Special Senses A&P 1

Special senses

convey specific stimuli from specialized sensory organs; smell, taste, vision, hearing, and vestibular sensation

special senses and general senses differ in significant ways

general senses involve detection of touch, pain, and temperature;

special sensory neurons detect very specific stimuli— light, sound waves, head movements, and chemicals (produce tastes and smells)

Olfactory system

allows for detection of odorants in air; transduces them into signals perceived as odors

Olfaction

initiated at olfactory epithelium three cell types: olfactory neurons, basal cells, and supporting cells

Olfactory neurons

(olfactory receptor cells) chemoreceptors detect chemical substances perceived as odors

Basal cells

continually replace olfactory neurons; continuously differentiate into new gustatory cells

supporting cells

surround olfactory neurons ; no role in taste sensation

Olfactory nerve

(CN I) combined axons of olfactory neurons

Gustatory sense (taste)

involves chemoreceptors that are stimulated by various chemicals

Tasting process

Complicated process, involving olfactory chemoreceptors,
thermoreceptors, and nociceptors, in addition to gustatory
chemoreceptors
• Begins with stimulation of specialized receptor cells (taste buds)
which are located on papillae (small raised structures on the tongue)
• Each taste bud is associated with sensory neuron that carries
information to CNS

Taste buds- three cell types:

Gustatory (taste) cells; Basal cells; supporting cells

Gustatory (taste) cells

specialized epithelial cells with microvilli; display receptors that detect different tastes; associated sensory neurons carry taste stimuli to CNS

Taste sensations

tastes relies on detection of five classes of chemicals: sweet, sour, salty, bitter, umami

sweet tastes

elicited by simple sugars (glucose, fructose)

Sour tastes

produced by hydrogen ions (citric acid in lemon juice)

salty tastes

elicited by presence of metal ions (sodium and potassium)

Bitter flavors

produced by nitrogen-containing compounds

Umami

taste associated with meat or broth; produced by glutamate or other amino acids

eyeballs

located in orbits; each eyeball occupies anterior one-third of orbit; Adipose tissue provides protective cushioning and occupies posterior two-thirds of orbit

Eyelids (palpebrae)

cover anterior region of orbit; prevent access by foreign objects and distribute tears during blinking; Orbicularis oculi muscle closes eyelids; levator palpebrae superioris elevates upper eyelid

Eyebrows

Hairs on ridge of brow form eyebrows; prevent perspiration from running into eyes; important for facial expression

Eyelashes

stiff hairs on edges of eyelids; associated with sensitive nerve endings; cause blinking when objects touch them; reduces eye injury

Conjunctiva

thin continuous epithelial membrane;

lines both posterior surfaces of eyelids and anterior surface of eyeball; translucent membrane in which tiny blood vessels can be seen

Palpebral conjuctiva

covers eyelid inner surface; turns back on itself to form bulbar or ocular conjunctiva; covers white part of eyeball

Lacrimal apparatus

produces and drains tears from eye

lacrimal gland

releases tears and mucus into tiny ducts; lubricates and washes away debris; blinking sweeps tears across eye surface; drain into passages that lead to nasal cavity

Extrinsic eye muscles

Six muscles originate from orbit wall; insert into outer layer of eyeball:

Superior rectus, inferior rectus, lateral rectus, medial rectus, superior oblique, and inferior oblique muscles; three cranial nerves provided innervation to six muscles

CN IV

innervates superior oblique

CN VI

innervates lateral rectus

CN III

innervates remaining four muscles

eyeball layers

fibrous layer, vascular layer, and neural layer

Fibrous layer

outermost layer; two components: sclera and cornea

Sclera

white part of eye; covers nearly entire eye; resists external or internal forces to maintain shape

Cornea

continuous with sclera anteriorly; Translucent instead of opaque; Avascular, allows light to pass into eyeball

Vascular layer

middle layer; lies directly beneath cornea and sclera; components: choroid; lens; ciliary body; suspensory ligaments; iris; pupil

Choroid

contains capillaries and pigment

Lens

slightly flattened sphere; behind pupil and iris; focuses light on retina

Ciliary body

contains ring of smooth muscle that surrounds lens

Suspensory ligaments

connects ciliary body to lens; allows for contraction and relaxation; changes shape of lens to focus light

Iris

colored region of anterior eye

Pupil

opening in center of iris through which light enters eyeball

Pupillary sphincter muscle

In iris; contracts during parasympathetic stimulation; Reduces size of pupil; restricts amount of light entering eyeball

