Ch 16 Senses

hearing

a response to vibrating air molecules

equilibrium

the sense of motion, body orientation, and balance

in the inner ear, which is a maze of fluid-filled passages and sensory cells; fluid is set in motion and sensory cells convert the motion into an informative pattern of action potentials

where do the senses of hearing and equilibrium reside?

sound

any audible vibration of molecules

a vibrating object pushes on air molecules; these push on other air molecules; air molecules hit the eardrum causing it to vibrate (sound waves are like compression waves)

how does sound work?

pitch

our sense of whether a sound is “high” or “low”; it is determined by vibration frequency

loudness

the perception of sound energy, intensity, or amplitude of the vibration; in decibels

high frequencies

high pitch noises have what kind of frequencies?

outer, middle, and inner ear

what are the three sections of the ear?

the transmission of sound to the inner ear (conduction)

what are the outer and middle ear only concerned with?

vibrations are converted to nerve signals

what happens in the inner ear?

outer ear

a funnel for conducting vibrations to the tympanic membrane (eardrum)

auricle

directs sound down the auditory canal; shaped and supported by elastic cartilage

external acoustic meatus/auditory canal

passage leading through the temporal bone to the tympanic membrane; guard hairs protect the outer end of the canal; has cerumen buildup

cerumen

mixture of secretions of ceruminous and sebaceous glands and dead skin cells

middle ear

located in the air filled tympanic cavity in temporal bone

tympanic membrane (eardrum)

closes the inner end of the auditory canal (separates it from the middle ear); vibrates freely in response to sound

tympanic cavity

this is continuous with mastoid air cells; contains the auditory ossicles

built up earwax

what keeps the tympanic membrane from vibrating?

auditory (eustachian) tube

connects middle ear to nasopharynx; equalizes air pressure on both sides of tympanic membrane; it is normally closed, but swallowing and yawning opens it; allows throat infections to spread to the middle ear

malleus

has long handle attached to inner surface of tympanic membrane (an auditory ossicle)

incus

articulates with malleus and stapes (an auditory ossicle)

stapes

shaped like a stirrup; footplate rests on oval window-where inner ear begins

stapes and malleus

where do the stapedius and tensor tympani muscles attach to?

otitis media

middle ear infection that is common in children; the auditory tube is short and horizontal in children so there is poor drainage; infections easily spread from throat to tympanic cavity and mastoid air cells

fluid accumulates in tympanic cavity producing pressure, pain, and impaired hearing; can spread, leading to meningitis; can cause fusion of ear ossicles and hearing loss

what are symptoms of otitis media?

bony labyrinth

passageways in the temporal bone; has the cochlea and three tubes (semicircular canal)

membranous labyrinth

fleshy tubes lining the bony labyrinth; it is filled with endolymph which is similar to intracellular fluid and it floats in perilymph which is similar to cerebrospinal fluid

labyrinth

vestibule and three semicircular ducts

cochlea

organ of hearing; winds around a screw-like axis of spongy bone; the threads of the screw form a spiral platform that supports the fleshy tube of the cochlea

scala vestibuli

superior chamber in the cochlea; it is filled with perilymph; begins at the oval window and spirals to apex

scala tympani

inferior chamber of the cochlea; filled with perilymph; begins at the apex and ends at the round window; the secondary tympanic membrane covers the round window

scala media

the cochlea duct and middle chamber of the cochlea; filled with endolymph; it contains the spiral organ which is the acoustic organ that converts vibrations into nerve impulses

spiral organ

has epithelium composed of hair cells and supporting cells; hair cells have long, stiff microvilli called stereocilia on apical surface and a gelatinous tectorial membrane rests on top of the stereocilia

there are four rows of hair cells; the inner hair cells are a single row that provides for hearing; the outer hair cells are three rows that adjusts the response of the cochlea to different frequencies and increases precision

what are the hair cells in the spiral organ?

ossicles concentrate the energy of the vibrating tympanic membrane on a much smaller area; ossicles create a greater force per unit area at the oval window and overcome the inertia of the perilymph; the ossicles and their muscles have a protective function (lessens the transfer of energy to the inner ear)

what is the ossicles roles in relation to the tympanic membrane?

