (red, blue and green), and rods detect tone of object and night vision. · Photoreceptors of rods and cones send impulse to brain through bipolar cells to optic nerves

28. optic nerve pass through thalamus optic nerve pass through thalamus cross path at ( optic chiasma), connecting to cross path at ( optic chiasma), connecting to occipital lobe of the cerebral cortex occipital lobe of the cerebral cortex Thus responding to light stimulation Thus responding to light stimulation And visual interpretation, or seeing occurs And visual interpretation, or seeing occurs Human vision is binocular Provides depth perception

29. Lens Accommodation Light must be focused to a point on the retina for optimal vision Light must be focused to a point on the retina for optimal vision The eye is set for distance vision (over 20 ft away) The eye is set for distance vision (over 20 ft away) The lens must change shape to focus for closer objects The lens must change shape to focus for closer objects

30. Short sight or near sightedness: Eye ball is stretched in length thus focusing the object in front of retina rather than on retina. concave lens correct the mistakeShort sight or near sightedness: Eye ball is stretched in length thus focusing the object in front of retina rather than on retina. concave lens correct the mistake

31. Long Sight or far sightedness: Eye ball is compressed such that the light is focused behind the retina instead of on the retina Convex lens fixes the mistakeLong Sight or far sightedness: Eye ball is compressed such that the light is focused behind the retina instead of on the retina Convex lens fixes the mistake

32. Ear Is the sense organ important for hearing and balance The ear is divided into three parts: Is the sense organ important for hearing and balance The ear is divided into three parts: Outer ear Outer ear Middle ear Middle ear Inner ear Inner ear

33. a. Outer ear : Is composed of Auricle (pinna) which directs sound waves into ear Auricle (pinna) which directs sound waves into ear And External auditory maetus (canal) lined with epithelial cells of skin called ceruminous glands, And External auditory maetus (canal) lined with epithelial cells of skin called ceruminous glands, They produce wax They produce wax Wax collects the dust particles Wax collects the dust particles

34. a. Outer ear : Tympanic membrane (or eardrum) connects outer ear to middle ear Tympanic membrane (or eardrum) connects outer ear to middle ear Sound waves reach tympanic membrane through pinna and Sound waves reach tympanic membrane through pinna and cause it to vibrate cause it to vibrate

35. b. Middle ear: b. Middle ear:  Connects the outer ear to inner ear  Filled with air cavity within the temporal bone  Consists of two passages:  One passage opens into Mastoid air cells of temporal bone and  Second passage opens into pharynx through auditory or Eustachian tubes  Auditory tube equalizes air pressure between outside air and middle air cavity

36. b. Middle ear: b. Middle ear: Is made of Is made of three small bones called auditory ossicles three small bones called auditory ossicles Malleus (hammer) Malleus (hammer) Incus (anvil) and Incus (anvil) and Stapes (stirrup) Stapes (stirrup) These bones are connected to the inner ear These bones are connected to the inner ear They amplify the vibrations from tympanic membrane and transfer the vibration to malleus  anvil  stirrup  inner ear They amplify the vibrations from tympanic membrane and transfer the vibration to malleus  anvil  stirrup  inner ear

37. Inner ear Inner ear Includes sense organs for hearing and balance Includes sense organs for hearing and balance consists of bony labyrinth: consists of bony labyrinth: vestibule vestibule cochlea (snail like structure) and cochlea (snail like structure) and 3 semicircular canals 3 semicircular canals And filled with perilymph (plasma like fluid) And filled with perilymph (plasma like fluid)

38. Organ of Corti Organ of Corti Located within the cochlea Located within the cochlea Cochlea is a bony structure Cochlea is a bony structure Has modified cells forming a structure called spiral organs or organ of corti. Has modified cells forming a structure called spiral organs or organ of corti. Organ of corti is specialized sensory haircells and filled with endolymph. Organ of corti is specialized sensory haircells and filled with endolymph. Organs of Hearing

39. Physiology of hearing Vibrations of air medium generate sound waves. Vibrations of air medium generate sound waves. The sound waves are collected by pinna and directed to external auditory maetus. The sound waves are collected by pinna and directed to external auditory maetus.

40. The sound waves cause vibrations of tympanic membrane, The sound waves cause vibrations of tympanic membrane, which moves ossicles which moves ossicles resulting sound waves being amplified. resulting sound waves being amplified. Amplified sound waves create waves in endolymph of the cochlea Amplified sound waves create waves in endolymph of the cochlea and activate haircells of spiral organ and activate haircells of spiral organ Physiology of hearing

41. This creates action potential, which is transmitted through vestibulocochlear nerve to This creates action potential, which is transmitted through vestibulocochlear nerve to pons( of brain stem) pons( of brain stem) to thalamus. to thalamus. From thalamus, impulse is directed to auditory cortex of temporal lobe From thalamus, impulse is directed to auditory cortex of temporal lobe and sound is perceived and sound is perceived

42. Sound is measured in decibels

43. Diseases related to sensory system Sensory function disease Specific structure Function affected Sense of smell Common cold Nasal epithelium Cannot smell visualglaucoma Build up of aqueous fluid due to blockage of ducts in the choroid Blindness caused due to damage to nerves vision Macular degeneration Degeneration of fova centralis( cones) due to age advancement Blind spot, faded colors vision Color blindness Cone proteins not made Cannot distinguish red, blue and green auditory Conduction deafness Fused middle ear bones Cannot hear from birth auditory Nerve deafness Cochlear cilia of nerve cell receptors degenerate due to age advancement Cannot hear