Well illustrated and explained PowerPoints of special senses

1. The Special Senses
(Hearing, Smell, Sight, Taste and
Balance)
CLASS: I M.Sc.,
UNIT: 4
PREPARED BY: A. BENNO SUSAI
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2. The Special Senses
• Taste, smell, sight, hearing, and balance
• Special sensory receptors
– Localized – confined to the head region
– Receptors are not free endings of sensory
neurons
– Special receptor cells
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3. The Chemical Senses: Taste and
Smell
• Taste – gustation
• Smell – olfaction
• Receptors – classified as
chemoreceptors
• Respond to chemicals
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4. Taste – Gustation
• Taste receptors
– Occur in taste buds
• Most are found on the surface of the tongue
• Located within tongue papillae
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5. Taste Buds
• Collection of 50-100 epithelial cells
• Contain three major cell types
– Supporting cells
– Gustatory cells
– Basal cells
• Contain long microvilli – extend through
a taste pore
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6. Taste Buds
Figure 16.1a, b
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7. Taste Sensation and the
Gustatory Pathway
• Four basic qualities of taste
– Sweet, sour, salty, and bitter
– A fifth taste – umami – “deliciousness”
• No structural difference among taste
buds
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8. Gustatory Pathway
• Taste information reaches the cerebral
cortex
– Primarily through the facial (VII) and
glossopharyngeal (IX) nerves
– Some taste information through the vagus
nerve (X)
– Sensory neurons synapse in the medulla
• Located in the solitary nucleus
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9. Gustatory Pathway from Taste
Buds
Figure 16.2
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10. Smell (Olfaction)
• Receptors are part of the olfactory
epithelium
• Olfactory epithelium composed of:
– Cell bodies of olfactory receptor cells
– Supporting cells – columnar cells
– Basal cells – form new olfactory receptor
cells
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11. Smell (Olfaction)
• Axons of olfactory epithelium
– Gather into bundles – filaments of the
olfactory nerve
– Pass through the cribriform plate of the
ethmoid bone
– Attach to the olfactory bulbs
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12. Olfactory Receptors
Figure 16.3a, b
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13. The Eye and Vision
• Visual organ – the eye
• 70% of all sensory receptors are in the
eyes
• 40% of the cerebral cortex is involved
in processing visual information
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14. Figure 16.5b
Accessory Structures of the Eye
• Lacrimal
apparatus – keeps
the surface of
the eye moist
– Lacrimal gland –
produces lacrimal
fluid
– Lacrimal sac –
fluid empties into
nasal cavity
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15. The Fibrous Tunic
• Most external layer of the eyeball
– Composed of two regions of connective
tissue
• Sclera – posterior five-sixths of the tunic
– White, opaque region
– Provides shape and an anchor for eye
muscles
• Cornea – anterior one-sixth of the fibrous
tunic
• Limbus – junction between sclera and cornea
• Scleral venous sinus – allows aqueous humor
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16. Medial View of the Eye
Figure 16.7a
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17. The Vascular Tunic
• The middle coat of the eyeball
• Composed of choroid, ciliary body, and iris
• Choroid – vascular, darkly pigmented
membrane
– Forms posterior five-sixths of the vascular tunic
– Brown color – from melanocytes
– Prevents scattering of light rays within the eye
• Choroid corresponds to the arachnoid and
piamaters
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18. Posterior View of the Anterior
Half of the Eye
Figure 16.9a
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19. The Vascular Tunic
• Ciliary body – thickened ring of tissue –
encircles the lens
• Composed of ciliary muscle
– Ciliary processes – posterior surface of the
ciliary body
– Ciliary zonule (suspensory ligament)
• Attached around entire circumference of the
lens
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20. The Vascular Tunic
Figure 16.8
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21. The Iris
• Visible colored part of the eye
• Attached to the ciliary body
• Composed of smooth muscle
• Pupil – the round, central opening
– Sphincter pupillae muscle (constrictor or
circular)
– Dilator pupillae muscle (dilator or radial)
• Act to vary the size of the pupil
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22. The Sensory Tunic (Retina)
• Retina – the deepest tunic
• Composed of two layers
– Pigmented layer – single layer of
melanocytes
– Neural layer – sheet of nervous tissue
• Contains three main types of neurons
– Photoreceptor cells
– Bipolar cells
– Ganglion cells
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23. Microscopic Anatomy of the
Retina
Figure 16.10a
Ganglion
cells
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24. Photoreceptors
• Two main types
– Rod cells – more sensitive to light
• Allow vision in dim light
– Cone cells – operate best in bright light
• Enable high-acuity, color vision
• Considered neurons
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25. Photoreceptors
Figure 16.11