the vibration of basilar membrane under hair cells and the hair cells move with the basilar membrane

what does the vibration of ossicles cause?

stereocilia of outer hair cells

is bathed in high potassium ion fluid (endolymph); this creates an electrochemical gradient; the tips are embedded in the tectorial membrane

single transmembrane protein at the tip functions as a mechanically gated ion channel; process: 1) stretchy protein filament connects ion channel of one stereocilium to the sidewall of the next 2) the tallest stereocilium is bent when the basilar membrane rises up toward the tectorial membrane 3) pulls on tip links and opens ion channels 4) K+ flows in and this depolarization causes the release of neurotransmitter 5) stimulates sensory dendrites and generates action potential in the cochlear nerve

explain stimulation of cochlear hair cells (stereocilium on inner hair cells)

variations in the intensity of cochlear vibrations

what do variations in loudness or amplitude cause?

soft sounds produce relatively slight up-and-down motion of the basilar membrane; louder sounds make the basilar membrane vibrate more vigorously (it triggers a higher frequency of action potentials and the brain interprets this as a louder sound)

how does the difference in loud and soft sounds affect the basilar membrane?

which part of the basilar membrane vibrates

what does pitch depend on?

at the basal end where the membrane is attached and it is stiff and narrow, the brain interprets the signals as high-pitched (large spirals); at the distal end which is wider and more flexible, the brain interprets the signals as low-pitched (tight spirals)

when does the brain interpret high-pitched vs low-pitched sounds?

conductive deafness

conditions interfere with transmission of vibrations to inner ear; can involve a damaged tympanic membrane, otitis media, blockage of the auditory canal, and ostosclerosis

otosclerosis

fusion of the auditory ossicles that prevents their free vibration

sensorineural deafness

death of hair cells or any nervous system elements concerned with hearing; occurs often in factory workers, musicians, and construction workers; tends to be more permanent than conductive deafness

equilibrium

coordination, balance, and orientation in 3D space; goes hand in hand with propioception

vestibular apparatus

constitutes receptors for equilibrium; includes the three semicircular ducts and two chambers

three semicircular ducts

detect only angular acceleration (dynamic equilibrium); part of the vestibular apparatus

two chambers

these are in the vestibular apparatus; they are the anterior saccule and posterior utricle; they are responsible for static equilibrium and linear acceleration

static equilibrium

the perception of the orientation of the head when the body is stationary; it is dependent upon gravity pushing down; sensory receptors bend in different directions

dynamic equilibrium

perception of motion or acceleration; it is associated with the semicircular canals

macula

a 3 by 3 mm patch of hair cells and supporting cells in the saccule and utricle; allows us to sense changes in movement in different directions in space

macula sacculi

lies vertically on the wall of the saccule

macula utriculi

lies horizontally on the floor of the utricle

40 to 70 stereocilia and one true cilium - kinocilium that is embedded in a gelatinous otolithic membrane

what does each hair cell have?

otoliths

calcium carbonate-protein granules that add to the weight and inertia and enhance the sense of gravity and motion; associated with kinocilium in hair cells

static equilibrium

when head is tilted, heavy otolithic membrane sags, bending the stereocilia and stimulating the hair cells

dynamic equilibrium

in car, linear acceleration detected as otoliths lag behind, bending the stereocilia and stimulating the hair cells

since they are nearly vertical, it responds to vertical acceleration and deceleration (dynamic equilibrium changes)

what are macula sacculi good at responding to?

static equilibrium

what are macula utriculi good at responding to?

rotary movements

what do the three semicircular ducts detect?

bony semicircular canals of the temporal bone hold membranous semicircular ducts; each duct is filled with endolymph and opens up as a dilated sac (ampulla) next to the utricle

explain the composition of the semicircular ducts

crista ampullaris

mound of hair cells and supporting cells in each ampulla which is a sac in the semicircular ducts; it consists of hair cells with stereocilia and a kinocilium buried in a mound of gelatinous membrane called the cupula

different planes

spatial orientation of semicircular canals causes ducts to be stimulated by rotation in what?

thicker gel (more viscous) is surrounded by less viscous gel (endolymph)

what is the “gel” like in the ampulla (sac in the semicircular ducts)?

