Module 5.2 objectives

How an Image is Focused on the Retina?

-'inverted' focused image falls on plane of retina -refracted light produces focused image behind retina -light 'bends' (refracts) upon entering new medium 1. The lens becomes more round. 2. The entering angle of the light increases 3. The light gets more refracted (bent), so the focused image now falls onto the retina

adaption in sensory receptors

-A characteristic of most sensory receptors is adaptation, in which the generator potential or receptor potential decreases in amplitude during a maintained, constant stimulus. -this causes the frequency of nerve impulses in the sensory neuron to decrease. Because of adaptation, the perception of a sensation may fade or disappear even though the stimulus persists. -when you first step into a hot shower, the water may feel very hot, but soon the sensation decreases to one of comfortable warmth even though the stimulus (the high temperature of the water) does not change

4. Integration of sensory input

-A particular region of the CNS receives and integrates (processes) the sensory nerve impulses. Conscious sensations or perceptions are integrated in the cerebral cortex. You seem to see with your eyes, hear with your ears, and feel pain in an injured part of your body because sensory impulses from each part of the body arrive in a specific region of the cerebral cortex, which interprets the sensation as coming from the stimulated sensory receptors.

2. transduction of the stimulus

-A sensory receptor converts the energy in the stimulus into a graded potential, a process known as transduction. Recall that graded potentials vary in amplitude (size), depending on the strength of the stimulus that causes them, and are not propagated. -Each type of sensory receptor exhibits selectivity: It can transduce (convert) only one kind of stimulus. For example, odorant molecules in the air stimulate olfactory (smell) receptors in the nose, which transduce the molecules' chemical energy into electrical energy in the form of a graded potential.

vallate papillae

-About 12 very large -or circumvallate papillae form an inverted V-shaped row at the back of the tongue. Each of these papillae houses 100-300 taste buds.

1. stimulation of sensory receptor

-An appropriate stimulus must occur within the sensory receptor's receptive field, that is, the body region where stimulation activates the receptor and produces a response

Conductive hearing loss

-As we get older we tend to lose the ability to hear higher frequencies. This most common form of sensorineural hearing loss is known as

binocular vision

-Because of the position of their eyes in their heads, many animals, such as horses and goats, see one set of objects off to the left through one eye, and an entirely different set of objects off to the right through the other. In humans, both eyes focus on only one set of objects

lens

-Behind the pupil and iris, within the cavity of the eyeball -Within the cells of the lens, proteins called crystallins, arranged like the layers of an onion, make up the refractive media of the lens, which normally is perfectly transparent and lacks blood vessels. -It is enclosed by a clear connective tissue capsule and held in position by encircling zonular fibers, which attach to the ciliary processes. -The lens helps focus images on the retina to facilitate clear vision/refract light

olfactory transduction

-Binding of an odorant to an olfactory receptor protein in an olfactory cilium stimulates a membrane protein called a G protein. -The G protein, in turn, activates the enzyme adenylyl cyclase to produce a substance called cyclic adenosine monophosphate (cAMP), a type of second messenger -The cAMP opens a cation channel that alllows Na+ and Ca2+ to enter the cytosol, which causes a depolarizing receptor potential to form in the membrane of the olfactory receptor cell. -If the depolarization reaches threshold, an action potential is generated along the axon of the olfactory receptor cell.

aqeous humor

-Both chambers of the anterior cavity are filled -a transparent watery fluid that nourishes the lens and cornea. -Aqueous humor continually filters out of blood capillaries in the ciliary processes of the ciliary body and enters the posterior chamber. -It then flows forward between the iris and the lens, through the pupil, and into the anterior chamber. -From the anterior chamber, aqueous humor drains into the scleral venous sinus (canal of Schlemm) and then into the blood. -Normally, aqueous humor is completely replaced about every 90 minutes.

central retinal vein

-Branches of the central retinal artery fan out to nourish the anterior surface of the retina; the central retinal vein drains blood from the retina through the optic disc. -Also visible are the macula lutea and fovea centralis, which are described shortly.

cones

-Brighter lights stimulate cones, which produce color vision. -Three types of cones are present in the retina: (1) blue cones, which are sensitive to blue light, (2) green cones, which are sensitive to green light, and (3) red cones, which are sensitive to red light. Color vision results from the stimulation of various combinations of these three types of cones. -Most of our experiences are mediated by the cone system, the loss of which produces legal blindness

central retinal artery

-Bundled together with the optic nerve are -a branch of the ophthalmic artery

Corpuscles of touch (Meissner corpuscles)

-Capsule surrounds mass of dendrites in dermal papillae of hairless skin -Onset of touch and low-frequency vibrations. -rapid

odorants

-Chemicals that bind to and stimulate the olfactory receptors in the olfactory cilia -Olfactory receptor cells respond to the chemical stimulation of an odorant molecule by producing a generator potential, thus initiating the olfactory response.

tastants

-Chemicals that stimulate gustatory receptor cells -Once a tastant is dissolved in saliva, it can make contact with the plasma membranes of the gustatory microvilli, which are the sites of taste transduction. -The result is a depolarizing receptor potential that stimulates exocytosis of synaptic vesicles from the gustatory receptor cell. -In turn, the liberated neurotransmitter molecules trigger graded potentials that produce nerve impulses in the first-order sensory neurons that synapse with gustatory receptor cells. -Receptors for tastants are located On gustatory hairs (cilia) on gustatory receptor cells in the taste bud

taste adaption

-Complete adaptation to a specific taste can occur in 1-5 minutes of continuous stimulation. Taste adaptation is due to changes that occur in the taste receptors, in olfactory receptors, and in neurons of the gustatory pathway in the CNS

two types of rapidly adapting touch receptors

-Corpuscles of touch or Meissner corpuscles: are touch receptors that are located in the dermal papillae of hairless skin. Each corpuscle is an egg-shaped mass of dendrites enclosed by a capsule of connective tissue. Because corpuscles of touch are rapidly adapting receptors, they generate nerve impulses mainly at the onset of a touch -Hair root plexuses: are rapidly adapting touch receptors found in hairy skin; they consist of free nerve endings wrapped around hair follicles. Hair root plexuses detect movements on the skin surface that disturb hairs. For example, an insect landing on a hair causes movement of the hair shaft that stimulates the free nerve endings.

bloodshot eyes

-Dilation and congestion of the blood vessels of the bulbar conjunctiva due to local irritation or infection

receptive field

-Discrimination between two similar stimuli (e.g., two points on body surface; two sounds of similar pitch) is dependent on the number of receptors within an area of 'sensory surface -Stimulation anywhere within the receptive field results in a signal from the same sensory afferent (sensory nerve

rhodopsin

-Each disc contains many copies of rhodopsin, the light receptor -Rhodopsin consists of opsin protein and retinal (a light-sensitive molecule derived from vitamin

Type II cutaneous mechanoreceptors (Ruffini corpuscles)

-Elongated capsule surrounds dendrites deep in dermis and in ligaments and tendons -Skin stretching and pressure -slow

tarsal glands

-Embedded in each tarsal plate is a row of elongated modified sebaceous glands are these -that secrete a fluid that helps keep the eyelids from adhering to each other

zonular fibers

-Extending from the ciliary process -that attach to the lens -The fibers consist of thin, hollow fibrils that resemble elastic connective tissue fibers

olfactory cilia

-Extending from the dendrite of an olfactory receptor cell are several nonmotile -which are the sites of olfactory transduction

Localization of Pain

-Fast pain is very precisely localized to the stimulated area. For example, if someone pricks you with a pin, you know exactly which part of your body was stimulated. Somatic slow pain also is well localized but more diffuse (involves large areas); it usually appears to come from a larger area of the skin. In some instances of visceral slow pain, the affected area is where the pain is felt. If the pleural membranes around the lungs are inflamed, for example, you experience chest pain.

example of visible light

-For example, light that has a wavelength of 400 nm is violet, and light that has a wavelength of 700 nm is red. -An object can absorb certain wavelengths of visible light and reflect others; the object will appear the color of the wavelength that is reflected. -For example, a green apple appears green because it reflects mostly green light and absorbs most other wavelengths of visible light. -An object appears white because it reflects all wavelengths of visible light. An object appears black because it absorbs all wavelengths of visible light.

