UNIT 8:SENSE ORGANS• Chemical senses• Sense of vision• Sense of hearing and balanceRefer to MADER, 2010: CHAPTER 38 P. 702 - 716
CHEMICAL SENSES The receptors responsible for taste andsmell – CHEMORECEPTORS 2 Types of chemical senses:1. Sense of Taste2. Sense of Smell
SENSE OF TASTE Taste receptors = TASTE BUDS Taste buds are located on tongue(mainly), hardpalate, pharynx and epiglottis. The tongue very rough, due to numerous papillae. 3 Types of papillae:- Fungiform- found on front and sides oftongue.- Foliate found on front 2/3 of tongue- Curcumvallate- found on the back of thetongue. The taste buds are located on the papillae
FUNCTIONS OF TASTE BUDS Chemical molecules in food, dissolve in the saliva. The molecules bind to the receptor proteins in themicrovilli of the taste buds. This stimulates the taste cells to send an impulsethrough the sensory nerve fibers. Impulse move to the parietal lobe of cerebrum. Taste is interpreted
5 PRIMARY TYPES OF TASTE Sweet Sour Bitter Salty Umami (Japanesesavory taste)- Certain regions of thetongue are moresensitive to particulartastes.
SENSE OF SMELL Receptor cells of smell are OLFACTORY CELLS Olfactory cells are located within olfactory epitheliumhigh in the roof of the nasal cavity.
PERCEPTION OF SMELL The gas molecules inthe air dissolves in themucus of the nasalcavity. It stimulates themicrovilli of olfactorycells. This cause an impulse tobe send from olfactorycell through the sensorynerve fibers, to theolfactory bulb in thetemporal lobe of thecerebrum. Smell is integrated andperceived.
SENSE OF VISION Photoreceptors are sensory receptors that aresensitive to light. Animals and humans with 2 eyes facing forwardhave 3D or stereoscopic vision, visual fieldsoverlap and each eye is able to view and objectfrom a different angle.
THE HUMAN EYEMain parts of the eye found in 3 main layers1. Outer layer (Cornea, Sclera)2. Middle layer (Choroid, ciliary body, iris)3. Inner layer (Retina – rods, cones, fovea) Other parts of importance:1. Lens (Attach to suspensory ligaments)2. Humors (Aqueous humor and vitreoushumor – Transmit light rays and supporteyeball)3. Optic nerves – Transmits impulses to thebrain
OUTER LAYER (STRUCTURE AND FUNCTION) The sclera: white outer layer, protectsand supports eyeball Cornea: Front transparent part of eye.Refracts light rays Conjunctiva: Transparent membrane(front). Moistens eye surface.
MIDDLE LAYER STRUCTURE AND FUNCTIONS Pupil: Hole in middle of eye. Black. Admits lightinto eye. The choroid: Pigmented 2nd layer. Absorb straylight. Contain blood vessels for nutrition andoxygen. The iris: Coloured part of the eye that regulatesthe size of the pupil and therefore light entrance The lens: Transparent biconvex structure thatrefract and focuses light on the retina
INNER LAYER, STRUCTURE AND FUNCTION The retina: contains photoreceptors(cones and rods)- Rods: Make black and white visionpossible/ overview sight- Cones: Make colour vision possible- Fovea centralis: Best image possible- Blind spot: place where nerves andblood vessels enter and leave the eyeball.No image can be seen if light is focusedon this point.
The eye is divided into two cavitiesseparated by the lens and cilliary body: The anterior cavity is filled with watery aqueous humor The posterior cavity is filled with jellylike vitreoushumorThe cilliary body produces the aqueoushumor
Fig. 50-18OpticnerveFovea (centerof visual field)LensVitreous humorOptic disk(blind spot)Central artery andvein of the retinaIrisRetinaChoroidScleraCiliary bodySuspensoryligamentCorneaPupilAqueoushumor
ACCOMMODATION The ability of the lens to change shape to enablethe eye to focus on near and far objects.=accommodation
VISUAL DISORDERSNearsightedness/Myopia Can see objects closer than6m, but not far objects. Have an elongated eyeball. When looking at a farobject, the image is focusedin front of the retina. These people can wearconcave lenses, whichdiverge the light rays so thatthe image can be focusedon the retinaFarsightedness/Hypermetropic Can see objects far but notnear objects. Have a shortened eyeball. When looking at a nearobject, the image is focusedbehind the retina. These people can wear aconvex lens, to increase thebending of light rays so thatthe image can be focused onthe retina
VISUAL DISORDER: ASTIGMATISM When the cornea orlens is uneven and theimage that you see isfuzzy. Can be corrected bywearing glasses withan unevenly groundlens to compensate forthe uneven cornea.
