exam 4/final part 2

special senses & endocrine

hearing

a response to vibrating air molecules

equilibrium

coordination, balance, and orientation in three-dimensional space

sound

\-any audible vibration of molecules

\-a vibrating object (e.g., tuning fork) pushes on air molecules

\-these, in turn, push on other air molecules

\-air molecules hitting the eardrum cause it to vibrate

pitch

\-our sense of whether a sound is “high” or “low”

\-determined by vibration frequency: hertz (Hz) or cycles/second

\-human hearing range is 20 to 20,000 Hz

\~infrasonic frequencies below 20 Hz

\~ultrasonic frequencies above 20,000 Hz

\-speech is 1,500 to 5,000 Hz, where hearing is most sensitive

\-most hearing loss with age is in range of 250 to 2,050 Hz

loudness

\-the perception of sound energy, intensity, or amplitude of the vibration

\-expressed in decibels (dB)

\-prolonged exposure to sounds > 90 dB can cause damage

auricle (pinna)

\-directs sound down the auditory canal

\-shaped and supported by elastic cartilage

auditory canal (external acoustic meatus)

\-passage leading through temporal bone to tympanic membrane

\-guard hairs protect outer end of canal

cerumen (earwax)

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

tympanic membrane (eardrum)

\-closes the inner end of the auditory canal (separates it from middle ear)

\-about 1 cm in diameter

\-vibrates freely in response to sound

auditory (eustachian) tube

\-connects middle-ear to nasopharynx

\-equalizes air pressure on both sides of tympanic membrane

\-normally closed, but swallowing or yawning open it

\-allows throat infections to spread to middle ear

malleus

has long handle attached to inner surface of tympanic membrane

incus

articulates with malleus and stapes

stapes

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

otitis media (middle-ear infection)

\-common in children

\-auditory tube is short and horizontal

\-infections easily spread from throat to tympanic cavity and mastoid air cells

middle ear infection symptoms

\-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

bony labyrinth

passageways in temporal bone

membranous labyrinth

fleshy tubes lining bony labyrinth

endolymph

\-similar to intracellular fluid

\-fills membranous labyrinth

perilymph

\-similar to cerebrospinal fluid

\-membranous labyrinth floats in this

cochlea

\-organ of hearing

\-winds 2.5 coils around a screw-like axis of spongy bone, the modiolus

\-threads of the screw forms a spiral platform that supports the fleshy tube

scala vestibuli

\-superior chamber

\-filled with perilymph

\-begins at oval window and spirals to apex

scala tympani

\-inferior chamber

\-filled with perilymph

\-begins at apex and ends at round window

scala media (cochlear duct)

\-middle chamber

\-filled with endolymph

\-contains spiral organ

spiral organ

\-has epithelium composed of hair cells and supporting cells

\-hair cells have long, stiff microvilli called stereocilia on apical surface

\-gelatinous tectorial membrane rests on top of stereocilia

\-has 4 rows of hair cells spiraling along its length

inner hair cells

\-single row of about 3,500 cells

\-provides for hearing

outer hair cells

\-three rows of about 20,000 cells

\-adjusts response of cochlea to different frequencies

\-increases precision

physiology of hearing

\-ossicles concentrate the energy of the vibrating tympanic membrane on an area 1/18 that size

\-ossicles create a greater force per unit area at the oval window and overcome the inertia of the perilymph

\-ossicles and their muscles have a protective function; lessen the transfer of energy to the inner ear

\-vibration of ossicles causes vibration of basilar membrane under hair cells; hair cells move with basilar membrane

stereocilia of outer hair cells

\-bathed in high K+ fluid, the endolymph

\-creating electrochemical gradient

\-outside of cell is +80 mV and inside of cell is near -40 mV

\-tip embedded in tectorial membrane

stereocilium on inner hair cells

\-single transmembrane protein at tip functions as a mechanically gated ion channel

\-stretchy protein filament (tip link) connects ion channel of one stereocilium to the sidewall of the next

\-tallest stereocilium is bent when basilar membrane rises up toward tectorial membrane

\-pulls on tip links and opens ion channels

\-K+ flows in; depolarization causes release of neurotransmitter

\-stimulates sensory dendrites and generates action potential in the cochlear nerve

sensory coding 1

\-variations in loudness (amplitude) cause variations in the intensity of cochlear vibrations

\-soft sound produces relatively slight up-and-down motion of the basilar membrane

\-louder sounds make the basilar membrane vibrate more vigorously

\~triggers higher frequency of action potentials

\~brain interprets this as louder sound

sensory coding 2

\-pitch depends on which part of basilar membrane vibrates

\-at basal end, membrane attached, narrow and stiff; brain interprets signals as high-pitched

