Ch 17: The Special Senses

Front 1

Describe the following parts that contribute to olfaction/ smell:
1.Olfactory receptors
2. Olfactory hairs
3. Supporting cells
4. Basal cells
5. Olfactory / Bowman's glands

Back 1

1.Olfactory receptors
= the first-order neurons of the olfactory pathway

2.Olfactory hairs
= the parts of the olfactory receptors that respond to inhaled chemicals
- project from the dendrite
- stimulated by odorants (chemicals that have an odor)

3.Supporting cells
= columnar epithelial cells of the mucous membrane lining the nose.
-provide physical support, nourishment, and electrical insulation for olfactory receptors
-detoxify chemicals that come in contact with the olfactory epithelium

4.Basal cells
= stem cells located between the bases of the supporting cells.
-continually undergo cell division to produce new olfactory receptors, which live for 1 month before being replaced.

5. Olfactory / Bowman’s glands
= glands within the connective tissue that supports the olfactory epithelium
-produce mucus that is carried to the surface of the epithelium by ducts.
-secretion moistens the surface of the olfactory epithelium and dissolves odorants so that transduction can occur.

Front 2

Olfactory receptors react to odorant molecules in the same way that most sensory receptors react to their specific stimuli: A generator potential (depolarization) develops and triggers one or more nerve impulses.
In some cases, an odorant binds to an olfactory receptor protein in the plasma membrane of an olfactory hair (Figure 17-2).

Describe this process:

Back 2

1.The olfactory receptor protein is coupled to a membrane protein called a G protein

2.G protein activates the enzyme adenylate cyclase.

3.Production of cyclic adenosine monophosphate (cAMP)
→ opening of sodium ion (Na+) channels
→ inflow of Na+ into olfactory receptor
→ depolarizing generator potential
→ generation of nerve impulse and propagation along axon of olfactory receptor.

Front 3

What does it mean when it is said that olfaction, like all the special senses, has a low threshold?

Example?

Back 3

Only a few molecules of certain substances need be present in air to be perceived as an odor.

Ex. the chemical methyl mercaptan, which smells like rotten cabbage and can be detected in concentrations as low as 1/25 billionth of a milligram per milliliter of air. Because the natural gas used for cooking and heating is odorless but lethal and potentially explosive if it accumulates, a small amount of methyl mercaptan is added to natural gas to provide olfactory warning of gas leaks.

Front 4

Define and describe odour adaptation

Back 4

= decreasing sensitivity
- occurs rapidly by about 50% in the first second after stimulation, but adapts slowly thereafter.

*Complete insensitivity to certain strong odors occurs about a minute after exposure. Apparently, reduced sensitivity involves an adaptation process in the central nervous system as well.

Front 5

Describe the Olfactory Pathway:

Back 5

-Olfactory (I) nerves (= bundles of unmyelinated axons of ofactory receptors) are on each side of the nose.

-they terminate in the brain in paired masses of gray matter called the olfactory bulbs.

-within the olfactory bulbs, the axon terminals of olfactory receptors form synapses with the dendrites and cell bodies of olfactory bulb neurons.

-Axons of olfactory bulb neurons extend & form the olfactory tract (see Fig 17-1b).

-Some of the axons of the olfactory tract project to the primary olfactory area of the cerebral cortex; the primary olfactory area is where conscious awareness of smell begins (see Fig 17-1d).

- From the primary olfactory area, pathways also extend to the frontal lobe/ orbitofrontal area (= an important region for odor identification and discrimination - area 11 in Fig 14.15).

*People who suffer damage in this area have difficulty identifying different odors.

Front 6

Describe the anatomical components for gestation/ taste:

1.Taste buds
2.Supporting cells
3.Taste pore
4.basal cells

Back 6

1.Taste buds
= an oval body consisting of three kinds of epithelial cells: supporting cells, gustatory receptor cells, and basal cells (see Figure 17-3c)
-most located on tongue; site of taste receptors

2.Supporting cells
- surround about 50 gustatory receptor cells in each taste bud.

3.Taste pore
= an opening in the taste bud
-allows each gustatory hair (single, long microvillus) to project to the external surface from each gustatory receptor cell

4.basal cells
= stem cells found at the periphery of the taste bud near the connective tissue layer
- produce supporting cells, which then develop into gustatory receptor cells.

Front 7

What role do basal cells play in taste buds?

Back 7

Basal cells develop into gustatory receptor cells.

Front 8

1.What are papillae?

2.Identify and describe the 3 different types of papillae that contain taste buds.

3.In addition, the entire surface of the tongue has filiform papillae. What are they?

Back 8

1. = elevations on the tongue where taste buds are found.
-provide a rough texture to the upper surface of the tongue

2a. vallate (circumvallate) papillae
-12 in total, large, circular
- form an inverted V-shaped row at the back of the tongue.
-Each papilla houses 100–300 taste buds

2b. Fungiform papillae
= mushroom-shaped elevations scattered over the entire surface of the tongue
-contain about five taste buds each.

2c. Foliate papillae (FŌ-lē-āt = leaflike)
-located in small trenches on the lateral margins of the tongue
-most of their taste buds degenerate in early childhood

3. = (FIL-i-form = threadlike) pointed, threadlike structures
-contain tactile receptors but no taste buds.
-increase friction between the tongue & food, making it easier for tongue to move food in the oral cavity.

Front 9

Describe tastants and the process that occurs when tastants are detected by the body.

Back 9

Tastants (=chemicals that stimulate gustatory receptor cells) dissolve in saliva.

1. Tastants make contact with the plasma membrane of the gustatory hairs, which are the sites of taste transduction.

2. Stimulates exocytosis. Synaptic vesicles fuse out of gustatory receptor cell.

c. Liberated neurotransmitter molecules trigger nerve impulses in the first-order sensory neurons that synapse with gustatory receptor cells (input sent to brain).

