8 - The General and Special Senses

Stimulus

Anything that causes a response in a tissue.

Sensation

Conscious awareness of a stimulus.

Projection

The perception that a sensation originates from the part of the body stimulated.

Special senses

Includes smell, taste, sight, hearing, and balance.

General senses

Includes touch, pressure, pain, temperature, vibration, itch, and proprioception.

Free nerve endings

Respond to pain, temperature, and itch.

Merkel's disks

Detect light touch and superficial pressure; located in the epidermis; a capsule surrounding a nerve ending.

Meissner's corpuscles

Respond to fine, discriminative touch; located just deep to the epidermis.

Ruffini's end-organs

Monitor continuous touch or pressure in the skin.

Pacinian corpuscles

Detect deep pressure, vibration, and position (proprioception); located in tendons and joints.

Localized; Diffuse

There are two kinds of pain. Rapidly conducted impulses give rise to sharp __________, pricking pain, whereas slowly propagated impulses give rise to __________, burning, aching pain.

Nerve

Local anesthesia suppresses pain by injecting chemicals near a __________.

Reticular formation

General anesthesia uses chemicals to inhibit consciousness in the __________.

Lateral spinothalamic tract; Dorsal columns

According to the gate-control theory, pain sensations (action potentials) transmitted in the __________ can be blocked by increased activity of the __________.

Referred pain

A painful sensation in a region of the body that is not the source of the pain stimulus is called __________.

Phantom pain

The perception of pain in the part of an appendage that has been amputated and is no longer present is called __________.

Olfactory neurons

Specialized cells in the epithelium of the nasal cavity; airborne molecules bind to receptors on these cells, producing action potentials.

Olfactory nerve

Formed by axons from the olfactory neurons; pass through the cribriform plate.

Olfactory bulb

Receives the olfactory nerves.

Olfactory tract

Relays action potentials from the olfactory bulb to the brain.

Olfactory cortex

Area of the frontal and temporal lobes that receives the olfactory tract.

Taste bud

Sensory structure that detects taste stimuli.

Papillae

Enlargements on the surface of the tongue; contain taste buds.

Taste cell

Makeup a taste bud; each has taste hairs that extend through a taste pore.

Eyebrows

Prevent perspiration from running down the forehead into the eye.

Eyelids

Protect the eye from foreign objects and lubricate the eye by spreading tears.

Conjunctiva

Thin, transparent membrane that covers the anterior surface of the eye and the inner surface of the eyelids.

Lacrimal gland

Produces tears.

Lacrimal canaliculi

Collect excess tears from the medial corner of the eye.

Nasolacrimal duct

Empties excess tears into the nasal cavity.

Extrinsic eye muslces

Move the eyeball.

Fibrous tunic

Outer layer of the eye, consisting of the sclera and cornea.

Vascular tunic

Middle layer of the eye, consisting of choroid, ciliary body, and iris.

Nervous tunic

Inner layer of the eye, consisting of the retina.

Sclera

Firm, opaque, white, outer posterior five sixths of the eye; maintains the shape of the eye and provides an attachment site for the extrinsic eye muscles.

Cornea

Avascular, transparent, anterior one sixth of the eye; allows light to enter the eye and also refracts light.

Choroid

Vascular tunic associated with the scleral portion of the eye; prevents light reflection.

Ciliary body

Contains ciliary muscles (smooth muscles) that attach by suspensory ligaments to the lens.

Lens

Flexible, biconvex, transparent disc.

Iris

Contains smooth muscle that regulates the amount of light entering the eye.

Pupil

The opening in the iris through which light passes.

Pigmented retina

Outer part of the retina; its black color prevents light reflection.

Sensory retina

Inner part of the retina containing rods and cones.

Rods

Photoreceptor cells that are very sensitive to light and function in dim light.

Cones

Photoreceptor cells responsible for color vision.

Rhodopsin

Photopigment in rods that breaks down when struck by light; vitamin A is necessary for its manufacture; lack of vitamin A results in night blindness.

Macula lutea

Small yellow spot near the center of the posterior retina.

Fovea centralis

Small pit with the highest concentration of cones and the greatest ability to most clearly detect images; located in the macula lutea.

Optic disc

Blind spot of the eye; place where blood vessels and the optic nerve pass through the wall of the eye.

Aqueous humor

Fills the anterior compartment of the eye; maintains pressure, refracts light, and provides nutrients to the inner eye surface.

Vitreous humor

Fills the posterior compartment of the eye; helps to maintain pressure within the eye and holds the lens and retina in place.

Refraction

Bending of light rays as they pass from air into some other, more dense substance.

