Senses

Stimuli

Changes in sensory information Detected by receptors Some pleasurable, some alert to danger, others with moment-to-moment information

odorant molecules

Chemicals that stimulate olfactory receptor cells enter the nasal cavity and dissolve at least partially in the watery fluids that surround the cilia before they can bond to receptor proteins on the cilia and be detected. Foods, flowers, and many other objects and substances release odorant molecules. An odorant molecule may bind to several of the almost 400 types of olfactory membrane receptors that are part of the olfactory receptor cells, depolarizing these cells and thereby generating action potentials if the depolarization reaches threshold

Modiolus

Core of cochlea thin, bony shelf (spiral lamina) extends out from the core and coils around it within the tube

ciliary body

thickest part of the middle tunic, extends anteriorly and inward from the choroid coat and forms a ring within the front of the eye immediately anterior to choroid composed of ciliary muscles and ciliary processes

retina

thin and delicate, but its structure is complex. It has distinct layers, including retinal pigment epithelium, neurons, nerve fibers, and limiting membranes five major groups of retinal neurons Outer pigmented layer and inner neural layer Pigmented layer - internal to choroid and attached to it provides vitamin A for photoreceptors (light-detecting cells) light rays passing through inner layer absorbed here Inner neural layer houses photoreceptors and associated neurons responsible for absorbing light rays, converts into nerve signals transmitted to brain under control of parasympathetic division via CN III

iris

thin diaphragm mostly composed of connective tissue and smooth muscle. Seen from the outside, it is the colored portion of the eye most anterior region colored portion of the eye composed of two layers of pigment-forming cells two groups smooth muscle fibers vascular and nervous structures peripheral edge continuous with ciliary body

Inner neural layer of Ora serrata

adjacent to posterior cavity, formed by ganglionic cells continued convergence with bipolar neurons axons extending from here through optic disc

Light passes through

air, cornea, aqueous humor lens, vitreous humor, inner two layers of retina

Eye Color

amount and distribution of melanin in the irises and the density of the tissue in the body of the iris determine eye color. If melanin is present only in the epithelial cells on the iris's posterior surface, the iris reflects more colors of light, and appears blue or green. When the same distribution of melanin is denser in the body of the iris, eye color is gray. When melanin is within the body of the iris as well as in the posterior epithelial covering, the iris appears brown

lacrimal sac

fluid moves into which lies in a deep groove of the lacrimal bone, and then into the nasolacrimal duct, which empties into the nasal cavity

Eyelids

form movable anterior covering over eye surface, formed by fibrous core (tarsal plate), tarsal muscles, orbicularis oculi, and tarsal glands thin covering of skin palpebra composed of four layers skin, muscle, connective tissue, and conjunctiva thinnest of the body, covers the lid's outer surface and fuses with its inner lining near the margin of the lid

utricle and a saccule

larger utricle communicates with (is continuous with) the saccule and the membranous portions of the semicircular canals; the saccule, in turn, communicates with the cochlear duct

Vallate papillae

least numerous, largest papillae arranged in inverted V on posterior dorsal tongue, each surrounded by deep, narrow depression most taste buds housed here

light adapted

light sensitivity of the eyes decreases greatly

rhodopsin

light-sensitive pigment in rods visual purple, and it is embedded in membranous discs stacked in these receptor cells molecules break down into molecules of a colorless protein called opsin and a yellowish organic molecule called retinal (retinene) synthesized from vitamin A. opsin in rods involved in transduction of dim light

iodopsins

light-sensitive pigments of cones similar to rhodopsin

visceral sensory receptors

located in walls of viscera respond to temperature, chemicals, stretch, pain

Muscle spindles

located throughout skeletal muscles. Each spindle consists of several small, modified skeletal muscle fibers (intrafusal fibers) enclosed in a connective tissue sheath. Each intrafusal fiber has near its center a specialized nonstriated region with the end of a sensory nerve fiber wrapped around it striated portions of the intrafusal fiber contract to keep the spindle taut at different muscle lengths. Thus, if the whole muscle is stretched, the muscle spindle is also stretched, triggering sensory impulses on its nerve fiber. These sensory fibers synapse in the spinal cord with lower motor neurons leading back to the same muscle. In this way, stretch of the muscle spindle triggers impulses that contract the skeletal muscle of which it is a part

umami

long been recognized in Japan only recently come to the attention of Western taste researchers. Umami arises from the binding of certain amino acids, including glutamic acid and aspartic acid, to specific receptors. The flavor enhancer monosodium glutamate (MSG), used in many prepared foods, is formed from glutamic acid and also stimulates umami receptors.

scala tympani

lower compartment extends from the apex of the spiral to a membrane-covered opening in the wall of the inner ear facing the tympanic cavity, called the round window filled with perilymph

stretch receptors

lungs sense degree of inflation

Foliate papillae

not well developed in humans, extend as ridges on posterior lateral tongue house only a few taste buds through early childhood

Frequency

number of waves moving past a point during specific time, measured in hertz (Hz) classified as high, medium, or low - interpreted as the pitch of a sound region of spiral organ stimulated by pressure waves varies according to sound frequency high-frequency sounds stimulate near oval window, low frequency sounds stimulate near helicotrema

Refractive index

number that represents comparative density of mediums

Sensation

occurs when sensory neurons reach threshold and the resulting action potentials cause the brain to become aware of that sensory event. A perception occurs when the brain interprets those sensory impulses. Thus, pain is a sensation, but realizing that you have just stepped on a tack is a perception

rays

often described as moving in straight lines

Peripheral retina

remaining regions contains primarily rods functions most effectively in low light

Tarsal Glands

sebaceous glands, produce secretion to prevent tear overflow keep eyelids from adhering

nerve fibers of three of these groups

photoreceptors, bipolar neurons, and ganglion cells—provide a direct pathway for impulses triggered in the photoreceptors to the optic nerve and brain

auricle

pinna include an outer, funnel-like structure funnel-shaped visible part of ear skin-covered, elastic cartilage-supported structure protects entry into ear and directs sound waves in

Amacrine cells

positioned between bipolar and ganglion cells process visual information between bipolar and ganglionic neurons Action potentials produced only by amacrine and ganglion cells others producing graded potentials

Intensity

refers to sound's loudness, measured in decibels (dB) inaudible sound, no decibels louder sounds increase distortion of specific region of spiral organ, increases rate of nerve signals to brain

fovea centralis

region of the retina that produces the sharpest vision.

Glandular cells of the conjunctiva

secrete a tearlike liquid that, together with the secretion of the lacrimal gland, moistens and lubricates the surface of the eye and the lining of the lids

parts of the labyrinths

semicircular canals vestibule Cochlea

projection

sensation forms, the cerebral cortex interprets it as coming from the receptors being stimulated. This process, which is closely related to perception

Proprioceptors

sense changes in the tensions of muscles and tendons detect body and limb movements detect skeletal muscle contraction and stretch, located in muscles, tendons, and joints provide awareness of body joint position and skeletal muscle contraction

Thermoreceptors

sense temperature change. respond to changes in temperature present in both skin and hypothalamus components of reflexes regulating body temperature

Taste buds

special organs of taste scattered in the roof of the mouth, the linings of the cheeks, and the walls of the pharynx be tasted must dissolve in saliva, which is the watery fluid rapidly undergo sensory adaptation have appearance of an onion enclosed by supporting cells contain numerous taste receptors, gustatory cells (only a 7 to 10 day life span) - constantly replaced by basal cells declining taste after age 50 - reduction in gustatory cell replacement and number of taste buds

alevator palpebrae superioris

superioris muscle arise from the roof of the orbit and are inserted in the connective tissue of the upper lid fibers contract, the upper lids are raised, and the eye opens

convex

surface causes light waves to converge About 75 percent of the refraction occurs when light passes from the air through the convex surface of the cornea. The light is refracted again by the convex surface of the lens and to a lesser extent at the surfaces of the fluids in the eye chambers. The lens is the only one of these structures that can change its amount of refraction to achieve a focused image (accommodation).