Vestibulocochlear (VIII)

-For the special sense of hearing, which of the following cranial nerves serves as the major pathway for signal transduction to the brain?

tickle

-Free nerve endings are thought to mediate the tickle sensation. This intriguing sensation typically arises only when someone else touches you, not when you touch yourself. -The solution to this puzzle seems to lie in the impulses that conduct to and from the cerebellum when you are moving your fingers and touching yourself that don't occur when someone else is tickling you.

Nociceptors cont.

-Free nerve endings in every body tissue except brain -pain -slow

Itch and tickle receptors

-Free nerve endings in skin and mucous membranes -Itching and tickling. -both slow and rapid

Warm receptors and cold receptors

-Free nerve endings in skin and mucous membranes of mouth, vagina, and anus -Warmth or cold -Initially rapid, then slow

Hair root plexuses

-Free nerve endings wrapped around hair follicles in skin -Movements on skin surface that disturb hairs -rapid

lacrimal puncta

-From here the tears pass medially over the anterior surface of the eyeball to enter two small openings called

gustatory pathway from textbook

-From the taste buds, nerve impulses propagate along these cranial nerves to the gustatory nucleus in the medulla oblongata. -From the medulla, some axons carrying taste signals project to the limbic system and the hypothalamus; others project to the thalamus. -Taste signals that project from the thalamus to the primary gustatory area in the insula of the cerebral cortex give rise to the conscious perception of taste and discrimination of taste sensations.

accommodation

-If the surface of a lens curves inward, like the inside of a hollow ball, the lens is said to be concave and causes light rays to refract away from each other. - The lens of the eye is convex on both its anterior and posterior surfaces, and its focusing power increases as its curvature becomes greater. -When the eye is focusing on a close object, the lens becomes more curved, causing greater refraction of the light rays. -This increase in the curvature of the lens for near vision:

sensory receptors and when they use certain nerve endings

-In sensory receptors that are free nerve endings or encapsulated nerve endings, if the receptor potential is large enough to reach threshold, it triggers one or more nerve impulses in the axon of the sensory neuron -In sensory receptors that are separate cells, the receptor potential triggers release of neurotransmitter through exocytosis of synaptic vesicles. The neurotransmitter molecules liberated from the synaptic vesicles diffuse across the synaptic cleft and produce postsynaptic potential (PSP), a type of graded potential, in the sensory neuron. If threshold is reached, the PSP will trigger one or more nerve impulses, which propagate along the axon into the CNS.

Joint kinesthetic receptors

-Lamellated corpuscles, type II cutaneous mechanoreceptors, tendon organs, and free nerve endings -Joint position and movement -rapid

optics of the eye:

-Light rays arrive from an object 'focused' onto sensory surface of the eye: 'retina' -focusing involves 'bending' of light rays: refraction

A third way to group sensory receptors is according to the type of stimulus they detect:

-Mechanoreceptors -Thermoreceptors -Nociceptors -Photoreceptors -Chemoreceptors -Osmoreceptors

olfactory (I) nerves

-On each side of the nose, some 40 or so bundles of axons of olfactory receptor cells form the right and left of nerve

Lamellated (pacinian) corpuscles

-Oval, layered capsule surrounds dendrites; present in dermis and subcutaneous layer, submucosal tissues, joints, periosteum, and some viscera. -High-frequency vibrations. -rapid

pain sensation

-Pain is indispensable for survival. It serves a protective function by signaling the presence of noxious, tissue-damaging conditions. From a medical standpoint, the subjective description and indication of the location of pain may help pinpoint the underlying cause of disease -Nociceptors, the receptors for pain, are free nerve endings found in every tissue of the body except the brain. Intense thermal, mechanical, or chemical stimuli can activate nociceptors. Tissue irritation or injury releases chemicals such as prostaglandins, kinins, and potassium ions (K+) that stimulate nociceptors.

superficial somatic pain

-Pain that arises from stimulation of receptors in the skin

phantom limb sensation

-Patients who have had a limb amputated may still experience sensations such as itching, pressure, tingling, or pain as if the limb were still there

Proprioceptive sensations

-Proprioceptive sensations allow us to recognize that parts of our body belong to us (self). They also allow us to know where our head and limbs are located and how they are moving even if we are not looking at them, so that we can walk, type, or dress without using our eyes. -Proprioceptive sensations arise in receptors termed proprioceptors. Those proprioceptors embedded in muscles (especially postural muscles) and tendons inform us of the degree to which muscles are contracted, the amount of tension on tendons, and the positions of joints. -Hair cells of the inner ear monitor the orientation of the head relative to the ground and head position during movements.

encapsulated nerve endings

-Receptors for other somatic and visceral sensations, such as pressure, vibration, and some touch sensations -their dendrites are enclosed in a connective tissue capsule that has a distinctive microscopic structure—for example, lamellated corpuscles -The different types of capsules enhance the sensitivity or specificity of the receptor.

specificity of sensation

-Regardless of stimulus 'modality,' all sensation is 'read' in the CNS as electrical signals (action potential) -We can 'discriminate' between different types of stimuli because different receptor 'types' respond preferentially to different stimuli 1. a mechanoreceptor is more sensitive to touch than to light 2. a photoreceptor is more sensitive to light than to touch

rod cell physiology:

-Rhodopsin activation closes sodium channels: -Opsin is type of receptor which activates enzymes that either synthesize or break down 'second messengers' -In this case, enzymes which break down cGMP are activated -cGMP normally binds to ligand-gated Na+channels in the plasmalemma to keep them open -No more EPSPs= hyperpolarization

Type I cutaneous mechanoreceptors (tactile discs)

-Saucer-shaped free nerve endings make contact with tactile epithelial cells in epidermis -Continuous touch and pressure. -slow

sebaceous ciliary glands

-Sebaceous glands at the base of the hair follicles of the eyelashes -release a lubricating fluid into the follicles. Infection of these glands, usually by bacteria, causes a painful, pus-filled swelling called a sty.

touch

-Sensations of touch generally result from stimulation of tactile receptors in the skin or subcutaneous layer.

Muscle spindles

-Sensory nerve endings wrap around central area of encapsulated intrafusal muscle fibers within most skeletal muscles. -most skeletal muscles.Muscle length -slow

separate cells

-Sensory receptors for some special senses are specialized -that synapse with sensory neurons. -These include hair cells for hearing and equilibrium in the inner ear, gustatory receptors in taste buds and photoreceptors in the retina of the eye for vision

Joint Kinesthetic Receptors

-Several types of joint kinesthetic receptors are present within and around the articular capsules of synovial joints. Free nerve endings and type II cutaneous mechanoreceptors in the capsules of joints respond to pressure. -Small lamellated corpuscles in the connective tissue outside articular capsules respond to acceleration and deceleration of joints during movement. -Joint ligaments contain receptors similar to tendon organs that adjust reflex inhibition of the adjacent muscles when excessive strain is placed on the joint.

receptive field rule

-Smaller receptive fields (increased density of receptors) permit high resolution discrimination -Areas with small receptive fields give us high resolution discrimination (involve many sensory neurons from which information is gathered and process -We have the greatest number of sensory neurons, all with smaller receptive fields, in the areas of the hands and face -Areas with a small receptive field have greater receptor density.

