Chapter 17 The Special Senses

Olfaction

sense of smell

olfactory organs

organs at the top of the nasal cavity containing olfactory receptors

olfactory sensory neurons

specialized receptor cells that are bipolar neurons with nonmotile olfactory cilia

olfactory epithelium

A mucous membrane at the top of the nasal cavity; contains supporting cells, and regenerative basal (stem) cells, and the olfactory receptor sensory neurons that respond to airborne molecules called odorants.

lamina propria

underlying layer of areolar tissue that supports the respiratory epithelium; contains numerous blood vessels, and nerves

Olfactory glands (Bowman's glands)

produce mucus that is used to dissolve odor molecules so that transduction (conversion into electrical impulses) may occur.

generator potential

a local change in the resting potential of a receptor cell in response to stimuli, which may initiate an action potential

receptor potential

A slow, graded electrical potential produced by a receptor cell in response to a stimulus

olfactory cortex

provides conscious awareness of different odors

cribriform plate

The horizontal plate of the ethmoid bone separating the cranial cavity from the nasal cavity.

depolarization

the inside of the membrane becomes less negative

synaptic delay

Neurotransmitter must be released, diffuse across the synapse, and bind to receptors
Synaptic delay - time needed to do this (0.3-5.0 ms)
Synaptic delay is the rate-limiting step of neural transmission

G-protein coupled receptors

A signal receptor protein in the plasma membrane that responds to the binding of a signaling molecule by activating a G protein. Also called a G protein-linked receptor.

cyclic AMP (cAMP)

Cyclic adenosine monophosphate, a ring-shaped molecule made from ATP that is a common intracellular signaling molecule (second messenger) in eukaryotic cells.

Gustation

sense of taste

flavour

A perceptual experience produced by a combination of taste and other sensations.

gustatory epithelial cells

taste receptor cells have microvilli called gustatory hairs that project into taste pores, bathed in saliva

taste hairs

microvilli that protrude from taste cells through pores of taste buds; sensitive parts of taste cells

taste buds

sensory organs in the mouth that contain the receptors for taste

circumvallate papillae

large papillae with taste buds

fungiform papillae

Mushroom-like protuberances often containing taste buds all over the tongue and concentrated in areas located on the sides and tip of the tongue.

filiform papillae

These are small, spike-like projections found all over the tongue. They are the most abundant papillae, but lack taste buds. They roughen the tongue and aid in food manipulation.

foliate papillae

located on lateral aspects of posterior tongue

insula

cerebral lobe located deep within lateral sulcus

umami taste

savory

tarsal glands (meibomian glands)

- modified sebaceous glands
- along inner margin of the eyelids
- lipid-rich secretions keep eyelids from sticking together

palpebral fissure

the elliptical open space between the eyelids

palpebrae

upper and lower eyelids

conjunctiva

mucous membrane lining the eyelids and covering the anterior portion of the sclera

cornea

the transparent outer covering of the eye

iris

a ring of muscle tissue that forms the colored portion of the eye around the pupil and controls the size of the pupil opening

pupil

the adjustable opening in the center of the eye through which light enters

lacrimal caruncle

fleshy elevation at the medial canthus; produces a whitish oily secretion

lacrimal puncta

two small pores that drain fluid/tears into the nose

lateral canthus

outer corner where the upper and lower eyelids meet

medial canthus

inner corner of the eye where the upper and lower eyelids meet

sclera

white of the eye

fibrous tunic of the eye

sclera and cornea

vascular tunic of the eye

contains iris, ciliary bodies, and choroid

uvea

vascular layer of the eye

neural tunic

retina

ora serrata

the serrated boundary between the ciliary muscle and the retina

lacrimal gland

the gland that secretes tears into ducts that empty into the eye

sebaceous glands

oil glands

lysozyme

an enzyme found in saliva and sweat and tears that destroys the cell walls of certain bacteria

