Biology - An Illustrated Guide to Science (794127), страница 32
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It links tothe back of the throat through theeu stachian tu be, which allows airpressure to be balanced on both sidesof the drum.● Crossing the space of the middleear are the au ditory ossicles: thehammer, anvil, and stirrup. Thesepass vibrations across the middleear and into the inner ear via theoval window.
The auditory ossiclesact as a mechanical amplifier andincrease the amplitude of the soundwaves as they pass.The inner eartympanum (eardrum)The inner ear is completelyencased in the bone of the skulland is a fluid-filled cavitycontaining the cochlea and thesem icircu lar can als.● Vibrations enter the inner ear throughthe oval window and are convertedinto pressure waves that pass alongthe coiled tube of the cochlea andleave through the round window.
Thecochlea can interpret these pressurewaves as sounds.● The vestibular apparatus—consistingof the semicircular canals, utrile,saccule, and vestibule—is the organ ofbalance.oval windowround windowvestibuleeustachian tube© Diagram Visual Information Ltd.●184HUMAN BIOLOGYKey wordsauditory ossiclecochleaotolithsemicircularcanalCoordination: hearingand balanceHearingsemicircular canalsPassage of sound waves through the earossicles:stapes (stirrup)Path of vibrationsSound entering the outer earpasses along the ear canal to theeardrum. Here it is converted tomovement and passes along theau ditory ossicles.● The stapes passes thesemovements into the cochlea,where fluids call perilymphand endolymph createpressure waves.
The frequencyof the pressure waves matchesthe frequency of the originalsound entering the ear.ear canalHearingcochleatympanum (eardrum)The pressure waves stimulate thehair cells of the organ of Corti, amembrane lying between thebasilar and tectorial membranes. Itis the movement of these hair cellsthat converts the vibrations intonerve impulses.● The auditory cortex in the brainreceives these impulses andinterprets them as sounds.●The sem icircu lar can als areconcerned with balance.● When the head moves, endolymph inthe canals moves due to momentum.The movement of the fluid disturbsthe otoliths, which are suspended onsensory hair cells.● The brain can use information fromthese sensory cells to detect bodymovements, even when other sourcesof information (e.g., visual) areunavailable.● Normally, balance is assessed usinginformation from both eyes and ears.sacculemalleus (hammer)●Balanceutricleincus (anvil)oval windowSide view of cochleacochleadirection of sound waves© Diagram Visual Information Ltd.●auditory nervecross sectionof cochleaCross section of cochleaperilymphtectorialmembraneorgan of Cortiendolymphsensory hair cellbranch ofauditorynervebasilar membraneperilymph185Coordination: eyestructureHUMAN BIOLOGYKey wordsoptic cortexoptic nervevitreous humorSightPartial section of eye to show orbit and extrinsic musclesoptic nerveextrinsic muscletear glandeyelidpupilirisExternal structureThe eye is a light-proof ball filled witha clear jelly-like substance.
The toughouter layer is called the sclera (seebottom diagram) and is transparent atthe front to let light in.● Muscles are attached to the sclera toturn the eye in its socket. A singleoptic n erve comes out of the back ofthe eye and connects directly to theoptic cortex at the back of the brain.●Internal structureThe eyeball is filled with a clear, jellylike substance called the vitreou shu m or. This keeps the eyeball fullyinflated—if it were to deflate it wouldnot be able to focus correctly.● The choroid is a layer found inside thesclera. It is black in color to helpreduce internal reflections.● Blood vessels in the choroid supplythe retina with food and oxygen, andtake away waste products.● Light entering the eye passes throughthe cornea, the transparent layer at thefront of the eye covered by theconjunctiva.
It refracts light to aidfocusing.● The iris, behind the cornea, is acolored ring of muscular tissue. Byaltering the size of the pupil, itscentral opening, it controls theamount of light entering the eye.● The aqueous humor connects thecornea with the lens and helpsmaintain the convex shape of thecornea necessary for the convergenceof light at the lens.● The transparent lens focuses light onto the retina.● The retina contains the light-sensitivecells called rods and cones. Rodsrespond to light level alone and enableblack and white vision in dim light.The brain combines information fromthese three cell types to produce a fullcolor image.