concave

surface causes light waves to diverge

Tactile corpuscles

(Meissner's) are small, oval masses of flattened connective tissue cells in connective tissue sheaths. Two or more sensory fibers branch into each corpuscle and end within it as tiny knobs. abundant in hairless areas of skin, such as the lips, fingertips, palms, soles, nipples, and external genital organs. They provide fine touch, such as distinguishing two points on the skin where an object touches, to judge its texture large, encapsulated oval receptors, formed from dendrites enclosed by modified neurolemmocytes, covered with dense irregular connective tissue found in dermal papillae of skin especially lips, palms, eyelids, nipples, genitals phasic receptors for discriminative touch

Lamellated corpuscles

(Pacinian) relatively large, ellipsoidal structures composed of connective tissue fibers and cells. They are common in the deeper dermal tissues of the hands, feet, penis, clitoris, urethra, and breasts and also in the connective tissue capsules of synovial joints. Heavier pressure and stretch stimulate lamellated corpuscles. They also detect vibrations in tissues

vestibular membrane

(Reissner's membrane) duct is separated from the scala vestibuli and from the scala tympani by a basilar membrane

auditory tube

(eustachian tube) connects each middle ear to the throat allows air to pass between the tympanic cavity and the outside of the body by way of the throat (nasopharynx) and mouth maintain equal air pressure on both sides of the tympanic membrane noticeable during rapid change in altitude. As a person descends from a high altitude, the air pressure on the outside of the tympanic membrane steadily increases. This may push the tympanic membrane inward, out of its normal position, impairing hearing. usually closed by valvelike flaps in the throat, which may inhibit air movements into the middle ear. Swallowing, yawning, or chewing aid in opening the flaps and can hasten equalization of air pressure.

external acoustic meatus

(external auditory canal) S-shaped tube passes into the temporal bone. Near this opening, hairs guard the tube

spiral organ

(organ of Corti) contains about 16,000 hearing receptor cells, is on the superior surface of the basilar membrane and stretches from the apex to the base of the cochlea Within the cochlear duct is the actual hearing machinery, a combination of membranes, hair cells, sensory epithelium and supporting cells, all resting on the basilar membrane This collection of structures is called the spiral organ Hair cells sensory receptors of inner ear for hearing, when stimulated release neurotransmitter molecules to sensory neurons covered on apical surface with long microvilli, stereocilia Tectorial membrane gelatinous structure inside the cochlear duct Hair cell stereocilia extend into the tectorial membrane

bony labyrinth

(osseous) cavity within the temporal bone

circular set

(pupillary constrictor) acts as a sphincter, and when it contracts, the pupil gets smaller and the intensity of the light entering decreases.

cochlear duct

(scala media) portion of the membranous labyrinth in the cochlea runs inside the tube opposite the spiral lamina, and together these structures divide the tube into upper and lower compartments. At the apex of the cochlea, beyond the tip of the cochlear duct, a small opening, the helicotrema, connects the perilymph in the upper and lower compartments and allows the fluid pressures in them to equalize ends as a closed sac at the apex

Interoceptive senses

(visceroceptive) associated with changes in viscera (blood pressure stretching blood vessels, an ingested meal stimulating pH receptors in the small

Fungiform papillae

- blocklike projections on tip and sides of tongue contain a few taste buds

Filiform papillae

- short and spiked, on anterior two-thirds do not house taste buds, assist in detecting texture and manipulating food

Conjunctival fornix

- space formed by junction of conjunctiva Contains numerous goblet cells - lubricate and moisten the eye Contains many blood vessels supply nutrients to avascular sclera Contains abundant nerve endings Does not cover surface of cornea so blood vessels don't interfere with passage of light

Conjunctiva

- specialized stratified squamous epithelium Continuous lining over external anterior eye - ocular conjunctiva Continuous lining over internal surface of eyelid - palpebral conjunctiva

fast pain fibers

A-delta fibers myelinated. They conduct impulses rapidly, at velocities up to 30 meters per second. These impulses are associated with the immediate sensation of sharp pain, which typically seems to originate in a local area of skin. This type of pain seldom continues after the pain-producing stimulus stops.

sour receptors

Acids stimulate intensity roughly proportional to the concentration of the hydrogen ions in the substance being tasted

Visual Receptors Characteristics

Almost spherical organ, mostly receding into skull orbit Orbit also with lacrimal gland extrinsic eye muscles blood vessels cranial nerves innervating eye Orbital fat cushions posterior and lateral eye, provides support and protection Three principal layers (or tunics) fibrous tunic, vascular tunic, retina Eye interior two cavities filled with fluid, lens between

Receptive field

Area of distribution of sensitive ends of receptor Inverse relationship between field size and ability to identify location If field small, precise location determined easily Broad field, only general region detected

perilymph

Between the bony and membranous labyrinths is a fluid secreted by cells in the wall of the bony labyrinth

slow pain fibers

C fibers unmyelinated. They conduct impulses more slowly than fast pain fibers, at velocities up to 2 meters per second. These impulses cause a delayed, dull, aching pain sensation that may be widespread and difficult to pinpoint. Such pain may continue after the original stimulus ceases. Although immediate pain is usually sensed as coming from the surface, delayed pain is felt in deeper tissues as well as in the skin. Visceral pain impulses are typically carried on C fibers.

Detecting smells

Deep breathing helps facilitate mixing of air in superior nasal cavity, helps diffusion of odor molecules into mucus layer Odorant-binding proteins soluble proteins within mucus display an affinity for variety of odorants, assist in concentration of odorants to olfactory hair receptors Olfactory pathway only a few stimulating molecules needed to bind olfactory cell receptors opens ion channels, results in local receptor potential across olfactory hairs, initiate action potential Olfactory pathway (continued) propagates signals through olfactory pathways, sensory information reaches cerebral cortex, allowing for conscious smell hypothalamus, controlling visceral reactions amygdala, odor recognition and emotional association Smell adaptation ion channels altered once receptors stimulated interferes with subsequent receptor potentials adaptation to odors occurring rapidly

Gustatory pathways

Dendritic ends of sensory neurons associated with multiple gustatory cells primarily components of facial and glossopharyngeal nerve facial innervating anterior two-thirds of tongue glossopharyngeal innervating posterior third Project first to medulla to synapse - triggers increased salivation and stomach secretions, triggers gag or vomiting in response to noxious stimuli Secondary neurons projecting to thalamus Tertiary neurons projecting to primary gustatory cortex in insula

Sound interperatation

Different frequencies of vibration move different regions along the length of the basilar membrane. A particular sound frequency bends the hairs of a specific group of receptor cells, activating them. Other frequencies activate receptor cells elsewhere along the cochlea. If sound activates receptors at different places along the basilar membrane simultaneously, we hear multiple tones at the same time. The greater the deflection of the basilar membrane pushing the hair cells upward against the tectorial membrane, the louder the sound. However, recall from chapter 10 that action potentials are all-or-none. More intense stimulation of the hair cells causes more action potentials per second to reach the brain, and we perceive a louder sound.

nervous tunic

Inner Layer

enkephalins and the amine serotonin

Enkephalins can suppress both acute and chronic pain impulses. Therefore, they can relieve strong pain sensations, much as morphine and other opiate drugs do. In fact, enkephalins were discovered because they bind to the same receptors on neuron membranes as does morphine. Serotonin stimulates other neurons to release enkephalins.