cutaneous sensation

-Somatic sensations that arise from stimulating the skin surface are cutaneous sensations sensations

eye twitch

-Sometimes a person may experience an annoying twitch in an eyelid, an involuntary quivering similar to muscle twitches in the hand, forearm, leg, or foot. -Twitches are almost always harmless and usually last for only a few seconds. They are often associated with stress and fatigue

smell (olfaction):

-Specialized sense organ: nose -Olfactory epithelium: at the roof of each nasal cavity houses sensory ability -Specialized sensory cell required? No. -Types of receptors used: chemoreceptors (for odorants) -With a total area of 5 cm2 (a little less than 1 in.2)

taste (gustation)

-Specialized sense organ: tongue: Taste buds in papillae house sensory ability -Specialized sensory cell required? Yes: gustatory receptor cells -Types of receptors used: chemoreceptors (for tastants) -However, gustation is much simpler than olfaction in that only five primary tastes can be distinguished: salty, sour, sweet, bitter, and umami. Salty taste is caused by the presence of sodium ions (Na+) in food

taste bud structure

-Specialized sensory cells called gustatory receptor cells each extend one long microvillus containing receptors for tastants through taste pore -Basal cells are stem cells for supporting cells which then develop into new gustatory receptor cells over time

papillae

-Taste buds are found in elevations on the tongue -which increase the surface area and provide a rough texture to the upper surface of the tongue

tears passage

-Tears then pass into two ducts, the superior and inferior lacrimal canaliculi, which lead into the lacrimal sac (within the lacrimal fossa) and then into the nasolacrimal duct. -This duct carries the lacrimal fluid into the nasal cavity just inferior to the inferior nasal concha where it mixes with mucus. An infection of the lacrimal sacs is called dacryocystitis -It is usually caused by a bacterial infection and results in blockage of the nasolacrimal ducts.

sensory function: general principles

-The Brain is the Organ of Sensation & Perception -Interpretation of sensory information is based on path traveled and destination in the brain -All signals are "sensed," but only ~10% is "perceived

olfactory tract

-The axons of the mitral cells form this

visual pathway from textbook

-The axons of the retinal ganglion cells form the optic (II) nerve which provide output from the retina to the brain. The optic (II) nerves pass through the optic chiasm, a crossing point of the optic nerves -Some axons cross to the opposite side, but others remain uncrossed. After passing through the optic chiasm, the axons, now part of the optic tract, enter the brain and most of them terminate in the lateral geniculate nucleus of the thalamus. -Here they synapse with neurons whose axons form the optic radiations, which project to the primary visual areas in the occipital lobes of the cerebral cortex, and visual perception begins. -Some of the fibers in the optic tracts terminate in the superior colliculi, which control the extrinsic eye muscles, and the pretectal nuclei, which control pupillary and accommodation reflexes.

sensory transduction-interpretation of afferent (sensory) input

-The brain 'assumes' that any signals coming in along a sensory afferent from a particular receptor (e.g., touch; photoreceptor) reflects stimulation by the appropriate stimulus (i.e., pressure; photon) -all other characteristics of the stimulus (e.g., intensity, duration) are conveyed by the frequencyand patternof the incoming signal

eye orbits

-The eyes sit in the bony depressions of the skull called the or-bits -help protect the eyes, stabilize them in three-dimensional space, and anchor them to the muscles that produce their essential movements.

Three cranial nerves contain axons of the first-order gustatory neurons that innervate the taste buds:

-The facial (VII) nerve serves taste buds in the anterior two-thirds of the tongue -the glossopharyngeal (IX) nerve serves taste buds in the posterior one-third of the tongue -vagus (X) nerve serves taste buds in the throat and epiglottis

taste buds:

-The receptors for sensations of taste are located in the taste buds -Most of the nearly 10,000 taste buds of a young adult are on the tongue, but some are found on the soft palate (posterior portion of the roof of the mouth), pharynx (throat), and epiglottis (cartilage lid over voice box). The number of taste buds declines with age. Each taste bud is an oval body consisting of three kinds of epithelial cells: supporting cells, gustatory receptor cells, and basal cells -he supporting cells surround about 50 gustatory receptor cells in each taste bud

palpebral fissure

-The space between the upper and lower eyelids that exposes the eyeball -its angles are known as the lateral commissure

thermal sensation

-Thermoreceptors are free nerve endings that have receptive fields about 1 mm in diameter on the skin surface. -Two distinct thermal sensations—coldness and warmth—are detected by different receptors

ophthalmoscope

-This layer's anatomy can be viewed with this -an instrument that shines light into the eye and allows an observer to peer through the pupil, providing a magnified image of the retina and its blood vessels as well as the optic (II) nerve -Several landmarks are visible through an ophthalmoscope.

two types of slowly adapting touch receptors

-Type I cutaneous mechanoreceptors: known as tactile (Merkel) discs, are saucer-shaped, flattened free nerve endings that make contact with tactile epithelial cells (Merkel cells) of the stratum basale. They are plentiful in the fingertips, hands, lips, and external genitalia. These receptors respond to continuous touch, such as holding an object in your hand for an extended period of time. -Type II cutaneous mechanoreceptors, or Ruffini corpuscles: are elongated, encapsulated receptors located in the dermis, subcutaneous layer, and other tissues of the body. They are highly sensitive to skin stretching, such as when a masseuse stretches your skin during a massage.

sensory transduction for gustation

-Upon binding to a tastant, a receptor potential is generated in a gustatory receptor, leading to release of neurotransmitter. -The released neurotransmitter triggers depolarization and AP formation in the first-order sensory neurons for taste

3. generation of nerve impulses

-When a graded potential in a sensory neuron reaches threshold, it triggers one or more nerve impulses, which then propagate toward the CNS. Sensory neurons that conduct impulses from the PNS into the CNS are called first order neurons

light in pupils

-When bright light stimulates the eye, parasympathetic fibers of the oculomotor (III) nerve stimulate the circular muscles or sphincter pupillae of the iris to contract, causing a decrease in the size of the pupil (constriction). In dim light, sympathetic neurons stimulate the radial muscles or dilator pupillae of the iris to contract, causing an increase in the pupil's size (dilation).

How does accommodation occur?

-When you are viewing distant objects, the ciliary muscle of the ciliary body is relaxed and the lens is flatter because it is stretched in all directions by taut zonular fibers -When you view a close object, the ciliary muscle contracts, which pulls the ciliary process and choroid forward toward the lens. This action releases tension on the lens and zonular fibers. -Because it is elastic, the lens becomes more spherical (more convex), which increases its focusing power and causes greater convergence of the light rays -Parasympathetic fibers of the oculomotor (III) nerve innervate the ciliary muscle of the ciliary body and, therefore, mediate the process of accommodation.

light adaptation

-When you emerge from dark surroundings (say, a tunnel) into the sunshine -your visual system adjusts in seconds to the brighter environment by decreasing its sensitivity.

olfactory glands

-Within the connective tissue that supports the olfactory epithelium -which produce mucus that is carried to the surface of the epithelium by ducts. The secretion moistens the surface of the olfactory epithelium and dissolves odorants so that transduction can occur.

olfactory receptors

-Within the plasma membranes of the olfactory cilia -proteins that detect inhaled chemicals

vitreous body

-Within the vitreous chamber is this -a transparent jellylike substance that holds the retina flush against the choroid, giving the retina an even surface for the reception of clear images. -It occupies about four-fifths of the eyeball. Unlike the aqueous humor, the vitreous body does not undergo constant replacement. -It is formed during embryonic life and consists of mostly water plus collagen fibers and hyaluronic acid. -The vitreous body also contains phagocytic cells that remove debris, keeping this part of the eye clear for unobstructed vision

ciliary muscle

-a circular band of smooth muscle. -Contraction or relaxation of the ciliary muscle changes the tightness of the zonular fibers, which alters the shape of the lens, adapting it for near or far vision