\-at distal end, 5 times wider and more flexible; brain interprets signals as low-pitched

conductive deafness

\-conditions interfere with transmission of vibrations to inner ear

\-damaged tympanic membrane, otitis media, blockage of auditory canal, and otosclerosis

otosclerosis

fusion of auditory ossicles that prevents their free vibration

sensorineural (nerve) deafness

\-death of hair cells or any nervous system elements concerned with hearing

\-factory workers, musicians, construction workers

vestibular apparatus

\-constitutes receptors for equilibrium

\-3 semicircular ducts detect only angular acceleration (dynamic equilibrium)

\-2 chambers: anterior saccule and posterior utricle; responsible for static equilibrium and linear acceleration

static equilibrium

\-the perception of the orientation of the head when the body is stationary

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

dynamic equilibrium

\-perception of motion or acceleration

\-linear acceleration: change in velocity in a straight line (elevator)

\-angular acceleration: change in rate of rotation (car turns a corner)

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

macula

a 2 by 3 mm patch of hair cells and supporting cells in the saccule and utricle

macula sacculi

\-lies vertically on wall of saccule

\-responds to vertical acceleration and deceleration

macula utriculi

lies horizontally on floor of utricle

otoliths

calcium carbonate-protein granules that add to the weight and inertia and enhance the sense of gravity and motion

semicircular ducts

\-detects rotary movement

\-bony semicircular canals of temporal bone hold membranous semicircular ducts

\-each duct is filled with endolymph and opens up as a dilated sac (ampulla) next to the utricle

crista ampullaris

consists of hair cells with stereocilia and a kinocilium buried in a mound of gelatinous membrane called the cupula (one in each duct)

vision (sight)

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

light

\-visible electromagnetic radiation

\-human vision is limited to wavelengths of light from 400 to 700 nm

\-must cause a photochemical reaction to produce a nerve signal

ultraviolet radiation

< 400 nm; has too much energy and destroys macromolecules

infrared radiation

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

optical components

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

cornea

transparent anterior cover; avascular

aqueous humor

\-serous fluid secreted by ciliary body into posterior chamber; posterior to cornea, anterior to lens

\-reabsorbed by scleral venous sinus at same rate it is secreted

lens

\-suspended by suspensory ligaments from ciliary body

\-changes shape to help focus light

\-rounded with no tension or flattened with pull of suspensory ligaments

retina

\-attached to eye only at optic disc (posterior exit of optic nerve) and ora serrata (anterior edge)

\-pressed against rear of eyeball by vitreous humor

\-detached retina causes blurry areas of vision and can lead to blindness

macula lutea

patch of cells on visual axis of eye

fovea centralis

\-pit in center of macula lutea

\-contains only 4,000 tiny cone cells (no rods)

\-no neuronal convergence

\-Each cone cell has “private line to brain”

\-high-resolution color vision (little spatial summation; less sensitivity to dim light)

optic disc

\-blind spot

\-optic nerve exits retina and there are no receptors here

formation of an image

\-light passes through lens to form tiny inverted image on retina

\-iris diameter controlled by two sets of contractile elements

\-pupillary constriction and dilation occurs

pupillary constrictor

\-smooth muscle encircling pupil

\-parasympathetic stimulation narrows pupil

pupillary dilator

\-spoke-like myoepithelial cells

\-sympathetic stimulation widens pupil

photopupillary reflex

\-pupillary constriction in response to light

\-mediated by autonomic reflex arc

\-brighter light signaled to pretectal region of midbrain

\-excites parasympathetic fibers in oculomotor nerve that travels to ciliary ganglion in orbit

\-postganglionic parasympathetic fibers stimulate pupillary constrictor

refraction

\-the bending of light rays

\-light passing through center of the cornea is not bent

\-light striking off-center is bent toward the center

\-aqueous humor and lens do not greatly alter the path of light

\-cornea refracts light more than lens does

\-lens merely fine-tunes image; becomes rounder to increase refraction for near vision

refractive index

\-measures of how much it retards light rays relative to air

\-the greater this is, the greater the angle of incidence, the more refraction

emmetropia

\-state in which eye is relaxed and focused on an object more than 6 m (20 ft) away

\-light rays coming from that object are essentially parallel

\-rays focused on 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 (blurry edges)

3)accommodation of lens: change in the curvature of the lens that enables you to focus on nearby objects

accommodation of lens

\-ciliary muscle contracts, suspensory ligaments slacken, and lens takes more convex (thicker) shape

\-light refracted more strongly and focused onto retina

near point of vision

closest an object can be and still come into focus (lengthens with age)

pigment epithelium

\-most posterior part of retina

\-absorbs stray light so visual image is not degraded

light-absorbing cells

rods and cones derive from same stem cells as ependymal cells of brain

rod cells

\-night, or scotopic, vision or monochromatic vision

\-uses visual pigment rhodopsin

cone cell

\-color, photopic, or day vision

\-outer segment tapers to a point

\-contain photopsin (iodopsin)

photopsin (iodopsin)

\-contains different amino acid sequences that determine wavelengths of light absorbed