External accessory structures

Eyebrows Eyelashes Eyelids tarsal glands lacrimal caruncle Conjunctiva Conjunctival fornix

Static Equilibrium

Gravity stimulates hair cells to respond. This usually happens when the head bends forward, backward, or to one side tilt the gelatinous mass of one or more maculae, and as the material sags in response to gravity, the hairs projecting into it bend. This action stimulates the hair cells, and they signal their associated neuron

vitreous humor

It is filled with a transparent, jellylike fluid

Refraction and the focusing of light

Light rays refracted when they pass between media of different densities media meet at a curved surface

vascular tunic

Middle Layer Middle layer of eye wall Also called uvea Houses extensive blood vessels, lymph vessels intrinsic muscles of the eye Three regions choroid ciliary body iris (uveal layer) includes the choroid coat, the ciliary body, and the iris

Tactile receptors

Most numerous type of receptor Mechanoreceptors located in dermis and subcutaneous layer Respond to touch, pressure, vibration Some simple dendritic ends of sensory neurons - unencapsulated Some wrapped with connective tissue or enclosed with glial cells - encapsulated Unencapsulated tactile receptors Dendritic ends of sensory neurons with no protective coat - three types Free nerve endings Root hair plexuses Tactile discs Encapsulated tactile receptors Wrapped by connective tissue or covered by glial cells, include: End bulbs - Lamellated corpuscles - Bulbous corpuscles - Tactile corpuscles -

Steps of the auditory sensory pathway

Movement of basilar membrane produces nerve signals propagated along cochlear nerve, terminate and synapse at cochlear nucleus in medulla Two sensory neurons extend from cochlear nucleus to inferior colliculus - involved in reflex in loud sounds, cause us to jump and turn head some neurons extend to superior olivary nuclei, involved in the reflex to loud sounds contract tensor tympani and stapedius to decrease ossicle movement (and protect against damage) Secondary neurons arrive at the thalamus for initial processing Axons from tertiary neurons in thalamus extend to primary auditory cortex in temporal lobe

Pathway characteristics

Optic nerves formed from converged ganglionic axons project from each eye, converge at the optic chiasm anterior to pituitary gland medial axons crossing to opposite side of brain, lateral regions remaining on same side Optic tracts extend laterally from optic chiasm composite of axons originating from both eyes Tectal system coordinates reflexive movements of eyes/head to visual stimuli Remaining optic tract axons extend to lateral geniculate nucleus within thalamus, then to visual cortex of occipital lobe Stereoscopic vision - left and right eyes with somewhat overlapping visual fields images processed into one, help determine object's proximity

fibrous tunic

Outer layer External layer of the eye wall Composed of posterior sclera and anterior cornea Sclera the "white" of the eye composed of dense irregular connective tissue provides eye shape protects eye's internal components attachment site for extrinsic eye muscles continuous with dura mater surrounding optic nerve Corena

Photopigments

Photopigments are constructed out of two major molecules: Contain protein, opsin several types, each transducing different wavelengths each photoreceptor with only one opsin type Contain light-absorbing molecule, called retinal, formed from vitamin A

Details of phototransduction (darkness)

Photoreceptors are actually slightly depolarized in darkness Cells have membrane potential of -40 mV Na+ channels in membrane kept open, Na+ enters cells - this flow of Na+ is called the dark current This dark current keeps calcium channels open, causing a continuous release of inhibitory neurotransmitter from photoreceptors The neurotransmitter binds to bipolar cells, keeping them hyperpolarized to -70 mV Hyperpolarized bipolar cells do not release excitatory neurotransmitter do not stimulate ganglion cell no nerve signal generated In light, opsin gets activated, cis-retinal changes in shape to trans-retinal (bleaching), dissociation reaction releases opsin This change in rhodopsin conformation causes a drop in cGMP levels - cGMP is a "second messenger", a common intracellular signaler mechanism that alters channel function The drop in cGMP levels closes those Na+ channels that create the dark current Reduced Na+ entry causes the plasma membrane of photoreceptors to hyperpolarize to -70 mV Hyperpolarization closes the calcium channels, which blocks release of inhibitory neurotransmitter Bipolar cells no longer inhibited, they depolarize and release their own neurotransmitter which binds to receptors in ganglion cells Generates signals transmitted via optic nerve to brain

Hair Cells

Receptor cells four parallel rows, with many hairlike processes known as stereovilli (also called stereocilia) that extend into the endolymph of the cochlear duct

Receptors

Respond to stimulus, initiate sensory input to CNS Range from simple structures to complex structures, sense organs act as transducers Change one form of energy into a different form Original energy specific to type of receptor e.g., light energy in eye, sound energy in ear Energy transduced to electrical energy and conducted along a sensory neuron If no stimulus, resting membrane potential is maintained across plasma membrane Modality gated channels within plasma membrane open in response to stimulus, initiating action potentials

Visual Pigments

Rods and cones contain light-sensitive pigments that decompose when they absorb light energy

Gustation

Sense of taste from molecules we eat and drink Gustatory cells are taste receptors housed in specialized organs, taste buds, found on tongue papilla The sensation of taste also involves mechanoreceptors and thermoreceptors which provide information about texture and temperature Gustatory cells are specialized neuroepithelial cells, chemoreceptors Dendritic ending of each formed by the receptive portion of the cell, gustatory microvillus - extends through opening in taste bud, taste pore, to surface Taste-producing molecules in food, dissolve in saliva, stimulate gustatory receptors through taste pore

Referred pain

Sensory nerve signals from certain viscera not perceived as originating from organ perceived as originating from dermatomes of skin The same ascending tract within the spinal cord houses cutaneous and visceral sensory neurons, and signals can get through the insulating membranes from the visceral neurons to the cutaneous sensory neurons Sensory cortex unable to differentiate actual and false stimuli, so the stimulus is localized incorrectly

Vestibular sensation pathways

Sensory neurons housed within vestibular ganglia monitor changes in activities of hair cells Equilibrium stimuli transmitted via vestibular branch of CN VIII to vestibular nuclei in medulla and cerebellum both integrate stimuli related to balance and equilibrium transmit signals through descending vestibulospinal tracts, helps maintain muscle tone and balance Vestibular nuclei also send signals to cranial nerve nuclei CN III, IV, and VI help control reflexive activities with head and eye movements Signals sent from vestibular nuclei and cerebellum to thalamus Sent eventually to cerebral cortex for awareness of body position

sensory receptors vs membrane receptors

Sensory receptors may be as small as individual cells or as large as complex organs such as the eye or ear. Sensory receptors respond to sensory stimuli. In contrast, membrane receptors are molecules such as proteins and glycoproteins on the cell membranes.

The pathway from sound wave to nerve signal

Sound waves funneled by auricle of external ear, enter external acoustic meatus Make tympanic membranes vibrate Sound waves amplified by ossicles, foot of stapes moving in oval window Transmits sound waves into pressure waves within inner ear Pressure waves continuing through perilymph and scala vestibuli Cause deformation of cochlear duct - displace specific regions of basilar membrane Causes distortion of hair cell stereocilia, causing changes in neurotransmitter release Sensory neurons stimulated - cell bodies housed within spiral ganglia in modiolus, nerve signals initiated in cochlear branch of CN VIII Vibrations in scala media transmitted to perilymph in the scala tympani - pressure wave absorbed at the round window (back into middle ear)

salt receptors

Stimulated by Ionized inorganic salts quality of the sensation that each salt produces depends upon the type of positively charged ion that it releases into solution, such as Na+ from table salt.

ampulla

Suspended in the perilymph of each bony canal is a membranous semicircular duct that ends in a swelling ampullae communicate with the utricle of the vestibule ampulla contains a ridge that crosses the tube and houses a sensory organ expanded region within each semicircular duct located at end farthest from utricle connection

Pain Pathways

The axons (fibers) that conduct impulses away from pain receptors are of two main types: fast pain fibers and slow pain fibers. event that stimulates pain receptors triggers impulses on both fast and slow pain fibers. The result is a dual sensation—a sharp, pricking pain, then a dull, aching pain that is more intense and may worsen over time. Chronic pain that resists relief and control can be debilitating. Upon reaching the spinal cord, these sensory fibers enter the gray matter of the posterior horn. There they synapse with neurons whose axons cross over to the opposite side of the spinal cord at that level and then ascend in the anterior and lateral spinothalamic tracts (anterolateral system). These pathways also involve one or more interneurons before reaching the long fibers that cross over and ascend to the brain. In the brain, most of the pain fibers synapse in the reticular formation, and from there impulses are conducted on fibers of still other neurons to the thalamus, hypothalamus, and cerebral cortex. Fibers of the spinothalamic tracts bring pain and temperature information directly to the thalamus.

olfactory bulbs

These fibers (which collectively form the first cranial nerves) synapse with neurons located in the enlargements structures that lie on either side of the crista galli of the ethmoid bone

semicircular canals

Three provide a sense of equilibrium

Converagence in eye

Thus, if light stimulates a rod, the brain cannot tell which one of many receptors has been stimulated. Such convergence is much less common among cones, so when a cone is stimulated, the brain is able to pinpoint the stimulation more accurately

Taste Hair

Tiny projections (microvilli) protrude from the outer ends of the taste cells and jut through the taste pore. These taste hairs are the sensitive parts of the receptor cells.

