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What do sensory receptors do?
Transduce energy into nerve impulses
How do different modalities of sensation arise?
From differences in neural pathways and synaptic connections
Chemoreceptors
Receptors for taste and smell
What are taste buds composed of?
50-100 specialized epithelial cells
What happens when taste buds are stimulated?
They produce action potentials and release neurotransmitters
Where are taste buds located?
In bumps on the tongue called papillae
What are the five categories of taste?
Salty
Sours
Sweet
Bitter
Umami
What factors influence taste?
Temperature
Texture
Concentration
Olfactory stimulation
Where are olfactory receptors located?
In the olfactory epithelium of the nasal cavity
what does the olfactory apparatus consist of?
bipolar olfactory sensory neurons
Sustentacular cells
Basal stem cells
What do sustentacular cells do?
Oxidize hydrophobic volatile odors
What do basal stem cells do in the olfactory apparatus?
Replace receptors damaged by the environment
What type of neurons are olfactory receptors?
Bipolar
How do olfactory receptors detect odorants?
Proteins in cilia bind to odorant molecules
How many genes code for olfactory receptors?
About 380
What happens when an odorant molecule binds to a receptor ?
It stimulates one protein in one sensory neuron
What is the role of G-proteins in olfaction?
They amplify the signal through activation
What does odor binding activate in olfactory receptors?
Adenylate cyclase
What does adenylate cyclase make when activated?
cAMP
What does cAMP do in olfactory receptors?
Opens Na+ and Ca2+ channels
What is produced when olfactory receptors are depolarized?
A graded depolarization that stimulates action potentials
How many G-proteins may be associated with one receptor protein?
Up to 50
What does the vestibular apparatus provide?
Sense of equilibrium
Where is the vestibular apparatus located?
In the inner ear
What are the components of the vestibular apparatus?
Otolith organs and semicircular canals
What do otolith organs detect?
Linear acceleration
What do semi circular canals detect?
Rotational acceleration
What is the structure of the inner ear?
A bony labyrinth surrounding a membranous labyrinth
What fluid is between the bony and membranous labyrinth?
Perilymph
What fluid is within the membranous labyrinth?
Endolymph
What are sensory hair cells?
Modified epithelial cells called vestibular hair cells
How are stereocilia arranged on hair cells?
In rows of increasing height
What happens when stereocilia bend toward the kinocilum?
The hair cell depolarizes
What happens when the sterocilia bend away from the kinocilium?
The hair cell hyperpolarizes
What do utricle and saccule provide information about?
Linear acceleration
What direction does the utricle detect acceleration?
Horizontal
What direction of acceleration does the saccule detect?
Vertical
What is the specialized epithelium in the utricle and saccule called?
Macula
What do sterocilia in the macula embed in?
A gelatinous otolithic membrane
What are otoliths?
Crystals of calcium carbonate
What do semicircular canals detect?
Rotation
What is the structure at the base of each semicircular duct called?
Ampulla
Where are hair cells located in the ampulla?
Embedded in the crista ampullaris
What happens to hair cells during rotation?
Endolymph circulates, bending them
What characterizes sound waves?
Frequency and intensity
How is frequency measured
In Hz
What is the human range of hearing frequency?
20-20,000Hz
What is intensity related to in sound waves?
Amplitude of the wave
What is the optimal range of sound intensity for humans?
0-80dB
What funnels sound waves into the ear?
The pinna (auricle)
What channels sound waves into the tympanic membrane?
The external auditory meatus
What is the middle ear filled with?
Air
What are the three bones in the middle ear called?
Auditory ossicles
What is the composition of the spiral organ?
Basilar membrane, inner hair cells, tectorial membrane
What happens when sound waves enter the scala media?
The tectorial membrane vibrates, bending the stereocilia
What opens K+ channels in the hearing process?
The bending of sterocilia facing the Endolymph
What occurs when K+ rushes into the cell?
The cell depolarizes
What neurotransmitter is released onto sensory neurons during hearing?
Glutamate
Where does K+ return to after depolarization in hearing?
To the perilymph at the base of the stereocilia
What is the first structure light passes through in the eye?
Cornea
What changes the shape of the pupil?
The pigmented iris muscle
What happens to light after it passes through the pupil?
It passes through the lens
What is the function of the lens in the eyes?
To change shape and focus the image
What fills the anterior and posterior chambers of the eye?
Aqueous humor
What do the ciliary bodies do?
Secrete aqueous humor
What happens if there is inadequate drainage of aqueous humor?
Glaucoma
What is accommodation in the eye?
the Ability to keep an object focused on the retina
What occurs during contraction of the ciliary muscles?
The lens thickens and rounds up
What happens when the ciliary muscle relaxes?
The lens thins and flattens
What is visual acuity?
Sharpness of vision
How is visual acuity measured?
At 20 feet with the Snellen Eye Chart
What is myopia?
Near-sightedness
What causes myopia?
Elongated eyeball
How is myopia corrected?
Concave lenses
What is hyperopia?
Farsightedness
What causes hyperopia?
Short eyeball
How is hyperopia corrected?
Convex lenses
What is astigmatism?
Asymmetry of the cornea and/or lens curvatures
How is astigmatism corrected?
Cylindrical lenses
What is the retina a forward extension of?
The brain
Where do neuron axons in the retina exit?
At the optic disc
What are the photoreceptors in the retina?
Rods and cones
What do rods allow in terms of vision?
Black and white vision in low light
What pigment do rods contain?
Rhodopsin
What does rhodopsin absorb best?
Green light (about 500nm)
What occurs during the bleaching reaction of rhodopsin?
Rhodopsin dissociates into retinaldehyde and ops in
What is retinaldehyde derived from?
Vitamin A
What is the visual cycle of retinal?
Conversion back into 11-cis form
What happens to photoreceptors in the dark?
They inhibit bipolar cells
What is the dark current?
Na+ channels in rods and cones are open
What happens when light hits photoreceptors?
Activation of a G-protein/2nd messenger system
What is the role of transducins?
Activation of phosphodiesterase
What happens to photoreceptors when Na+ channels close?
They hyperpolarize and lift inhibition on bipolar cells
What do cones allow in terms of vision?
color vision and greater visual acuity
What are the types of cones based on wavelength and color?
S: short, blue
M: medium green
L: long, red
What is the fovea centralis?
The point of best vision in the retina
What allows great visual acuity at the fovea centralis?
1:1 relationship with ganglion cells
What increases light sensitivity in the retina?
convergence of rods onto a single ganglion cell
What do saccadic eye movements do?
Shift parts of the visual field onto the fovea
Three chambers of the cochlea
Scala vestibuli, scala media, scala tympani
