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Receptors are

Structures that detect stimuli. Range in complexity from simple dendritic endings to complex sensory organs. Monitors external & internal environmental conditions & conduct info about stimuli to CNS. We are aware of some specific stimuli


Receptive field is

Entire area through which the sensitive ends of the receptor cell are distributed.


Describe what is means if the receptive field is small

Precise localization & sensitivity are easily determined


Describe what it means if the receptive field is broad

Only detects general region of a stimulus


Describe why or why not it would be an advantage or disadvantage to have all receptors have small receptive fields

The number of receptors in the body would have to increase to detect environmental stimuli. The energy costs to maintain the activity would be enormous



All receptors act as transducers. Structures that transform the energy of one system (e.g. heat) into a different form of energy (e.g. a nerve impulse)


How does the size of the receptive field influence sensitivity

If the receptive field is small we get a precise localization & sensitivity are easily determined. A broad field only detects the general region of the stimulus


Receptors can either be

Tonic or phasic


Tonic receptors

Respond continuously to stimuli at a constant rate; (e.g. balance receptors in the ear that keep the head upright)


Phasic receptors

Detect new stimulus or a change in a stimulus that has already been applied, but over time sensitivity decreases. (e.g. tactile receptors of the skin that sense the increased pressure if we are pinched)



Phasic receptors can undergo adaptation. Change in which a reduction in sensitivity to a continually applied stimulus


General senses

Temp., pain, touch, stretch, & pressure. Receptors are distributed throughout the skin and organs


Special senses

Gustation, olfaction, vision, equilibrium, & hearing. Receptors housed w/in complex organs in the head


3 criteria used to describe receptors

Receptor distribution, stimulus origin, and modality of stimulus


Receptors are subdivided into two categories

Somatic receptors, visceral receptors


Somatic receptors

Housed w/in the body wall; include receptors for external stimuli, including chemicals, temp. pain, touch, proprioception & pressure


Visceral receptors

located in walls of the viscera; respond to chemicals, temp. and pressure & sometimes called interoceptors or visceroceptors


Receptors for special senses

Located w/in some sense organs & housed only in the head


What are the 5 special senses

1) Gustation (taste)
2) Olfaction (smell)
3) Vision
4) Equilibrium
5) Hearing (audition)



Detect stimuli from the external environment. Receptors in skin are exteroceptors because external simuli typically cause sensations to the skin. Receptors for special senses are considered exteroceptors


Phantom pain

Sensation associated w/ a body part that has been removed. The stimulation of a sensory neuron pathway from the removed limb on the remaining intact portion of the pathway propagates nerve impulses & conducts them to the CNS, where they are interpreted as originating in the amputated limb.


How can people still feel sensations after a limb has been removed?

Because the cell bodies of the sensory neurons that provided sensation to the limb remain alive because they were not part of that limb


Referred pain

Occurs when impulses from certain viscera are perceived as originating not from the organ, but in dermatomes of the skin. Numerous cutaneous & visceral neurons conduct nerve impulses through the same ascending tracts w/in the spinal cord. As a result impulses conducted along ascending pathways may be localized incorrectly. The sensory cortex in the brain is unable to differentiate between the actual & false sources of the stimulus



Also called visceroceptors. Detect stimuli in internal organs (viscera). Primarily stretch receptors in the smooth muscle of these organs. Report on pressure, chemical changes in the visceral tissue, & temp.


Are we aware of interceptors?

Most of the time we are unaware, but when the smooth muscle stretches to a certain point (when eating a large meal) we may become aware of these sensations



Located in muscles, tendons, and joints. Detect body and limb movements, skeletal muscle contraction and stretch, & changes in joint capsule structure


What do proprioceptors play in our awareness of our body joints?

Even if your not looking at your body joints, you are aware of their positioning & the state of contraction of your skeletal muscles, because proprioceptors send this info to the cns



Detect chemicals such as specific molecules dissolved in fluid in our external & internal environments, including ingested food & drink, body fluids, & inhaled air


Give an example of chemoreceptors

The receptors in taste buds on our tongue because they respond to the specific molecules in injested food. Also chemoreceptors in some of our blood vessels monitor the concentration of O2 & carbon dioxide molecules in our blood



Respond to changes in temp.