PHOTORECEPTORS Found in the retina of the eye. 2 Types: Rods and Cones They consist of an outer segment and an innersegment joined by a stalk. Visual pigment found in rods, is a deep-purplepigment called Rhodopsin. Rods are sensitive to light and are therefore suitedfor night vision (black and white) and peripheralvision. Rods found on either side of fovea- the furtheraway from the fovea – the more rods present.
The cones, are primary located in the foveacentralis, the further away from the fovea the lessthe cones. Activated by bright light Cones allow us to detect fine detail and colour. Cones contain 3 pigments –B (blue), G (green) andR (red) In colour blindness, a person lack certain of thesepigments.
INTEGRATION OF VISUAL SIGNALS IN THERETINA Light enter the eye through the cornea, aqueoushumor, pupil, lens, vitreous humor and focuseson the retina. Light stimulates the photoreceptors (rods andcones) in the retina. Retina sends an impulse to the optic nerves Optic nerves send an impulse to the occipital lobeof the cerebrum Where sight is integrated.
THE SENSE OF HEARING AND BALANCE The ear has two sensory functions: Hearing andBalance. The sensory receptors for both of these is locatedin the inner ear, and each consist of hair cells andcillia which are sensitive to mechanical stimulation.They are called machanoreceptors.
FUNCTIONS OFDIFFERENTPARTS OF THEEAROUTER EARMIDDLE EARINNER EAR
THE OUTER EAR Pinna – Concentrate sound waves in the direction of theexternal auditory canal. External Auditory canal – Transport sound waves from the pinna to the tympanicmembrane. - Contain fine hairs and cerumin glands that secrete cerumin(earwax) to help guard the ear against foreign material andinsects. (smell) Tympanic membrane – A thin membrane that covers the opening between the inner-and middle ear. - Converts soundwaves into vibrations. (starts to vibrate)
MIDDLE EAR 3 Bony ossicles e.g.: (start to vibrate): - Malleus – transmit vibration to incus - Incus – transmit vibrations to stapes - Stapes – transmit vibrations to oval window (fenestraovalis) Oval window – start to vibrate and cause waves inliquid (perilymph) in cochlea. Eustachian tube – Equalize the pressure between theatmosphere and the inside of the ear. (Connested withthe pharynx)
INNER EAR Cochlea: - Snail shaped canal. - Divided in 3 canals separated by membranes - Vestibular canal(scale vestibuli) – top canal, filled withperilymph. Receives vibration from oval window, form wavesin perilymph, causes Reissner membrane to form waves. - Cochlear canel (Scala media) – middle canel, filled withendolymph. Form waves in enolymph, that causes Basilarmembrane to wave up and down. Contains the receptor cellsfor hearing: Organ of Corti - which pushes the stereociliaagainst the tectorial membrane, causes an impulse whichis send through the cochlear nerves to the temporal lobeof the brain for integration. - Tympanic canal (Scala tympani)– bottom canal, filled withperilymph. Form waves which are carried to the roundwindow (fenestra rotunda). Round Window: absorb excess sound waves to preventechoing in the ear.
COCHLEACross section through cochleaCochlear unrolled
INNER EAR: SEMI CIRCULAR CANALS Contain machanorecepters (cristae) – detectrotational or angular movement of the head. Cristae- located in the ampulla (enlarged base ofsemi circular canals)in the endolymph found in thesemi circular canals. - Consist of hair cells, supporting cells, stereocilliaimbedded in a gelatin capsule called cupula, andnerve fibers. Movement of the head causes the endolymph tomove around in the ampulla, the cupula moves,bending the stereocilia, causing an impulse sendthrough the vestibular nerve to the cerebellum ofthe brain for integration.
INNER EAR: UTRICULUS AND SACCULUS Enlarged area below the semi circular canals. Contain mechanoreceptors (macula) – that detectsstraight line movement of the head in any direction– gravitational equilibrium. Macula: -Consist of hair cells with stereocilia embedded in agelatin membrane called otolithic membrane withotoliths (crystals) ontop, supporting cells andvestibular nerves. - If a person stops suddenly, the endolymph in theutriculus and sacculus move around, the otolithicmembrane moves, bending the stereocilia, whichsends an impulse through the vestibular nerves tothe cerebellum of the brain to maintain balance.