Concave lens

Type of lens that causes light rays to diverge.

Convex lens

Type of lens that causes light rays to converge.

Focal point

Where converging light rays cross.

Focusing

Act of causing light rays to converge to form an image.

Cornea

Part of the eye that produces the greatest amount of convergence of light.

Lens

Part of the eye that accomplishes fine adjustments in focusing by changing shape.

Accommodation

Process of allowing the lens to assume a more spherical (convex) shape; enables the eye to focus objects that are closer than 20 feet.

Contracted

Condition of the ciliary muscles during accommodation.

Relaxed

Condition of the ciliary muscles for distant vision (greater than 20 feet).

Optic nerve

Leaves the eye and passes through the optic foramen.

Optic chiasma

Point where some of the axons in the optic nerves cross to opposite sides of the brain.

Optic tract

Axons between the optic chiasma and the thalamus.

Optic radiations

Axons extending from the thalamus to the visual cortex.

Visual cortex

Part of the occipital lobes of the brain responsible for vision.

Visual field

Image seen by each eye.

Auricle

Fleshy part of the external ear on the outside of the head.

External auditory meatus

Passageway that leads to the tympanic membrane.

Cerumen

Modified sebum, commonly called earwax, that helps to prevent foreign objects from reaching the tympanic membrane.

Tympanic membrane

Thin membrane that separates the external and middle ear; vibrates in response to sound waves; also called the eardrum.

Oval window

Opening between the middle and inner ear; contains the stapes.

Round window

Membrane-covered opening between the middle and inner ear.

Auditory ossicles

Ear bones that transmit and amplify vibrations of the tympanic membrane to the oval window; the malleus, incus and stapes.

Mastoid air cells

Spaces in the temporal bone that are connected to the middle ear.

Auditory tube

Structure that enables air pressure to be equalized between the outside air and the middle ear; the eustachian tube.

Osseous labyrinth

Interconnecting tunnels and chambers within the temporal bone.

Membranous labyrinth

Membranes that are found within the osseous labyrinth.

Endolymph

Fluid within the membranous labyrinth.

Perilymph

Fluid between the osseous and membranous labyrinth.

Cochlea

Part of the inner ear involved with hearing.

Semicircular canals; vestibule

Two parts of the inner ear involved with balance.

Vestibular membrane

Membrane separating the scala vestibuli and the cochlear duct.

Basilar membrane

Membrane separating the scala tympani and the cochlear duct.

Scala vestibuili

The space that connects to the oval window.

Scala tympani

The space that connects to the round window.

Cochlear duct

The space that contains the spiral organ.

Tectorial membrane

The spiral organ rests on the basilar membrane and its hair cells extend to this membrane.

Auricle; tympanic membrane

Sound waves in the air are collected by the __________ and conducted by the external auditory meatus to the __________, which vibrates.

Malleus; Incus; Stapes

The vibrations are transferred to the auditory ossicles. Vibration of the __________, which is attached to the tympanic membrane, causes vibration of the __________, which is attached to the __________.

Oval window; perilymph

Movement of the stapes within the __________ produces vibrations in the __________ of the scala vestibuli.

Round window

Because the scala vestibuli is connected to the scala tympani, perilymph movement causes the membrane of the __________ to move.

Vestibular

Movement of the stapes within the oval window produces vibrations of the perilymph of the scala vestibuli. The vibrations of the perilymph cause the __________ membrane to vibrate.

Endolymph; basilar

The vibration of this membrane causes the __________ of the cochlear duct to vibrate, which in turn causes the __________ membrane to vibrate.

Hair cells; tectorial

The spiral organ rests on this membrane, and as the membrane moves it cause the __________ of the spiral organ, which are embedded in the __________ membrane to bend.

Action potentials

The bending of the hair cells results in the production of __________ that are conducted to the brain through the cochlear branch of the vestibulocochlear nerve.

Pitch; volume

Sounds with different __________ cause different regions of the basilar membrane to vibrate, whereas sounds with increased __________ cause the basilar membrane to vibrate more intensely.

D

The type of receptor associated with pain and itch sensations.

a. Merkel's disks

b. Pacinian corpuscles

c. Meissner's corpuscles

d. free nerve endings

D

Pain sensations

a. are conducted rapidly or slowly.

b. can be blocked by input from the dorsal columns.

c. can be felt at body locations that are not a source of pain stimulation.

d. all of the above

E

Olfactory neurons

a. have projections called cilia.

b. have axons that combine to form the olfactory nerves.

c. connect to the olfactory bulb.

d. have receptors that react with molecules dissolved in fluid.

e. all of the above