SMELL

1) Olfaction (sense of smell) is provided by a pair of olfactory organs.

2) Each  olfactory organ consists of

a) olfactory epithelium (contains olfactory receptors, supporting cells, and basal cells)

b) olfactory glands (continuously secretes a mucous layer which covers epithelium keeping are free of dust and debris and overpowering smells)

3) Odors must diffuse into the mucus before they stimulate the olfactory receptors (each receptor has cilia extending into the mucus to receive the stimuli).

4) Olfactory reception begins as....                                                        

l) Dissolved chemicals first change the permeability of the receptor membrane producing an action potential. There are about 10-20 million olfactory receptors/5 cubic centimeters.  The surface area of a German Shepherd is 72x as great as ours.

2) Axons from the olfactory receptors then join together into 20 or more bundles and attach to the olfactory bulbs, then the impulse is carried through the olfactory nerve to the olfactory cortex.

3) Olfaction is the only sensory information that bypasses the thalamus (the thalamus filters all sensory information except for olfaction).   The sense of smell for this reason can produce profound emotional and behavioral responses.  An example is in the perfume industry and also natural odors that may trigger sexual responses.

TASTE

1) Gustation (sense of taste) is dependent upon gustatory or taste receptors along the surface of the tongue, and adjacent portions of the pharynx and larynx.

2) Taste receptors are found in organs called taste buds.  Taste buds are located along the sides of epithelial projections called papillae where they are protected from mechanical stress involved in chewing food.

3) The largest papillae called the circumvallate papillae forms a "V" toward the attached base of the tongue and contains most of our taste buds.

4) Taste buds consist of...

a) gustatory cells with microvilli (taste hairs) extending through taste pores

b) supporting cells between the gustatory cells

5) There are four primary taste sensations : sweet, salt, sour, and bitter. The threshold for each varies and they respond more to unpleasant rather than pleasant tastes. Each taste sensation  is detected on different regions of the tongue: sweet and salty (tip of the tongue); sour (sides of the tongue); bitter (near the back of the tongue) page 560.

6) Taste is carried to the medulla, and then to the thalamus and relayed to portions of the sensory cortex for analysis by the vagus, facial and glossopharyngeal nerves. Texture of food and "hot" peppery food is transmitted by the trigeminal nerve.

7) Gustation is several times more sensitive when olfaction is working properly.

VISION (THE EYE)

I) Accessory structures of the eye:

a) The eyelids or palpebrae consists of....

-----upper and lower eyelids which are extensions of the skin.  Points of attachments called the medial and lateral canthus---

------Blinking of the eyelids keep the surfaces of the eyes lubricated and free from dust; they can also be closed firmly for protection----

-----Eyelashes are hairs that protect the eye from dust and insects.---

b) Associated exocrine glands.....

-----There are large modified sebaceous glands with each eyelash which secrete a lipid rich substance that prevents eyelids from sticking together. Infection in a sebaceous gland of one of the eyelids produces a sty--

-----The lacrimal curuncle at the medial canthus produces gritty  secretions ("sleepers").---

c) The conjunctiva (superficial epithelium of the eye). It is the epithelium which is continuous with the inner lining of the eyelid. (inflammation of infection of the conjunctiva results in conjunctivitis or pink eye).

d) The lacrimal apparatus which consists of the lacrimal gland, lacrimal canals, and the nasolacrimal duct. Tears which reduce friction, removes debris, and prevents eye infections (contain lysozyme)  are produced by the lacrimal glands.   Blinking sweeps the tears to the medial canthus into the lacrimal canals, and then into the lacrimal sac and finally through the lacrimal duct into the nasal cavity to be disposed of by the acids of the stomach when swallowed (page 565).

e) Six extrinsic eye muscles (oculomotor muscles: inferior, lateral, superior, and medial rectus along with the inferior and superior obliques. Each muscle functions in a different action (page 567).

