Chapter 12Chapter 12

SensesSenses

Chapter OutcomesChapter Outcomes

Explain the difference between sensory Explain the difference between sensory reception, sensation, and perceptionreception, sensation, and perception

Describe the process of sensory Describe the process of sensory adaptationadaptation

Distinguish between the major sensory Distinguish between the major sensory receptors in the human bodyreceptors in the human body

Describe the principal structures of the Describe the principal structures of the human eye and their functionshuman eye and their functions

Chapter OutcomesChapter Outcomes

Observe the principal features of the Observe the principal features of the mammalian eye and perform experiments mammalian eye and perform experiments that demonstrate the functions of the that demonstrate the functions of the human eyehuman eyeDescribe several eye disorders and Describe several eye disorders and treatmentstreatmentsDescribe how the structures of the human Describe how the structures of the human ear support the functions of hearing and ear support the functions of hearing and balancebalance

Chapter OutcomesChapter Outcomes

Explain how humans sense their Explain how humans sense their environment through taste, smell, and environment through taste, smell, and touchtouch

Explain how small doses of neurotoxins Explain how small doses of neurotoxins can be used as painkillerscan be used as painkillers

12.1- Sensory Reception, 12.1- Sensory Reception, Sensation & PerceptionSensation & Perception

What is the difference between these What is the difference between these three?three?

ReceptionReception

SensationSensation

PerceptionPerception

Sensory ReceptorsSensory Receptors

Our sensory neurons are attached to Our sensory neurons are attached to receptors that are activated by specific receptors that are activated by specific stimulistimuli

These sensory receptors are highly These sensory receptors are highly modified ends (dendrites) of sensory modified ends (dendrites) of sensory neuronsneurons

We have a number of different types of We have a number of different types of receptors in our bodyreceptors in our body

Receptor Stimulus Information Provided

Taste Chemical Taste buds identify specific chemicals

Smell Chemical Olfactory cells detect presence of chemicals

Pressure Mechanical Movement of skin or changes in body surface

Proprioreceptors Mechanical Movement of limbs

Balance (ear) Mechanical Body movement

Outer Ear Sound Signals sound waves

Eye Light Signals change in light intensity, movement & colour

Thermoregulators Heat Detect flow of heat

Groups of ReceptorsGroups of Receptors

Often receptors are grouped in specific Often receptors are grouped in specific organs which are specialized to respond to organs which are specialized to respond to a single stimuli (such as organs for taste, a single stimuli (such as organs for taste, smell, hearing and vision)smell, hearing and vision)

The sensations that we receive from these The sensations that we receive from these receptors are actually produced in the receptors are actually produced in the brain – if transmission from the sensory brain – if transmission from the sensory neuron is blocked, the sensation stopsneuron is blocked, the sensation stops

In general, the stimuli that we respond to In general, the stimuli that we respond to are those most relevant to our survivalare those most relevant to our survivalFor example, our range of hearing and For example, our range of hearing and vision is limited compared to other vision is limited compared to other animals, even though the other stimuli are animals, even though the other stimuli are presentpresentOur senses can also undergo sensory Our senses can also undergo sensory adaptationadaptationThis occurs when a receptor becomes This occurs when a receptor becomes accustomed to a particular stimulus being accustomed to a particular stimulus being present present

Sensory Adaptation ExamplesSensory Adaptation Examples

Ever notice that some strong smells, over Ever notice that some strong smells, over time, seem to disappear?time, seem to disappear?

However, if you leave that environment However, if you leave that environment and return, the smell has seemingly and return, the smell has seemingly reappearedreappeared

This phenomenon is due to your sense of This phenomenon is due to your sense of smell becoming accustomed to that strong smell becoming accustomed to that strong smellsmell

We can also become accustomed to We can also become accustomed to temperature changestemperature changes

For instance, before you step into a warm For instance, before you step into a warm shower, the bathroom might seem shower, the bathroom might seem relatively warmrelatively warm

However, after the shower, you step out However, after the shower, you step out and feel very coldand feel very cold

This is because your body becomes This is because your body becomes accustomed to the warmer temperatures accustomed to the warmer temperatures of the showerof the shower

12.2 - The Eye12.2 - The Eye

The eye consists of three layers:The eye consists of three layers:

1.1. The ScleraThe Sclera

Outermost portion of the eyeOutermost portion of the eye

Includes the cornea & aqueous humorIncludes the cornea & aqueous humor

2.2. Choroid LayerChoroid Layer

Contains pigments that prevent light from Contains pigments that prevent light from scatteringscattering