Microscopic structure

-a microscopic level, sensory receptors may be one of the following: (1) free nerve endings of first-order sensory neurons, (2) encapsulated nerve endings of first-order sensory neurons, or (3) separate cells that synapse with first-order sensory neurons.

hyposmia

-a reduced ability to smell, affects half of those over age 65 and 75% of those over age 80

fovea centralis

-a small depression in the center of the macula lutea, contains only cones. -In addition, the layers of bipolar and ganglion cells, which scatter light to some extent, do not cover the cones here; these layers are displaced to the periphery of the fovea centralis. As a result, the fovea centralis is the area of highest visual acuity -A main reason that you move your head and eyes while looking at something is to place images of interest on your fovea centralis

pressure

-a sustained sensation that is felt over a larger area than touch, occurs with deeper deformation of the skin and subcutaneous layer. -The receptors that contribute to sensations of pressure are type I and type II mechanoreceptors. - These receptors are able to respond to a steady pressure stimulus because they are slowly adapting.

tarsal plate

-a thick fold of connective tissue that gives form and support to the eyelids

conjunctiva

-a thin, protective mucous membrane composed of nonkeratinized stratified squamous epithelium with numerous goblet cells that is supported by areolar connective tissue

cornea

-a transparent coat that covers the colored iris. -Because it is curved, the cornea helps focus light onto the retina. -Its outer surface consists of nonkeratinized stratified squamous epithelium. -The middle coat of the cornea consists of collagen fibers and fibroblasts, and the inner surface is simple squamous epithelium. -Since the central part of the cornea receives oxygen from the outside air, contact lenses that are worn for long periods of time must be permeable to permit oxygen to pass through them. -Admits and refracts (bends) light.

how many olfactory receptors does the human nose have?

-about 10 million olfactory receptors, of which there are about 400 different functional types -Each type of olfactory receptor can react to only a select group of odorants. Only one type of receptor is found in any given olfactory receptor cell. -Therefore, 400 different types of olfactory receptor cells are present in the olfactory epithelium.

Rapidly adapting receptors

-adapt very quickly -They are specialized for signaling changes in a stimulus. -Receptors associated with pressure, touch, and smell are rapidly adapting.

rods

-allow us to see in dim light, such as moonlight. Because rods do not provide color vision, in dim light we can see only black, white, and all shades of gray in between -A person who loses rod vision mainly has difficulty seeing in dim light and thus should not drive at night. -The outer segment of each rod contains a stack of about 1000 discs, piled up like coins inside a wrapper.

Age-related macular disease (AMD)

-also known as macular degeneration, is a degenerative disorder of the retina in persons 50 years of age and older. In AMD, abnormalities occur in the region of the macula lutea, which is ordinarily the area of most acute vision

amplitude of a receptor

-amplitude of a receptor potential varies with the intensity of the stimulus, with an intense stimulus producing a large potential and a weak stimulus eliciting a small one. -Similarly, large generator potentials or receptor potentials trigger nerve impulses at high frequencies in the first-order neuron, in contrast to small generator potentials or receptor potentials, which trigger nerve impulses at lower frequencies.

two-point discrimination test

-an indirect measure of cutaneous touch receptor density. -A subject is touched by 2 closely spaced points and asked if he or she can feel both points. -The objects are moved farther apart until 2 points can be felt. -An area of skin with a greater density of touch receptors is more sensitive to touch and can discriminate between 2 points closer together than an area with a lower density of touch receptors.

color blindness

-an inherited inability to distinguish between certain colors, result from the absence or deficiency of one of the three types of cones. The most common type is red-green color blindness, in which red cones or green cones are missing.

ciliary body

-anterior portion of the vascular tunic, the choroid becomes the ciliary body -It extends from the ora serrata, the jagged anterior margin of the retina, to a point just posterior to the junction of the sclera and cornea. -Like the choroid, the ciliary body appears dark brown in color because it contains melanin-producing melanocytes. In addition, the ciliary body consists of ciliary processes and ciliary muscle. -Secretes aqueous humor and alters shape of lens for near or far vision (accommodation).

pupil

-appears black because, as you look through the lens, you see the heavily pigmented back of the eye (choroid and retina). However, if bright light is directed into the pupil, the reflected light is red because of the blood vessels on the surface of the retina. It is for this reason that a person's eyes appear red in a photograph ("red eye") when the flash is directed into the pupil.

free nerve endings

-are bare (not encapsulated) dendrites; they lack any structural specializations that can be seen under a light microscope -Receptors for pain, temperature, tickle, itch, and some touch sensations

supporting cells

-are columnar epithelial cells of the mucous membrane lining the nose. -They provide physical support, nourishment, and electrical insulation for the olfactory receptor cells and help detoxify chemicals that come in contact with the olfactory epithelium

photopigments

-are integral proteins in the plasma membrane of the outer segment. In cones the plasma membrane is folded back and forth in a pleated fashion; in rods the pleats pinch off from the plasma membrane to form discs

exteroceptors

-are located at or near the external surface of the body; they are sensitive to stimuli originating outside the body and provide information about the external environment. -The sensations of hearing, vision, smell, taste, touch, pressure, vibration, temperature, and pain are conveyed by exteroceptors.

proprioceptors

-are located in muscles, tendons, joints, and the inner ear. -They provide information about body position, muscle length and tension, and the position and movement of your joints.

Foliate papillae

-are located in small trenches on the lateral margins of the tongue, but most of their taste buds degenerate in early childhood.

Fungiform papillae

-are mushroom-shaped elevations scattered over the entire surface of the tongue that contain about five taste buds each.

Three different cone photopigments

-are present in the retina, one in each of the three types of cones, green cones, and red cones). Color vision results from different colors of light selectively activating the different cone photopigments.

Mechanoreceptors

-are sensitive to mechanical stimuli such as the deformation, stretching, or bending of cells. -provide sensations of touch, pressure, vibration, proprioception, and hearing and equilibrium. -They also monitor the stretching of blood vessels and internal organs.

tendon organs

-are slowly adapting receptors located at the junction of a tendon and a muscle. By initiating tendon reflexes tendon organs protect tendons and their associated muscles from damage due to excessive tension. (When a muscle contracts, it exerts a force that pulls the points of attachment of the muscle at either end toward each other. This force is the muscle tension.) -Each tendon organ consists of a thin capsule of connective tissue that encloses a few tendon fascicles (bundles of collagen fibers) -When tension is applied to a muscle, the tendon organs generate nerve impulses that propagate into the CNS, providing information about changes in muscle tension. The resulting tendon reflexes decrease muscle tension by causing muscle relaxation.

muscle spindles

-are the proprioceptors that monitor changes in the length of skeletal muscles and participate in stretch reflexes. By adjusting how vigorously a muscle spindle responds to stretching of a skeletal muscle, the brain sets an overall level of muscle tone, the small degree of contraction that is present while the muscle is at rest. -Each muscle spindle consists of several slowly adapting sensory nerve endings that wrap around 3 to 10 specialized muscle fibers, called intrafusal fibers -Muscle spindles are interspersed among most skeletal muscle fibers and aligned parallel to them. In muscles that produce finely controlled movements, such as those of the fingers or eyes as you read music and play a musical instrument, muscle spindles are plentiful.

somatic sensation

-arise from stimulation of sensory receptors embedded in the skin or subcutaneous layer; in mucous membranes of the mouth, vagina, and anus; and in skeletal muscles, tendons, and joints. -The sensory receptors for somatic sensations are distributed unevenly—some parts of the body surface are densely populated with receptors, and others contain only a few.

night blindness

-as a result, the person cannot distinguish between red and green. Prolonged vitamin A deficiency and the resulting below-normal amount of rhodopsin

common defects - presbyopia

-as lens ages, it loses elasticity -even when tension on the suspensory ligaments is relieved, lens retains its elongated shape -Failure to 'round up' means the image of close-up objects cannot be focused on the retina -Loss of this ability to accommodate means the 'aged' eye can't focus on close-up object -result: reading glasses

Jim and Alex take the two-point discrimination test. Alex first detects 2 points on his back when the calipers were at a distance of 2 inches and Jim first detects 2 points on his forearm when the calipers were at a distance of 1.5 inches. 1) Which body area is less represented in the primary somatosensory cortex?