Located in the eye, detect changes in light intensity, color, & movement



Respond to touch, pressure, vibration, & stretch. Most of the cutaneous receptors are mechanoreceptors, because they respond to pressure & touch on the skin. Also located in the ear for equilibrium & hearing



Detect changes in pressure w/in body structures. These sensory receptors branch repeatedly w/in the connective tissues in vessel or organ walls, especially the elastic layer


Any pressure stimulus that causes wall deformation results in a?

change in the nerve impulse rates from the receptors & a pressure sensation



Respond to pain caused by either external or internal stimuli


Somatic nociceptors detect?

Chemical, heat, or mechanical damage to the body surface or skeletal muscles


Exposed to acid, touching a hot pan, or sprained ankle stimulate what?

Somatic nociceptors


Visceral nociceptors detect?

Internal body damage w/in the viscera due to excessive stretching of smooth muscle, O2 deprivation of the tissue, or chemicals released from damaged tissue


Cutaneous receptors

Receptors in your skin


Free nerve endings

Terminal branches of dendrites. Least complex of tactile receptors & reside closest to the surface of the skin, usually in the papillary layer of the dermis. Primarily detect pain and temp. stimuli but some also detect light touch & pressure


Root hair plexuses

Specialized free nerve endings that form a weblike sheath around hair follicles in the reticular layer of the dermis. Any movement or displacement of the hair changes the arrangement of these branching dendrites, initiating a nerve impulse. They quickly adapt & our conscious awareness subsides until restimulated


Tactile corpuscles

Previously called Meissner corpuscles, they are physically different from the unencapsulated tactile discs. large encapsulated oval receptors, formed from highly intertwined dendrites enclosed by modified neurolemmocytes, which are then covered w/ dense irregular connective tissue. Phasic receptors for light touch, shapes, & texture. Housed w/in the dermal papillae of the skin, especially in the lips, palms, eyelids, nipples, & genitals


Lamellated corpuscles

Previously called Pacinian corpuscles. Large receptors that detect deep pressure & high frequency vibration. Center of the receptor houses several dendrite endings of sensory neurons wrapped w/in numerous concentric layers of flat, fibroblast like cells. This structure ensures that only deep pressure stimuli will activate the receptor. Found deep w/in the reticular layer of the dermis; in the subcutaneous layer of the palms of the hands, soles of the feet, breasts and external genitalia; int he synovial membranes of joints, & in the walls of some organs


Krause bulbs

Located near the border of stratified squamous epithelium in the mucous membranes of the oral cavity, nasal cavity, vagina, & anal canal. Detect light pressure stimuli & low frequency vibration


Ruffini corpscles

Detect both continuous deep pressure & distortion in the skin. Tonic receptors that do not exhibit adaptation; housed w/in the dermis & subcutaneous layer


Golgi tendon organ

Nerve endings located w/in tendons near a muscle tendon junction


Gustatory cells w/microvilli

The dendritic ending of each gustatory cell is formed by a slender gustatory microvilli, sometimes called a taste hair. The extend throuhout an opening in the taste bud, called a taste pore, to the surface of the tongue. This is the receptive portion of the cell.


Within the oral cavity saliva keeps the environment moist; molecules in food dissolve in the saliva & stimulate the

Gustatory microvilli. These are classified as chemoreceptors because food molecules dissolve in saliva before they can be tasted The gustatory cells w/in the taste buds are specialized neuroepithelial cells that have a 7-10 day life span


What stem cells constantly replace the gustatory cells?

Basal cells. Beginning at about age 50, our ability to distinguish between different tastes declines due to reduction in both gustatory cell replacement & the number of taste buds


What are the 5 basic taste sensations?

Salty, sweet, sour, bitter, unami


Salty tastes

Caused by metal ions such as potassium of sodium ion in food or drink


Sweet tastes

Result from the presence of organic compounds such as sugar


Sour tastes

Caused by hydrogen ions from acids, such as those found in lemons, limes, & other fruits


Bitter tastes

Caused by alkaloids (such as those in brussel sprouts) toxins, or poisons



A pleasant taste that has been described as chicken soup like & caused by amino acids such as glutamate or aspartate


For the basic taste sensations, the threshold required to stimulate the receptor



Our taste receptors are more sensitive to?

Bitter and sour stimuli, since those sensations might indicate something toxic or poisonous in our food


Employing a combination of taste modalities allows us to

Perceive a wide variety of tastes


In the past, researchers though certain tastes were best interpreted along specific regions of the tongue; however recent research has found that?

These taste maps were incorrect & that taste sensations are spread over broader regions of the tongue than previously thought


Which cranial nerves receives taste sensations from the tongue?

Cranial nerves VII & IX (Facial & glossopharyngeal)


The sense of smell



Why is smell also referred to as remote chemoreception?