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26. Rhodopsin – Visual purple
Rhodopsin
Bathorhodopsin
Lumirhodopsin
Metarhodopsin I
Metarhodopsin II
All – trans retinal
All – trans retinol (Vitamin A)
Photoisomerization
Scotopsin
11 – cis retinal
11 – cis retinol
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27. Regional Specializations of the
Retina
• Macula lutea – contains mostly cones
• Fovea centralis – contains only cones
– Region of highest visual acuity
• Optic disc – blind spot
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28. Figure 16.10c
Blood Supply of the Retina
• Retina receives
blood from two
sources
– Outer third of the
retina – supplied
by capillaries in
the choroid
– Inner two-thirds
of the retina –
supplied by central
artery and vein of
the retina DEPARTMENT OF
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29. Internal Chambers and Fluids
• The lens and ciliary zonules divide the
eye
• Posterior segment (cavity)
– Filled with vitreous humor
• Clear, jelly-like substance
• Transmits light
• Supports the posterior surface of the lens
• Helps maintain intraocular pressure
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30. Internal Chambers and Fluids
• Anterior segment
– Divided into anterior and posterior
chambers
• Anterior chamber – between the cornea and iris
• Posterior chamber – between the iris and lens
• Filled with aqueous humor
– Renewed continuously
– Formed as a blood filtrate
– Supplies nutrients to the lens and cornea
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31. Internal Chambers and Fluids
Figure 16.8
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32. The Lens
•A thick, transparent, biconvex disc
•Held in place by its ciliary zonule
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33. Lens, Zonule Fibers, & Ciliary Muscles
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34. Lens Epithelium
capsule
epithelium
fibers
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35. The Eye as an Optical Device
• Structures in the eye bend light rays
• Light rays converge on the retina at a
single focal point
• Light bending structures (refractory
media)
– The lens, cornea, and humors
• Accommodation – curvature of the lens
is adjustable
– Allows for focusing on nearby objects
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36. Visual Pathways
• Most visual information travels to the
cerebral cortex
• Responsible for conscious “seeing”
• Other pathways travel to nuclei in the
midbrain and diencephalon
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37. Visual Pathways to the Cerebral
Cortex
• Pathway begins at the retina
– Light activates photoreceptors
– Photoreceptors signal bipolar cells
– Bipolar cells signal ganglion cells
– Axons of ganglion cells exit eye as the optic
nerve
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38. Visual Pathways to the Cerebral
Cortex
• Optic tracts send axons to:
– Lateral geniculate nucleus of the thalamus
• Synapse with thalamic neurons
• Fibers of the optic radiation reach the primary
visual cortex
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39. Visual Pathways to the Brain and Visual Fields
Figure 16.15a
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40. Visual Pathways to Other Parts of the
Brain
• Some axons from the optic tracts
– Branch to midbrain
• Superior colliculi
• Pretectal nuclei
• Other branches from the optic tracts
– Branch to the suprachiasmatic nucleus
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41. Normal Opthalmoscopic View
of Eye
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42. Disorders of the Eye and Vision:
Macular Degeneration
• Age-related macular degeneration
(AMD)
– Involves the buildup of visual pigments in
the retina
Dry
Wet
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43. Macular Degeneration
Simulation
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44. Disorders of the Eye and Vision:
Retinopathy
• Retinopathy in diabetes
– Vessels have weak walls – causes
hemorrhaging and blindness
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45. Disorders of the Eye and Vision:
Trachoma
• Trachoma – contagious infection of
the conjunctiva
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46. The Ear: Hearing and
Equilibrium
• The ear – receptor organ for hearing
and equilibrium
• Composed of three main regions
– Outer ear – functions in hearing
– Middle ear – functions in hearing
– Inner ear – functions in both hearing and
equilibrium
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47. The Outer (External) Ear
• Composed of:
– The auricle (pinna)
• Helps direct sounds
– External acoustic meatus
• Lined with skin
– Contains hairs, sebaceous glands, and
ceruminous glands
– Tympanic membrane
• Forms the boundary between the external
and middle ear
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48. The Outer (External) Ear
Figure 16.17a
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49. The Middle Ear
• The tympanic cavity
– A small, air-filled space
– Located within the petrous portion of the temporal
bone
• Medial wall is penetrated by:
– Oval window
– Round window
• Pharyngotympanic tube (auditory or
eustachian tube)
– Links the middle ear and pharynx
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50. Structures of the Middle Ear
Figure 16.17b
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51. Figure 16.19
The Middle Ear
• Ear ossicles –
smallest bones in
the body
– Malleus – attaches to
the eardrum
