General Senses

special senses

olfaction, gustation, vision, hearing

smell and taste

complementary senses that let us know whether a substance should be savored or avoided

smell receptors are excited by

chemicals dissolved in nasal fluids

taste receptors respond to

chemicals dissolved in saliva

olfactory epithelium

organ of smell

where is the olfactory epithelium located

roof of nasal cavity

olfactory epithelium contain

olfactory sensory neurons

supporting cells

surround and cushion olfactory receptor cells

olfactory stem cells location

lies at base of epithelium

thin apical dendrites terminate

in knob

long, largely nonmotile cilia

radiate from knob and is covered by mucus

bundles of nonmyelinated axons of olfactory receptor cells

gather in fascicles and make up filaments of olfactory nerve

how many odorant receptors do we have

350

smells can be made up of how many odorants

100

pain and temp receptors location

nasal cavity

in order to smell a substance

it must be volatile, in a gaseous state, odorant must be able to dissolve in olfactory

the olfactory pathway

is the neural pathway involved in the perception of smell, starting from the olfactory receptors in the nasal cavity and ending in the olfactory bulb in the brain.

where are filaments of olfactory nerves synapse with mitral cells are located

in overlying olfactory bulb

mitral cells

are second-order neurons that form olfactory tract

where does synapse occur

glomeruli

what do mitral cells do

amplify, refine, and relay signals

olfactory reception

begins with binding of odorant to G protein-coupled receptors which creates generator potential

generator potential

depolarization

afferent fibers

leave olfactory epithelium

afferent fibers

collect into 20 or more bundles, penetrate cribiform plate of ethmoid, reach olfactory bulbs of cerebrum where first synapse occurs

axons leaving olfactory bulb

travel along olfactory tract to olfactory cortex, hypothalamus, and limbic system

which type of sensory information reaches the cerebral cortex directly

olfactory information

where re all sensations relayed through

the thalamus

smell is consciously interpreted and identified in

frontal lobe

gustation

provides information about foods and liquids consumed

gustatory epithelial cells

found in taste buds and

where are gustatory epithelial cells distributed

Distributed on superior surface of tongue and portions of pharynx and larynx

what are gustatory epithelial cells associated with

epithelial projections (lingual papillae) on surface of tongue

taste buds

sensory organ for taste

papillae

peglike projections of tongue mucosa

fungiform papillae

tops of there mushroom-shaped structures house most taste buds; scattered across tongue

vallate papillae

largest taste buds with 8-12 forming “v” at back of tongue

foliate papillae

on side walls of tongue

each taste bud consists of

50-100 flask-shaped epithelial cells (gustatory and basal)

gustatory epithelial cells

taste receptor cells that have microvilli that project into taste pores, bathed in saliva

gustatory hairs

taste receptor cells that have microvilli

sensory dendrites coiled around gustatory epithelial cells

send taste signals to the brain

basal epithelial cells

dynamic stem cells that divide every 7-10 days

5 basic taste sensations

sweet, sour, salty, bitter, umami

sweet

sugars, saccharin, alcohol, some amino acids, some lead salts

sour

hydrogen ions in salt

salty

metal ions (norganic salts); sodium chloride tastes saltiest

bitter

alkaloids such as quinine and nicotine, caffine, and nonalkaloids such as asprin

umami

amino acids glutamate and aspartate; example: beef (meat) or cheese taste, and monosodium glutamate

to be able to taste a chemical it must

be dissolved in saliva, diffuse into taste pore, contact gustatory hairs

adaptation

3-5 seconds, complete adaptation in 1-5 minutes

most sensitive

bitter receptors

binding of food chemical (tastant)

depolarizes cell membrane of gustatory epithelial cell membrane, causing release of neurotransmitter

neurotransmitter binding

dendrite of sensory neuron and initiates a generator potential that lead to action potentials

depolarization (salty)

Na+ influx that directly causes depolarization

sour depolarization

H+ acting intracellularly by opening channels that allow for other cations to enter

gustducin activation

causes release of stored Ca2+ that opens cation channels, causing depolarization and release of neurotransmitter ATP

main cranial nerves that carry taste impulses

facial, glossopharyngeal, vagus

facial nerve (VII)

carries impulses from anterior two-thirds of tongue

glossopharyngeal (X)

carries impulses from posterior one-third and pharynx

vagus nerve

transmits from epiglottis and lower pharynx

how are mechanoreceptors of the inner ear stimulated

fluids are stirred

receptors for hearing and balance

respond to separate stimuli and are activated independently

three major areas of ear

external, middle, internal

external

hearing only

middle

hearing only

internal

hearing and equilibrium

sound

is a pressure disturbance produced by a vibrating object and propagated by a molecules of the medium; sound travels more slowly than light

two physical properties

frequency and amplitude

frequency

number of waves that pass a given point in a given time

pure tone

has crests and troughs that repeat at specific intervals

wavelength

distance between consecutive crests or troughs of a wave.

shorter wavelength

higher frequency

frequency range of human hearing

20-20,000 hertz most sensitive between 1500 and 4000 Hz

pitch

perception of different frequencies

amplitude

height of sine wave crests

loudness

our interpretation of sound intensity

normal range

0-120 dB

pathway of sound

air, membranes, bones, fluid

tympanic membrane

sound waves enter external acoustic meatus and strike tympanic membrane, causing it to vibrate

auditory ossicles

transfer vibration of eardrum to oval window

scala vestibuli

stapes movement causes wave motions in perilymph, forcing fluid adjacent to oval window medially; membrane of round window acts as pressure valve

helicotrema path

very-low-frequency sounds do not activate the spiral organ and so are below the range of hearing

basilar membrane path

sounds in hearing range go through cochlear duct, vibrating basilar membrane, causing action potentials to be sent to the brain

vestibular apparatus

equilibrium receptors in semicircular canals and vestibule

vesitbular receptors

monitor static equilibrium (linear acceleration and head position with respect to gravity)

semicircular canal receptors

monitor dynamic equilibrium (changes in head rotation)

maculae

sensory receptor organs (one in each saccule wall and one in each utricle wall), monitor position of head in space, play a key role in control of posture, respond to linear acceleration, but not rotation

crista ampullaris (crista)

receptor for rotational acceleration