Dynamic Equilibrium

Two of them, the anterior canal and the posterior canal, are oriented vertically, whereas the third, the lateral canal is horizontal head or torso moves, the semicircular canals move as well, but initially the fluid inside the membranous ducts tends to remain stationary because of inertia. (Imagine turning rapidly while holding a full glass of water.) This bends the cupula in one or more of the semicircular canals in a direction opposite that of the head and torso movement, and the hairs embedded in it also bend. The moving of the hairs stimulates the hair cells to signal their associated neurons, and as a result, impulses are conducted to the brain Parts of the cerebellum are particularly important in interpreting impulses from the semicircular canals. Analysis of such information allows the brain to predict the consequences of rapid body movements, and by modifying signals to appropriate skeletal muscles, the cerebellum can maintain balance. Various proprioceptors, particularly those associated with the joints of the neck, inform the brain about the position of body parts. The eyes detect changes in posture that result from body movements.

Vibrations entering cochlea

Vibrations entering the perilymph at the oval window travel along the scala vestibuli and pass through the vestibular membrane to enter the endolymph of the cochlear duct, where they move the basilar membrane. After passing through the basilar membrane, the vibrations enter the perilymph of the scala tympani, and movement of the membrane covering the round window dissipates their force into the air in the tympanic cavity

Vision

Visual stimuli help us form specific detailed visual images of objects Photoreceptors - used to detect light, color, and movement

Resolving power

ability to form separate and distinct images of close objects

tectorial membrane

above hair cells attached to the bony shelf of the cochlea. It passes like a roof over the receptor cells, contacting the tips of their hairs

cornea

anterior sixth of the outer tunic bulges forward as the transparent window of the eye. The cornea helps focus entering light rays convex transparent structure forms anterior one-sixth of tunic outer edge adjoins sclera at the limbus inner simple squamous epithelium outer stratified squamous epithelium, corneal epithelium contains no blood vessels external epithelium nutrients and oxygen from lacrimal gland fluid internal epithelium nutrients and gases from fluid in anterior chamber convex shape refracting light rays coming into the eye

optic chiasma

anterior to the pituitary gland, these nerves give rise to the X-shaped some of the fibers cross over fibers from the nasal (medial) half of each retina cross over, whereas those from the temporal (lateral) halves do not

Refracted image

appears upside down and backwards

Exteroreceptive senses

are associated with changes at the body surface. They include the senses of touch, pressure, temperature, and pain.

Mechanoreceptors

are of several types and sense mechanical forces by detecting changes that deform the receptors. They include a number of receptors in the skin that respond to physical contact, and several receptors in the ear that provide information about balance and vibrations from sound respond to touch, pressure, vibration, and stretch most cutaneous receptors also located in ear

Refraction greatest

as rays pass into cornea maximal refractive index here lens shape changeable to focus light rays on retina

Proprioceptive senses

associated with changes in muscles and tendons and in body position.

stapedius

attached to the posterior side of the stapes and the inner wall of the tympanic cavity. It pulls the stapes outward when it contracts

malleus

attached to the tympanic membrane, helping to maintain its conical shape. When the tympanic membrane vibrates, the malleus vibrates in unison with it. The malleus vibrates the incus attached to medial surface of tympanic membrane resembles a hammer in shape

Equilibrium

awareness and monitoring of head position Information is sent to brain to help keep our balance Monitored by the other parts of the membranous labyrinth, the utricle, saccule, semicircular ducts Static equilibrium - position sense when body is steady monitored by utricle and saccule Linear acceleration - e.g., tilting your head to look at shoes also detected by utricle and saccule Angular acceleration - rotational movements of the head e.g., skater spinning on ice monitored by semicircular ducts

Olfactory nerves (CN I)

axon bundles of mitral and tufted cells project posteriorly along inferior frontal lobe surface, directly to primary olfactory cortex in temporal lobe projects to hypothalamus, amygdala, and other regions do not project to thalamus unlike other sensory information

optic nerves

axons of the ganglion cells in the retina leave the eyes

Rhodopsin activation

before light activation, retinal portion is in a bent shape, cis-retinal upon exposure to light, straightens into trans-retinal form and dissociates (falls off) from opsin as phototransduction occurs The dissociation causes rhodopsin to change from bluish-purple to colorless, termed bleaching reaction The dissociation reaction reduces the rhodopsin amount in rods

Regulation of Pain Pathways

begins when pain impulses reach the level of the thalamus cerebral cortex must judge the intensity of pain and locate its source, and it is also responsible for emotional and motor responses to pain. areas of gray matter in the midbrain, pons, and medulla oblongata, regulate the flow of pain impulses from the spinal cord special neurons in these areas descend in the lateral funiculus to various levels within the spinal cord. The impulses stimulate the ends of certain nerve fibers to release biochemicals that can block pain signals by inhibiting presynaptic nerve fibers in the posterior horn of the spinal cord. inhibiting substances released in the posterior horn are neuropeptides called enkephalins and the amine serotonin

Horizontal cells

between photoreceptor layer and bipolar cells integrate stimuli sent from photoreceptors of other layers

anterior chamber

between the cornea and the iris

posterior chamber

between the iris and the vitreous humor, occupied by the lens

Between Scala vestibule and scala tympani

between them is filled with endolymph

optic nerve

blood vessels pierce the sclera. The dura mater that encloses these structures is continuous with the sclera

vestibule

bony chamber between the cochlea and the semicircular canals, houses membranous structures that serve both hearing and equilibrium

Inner Tunic

consists of the retina, which contains the visual receptor cells (photoreceptors). This nearly transparent sheet of tissue is continuous with the optic nerve in the back of the eye and extends forward as the inner lining of the eyeball. It ends just behind the margin of the ciliary body.

auditory ossicles

bounded by the tympanic membrane laterally and the inner ear medially and houses three small bones Amplify and transmit sound waves into inner ear Vibrate when sound waves strike tympanic membrane Cause stapes' footplate to move in and out of oval window Movement initiating pressure waves in inner ear fluid Tympanic membrane 20 times greater in diameter than footplate sounds transmitted across middle ear amplified 20-fold Stapedius and tensor tympani two tiny skeletal muscles within middle ear restrict ossicle movement when loud noises occur protect receptors in inner ear

lens fibers

cells divide, and the new cells on the surface of the lens capsule differentiate into specialized columnar epithelial cells constitute the substance of the lens fiber production continues slowly throughout life, thickening the lens from front to back deeper lens fibers are compressed toward the center of the structure

macula lutea

central region of the retina is a yellowish spot occupies about 1 square millimeter. rounded, yellowish region lateral to optic disc contains fovea centralis, depressed pit highest proportion of cones and few rods area of sharpest vision

ciliary processes

ciliary body are radiating folds contain capillaries secreting aqueous humor

lens capsule

clear, membranelike structure largely composed of intercellular material quite elastic, a quality that keeps it under constant tension lens can assume a globular shape suspensory ligaments attached to the margin of the capsule are also under tension, and they pull outward, flattening the capsule and the lens. strong deformable transparent structure, bounded by fibrous elastic capsule Composed of precisely arranged layers of cells have lost their organelles, filled completely by crystallin protein Focuses incoming light onto the retina - shape determines degree of light refraction Ciliary muscles contract/relax, transmit tension to lens via suspensory ligaments, lens changes shape when relaxed, tension of suspensory ligaments increases, causes lens to flatten necessary to view distant objects - default position for the lens opposite process initiated for close objects contraction of muscle reduces suspensory ligaments' tension lens more spherical process termed accommodation

Visual acuity

clearness of vision, dependent upon bending of light rays as enter eye sensitivity of neuronal elements in retina ability to interpret image in the brain