II) Structure of the Eyeball

1) Diameter of the eyeball is 2.5 cm, and has a mass of 8 grams.  It shares the space within the orbit with the extrinsic eye muscles, lacrimal gland, cranial nerves, blood vessels and orbital fat (for padding and insulation).

2) The "eyeball" is divided into two cavities:

a) the posterior cavity (vitreous chamber) contains the gelatinous vitreous body

b) the anterior cavity which is divided into the anterior and posterior chambers.  Each chamber is separated by the iris.  The cavity is filled with thinner less viscous aqueous humor.  The canal of Schlemm returns the aqueous humor to the venous system.

3) The wall of the eye contains three layers or tunics:

----The fibrous tunic which is the most outermost and functions in support and protection.  It also provides a place of attachment for the extrinsic eye muscles, and assists in the focusing process.  It consists of the sclera (white of the eye) which contains collagen and elastic fibers. The sclera is thickest over the posterior surface where the extrinsic muscles attach.  The fibrous tunic also contains the transparent cornea which is continuous with the sclera.  The collagen fibers within the cornea are arranged in parallel layers allowing light to pass through---

----The vascular tunic (the middle layer) contains blood vessels, and lymphatics, and the intrinsic eye muscles found in the iris and around the lens of the eye. The vascular tunic consists of three parts:

a) The iris which contains pigmented cells for eye color along with two layers of smooth muscle which contract changing the diameter of the central opening called the pupil.

b) The ciliary body which consists of the ciliary muscle which is a band of muscle which attaches to the suspensory ligaments.   The suspensory ligaments position the lens so light will pass through the center of the lens. Contraction and relaxation of the ciliary muscle enables the lens to change shape in the focusing process.

c) The choroid is located under the fibrous tunic  and posterior to the ciliary body.  It contains the capillary network that delivers oxygen and nutrients.

----The Neural tunic is also called the retina.  It consists of two layers: an other thin pigment and a thick inner layer (the neural retina). The neural retina consists of:  photoreceptors, supporting cells and neurons, and blood vessels.  The neural retina forms a "cup" forming the posterior and lateral boundaries of the posterior cavity  (page 569).---

4) Neural Retina Organization

a) Contains photoreceptors:

-----rods for night vision and seeing in dim light, 125 million rods found on the sides of the retina--

-----cones for color vision and clearer vision, three types of cones to detect three primary colors of light (red, green, and blue), 6 million cones found on the bottom (posterior region) of the eye along with some rods.  The macula lutea (yellow spot) is where the image arrives if you look directly at something and has no rods present at all, only cones. In the center of the macula lutea is the fovea centralis (the center for color vision and the site of sharpest vision) where are found the greatest concentration of cones in the retina-----

b) Contains bipolar cells:

---about 6 million, the photoreceptors synapse with them---

c) Contains ganglion cells:

----The bipolar cells synapse with ganglion cells which face the posterior cavity----

d) Contain horizontal and amacrine cells which regulate the information between the photoreceptors and ganglion cells adjusting the sensitivity of the retina like adjusting the contrast on a TV set.

e) Contains the optic disc which is a circular region medial to the fovea. It is the origin of the optic nerve.  Axons from 1 million ganglion cells emerge here and transmit impulses to the optic nerve and then to the thalamus.  The optic disc has no photoreceptors and is called the blind spot (page 571).

III) VISUAL ABNORMALITIES:

1) Glaucoma--interference with normal circulation of the aqueous humor The aqueous humor normally re-enters the venous system by the canal of Schlemm.  Interference with this reabsorption causes a buildup in pressure within the anterior chamber which can distort the retina and optic disc and cause blindness.