Includes the:Includes the:

IrisIris

PupilPupil

Ciliary MusclesCiliary Muscles

3.3. RetinaRetina

Composed of three layers of cells:Composed of three layers of cells:

Rods & ConesRods & Cones

Bipolar CellsBipolar Cells

Ganglion Cell LayerGanglion Cell Layer

The RetinaThe Retina

The Fovea CentralisThe Fovea Centralis

This is a region in the center of the retina This is a region in the center of the retina that contains a dense bundle of conesthat contains a dense bundle of cones

The lens of the eye focuses the majority of The lens of the eye focuses the majority of the light on this areathe light on this area

The fovea produces sharp colour imagesThe fovea produces sharp colour images

Surrounding this area are rods which pick Surrounding this area are rods which pick up low-intensity black & white lightup low-intensity black & white light

Vision – The LensVision – The Lens

Images form on the retina because of the Images form on the retina because of the focal length of the lensfocal length of the lensUnlike plastic or glass lenses, the lens of Unlike plastic or glass lenses, the lens of the eye can change its shape, which the eye can change its shape, which makes it able to focus on near and far makes it able to focus on near and far objectsobjectsObjects 6 m (20 ft) from the eye should be Objects 6 m (20 ft) from the eye should be focused without any change to the lens’ focused without any change to the lens’ normal shapenormal shape

The Chemistry of VisionThe Chemistry of Vision

Rods and cones contain a light-sensitive Rods and cones contain a light-sensitive pigment known as rhodopsinpigment known as rhodopsinIn the absence of light, rods release inhibitory In the absence of light, rods release inhibitory neurotransmitters that inhibits nearby nerve cellsneurotransmitters that inhibits nearby nerve cellsWhen light hits this pigment it is split into two When light hits this pigment it is split into two components: Opsin (a protein) and retinene (a components: Opsin (a protein) and retinene (a form of vitamin A)form of vitamin A)This division stops the release of the inhibitory This division stops the release of the inhibitory transmitter, allowing transmission of an impulse transmitter, allowing transmission of an impulse to the optic nerveto the optic nerve

RegenerationRegeneration

As indicated by the previous diagram, the As indicated by the previous diagram, the breakdown of rhodopsin is much faster breakdown of rhodopsin is much faster than its regenerationthan its regenerationThis is responsible for the afterimages that This is responsible for the afterimages that are often seen after looking at a single are often seen after looking at a single object for a long time or at a bright lightobject for a long time or at a bright lightBright light can cause temporary blindness Bright light can cause temporary blindness because the rhodopsin is not regenerated because the rhodopsin is not regenerated in sufficient amounts to maintain visionin sufficient amounts to maintain vision

Colour VisionColour Vision

The cones used for colour vision come in The cones used for colour vision come in three varieties – red, green and bluethree varieties – red, green and blue

Slight changes in the opsin component of Slight changes in the opsin component of rhodopsin are responsible for the various rhodopsin are responsible for the various cones’ sensitivities to different colours of cones’ sensitivities to different colours of lightlight

The following diagram shows the subtle The following diagram shows the subtle differences in the opsin moleculesdifferences in the opsin molecules

As you can see, there are subtle changes to the As you can see, there are subtle changes to the amino acids that make up these proteinsamino acids that make up these proteins

Colour BlindnessColour Blindness

Colour blindness is caused when one or Colour blindness is caused when one or more of the colour cones are defectivemore of the colour cones are defective

This is caused by a mutation in the genes This is caused by a mutation in the genes that create the opsin moleculesthat create the opsin molecules

These mutations alter the sequence of These mutations alter the sequence of amino acids that make up the opsin, and amino acids that make up the opsin, and therefore change its shape and functiontherefore change its shape and function

Types of Colour BlindnessTypes of Colour Blindness

There are a number of different types of There are a number of different types of colour blindnesscolour blindnessA rare case, known as monochromacy, A rare case, known as monochromacy, occurs when a person lacks all three occurs when a person lacks all three colour pigments and can distinguish no colour pigments and can distinguish no colour at allcolour at allMore common is dichromacy, where one More common is dichromacy, where one of the pigments is absent – this is often of the pigments is absent – this is often inherited and affects males more often inherited and affects males more often than femalesthan females