Auditory Pathways

cochlear branches of the vestibulocochlear nerves enter the auditory nerve pathways that extend into the medulla oblongata and proceed through the midbrain to the thalamus. From there they pass into the auditory cortices of the temporal lobes of the cerebrum, where they are interpreted. On the way, some of these fibers cross over, so that impulses arising from each ear are interpreted on both sides of the brain

wavelength

colors are described either by a physical property simply by the name, such as blue, red, or green. The color perceived depends upon which cones the light in a given image stimulates. If all three types of cones are stimulated with equal intensity, the light is perceived as white, and if none are stimulated, it is seen as black. Examination of the retinas of different people reveals that individuals have unique patterns of these three cone types, all apparently able to provide color vision. Some parts of the retina are even normally devoid of one particular type, yet the brain integrates information from all over to "fill in the gaps," creating a continuous overall image. People who lack a cone type due to a mutation are colorblind

Outer neural layer of Ora serrata

composed of photoreceptor cells, contain pigment molecules that react to light two types of photoreceptor cells: rods and cones

tarsal glands

connective tissue layer of the eyelid, which helps give it form, contains many modified sebaceous glands carry the oily secretions of these glands to openings along the borders of the lids. This secretion helps keep the lids from sticking together.

nociceptors

consist of free nerve endings widely distributed throughout the skin and internal tissues, except in the nervous tissue of the brain, which lacks pain receptors sensitive to mechanical damage, while others are particularly sensitive to temperature extremes. Some pain receptors are most responsive to chemicals, such as hydrogen ions, potassium ions, or specific breakdown products of proteins, histamine, and acetylcholine deficiency of blood flow (ischemia) and the resulting deficiency of oxygen (hypoxia) in a tissue also trigger pain sensation

Tears

contain an enzyme, lysozyme, that has antibacterial properties, reducing the risk of eye infections. Tear glands secrete excessively when a person is upset or when the conjunctiva is irritated. Tears spill over the edges of the eyelids, and the nose fills with fluid. When a person cries, parasympathetic nerve fibers conduct motor impulses to the lacrimal glands.

sclera

cornea is continuous white portion of the eye makes up the posterior five-sixths of the outer tunic and is opaque due to many large, seemingly disorganized collagen and elastic fibers. The sclera protects the eye and is an attachment for the extrinsic muscles

eyebrows

curved rows of thick, short hairs at superior edge of orbit along supraorbital ridge prevent sweat from dripping into open eyes

cyclic guanosine monophosphate (cGMP)

darkness, a nucleotide sodium and calcium channels open in portions of the receptor cell membranes. The resultant release of neurotransmitter by the rods inhibits the generation of action potentials along the optic nerve When rhodopsin molecules absorb light, they change shape and release opsin, in trillionths of a second. The released opsin then becomes an active enzyme, which activates a second enzyme (transducin), which, in turn, activates another enzyme (phosphodiesterase). The third enzyme of this series breaks down cGMP, and as the concentration of cGMP decreases, sodium and calcium channels close, and the receptor cell membrane hyperpolarizes (see chapter 10, p. 375). The degree of hyperpolarization is directly proportional to the intensity of the light stimulating the receptor cells.

End bulbs

dendritic endings of sensory neurons in connective tissue located in skin dermis, mucous membranes of oral cavity, nasal cavity, vagina, anal canal detect light pressure stimuli and low-frequency vibration

Phasic receptors

detect new stimulus or change in stimulus, but sensitivity decreases over time e.g., tactile receptors of skin can undergo adaptation, a reduction in sensitivity to continuously applied stimulus e.g., loss of awareness of pressure while sitting in a chair

Exteroceptors

detect stimuli from external environment receptors in the skin receptors for special senses receptors on membranes lining - nasal cavity, oral cavity, etc.

Interoceptors

detect stimuli in internal organs primarily stretch receptors in smooth muscle walls mostly unaware of these sensations also temperature, pressure, chemical changes, perceived pain

Rhodopsin regeneration

dissociated trans-retinal transported to the pigmented layer retinal converted back to bent cis-retinal form transported back to the rod, associates with opsin and reforms rhodopsin To much light interferes with the relatively slow regeneration process - rods nonfunctional in bright light

tympanic membrane

eardrum meatus terminates with the tympanic membrane

Ora serrata

edge of retina, margin between photosensitive posterior and nonphotosensitive anterior anterior region covering ciliary body and posterior side of iris Three cell layers forming neural layer Outer neural layer Middle neural layer Inner neural layer

tympanic reflex

elicited in about one-tenth of a second after a loud, external sound. The reflex contracts the muscles, and the malleus and stapes move. As a result, the bridge of ossicles in the middle ear becomes more rigid, reducing its effectiveness in transferring vibrations to the inner ear reduces pressure from loud sounds that might otherwise damage the hearing receptors. Ordinary vocal sounds also elicit the tympanic reflex, such as when a person speaks or sings. This action muffles the lower frequencies of such sounds, improving the hearing of higher frequencies, which are common in human vocal sounds. In addition, the tensor tympani muscle maintains tension on the tympanic membrane. This is important because a loose tympanic membrane would not be able to effectively transmit vibrations to the auditory ossicles.

orbicularis oculi

encircle the opening between the lids and spread out onto the cheek and forehead acts as a sphincter that closes the lids when it contracts

posterior cavity

enclosed by the lens, ciliary body, and retina is the largest compartment of the eye It is filled with a transparent, jellylike fluid called vitreous humor, which with some collagen fibers comprise the vitreous body

Visual field

entire area observed when eye focused on single point focus different parts onto retina by stereoscopic vision left region focused on right side of retina (and vice versa) two images sent to brain for interpretation

Hearing receptor

epithelial cells respond to stimuli some what like neurons when a receptor cell is at rest, its membrane is polarized. When its hairs bend, selective ion channels open and its cell membrane depolarizes. The membrane then becomes more permeable, specifically to calcium ions. The receptor cell has no axon or dendrites, but it does have neurotransmitter-containing vesicles in the cytoplasm near its base. As calcium ions diffuse into the cell, some of these vesicles fuse with the cell membrane and release neurotransmitter to the outside. The neurotransmitter stimulates the dendritic ends of nearby sensory neurons, and in response their axons conduct impulses along the cochlear branch of the vestibulocochlear nerve

eyelashes

extend from margins of eyelids prevent large objects coming into contact with eye

basilar membrane

extends from the bony shelf of the cochlea and forms the floor of the cochlear duct many thousands of elastic fibers and becomes thinner from the base of the cochlea to its apex

extrinsic muscles

eye arise from the bones of the orbit and are inserted by broad tendons on the eye's tough outer surface. Six such muscles move the eye in different directions

Visual Accessory Organs

eye, lacrimal gland, and associated extrinsic muscles are housed in the orbital cavity of the skull orbit, lined with the periosteum of various bones, also contains fat, blood vessels, nerves, and connective tissues.

optic tract

fibers from the nasal half of the left eye and the temporal half of the right eye form fibers from the nasal half of the right eye and the temporal half of the left eye form the left optic tract. nerve fibers continue in the optic tracts, and before they reach the thalamus, a few of them enter nuclei that function in various visual reflexes. Most of the fibers, however, enter the thalamus and synapse in a part of its posterior portion (lateral geniculate body)

Tactile discs

flattened nerve endings, extend to specialized tactile cells located in stratum basale of epidermis tonic receptors for fine touch

Otolithic membrane

formed of gelatinous layer and otoliths, small masses of calcium carbonate crystals (help increase weight of otolithic membrane covering hair cells) positione influenced by head position - alter position, bends stereocilia and kinocilium, changes amount of neurotransmitter released

sharpest vision

fovea centralis in the macula lutea, lacks rods but has densely packed cones with few or no converging fibers. Also, the overlying layers of the retina, as well as the retinal blood vessels, are displaced to the sides in the fovea, which more fully exposes the receptors to incoming light. Consequently, to view something in detail, a person moves the eyes so that the important part of an image falls upon the fovea centralis.

