Chapter 8: Special SensesPart 2

Anatomy of the Ear

• Broken into 3 major parts– External Ear

– Middle Ear (ossicles)

– Internal Ear – Internal Ear

Outer Ear

• Auricle (pinna)

• External auditory canal (meatus)

• Tympanic membrane

Middle Ear

• Three auditory ossicles (bones)– malleus (hammer)– incus (anvil)– stapes (stirrup)– stapes (stirrup)

• Oval window: transmits vibrations from the stapes to the inner ear fluid

• Eustachian tube (auditory tube): connects inner ear to the pharynx; equalizes pressure

Inner Ear

• Bony Labyrinth (filled with perilymph) (membranous labyrinth is enclosed inside the bony labyrinth, filled with endolymph)

Cochlea (Organ of Corti)– Cochlea (Organ of Corti)– Vestibule– Semicircular canal (equilibrium)

• Round Window• Cranial Nerve VIII (Vestibulocochlear)

Path of Hearing

• Sound waves enter the external auditory meatus � pass through the external auditory canal � causes the tympanic membrane to vibrate �malleus, incus, and stapes vibrate in malleus, incus, and stapes vibrate in sequence � oval window vibrate �perilymph in cochlear� endolymph(organ of corti) � hair cells vibrate �auditory nerve � brain’s temporal lobe (interpretation)

Balance and Posture

• Vestibular apparatus and Semicircular canals

Static Equilibrium

• Maculae (sensory receptors for static equilibrium) located inside the vestibular apparatus

• Change in body position � movement of • Change in body position � movement of otoliths � movement of hairs �generate a potential in hair cells �action potential in cranial nerve VIII �pons � cerebellum

Dynamic Equilibrium

• Crista ampullaris: receptors for dynamic equilibrium) located in the ampulla of each semicircular canal

• Change in body position � movement of fluid within canals movement of

• Change in body position � movement of fluid within canals � movement of cupula � movement of hairs �generates potential in hair cells �action potential in cranial nerve VIII �pons � cerebellum

The Sense of Smell (Olfaction)

• Olfaction detects chemicals in solution

• The Olfactory epithelium (organ for smell) is located in the roof of each nasal cavity.nasal cavity.– 5 million olfactory receptor cells

– protected & cushioned by supporting cells

The Chemical Senses

• Taste (gustatory) & Smell (olfactory)

• Chemoreceptors: respond to chemicals in an aqueous solution.– Taste: food chemicals – Taste: food chemicals

– Smell: airborne chemicals

• The receptors of taste & smell complement each other and respond to many of the same stimuli

Olfactory Receptor Cells

• Bipolar neurons, each with thin dendrite that terminates in a knob bearing several long cilia called olfactory hairs

• Olfactory hairs protrude outward and • Olfactory hairs protrude outward and are covered with mucus produced by the olfactory glands.

Olfactory Pathway

• Chemicals (gaseous odors) react with olfactory hairs � impulse in olfactory neurons �olfactory bulb � olfactory tracts � olfactory area of the cerebral tracts � olfactory area of the cerebral cortex (interpretation of smell)

The Sense of Taste

• Taste buds: sensory receptors for taste– Location: tongue, soft palate, cheeks,

pharynx, epiglottispharynx, epiglottis

– 10,000 taste buds (most on the tongue)

The Taste Bud

• Globular structure consisting of 40-60 epithelial cells– supporting cells

– taste cells (gustatory cells)– taste cells (gustatory cells)• Gustatory hairs (microvilli) extend from the cell

through a taste pore

– basal cells • produce new taste cells every 7-10 days

Taste Buds and the Tongue

• Papillae: Projections in the tongue mucosa (taste buds are found here)– gives tongue the abrasive feeling

Types of Papillae

• Circumvallate: – found in the back of the tongue

• Foliate (Filiform)– back sides of tongue– back sides of tongue

• Fungiform:– scattered all over tongue

– mostly at tip & sides

Sensation of Taste

• Sweet (sugar, saccharin, some aa)

• Sour (H+)

• Salty (Metal ions, Na+)

• Bitter (alkaloids such as quinine, nicotine, • Bitter (alkaloids such as quinine, nicotine, caffeine)

• Combinations of the above & the sense of smell (80% taste) give rise to other tastes

Mechanism for Taste

• Chemicals in food dissolve in saliva and diffuse into the taste pore & contact the gustatory hairs.

• Taste cells do not generate action • Taste cells do not generate action potentials, but their receptor potentials summate to trigger an action potential in the associated sensory neurons.

Mechanism for Taste

• Chemicals react with taste hairs �generate action potential in Cranial nerves VII, IX, X � medulla �thalamus � gustatory area of the thalamus � gustatory area of the cerebral cortex (parietal lobe)