Special Senses Chapter 8 Ear outer middle inner

Special Senses Chapter 8

Ear (outer, middle, inner) • Hearing and equilibrium

External Ear • Hearing only! • Auricle (pinna) • External acoustic meatus (auditory canal) • Ends at the tympanic membrane

Ear (outer, middle, inner)

Middle Ear • Air-filled cavity within the temporal bone • Only involved in the sense of hearing

Ear (outer, middle, inner)

Inner Ear (Bony Labyrinth) • Hearing and balance • Filled with perilymph • Bony chambers ▫ Vestibule ▫ Cochlea ▫ Semicircular canals

Inner Ear (Bony Labyrinth) Vestibule has two functions: ▫ Static equilibrium ▫ Dynamic equilibrium

Ear (outer, middle, inner)

• Maculae—receptors in the vestibule ▫ Report on the position of the head ▫ Send information via the vestibular nerve

• Maculae—receptors in the vestibule ▫ Report on the position of the head ▫ Send information via the vestibular nerve

• Crista ampullaris—receptors in the semicircular canals ▫ Tuft of hair cells ▫ Cupula (gelatinous cap) covers the hair cells

Organs of Hearing • Organ of Corti ▫ Located within the cochlea ▫ Receptors = hair cells on the basilar membrane ▫ tectorial membrane is capable of bending hair cells ▫ Cochlear nerve attached to hair cells sends nerve impulses

Mechanisms of Hearing • Vibrations from sound waves move tectorial membrane • Hair cells are bent by the membrane

Mechanisms of Hearing

Mechanisms of Hearing

Olfaction—The Sense of Smell • Olfactory receptors are in the roof of the nasal cavity ▫ Neurons with long cilia ▫ Chemicals must be dissolved in mucus for detection

Olfactory

Sense of Taste • Taste buds house the receptor organs • Location of taste buds ▫ Most are on the tongue ▫ Soft palate ▫ Cheeks

The Tongue and Taste • Tongue covered with projections called papillae ▫ Filiform papillae—sharp with no taste buds ▫ Fungifiorm papillae—rounded with taste buds ▫ Circumvallate papillae—large papillae with taste buds

The Tongue and Taste • Impulses are carried to the gustatory complex by several cranial nerves because taste buds are found in different areas

Taste Sensation • • Sweet receptors(sugars) Sour receptors Bitter receptors Salty receptors

Developmental Aspects • Formed early in embryonic development • Eyes are outgrowths of the brain • All special senses are functional at birth ▫ At birth babies eyes are sensitive to light so pupils remain very small ▫ Over a few months pupils start to dilate and eyes begin to focus on closer objects ▫ Focusing the eyes is learned

Chemical Senses: Taste and Smell • Both senses use chemoreceptors • Both senses complement each other and respond to many of the same stimuli