Because an object can be at a distance & we may be able to sense its odor


Compared to many other animals, olfaction in humans is?

Not highly developed because we don't require olfactory info. to find food or communicate w/others


What is w/in the nasal cavity?

Paired olfactory organs which are the organs of smell


What are the olfactory organs composed of?

Several components. An olfactory epithelium that lines the superior part of the nasal septum. Internal to the epithelium is an areolar connective tissue layer called lamina prop rid. Included w/in the collagen fibers & ground substance of this layer are mucin-secreting structures called olfactory glands (bowman glands) & many blood vessels and nerves


Which cell types compose the olfactory epithelium?

Olfactory receptor cells (also called olfactory neurons), which detect odors; supporting cells, which sandwich the olfactory neurons & sustain and maintain the receptors; basal cells; which function as stem cells to replace olfactory epithelium components


Olfactory receptor cells are?

Bipolar neurons that have undergone extensive differentiation and modification


At the apical surface of each neuron, the neck and apical head together form?

A thin, knobby projection that extends into the mucous covering the olfactory epithelium


What are olfactory hairs?

Numerous, thin, unmyelinated, cilia like extensions that project from each knob of the neuron into the overlying mucus. They house receptors fro airborne molecules. They are immobile & usually appear as a tangled mass w/in the mucus layer


What does deep breathing do to olfactory receptor cells?

It causes the inhaled air to mix & swirl, so both fat & water soluble odor molecules diffuse into the mucus layer covering the olfactory receptor cells. Receptor proteins on the olfactory hairs detect specific molecules. Airborne molecules dissolved in the mucus lining bind to the receptors. Depending upon which receptors are stimulated, diff. smells will be detected once the receptors are stimulated, adaptation occurs rapidly


How do strong odors dissipate?

An initial strong smell (such as rotting food in a trash can that hasn't been emptied for a week) may seem to dissipate as your olfactory receptors adapt to the foul odor


In contrast to the 5 basic taste sensations, the olfactory system can recognize as many as?

8 diff. primary odors as well as many thousands of other chemical stimuli


What are the primary odors?

Those that are detectable by a large number of people, such as camphorous, fishy, malty, minty, musky, & sweaty


What are secondary odors?

Those produced by a combination of chemicals and not detected or recognized by everyone. For example some flower blossoms exhibit almost 100 odoriforous compounds & individuals in the general population vary widely in their ability to recognized some or all of these


Olfactory receptors cells are one of the few types of neurons that undergo?

Mitosis to replace aged cells


Gustatory receptors & the number of olfactory receptor cells both decline with?

Age, thus olfactory neurons lose their sensitivity to odors. An elderly individual has a decreased ability to recognized odor molecules


Tarsal gland

Previously called meibomian glands. Sebaceous glands that produce a secretion to prevent tear overflow from the open eye and keep the eyelids from adhering together


Lacrimal gland

Located w/in the superlateral depression of each orbit. Composed of an orbital or superior part & a palpebral or inferior part. It continuously produces tears


Fibrous tunic

External layer of the eyeball. Composed of the anterior cornea & the posterior sclera


Vascular tunic

Middle layer of the eyeball, also called the uvea. Composed of 3 distinct regions; from posterior to anterior, they are the choroid, the ciliary body, & the iris. It houses an extensive array of blood vessels, lymph vessels, & the intrinsic muscles of the eye



Most extensive & posterior region of the vascular tunic. Houses a vast network of capillaries, which supply both nutrients & O2 to the retina (inner layer of the eyeball). Cells of the choroid are filled w/pigment from the numerous melanocytes in this region. The melanin pigment is needed to absorb extraneous light that enters the eye, allowing the retina to clearly interpret the remaining light rays & form a visual image



Inner layer of the eye wall, also called internal tunic or neural tunic. Composed of 2 layers: an outer pigmented layer & and inner neural layer


This layer of the retina is responsible for receiving light rays & converting them into nerve impulses that are transmitted to the brain?

Neural layer


Photoreceptor cells

The outermost layer of the neural layer is composed of photoreceptor cells of two types, cones & rods



One of two types of photoreceptor cells. Have a cone shaped outer part & function in high intensity light & in color vision



One of two types of photoreceptor cells. Have a rod shaped outer part & function in dim light



Process of making the lens more spherical to view close up objects. Controlled by the parasympathetic division of the ANS



Small opacities w/in the lens that may coalesce to completely obscure the lens. Major cause of blindness world wide


External ear

Skin covered, primarily cartilaginous structure called the auricle, or pinna. A funnel-shaped, & serves to protect the entry into the ear & to direct sound waves into the external acoustic meatus


External acoustic meatus

Bony tube which extends medially & slightly superiorly from the lateral surface of the head. Terminates into the tympanic membrane


Tympanic membrane

Or eardrum, a delicate, funnel-shaped epithelial sheet that is partition between the external and middle ear. Vibrates when sound waves hit it. These vibrations provides the means for transmission of sound wave energy into the middle and inner ear


The narrow external opening in the external acoustic meatus prevents what?

