I. Olfactory Sensations: Smell

A. Anatomy Diagram

• 10-100 million olfactory receptors lie in nasal epithelium; superior portion of nasal cavity
• Olfactory epithelium composed of three kinds of cells:
  • Olfactory receptors - bipolar neurons with dendrites extending into nasal cavity
  • Supporting cells - columnar epithelium of mucous membrane lining the nose
  • Basal cells - olfactory receptor stem cells that lie between supporting cell bases
• Olfactory nerve consists of olfactory bulb and olfactory tract

B. Physiology Diagram

• Detection of primary scents
• Recognition of many scents due to patterns of activity in the brain that arise from activation of different combinations of olfactory receptors
• Chemicals cause depolarization of bipolar neurons

II. Gustatory Sensations: Taste

A. Anatomy Diagram

• 10,000 taste buds (mostly tongue, but also soft palate, pharynx, and larynx)
• Taste bud contain three types of cells:  Diagram
  • Supporting cells - form a capsule
  • Gustatory receptor cells - contain gustatory hairs that project from taste pore
  • Basal cells - gustatory stem cells
• Taste buds found in elevations on tongue called papillae (circumvallate, fungiform, and filiform)

B. Physiology  Diagram

• Chemicals are dissolved in saliva and then come in contact with gustatory hairs which cause depolarization
• Four taste sensations: sour, salty, bitter, and sweet

III. Visual Sensations

A. Anatomy Diagram

• Accessory structures: eyelids, tarsal plate and tarsal glands, conjunctiva, eyelashes, eyebrows, and lacrimal apparatus
• Muscles: rectus, oblique, and levator palpebrae superioris
• Tunics of the eyeball:
  • Fibrous tunic - cornea and sclera
  • Vascular tunic - choroid, ciliary body (process and muscle), iris, pupil,
  • Nervous tunic - optic disc, retinal artery and vein, macula lutea, and central fovea
• Lens (held in place by suspensory ligaments attached to the ciliary body)
• Cavities:
  • Anterior - filled with aqueous humor and divided into two chambers (anterior and posterior)
  • Posterior - between lens & retina & filled with a jellylike substances vitreous humor

B. Image Formation Diagram

• Refraction of light rays (bending of light) by the anterior and posterior surfaces of the cornea as well as refraction by the lens cause light rays to come into exact focus on the retina
• Images focused on the retina are inverted
• Accommodation - a change in the curvature of the eye lens to adjust for vision at various distances
• Near point vision - minimum distance from the eye that an object can be clearly focused with maximum effort; loss of accommodation is called presbyopia
• Abnormalities: myopia (nearsightedness) and hyperopia (farsightedness)

IV. Auditory Sensations and Equilibrium

A. Anatomy Diagram Diagram Diagram Diagram

• Eternal ear - auricle (pinna), helix, lobule, external auditory canal, tympanic membrane, and ceruminous glands
• Middle ear - tympanic atrum (connected to Eustachian tube), and auditory ossicles (malleus, incus, and stapes); stapes is connected to oval window of inner ear
• Inner ear - bony labyrinth (semicircular canals, vestibule containing the utricle and saccule, and cochlea containing scala tympani, scala vestibuli, cochlear duct, vestibular membrane, basilar membrane, tectorial membrane and organ of Corti) and membranous labyrinth

B. Physiology of Hearing Diagram

• Auricle directs sound waves into the external auditory canal
• Eardrum vibrates according to high and low frequency sounds
• Vibration is transmitted from the eardrum to the malleus to the incus and then to stapes
• Stapes vibrates, pushing the membrane of the oval window in and out
• Movements of the oval window cause fluid pressure waves in perilymph of cochlea
• Pressure waves are transmitted from the scala vestibuli to the scala tympani and then into the round window
• Pressure waves deform walls of scala vestibuli and scala tympani, collectively causing the vestibular membrane to move (pressure in endolymph increases & decreases)
• Pressure fluctuations in endolymph move the basilar membrane
• Hairs of the organ of Corti, connected to the basilar membrane, move against the tectorial membrane and cause the generation of nerve impulses

C. Physiology of Equilibrium

Two kinds of equilibrium...

1. Static equilibrium - maintenance of the position of the body relative to the force of gravity; macules located in the utricles and saccules are involved in static equilibrium; macules are composed of a basement membrane, hair cells, otolithic membrane, and otoliths
2. Dynamic equilibrium - maintenance of the body position (mainly in head) in response to sudden movements such as rotation, acceleration, and deceleration; crista located in ampulla of semicircular canals involved in dynamic equilibrium