Chapter 17 (Special Senses)

Olfaction

sense of smell

Anatomy of Olfaction

olfactory epithelium and supporting cells (provide physical support)

• nose → odoric particles → nostrils → nasal cavity → olfactory epithelium

Olfactory Epithelium

seperated from brain with the ethmoid bone

Olfactory Sensory Neuron

First order neuron with olfactory cilia (picks up odors)

Transduction

conversion of a stimulus into a graded potential (reach threshold → action potential)

Basal Epithelial Cells

stem cells → transforms into ne olfactory cells (regeneration) (2 month lifespan)

Olfactory Gland (Bowman’s Gland)

secretes mucus → keeps environment; odorant molecules diffuse → cilia hair cells access (stimulates better)

Physiology of Olfaction

10 million olfactory receptors (about 400 types/varieties)

Olfaction Adaptation

few molecules needed to be picked up as an odor → rapidly adapting sense (ex. perfume or cologne)

• only way to smell again is to change the intensity

Olfactory Pathway

route taken by olfactory information from stimulus to brain; only sensation that reaches cerebral cortex without synapsing in thalamus

1. stimulus

2. transduction

3. olfactory sensory neuron

4. cilia

5. depolarized

6. action potential

7. olfactory nerve (I)

8. brain

9. cribriform plate (ethmoid bone)

10. olfactory bulb

11. synapses with secondary neuron

12. olfactory tract

13. olfactory cortex (temporal lobe)

Olfaction and Memory

some axons will go to the limbic system which is why smell has a strong association with memory

Gustation

sense of taste

Anatomy of Gustation

Taste bud, supporting epithelial cells, gustatory epithelial cells, Microvilli, basal epithelial cells

Taste Buds

sense organ → picks up on stimuli → chemical stimulus; Lingual papillae

Lingual Papillae

elevations on tongue; located on the tongue, soft palate (back of mouth cavity; roof of mouth), upper pharynx, nasal cavity, epiglottis

• increase surface area of tongue to provide more area to receive chemicals; rough surface on tongue

Supporting Epithelial Cells

surrounds gustatory cells (main players) → attached to microvilli → in taste pores → synapse with dendrites of first order neurons

• regenerates every 10 days

Basal Epithelial Cells

stem cells → produce supporting cells that make gustatory cells

Vallate Papillae

rounded; v-shaped on back of tongue

Fungiform Papillae

mushroom shape; scattered on surface of tongue with five taste buds each

Foliate Papillae

small trenches → lateral edges on tongue (young children only)

Filiform Papillae

thread-like; tactile receptor; no taste buds

Gustation and Olfaction

odors from food can travel up to olfactory sensory neurons (gives full taste)

5 Primary Tastes

sweet, salty, sour, bitter, umangi

Tastants

chemicals stimulate gustatory epithelial cells

Physiology of Gustation

1. food molecules dissolve in saliva

2. needs to reach microvilli

3. stimulation of synaptic vesicles released from gustatory cells

4. graded potential

5. nerve impulses

6. brain

Gustatory Cells

has all types of cells that can pick up all tastes

Gustatory Pathway

1. first-order gustatory neuron (connected to taste buds)

2. cranial nerves (VII, IX, X)

3. medulla

4. other parts of the brain (some go to limbic system or thalamus to cortex)

Vision

sense of sight

Anatomy of Vision

Eyelids, Eyebrows, Eyelashes, Lacrimal apparatus, Extraocular muscles

Eyelids

shade, protect, lubricates the eye (sun, sleeping, excessive light, foreign objects, move across the membrane)

Eyebrows

types of hair that protects foreign objects from landing in the eye; precipitation rays from sun

Eyelashes

types of hair that protects foreign objects from landing in the eye

Lacrimal Apparatus

internal; collection of structures produce and drain fluids (lacrimal fluids)

• shaped of almond → drains into several ducts → wash over surface of eye in conjunctiva (spread by blinking) pass to anterior eye → punta region → nasal sinuses

Lacrimal Fluids

tears; protect lubricates eyes

Extraocular Muscles

move eye in every direction possible (many muscles; small units); precise and detailed

Fibrous Layer

superficial; cornea and sclera

Vascular Layer

choroid and ciliary body and iris (pigment)

Retinal Layer

inner layer → beginning of visual pathway

Cornea

transparent layer → helps focus on retina

Sclera

white part → dense connective tissue (fibrous collagen) → entire eyeball but cornea → provides shape/protection

Aqueous Humor

manages pressure; transparent watery fluid in anterior segment of eye; drains into sinuses in junctions of sclera and cornea, filters capillaries, nourishes lens

Choroid

highly vascularized membrane/layer of tissue lines internal part of sclera (produces melanin; reduces reflection and lights (keeps vision bright)

Ciliary Body

anterior part of vascular layer; blood capillaries; secretes aqueous humor; ligaments attach to lens; smooth muscle controls shape of lens (bends lens to sharpen vision)

Iris

colored portion of eyeball; flattened; melanocytes; smooth muscles → allows more/less light in the eye → regulates the dilation of pupils