2) Accommodation problems--- Accommodation is the process of focusing an image on the retina by changing the shape of the lens.   Examples of accommodation problems include:

----Emmetropia --- normal accommodation (emmetro - proper measure)

----Myopia --- "nearsightedness" occurs when the eyeball is too deep and the image is focused in front of the retina when viewing objects far away. It can be corrected by a concave (diverging) lens.----

----Hyperopia--- " farsightedness" occurs when the eyeball is too shallow. The image is focused behind the retina when viewing objects close (reading distance of a book or newspaper). It can be corrected by a convex (converging) lens.---

----Astigmatism--- irregularities in the shape of the lens or cornea and corrected by glasses or special contacts.---

3) Color Blindness---Occurs when one or more classes of cones are absent or nonfunctional.  The most common occurs when the red cones are missing or nonfunctional (individuals cannot distinguish between red and green). It is more common among males (a sex linked trait) (10% of all men and .67% of all women are color blind).  Total color blindness is rare (1 in 300,000 have no cones at all).

IV) VISUAL ACUITY

a) determined by the snellin eye chart...

--- 20/20--- normal vision  (for a "normal" person at 20 feet they can read details that a normal person should read)

---20/15---better than average, can see details that would be clear to the normal eye at a distance of 15 feet---

---20/30---less than average, must be 20 feet from an object to see details that a normal person could discern at 30 feet---

---Below 20/200--a person is legally blind, even if they wear contacts or glasses.  Caused by diabetes, cataracts, glaucoma, corneal scarring, retinal detachment, accidents, and heredity.---

V) VISUAL PHYSIOLOGY

1) Visual pigments are found in membrane discs of the photoreceptors which are derivatives of rhodopsin. Rhodopsin consists of an enzyme called opsin bound to the pigment retinal.  Retinal is made from vitamin A and is identical in both rods and cones, but opsin is different in each rod and the 3 types of cones   

2) Photoreception occurs in the following steps....

a) A photon strikes a rhodopsin molecule in the membrane discs

b) The photon is absorbed and a change in the retinal component activates opsin

c) Bleaching occurs in which rhodopsin breaks down into retinal and opsin.

d) The retinal must be converted back into its former shape in order to recombine with opsin.  This occurs by way of ATP, and bleaching occurs when you see dots as from a flashbulb camera or snow blindness.

e) Retinal and opsin are combined again to form rhodopsin. This is called recovery.

f) The arrival of the photon alters the membrane potential (produces an action potential) and begins an impulse along the optic nerve.

HEARING AND EQUILIBRIUM (THE EAR)

Equilibrium informs us of the position of our body in space by monitoring gravity, linear acceleration, and rotation.

Hearing enables us to detect and interpret sound waves

I) THE ANATOMY OF THE EAR

A) The External Ear:

----The pinna (auricle): protects the opening into the ear, provides directional sensitivity to the ear---

---The external auditory canal carries sound to the eardrum, contains ceruminous glands that secrete cerumen (ear wax) which slows the growth of microorganisms, reducing the chances for infection, also contains outwardly projecting hairs that prevent insects and foreign objects from entering.

---The tympanum (eardrum) marks the end of the outer ear

B) The Middle Ear:

---The tympanic cavity which is filled with air from the nasopharynx through the auditory tube (pharyngotympanic tube or eustachian tube) which permits an equalization of pressure on each side of the eardrum (can allow microorganisms in causing a middle ear infection called otitis media).--

---The auditory ossicles which are three tiny bones (malleus, incus, and the stapes) that connect the tympanum with the inner ear.  The base of the stapes is attached to the inner ear by way of a membrane called the oval window.----

***The tympanum is much larger than the oval window and is very sensitive. Sound is amplified into the oval window and loud noises can be controlled by two muscles:

---the tensor tympanum (pulls on the tympanum reducing vibrations from the tympanum---

----the stapedius (pulls on the stapes reducing vibrations to the oval window---

C) THE INNER EAR

----The membraneous labyrinth: collection of tubes and chambers filled with a fluid called endolymph.  It contains the receptors for equilibrium and hearing.---

---The bony labyrinth: shell of bone surrounding the membraneous labyrinth where another fluid called the perilymph is found between the bony and the membraneous labyrinth.  The bony labyrinth contains three parts:

1) The vestibule contains two membraneous sacs: the saccule and the utricle. Receptors in them provide sensations of gravity and linear acceleration.