– Incus – between the
malleus and stapes
– Stapes – vibrates
against the oval
window
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52. DEPARTMENT OF
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53. The Inner (Internal) Ear
• Inner ear – also called the labyrinth
• Lies within the petrous portion of the
temporal bone
• Bony labyrinth – a cavity consisting of
three parts
– Semicircular canals
– Vestibule
– Cochlea
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54. The Inner (Internal) Ear
Figure 16.17b
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55. The Inner (Internal) Ear
• Membranous labyrinth
– Series of membrane-walled sacs and ducts
– Fit within the bony labyrinth
– Consists of three main parts
• Semicircular ducts
• Utricle and saccule
• Cochlear duct
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56. The Inner (Internal) Ear
• Membranous labyrinth (continued)
– Filled with a clear fluid – endolymph
• Confined to the membranous labyrinth
– Bony labyrinth is filled with perilymph
• Continuous with cerebrospinal fluid
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57. The Membranous Labyrinth
Figure 16.20
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58. The Vestibule
• The central part of the bony labyrinth
• Lies medial to the middle ear
– Utricle and saccule – suspended in perilymph
• Two egg-shaped parts of the membranous labyrinth
• House the macula – a spot of sensory epithelium
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59. The Vestibule
• Macula – contains receptor cells
– Monitor the position of the head when the
head is still
– Contains columnar supporting cells
– Receptor cells – called hair cells
• Synapse with the vestibular nerve
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60. Anatomy and Function of the Maculae
Figure 16.21a
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61. Anatomy and Function of the
Maculae
Figure 16.21b
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62. The Semicircular Canals
• Lie posterior and lateral to the
vestibule
• Anterior and posterior semicircular
canals
– Lie in the vertical plane at right angles
• Lateral semicircular canal
– Lies in the horizontal plane
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63. The Semicircular Canals
Figure 16.20
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64. The Semicircular Canals
• Semicircular duct – snakes through
each semicircular canal
• Membranous ampulla – located within
bony ampulla
– Houses a structure called a crista
ampullaris
• Cristae contain receptor cells of rotational
acceleration
– Epithelium contains supporting cells and
receptor hair cells
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65. Structure and Function of the Crista
Ampullaris
Figure 16.22
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66. The Cochlea
• A spiraling chamber in the bony
labyrinth
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67. The Cochlea
Figure 16.23a–c
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68. The Cochlea
• The cochlear duct (scala media) –
contains receptors for hearing
– Lies between two chambers
• The scala vestibuli
• The scala tympani
– The vestibular membrane – the roof of the
cochlear duct
– The basilar membrane – the floor of the
cochlear duct
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69. The Cochlea
• The cochlear duct (scala media) –
contains receptors for hearing
– Organ of Corti – the receptor epithelium
for hearing
– Consists of:
• Supporting cells
• Inner and outer hair cells (receptor cells)
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70. The Role of the Cochlea in
Hearing
Figure 16.24
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71. Equilibrium and Auditory
Pathways
• The equilibrium pathway
– Transmits information on the position and
movement of the head
– Most information goes to lower brain
centers (reflex centers)
• The ascending auditory pathway
– Transmits information from cochlear
receptors to the cerebral cortex
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72. Auditory Pathway from the Organ of
Corti
Figure 16.25
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73. Disorders of Equilibrium and Hearing:
Motion Sickness
• Motion sickness (Kinetosis ) –
carsickness, seasickness
– Popular theory for a cause – a mismatch of
sensory inputs
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74. Disorders of Equilibrium and Hearing:
Meniere’s Syndrome
• Meniere’s syndrome – equilibrium is
greatly disturbed
– Excessive amounts of endolymph in the
membranous labyrinth
Normal Meniere’s
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75. Disorders of Equilibrium and Hearing:
Conduction Deafness
• Deafness
– Conduction deafness
• Sound vibrations cannot be conducted to the inner
ear
– Ruptured tympanic membrane, otitis media,
otosclerosis
Normal tympanic
membrane
Otitis media
Ruptured tympanic
membrane
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76. Disorders of Equilibrium and Hearing:
Sensorineural Deafness
• Deafness
• Sensorineural deafness
– Results from damage to any part of the
auditory pathway
mild
severe
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77. REFERNCES
• Arthur C. Guyton, 2005, Text Book of
Medical Physiology, WB Saunders’s, USA.
• Gerald J. Tortora and Sandra Reynolds.
2003. Principles of Anatomy and
Physiology. (10th Edition). John Wiley and
Sons. Inc. Pub. New York.
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