Large objects from entering & damaging the tympanic membrane. Near its entrance, fine hairs help guard the opening


Deep w/in the external ear canal are ceruminous glands which produce?

A waxlike secretion called cerumen, which combines w/dead, sloughed skin cells to form earwax. This material may help reduce infection w/in the external acoustic meatus by impeding microorganism growth


Middle ear

Contains an air filled tympanic cavity. Medially, a bony wall that houses the oval window & round window separates the middle ear from the inner ear


The tympanic cavity in the middle ear maintains an open connection w/ the atmosphere through the?

Auditory tube


Auditory tube?

The middle ear also called the pharyngotympanic tube or eustachian tube. This passageway opens into the nasopharynx (upper throat) from the middle ear. It has a normally closed slit-like opening at its connection to the nasopharynx. Air movement through this tube occurs as a result of chewing, yawning, & swallowing, which allows the pressure to equalize in the middle ear



People with this condition have trouble seeing close up objects, & are called "farsighted". In this condition only converted rays (those that come from distant points) can be brought to focus on the retina. This cause is a short eyeball; parallel light rays from objects close to the eye focus posterior to the retina



People w/this condition have trouble seeing far away objects, also called "nearsighted". Only rays relatively close to the eye focus on the retina. The cause is a long eyeball; parallel light rays from objects at some distance from the eye anterior to the retina w/in the vitreous body



Laster-assisted in situ keratomileusis. Can treat nearsightedness, farsightedness & astigmatism. It removes tissue from the inner, deeper layer of the cornea, which is less likely to regrow than surface tissue, so less vision regression occurs


Auditory ossicles

In the tympanic cavity of the middle ear are the 3 smallest bones of the body. They are from lateral to medial the malleus (hammer), the incus (anvil), & the stapes (stirrup). These are responsible for amplifying sound waves & transmitting them into the inner ear via the oval window



Hearing organs are housed w/in the cochlea in both inner ears. It is a snail-shaped spiral chamber in the bone of the inner ear. It has a modiolus (spongy bone axis). Protected w/in the core of the modiolus, the membranous labyrinth houses the spiral organ (organ of corti), which is responsible for hearing



The number of waves that move past a point during a specific amount of time. Measured in hertz (Hz), & is classified as high, medium, or low. Humans can detect sounds having frequencies int he range from 20 hertz to 20 kilohertz


Inner ear

Located w/in the petrous part of the temporal bone, where there is a bony labyrinth (spaces or cavities). W/in the bony labyrinth are membranous labyrinth (membrane lined fluid filled tubes & spaces). Receptors equilibrium and hearing are housed, along w/supporting cells, w/in a sensory epithelium lining part of the membranous labyrinth



Fluid in the space between the outer walls of the bony labyrinth & the membranous labyrinth. Similar in composition to both extracellular fluid & cerebrospinal fluid (CSF). In the inner ear, it suspends, supports, & protects the membranous labyrinth from the wall of the bony labyrinth



Fluid in the membranous labyrinth. Exhibits a low sodium & high potassium concentration similar to that of intracellular fluid



Part of the bony labyrinth of the vestibular complex contains two sac-like, membranous, labyrinth parts; utricle & saccule which are interconnected through a narrow passageway



Vestibular organs for equilibrium & balance w/in the bony labyrinth. Interconnected through a narrow passageway w/ the saccule



Vestibular organs for equilibrium & balance w/in the bony labyrinth. Interconnected w/the utricle through a narrow passageway



Molecules that have an effect on specific organs


Target cells

Cells w/specific receptors for a hormone (enabling the hormone to bind to the cell) respond to that hormone


Target organ

Organs that contain target cells


Feedback loop

Hormone levels are regulated by a self adjusting mechanism called feedback which means the product of a pathway acts back at an earlier step in the pathway to regulate the pathways activity


What are the 2 types of feedback loops?

Negative and positive


Negative feedback loop

A stimulus starts a process, & eventually the hormone secreted or a product of its effects causes the process to slow down or turn off. Most hormonal systems work by this