Ears, Nose, Tongue

how to classify receptors

based on

• type of stimulus they detect

• location in body

• structural complexity

mechanoreceptors

classification by stimulus type

• respond to touch, pressure, vibration, and stretch

thermoreceptors

classification by stimulus type

• sensitive to changes in temperature

photoreceptors

classification by stimulus type

• respond to light energy

chemoreceptors

classification by stimulus type

• respond to chemicals

nociceptors

classification by stimulus type

• sensitive to pain-causing stimuli

exteroceptors

classification by location

• respond to stimuli arising outside body

• receptors in skin for touch, pressure, pain and temperature

• most special sense organs

interoceptors

classification by location

• respond to stimuli arising in internal viscera and blood vessels

• sensitive to chemical changes, tissue stretch, and temperature changes

• sometimes cause discomfort but usually unaware of their workings

proprioceptors

classification by location

• respond to stretch in skeletal muscles, tendons, joints, ligaments, and connective tissue covering of bones and muscles

• inform brain of one’s movements

simple receptors for general senses

classification by receptor structure

• tactile sensations (touch, pressure, stretch, vibration), temperature, pain, and muscle sense

• modified dendritic endings of sensory neurons

• either non-encapsulated (free) or encapsulated

receptors for special senses

classification by receptor structure

• vision, hearing, equilibrium, smell, and taste

non-encapsulated (free) nerve endings

• abundant in epithelia and connective tissues

• most nonmyelinated, small-diameter group C fibers; distal endings have knoblike swellings

• respond mostly to temperature and pain; some to pressure-induced tissue movement; itch

encapsulated dendritic endings

all mechanoreceptors in connective tissue capsule

• tactile corpuscles- discriminative touch

• lamellar corpuscles- deep pressure and vibration

• bulbous corpuscles- deep continuous pressure

• muscle spindles- muscle stretch

• tendon organs- stretch in tendons

• joint kinesthetic receptors- joint position and motion

sensation

the awareness of changes in the internal and external environment

perception

the conscious interpretation of those stimuli

olfactory epithelium

• roof of nasal cavity

• contains olfactory sensory neurons

• olfactory stem cells lie at base of epithelium

• bundles of unmyelinated axons of olfactory receptor cells form olfactory nerve (cranial nerve I)

physiology of smell

• gaseous odorant must dissolve in mucous of the olfactory epithelium

• activation of olfactory sensory neurons

  • dissolved odorants bind to receptor proteins in the olfactory epithelium

olfactory pathway

• olfactory receptor cells synapse with mitral cells in glomeruli of olfactory bulbs

• mitral cells amplify, refine, and relay signals

• impulses from activated mitral cells travel via olfactory tracts to temporal lobe of olfactory cortex

• some information to frontal lobe

  • smell is interpreted and identified

• some information to hypothalamus, amygdala, and other regions of limbic system

  • emotional response to odor elicited

taste buds and the sense of taste

• receptor organs are taste buds

  • most of 10,000 taste buds on tongue papillae

    • on tops of fungiform papillae

    • on side walls of foliate and circumvallate papillae

  • few on the soft palate, cheeks, pharynx, epiglottis

basic taste sensations

• sweet- sugars, saccharin, alcohol, some amino acids, some lead salts

• sour- hydrogen ions in solution

• salty- metal ions (inorganic salts)

• bitter- alkaloids such as quinine and nicotine; aspirin

• umami- amino acids glutamate and aspartate

physiology of taste

• must be dissolved in saliva

• diffuse into taste pore

• contact gustatory epithelium

gustatory pathway

• cranial nerves VII and IX carry impulses from taste buds to solitary nucleus of medulla

• impulses then travel to thalamus and from there fibers branch to

  • gustatory cortex in the insula

  • hypothalamus and limbic system (appreciation of taste)

role of taste

• triggers reflexes involved in digestion

• increase secretion of saliva into mouth

• increase secretion of gastric juice into stomach

• may initiate protective reactions

  • gagging

  • reflexive vomiting

influence of other sensations on taste

• taste is 80% smell

• thermoreceptors, mechanoreceptors, and nociceptors in the mouth also influence tastes

three major areas of ear

• external (outer) ear- hearing only

• middle ear (tympanic cavity)- hearing only

• internal (inner) ear- hearing and equilibrium

  • receptors for hearing and balance respond to separate stimuli

  • are activated independently

anatomy of external ear

• auricle

• external acoustic meatus

• tympanic membrane

auricle (pinna) characteristics

• composed of helix (rim); lobule (earlobe)

• funnels sound waves into auditory canals

external acoustic meatus (auditory canal) characteristics

• short, curved tube line with skin bearing hairs, sebaceous glands, and ceruminous glands

• transmits sound waves to eardrum

tympanic membrane (eardrum) characteristics

• boundary between external and middle ears

• connective tissue membrane that vibrates in response to sound

• transfers sound energy to bones of the middle ear

middle ear (tympanic cavity) characteristics

• a small, air-filled, mucosa-lined cavity in temporal bone

  • flanked laterally by eardrum

  • flanked medially by a bony wall containing oval and round windows

• pharyngotympanic tube- connects middle ear to nasopharynx, equalizing pressure in middle ear cavity with external air pressure

ear ossicles

• three small bones in tympanic cavity: the malleus, incus, and stapes

  • suspended by ligaments and joined by synovial joints

  • amplify the sound wave and transmit vibratory motion of eardrum to inner ear through oval window

two major divisions of internal ear

• bony labyrinth

  • tortuous channels in temporal bone

  • three regions: vestibule, semicircular canals, and cochlea

  • filled with perilymph

• membranous labyrinth

  • series of membranous sacs and ducts

  • filled with potassium-rich endolymph

vestibule

• central egg-shaped cavity of bony labyrinth

• contains two membranous sacs

  • saccule and utricle

• these sacs house equilibrium receptors and respond to gravity and changes in the position of the head

the cochlea

• a spiral, conical, bony chamber

• cavity of cochlea divided into three chambers

  • scala vestibuli- contains perilymph

  • scala media (cochlear duct)- contains endolymph

  • scala tympani- contains perilymph