Unit 15: Key terms
Sensory receptors
collect information from the environment, and rely it to the CNS on sensory neurons, link the nervous system to internal and external changes or events, can be specialized cells or multicellular structures
General senses
receptors that are widely distributed throughout the body, skin, various organs and joints
Special senses
specialized receptors confined to structures in the head, eyes, ears, nose, and mouth
Special senses cont.
Smell, taste, hearing and equilibrium, sight
Olfactory system
allowing for detection of odorants in air transduces them into signals perceived as odors
Olfactory organs
cover upper parts of nasal cavity, superior nasal conchae and a portion of the nasal septum
Olfaction
initiated at olfactory epithelium
Olfactory epithelium
small region of specialized cells in superior nasal cavity
Olfactory neurons
(olfactory receptor cells), modified bipolar neurons: chemoreceptors detect chemical substances perceived as odors
Supporting cells
columnar cells, surround olfactory neurons
Olfactory nerve (CN 1)
combined axons of olfactory neurons
Olfactory bulb
sits above cribriform plate of ethmoid bone, inferior to frontal lobe of brain
Olfactory tract
axons that exit olfactory bulb, travel to other regions of CNS for interpretation
Gustation
the sense of taste
Taste buds
organs of taste, located on papillae of tongue, roof of mouth, linings of cheeks and walls of pharynx, about 10,000 of these, each with 50-150 taste cells
Taste receptors
chemoreceptors
Taste cells
modified epithelial cells that function as receptors, replaced every 3 days
Taste hairs
microvilli that protrude from taste cells through pores of taste buds, sensitive parts of taste cells
5 primary taste sensations
sweet, sour, saltly, bitter, umami, each flavor results from 1 primary taste sensations or a combination
Sweet
stimulated by carbohydrates
Sour
stimulated by acids (H+)
Salty
stimulated by salts (Na+ or K+)
Bitter
stimulated by many organic compounds, Mg and Ca salts
Umami
stimulated by some amino acids, MSG
Sense of sight
visual receptors are found in the eye
Accessory organs for sense of sight
upper and lower eyelids, eyelashes, lacrimal apparatus, extrinsic eye muscles
Eyelids
palpebrae, composed of 4 layers, skin, muscle, connective tissue, conjunctiva
Orbicularis oculi
muscle that closes eyelid
Levator palpebrae superioris
muscle that opens eyelid
Tarsal glands
secrete oil onto eyelashes
Conjunctiva
mucous membrane lines eyelid an covers portion of eyeball
Lacrimal apparatus
lacrimal gland, canaliculi, lacrimal sac, nasolacrimal duct
Lacrimal gland
in orbit, lateral to eye, secretes tears
Canaliculi
2 ducts that collect tears
Lacrimal sac
collects tears from canaliculi, lies in groove in lacrimal bone
Nasolacrimal duct
collects from lacrimal sac, empties tears into nasal cavity
Superior rectus
rotates eye up and medially
Inferior rectus
rotates eye down and medially
Medial rectus
rotates eye medially
Lateral rectus
rotates eye laterally
Superior oblique
rotates eye down and laterally
Inferior oblique
rotates eye up and laterally
Structure of the eye
hollow, spherical organ of sight, wall has 3 layers, outer (fibrous) tunic, middle (vascular) tunic, inner (nervous) tunic
Outer (fibrous) tunic
cornea + sclera
Cornea
transparent, helps focus light rays, transmits and refracts light
Sclera
white, opaque, protects the eye, attaches muscles, pierced by the optic nerve and blood vessels
Middle (vascular) tunic
choroid coat + ciliary body + iris
Choroid coat
provides blood supply, contains melanocytes, melanin absorbs extra light
Ciliary body
thickest portion, pigmented, forms a ring to hold the lens, changes lens shape for focusing
Iris
anterior to the ciliary body, in front of the lens, pigmented, makes the color of your eye, controls light entering eye, changes size of pupil
The anterior portion of the eye
anterior cavity of eye, between cornea and lens, is filled with a watery fluid, aqueous humor
Lens
transparent, biconvex, lies behind iris, elastic, held in place by suspensory ligaments of ciliary body helps focus light rays, and changes shape for long-distance or close vision
Ciliary body cont.
