Chapter 15: Special Senses Study Guide

Draw the effects of how light is focused in a person with an astigmatism

- Astigmatism ▪ Unequal curvatures in different parts of cornea or lens ▪ Corrected with cylindrically ground lenses or laser procedures

Identify the three main regions of the human ear

- External (outer) ear: hearing only - Middle ear (tympanic cavity): hearing only - Internal (inner) ear: hearing and equilibrium

Hair cells in the Organ of Corti send action potentials to the temporal lobe via which nerve?

- Hair cells are sandwiched between tectorial and basilar membranes • The cochlear branch of nerve VIII runs from spiral organ to brain

1. List the bones of the middle ear in order from lateral to medial, giving both the common name and anatomical names.

- Malleus: the "hammer" is secured to eardrum - Incus: the "anvil" - Stapes: the "stirrup" base fits into oval window

Compare and contrast the locations of endolymph and perilymph in the inner ear.

- Membranous labyrinth; series of membranous sacs and ducts contained in bony labyrinth; filled with potassium-rich endolymph - Scala vestibule: abuts oval window, contains perilymph - Scala media (cochlear duct): contains endolymph - Scala tympani: terminates at round window; contains perilymph

Compare and contrast myopia and hyperopia.

- Myopia (nearsightedness) ▪ Eyeball is too long, so focal point is in front of retina ▪ Corrected with a concave lens - Hyperopia (farsightedness) ▪ Eyeball is too short, so focal point is behind retina ▪ Corrected with a convex lens

Describe the 5 basic taste sensations.

1. Sweet—sugars, saccharin, alcohol, some amino acids, some lead salts 2. Sour—hydrogen ions in solution 3. Salty—metal ions (inorganic salts); sodium chloride tastes saltiest 4. Bitter—alkaloids such as quinine and nicotine, caffeine, and nonalkaloids such as aspirin 5. Umami—amino acids glutamate and aspartate; example: beef (meat) or cheese taste, and monosodium glutamate

What is accommodation in regards to vision?

Accommodation is the adjustment of the optics of the eye to keep an object in focus on the retina as its distance from the eye varies. It is the process of adjusting the focal length of a lens. ▪ Accommodation of the lenses - Changing lens shape to increase refraction - Near point of vision • Closest point on which the eye can focus - Presbyopia: loss of accommodation over age 50

What are cataracts?

Cataract is the clouding of the eye's natural lens. It is the most common cause of vision loss in people over age 40 and is also the principal cause of blindness in the world. Types of cataracts include: A subcapsular cataract occurs at the back of the lens. • Clouding of lens - Consequence of aging, diabetes mellitus, heavy smoking, frequent exposure to intense sunlight - Some congenital - Crystallin proteins clump - Vitamin C increases cataract formation - Lens can be replaced surgically with artificial lens

What does the lens do to images as they pass on to the retina?

Changes shape to precisely focus light on retina The light rays then pass through the lens, which changes shape so it can further bend the rays and focus them on the retina. ... These cells in the retina convert the light into electrical impulses. The optic nerve sends these impulses to the brain, which produces an image.

What exactly is color blindness in terms of cone pigments?

Color blindness occurs when one or more types of cones are either totally absent, or has a limited spectral sensitivity. By far the most common is congenital (hereditary) red green color blindness, meaning the L-cones and/or M-cones are either damaged or absent. • Color blindness: • lack of one or more cone pigments • Inherited as an X-linked condition, so more common in males - As many as 8-10% of males have some form • The most common type is red-green, in which either red cones or green cones are absent - Depending on which cone is missing, red can appear green, or vice versa - Rely on different shades to get cues of color

Which of these two types of deafness is often the result of prolonged exposure, perhaps over a lifetime, to loud music and is due to the gradual stiffening of the hair cells located in one of the major structures of the inner ear?

Conduction deafness

Which two structures of the eye "bend" light?