-back

The perception of slow pain

-begins a second or more after a stimulus is applied. It then gradually increases in intensity over a period of several seconds or minutes. Impulses for slow pain conduct along small-diameter, unmyelinated C fibers. -This type of pain, which may be excruciating, is also referred to as chronic, burning, aching, or throbbing pain. -Slow pain can occur both in the skin and in deeper tissues or internal organs. An example is the pain associated with a toothache. -You can perceive the difference in onset of these two types of pain best when you injure a body part that is far from the brain because the conduction distance is long. -When you stub your toe, for example, you first feel the sharp sensation of fast pain and then feel the slower, aching sensation of slow pain.

process of sensation

-begins in a sensory receptor, which can be either a specialized cell or the dendrites of a sensory neuron. - A given sensory receptor responds vigorously to one particular kind of stimulus, a change in the environment that can activate certain sensory receptors. -A sensory receptor responds only weakly or not at all to other stimuli. This characteristic of sensory receptors is known as selectivity -1st step=stimulation of the sensory receptor

somatic senses

-body surface -exteroceptors -tactile sensations, pain, proprioception -touch, pressure, vibration, itch, and tickle

Slowly adapting receptors

-by contrast, adapt slowly and continue to trigger nerve impulses as long as the stimulus persists. -Slowly adapting receptors monitor stimuli associated with pain, body position, and chemical composition of the blood.

myopia

-consequences of the shape of the eye -'long' eyeball -nearsightedness: uncorrected images falls in front of retina -which occurs when the eyeball is too long relative to the focusing power of the cornea and lens, or when the lens is thicker than normal, so an image converges in front of the retina. Myopic individuals can see close objects clearly, but not distant objects

hyperopia

-consequences of the shape of the eye -'short' eyeball -farsightedness: uncorrected images fall behind retina -the eyeball length is short relative to the focusing power of the cornea and lens, or the lens is thinner than normal, so an image converges behind the retina. Hyperopic individuals can see distant objects clearly, but not close ones

structures and chambers of the eye:

-cornea -aqueous humor -lens -sclera -choroid -vitreous humor -retina -optic nerve

Thermoreceptors

-detect changes in temperature. -Temperature receptors adapt to a constant stimulus by decreasing the number of action potentials they send over time.

Chemoreceptors

-detect chemicals in the mouth (taste), nose (smell), and body fluids

Photoreceptors

-detect light that strikes the retina of the eye

Osmoreceptors

-detect the osmotic pressure of body fluids

wavelength

-distance between two consecutive peaks of an electromagnetic wave -range from short to long; for example, gamma rays have wavelengths smaller than a nanometer, and most radio waves have wavelengths greater than a meter.

lacrimal glands

-each about the size and shape of an almond, secrete lacrimal fluid, which drains into 6-12 excretory lacrimal ducts that empty tears onto the surface of the conjunctiva of the upper lid -supplied by parasympathetic fibers of the facial (VII) nerves

convergence

-efers to this medial movement of the two eyeballs so that both are directed toward the object being viewed, for example, tracking a pencil moving toward your eyes. -The nearer the object, the greater the degree of convergence needed to maintain binocular vision. The coordinated action of the extrinsic eye muscles brings about convergence.

Electromagnetic radiation

-energy in the form of waves that radiates from the sun. -There are many types of electromagnetic radiation, including gamma rays, x-rays, UV rays, visible light, infrared radiation, microwaves, and radio waves

From superficial to deep, each eyelid consists of:

-epidermis, dermis, subcutaneous tissue, fibers of the orbicularis oculi muscle, a tarsal plate, tarsal glands, and conjunctiva

parts of gustation

-epiglottis -palatine tonsil -lingual tonsil -vallate papilla -fungiform papilla -filiform papilla -foliate papilla

group sensory receptors is based on the location of the receptors and the origin of the stimuli that activate them:

-exteroceptors -interoceptors -proprioceptors

visible light

-eyes are responsible for the detection of this -the part of the electromagnetic spectrum with wavelengths ranging from about 400 to 700 nm. -Visible light exhibits colors: The color of visible light depends on its wavelength

parts of the body used for smell:

-frontal lobe of cerebrum -olfactory tract -olfactory bulb -olfactory epithelium -nose -superior nasal concha

Gustatory microvilli

-gustatory hairs) project from each gustatory receptor cell to the external surface through the taste pore, an opening in the taste bud.

referred pain

-in many instances of visceral pain, the pain is felt in or just deep to the skin that overlies the stimulated organ, or in a surface area far from the stimulated organ

taste aversion

-in which people and animals quickly learn to avoid a food if it upsets the digestive system

special senses

-include the sensory modalities of: - smell: ('olfaction') -in sense organs in nose - taste: ('gustation') -in sense organs in tongue -sight: ('vision') -in sense organ which is the eye -hearing: ('audition') -in sense organ in inner ea -equilibrium or balance: ('equilibrium') -in sense organs in inner ea

tactile sensations

-include touch, pressure, vibration, itch, and tickle. -they arise by activation of some of the same types of receptors -Tactile receptors in the skin or subcutaneous layer include corpuscles of touch, hair root plexuses, type I cutaneous mechanoreceptors, type II cutaneous mechanoreceptors, lamellated corpuscles, and free nerve endings

chalazion

-infection of the tarsal glands produces a tumor or cyst on the eyelid

visceral senses

-internal organs!! -interoceptors -organ pressure, stretch, chemicals, nausea, hunger, etc -provide information about conditions within internal organs, for example, pressure, stretch, chemicals, nausea, hunger, and temperature..

lacrimal apparatus

-is a group of structures that produces and drains lacrimal fluid or tears in a process called lacrimation

hyaloid canal

-is a narrow channel that is inconspicuous in adults and runs through the vitreous body from the optic disc to the posterior aspect of the lens. In the fetus, it is occupied by the hyaloid artery

acupuncture

-is a type of therapy that originated in China over 2000 years ago. -It is based on the idea that vital energy called qi flows through the body along pathways called meridians.

macula lutea

-is in the exact center of the posterior portion of the retina, at the visual axis of the eye -Region in the center of visual field for vision -Region contains primarily cone photoreceptors and very few to none of the rod photoreceptors -The center of the macula lutea is the fovea centralis, the central point in our field of visio

perception

-is the conscious interpretation of sensations and is primarily a function of the cerebral cortex. -We have no perception of some sensory information because it never reaches the cerebral cortex. -For example, certain sensory receptors constantly monitor the pressure of blood in blood vessels.

vascular tunic

-is the middle layer of the eyeball. It is composed of three parts: choroid, ciliary body, and iris

Kinesthesia

-is the perception of body movements

choroid

-is the posterior portion of the vascular tunic, lines most of the internal surface of the sclera. Its numerous blood vessels provide nutrients to the posterior surface of the retina. -The choroid also contains melanocytes that produce the pigment melanin, which causes this layer to appear dark brown in color. Melanin in the choroid absorbs stray light rays, which prevents reflection and scattering of light within the eyeball. -As a result, the image cast on the retina by the cornea and lens remains sharp and clear -Provides blood supply and absorbs scattered light

Ophthalmology

-is the science that deals with the eyes and their disorders.

scleral venous sinus

-junction of the sclera and cornea is an opening -A fluid called aqueous humor, which will be described later, drains into this sinus

Jim and Alex take the two-point discrimination test. Alex first detects 2 points on his back when the calipers were at a distance of 2 inches and Jim first detects 2 points on his forearm when the calipers were at a distance of 1.5 inches. 2) Does a region of the body with lesser representation in the primary somatosensory cortex have smaller or larger receptive fields in comparison to a body region that is more highly represented?