Cones need a higher lightintensity to function than rods do.eyeballbone of orbitconjunctivaeyelidVertical sectionextrinsic musclesuspensory ligamentslensvitreous humoraqueous humorpupilopticnerveirisretinacorneachoroidscleraconjunctiva© Diagram Visual Information Ltd.●186HUMAN BIOLOGYKey wordsneuronCoordination: lightsensitivityRetinaV ertical section of eyeRetinaThere are two types of light-sensitivecells in the retina: rods, which aremost numerous and provide vision indim light; and cones, which work inbright light and provide color vision.Cones exist in three different forms,with each one responding to a slightlydifferent color of light (broadly red,green, and blue).● The cells contain visual pigments.When light strikes the cell, it istemporarily bleached, producing anelectrical signal. These signals areconveyed to the brain as nerveimpulses via connecting n eu ron s andsensory nerve fibers.●retinal structureretinachoroidscleraRetinal structurechoroid© Diagram Visual Information Ltd.retinaconeassociation neuronsynapsesensoryfibersrodpigmentlayer187Coordination: endocrinesystemEndocrine glandsHUMAN BIOLOGYKey wordsadrenalinbasal metabolicrateendocrine glandhormonehypothalamusMaleinsulinpituitary glandpineal glandpituitary glandEndocrine glandsEn docrin e glan ds, sometimes calledductless glands, produce secretionsthat pass directly into the blood.● Endocrine secretions are calledhorm on es and change the functioningof a distant organ in the body.
So, thehormone adren alin , produced by theadrenal gland, increases the heart rate.● The organ affected by a particularhormone is called the target organ.●thyroid glandparathyroidglandsthymusadrenalglandsHormonal coordinationHormonal coordination is used by thebody to control many long-termchanges, e.g., growth anddevelopment.● The most important endocrine glandin the body is the pitu itary glan d,which secretes hormones that regulateother endocrine glands.●pancreastestesFemaleKey endocrine glandsThe adrenal glands secrete adrenalin,which stimulates the body to producea “fight or flight” response to stress.● Testes and ovaries secrete a range ofhormones to control sexualdevelopment.● The thyroid gland secretes a hormonethat controls the basal m etabolic rate.● The pancreas contains cells thatsecrete in su lin , which reduces thelevel of sugar in the blood.● Parathyroid glands produce hormonesthat regulate the amount of calciumand phosphorus in the body.● The pineal gland secretes melatonin,which plays a role in sleep, aging, andreproduction.● The thymus and the pituitary andhypothalamus in the brain also haveendocrine functions.● The thymus gland is also involved inthe production of T-lymphocytes,essential components of the immunesystem.hypothalamuspituitary glandpineal glandthyroid glandparathyroidglandsthymusadrenalglandspancreasovaries© Diagram Visual Information Ltd.●188HUMAN BIOLOGYKey wordsendocrine glandhormonehypothalamuspituitary glandCoordination: pituitaryglandHormones produced by the pituitary glandhypothalamusThe “master gland”The pitu itary glan d is called the“master gland” because it secreteshorm on es that control the activity of arange of other en docrin e glan ds.● The pituitary gland consists of twotypes of tissue: endocrine at theanterior, and nervous at the posterior.Development in the embryo clearlyshows the two sources of tissues thatmake up this hybrid organ.● The posterior lobe is connected to thebrain through the hypothalam u s.These connections link the twocoordination systems in the body: thenervous system and the endocrinesystem.●12anterior lobeThe anterior lobeThe anterior lobe secretes hormonesthat influence the activity of glandslike the adrenal, thyroid, and gonads.● Growth hormone regulates the growthof long bones.● Prolactin stimulates the mammaryglands to secrete milk.posterior lobepituitary●34The posterior lobeHormones secreted by the posteriorlobe tend to produce more rapidshort-lived responses than hormonesfrom the anterior lobe.● Vasopressin (an anti-diuretichormone) increases waterreabsorption by the kidney to producemore concentrated urine.● Oxytocin stimulates the contraction ofuterine muscles during childbirth.© Diagram Visual Information Ltd.●5671 Oxytocin: contraction ofsmooth muscle of uterus.2 Vasopressin: anti-diuretichormone, reduces volumeof urine produced by kidney.3 Thyroid stimulatinghormone: stimulates thyroidto produce thyroxine.4 Prolactin: stimulatesmammary glands tosecrete milk.5 Adrenocorticotrophichormone: stimulatesadrenal cortex to secreteadrenocorticoid hormones.6 Gonadotrophic hormone:stimulates ovaries or testesto secrete sex hormones.7 Growth hormone:regulates growth in body.189Locomotion: skeletonHUMAN BIOLOGYKey wordsSkeletonaxial skeletonpentadactyl limbcraniummandible (lower jaw)BonesThe adult human skeleton contains206 bones, though some are so closelyfused together (e.g., the plates of theskull) that they effectively form asingle bone.● The largest bones in the body are thefemurs of the legs.
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