Special Senses

Organs of EquilibriumEquilibrium receptors of the inner ear are

called the vestibular apparatusVestibular apparatus has two functional

partsStatic equilibriumDynamic equilibrium

Organs of Equilibrium

Figure 8.14a–b

Static EquilibriumMaculae—receptors in the vestibule

Report on the position of the headSend information via the vestibular nerve

Anatomy of the maculaeHair cells are embedded in the otolithic

membraneOtoliths (tiny stones) float in a gel around the

hair cellsMovements cause otoliths to bend the hair

cells

Structure and Function of Maculae

Figure 8.13a

Structure and Function of Maculae

Figure 8.13b

Dynamic EquilibriumCrista ampullaris—receptors in the

semicircular canalsTuft of hair cellsCupula (gelatinous cap) covers the hair cells

Dynamic Equilibrium

Figure 8.14c

Dynamic EquilibriumAction of angular head movements

The cupula stimulates the hair cellsAn impulse is sent via the vestibular nerve to

the cerebellum

Organs of HearingOrgan of Corti

Located within the cochleaReceptors = hair cells on the basilar

membraneGel-like tectorial membrane is capable of

bending hair cellsCochlear nerve attached to hair cells

transmits nerve impulses to auditory cortex on temporal lobe

Organs of Hearing

Figure 8.15a

Organs of Hearing

Figure 8.15b

Mechanism of HearingVibrations from sound waves move

tectorial membraneHair cells are bent by the membraneAn action potential starts in the cochlear

nerveContinued stimulation can lead to

adaptation

Mechanism of Hearing

Figure 8.16a

Mechanism of Hearing

Figure 8.16b–c

Olfaction—The Sense of Smell

Olfactory receptors are in the roof of the nasal cavityNeurons with long ciliaChemicals must be dissolved in mucus for

detectionImpulses are transmitted via the olfactory

nerveInterpretation of smells is made in the

cortex

Olfactory Epithelium

Figure 8.17

The Sense of TasteTaste buds house the receptor organsLocation of taste buds

Most are on the tongueSoft palateCheeks

Taste Buds

Figure 8.18

The Tongue and TasteThe tongue is covered with projections

called papillaeFiliform papillae—sharp with no taste budsFungifiorm papillae—rounded with taste budsCircumvallate papillae—large papillae with

taste budsTaste buds are found on the sides of

papillae

Structure of Taste BudsGustatory cells are the receptors

Have gustatory hairs (long microvilli)Hairs are stimulated by chemicals dissolved

in saliva

Structure of Taste BudsImpulses are carried to the gustatory

complex by several cranial nerves because taste buds are found in different areasFacial nerveGlossopharyngeal nerveVagus nerve

Taste SensationsSweet receptors(sugars)

SaccharineSome amino acids

Sour receptorsAcids

Bitter receptorsAlkaloids

Salty receptorsMetal ions

Developmental Aspects of the Special SensesFormed early in embryonic developmentEyes are outgrowths of the brainAll special senses are functional at birth

Chemical Senses: Taste and SmellBoth senses use chemoreceptors

Stimulated by chemicals in solutionTaste has four types of receptorsSmell can differentiate a large range of

chemicalsBoth senses complement each other and

respond to many of the same stimuli

Developmental Aspects of the Special SensesEye problems

Strabismus—“crossed eyes” results from unequal pulls by the external eye muscles in babies

Ophthalmia neonatorum—conjunctivitis resulting from mother having gonorrhea. Baby’s eyelids are swollen and pus is produced

Developmental Aspects of the Special SensesEye problems

Presbyopia—“old vision” results from decreasing lens elasticity that accompanies aging

Developmental Aspects of the Special SensesEar problems

Presbycusis—type of sensorineural deafnessOtosclerosis—ear ossicles fuse