Lecture Exam 2 - Chapter 17 Study Guide

Question 1

About how many olfactory receptors do we have? Where are they located?

Answer 1

We have 10-100 million olfactory receptors
in our noses.

Olfactory receptors present in a specialized olfactory epithelium.

Olfactory epithelium covers the inferior surface of the cribriform plate. Extends along superior nasal concha.

Question 2

What cells are present in the olfactory epithelium and what are their functions?

Answer 2

Olfactory receptors

Supporting cells:
Columnar epithelial cells in mucous membrane of nose. Provide nutrients, electrical insulation and
support to the olfactory receptors. Provide a role in detoxification of chemicals

Basal cells: Stem cells - cells with a capacity to divide and differentiate. Basal cells replace the olfactory receptors that have a lifespan of only about a month. (this is unusual as mature neurons are
usually not replaced)

Question 3

What is the purpose of Bowman’s glands?

Answer 3

Provide mucous to cover the surface of the olfactory
epithelium.

Provide lubrication and helps dissolve some odorants.

Question 4

Know the olfactory pathway from the olfactory receptors to higher brain centers.

Answer 4

Axons from olfactory receptors extend through foramina in the cribriform plate of the ethmoid bone.

Bundles of axons form the left and right olfactory nerves that terminate in the olfactory bulbs.

Axons extend along olfactory tract to the limbic system and olfactory area of frontal lobe.

Question 5

Understand the mechanism by which odorants generate an action potential.

Answer 5

1) Odorant molecule binds to receptor
2) Binding activates a G protein that activates
adenylate cyclase resulting in production of
cAMP.
3) cAMP opens sodium ion channels.
4) Sodium ions enter resulting in a depolarization
that may activate an action potential.
5) The action potential propagates along the axon of
the olfactory receptor.

Question 6

What is meant by odor threshold and adaptation?

Answer 6

Olfactory sensation has low threshold - takes only a few molecules of some odorants to get a response.
e.g. methyl mercaptan - this is the odorant added to natural gas to make it smell.

Adaptation - decreased sensitivity - can occur rapidly.

Question 7

What different tastes can be detected?

Answer 7

Only 5 primary tastes can be detected:

Sour, sweet, bitter, salty, umami (Japanese for meaty or savory and believed to be stimulated by monosodium glutamate).

Question 8

Describe the anatomy of a taste bud.

Answer 8

Taste buds contain 3 types of cells: gustatory
receptors, basal cells and supporting cells. Found
on elevations of tongue called papillae.

Question 9

How are gustatory receptors activated?

Answer 9

Each receptor has a gustatory hair which is a single long microvillus that extends to the surface if the epithelium through a taste pore.

A receptor potential is generated when a stimulus (called a tastant) comes in contact with the gustatory hairs.

Question 10

Describe the gustatory pathway from mouth to higher brain centers.

Answer 10

Different tastants stimulate receptor potential in different ways:

Salty foods - sodium ions eneter gustatory receptor via sodium channels resulting in depolarization and release of neurotransmitter.

Sour foods - the H+ ions (from the acidity) are thought to enter through channels resulting in a depolarization and release of neurotransmitter.

Sweet, bitter and umami tastes require G protein-linked pathways to release neurotransmitter.

Question 11

Understand the organization of the electromagnetic spectrum.

Answer 11

Organized by different wavelengths, with microwaves and radio waves on the longer wavelength end and UV and X rays on the higher end (very brief summary)

Question 12

Where in the spectrum does visible light fall?

Answer 12

Visible light is in the part of the spectrum with

wavelengths ranging from 400-700nm.

Question 13

What generates color?

Answer 13

Color is dependent on the wavelength of the light -
objects absorb certain wavelengths and reflect
others.

Question 14

Know the location and function of accessory eye structures.

Answer 14

Eyelids

Eyelashes and Eyebrows

Lacrimal apparatus - lacrimal glands
supplied by parasympathetic fibers.
Secretions (tears) contain some mucus and
lysozyme (antibacterial).

Question 15

Know the anatomy of the eyeball.

Answer 15

Retina, Lens, Ciliary Body, Choroid, Sclera, etc. From lab.

Question 16

What controls entry of light into the eye?

Answer 16

Autonomic Nervous System

Question 17

Know the structure of the retina and organization of the different layers.

Answer 17

Photoreceptive layer on bottom over pigmented epithelium of retina. Bipolar cell layer on top of that and ganglion cell layer on top of that.

Question 18

What types of photoreceptors are present in the retina? How many of each?

Answer 18

6 million cones

120 million rods

Question 19

Explain the mechanism by which photoreceptors allow us to see.

Answer 19

Rods allow us to see in dim light

Cone stimulated by brighter light - allow for color vision.
3 types of cones:
Blue cones - sensitive to blue light
Green cones - sensitive to green light
Red cones sensitive to red light

Question 20

Know the meanings of the terms emmetropic, myopic and hypermetropic and where the
image would fall in each of these situations.

