1. Special senses

2. Special senses Taste, smell, sight, hearing, and balance
Special sensory receptors
Large complex organs (eyes, ears)
Localized clusters of receptors (taste buds)
confined to the head region

3. The eye and vision

4. eyes Visual organs 70% of all sensory receptors are in the eyes
40% of the cerebral cortex is involved in processing visual information

5. Accessory structures of the eyes
Lacrimal apparatus – keeps the surface of the eye moist
Lacrimal gland – produces lacrimal fluid
Lacrimal sac – fluid empties into nasal cavity

6. Accessory structures of the eyes, cont.
Eyelids- anterior protection
Eyelashes
Meibomian glands
Modified sebaceous glands at eyelid edges
Secrete oily lubricant for the eye
Ciliary glands
Between eyelashes
Modified sweat glands
Conjuctiva
Delicate membrane that lines eyelids and covers part of eye.
Fuses with corneal epithelium
Secretes mucus to keep eyes moist

7. Eye movement
Controlled by 6 external muscles

8. Internal structure of the eyes
Hollow sphere.
Fluid filled interior- helps maintain shape
Walls composed of 3 tunics
Fibrous tunic- outermost (white of the eye)
Thick connective tissue
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 transparent window
Limbus – junction between sclera and cornea
Scleral venous sinus – allows aqueous humor to drain

10. Internal eye structure cont.
Vascular tunic- middle coat
Composed of choroid, ciliary body, and iris
Choroid – vascular, darkly pigmented membrane
Brown color – from melanocytes
Prevents scattering of light rays within the eye
Choroid corresponds to the arachnoid and pia maters
Ciliary body- attachment to lens and iris
Iris- smooth muscle fibers that act like the diaphragm of a camera.
Pupil- opens to let light in

12. Dilation of the pupil

13. Internal eye structure cont.
Sensory tunic- innermost layer (retina)
Composed of two layers
Pigmented layer – single layer of melanocytes
Neural layer – sheet of nervous tissue
Contains three main types of neurons
Photoreceptor cells
Rod cells – more sensitive to light
Allow vision in dim light
Cone cells – operate best in bright light
Enable high-acuity, color vision
Bipolar cells
Ganglion cells

14. Regional Specializations of the Retina
Macula lutea – contains mostly cones
Fovea centralis – contains only cones
Region of highest visual acuity
Optic disc – blind spot

15. Medial View of the Eye

16. Internal chambers and fluids
The lens and ciliary zonules divide the eye
Posterior cavity
Filled with vitreous humor
Clear, jelly-like substance
Transmits light
Supports the posterior surface of the lens
Helps maintain intraocular pressure

17. Internal Chambers and Fluids
Anterior cavity
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

18. The Lens
A thick, transparent, biconvex disc held in place by its ciliary zonule.

19. Homeostatic imbalance
Color Blindness
Lacking one type of cone
Cataracts
Lens becomes hard and opaque due to age
Glaucoma
Increased pressure in eyes due to lack of drainage for aqueos humor

20. Light and focus 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

21. Visual pathways to the brain
Each side of the brain receives images from both eyes.
Each eye sees a slightly different view, but visual fields overlap.
This gives us binocular vision.

22. Homeostatic imbalance
Age-related macular degeneration (AMD)
Involves the buildup of visual pigments in the retina
Wet

23. Homeostatic imbalance
Retinopathy in diabetes
Vessels have weak walls – causes hemorrhaging and blindness

24. The ear: hearing and balance

25. Anatomy of 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

26. The Outer (External) Ear
The part we think of as the ear.
The auricle (pinna)
Helps direct sounds
External acoustic meatus
Canal lined with skin
Contains hairs, sebaceous glands, and ceruminous glands (secrete yellow wax)
Tympanic membrane
Forms the boundary between the external and middle ear

28. The Middle Ear The tympanic cavity Medial wall is penetrated by:
A small, air-filled space
Located within the petrous portion of the temporal bone
Contains ossicles that transmit vibration from eardrum to fluids of inner ear.
Malleus (hammer)
Incus (anvil)
Stapes (stirrup)
Medial wall is penetrated by:
Oval window
Round window
Pharyngotympanic tube (auditory or eustachian tube)
Links the middle ear and pharynx

29. The Inner (Internal) Ear
Inner ear – also called the bony labyrinth
Lies within the petrous portion of the temporal bone behind the eye socket
cavity consisting of three parts
Semicircular canals
Vestibule
Cochlea

31. The Inner Ear, cont. Membranous labyrinth
Series of membrane-walled sacs and ducts within the bony laryrinth.
Consists of three main parts
Semicircular ducts
Utricle and saccule
Cochlear duct
Filled with a clear fluid – endolymph
Confined to the membranous labyrinth
Bony labyrinth is filled with perilymph
Continuous with cerebrospinal fluid

32. The Membranous Labyrinth
Figure 16.20

33. The Vestibule
The central part of the bony labyrinth (actually a cavity)
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 that 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

34. 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

35. The Semicircular Canals

36. The Semicircular Canals
Semicircular duct – snakes through each semicircular canal
Membranous ampulla – located within bony ampulla
Houses a structure called a crista ampullaris
Responsible for maintaining static equilibrium.

37. Structure and Function of the Crista Ampullaris
Figure 16.22

38. The Cochlea A spiraling chamber in the bony labyrinth
contains receptors for hearing

39. 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

40. Disorders of Equilibrium and Hearing: Motion Sickness
Motion sickness – carsickness, seasickness
Popular theory for a cause – a mismatch of sensory inputs

41. 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

42. Disorders of Equilibrium and Hearing
Deafness
Conduction deafness
Sound vibrations cannot be conducted to the inner ear
Ruptured tympanic membrane, otitis media, otosclerosis
Otitis media
Normal tympanic
membrane
Ruptured tympanic
membrane

43. Disorders of Equilibrium and Hearing:
Deafness
Sensorineural deafness
Results from damage to any part of the auditory pathway
mild
severe

44. The Chemical Senses: Taste and Smell

45. Taste – Gustation Taste receptors Occur in taste buds
Most are found on the surface of the tongue
Located within tongue papillae (circumvallate and fungiform)
Collection of epithelial cells
Contain three major cell types
Supporting cells
Gustatory cells-respond to chemicals in saliva
Contain long microvilli – extend through a taste pore
Basal cells

46. Taste Buds

47. Taste Sensation and the Gustatory Pathway
Four basic qualities of taste
Sweet (responds to sugars and amino acids)
Sour (respond to hydrogen ions or acidity)
Salty (respond to metals)
Bitter (responds to alkaloids)
No structural difference among taste buds

48. 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

49. Smell (Olfaction)
Receptors occupy a postage-stamp sixe area in the roof of each nasal cavity.
Olfactory receptor cells
Neurons with olfactory hairs that transmit to the olfactory nerve.