-larger

vitreous chamber

-larger posterior cavity of the eyeball -which lies between the lens and the retina. -Contains vitreous body that helps maintain shape of eyeball and keeps retina attached to choroid.

life span of gustatory receptor cells

-life span of about 10 days -This is why it does not take taste receptors on the tongue too long to recover from being burned by that too hot cup of coffee or cocoa. -At their base, the gustatory receptor cells synapse with dendrites of the first-order neurons that form the first part of the gustatory pathway

palpebral conjunctiva

-lines the inner aspect of the eyelids

Cold receptors

-located in the stratum basale of the epidermis and are attached to medium-diameter, myelinated A fibers, although a few connect to small-diameter, unmyelinated C fibers. -Temperatures between 10° and 35°C (50 − 95°F) activate cold receptors

detached retina

-may occur due to trauma, such as a blow to the head, in various eye disorders, or as a result of age-related degeneration. -The detachment occurs between the neural portion of the retina and the pigmented epithelium. Fluid accumulates between these layers, forcing the thin, pliable retina to billow outward. -The result is distorted vision and blindness in the corresponding field of vision.

LASIK

-most common type of refractive surgery -After anesthetic drops are placed in the eye, a circular flap of tissue from the center of the cornea is cut. The flap is folded out of the way, and the underlying layer of cornea is reshaped with a laser, one microscopic layer at a time. -A computer assists the physician in removing very precise layers of the cornea. After the sculpting is complete, the corneal flap is repositioned over the treated area. -A patch is placed over the eye overnight, and the flap quickly reattaches to the rest of the cornea.

Where does refraction take place in the eye?

-most occurs in cornea -lens does critical fine tuning

three types of proprioceptors:

-muscle spindles, tendon organs, and joint kinesthetic receptors

constriction of the pupil

-narrowing of the diameter of the hole through which light enters the eye due to the contraction of the circular muscles of the iris. -This autonomic reflex occurs simultaneously with accommodation and prevents light rays from entering the eye through the periphery of the lens. -Light rays entering at the periphery would not be brought to focus on the retina and would result in blurred vision. The pupil, as noted earlier, also constricts in bright light.

The perception of fast pain

-occurs very rapidly, usually within 0.1 second after a stimulus is applied, because the nerve impulses propagate along medium-diameter, myelinated A fibers. -This type of pain is also known as acute, sharp, or pricking pain. The pain felt from a needle puncture or knife cut to the skin is fast pain. -Fast pain is not felt in deeper tissues of the body.

refraction

-occurs when light passes from one medium (e.g., air) into another (e.g., water) -When light rays traveling through a transparent substance (such as air) pass into a second transparent substance with a different density (such as water), they bend at the junction between the two substances -As light rays enter the eye, they are refracted at the anterior and posterior surfaces of the cornea. Both surfaces of the lens of the eye further refract the light rays so they come into exact focus on the retina.

parts of olfactory receptor cells

-olfactory receptor cell -olfactory cilia -dendrite -supporting cell

The upper and lower eyelids

-or palpebrae, shade the eyes during sleep, protect the eyes from excessive light and foreign objects, and spread lubricating secretions over the eyeballs -The upper eyelid is more movable than the lower and contains in its superior region the levator palpebrae superioris muscle

interoceptors

-or visceroceptors are located in blood vessels, visceral organs, muscles, and the nervous system and monitor conditions in the internal environment. -The nerve impulses produced by interoceptors usually are not consciously perceived; occasionally, however, activation of interoceptors by strong stimuli may be felt as pain or pressure.

bulbar conjunctiva

-passes from the eyelids onto the surface of the eyeball, where it covers the sclera (the "white" of the eye) but not the cornea, which is a transparent region that forms the outer anterior surface of the eyeball.

intraocular pressure

-pressure in the eye -produced mainly by the aqueous humor and partly by the vitreous body; normally it is about 16 mmHg (millimeters of mercury). -The intraocular pressure maintains the shape of the eyeball and prevents it from collapsing. Puncture wounds to the eyeball may lead to the loss of aqueous humor and the vitreous body. -This in turn causes a decrease in intraocular pressure, a detached retina, and in some cases blindness.

lacrimal fluid

-produced by these glands is a watery solution containing salts, some mucus, and lysozyme a protective bactericidal enzyme. -The fluid protects, cleans, lubricates, and moistens the eyeball. After being secreted from the lacrimal gland, lacrimal fluid is spread medially over the surface of the eyeball by the blinking of the eyelids. -Each gland produces about 1 mL of lacrimal fluid per day.

ciliary processes

-protrusions or folds on the internal surface of the ciliary body. They contain blood capillaries that secrete aqueous humor.

electromagnetic spectrum

-range of electromagnetic radiation

general senses

-refer to both somatic senses and visceral senses.

sensory function: special senses/somatic (ex)

-require specialized organs/ receptors are all concentrated in specific locations in the head -light -sound -gravity -taste -smell

Nociceptors

-respond to painful stimuli resulting from physical or chemical damage to tissue.

vibration

-result from rapidly -repetitive sensory signals from tactile receptors -receptors for vibration sensations are lamellated corpuscles and corpuscles of touch. -A -lamellated corpuscle, or pacinian corpuscle (pa-SIN-?-an), consists of a nerve ending surrounded by a multilayered connective tissue capsule that resembles a sliced onion. -Like corpuscles of touch, -lamellated corpuscles adapt rapidly. They are found in the dermis, subcutaneous layer, and other body tissues. -Pacinian corpuscles -respond to high-frequency vibrations, such as the vibrations you feel when you use a power drill or other electric tools.

visceral pain

-results from stimulation of nociceptors in visceral organs. -If stimulation is diffuse (involves large areas), visceral pain can be severe. Diffuse stimulation of visceral nociceptors might result from distension or ischemia of an internal organ. -For example, a kidney stone or a gallstone might cause severe pain by obstructing and distending a ureter or bile duct.

types of pain

-slow and fast

two types of photoreceptors

-specialized cells in the photoreceptor layer that begin the process by which light rays are ultimately converted to nerve impulses -rods and cones -Each retina has about 6 million cones and 120 million rods.

basal cells of gustation

-stem cells found at the periphery of the taste bud near the connective tissue layer, produce supporting cells, which then develop into gustatory receptor cells.

Basal cells

-stem cells located between the bases of the supporting cells. They continually undergo cell division to produce new olfactory receptor cells, which live for only about two months before being replaced. -This process is remarkable considering that olfactory receptor cells are neurons, and as you have already learned, mature neurons are generally not replaced.

deep somatic pain

-stimulation of receptors in skeletal muscles, joints, tendons, and fascia

Six extrinsic eye muscles that move each eye:

-superior rectus, inferior rectus, lateral rectus, medial rectus, superior oblique, and inferior oblique -They are supplied by the oculomotor (III), trochlear (IV), or abducens (VI) nerves

There are four modalities of somatic sensation:

-tactile, thermal, pain, and proprioceptive.

sclera

-the "white" of the eye, is a layer of dense connective tissue made up mostly of collagen fibers and fibroblasts. -The sclera covers the entire eyeball except the cornea; it gives shape to the eyeball, makes it more rigid, protects its inner parts, and serves as a site of attachment for the extrinsic eye muscles. -Provides shape and protects inner parts.

weight discrimination

-the ability to assess the weight of an object. -This type of information helps you to determine the muscular effort necessary to perform a task. For example, as you pick up a shopping bag, you quickly realize whether it contains books or feathers, and you then exert the correct amount of effort needed to lift it.

