1. Anatomy and Physiology I
BIOL 2401
Chapter 17 Special Senses

2. Special Senses Special senses Smell – Olfactory sense
Taste – Gustatory sense
Vision sense
Hearing (auditory sense) and equilibrium
Housed in complex sensory organs 2

3. Olfactory Sense Located in the superior lining of the nasal cavity.
The receptors are part of the nasal epithelium.
Threshold of the olfactory receptor is low - only a few molecules of a chemical can stimulate the receptor.
Olfactory receptors are rapidly adapting (phasic receptors). 3

4. Olfactory Sense Olfactory epithelium is composed of:
Olfactory receptors
bipolar neurons with olfactory hairs embedded in mucus secretion.
Supporting cells
columnar epithelial cells.
Basal cells (stem cells)
replace receptors and supporting cells.
Olfactory (Bowman’s) glands
produce mucus to line the nasal cavity.
Chemicals enter the nasal cavity  stimulate olfactory cilia  Olfactory receptors generate impulses  nerve impulses travel through the cribriform plate of the ethmoid bone  to the olfactory bulbs  to the olfactory tracts  finally to the cerebral cortex and limbic system. 4

5. Gustatory Sense Located on the tongue, soft palate & pharynx.
The receptors are on the lateral walls of the papillae.
Threshold of the gustatory receptor is low - only a few molecules of a chemical can stimulate the receptor.
Gustatory receptors are rapidly adapting – phasic. 5

6. Gustatory Sense Taste buds are composed of 3 types of cells:
Supporting cells
Epithelial cells, support the receptors.
Gustatory receptors
Epithelial cells with gustatory hair projects into taste pore.
Basal cells
Replace receptor and support cells.
Chemicals dissolve in saliva  contact gustatory hairs  receptors generate impulses  impulses travel via cranial nerves (V, VII, IX and X (vagus)  to thalamus & hypothalamus  to the primary gustatory area on parietal lobe of the cerebral cortex  conscious perception of taste. 6

7. Vision Sense Vision sense is to make brain aware of the environment.
There are several structures involved:
Eyeballs
Eyelids
Lacrimal glands 7

8. Vision Sense
Eyelashes & eyebrows help protect from foreign objects, perspiration & sunlight. 8

9. Vision Sense – Eyelids (Palpebrae)
Composed of:
skin covering orbicularis oculi muscle
to open and close the eye
Eyelashes - hair lining the eyelids to protect the eye surface.
Tarsal glands
oily secretions
To keep the eye lids from adhering to each other
Conjunctiva
palpebral & bulbar (ocular)
stops at corneal edge
Palpebral fissure is the gap
between the eyelids. 9

10. Vision Sense – Eye Muscles
Six muscles:
allow the eyeball to move in different directions.
inserted on the outer surface of the eyeball.
4 rectus muscles -- superior, inferior, lateral and medial. Move the eyeball up, down, laterally or medially.
2 oblique muscles -- superior and inferior. Help in rolling the eyeball around in a circle. 10

11. Vision Sense – Lacrimal Apparatus
Lacrimal fluid/tears:
spread over the eye by blinking.
Protects, lubricates and cleans the eye surface.
contains water, mucus, salts and bactericidal enzyme called lysozyme.
Flow: Lacrimal gland  secrets lacrimal fluid  fluid is spread over the eye surface  fluid drained into lacrimal punctum  into lacrimal ducts  lacrimal sac  nasolacrimal duct  nasal cavity  drained back into pharynx  into digestive system. 11

12. Vision Sense – Eyeball The wall of the eye is made of three layers:
Fibrous Tunic (outer layer)
Vascular Tunic (middle layer)
Nervous Tunic (inner layer) 12

13. Vision Sense – Eyeball Nourished by tears & aqueous humor
1. Fibrous tunic is divided into two parts:
Sclera: “White” of the eye
Dense irregular connective tissue layer -- collagen & fibroblasts
Provides shape, support and site for muscle attachment
Cornea: Transparent
Helps focus light (refraction)
Epithelial and connective tissue
Nourished by tears & aqueous humor
Transplants - common & successful; no blood vessels - so no antibodies to cause rejection 13

14. Vision Sense – Eyeball 2. Vascular tunic is divided into three parts:
Choroid
blood vessels to provide nutrients to the eye layers
pigment in melanocytes absorb scattered light
Ciliary body
Ciliary processes that secretes aqueous humor
ciliary muscle
smooth muscle to change the shape of the lens
Iris
Colored portion of eye
Hole in center is pupil
Function is to regulate amount of light entering eye
Autonomic reflex - circular and radial muscle fibers to regulate the size of the pupil 14

15. Vision Sense – Eyeball 3. Nervous tunic: Pigmented epithelium
Non-visual portion - absorbs stray light & helps keep image clear
Photoreceptor layer
Other cell layers (modify the signal)
bipolar cells
ganglion neuron layer 15

16. Vision Sense –Photoreceptors
Named for shape of outer segment - dendrite
Receptors transduce light energy into a receptor potential in outer segment
Photopigment integrated in the membrane of outer segment membrane
Rods
Rod shaped dendrite
Activated by dim light
Forms B&W image
Contain a single type of photopigment - rhodopsin
Cones
Cone shaped dendrite
Activated by brighter light
Forms sharp & color image
Contain one of three different kinds of photopigments (RGB) - photopsins 16

17. Vision Sense Blind Spot and Fovea Blind Spot
Place where the optic nerve exits
Blood vessels enter/exit
No rods or cones
No image is formed
Fovea
Place with maximum density of rods or cones
Sharpest image is formed
Image formed most often 17