optic radiations

from lateral geniculate body this region, the visual sensory fibers enter pathways that lead to the visual cortex of the occipital lobe

cochlea

functions in hearing tube shaped a bit like a snail shell, coiled around a bony core, the modiolus Cochlea

ciliary muscles

groups of smooth muscle cells that constitute - bands of smooth muscle suspensory ligaments extend from muscle to lens contraction changes tension on ligaments, altering lens shape

taste cells

gustatory cells taste bud includes a group of modified epithelial cells function as sensory receptors taste buds houses 50 to 150 somewhat spherical, with an opening, the taste pore, on its free surface contains taste hair Interwoven among and wrapped around the taste cells is a network of sensory fibers whose ends closely contact the receptor cell membranes

crista ampullaris

has a number of sensory hair cells and supporting cells elevated region on ampulla covered by epithelium of supporting cells and hair cells connected to...

rods

have long, thin projections at their terminal ends The retina has about 100 million rods Rods are hundreds of times more sensitive to light than are cones, and as a result, rods provide vision in dim light colorless (black and white) vision single rod cell may have 2,000 interconnected discs, derived from the cell membrane Longer and narrower than cones Primarily located in peripheral regions of neural layer Especially important in dim light Detect movement well but have poor sharpness Cannot distinguish color

cones

have short, blunt projections. 3 million cones. Detect color provide sharp images, whereas rods produce more general outlines of objects nerve fibers associated with many rods may converge, so their impulses may be conducted to the brain on a single nerve fiber concentration of cones decreases in areas farther away from the macula lutea whereas the concentration of rods increases in these areas Activated by high-intensity light Provide precise visual sharpness and color recognition Primarily located in fovea centralis Subdivided into three types of cones, each best detecting different wavelengths

somatic sensory receptors

housed within the skin, joints, muscles, tendons detect pressure, vibration, pain, stretch

Cell transmission

hyperpolarization reaches the synaptic end of the cell, inhibiting release of neurotransmitter. Decreased release of neurotransmitter by photoreceptor cells triggers action potentials in nearby retinal neurons. Consequently, impulses are conducted away from the retina, through the optic nerve, and into the brain, where they are interpreted as vision. This process is essentially the same in both rods and cones.

common nerve pathways

impulses from the heart seem to be conducted over the same nerve pathways as those from the skin of the left shoulder and the inside of the left upper limb

Photoreceptors

in the eyes respond to light energy of sufficient intensity located in the eye detect changes in light intensity, color, movement

lacrimal gland

in the orbit, superior and lateral to the eye secretes tears continuously, which pass through tiny tubules and flow downward and medially across the eye. Two small ducts (superior and inferior canaliculi) collect tears, and their openings (puncta) can be seen on the medial borders of the eyelids

Visceral Senses

include lamellated corpuscles and free nerve endings. The information these receptors convey includes the sense of fullness after eating a meal, the discomfort of intestinal gas, and the pain that signals a heart attack.

incus

incus passes the movement on to the stapes middle ossicle resembling an anvil

labyrinth

inner ear is a complex system of intercommunicating chambers and tubes ear has two such regions—the bony labyrinth and the membranous labyrinth.

aqueous humor

inner surface of the ciliary body continuously secretes a watery fluid into the posterior chamber fluid circulates from this chamber through the pupil fluid in anterior chamber filtrate of blood plasma resembling cerebrospinal fluid produced by ciliary processes secreted into posterior chamber flows through pupil into anterior chamber continually resorbed into vascular space, scleral venous sinus, located in limbus drains into nearby veins provides nutrients and oxygen to lens and cornea helps maintain chemical environment within anterior cavity

tensor tympani

inserted on the medial surface of the malleus and is anchored to the cartilaginous wall of the auditory tube. When it contracts, it pulls the malleus inward

Middle neural layer of Ora serrata

internal to photoreceptor layer, layer of bipolar cells rods and cones synapsing on these dendrites convergence of visual signals from multiple photoreceptors

anterior cavity

iris extends forward from the periphery of the ciliary body and lies between the cornea and the lens. It divides the space separating these parts anterior to lens and posterior to cornea further subdivided into two chambers anterior chamber, between iris and cornea posterior chamber, between lens and iris

pupil

is a circular opening in the center of the iris, and into the anterior chamber fills the space between the cornea and the lens, providing nutrients and maintaining the shape of the front of the eye. It leaves the anterior chamber through veins and a special drainage canal, called the scleral venous sinus (canal of Schlemm), in the wall of the anterior chamber at the junction of the cornea and the scler black opening at center of iris pupil size controlled by two smooth muscle layers controls amount of light entering the eye only one layer contracting at a time

cupula

maculae, the hairs of the hair cells extend upward into a domeshaped gelatinous mass hair cells are connected at their bases to dendrites of neurons that make up part of the vestibular branch of the vestibulocochlear nerve overlying gelatinous dome kinocilia and stereocilia embedded here extends across semicircular duct to roof over ampulla

three auditory ossicles

malleus, the incus, and the stapes attached to the wall of the tympanic cavity by tiny ligaments and are covered by mucous membrane. These bones bridge the tympanic membrane and the inner ear, transferring vibrations between these parts form a lever system that helps increase (amplify) the force of the vibrations as they pass from the tympanic membrane to the oval window large surface of the tympanic membrane to a much smaller area at the oval window, the vibrational force strengthens as it travels from the outer to the inner ear. As a result, the pressure (per square millimeter) that the stapes applies at the oval window is about twenty-two times greater than that which sound waves exert on the tympanic membrane.

referred pain

may feel as if it is coming from some part of the body other than the part being stimulated may derive from common nerve pathways that sensory impulses coming both from skin areas and from internal organs use

Proprioception

mechanoreceptors that send information to the CNS about body position and the length and tension of skeletal muscles. Recall that lamellated corpuscles function as pressure receptors in joints. The other main proprioceptors are stretch receptors: muscle spindles and Golgi tendon organs.

optic disc

medial to the fovea centralis nerve fibers from the retina leave the eye and become parts of the optic nerve central artery and vein also pass through at the optic disc. These vessels are continuous with capillary networks of the retina, and together with vessels in the underlying choroid coat, they supply blood to the cells of the inner tunic. The optic disc lacks receptor cells, so it is commonly referred to as the blind spot of the eye contains no photoreceptors where ganglion axons exit toward brain commonly termed the blind spot

Pain receptors

nociceptors respond to tissue damage. Triggering stimuli include exposure to excess mechanical, electrical, thermal, or chemical energy. respond to painful stimuli somatic nociceptors chemical, heat, or mechanical damage to surface or skeletal muscles visceral nociceptors detect internal body damage within viscera e.g., oxygen deprivation, overstretched smooth muscles, tissue trauma

Olfactory receptor cells

membrane receptor molecules, sense odors similar to those for taste in that they are chemoreceptors sensitive to chemicals dissolved in liquids. The two chemical senses function closely together and aid in food selection, because we smell food at the same time we taste it. It is often difficult to tell what part of a food sensation is due to smell and what part is due to taste Primary neuron in sensory pathway for smell Bipolar neuron with single dendrite and unmyelinated axon Olfactory hairs unmyelinated extensions projecting from dendrites house receptor proteins for detecting specific odorant molecule Olfactory nerves (not the olfactory nerve) formed from bundles of axons of olfactory cells project through cribiform plate of ethmoid bone enter olfactory bulbs

endolymph

membranous labyrinth is a slightly different fluid

special senses

more specialized receptors and are confined to structures in the head, such as the eyes and ears. Specialized receptors confined to structures in the head Eyes, ears, nose and mouth

conjunctiva

mucous membrane that lines the inner surfaces of the eyelids and folds back to cover the anterior surface of the eyeball, except for its central portion (cornea) tissue that lines the eyelids is relatively thick, the conjunctiva that covers the eyeball is very thin. It is also freely movable and transparent, so that blood vessels are clearly visible beneath it.