Answer 20

Emmetropic = normal eye, clear image focused on the retina

Myopic = nearsighted (difficult to see far away), the image converges in front of the retina

Hypermetropic = farsighted (difficult to see close up), image converges behind the retina

Question 21

What type of lenses are necessary to correct

near and far-sightedness.

Answer 21

nearsightedness/myopia = concave lens
farsightedness/Hypermetropia = convex lens

Question 22

What is accommodation with respect to vision?

Answer 22

When the eye is focusing on a close object, the lens becomes more curved, causing greater refraction of light rays.

This ability to respond to focus (accommodation) decreases with age because the lens loses elasticity.

Lens curvature controlled by contraction of the ciliary muscle.

Question 23

How does LASIK surgery work and why? How is the surgery performed?

Answer 23

a flap of tissue cut away from center of
cornea and the cornea reshaped with a
laser.

Question 24

Know the types of photopigments present in the eye and the mechanisms by which they
work.

Answer 24

The photopigment in rods is called rhodopsin.

There are 3 cone photopigments - one for each
of the 3 types of cones (blue, green, red). Color
vision results from different colors of light
selectively activating the different cone
photopigments.

When they absorb light they undergo a structural
change initiating the production of a receptor
potential.

Question 25

Know the visual pathway from eyes to higher brain centers.

Answer 25

Light enters through the eye and hits the pigmented epithelia of the retina, and is processed by the photoreceptor layer on top. The photoreceptor layer responds to the light waves and sends signals through the bipolar and ganglion cell layer and into the optic nerve, through the optic chiasm and into the visual processing center of of the brain.

Question 26

What causes color blindness?

Answer 26

Inherited inability to distinguish between certain
colors - due to absence or deficiency of one of the
3 types of cones.
Most common is red-green color-blindness in
which red or green cones are missing.
Prolonged Vitamin A deficiency may cause below
normal amounts of rhodopsin and inability to see
in low light.

Question 27

Know the anatomy of the ear and what components are important in hearing and equilibrium respectively.

Answer 27

3 main regions:
Outer ear - auricle, external ear canal,
tympanic membrane (ear drum).
Middle ear - auditory ossicles (malleus,
incus and stapes) .
Inner ear - (labyrinth).

Question 28

Explain the units used for frequency and intensity of hearing and what they mean.

Answer 28

Frequency: Frequency of sound vibration is called
pitch. The higher the frequency of
vibration, the higher the pitch.
Human ear can detect sounds that vibrate in 500-5000 hertz range most acutely.
1Hz = 1 cycle/second.
Entire audible range is from 20-20,000Hz

Intensity: Larger the intensity of a vibration - the
louder the sound. Intensity of sound measured in decibels (dB).
Increase of 1dB = 10 fold increase in sound intensity.

Question 29

Describe the steps that take place to convert sound waves to nerve impulses and where
each step takes place.

Answer 29

1. The Auricle directs sound waves in to the external auditory canal.
2. when sound waves strike the tympanic membrane, the alternating high- and low-pressure of the air causes the tympanic membrane to vibrate back and forth.
3. The centra area of the eardrum connects to the malleus, which also starts to vibrate, transmitting the vibration to the incus and then to the stapes.
4. As the stapes moves back and forth, it pushes the membrane of the oval window in and out. The oval window vibrates about 20 times more vigorously than the eardum.
5. the movement of the oval window sets up fluid pressure waves in the perilymph of the cochlea. As the oval window bulges inward, it pushes on he perilymph of the scala vestibuli.
6. Pressure waves are transmitted from the scala vestibuli to the scala tympani and eventually to the round window, causing it to bulge outward into the middle ear.
7. As the pressure waves deform the walls of the scala vestibuli and scala tympani, they also push the vestibular membrane back and forth, creating pressure waves in the endolymph inside the cochlear duct
8. The pressure waves in the endolymph cause the basilar membrane to vibrate, which moves the hair cells of the spiral organs against the tectorial memebrane. This leads to the bending of th ehair cell sterocilia, which produces receptor potentials that ultimately lead to the gneration of nerve impulses.

Question 30

How does a cochlea implant work?

Answer 30

Device that converts sound into electrical signals to be translated by brain.

Consists of external portion:
a microphone
a sound processor
a transmitter

And internal portion:
internal receiver
electrodes implanted in cochlear where they trigger nerve impulses.

Question 31

Explain how hair cells can detect movement and where in the ear this occurs.

Answer 31

Walls of saccule and utricle contain
thickened region called the macula.

Maculae consist of hair cells and
supporting cells. The supporting cells
secrete a thick gelatinous membrane called
the otolithic membrane. when we move our head, gravity moves the otoliths, which pull of the otolithic membrane, which in turn pulls the hairs of the membrane which opens and closes mechanically gated channels.