Chapter 19

Sensory receptors

• structures that detect stimuli

• Can be structurally complex sense organs (the eye) or very simple endings of single neurons (dendritic endings in skin)

transducers

• Receptors act as _________—they change one form of energy into another

• Example: Visual receptors change light energy into electrical energy on the optic nerve

receptive fields

Receptors have ____________: Areas through which their sensitive ends are distributed

adaptation

Receptors exhibit _________: With prolonged exposure to a constant stimulus, they decrease action potential firing

Tonic receptors

slowly adapt (only slowly decrease firing in response to a constant stimulus)

Phasic receptors

rapidly adapt to constant stimuli (fire only in response to changing stimuli)

General sense receptors

distributed throughout the skin and organs

Special sense receptors

• housed in complex organs in the head

• specialized, complex sense organs

• Special senses are smell, taste, vision, hearing, and equilibrium

Receptor distribution, stimulus origin, modality of stimulus

Three criteria are used to describe receptors:

Somatic sensory receptors

• found in skin, mucous membranes lining body cavities, joints, muscles, tendons

• Monitor a variety of stimuli including texture, pressure, temperature, pain, vibration, and stretch

Visceral sensory receptors

• in the walls of internal organs and blood vessels

• Detect stretch, chemical concentrations, temperature, and pain

Exteroceptors

• detect stimuli from external environment

• Include receptors in skin, in body cavity linings and in special sense organs

• detect stimuli in internal organs

• Include stretch receptors in smooth muscle as well as receptors for pain, pressure, temperature, and chemical changes in viscera

Proprioceptors

• detect stimuli pertaining to body position

• Found in muscles, tendons, and joints

modality

Classification by ________ of stimulus depends on the stimulating agent

Chemoreceptors

Detect specific molecules dissolved in fluid

Thermoreceptors

Detect changes in temperature

Photoreceptors

Detect changes in intensity, color, and position of light

Mechanoreceptors

Detect touch, pressure, vibration, and stretch

Baroreceptors

Detect pressure changes within body structures

Nociceptors

Detect painful stimuli

Phantom pain

a sensation associated with a part of the body that has been removed

Phantom limb syndrome

Excitation of a CNS neuron that was formerly excited by the amputated limb is interpreted as pain in that limb

Referred pain

occurs when impulses from certain viscera are perceived as originating not from the organ but in a dermatome of the skin

T1–T5

Heart attack may be referred to dermatomes of _____

Source of referred pain

Common sites of referred pain

Tactile receptor

• The most numerous type of sensory receptor

• They are mechanoreceptors that react to touch, pressure, and vibration

• Located in the dermis and subcutaneous layer

Unencapsulated

Type of tactile receptor whose endings not wrapped in connective tissue or glial cells

encapsulated

Type of tactile receptor whose endings are wrapped in connective tissue or glial cells

Free nerve endings, root hair plexuses, tactile discs

3 types of unencapsulated nerve endings

Free nerve endings

found in papillary layer of dermis and deep epidermis

root hair plexuses

surround hair follicles in dermis

Tactile discs

associated with tactile cells in stratum basale of epidermis

tactile cells

Tactile discs: associated with ____________ in stratum basale of epidermis

End bulbs, Lamellated corpuscles, Bulbous corpuscles, Tactile corpuscles

Four types of encapsulated tactile receptors

End Bulbs

in skin and mucous membranes of oral and nasal cavities, vagina, and anal canal

Lamellated corpuscles

in dermis, subcutaneous tissue, synovial membranes, and some viscera

Bulbous corpuscles

in dermis and subcutaneous layer

Tactile corpuscles

in dermal papillae, especially lips, palms, eyelids, nipples, and genitals

Free nerve ending

Root Hair plexus

Tactile/Merkel disc

End Bulb

Lamellated Corpuscle

Bulbous corpuscle

Tactile corpuscle

olfaction

the sense of smell

Odorants

dissolved in mucus of nasal cavity and detected

Sense of smell

Not as sensitive in humans compared to many other animals

Olfactory epithelium

lining superior nasal cavity consists of three distinct cell types

Olfactory receptors, Supporting cells, Basal cells

lining superior nasal cavity consists of three distinct cell types- name the three cell types.