vision

perception of objects in the environment by means of light they emit or reflect

light

visible electromagnetic radiation; it causes a photochemical reaction to produce a nerve signal

400 to 700 nm

what is the wavelengths of light that human vision is limited to?

ultraviolet radiation

infrared radiation

>700 nm; to little energy to cause a photochemical reaction, but it does warm the tissues

optic components

transparent elements that admit light, refract light rays, and focus images on retina: cornea (transparent anterior cover), aqueous humor, lens, and vitreous body

aqueous humor

serous fluid secreted by ciliary body and fills the space between the cornea and the lens; it is reabsorbed by scleral venous sinus at the same rate it is secreted

the cornea and lens are avascular, but they need nutrients delivered and waste taken out

why do you need constant circulation of aqueous humor?

lens

fibers which are flat, tightly compressed, and transparent cells form it; it is suspended by suspensory ligaments from the ciliary body

changes shape to help focus light; it is either rounded with no tension or flattened and pulling the suspensory ligaments

how does the lens work?

vitreous humor

fills the posterior segment; fills the space between the lens and the retina

retina

attached to eye only at the optic disc and ora serrata; it is pressed against the rear of the eyeball by vitreous humor; has blood vessels

blurry areas of vision and can lead to blindness

what can a detached retina cause?

macula lutea

patch of cells on the visual axis of eye; has the highest concentration of photoreceptors in the eye (especially cones)

fovea centralis

pit in center of macula lutea; has a high concentration of cones

the downside of extra photoreceptors is the more you have, the more neurons you need in the brain to process information and neurons are the most energy demanding in the cell

why is there only a high concentration of cones in the macula lutea?

optic disc

blind spot; optic nerve exits retina and there are no receptors there; its where all the blood vessels in the retina originate; there are also a lot of myelinated axons coming out of it which physically blocks light

visual filling

brain fills in areas; the brain ignores unavailable information until saccades (fast eye movements) redirect gaze

light passes through lens to form tiny inverted image on retina; the iris diameter is controlled by two sets of contractile elements

how does formation of an image occur?

pupillary constrictor

smooth muscle encircling the pupil; parasympathetic stimulation narrows the pupil

pupillary dilator

spoke-like myoepithelial cells; sympathetic stimulation widens the pupil

when light intensity changes and when gaze shifts between distant and nearby objects

when does pupillary constriction and dilation occur?

photopupillary reflex

pupillary constriction in response to light; it is mediated by the autonomic reflex arc; subconscious; keeps us from overwhelming our receptors

a brighter light is signaled to the pretectal region of the midbrain; it excites parasympathetic fibers in oculomotor nerve that travels to ciliary ganglion in orbit; postganglionic parasympathetic fibers stimulate pupillary constrictor

how is the photopupillary reflex mediated by the autonomic reflex arc?

refraction

the bending of light rays

300,000 km/s in a vacuum but slower in air, water, glass, or other media

what is the speed of light?

refractive index

a measure of how much a medium retards light rays relative to air

more refraction

what does a greater refractive index and a greater angle of incidence lead to?

light passing through center is not bent, but light striking off center is bent toward the center

what is the difference between light passing through the center of cornea or off center?

aqueous humor and the lens do not greatly alter the path of light; the cornea refracts light more than the lens does; the lens fine-tunes images and it becomes rounder to increase refraction for near vision

how do aqueous humor, the lens, and the cornea affect the path of light?

emmetropia

state in which eye is relaxed and focused on an object more than 6 m away; light rays coming from that object are essentially parallel and the rays focus on the retina without effort (light rays coming from a closer object are too divergent to be focused without effort)

near response

adjustment to close-range vision requires three processes

1) convergence of eyes - eyes orient their visual axis toward object 2) constriction of pupil - blocks peripheral light rays and reduces spherical aberration or blurry edges 3) accommodation of lens - change in the curvature of the lens that enables you to focus on nearby objects

what are the three processes required for near response?

ciliary muscle contracts, suspensory ligaments slacken, and lens takes more convex (thicker) shape; light is refracted more strongly and focused onto the retina

how does the accommodation of the lens occur in the near response?