vision

-the act of seeing, is extremely important to human survival because it allows us to view potentially dangerous objects in our surroundings. -More than half the sensory receptors in the human body are located in the eyes, and a large part of the cerebral cortex is devoted to processing visual information

lens divides the interior of the eyeball into two cavities:

-the anterior cavity and vitreous chamber.

iris

-the colored portion of the eyeball, is shaped like a flattened donut. It is suspended between the cornea and the lens and is attached at its outer margin to the ciliary processes. It consists of melanocytes and circular and radial smooth muscle fibers. -The amount of melanin in the iris determines the eye color. The eyes appear brown to black when the iris contains a large amount of melanin, blue when its melanin concentration is very low, and green when its melanin concentration is moderate. -A principal function of the iris is to regulate the amount of light entering the eyeball through the pupil

sensation

-the conscious or subconscious awareness of changes in the external or internal environment -nature of the sensation and the type of reaction generated vary according to the ultimate destination of nerve impulses (action potentials) that convey sensory information to the CNS

filiform papillae

-the entire surface of the tongue has this -These pointed, threadlike structures contain tactile receptors but no taste buds. They increase friction between the tongue and food, making it easier for the tongue to move food in the oral cavity. Physiology of Gustation

the accessory structures of the eye

-the eyelids, eyelashes, eyebrows, the lacrimal (tear-producing) apparatus, and extrinsic eye muscles.

Olfactory receptor cells

-the first-order neurons of the olfactory pathway. -Each olfactory receptor cell is a bipolar neuron with an exposed knob-shaped dendrite and an axon projecting through the cribriform plate that ends in the olfactory bulb.

How is light entry into the eye controlled?

-the iris regulates light entry

itch

-the itch sensation results from stimulation of free nerve endings by certain chemicals, such as bradykinin or histamine, or antigens in mosquito saliva injected from a bite, often because of a local inflammatory response (bradykinin, a kinin, is a potent vaso-dilator). -Scratching usually alleviates itching by activating a pathway that blocks transmission of the itch signal through the spinal cord.

Structure of the eyelid

-the lateral commissure, which is narrower and closer to the temporal bone, and the medial commissure, which is broader and nearer the nasal bone. -In the medial commissure is a small, reddish elevation, the lacrimal caruncle, which contains sebaceous (oil) glands and sudoriferous (sweat) glands. -The whitish material that sometimes collects in the medial commissure comes from these glands.

near point of vision

-the minimum distance from the eye that an object can be clearly focused with maximum accommodation. This distance is about 10 cm (4 in.) in a young adult.

emmetropic eye

-the normal eye

Phototransduction

-the process by which light energy is converted into a receptor potential in the outer segment of a photoreceptor. In most sensory systems, activation of a sensory receptor by its adequate stimulus triggers a depolarizing receptor potential.

optic disc

-the site where the optic (II) nerve exits the eyeball. -also called the blind spot. Because it contains no rods or cones, we cannot see images that strike the blind spot. Normally, you are not aware of having a blind spot, but you can easily demonstrate its presenc

anterior cavity

-the space anterior to the lens—consists of two chambers. 1. The anterior chamber lies between the cornea and the iris. 2. The posterior chamber lies behind the iris and in front of the zonular fibers and lens -Contains aqueous humor that helps maintain shape of eyeball and supplies oxygen and nutrients to lens and cornea.

fibrous tunic

-the superficial layer of the eyeball and consists of the anterior cornea and posterior sclera

taste thresholds

-the threshold for taste varies for each of the primary tastes. The threshold for bitter substances, such as quinine, is lowest. Because poisonous substances often are bitter, the low threshold (or high sensitivity) may have a protective function. -The threshold for sour substances (such as lemon), as measured by using hydrochloric acid, is somewhat higher. -The thresholds for salty substances (represented by sodium chloride), and for sweet substances (as measured by using sucrose) are similar, and are higher than those for bitter or sour substances.

retina

-third and inner layer of the eyeball -lines the posterior three-quarters of the eyeball and is the beginning of the visual pathway -The surface of the retina is the only place in the body where blood vessels can be viewed directly and examined for pathological changes, such as those that occur with hypertension, diabetes mellitus, cataracts, and age-related macular disease. -Receives light and converts it into receptor potentials and nerve impulses. Output to brain via axons of ganglion cells, which form optic (II) nerve

dark adaption

-when you enter a darkened room such as a theater, your visual system undergoes -its sensitivity increases slowly over many minutes. -The difference in the rates of bleaching and regeneration of the photopigments in the rods and cones accounts for some (but not all) of the sensitivity changes during light and dark adaptation.

eyebrows

-which arch transversely above the upper eyelids, help protect the eyeballs from foreign objects, perspiration, and the direct rays of the sun

warm receptors

-which are not as abundant as cold receptors, are located in the dermis and are attached to small-diameter, unmyelinated C fibers; they are activated by temperatures between 30° and 45°C (86 − 113°F). -Cold and warm receptors both adapt rapidly at the onset of a stimulus, but as noted earlier in the chapter they continue to generate impulses at a lower frequency throughout a prolonged stimulus

olfactory bulbs

-which contain ball-like arrangements called glomeruli

Astigmitism

-which either the cornea or the lens has an irregular curvature. As a result, parts of the image are out of focus, and thus vision is blurred or distorted.

eyelashes

-which project from the border of each eyelid

During a visit to the ophthalmologist you are asked to perform an astigmatism test using the chart above, during the procedure some lines seem to be darker than the others. Would that be a symptom of astigmatism?

-yes

the wall of the eyeball consists of three layers:

1) fibrous tunic (2) vascular tunic (3) retina (inner tunic).

gustatory pathway

1. 1st order gustatory sensory nerves in three cranial nerves (VII, IX and X) send APs to the gustatory nucleusin the medulla. 2.Axons then carry taste signals to the limbic system, hypothalamus and thalamus 3. some axons carry taste signals from the thalamus to the primary gustatory area in the parietal lobes of the cerebral cortex for conscious perception of taste

the olfactory pathway

1. 1st order olfactory sensory nerves (cranial nerve I) send APs to the olfactory bulb located below the frontal lobes 2.Some olfactory bulb neuron axons then carry APs to the primary olfactory-area in cerebral cortex area in the temporal lobes of the cerebral cortex for conscious perception of smell

Based on stimulus modality, there are three overall types of stimuli detected for special senses:

1. Hearing, Balance (mechanoreceptors for wave motion and pull of gravity) 2. Taste, Smell (chemoreceptors for 'tastants' and 'odorants') 3. Sight ('photoreceptors' for photons of light)

Two critical issues associated with the special sense of vision:

1. How is an image formed and displayed on the sensory surface of the eye? 2. How is the stimulus of a photon striking the sensory surface 'transduced' into an electrical event?

the operation of a photoreceptor in the absence of light

1. In darkness, cis-retinal is the form of retinal associated with the photopigment of the photoreceptor. Photopigment molecules are present in the disc membranes of the photoreceptor outer segment. 2. Another important occurrence during darkness is that there is a high concentration of cyclic GMP (cGMP) in the cytosol of the photoreceptor outer segment. This is due to the continuous production of cGMP by the enzyme guanylyl cyclase in the disc membrane. 3. After it is produced, cGMP binds to and opens nonselective cation channels in the outer segment membrane. These cGMP-gated channels mainly allow Na+ ions to enter the cell. 4. The inflow of Na+, called the dark current, depolarizes the photoreceptor. As a result, in darkness, the membrane potential of a photoreceptor is about −40 mV. This is much closer to zero than a typical neuron's resting membrane potential of −70 mV. 5. The depolarization during darkness spreads from the outer segment to the synaptic terminal, which contains voltage-gated Ca2+ channels in its membrane. The depolarization keeps these channels open, allowing Ca2+ to enter the cell. The entry of Ca2+ in turn triggers exocytosis of synaptic vesicles, resulting in tonic release of large amounts of neurotransmitter from the synaptic terminal. The neurotransmitter in rods and cones is the amino acid glutamate (glutamic acid). At synapses between rods and some bipolar cells, glutamate is an inhibitory neurotransmitter: It triggers inhibitory postsynaptic potentials (IPSPs) that hyperpolarize the bipolar cells and prevent them from sending signals on to the ganglion cells