forms internal ring around the front of the eye, ciliary processes are the radiating folds, ciliary muscles contract and relax to move lens, suspensory ligaments hold lens in position
Pupil
window or opening in the center of the iris, dim light->pupil dilates, bright light -> pupil constricts
Inner (nervous) tunic
consists of retina, pigmented layer, neural layer
Retina
contains visual receptors (photoreceptors), continuous with optic nerve in back of eye, ends just behind margin of the ciliary body toward front of eye, composed of several layers
Macula lutea
yellowish spot in the retina
Fovea centralis
center of macula lutea produces sharpest vision via photoreceptors
Optic disc
blind spot, contains no photoreceptors, found where nerve fibers from retina leave eye to become optic nerve
Posterior cavity
space enclosed by lens, ciliary body, and retina, contains vitreous humor
Vitreous humor
think gel that supports internal structures and maintains shape of eye
Cones
function best in bright light for processing high-resolution color vision
Rods
do not detect colors: most sensitive in low light and as a component of peripheral vision
Photoreceptors
synapse with bipolar cells
Bipolar cells
neurons that communicate with retinal ganglion cells
Retinal ganglion cells
in anteriormost region of retina, axons from optic nerve (CN 2)
Horizontal cells and amacrine cells
involved in image processing
Ear
organ of hearing
3 sections of ear
outer (external) ear, middle ear, inner (internal) ear
Parts of the outer ear
auricle (pinna), external acoustic meatus, tympanic membrane (eardrum)
Auricle (pinna)
funnel-shaped, collects sound waves
External acoustic meatus
s-shaped tube, carrier sound to tympanic membrane, terminates at tympanic membrane
Tympanic membrane (eardrum)
vibrates in response to sound waves
Parts of the middle ear
tympanic cavity, auditory ossicles, oval window, auditory (eustachian) tube
Tympanic cavity
air-filled space in temporal bone
Auditory ossicles
3 tiny bones, vibrate in response to tympanic membrane vibrations: amplify force, malleus, incus, and stapes, hammer, anvil, and stirrup
Oval window
opening in wall of tympanic cavity, stapes vibrates against it to move fluids in inner ear
Auditory (eustachian) tube
connects the middle ear to the throat, helps maintain equal pressure on both sides of the tympanic membrane, usually closed by valve-like flaps in throat
Parts of the inner (internal) ear
a complex system of labyrinths, osseous (bony) labyrinth, membranous labyrinth
Osseous (bony) labyrinth
bony canal in temporal bone, filled with perilymph fluid
Membranous labyrinth
tube of similar shape that lies within osseous labyrinth, filed with endolymph fluid
Windows of the inner ear
2 membrane-covered "windows" in the wall of the bony labyrinth, oval window, round window
Oval window
opening in the all of the tympanic cavity, through which the stapes transfers vibrations to the fluid of the inner ear, these vibrations stimulate hearing receptors
Round window
window in the wall of the inner ear facing the tympanic cavity, through which excess vibrations dissipate into the tympanic cavity
3 parts of labyrinths
cochlea, semicircular canals, vestibule
Cochlea
functions in hearing
Semicircular canals
function in dynamic equilibrium
Vestibule
functions in static equilibrium contains chambers: utricle and saccule
Static equilibrium
senses position of head when body is not moving, receptors are found in vestibule of inner ear
Dynamic equilibrium
senses rotation and movement of the head and body, receptors are found in semicircular canals
Utricle and saccule
are expanded chambers of the membranous labyrinth of the vestibule, each contains a macula, an organ of static equilibrium
Macula
a patch of hair cells and supporting cells
Cochlea
spiral, snail-shaped tube, widest at its base and progressively narrower toward its tip, coiled around body core or axis, the modiolus
Modiolus
bony core or axis the cochlea coils around
Spiral lamina
a bony shelf that coils around cochlea
3 compartments of the cochlea
scala vestibuli, scala tympani, cochlear duct
Scala vestibuli
upper compartment, leads from an oval window to the apex of the spiral, part of a bony labyrinth
Scala tympani
lower compartment, extends from apex of the cochlea to round window, part of bony labyrinth
Cochlear duct
middle compartment, portion of membranous labyrinth in cochlea
Vestibular membrane
sheet of epithelium, forms a boundary between the cochlear duct and scala vestibule, separates endolymph from perilymph