Pupil

hole in the iris; increases the light that enters (iris contraction); decreased in diameter

Optic Disc

blind spot; optic nerve exits the eye → no photoreceptors

Photoreceptor Layer

Neural or sensory cells are; specialized cells that convert light rays to nerve impulses

Rods

dim light (120 million)

Cones

gives colors (6 million); green, blue, and red

Macula

center of retina on posterior

Fovea Centralis

depression in center of macula; contains cones; highest visual acuity/sharpness

Lens

behind the pupil; transparent; lacks blood vessels; focuses images on retina; divides eye structure into anterior and posterior

Anterior Segment

smaller, space between cornea and lens filled with aqueous humor

Posterior Segment

behind the lens, contains vitreous humor, lens to retina

Vitreous Humor

transparent jelly-like substance that holds the retina against other surfaces of the eyeball

• if something happens to this the retina can separate

Intraocular Pressure

maintained by aqueous humor and partially vitreous humor; maintains shape of eyeball and prevents collapsing

Vision Physiology

creates an image through refraction

• images focused on retina are inverted/upside down → brain converts it for you

• visual information from right half of eyes visual field conveyed to left side of brain and vise versa

Refraction

bending of light through a medium (less if further away); 75% at cornea, 25% at lens

Accommodation

lens has to further refract the images because of the distance (increase curvature based on location)

Emmetropic

normal vision

Myopia

nearsightedness; images converges in front of the retina

Hyperopia

farsightedness; behind the retina

Astigmatism

an irregular curvature of lens or cornea (parts of image is out of focus)

Convergence

medial movement of eyeballs to view an object (closer increases; eye moves inwards)

Binocular Vision

depth vision; both images focus on an image

Visual Pathway

1. stimuli

2. graded potential; absorption of light from photo pigment (protein in outer segment of photoreceptors)

3. receptor potential; rods and cones to brain

4. axon from retinal ganglion cell (optic nerve II)

5. optic chiasm

6. optic tract

7. brain (thalamus)

8. synapses with neurons; primary visual cortex (occipital lobe)

Hearing

ability to perceive sound

Anatomy of External Ear

Auricle, External acoustic meatus, Tympanic membrane, Ceruminous glands

Anatomy of Middle Ear

Auditory ossicles (Malleus, Incus, Stapes), Vestibular window, Cochlear window, Auditory tube

Anatomy of Inner Ear

Bony Labyrinth, Perilymph Membranous Labyrinth, Endolymph, Vestibule, Utricle / saccule, Semicircular canals, Ampulla, Vestibular gangli, Cochlea, Cochlear duct, Scala vestibuli, Scala tympani, Organ of Corti, Stereocilia, Tectorial membrane, Vestibulococlear nerve

Auricle (pinna)

outermost structure; see outside a person’s head → directs sound waves to a person’s head

External Acoustic Meatus (ear canal)

long canal that leads to the head → ear drum

Tympanic Membrane

ear drum

Ceruminous Glands

special sweat glands that secrete ear wax (cerumen)

Cerumen

ear wax; prevents dust and anything foreign staying there

Ossicles

3 smallest bones in the body; malleus, stapes,and incus

Malleus (hammer)

adjacent and touching tympanic membrane

Incus (anvil)

middle bone in the ossicles

Stapes (stirrup)

connects to the vestibular window; bone in the ossicle

Vestibular Window

oval window

Cochlear Window

opening to inner ear

Auditory Tube

connects middle ear to nasopharnyx; where you get ear infections (mucus clouds it); regulates pressure

Bony Labyrinth

set of cavities divided into other sections; 3 canals that run perpendicular to each other

Perilymph

fluid similar to cerebrospinal fluid; surrounds membranous labyrinth

Membranous Labyrinth

houses receptors for hearing and equilibrium; filled with endolymph

Endolymph

higher in potassium; similar to perilymph

Vestibule

oval central portion of bony labyrinth

Utricle/Saccule

region of membranous labyrinth; region thickens

Semicircular Canals

bony canals that lie in right angles to each other

Ampulla

enlargement at semicircular canals

Vestibular Ganglia

cell body of sensory neuron for equilibrium

Cochlea

bony spiral canal; 3 channels (cochlear duct, scala vestibuli, scala tympani)

Cochlear Duct

continuous of membrane labyrinth filled with endolymph

Scala Vestibuli

channel above cochlear duct and ends at vestibular window; filled with perilymph

Scala Tympani

filled with perilymph

Organ of Corti

rests on vestibular membrane; coil sheet of epithelial cells; hair cells

Stereocilia

microvilli (receptor cells for hearing); apical; endolymph; basa; emd synapses with first order neuron

Tectoral Membrane

flexible, gelatinous membrane that covers hair cells, where stereocilia embedded

Vestibulocochlear Nerve

axon of first order neurons collect and leave; membrane separates duct from scala vestibuli

Inner Hair Cells

receptors of hearing (mechanical vibration of sound → signal)