Protection of the ear

narrow external acoustic meatus prevents large objects from entering fine hairs guards opening cerumen, waxlike secretion of ceruminous glands combines with dead sloughed cells to form earwax may help impede growth of microorganisms

bright light

nearly all of the rhodopsin in the rods decomposes, sharply reducing the sensitivity of these receptors (the rhodopsin loses its purplish color as a result, and is said to have "bleached"). The cones continue to function, however, and in bright light, we therefore see in color. In dim light, rhodopsin can be regenerated from opsin and retinal faster than it is broken down. This regeneration requires cellular energy, which ATP provides (see chapter 4, p. 126). Under these conditions, the rods continue to function and the cones remain unstimulated. Hence, we see only shades of gray in dim light.

horizontal cells and amacrine cells

nerve fibers of the other two groups of retinal cells pass laterally between retinal cells modify the pattern of impulses conducted on the fibers of the direct pathway.

endorphins

neuropeptides with pain-suppressing, morphinelike actions. They are found in the pituitary gland and in regions of the nervous system, such as the hypothalamus, that relay pain information. Enkephalins and endorphins are released in response to extreme pain, providing natural pain control.

olfactory tracts

olfactory bulbs, the sensory impulses are analyzed, and as a result, additional impulses travel portions of the limbic system brain center for memory and emotions

Olfactory Organs

olfactory receptor cells, also include epithelial supporting cells yellowish brown masses within pinkish mucous membrane. They cover the upper parts of the nasal cavity, the superior nasal conchae, and a portion of the nasal septum bipolar neurons surrounded by columnar epithelial cells knobs at the distal ends of their dendrites covered with hairlike cilia cilia project into the nasal cavity and are the sensitive portions of the receptor cells. Each of a person's 12 million olfactory receptor cells has ten to twenty cilia. Olfactory epithelium - lines superior region of nasal cavity, composed of: olfactory receptor cells detect odors supporting cells sustain receptors basal cells replace olfactory receptor cells every 40 to 60 days Lamina propria areolar connective tissue layer internal to olfactory epithelium houses blood vessels and nerves Olfactory glands housed in lamina propria help form mucous with supporting cells covers exposed surface of olfactory epithelium

ceruminous glands

opening and tube are lined with skin that has many modified sweat glands called ceruminous glands, which secrete wax (cerumen). The hairs and wax help keep large foreign objects, such as insects, out of the ear

stretch reflex

opposes the lengthening of the muscle and helps maintain the desired position of a limb despite gravitational or other forces tending to move it

blind spot of the eye

optic disc lacks receptor cells, so it is commonly referred to as the blind spot of the eye

Dilator pupillae muscle

organized in a radial pattern controlled by sympathetic division of the ANS to dilate contracts and dilates pupil when stimulated by low light level

vestibule

organs of static equilibrium bony chamber between the semicircular canals and the cochlea

Head upright

otolithic membrane applying pressure directly on hair cells, minimal stimulation of hair cells

Visceral Pain

pain receptors are the only receptors in viscera whose stimulation produces sensations visceral tissues are subjected to more widespread stimulation, such as when intestinal tissues are stretched or when the smooth muscle in the intestinal walls undergoes spasms, a strong pain sensation may follow

Light Refraction

person sees an object, either the object is giving off light, or it is reflecting light from another source. Rays of light enter the eye, and an image of what is seen focuses upon the retina. The light rays must bend to be focused occurs when light rays pass at an angle from a medium of one density into a medium of a different density

strabismus

person whose eyes are not coordinated well enough to align has

Choroid Coat

posterior five-sixths of the globe of the eye, loosely joins the sclera. Blood vessels pervade the choroid coat and nourish surrounding tissues. The choroid coat also contains abundant pigment-producing melanocytes that give it a brownish-black appearance. The melanin of these cells absorbs excess light and helps keep the inside of the eye dark. most extensive posterior region houses vast capillaries supporting the retina cells filled with pigment from melanocytes - pigment absorbing extraneous light

Posterior Cavity

posterior to lens and anterior to retina occupied by vitreous humor transparent, gelatinous fluid fills space between lens and retina helps maintain eye shape supports retina transmits light from lens to retina

baroreceptors

pressoreceptors certain blood vessels detect changes in blood pressure detect changes in stretch or distension branch repeatedly in vessel or organ walls stimulated by changes in wall deformation involved in regulation of blood pressure

sensory adaptation

prioritize the sensory input it receives, or incoming unimportant information would be overwhelming ability to ignore unimportant stimuli may reflect a decreased response to a particular stimulus from the receptors (peripheral adaptation) or along the CNS pathways leading to the sensory regions of the cerebral cortex (central adaptation)

Phototransduction

process by which photoreceptors activated Photopigments within cell discs altered by light in cone cells undergoes similar process cis-retinal transformed to trans-retinal bleaching reaction regeneration more quick than rhodopsin regeneration process not as negatively affected by bright light

Lacrimal apparatus

produces, collects, and drains lacrimal fluid from eye Lubricates anterior surface of eye, reduces friction from eyelid movement Cleanses and moistens eye surface, helps prevent bacterial infection through action of antibacterial enzyme, lysozyme Lacrimal gland located in superolateral depression of orbit continuously produces lacrimal fluid, washed over eyes by blinking eyelids, fluid transferred to lacrimal caruncle on medial eye consists of the lacrimal gland secretes tears, and a series of ducts, which carry the tears into the nasal cavity

radial set

radial set (pupillary dilator) contracts, the diameter of the pupil increases and the intensity of the light entering increases.

sensation

raw form in which these receptors send information to the brain Conscious awareness of sensory information Only stimuli that reaches the cerebral cortex counts as sensation, we are aware of only a fraction of stimuli Much input is relayed to lower areas of the brain, and a response initiated without awareness e.g., stimuli regarding blood pressure or carbon dioxide levels

Nasolacrimal duct

receives fluid from lacrimal sac, drains fluid into lateral side of nasal cavity, mixes with mucus

papillae

resemble orange sections and associate on the surface of the tongue with tiny elevations epithelial and connective tissue elevations on dorsal tongue surface, several types: Filiform papillae Fungiform papillae Vallate papillae Foliate papillae

Sphincter pupillae muscle

resembles concentric circles under control of parasympathetic division via CN III constricts pupil in response bright light

Tonic receptors

respond continuously to stimuli at constant rate e.g., balance receptors in inner ear sensitivity stays same over time

Chemoreceptors

respond to changes in the concentration of chemicals. Receptors associated with the senses of smell and taste are of this type. Chemoreceptors in internal organs detect changes in the blood concentrations of oxygen, hydrogen ions, glucose, and other chemicals. detect chemicals dissolved in fluid chemicals from food, body fluids, inhaled air e.g., tastebuds on tongue e.g., chemoreceptors in blood vessels monitor oxygen and carbon dioxide in blood

cold receptors

respond to colder temperatures most sensitive to temperatures between 10°C (50°F) and 20°C (68°F). Temperature dropping below 10°C also stimulates pain receptors, producing a freezing sensation.

warm receptors

respond to warmer temperatures most sensitive to temperatures above 25°C (77°F) and become unresponsive at temperatures above 45°C (113°F). Temperatures near and above 45°C also trigger pain receptors, producing a burning sensation.

Photoreceptors detailed

retinal pigment epithelium absorbs light that the receptor cells do not absorb, and with the pigment of the choroid coat, keeps light from reflecting off the surfaces inside the eye. The retinal pigment epithelium also stores vitamin A, which the receptor cells use to synthesize visual pigments. stimulated only when light reaches them. A light image focused on an area of the retina stimulates some receptors, which conduct impulses to the brain. However, the impulse leaving each activated receptor provides only a small portion of the information required for the brain to interpret a complete scene

Dark adaptation

return of sensitivity to low light levels after bright light cones initially nonfunctional in low light rods still bleached from bright light conditions, may take 20 to 30 minutes to see well

dark adapted

rods have converted the available opsin and retinal to rhodopsin increases about 100,000 times, and the eye dark-adapted eyes to see in dim light

Lateral rectus

rotates the eye away from the midline.

Superior oblique

rotates the eye downward and away from the midline.

Inferior rectus

rotates the eye downward and toward the midline.

Medial rectus

rotates the eye toward the midline.

Inferior oblique

rotates the eye upward and away from the midline.