*Salty food: Na+ ions enter gustatory receptor cells via Na+ channels in plasma membrane.
-Accumulation of Na+ inside causes depolarization, causing neurotransmitter release.

*Sour tastants: H+ ions flow into gustatory receptor cells via H= channels.
-Accumulations of H+ causes depolarization, causing neurotransmitter release.

*Other tastants (sweet, bitter & umami) do not themselves enter gustatory receptors cells.
-Bind to receptors on the plasma membrane that are linked to G proteins.
-G proteins activate second messengers (chemicals) inside the gustato

Front 10

If all tastants cause release of neurotransmitter from many gustatory receptor cells, why do foods taste different?

Back 10

Different tastes arise from activation of different groups of taste neurons.

Front 11

Discuss the Gustatory Pathway.

Back 11

1. Three cranial nerves (that contain axons of the first-order gustatory neurons) stimulate the taste buds.

2. Nerve impulses (from taste buds) travel along the cranial nerves to the gustatory nucleus in the medulla oblongata.

3. Some axons (from medulla) carrying taste signals project to the limbic system and the hypothalamus; some to thalamus.

4.Result: perception of taste.

Front 12

Identify and describe the accessory structures of the eye.

Back 12

1.Eyelids/ Palpebrae
= shade the eyes during sleep, protect the eyes from excessive light and foreign objects, and spread lubricating secretions over the eyeballs (Figure 17-5).

2. Eyelashes & Eyebrows
= help protect the eyeballs from foreign objects, perspiration, and the direct rays of the sun.

3.Lacrimal (tearing apparatus)
= a group of structures that produces and drains lacrimal fluid/ tears (=a watery sol’n containing salts, some mucus, and lysozyme (= a protective bactericidal enzyme); the fluid protects, cleans, lubricates, and moistens the eyeball; spread over the surface of eyeball by blinking action).
-The lacrimal glands (each the size & shape of an almond) secrete lacrimal fluid, which drains into:
excretory lacrimal ducts (= empty tears onto surface eye Fig 17-6b)
--> lacrimal puncta (2 small openings)
--> lacrimal canals
--> lacrimal sac
--> nasolacrimal duct (= carries lacrimal fluid into nasal cavity)

4.Extrinsic eye muscles
= extend from the walls of the bony orbit to the scle

Front 13

How large is the adult eyeball?

Back 13

About 2.5cm (1in) in diameter; only one-sixth is exposed

Front 14

Identify and describe the three layers of the wall of the eyeball and each of its parts.

Back 14

1)Fibrous tunic
= the superficial layer of the eyeball and consists of the anterior cornea and posterior sclera (Fig 17-7)

a)Cornea = a transparent coat that covers the colored iris; its curved shape helps focus light onto retina.

b)Sclera = white of eye; layer of dense connective tissue made up mostly of collagen fibers & fibroblasts; covers entire eyeball except the cornea; gives shape to eyeball; makes it more rigid; protects its inner parts; serves as a site of attachment for the extrinsic eye muscles.

c) Scleral venous sinus (canal of Schlemm) = an opening at junction of the sclera and cornea; aqueous humor (fluid) drains into this sinus (Fig 17-7)

(2) Vascular tunic
= the middle layer of the eyeball
-Composed of three parts:

a) choroid = posterior portion of the vascular tunic
- lines most of the internal surface of the sclera
-has numerous blood vessels that provide nutrients to the posterior surface of the retina.
-contains melanocytes that produce melanin (=pigment that causes this layer to

Front 15

Which division of the autonomic nervous system causes pupillary constriction? Which causes pupillary dilation?

Back 15

The parasympathetic division of the ANS causes pupillary constriction; the sympathetic division causes pupillary dilation.

Front 16

Identify and descrive the 2 layers of the retina:

Back 16

1.pigmented layer = a sheet of melanin-containing epithelial cells
-the melanin, like in the choroid, helps to absorb stray light rays
2.neural layer = a multilayered outgrowth of the brain that processes visual data extensively before sending nerve impulses into axons that form the optic nerve.

Front 17

Identify the 3 distinct layers of retinal neurons.
Identify the 2 other types of cells present in the second layer.

Back 17

1.photoreceptor layer

2.bipolar cell layer
- a.horizontal cells
- b.amacrine cells
-Both of these cells modify the signals being transmitted along the pathway from photoreceptors to bipolar cells to ganglion cells.

3.ganglion cell layer
*Note that light passes through the ganglion and bipolar cell layers and both synaptic layers before it reaches the photoreceptor layer.

Front 18

What are the two types of photoreceptors, and how do their functions differ?

Back 18

The two types of photoreceptors are rods and cones. Rods provide black-and-white vision in dim light; cones provide high visual acuity and color vision in bright light.

Front 19

What are photoreceptors?

Identify and describe the 2 types of photoreceptors.

Back 19

= specialized cells that begin the process by which light rays are ultimately converted to nerve impulses.

1.Rods (~ 6 million)
-Allow us to see in dim light
-Do not provide color vision; therefore, in dim light we can see only black, white, and all shades of gray in between.

2.Cones (~ 120 million)
-stimulated by brighter lights
- produce color vision

Front 20

Starting from photoreceptors, where does the information flow to next?

Back 20

Photoreceptors --> bipolar cells --> ganglion cells

*The axons of ganglion cells extend to the optic disc (aka. blindspot) and exit the eyeball as the optic (II) nerve.

Front 21

Why can’t we see an image that strikes the blind spot/ optic disc?

Back 21

Because it contains no rods or cones.