Special senses

(continued)

Receptors are classified into 3 types

• Exteroceptors – located near the body surface, are specialized to perceive stimuli from the external environment; other exteroceptors include receptors for vision, hearing, smell and taste

• Interoceptors – are specialized to perceive sensory information from visceral organs

• Proprioceptors – located in joint capsules, tendons, muscle spindles, inner ear, are specialized to perceive information that relates to an awareness of the body in space and movement

Anatomy of the vestibulo-cochlear organ

Vestibulo-cochlear organ includes• Outer ear– Auricula– External acoustic meatus – Tympanic membrane

• Middle ear– Tympanic cavity– Three ossicles: malleus, incus, stapes– Auditory (Eustachian) tube

• Inner ear– Bony and membranous labyrinths

External acoustic meatus

Middle ear

Bony, membranous and sensory labyrinths

Inner ear

• Bony labyrinth– Cochlea– Vestibulum– Three semicircular canals

• Membranous labyrinth– Cochlear duct– Sacculus and Utriculus– Three semicircular ducts

• Sensory labyrinth

Macula of the utricle: hair cells

Hair cells of the maculae

Crista ampullaris of the semicircular duct

LM of the crista ampullaris and of macula

SEM of the hair cells and the otoliths

Organ of Corti in the cochlear duct

Axial section through the cochlea

LM of the organ of Corti

SEM of the organ of Corti hair cells

Histophysiology of the organ of Corti

Olfactory perception

(odors detection)

The olfactory region

LM of the human olfactory mucosa

EM of the rat olfactory epithelium

Taste perception

(taste buds)

Lingual papillae and a taste bud

LM of taste buds in circumvallatae papilla

EM of a taste bud

Mechanoreceptors include• Nonencapsulated– peritrichial and corneal naked nerve endings– Merkel’s disks

• Encapsulated– Meissner’s corpuscles– Pacinian corpuscles– Ruffini’s corpuscles– Krause’s end bulbs– Golgi tendon organs– Muscle spindles

Various types of mechanoreceptorsA, Merkel’s disk; B, Meissner’s corpuscle; C, Pacinian corpuscle; D, Peritrichial nerve endings; E, Ruffini’s corpuscle; F, Krause’s end bulb; G, Muscle spindle;

H, Golgi tendon organ

Free nerve endings

Merkel’s cells and Merkel’s disks

Meissner’s and Pacinian corpuscles

Muscle spindle