Pupillary dilator muscle

in iris; contracts during sympathetic activation; allows pupil to increase in size; more light enters eyeball

Neural layer

innermost layer of the eyeball; known as retina; composed of two layers superficial layers; deep layer

Superficial layer

thin, pigmented epithelium; reduces light scattering and nourishes photoreceptors

Deep layer

consists of photoreceptor cells and cells that form optic nerve

Photoreceptor cells

detect and transduce light stimuli into electrical signals

Rods

black and white vision in low light levels and also peripheral visionC

Cones

high-acuity color vision in higher light levels

Optic disc

location where axons of optic nerve exit from retina; does not capture visual images; called blind spot

cavities and chambers of eye

eyeball is divided into anterior and posterior cavities by lens and ciliary body

Posterior cavity

larger cavity behind lens; filled with gelatinous material (vitreous humor)V

Vitreous humor

(vitreous body) made mostly of collagen and water; helps maintain eyeball shape

Anterior cavity

in front of lens and ciliary body; further divided into anterior and posterior chambers; both filled with aqueous humor

Posterior chamber

between lens and iris

Anterior chamber

between iris and cornea

Aqueous humor

watery fluid secreted by ciliary body

Scleral venous sinus

blood vessel network at anterior edge of iris; drains aqueous humor out of anterior chamber

Vision

perception of light reflected by various objects; eyes and visual pathways in CNS can determine object’s size, shape, and color; object distance, rate, and direction of movement can also be interpreted

convex lens

surface that bulges outward in middle region; causes light rays to bend inward, or converge as they pass though

Concave lens

thicker on edge and depressed in middle region; causes light rays to diverge or spread out (unfocused)

Focused

when rays converge on one point (focal point) said to be…

Clear vision requires

light rays are focused directly on retina

Cornea

provides refractive power as light passes through it

Lens

provides for fine tuning and refractive adjustment

Events that allow for lens shape changes

ciliary body surrounding lens relaxes when viewing distant objects; ciliary body contracts when viewing nearby object

Pupillary constriction

limits amount of scattered light that makes objects appear blurry

Convergence

process by which eyeballs move more medially to direct light rays on to photoreceptors

Cell types layered in retina

Cones and Rods

Cones

function best in bright light for processing high-resolution color vision

Rods

Do not detect colors; most sensitive in low light and as component of peripheral vision

Ear

associated with sense of hearing; divided into three regions: external, middle, and internal

Auricle (pinna)

Elastic cartilage with exception of fleshy lobule; funnels sound waves into external auditory canal

External auditory canal (external auditory meatus)

Tunnel through temporal bone; terminates at tympanic membrane; lined with modified sweat glands (ceruminous glands); secrete cerumen (ear wax)'; ear wax lubricates and waterproofs canal and tympanic membrane; traps and removes debris before it reaches tympanic membrane

Tympanic membrane

separates outer and middle ear; connected to tiny bone (ossicle); enables energy of sound waves to reach inner ear

Middle ear

hollow; air-filled, mucous membrane lined chamber within temporal bone; forms lateral boundary and wall of inner ear defines medial boundary

Pharyngotympanic tube (auditory tube)

connects nasopharynx with middle ear; equalizes air pressure on both sides of tympanic membrane

Auditory ossicles

three tiny bones within middle ear; connected to one another at synovial joints; form bridge that links tympanic membrane to outer wall of inner ear

Inner ear

three regions cochlea; vestibule; and semicircular canals

Cochlea

contains the receptor organ for hearing; contains specialized hair cells with stereocilia; The movement of stereocilia eventually triggers an action potential in the cochlear nerve which joins the vestibulocochlear nerve (CN VIII)

Vestibule

wall features membranous oval window; houses utricle and saccule; Convey stimuli about head tilting and linear movement via neurons of vestibular division of vestibulocochlear nerve.

Semicircular canals (three tubes)

Anterior, posterior, and lateral semicircular ducts can detect rotational movement of head in any body plane

Ampulla (in semicircular canals)

enlarged bulb at base of each duct; contains receptor cells innervated by vestibular division of CN VII

Electrical signals that can be processed by brain

Ears detect and transduce sound waves into

Sound waves

generated by displacement of air molecules; Every sound has certain pitch (frequency); determined by how many times object vibrates back and fourth during certain period; measured in hertz (Hz)

Loudness or amplitude of sound

measured in decibels (dB); Greater force placed on object produces louder sound