Chapter 8 Special Senses

The Ear Houses two senses Receptors Hearing Equilibrium (balance) Sound receptors Mechanoreceptors Both stimulated by the movement of fluid

Anatomy of the Ear The ear is divided into three major areas Outer (external) ear Middle ear Inner (internal) ear

Outer (external) Ear Involved in hearing only Structures of the external ear Pinna (auricle) External auditory canal

The External Auditory Canal Short, narrow chamber in the temporal bone of the skull Lined with skin Ceruminous (wax) glands are present that secrete earwax or cerumen Sound waves entering the canal eventually hit the tympanic membrane or eardrum and cause it to vibrate Canal ends at the eardrum, which separates the outer from the middle ear

The Middle Ear or Tympanic Cavity Air-filled cavity within the temporal bone Only involved in the sense of hearing Pharyngotympanic (auditory) tube Runs obliquely downward to link the middle ear cavity with the throat Allows for equalizing pressure during yawning or swallowing Tube is otherwise collapsed

Bones of the Tympanic Cavity 3 of the smallest bones in the body span the cavity (ossicles) Malleus (hammer) Incus (anvil) Stapes (stirrup)

Bones of the Tympanic Cavity Vibrations from the eardrum moves the malleus These 3 bones transfer sound to the inner ear

Inner Ear or Bony Labyrinth A maze of bony chambers within the temporal bone Cochlea Vestibule Semicircular canals

Inner Ear or Bony Labyrinth Includes sense organs for hearing & balance Filled with perilymph

Mechanism of Equilibrium Equilibrium has two functional parts Static equilibrium Receptors in the vestibule Dynamic equilibrium Receptors in the semicircular canals

Static Equilibrium Maculae – receptors within the vestibule Report on the position of the head with respect to the pull of gravity when the body is not moving (static = rest) Anatomy of the maculae Hair cells are embedded in the otolithic membrane Otoliths (tiny stones) float in a gel around the hair cells Movements cause otoliths to bend the hair cells  sends impulses along the vestibular nerve to the cerebellum of the brain

Function of Maculae

Dynamic Equilibrium Responds to angular or rotatory movements of the head Crista ampullaris – receptors found within the semicircular canals Tuft of hair cells are covered with a gelatinous cap called the cupula

Dynamic Equilibrium During angular head movements The cupula stimulates the hair cells An impulse is sent via the vestibular nerve to the cerebellum

Mechanism of Hearing Organ of Corti Located within the cochlea Hearing receptors  hair cells on the basilar membrane Gel-like tectorial membrane is capable of bending hair cells Cochlear nerve attached to hair cells transmits nerve impulses to auditory cortex on temporal lobe

Hearing- Anatomy of the Cochlea

Mechanisms of Hearing Vibrations from sound waves move tectorial membrane Hair cells are bent by the membrane An action potential starts in the cochlear nerve Continued stimulation can lead to adaptation

Chemical Senses: Taste & Smell Both senses use chemoreceptors Stimulated by chemicals in solution 5 types of taste receptors Smell (olfactory) receptors Sensitive to a much wider range of chemicals Receptors for both senses complement each other and respond to many of the same stimuli

Olfaction – The Sense of Smell Olfactory receptors are in the roof of each nasal cavity Neurons with long cilia (olfactory hairs) Chemicals must be dissolved in mucus for detection Impulses are transmitted via the olfactory nerve Interpretation of smells is made in the olfactory cortex of the brain

Olfactory Epithelium

The Sense of Taste Taste receptors  Taste buds (Widely scattered throughout the oral cavity) Location of taste buds Most are on the tongue Soft palate Inner surface of the cheeks

The Tongue and Taste The tongue is covered with 3 types of projections called papillae Sharp or Filiform papillae – no taste buds Fungifiorm papillae – rounded with taste buds Circumvallate papillae – large papillae with taste buds Taste buds are found on the sides of papillae

Structure of Taste Buds Gustatory cells Have gustatory hairs (long microvilli) Hairs are stimulated by chemicals dissolved in saliva and transmit impulses to the brain

Structure of Taste Buds Impulses are carried to the gustatory complex by several cranial nerves because taste buds are found in different areas Facial nerve Glossopharyngeal nerve Vagus nerve

Anatomy of Taste Buds

Taste Sensations Sweet receptors Sour receptors Bitter receptors Sugars Saccharine Some amino acids Sour receptors Acids Bitter receptors Alkaloids Salty receptors Metal ions Umami Glutamate- “Beef taste” of steak

Reasons not to get your tongue pierced… Chipped or broken teeth Infection And possibly death

Girl who almost died from a brain abscess following a tongue piercing She had part of her skull removed to relieve pressure caused by the infection She can still feel the soft spot where the skull is missing Rare, but real

Reasons not to get your tongue pierced… Blood loss The tongue contains large blood vessels, and you're in trouble if one of them is perforated. You could end up having to have the vessel closed surgically in hospital. There is also the possibility of hitting and damaging a nerve Imagine life with a tongue that doesn't work properly! Lingering pain Cases of neuralgia  - severe, long-lasting nerve pain Hepatitis or HIV Unsterile instruments are a great way to spread these and other infections

Still not convinced? If you must do this, be sure to go to a reputable clinic, and be very sure that they do things properly: autoclave sterilization and gloves. As we had tried to teach you with tattooing, be a smart consumer! 

Extra slides…

Developmental Aspects of the Special Senses Formed early in embryonic development Eyes are outgrowths of the brain All special senses are functional at birth Slide 8.42 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Tonsils

Middle Ear Infections website website use of tubes Normal slight severe ear infection

Tubes for Middle Ear infections How Are Ear Tubes Inserted? Ear tubes are inserted through an outpatient surgical procedure called a myringotomy. A myringotomy refers to an incision (a hole) in the ear drum or tympanic membrane. This is most often done under a surgical microscope with a small scalpel (tiny knife), but it can also be accomplished with a laser.  If an ear tube is not inserted, the hole would heal and close within a few days. To prevent this, an ear tube is placed in the hole to keep it open and allow air to reach the middle ear space (ventilation).   Ear Tube Surgery  A light general anesthetic (laughing gas) is administered for young children. Some older children and adults may be able to tolerate the procedure without anesthetic. A myringotomy is performed and the fluid behind the ear drum (in the middle ear space) is suctioned out. The ear tube is then placed in the hole. Ear drops may be administered after the ear tube is placed and may be necessary for a few days. The procedure usually lasts less than 15 minutes and patients awaken quickly. Sometimes the otolaryngologist will recommend removal of the adenoid tissue (lymph tissue located in the upper airway behind the nose) when ear tubes are placed.  This is often considered when a repeat tube insertion is necessary. Current research indicates that removing adenoid tissue concurrent with placement of ear tubes can reduce the risk of recurrent ear infection and the need for repeat surgery.

Ear Disorders Vertigo-website Tinnitus-website

Adaptation and Threshold for Taste and Smell Adaptation: decreasing sensitivity Threshold: minimal amount of stimulus needed to illicit a response. Taste: Adapt: complete 1-5 minutes Threshold: bitter lowest (poisons), sour, salt & sweet Smell: Adapt: 50% after 1 sec. Threshold: very low 1/25,000,000,000mg/ml.