Ch. 15: Special Senses

Special senses

Those senses with highly localized receptors that provide specific information about the environment.

How many primary odors are there that an average person can recognize?

Seven

How many different odors via the olfactory epithelium are there?

4000

What are the dendrites (ends) of an olfactory neuron called?

olfactory vesicles

What do cilia (olfactory hairs) of olfactory neuron embedded in mucus do? (3 things)

1. Odorants dissolve in mucus
2. Attach to receptors
3. Cilia depolarize as a result of the action potential

Can one olfactory receptor respond to more than one type of odor?

yes

What is unique about olfactory neurons compared to most other neurons?

olfactory neurons are replaced every two months, most neurons are permanent

Odorant Binding to Membrane of Olfactory Hair (figure)

Olfactory neuronal pathway

bipolar olfactory neurons -> cribriform plate -> olfactory bulbs and synapse -> olfactory tract -> olfactory cortex (lateral olfactory area, medial olfactory area, intermediate olfactory area)

What is unique about olfactory information?

It goes directly to the olfactory cortex of the frontal/temporal lobes - it doesn't pass through the thalamus like all the other major sensations

Lateral olfactory area

conscious perception – smell

Medial olfactory area

visceral/emotional (instinctive) reactions to odors

Intermediate olfactory area

receives information from the medial and lateral olfactory areas (APs carried by axons in this area modulate the activity of the neurons in the olfactory bulb, enhancing rapid adaptation of the olfactory system)

Olfactory Neuronal Pathways and Cortex (figure)

How many primary odors have been identified?
A. eight
B. six
C. seven
D. eleven

C. seven

Olfactory neurons
A. Have projections called cilia.
B. Connect to the olfactory bulb.
C. Have receptors that react with odorants dissolved in mucus.
D. All of the above.

D. All of the above.

Where are taste buds primarily located?

on papillae (specialized tongue structures)

Vallate papillae

Largest but just 8-12 in V between anterior/posterior parts of tongue (have taste buds)

Fungiform papillae

Mushroom-shaped and scattered on superior surface of tongue - they look like "small red dots” interspersed among the filiform papillae (have taste buds)

Foliate papillae

Leaf-shaped and in folds on sides of tongue (have the most sensitive taste buds, but decrease in number with age)

Filiform papillae

filament-shaped and the most numerous (no taste buds)

How many tastebuds on the tongue?

approximately 10,000

The sensory cells of each taste bud are called

taste or gustatory cells

How often are gustatory cells replaced?

every 10 days

How many taste cells on each taste bud?

about 50

Taste cells have _____.

microvilli (gustatory hairs) extending into taste or gustatory pores

Tastants

chemical molecules that dissolve in saliva and enter the taste pore by various mechanisms, causing the taste cell to depolarize

Do taste cells have axons?

No, they don’t generate their own action potentials

What happens after the taste cells depolarizes?

Neurotransmitters are released from the taste cells and stimulate action potentials in the axons of sensory neurons associated with them

Taste Buds (figure)

Sour taste

Most sensitive on lateral aspects of tongue (produced by acids)

Salty taste

Most sensitive on the tip of tongue (produced by metal ions)

Bitter taste

Most sensitive on the posterior part of the tongue (produced by alkaloids, most of which are toxic)

Sweet taste

Most sensitive on the tip of the tongue (produced by sugars, some carbohydrates, and some proteins, but can be fooled - NutraSweet = aspartame)

Umami taste

Scattered sensitivity (produced by amino acids, like glutamate)

Which tastant has the highest threshold sensitivity?

salty and sweet

Which tastant has the lowest threshold sensitivity?

bitter

Which tastes do humans tend to crave?

sweet, salty, and umami tastes

Actions of the Major Tastants (figure)

(a) Salty
(b) Sour
(c) Sweet
(d) Bitter
(e) Umami

Which of these is not one of the basic tastes?
A. spicy
B. salt
C. umami
D. sour

A. spicy

Which of these types of papillae have no taste buds associated with them?
A. circumvallate
B. filiform
C. foliate
D. fungiform

B. filiform

What 3 things affect taste?

1. Texture (affects the perception of taste)
2. Temperature
3. Olfaction

At what levels does taste very rapidly adapt?

at level of the taste buds and within CNS

Why is bitter the most sensitive threshold?

Many alkaloids are poisonous

What are the 3 cranial nerves involved in sense of taste and what portion of the tongue do they innervate?

1. VII: Facial (anterior 2/3 tongue)
2. IX: Glossopharyngeal (posterior 1/3 tongue, the vallate papillae, and the superior pharynx.)
3. X: Vagus (posterior tongue)

3 cranial nerves that make up the pathway for taste

1. Chorda tympani (part of facial nerve VII): sensation to anterior 2/3 of tongue, except from the vallate papillae
2. Glossopharyngeal nerve (IX)
3. Vagus nerve (X): carries a few fibers for taste from epiglottis and the root of the tongue

Neuronal pathway for taste

APs from the cranial nerves -> medulla oblongata (tractus solitarius) -> thalamus -> taste area of cortex (extreme inferior end of postcentral gyrus)

DO: Name the four types of papillae found on the tongue.