Photopigments respond to light in the following cyclical process

1. Isomerization: In darkness, retinal has a bent shape, called cis-retinal, which fits snugly into the opsin portion of the photopigment. When cis-retinal absorbs a photon of light, it straightens out to a shape called trans-retinal. This cis-to-trans conversion is called isomerization and is the first step in visual transduction. After retinal isomerizes, chemical changes occur in the outer segment of the photoreceptor. These chemical changes lead to the production of a receptor potential ( 2. Bleaching: In about a minute, trans-retinal completely separates from opsin. Retinal is responsible for the color of the photopigment, so the separation of trans-retinal from opsin causes opsin to look colorless. Because of the color change, this part of the cycle is termed bleaching of photopigment. 3. Conversion: An enzyme called retinal isomerase converts trans-retinal back to cis-retinal. 4. Regeneration: The cis-retinal then can bind to opsin, reforming a functional photopigment. This part of the cycle—resynthesis of a photopigment—is called regeneration

Phototransduction by Rods and Role of Retinal Layers:

1. Light photon actives rhodopsin 2.This activates an enzyme that breaks down cyclic GMP (cGMP) 3.cGMP-gated sodium channels close 4.The rod hyperpolarizes 5.Glutamate release is reduced 6.Low glutamate release by photoreceptors results in APs from ganglion cel

visual pathway

1. Most of the retinal ganglion cell axons (cranial nerve II) send APs to the lateral geniculate nucleus of the thalamus-NOTE: -50% of retinal ganglion cell axons decussate (cross over) at the optic chias 2. Neuron axons from the lateral geniculate nucleus then carry visual signals to the primary visual are in the occipital lobe of the cerebral cortex for conscious perception of sight -right hemisphere perceives the left field of vision from both eyes, and left hemisphere perceives the right field of vision from both eyes

sensory transduction-common steps:

1. Stimulus arrives at receptor and alters membrane potential of receptor -results in a 'graded potential' -graded potentials can be depolarizing (EPSP) or hyperpolarizing (IPSP) 2. The rate of EPSPs generation in the sensory neuron determines the rate of nerve impulse (AP) production in them 3. APs travel to CNS along a specific afferent pathway 4.CNS interprets/processes these incoming sign

dissection of cow eye

1. Using gloves, obtain a cow eye and rinse it to remove excess preservative. 2. The posterior portion of the eye may be encased in adipose tissue. Carefully remove the adipose tissue protecting the optic nerve. 3. Identify the external eye structures: cornea, sclera, optic nerve, and extrinsic eye muscles. The preservative causes the cornea to change from being transparent and smooth to opaque and wrinkled 4. Using the point of a scalpel, punch an opening 1/414-inch posterior to the cornea through the very tough sclera. Be careful not to squeeze the eyeball too tightly or liquid may squirt out. Use the scissors to cut an incision all the way around the eyeball, separating it into two parts. 5. Carefully separate the anterior and posterior parts of the eyeball so the vitreous body remains in the posterior part of the eyeball and the lens in the anterior part. 6. Carefully remove the lens, noting the transparent suspensory ligaments that are attached to the lens. 7. Using Figure 24.5(b), identify the following structures in the anterior portion of the eyeball: pupil, iris, and ciliary muscle. 8. Carefully remove the vitreous body from the posterior portion of the eyeball. Refer to Figure 24.5(b) to identify the structures in the posterior portion of the eyeball. The retina, a thin beige layer, will probably separate from the choroid. The only point of attachment of the retina to the wall of the eyeball is at the optic disc. 9. Pull the retina away from the choroid, the dark middle layer of the eyeball that contains the pigment melanin. The choroid of the cow's eye has an iridescent reflecting surface called the tapetum lucidum that is not found in humans. The tapetum lucidum reflects light within the eye and enables animals to see in low-light conditions. 10. Separate the choroid from the sclera. Observe how the three coats or tunics—the retina, choroid, and sclera—form the wall of the eyeball.

The absorption of light and isomerization of retinal initiates chemical changes in the photoreceptor outer segment that allow photo transduction to occur

1. When light strikes the retina, cis-retinal undergoes isomerization to trans-retinal. 2. Isomerization of retinal causes activation of a G protein known as transducin that is located in the disc membrane. 3. Transducin in turn activates an enzyme called cGMP phosphodiesterase, which is also present in the disc membrane. 4. Once activated, cGMP phosphodiesterase breaks down cGMP. The breakdown of cGMP lowers the concentration of cGMP in the cytosol of the outer segment. 5. As a result, the number of open cGMP-gated channels in the outer segment membrane is reduced and Na+ inflow decreases. 6. The decreased Na+ inflow causes the membrane potential to drop to about −65 mV, thereby producing a hyperpolarizing receptor potential. 7. The hyperpolarization spreads from the outer segment to the synaptic terminal, causing a decrease in the number of open voltage-gated Ca2+ channels. Ca2+ entry into the cell is reduced, which decreases the release of neurotransmitter from the synaptic terminal. Dim lights cause small and brief receptor potentials that partially turn off neurotransmitter release; brighter lights elicit larger and longer receptor potentials that shut down neurotransmitter release more completely. Thus, light excites the bipolar cells that synapse with rods by turning off the release of an inhibitory neurotransmitter! The excited bipolar cells subsequently stimulate the ganglion cells to form action potentials in their axons

many general senses that are simplified to 5 types (based on stimulus modality)

1. pain ('nociceptors') 2.Temperature ('thermoreceptors') 3.Tactile sensation (touch, pressure, tickle, proprioception, vibration, by 'mechanoreceptors') 4.Chemical stimuli ('chemoreceptors' for O2, itch, etc.) 5.Osmotic pressure ('osmoreceptor) -receptors distributed throughout body (particularly on body surfaces, and not collected within specialized 'sense organs')

For a sensation to arise, the following four events typically occur

1. stimulation of the sensory receptor 2. transduction of the stimulus 3. generation of nerve impulses 4. integration of sensory input

sensory function: general senses (ex)

1.Itch 2.Oxygen levels 3.Pain 4.Pressure 5.Proprioception 6.Stretch 7.Temperature 8.Tickle 9.Touch 10. Vibration and more

Three types of taste buds

1.Vallate 2.Fungiform 3.filiform

structural and functional characteristics of sensory receptors can be used to group them into these different classes:

(1) microscopic structure (2) location of the receptors and the origin of stimuli that activate them (3) type of stimulus detected.

olfactory epithelium

- Olfactory receptor cells detect odorants -Odorants must first dissolve in mucus to bind to receptors -Olfactory receptors are neurons, and their axons are cranial nerve -Olfactory glands produce mucus for chemosensation -Supporting cells provide physical and functional support -Basal cells are stem cells for olfactory receptors -Parts of CN I pass through Cribriform plate of ethmoid bone -Cranial nerve I synapses with Mitral cells in the olfactory bulb -Mitral cell axons travel along the olfactory tract to deliver sensory information to the brain

absorption of light by a photopigment (visual pigment):

- a colored protein that undergoes structural changes when it absorbs light, in the outer segment of a photoreceptor -The first step in visual transduction:

receptor potentials

- in sensory cells cause neurotransmitter release, which causes an EPSPin associated sensory neuron -A sensory receptor responds to a stimulus by generating a graded potential

refraction abnormalities

myopia, hyperopia, astigmatism,