Chapter 8Special Senses

The EarThe Ear Houses two senses

Hearing

Equilibrium (balance)

Receptors

Sound receptors

Mechanoreceptors

Both stimulated by the movement of fluid

Anatomy of the EarAnatomy of the Ear

The ear is divided into three major areas Outer (external) ear

Middle ear

Inner (internal) ear

Outer (external) EarOuter (external) Ear

Involved in hearing only

Structures of the external ear Pinna

(auricle)

External auditory canal

The External Auditory CanalThe 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 CavityThe 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 CavityBones 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 CavityBones of the Tympanic Cavity

Vibrations from the eardrum moves the malleus

These 3 bones transfer sound to the inner ear

Inner Ear or Bony LabyrinthInner Ear or Bony Labyrinth

A maze of bony chambers within the temporal bone

Cochlea

Vestibule

Semicircular canals

Inner Ear or Bony LabyrinthInner Ear or Bony Labyrinth

Includes sense organs for hearing & balance

Filled with perilymph

Mechanism of EquilibriumMechanism of Equilibrium Equilibrium has two functional parts

Static equilibrium

Receptors in the vestibule

Dynamic equilibrium

Receptors in the semicircular canals

Static EquilibriumStatic 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 MaculaeFunction of Maculae

Dynamic EquilibriumDynamic 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 EquilibriumDynamic Equilibrium

During angular head movements

The cupula stimulates the hair cells

An impulse is sent via the vestibular nerve to the cerebellum

Mechanism of HearingMechanism 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 CochleaHearing- Anatomy of the Cochlea

Mechanisms of HearingMechanisms 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 & SmellChemical 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 SmellOlfaction – 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 EpitheliumOlfactory Epithelium

The Sense of TasteThe 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 TasteThe 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 BudsStructure 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 BudsStructure 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 BudsAnatomy of Taste Buds

Taste SensationsTaste Sensations Sweet receptors

Sugars Saccharine Some amino acids

Sour receptors Acids

Bitter receptors Alkaloids

Salty receptors Metal ions

Umami Glutamate- “Beef taste” of steak

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

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! 

Developmental Aspects of the Developmental Aspects of the Special SensesSpecial Senses

Slide 8.42Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Formed early in embryonic development

Eyes are outgrowths of the brain

All special senses are functional at birth

Normal slight severe ear infection

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.

Vertigo-website Tinnitus-website

Adaptation: decreasing sensitivity Threshold: minimal amount of

stimulus needed to illicit a response. Taste:

Adapt: complete 1-5 minutesThreshold: bitter lowest (poisons), sour,

salt & sweet Smell:

Adapt: 50% after 1 sec. Threshold: very low

1/25,000,000,000mg/ml.