lacrimal sac

structure that collects tears before emptying into the nasolacrimal duct

anterior cavity of eye

filled with aqueous humor

posterior cavity of eye

filled with vitreous humor

anterior chamber of eye

between cornea and iris

posterior chamber of eye

between iris and lens

ciliary processes

epithelial tissue folds on the inner surface of the ciliary body that secrete aqueous humor

ciliary muscle

muscle that helps focus light on the retina by controlling the curvature of the lens of the eye

ciliary body

ring of tissue behind the peripheral iris that is composed of ciliary muscle and ciliary processes

choroid

middle, vascular layer of the eye, between the retina and the sclera

melanin

a dark brown to black pigment occurring in the hair, skin, and iris of the eye in people and animals. It is responsible for tanning of skin exposed to sunlight.

melanocytes

cells that produce melanin

corneal limbus

border between cornea and sclera

suspensory ligaments

hold the lens in place

ciliary zonule

suspensory ligaments that attaches the ciliary body to the lens

rods

Photoreceptors in the retina that are especially sensitive to dim light but not to colors.

cones

photoreceptors that detect color, operate under normal daylight conditions, and allow us to focus on fine detail

fovea centralis

area consisting of a small depression in the retina containing cones and where vision is most acute (sensitive)

macula lutea

yellowish spot on the back of the retina; contains the fovea

optic disc

Region at the back of the eye where the optic nerve meets the retina. It is the blind spot of the eye because it contains only nerve fibers, no rods or cones, and is thus insensitive to light.

scleral venous sinus

drains the aqueous humor from the eye

intra-ocular pressure

pressure within the eyeball

cataract

clouding of the lens of the eye

visual acuity

sharpness of vision

visual accommodation

the ability of the lens of the eye to change shape to bring objects at different distances into focus

myopia

nearsightedness

hyperopia

farsightedness

emmetropia

normal vision

photoreceptors

rods and cones

rhodopsin

A light-sensitive pigment found in the rod cells that is formed by retinal and opsin.

retinal

a chemical synthesized from vitamin A; joins with an opsin to form a photopigment

opsin

A membrane protein bound to a light-absorbing pigment molecule.

blue cones

sensitive to blue light

red cones

sensitive to red light

green cones

sensitive to green light

dark current

the inward sodium current that occurs in photoreceptors in the dark

phosphodiesterase (PDE)

cytosolic enzyme that deactivates and degrades cGMP

cGMP

cyclic guanosine monophosphate

optic nerve

each of the second pair of cranial nerves, transmitting impulses to the brain from the retina at the back of the eye.

colour blindness

an abnormal condition caused by an X-linked recessive allele and characterized by the inability to clearly distinguish different colours of the visible light spectrum.

optic chiasm

the point at which the optic nerves from the inside half of each eye cross over and then project to the opposite half of the brain

circadian rhythm

the biological clock; regular bodily rhythms that occur on a 24-hour cycle

auricle

external ear

pinna

external ear

tympanic membrane

The eardrum. A structure that separates the outer ear from the middle ear and vibrates in response to sound waves.

ossicles

three tiny bones in the middle ear; malleus, incus, stapes

ceruminous glands

modified sweat glands, located in external ear canal, secretes cerumen (earwax)

tensor tympani muscle

a middle-ear muscle that is attached to the malleus. This muscle contracts in response to intense sound and to tactile stimulation of the force.

stapedius muscle

reduces movement of stapes at oval window

kinocilium

This is a large hair cell important in the detection of the head's position. Whether the displacement of the stereocilia is towards or away from this determines whether it is excitatory or inhibitory.

stereocilia

small hairlike projections on the tops of inner and outer hair cells

utricle

A small, fluid-filled sac in the vestibular system above the saccule that responds to static positions of the head.

saccule

the smaller of two sacs within the membranous labyrinth of the vestibule in the inner ear

otoliths

small crystals in the fluid-filled vestibular sacs of the inner ear that, when shifted by gravity, stimulate nerve cells that inform the brain of the position of the head

sound waves

a wave of compression and rarefaction, by which sound is propagated in an elastic medium such as air.

bony labyrinth

passageways in temporal bone