4a. Sensory Systems Flashcards
Taste Receptors
Characteristic distribution, regions are a mixture
Some overlap in response
Taste is a combination of the categories
Tongue also has mechanoreceptors and thermoreceptors
Taste Receptors: Categories
sour (foliate papillae) sweet (fungiform papillae) salty (fungiform papillae) bitter (circumvallate papillae) umami (fungiform papillae)
Taste Buds
Location of taste receptors
On tongue and other areas of mouth
Grouped in each of 3 types of papillae on tongue
1 bud = ~50 receptors
Taste Receptor: Hairs
Project into taste pore - pick up taste stimuli
Taste Transduction
- Dissolved substances initiate transduction (substance must be dissolved in saliva to come in contact with R)
- Depolarizing R potentials
- Some taste R have voltage gated Na channels, make AP and release ATP
- Other taste R have voltage gated Ca channels and release vesicles of ATP (ATP release as NT - depolarizes primary afferent nerve ending)
- Peripheral endings of CN VII, IX, X depolarize - fire faster
CN for Conscious Perception of Taste
CN VII Facial
CN IX Glossopharnygeal
CN X Vagus
Mostly 7 and 9
Taste Receptors: Modified Epithelial Cells
Depolarizing receptor potentials –> release of NT ATP –> AP in primary neuron
Salt
NaCL
Sour
H+ in citric acid
Sweet
Sugar (glucose)
Bitter
Alkaloids (quinine)
Umami
L glutamate
Taste Pathways
- taste receptors
- cranial nerves (1 neuron)
- brainstem - nucleus solitarius (2 neuron)
- Thalamus (3 neuron)
- Gustatory cortex - insula
Limbic System
Provides affective dimension of taste (emotional context)
Olfactory Receptors
primary afferent neurons - not a separate cell
In olfactory mucosa
Odorant molecules bind to receptors in cilia in mucus layer
CN I (olfactory) goes through cribriform plate to connect with olfactory receptor in olfactory mucosa
Olfactory Transduction
- Olfactory R binds odorant molecules –> activates G protein
- Increase in intracellular cAMP
- cAMP gated cation channels open - Ca2+ enters
- Depolarization - Cl- leaves through Ca2+ gated Cl- channels
- Depolarization travels to initial segment of olfactory nerve
- AP generated
Axons from olfactory receptors leave olfactory epithelium …
Travel ventrally to olfactory bulb - pass through cribriform plate
fractures of cribriform plate can sever olfactory neurons –> disorders
Odor Discrimination
Enabled by variations in receptor molecule
Olfactory Pathway
- olfactory receptors (1 neuron: CNI (olfactory))
- olfactory bulb: apical dendrites of mitral cells (2 neuron)
- primary olfactory cortex (piriform cortex)
Also project to amygdala, limbic system
NO RELAY IN THALAMUS
Outer Ear (anatomy, function)
Direct sound through ear canal to tympanic membrane
helix
auricle
auditory canal
earlobe
Middle Ear (function, anatomy)
Begins process of transmitting vibrations to inner ear
tympanic membrane?
ossicles (stapes, incus, malleus)
Inner Ear (function, anatomy)
Transmits sound and balance information to brain
semicircular ducts? vestibular nerve cochlear nerve cochlea round window? tympanic cavity? tensor tympani muscle auditory tube
Cochlea
Contains receptor cells
Coils 2.5 around modiolus (bony pillar)
3 chambers:
- scala tympani
- scala media
- scala vestibuli
2 fluids:
- perilymph
- endolymph
Hair cells sit in cochlear duct
Perilymph
Fills scala vestibuli and scala tympani (continuous)
Similar composition to ECF
Movement –> bulges in cochlear duct –> activation of basilar membrane
Endolymph
Fill scala media (cochlear duct)
Chemically similar to ICF (K+ rich)
Produced continuously via active pumping mechanism –> positive electrical potential inside ear (+80mV)
Membranes of Cochlea
- Reissner’s/vestibular membrane
- Basilar membrane
- Tectorial membrane
Reissner’s Membrane
Roof of cochlear duct
Basilar Membrane
Fibrous floor of cochlear duct
Supports organ of corti
Near oval window: narrow, thick
Near cochlear apex: wider, thinner
Tectorial Membrane
Overhanging membrane of organ of corti
In contact with stereocilia of hair cells
Role of Sense of Hearing
Translate pressure waves of perilymph and endolymph to electrical signal and acoustic sensation
Bending of cilia produces change in K+ conductance
Toward kinocilium: increases K+ influx
Away from kinocilium: decreases K+ influx
Kinocilium = tallest sterocilia
Basilar Membrane: Fibers
Span the width like the strings of a harp
Near oval window: short, stiff
-resonate with HIGH frequency waves
Near cochlear apex: longer, floppier
-resonate with lower frequency waves
Sound
Pressure disturbance originated from a vibrating object
Propagated by molecules of medium (air, liquid)
Normally manifests as pressure or sound wave
Frequency
Number of sound waves that pass a given point in a given time
Hertz
Shorter wavelength = high frequency
Pitch
Our ears perceive different frequencies as pitch
higher frequency = higher pitch
ability to distinguish pitch and loudness depends on ability of cochlea to respond differently to vibrations of different amplitude and frequency
Tuning Fork
Pure sound - single frequency
Most sounds are a mixture of frequencies
Place Coding
Frequency sensitivity of IHCs depends on their position along basilar membrane of cochlea
Loudness
An increase in AP firing
Related to amplitude of sound waves
Measure of sound intensity
Decibels
Severe Hearing Loss
Frequent/prolonged exposure to sound greater than 90 dB
Sound source directly in front, in back, over midline of head…
Intensity and timing cues will be the same for both ears
Sound coming from one side…
Nearer hair cells activated:
- slightly earlier
- more vigorously
Superior Olivary Nucleus
Functions in biaural hearing
Compares signals from R and L ear to identify direction from which a sound is coming
Conductive Deafness
BC>AC
Sound vibrations don’t go from air to ossicles as well as they should (loss of air conduction)
Effects auditory canal and middle ear
Conductive Deafness: Causes
Ear wax buildup
Fluid buildup from infection
Puncture of eardrum
Conductive Deafness: Results
Loss of loudness
Loss of clarity
Sounds are weak, muffled, distorted
Nerve Deafness
Sensorineuronal
Both air and bone conduction decreased
Auditory nerve damage (loss of air and bone conduction)
Effects cochlea, nerve, cochlear nucleus
Nerve Deafness: Causes
Ototoxic drugs
Prolonged exposure to loud sounds
Inner ear infections
Rinne Test
Use a tuning fork to determine air conduction (AC) and bone conduction (BC)
Normal Hearing in Adults
0-25 dB
Most Important Frequencies for Speech
250-6000 Hz
Presbycusis
Gradual loss of hearing associated with aging
Due to gradual cumulative loss of hair cells and neurons
Presbycusis: Loss
Loss of ability to hear consonants
Loss of high frequency sounds
Difficulty screening out background noise