Superior rectus

rotates the eye upward and toward the midline.

Bulbous corpuscles

sensory dendritic endings within connective tissue found in dermis and subcutaneous layer, joint capsules detect continuous deep pressure and distortion in the skin, do not exhibit adaptation

Head tilted toward kinocilium

shift of otolithic membrane with stereocilia distortion, depolarization of hair cells and increased neurotransmitter release increased nerve signal frequency along vestibular branch of CN VIII

Head tilted away from kinocilium

shift of otolithic membrane with stereocilia distortion, hyperpolarization of hair cells, neurotransmitter release inhibited decreased nerve signal frequency along vestibular branch of CN VIII brain interpretation of changes to determine direction of head tilt

Free nerve endings

simplest receptors, are common in epithelial tissues, where they lie between epithelial cells. They are responsible for the sensation of itching terminal branches of dendrites, least complex of tactile receptors reside closest to surface of skin, also located in mucous membranes detect pain and temperature primarily, also light touch and pressure

lacrimal caruncle

small reddish body at medial commissure ciliary glands housed in caruncle, form secretory products contribute to gritty material around eyelids after waking

Root hair plexuses

specialized free nerve endings, form weblike sheath around hair follicles signal initiated by hair movement quickly adapt, conscious awareness subsiding quickly

Photopsin

specific opsin associated with retinal in cone cells three different proteins providing for different absorption in cones

round window

spiral to a membrane-covered opening in the wall of the inner ear facing the tympanic cavity filled with perilymph

stapes

stapes to an opening in the wall of the tympanic cavity called the oval window. Vibration of the stapes, which acts like a piston at the oval window, transfers the vibrations to a fluid within the inner ear. These vibrations of the fluid stimulate the hearing receptors. resembles a stirrup has disclike footplate fitting into oval window marks lateral wall of inner ear

Stereoscopic vision

stereopsis simultaneously perceives distance, depth, height, and width of objects. Such vision is possible because the pupils are 6-7 centimeters apart close objects (less than 20 feet away) produce slightly different retinal images requires vision with two eyes (binocular vision)

Sweet receptors

stimulated by carbohydrates, but a few inorganic substances, including some salts of lead and beryllium, also elicit sweet sensations

Olfactory Stimulation

stimulated receptors encode specific smells, but a leading hypothesis is that each olfactory receptor cell has many copies of only one type of olfactory receptor membrane protein, but that a receptor protein can bind several related types of odorant molecules. In addition, any one odorant molecule can bind several types of olfactory receptors. The brain interprets this binding information as an olfactory code high in the nasal cavity above the usual pathway of inhaled air, so in order to smell a faint odor, a person may have to sniff and force air up to the receptor areas. Olfaction undergoes sensory adaptation rather rapidly, so the intensity of an odor drops about 50% within a second following the stimulation. Within a minute, the receptors may become almost insensitive to a given odor. This is why the odor of a fish market becomes tolerable quickly. However, olfactory receptors that have adapted to one scent remain sensitive to others. The olfactory receptor neurons are the only nerve cells in direct contact with the outside environment, and as such are prone to damage. Fortunately, basal cells along the basement membrane of the olfactory epithelium regularly divide and yield cells that differentiate to replace lost olfactory receptor neurons. These neurons are unusual in that they are regularly replaced when damaged.

accommodation

suspensory ligaments relaxes, the elastic capsule rebounds, and the lens surface becomes more convex occurs in the lens when the eye focuses to view a close object. other muscle extends back from fixed points in the sclera to the choroid coat. When the circular muscle contracts, the diameter of the ring formed by the ciliary processes decreases; when the other muscle contracts, the choroid coat is pulled forward, and the ciliary body shortens. Both of these actions relax the suspensory ligaments, thickening the lens. In this thickened state, the lens is focused for viewing objects closer than before

Taste Sensations

sweet, sour, salty, bitter, and umami Sensitive to one

Taste Pathways

taste receptor cells in the anterior two-thirds of the tongue travel on fibers of the facial nerve (VII); impulses from receptors in the posterior one-third of the tongue and the back of the mouth pass along the glossopharyngeal nerve (IX); and impulses from receptors at the base of the tongue and the pharynx travel on the vagus nerve (X). These cranial nerves conduct the impulses into the medulla oblongata. From there, impulses ascend to the thalamus and are directed to the gustatory cortex of the cerebrum, located in the insula.

Golgi tendon organs

tendons close to their attachments to muscles organ connects to a set of skeletal muscle fibers and is innervated by a sensory neuron high thresholds, and increased tension stimulates them produce a reflex that inhibits contraction of the muscle whose tendon they occupy stimulate a reflex with an effect that is the opposite of a stretch reflex reflex also helps maintain posture, and it protects muscle attachments from being pulled away from their insertions by excessive tension

general senses

those with receptors widely distributed throughout the body, including the skin, various organs, and joints Receptors that are widely distributed throughout the body Skin, various organs and joints

membranous labyrinth

tube that lies within the bony labyrinth and has a similar shape

Lacrimal puncta

two small openings in each lacrimal caruncle, drain fluid through lacrimal canaliculus into lacrimal sac

middle ear

tympanic cavity air-filled space in the temporal bone that separates the outer and inner ears Located within petrous part of temporal bone Contains air-filled tympanic cavity sound transmitted through here via tiny bones called auditory ossicles Bound medially by bony wall houses oval window and round window separates middle ear from inner ear

scala vestibuli

upper compartment leads from the oval window to the apex of the spiral filled with perilymph

macula

utricle and saccule each has a small patch of hair cells and supporting cells on its wall head is upright, the hairs of the macula in the utricle project vertically, while those in the saccule project horizontally both the utricle and saccule, the hairs contact a sheet of gelatinous material (otolithic membrane) that has crystals of calcium carbonate (otoliths) embedded on its surface. These particles add weight to the gelatinous sheet, making it more responsive to changes in position. The hair cells, which are the sensory receptors, have dendrites of sensory neurons wrapped around their bases. These neurons are associated with the vestibular portion of the vestibulocochlear nerve. also participate in the sense of dynamic equilibrium

bitter receptors

variety of chemicals stimulates many organic compounds. Inorganic salts of magnesium and calcium produce bitter sensations, too. Extreme sensitivity to bitter tastes is inherited, which is why diet colas taste sweet to some people but are bitter to others. Twenty-five types of bitter receptors have been identified. Quite a few of them detect flavors unique to fermented foods. One group of bitter compounds of medical interest are the alkaloids, which include a number of poisons such as strychnine, nicotine, and morphine. Spitting out bitter substances may be a protective mechanism to avoid ingesting poisonous alkaloids in foods.

perception

way the brain interprets this information

vitreous body

which with some collagen fibers comprise the

Detection of rotational movement

with head rotation, fluid endolymph lags behind head movement pushes against cupula, causing bending of stereocilia results in altered neurotransmitter release from hair cells and stimulation of sensory neurons bending of stereocilium in direction of kinocilium leads to increased frequency of nerve signals response primarily to changes in velocity With the three different orientations of ducts, provides information on three dimensional rotational movement

Inner Ear

within petrous part of temporal bone The spaces within the temporal bone containing the hearing and equilibrium structures are called bony labyrinth Floating within the bony labyrinth are membrane-lined fluid-filled tubes, the membranous labyrinth The membranous labyrinth contains endolymph, similar to intracellular fluid In the space between the membranous labyrinth and the temporal bone is another fluid, perilymph similar to interstitial fluid suspends, supports, and protects membranous labyrinth when the ossicles vibrate, sound waves are passed from the middle ear into the perilymph The bony labyrinth is partitioned into three sections each containing membranous labyrinth Cochlea houses cochlear duct, the hearing apparatus Vestibule contains two saclike, membranous parts for equilibrium sensation utricle and saccule, interconnected and positioned at right angles semicircular canal contains the semicircular ducts for equilibrium (position sense)

suspensory ligaments

zonular fibers strong but delicate fibers extend inward from the ciliary processes and hold the transparent lens in position The body of the lens, which lacks blood vessels, lies directly behind the iris and pupil and is composed of specialized epithelial cells.