Olfactory receptor cells

• detect odors

• specialized bipolar neurons that are the primary cells in smell pathway

Supporting cells

• sustain the olfactory receptor cells

Basal cells

• replace olfactory receptors

• neural stem cells that replace gustatory cells (regeneration every 7 to 9 days)

lamina propia

Deep to the epithelium is the

olfactory glands

Lamina propia contains mucin-secreting ___________

Olfactory organs

olfactory hairs (cilia)

• Each Olfactory receptor cell has a single dendrite with many _______________ containing receptors for one odorant molecule

• Depending on which receptor cells are stimulated, different smells will be perceived

olfactory nerves

Bundles of axons of olfactory receptor cells form

Sniffing or breathing deeply

needed to mix air with mucus of olfactory epithelium

eight

• We recognize as many as ______ primary odors (for example, minty) and thousands of other chemical stimuli

• Secondary odors are produced by combinations of chemicals and not recognized by all individuals

aging

Although olfactory receptor cells can be mitotically replaced, this declines with _______ (as does sensitivity to odors)

Olfactory bulbs

• Axons from bipolar neurons of the nasal mucosa pass through foramina of cribriform plate and enter here

• contain mitral and tufted cells

• Olfactory bulbs contain about 2,000 olfactory glomeruli where olfactory cells converge

olfactory tracts

Neurons within olfactory bulbs project axon bundles, called ____________, to olfactory cortex of temporal lobe

Gustation

sense of taste

Gustatory (taste) cells

taste receptors housed in specialized organs termed taste buds

papillae

aste buds are located on the dorsal surface of the tongue in epithelial and connective tissues elevations called

Filiform, fungiform, vallate, foliate

4 types of papillae

Filiform papillae

Small numerous bumps lacking taste buds

Fungiform papillae

Mushroom-shaped bumps on tip and sides of tongue containing a few taste buds

vallate pappilae

Round bumps arranged in a “V” on posterior dorsal surface of tongue; contain many taste buds

foliate papillae

Subtle ridges on posterior lateral surface of tongue housing a few taste buds in early childhood

tastants

Gustatory cells detect ___________ (molecules and ions) in food

gustatory microvillus

Gustatory cells are neuroepithelial cells with a dendritic _____________ (taste hair) that is the receptive portion of the cell

taste pore

The taste hair extends through the ____________

Basal cells

neural stem cells that replace gustatory cells (regeneration every 7 to 9 days)

Tongue papillae and taste buds

Sweet, sugar, sour, bitter, umami

5 taste sensations

sour

taste sensations- acids

bitter

taste sensations- alkaloids

Umami

taste senation- amino acids

CN IX - glossopharyngeal

Taste buds from posterior two-thirds of tongue conduct gustatory information to CNS through which cranial nerve?

smell

Ability to taste relies heavily on sense of _________

Gustatory pathway

photoreceptors

Eyes use ___________ to help form visual images of the environment

Accessory structures

______________ of the eye protect against foreign objects and ensure that the eye surface remains clean and moist

Eyebrow

thick short hairs along superior orbital ridge; prevent sweat from dripping into the eye

Eyelashes

hairs on margins of eyelids that prevent large foreign objects from contacting eyes

Eyelids

movable anterior protective coverings for eye

Tarsal glands

sebaceous glands within eyelids; secretion prevents overflow of tears and sticking together of eyelids

Palpebral fissure

space between eyelids

Medial and lateral palpebral commissures

corners of eyes

Lacrimal caruncle

medial pink bump containing ciliary glands that produce gritty secretion

Eye and accessory structures

Conjunctiva

• lining over the anterior surface of eye and internal surface of eyelid

• Stratified columnar epithelium

• Space where it folds back on itself is conjunctival fornix

• Contains blood vessels and nerves

• Contains goblet cells that lubricate eye

• Does not cover cornea

Conjunctival fornix

Space where conjunctiva folds back on itself