Four different surfaces bend the light as it enters the eye: the cornea, the aqueous humor, the lens, and the vitreous humor. When all four of these bend the light appropriately, you see a focused image of the object.

What does "filling in" refer to in regards to the retina?

In vision, filling-in phenomena are those responsible for the completion of missing information across the physiological blind spot, and across natural and artificial scotomata. ... When a textured stimulus is presented centered on but extending beyond the region of the blind spot, a continuous texture is perceived.

Describe how an odorant receptor functions.

Olfactory receptor, also called smell receptor, protein capable of binding odour molecules that plays a central role in the sense of smell (olfaction). ... The cilia are covered by the mucus of the nasal cavity, facilitating the detection of and response to odour molecules by olfactory receptors. Smell receptors are excited by chemicals dissolved in nasal fluids .

Which structure in the eye can be transplanted without fear of rejection? Why?

The cornea can repair itself because it is not a living tissue, it has no nerve supply and has no blood supply

What are the two internal cavities of the eye and what is found in each?

The eye is also divided into two cavities: the anterior cavity and the posterior cavity. The anterior cavity is the space between the cornea and lens, including the iris and ciliary body. It is filled with a watery fluid called the aqueous humor.

The innermost tunic of the eye is the _?_.

The retina is a light-sensitive layer of nervous tissue composed of multiple sensory cells, so-called light- or photoreceptor cells, as well as associated nerve cells and other types of cells, all working together to make a person see.

Describe the detailed pathway of a sound wave as it travels through all three main regions of the ear with words AND a picture.

The sound waves travel from the outer ear and in through the auditory canal, causing the eardrum, or tympanic membrane, to vibrate. This, in turn, causes the three small bones, known as the ossicles, or the hammer, the anvil and the stirrup, in the middle ear to move. The vibrations move via the oval window through the fluid in the cochlea in the inner ear, stimulating thousands of tiny hair cells. This results in the transformation of the vibrations into electrical impulses finally perceived by the brain as sound.

How does the structure, from the previous question number, assist in establishing the pressure in the middle ear?

equalize pressure in middle ear cavity with external air pressure ▪ Tympanic membrane cannot vibrate efficiently if pressures on both sides are not equal - Sounds are distorted

Describe the 3 nerves that carry gustatory sensations to the brain.

facial nerve glossopharangyle vagus

What is emmetropia?

normal vision

The outermost tunic or layer of the eye is the _?_.

sclera

Describe the structure used to detect rotational motion.

semicircular canals • Semicircular canals - Three canals oriented in three planes of space: anterior, lateral, and posterior ▪ Anterior and posterior are at right angles to each other, whereas the lateral canal is horizontal - Membranous semicircular ducts line each canal and communicate with utricle - Ampulla: enlarged area of ducts of each canal that houses equilibrium receptor region called the crista ampullaris ▪ Receptors respond to angular (rotational) movements of the head

The middle tunic of the eye is the_?_.

the choroid, the ciliary body, and the iris, from posterior to anterior

What's another name for the eardrum?

tympanic membrane

What is the name given to the thin, fibrous strands that connect the lens of the eye to the ciliary body? While you're at it, what is the function of the ciliary body?

zonular fiber

What is the collective name given to the three bones that make up the middle ear?

• Auditory ossicles: three small bones in tympanic cavity, named for their shape: - Malleus: the "hammer" is secured to eardrum - Incus: the "anvil" - Stapes: the "stirrup" base fits into oval window ▪ Synovial joints allow malleus to articulate with incus, which articulates with stapes ▪ Suspended by ligaments; transmit vibratory motion of eardrum to oval window Tensor tympani and stapedius muscles contract reflexively in response to loud sounds to prevent damage to hearing receptors

What is the name of the structure that acts as the receptor organ for hearing?

• Cochlea

Compare and contrast the two types of deafness discussed in class.