Circumvallate, filiform, fungiform, foliate

4 accessory structures of the visual system

eyebrows, eyelids, eyelashes, and conjunctiva

What is the function of eyebrows to the visual system?

provide shade, prevent sweat from running into eyes

3 parts of the eyelids (palpebrae)

1. Palpebral fissure: space between eyelids
2. Canthi (lateral and medial): where eyelids meet
3. Caruncle: a reddish-pink mound housed by the medial canthus that consists of modified sweat & sebaceous glands

5 layers of the eyelid (outer -> inner)

1. a thin layer of skin on the external surface
2. a thin layer of areolar connective tissue
3. a layer of skeletal muscle consisting of the orbicularis oculi and levator palpebrae superioris muscles
4. the tarsal plate, which is a layer of dense connective tissue that maintains the shape of the lid
5. the palpebral conjunctiva

Eyelashes

double/triple row of hairs on the external edge of the eyelid with Ciliary glands and Meibomian glands

Ciliary glands are

modified sweat glands that empty into the hair follicles of eyelashes

Meibomian glands are

sebaceous glands at the inner margins of the eyelids that produce sebum

Conjunctiva:

thin transparent mucous membrane

Palpebral conjunctiva:

covers the inner surface of the eyelids

Bulbar conjunctiva:

covers the anterior surface of the eye (except over pupil)

Subconjunctival hemorrhage

Sty

Ciliary gland

Chalazion

Meibomian gland

Lacrimal apparatuses (3 things)

1. Lacrimal gland
2. Lacrimal canaliculi
3. Lacrimal sac (leads to the nasolacrimal duct)

What does the lacrimal gland do?

produces tears to moisten, lubricate, and wash

Tears pass over the eye and contain what?

water, salts, mucus and lysozymes

What do the lacrimal canaliculi do?

collect excess tears via openings called puncta

Lacrimal sac leads to nasolacrimal duct, which

opens into nasal cavity

What does a blocked nasolacrimal duct look like?

Tears…
A. are released onto the surface of the eye near the medial corner of the eye.
B. in excess cause a sty.
C. pass through the nasolacrimal duct directly into the oral cavity.
D. contain water, salts, mucus and lysozymes.

D. contain water, salts, mucus and lysozymes.

The 6 extrinsic eye muscles:

1. Superior rectus
2. Inferior rectus
3. Later rectus
4. Medial rectus
5. Superior oblique
6. Inferior oblique

Anatomy of the Eye (figure)

3 layers/tunics of the eye and what they are made up of

1. Fibrous: sclera and cornea
2. Vascular: choroid, ciliary body, iris
3. Nervous: retina

Sclera:

Posterior (5/6) white outer layer (made up of opaque, dense collagenous CT/elastic fiber) that maintains shape, protects, and provides for muscle attachments

What is the sclera continuous with?

the cornea

Cornea:

an avascular, transparent CT layer made of small collagen fibers and proteoglycans (stratified squamous epithelium on outer surface) that refracts light

Why does the cornea have a low water content?

water scatters light

What was one of the first tissues to be transplanted?

the cornea

Vascular layer:

contains most of the blood vessels of the eye (from internal carotid artery) and melanin

Iris:

the colored part of eye that controls entering light with smooth muscles

2 groups of the iris's smooth muscle

1. Sphincter pupillae
2. Dilator pupillae

Sphincter pupillae:

constriction of the pupil (innervated by parasympathetic fibers from CN III - oculomotor)

Dilator pupillae:

dilation of the pupil (innervated by sympathetic fibers)

Ciliary body:

produces the aqueous humor that fills the anterior chamber

Ciliary muscles:

smooth muscles attached to suspensory ligaments of lens that control the lens shape

Choroid:

portion of the vascular tunic associated with the sclera (it is very thin and pigmented)

2 layers of the retina

1. Pigmented layer
2. Neural layer

Pigmented Layer:

outer layer of the retina that is pigmented simple cuboidal epithelium

What does the pigment of the pigmented layer and choroid help to do?

helps reduce light scatter

Neural Layer:

inner layer of the retina that contains the photoreceptor cells (rod and cone cells)

What does the lens focus light on?

macula lutea and fovea centralis

Macula lutea

small “yellow spot”

Fovea centralis:

area of greatest visual acuity where photoreceptor cone cells are tightly packed

Optic disc:

the blind spot in vision where blood vessels enter/exit eye and nerve processes from retina exit eye as optic nerve

What does the aqueous humor help to do? (3 things)

1. maintains intraocular pressure
2. provides nutrients to structures
3. refracts light

What is the aqueous humor produced by?

ciliary processes

Where does the aqueous humor exit through?

canal of Schlemm/scleral venous sinus

Glaucoma

increase in intraocular pressure by aqueous humor buildup

What does the vitreous humor help to do? (3 things)

1. maintains intraocular pressure
2. holds lens and retina in place
3. refracts light

What do the suspensory ligaments attached to the ciliary processes do?

change shape as ciliary muscles contract/relax

What is the Lens made of?

Cuboidal epithelial cells that produce lens fibers that lose their nucleus and accumulate proteins called crystallins

What is the crystalline lens is covered by?

a highly elastic, transparent capsule