Chapter 10: Sensory Physiology

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?

1. Salty

2. Sours

3. Sweet

4. Bitter

5. 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