• Conduction deafness - Blocked sound conduction to fluids of internal ear ▪ Causes include impacted earwax, perforated eardrum, otitis media, otosclerosis of the ossicles • Sensorineural deafness - Damage to neural structures at any point from cochlear hair cells to auditory cortical cells - Typically from gradual hair cell loss

List the three different tunics of the eyeball (in order from most superficial to deep) - including the structures (and their functions) found in each tunic.

• Fibrous layer - Outermost layer; dense avascular connective tissue - Two regions: sclera and cornea ▪ Sclera - Opaque posterior region - Protects and shapes eyeball - Anchors extrinsic eye muscles - Posteriorly, where optic nerve exits, sclera is continuous with dura mater of brain ▪ Cornea - Transparent anterior one-sixth of fibrous layer • Forms clear window that lets light enter and bends light as it enters eye - Epithelium covers both surfaces • Outer surface protects from abrasions • Inner layer, corneal endothelium, contains sodium pumps that help maintain clarity of cornea - Numerous pain receptors contribute to blinking and tearing reflexes • Vascular layer - Middle pigmented layer of eye, also called uvea - Three regions: choroid, ciliary body, and iris ▪ Choroid region - Posterior portion of uvea - Supplies blood to all layers of eyeball - Brown pigment absorbs light to prevent scattering of light, which would cause visual confusion ▪ Ciliary body - Anteriorly, choroid becomes ciliary body - Thickened ring of tissue surrounding lens - Consists of smooth muscle bundles, ciliary muscles, that control shape of lens - Capillaries of ciliary processes secrete fluid for anterior segment of eyeball - Ciliary zonule (suspensory ligament) extends from ciliary processes to lens • Holds lens in position ▪ Iris - Colored part of eye that lies between cornea and lens, continuous with ciliary body - Pupil: central opening that regulates amount of light entering eye • Close vision and bright light cause sphincter pupillae (circular muscles) to contract and pupils to constrict; parasympathetic control • Distant vision and dim light cause dilator pupillae (radial muscles) to contract and pupils to dilate; sympathetic control • Changes in emotional state—pupils dilate when subject matter is appealing or requires problem-solving skills • Inner layer (retina) - Retina originates as an outpocketing of brain - Contains: ▪ Millions of photoreceptor cells that transduce light energy ▪ Neurons ▪ Glial cells - Delicate two-layered membrane ▪ Outer pigmented layer ▪ Inner neural layer

What causes glaucoma and how does a doctor test for it?

• Glaucoma: • condition in which drainage of aqueous humor is blocked, causing fluid to back up and increase pressure within eye • Pressures may increase to dangerous levels and compress retina and optic nerve, leading to blindness • Symptoms: few early signs, but late signs include seeing halos around lights and blurred vision

Identify the name and function of the structure that connects the middle ear with the throat.

• Pharyngotympanic (auditory) tube: connects middle ear to nasopharynx - Formerly called eustachian tube - Usually flattened tube, but can be opened by yawning or swallowing to equalize pressure in middle ear cavity with external air pressure ▪ Tympanic membrane cannot vibrate efficiently if pressures on both sides are not equal - Sounds are distorted

Make sure you really, really understand the order of cells that are stimulated when light reaches the retina!

• Photoreceptors and bipolar cells generate only graded potentials (EPSPs and IPSPs), not APs • When light hyperpolarizes photoreceptor cells, they stop releasing inhibitory neurotransmitter glutamate to biopolar cells • Bipolar cells (no longer inhibited) depolarize, release neurotransmitter onto ganglion cells • Ganglion cells generate APs transmitted in optic nerve to brain

Describe the stucture which enables us to detect gravity and linear acceleration.

• Vestibule - Central egg-shaped cavity of bony labyrinth - Contains two membranous sacs ▪ Saccule is continuous with cochlear duct ▪ Utricle is continuous with semicircular canals - Sacs house equilibrium receptor regions (maculae) that respond to gravity and changes in position of head

List the main structures (and their functions) of the outer ear.

The function of the outer ear is to collect sound waves and guide them to the tympanic membrane.