18. Vision Sense Lens Lens Nonvascular
Located just behind the pupil and iris
Filled with clear proteins - crystallins
Focuses light on nervous tunic 18

19. Vision Sense Cavities Cavities Anterior cavity
Anterior to the lens; divided into: Anterior chamber - cavity anterior to iris Posterior chamber - cavity between lens and iris
Filled with aqueous humor - produced by ciliary body
Vitreous/posterior cavity
Posterior to the lens
Filled with jelly-like vitreous humor
Formed once during embryonic life
Maintains shape of the eyeball 19

20. Secretion and Reabsorption of Aqueous Humor
Physiology of Vision
Secretion and Reabsorption of Aqueous Humor
Secreted by ciliary body.
Reabsorbed by scleral venous sinus. 20

21. Regulation of Pupil Size
Physiology of Vision
Regulation of Pupil Size
Pupil - regulate light entering the eye. Pupillary radial muscle  dilation the pupil. Pupillary sphincter muscle  constriction of pupil. 21

22. Refraction and Image Formation
Physiology of Vision
Refraction and Image Formation
Image is formed on retina (nervous tunic).
The image is upside down and reversed. 22

23. Shape of the Lens and Image Formation
Physiology of Vision
Shape of the Lens and Image Formation
Ciliary muscles help change the shape of the lens.
Changing the shape of the lens  Image is focused on the retina. 23

24. Physiology of Vision – Optic Pathway
Absorption of light by photopigments in rods and cones (photoreceptors).
Impulses are conveyed through the retina to the optic nerve.
Optic nerves cross (optic chiasm).
Optic tract passes through the thalamus.
Tracts eventually reach the occipital lobes of the cerebral cortex.
Brain learns to work with that information 24

25. Physiology of Vision – Optic Chiasm
Left occipital lobe sees right side of the world.
Right occipital lobe sees left side of the world. 25

26. Physiology of Vision – Eyesight Disorders26

27. Other Disorders of the Eye
The following are the common disorders of the eye: Conjunctivitis: inflammation of conjunctiva due to bacterial or viral infection. Cataract: where the lens becomes cloudy due to age related denaturation of proteins. Glaucoma: increased pressure due to accumulation of aqueous humor in the anterior cavity; may affect vision. Colorblindness: inability to see colors due to absence of specific cone cells; sex-linked disorder. Macular degeneration: loss of acute vision due to degeneration of retina; heredity, infection, trauma or aging. Retinal detachment: separation of retina from choroid that causes disconnection of blood and nerve supply to retina; loss of eyesight.

28. Auditory Sense and Sense of Equilibrium
The external (outer) ear.
The middle (tympanic cavity) ear.
The internal (inner) ear. 28

29. Auditory Sense and Sense of Equilibrium
External Ear
Collects and directs sound waves inwards
Composed of
auricle or pinna
cartilage covered with skin
external auditory canal
passage through the temporal bone
ceruminous glands produce cerumen (ear wax)
tympanic membrane/eardrum
thin membrane 29

30. Auditory Sense and Sense of Equilibrium
Middle Ear
Air filled cavity
Connects external ear with internal ear
Has 3 ossicles
malleus (attached to eardrum), incus, & stapes (attached to the membrane on inner ear (oval window)
Amplify vibration sound stimulus
Eustachian (Auditory) tube leads to nasopharynx
helps to equalize pressure on both sides of eardrum 30

31. Auditory Sense and Sense of Equilibrium
Inner Ear
Labyrinth is divided into three parts:
Cochlea
contains receptors for hearing
Vestibule
contain receptors for static equilibrium
Semicircular canals
contain receptors for dynamic equilibrium 31

32. Auditory Sense - Cochlea
Shell shaped region of the labyrinth
Has fluid canals (scala tympani and scala vestibuli) extending from oval window to round window
Located between the canals is the spiral organ or organ of Corti
Has mechanoreceptors (hair cells) that are stimulated by the movement of the fluid in the canals
Impulses from cochlea  cochlear nerve  vestibulocochlear nerve auditory area in the temporal lobe of the cerebrum 32

33. Internal Structure of Cochlea33

34. Auditory Sense Pathway34

35. Sense of Static Equilibrium - Vestibule
maintain the position of the body (head) relative to the force of gravity
receptors (hair cells with cilia) within the vestibule (saccule & utricle)
supporting cells secrete gelatinous layer
gelatinous layer contains calcium carbonate crystals (otoliths) that move when you tip your head. 35

36. Sense of Static Equilibrium - Vestibule
Movement of cilia
release of neurotransmitter
impulse is generated on the vestibular nerve
vestibulocochlear nerve
medulla and cerebellum of brain
cerebellum updates sensory information going to the motor areas of the cerebral cortex
motor cortex can then adjust its signals to maintain balance 36

37. Sense of Dynamic Equilibrium – Semicircular Canals
maintain the balance during movement of the body or body part
composed of three canals attached to the vestibule
receptors (hair cells with cilia) within the ampullae at the base of the canals
supporting cells secrete gelatinous layer
when the body moves, fluid movement in the canals stimulates hair cells 37

38. Sense of Dynamic Equilibrium – Semicircular Canals
Movement of cilia  release of neurotransmitter  impulse is generated on the ampullary nerve  vestibulocochlear nerve  medulla and cerebellum of the brain  cerebellum updates sensory information going to the motor areas of the cerebral cortex  motor cortex can then adjust its signals to maintain balance 38

39. Ear Disorders Motion sickness
Dysfunctions caused by stimulation of semicircular canals during motion
Otitis Media
Infections in the middle ear
Deafness: Significant or total hearing loss.
Sensorineural Deafness
Conduction deafness