\-90 secs for 50% regeneration after bleaching

histology of the retina

\-pigment epithelium

\-rod and cone cells

\-bipolar cells

\-ganglion cells

bipolar cells

\-rods and cones synapse on bipolar cells

\-synapse on ganglion cells

ganglion cells

\-single layer of large neurons near vitreous

\-axons form optic nerve

\-some absorb light with pigment melanopsin and transmit signals to brainstem

melanopsin

detect light intensity for pupil control and circadian rhythms; do not contribute to visual image

light changes rhodopsin

\-in dark, retinal is bent (cis-retinal) and retinal and opsin are together

\-in light, retinal molecule straightens (trans-retinal), and retinal dissociates from opsin (bleaching)

\-to reset, it takes five minutes to regenerate 50% of bleached rhodopsin

generating the optic nerve signal

\-in dark, rods steadily release the neurotransmitter glutamate from basal end of cell

\-when rods absorb light, glutamate secretion ceases

\-bipolar cells are sensitive to these on and off pulses of glutamate secretion, some bipolar cells inhibited by glutamate and excited when secretion stops, these cells excited by rising light intensities

\-when bipolar cells detect fluctuations in light intensity, they stimulate ganglion cells directly or indirectly

\-ganglion cells are the only retinal cells that produce action potentials

\-ganglion cells respond to the bipolar cells with rising and falling firing frequencies

\-via optic nerve, these changes provide visual signals to the brain

duplicity theory of vision

\-explains why we have both rods and cones

\-a single type of receptor cannot produce both high sensitivity and high resolution

\-it takes one type of cell and neural circuit for sensitive night vision

\-it takes a different cell type and neuronal circuit for high-resolution daytime vision

dual vision system

\-rods are sensitive and react even in dim light

\-extensive neuronal convergence

\-600 rods converge on one bipolar cell

\-many bipolar cells converge on each ganglion cell

\-results in high degree of spatial summation

\-one ganglion cell receives information from 1 mm2 of retina producing only a coarse image

\-edges of retina have widely spaced rod cells that act as motion detectors (low resolution system only; can’t resolve finely detailed images)

color vision

\-Primates have well-developed color vision

\-3 types of cones are named for absorption peaks of their photopsins

\~short-wavelength (S) cones peak sensitivity at 420 nm

\~medium-wavelength (M) cones peak at 531 nm

\~long-wavelength (L) cones peak at 558 nm

\-color perception based on mixture of nerve signals representing cones of different absorption peaks

stereoscopic vision (depth perception)

\-ability to judge distance to objects

\-requires two eyes with overlapping visual fields which allows each eye to look at the same object from different angles

fixation point

\-point in space on which the eyes are focused

\-looking at an object within 100 feet, each eye views from slightly different angle

\-provides brain with information used to judge position of objects relative to this point

senescence of vision

\-loss of flexibility of lenses (presbyopia)

\-cataracts (cloudiness of lenses) becomes common

\-night vision is impaired due to fewer receptors, vitreous body less transparent, pupil dilators atrophy, and enzymatic reactions become slower

\-glaucoma risks increase

senescence of hearing

\-tympanic membrane and ossicle joints stiffen

\-hair cells and auditory nerve fibers die

\-death of vestibular neurons results in dizziness

gap junctions

pores in cell membrane allow signaling molecules, nutrients, and electrolytes to move from cell to cell

neurotransmitters

released from neurons to travel across synaptic cleft to second cell

paracrines

secreted into tissue fluids to affect nearby cells

hormones

chemical messengers that are transported by the bloodstream and stimulate physiological responses in cells of another tissue or organ, often a considerable distance away

endocrine system

glands, tissues, and cells that secrete hormones

endocrinology

the study of this system and the diagnosis and treatment of its disorders

endocrine glands

organs that are traditional sources of hormones

exocrine glands

\-have ducts; carry secretion to an epithelial surface or the mucosa of the digestive tract: “external secretions”

\-extracellular effects (food digestion)

endocrine glands

\-no ducts

\-contain dense, fenestrated capillary networks which allow easy uptake of hormones into bloodstream

\-”internal secretions”

\-intracellular effects such as altering target cell metabolism

liver cells

\-defy rigid classification

\-releases hormones, releases bile into ducts, releases albumin and blood-clotting factors into blood (not hormones)

speed and persistence of response (nervous)

reacts quickly (ms timescale), stops quickly

adaptation to long-term stimuli (nervous)

response declines (adapts quickly)

area of effect (nervous)

targeted and specific (one organ)

speed and persistence of response (endocrine)

reacts slowly (seconds or days), effect may continue for days or longer

adaptation to long-term stimuli (endocrine)

response persists (adapts slowly)

area of effect (endocrine)

general, widespread effects (many organs)

target cells

\-those organs or cells that have receptors for a hormone and can respond to it

\-some possess enzymes that convert a circulating hormone to its more active form