2) The semicircular canals contain semicircular ducts which contain receptors that are stimulated by the rotation of the head.

****the vestibule and the semicircular canals together form the vestibular complex.

3) The cochlea contains the cochlear duct which contains receptors which provide the sense of hearing.  The cochlear duct is sandwiched between a pair of perilymph filled chambers.

---Receptors in the inner ear are called hair cells and they communicate with a sensory neuron. The free surface supports 8-100 microvilli called stereocilia.  Movement of the stereocilia distorts the hair cell surface: in one direction it stimulations hair cells and in the other direction it inhibits the hair cells.

D) EQUILIBRIUM

I) Rotational Movement:

1) detected by the semicircular ducts: the anterior, posterior and lateral semicirculaar ducts.

2) Each duct contains a swollen region called the ampulla which contains the sensory receptors.

3) Steriocilia are imbedded in a gelatinous structure called the cupula in each ampulla.

4) When rotation occurs in the plane of a canal, hair cells are stimulated by the movement of the endolymph.

Examples include:

---shaking the head no: involves stimulation in the lateral simicircular duct--

---nodding yes: stimulation in the anterior duct--

---tilting head from side to side---stimulation in the posterior duct---

****Three dimensions in space

II) GRAVITY AND LINEAR ACCELERATION

1) detected in the the utricle and saccule

2) hair cells are found in an oval shaped macula (a macula in the utricle and one in the saccule)

3) steriocilia also are in a gelatinous mass, but with mineral crystals on top. One type of crystal is the otolith and pushes the sensory hairs downward rather side to side.

****Going down in an elevator the otoliths lag behind (since they are dense and heavy). We are aware of the initial downward movement, but once the elevator reaches a constant speed we are no longer aware of it (otoliths catch up until we stop.  This is determined by the saccular maculae

****Linear acceleration does the same same but is determined by the utricle maculae

*****Vestibular sensations are carried to the brain by the vestibulocochlear nerve

III) HEARING

1) received by receptors in the cochlear duct

2) frequency determined by the part of the cochlear duct stimulated; intensity by the number of hair cells stimulated

3) Three ducts are in the cochlea:

----vestibular duct (scali vestibuli) which contains perilymph---

-----cochlear duct (scali media) which contains endolymph---

----tympanic duct (scali tympanum) which contains perilymph---

****vestibular duct and the tympanic duct are interconnected at the tip of the cochlear spiral (both encased by the bony labyrinth everywhere except at the oval window. The base of the vestibular duct and the round window at the base of the tympanic duct

4) Hair cells are present in the cochlear duct in the organ of corti (spiral organ).  The organ of corti sits atop the basilar membrane which separates the cochlear duct from the tympanic duct

5) Hair cells are in longitudinal rows and the stereocilia are in contact with the tectorial membrane (attached to the inner wall of the cochlear duct).

6) When the basilar membrane bounces up and down, the stereo cilia are distorted when pushed against the tectorial membrane( in response to pressure waves in the perilymph, when sound waves arrive at the tympanum.  

7) Impulses carried from the cochlear branch of the vestibulocochlear nerve to the medulla, and to the auditory cortex of the temporal lobe (after being "filtered" through the thalamus).

8) High and low frequencies are detected:

a) hearing range of humans: 20 Hz to 20,000 Hz and is detected in varying degrees in the cochlea

****Frequency of sound waves vary.....

Ultrasonic sound:

100,000 Hz                        Bats

50,000 Hz                           Dogs

Audible range (range of human hearing):

20,000 Hz

10,000 Hz  (limit for older people)

20 Hz