List the two major muscles of the middle ear? What is their purpose?

There are two muscles which serve a protective function in the middle ear; the tensor tympani and stapedius. They contract in response to loud noise, inhibiting the vibrations of the malleus, incus and stapes, and reducing the transmission of sound to the inner ear.

Explain the normal flow of aqueous humor.

aqueous humor, a plasma like fluid continuously formed (unlike vitreous humor) by capillaries of ciliary processes - Drains via scleral venous sinus (canal of Schlemm) at sclera-cornea junction - Supplies nutrients and oxygen mainly to lens and cornea but also to retina, and removes wastes

Describe three types of taste buds.

papillae, peglike projections of tongue mucosa ▪ Fungiform papillae: tops of these mushroom-shaped structures house most taste buds; scattered across tongue ▪ Foliate papillae: on side walls of tongue ▪ Vallate papillae: largest taste buds with 8-12 forming "V" at back of tongue

Where in the retina would you find a higher concentration of rods?

▪ Macula lutea area at posterior pole lateral to blind spot - Contains mostly cones

What is the name given to the structure within the eye that has a dense concentration of cones. Which region of the eye consists of cones only?

▪ Macula lutea area at posterior pole lateral to blind spot - Contains mostly cones Fovea centralis: tiny pit in center of macula lutea that contains all cones, so is region with best visual acuity

Describe the composition of a normal lens that allows light to pass through it virtually unobstructed?

Lenses of eyes can also refract light because they are curved on both sides - Convex: thicker in center than at edges - Concave: thicker at edges than in center - Convex lenses bend light passing through it, so that rays converge at focal point ▪ Image formed at focal point is upside-down and reversed from left to right - Concave lenses disperse light, preventing light from being focused • Lens - Biconvex, transparent, flexible, and avascular - Changes shape to precisely focus light on retina - Two regions: ▪ Lens epithelium: anterior region of cuboidal cells that differentiate into lens fiber cells ▪ Lens fibers: form bulk of lens and are filled with transparent protein crystallin - Lens fibers are continually added, so lens becomes more dense, convex, and less elastic with age

What is the clinical significance of the optic disc (blind) spot? What structures are found in this region?

found in Neural layer of the retina ▪ Optic disc - Site where optic nerve leaves eye - Lacks photoreceptors, so referred to as blind spot

Identify where high and low sound frequencies are received in the cochlea.

hight pitches at base low pitches at apex of Basilar Membrane

Have a general idea of where an action potential goes from the cochlear branch of the vestbulocochlear nerve into other regions of the brain to be processed.

https://youtu.be/_F5yvbCSIdQ

Describe Light and Dark Adaptation. Explain, in terms of bleaching, why it takes some time for your eyes to adjust to a dark movie theater when coming from the bright outdoors.

• Light adaptation - When moving from darkness into bright light we see glare because: ▪ Both rods and cones are strongly stimulated ▪ Large amounts of pigments are broken down instantaneously, producing glare ▪ Pupils constrict - Visual acuity improves over 5-10 minutes as: ▪ Rod system turns off ▪ Retinal sensitivity decreases ▪ Cones and neurons rapidly adapt • Dark adaptation happens slower - When moving from bright light into darkness, we see blackness because: ▪ Cones stop functioning in low-intensity light ▪ Bright light bleached rod pigments, so they are still turned off ▪ Pupils dilate - Rhodopsin accumulates in dark, so retinal sensitivity starts to increase ▪ Transducin returns to outer segments ▪ Sensitivity increases within 20-30 minutes

Describe the functions of rods and cones.

▪ Retina has quarter-billion photoreceptors that are one of two types: - 1. Rods- ▪ Dim light, peripheral vision receptors ▪ More numerous and more sensitive to light than cones ▪ No color vision or sharp images ▪ Numbers greatest at periphery - 2. Cones ▪ Vision receptors for bright light ▪ High-resolution color vision