Types of Colour BlindnessTypes of Colour Blindness

A third type of colour blindness is A third type of colour blindness is anomalous trichromacy, where all three anomalous trichromacy, where all three pigments are present, but have altered pigments are present, but have altered spectral sensitivityspectral sensitivity

It often results in a difficulty in It often results in a difficulty in distinguishing between red and green distinguishing between red and green hues (most common) or yellow and blue hues (most common) or yellow and blue hues (very rare) hues (very rare)

Types of DichromacyTypes of Dichromacy

Protanopia – an absence of red colour Protanopia – an absence of red colour receptors; red will appear darkreceptors; red will appear dark

Deuteranopia – green photoreceptors Deuteranopia – green photoreceptors are absent, and it affects red-green are absent, and it affects red-green colour distinctioncolour distinction

Tritanopia – total absence of blue Tritanopia – total absence of blue receptorsreceptors

What does dichromacy look like?

Other Common Vision DefectsOther Common Vision Defects

There are a number of other common There are a number of other common vision defectsvision defects

1.1. GlaucomaGlaucomaCaused by increased pressure in the Caused by increased pressure in the aqueous humoraqueous humorThis pressure causes the blood vessels This pressure causes the blood vessels in the retina to collapsein the retina to collapseThe rods and cones die because of a The rods and cones die because of a lack of oxygen and other nutrientslack of oxygen and other nutrients

Glaucoma can be treated with medication Glaucoma can be treated with medication or surgeryor surgery

Medications aim at reducing the pressure Medications aim at reducing the pressure within the aqueous humor by either within the aqueous humor by either helping it drain or reducing the production helping it drain or reducing the production of the aqueous humorof the aqueous humor

Laser or microsurgery can be used to cut Laser or microsurgery can be used to cut a small hole to relieve the fluid pressure, a small hole to relieve the fluid pressure, but this is not a permanent solutionbut this is not a permanent solution

2. Cataracts2. Cataracts

Cataracts are caused by the lens Cataracts are caused by the lens becoming more opaquebecoming more opaque

This prevents light from coming through This prevents light from coming through and reaching the retinaand reaching the retina

Cataracts can be treated by replacing the Cataracts can be treated by replacing the damaged lens with an artificial one using damaged lens with an artificial one using surgerysurgery

http://upload.wikimedia.org

3.3. AstigmatismAstigmatism

Astigmatism occurs when the lens is Astigmatism occurs when the lens is irregularly-shaped and only correctly irregularly-shaped and only correctly focuses in one planefocuses in one plane

This can be countered by using an This can be countered by using an external lens to compensate for the external lens to compensate for the irregular shape of the lens in the eyeirregular shape of the lens in the eye

4.4. Myopia (Nearsightedness)Myopia (Nearsightedness)

Myopia occurs when the eyeball is “too Myopia occurs when the eyeball is “too long” and the image from the lens long” and the image from the lens focuses in front of the retinafocuses in front of the retina

This is treated by using a biconcave lens This is treated by using a biconcave lens to diverge the light rays before they to diverge the light rays before they reach the lensreach the lens

5.5. Hyperopia (farsightedness)Hyperopia (farsightedness)The main contributing factor to hyperopia The main contributing factor to hyperopia is an eye that is “too short”, resulting in is an eye that is “too short”, resulting in the image being focused behind the the image being focused behind the retinaretinaA convex lens can be used to converge A convex lens can be used to converge the light rays before they reach the lens, the light rays before they reach the lens, which refocuses the light on the retinawhich refocuses the light on the retinaAs well, as we age, our lens becomes As well, as we age, our lens becomes less elastic and we lose the ability to less elastic and we lose the ability to focus on near objectsfocus on near objects

The Blind SpotThe Blind Spot

Where the ganglion cells merge, they form Where the ganglion cells merge, they form the optic nervethe optic nerve

At the point where the optic nerve enters At the point where the optic nerve enters the retina, it creates a region that has no the retina, it creates a region that has no rods or conesrods or cones

This is known as the blind spotThis is known as the blind spot

Visual InterpretationVisual Interpretation

Messages from the eyes travel through the optic Messages from the eyes travel through the optic nerves to the brainnerves to the brainOnce in the brain, the pieces of visual Once in the brain, the pieces of visual information are sorted, processed, and information are sorted, processed, and integrated to produce a 3-D imageintegrated to produce a 3-D imageAspects of sight such as movement, colour, Aspects of sight such as movement, colour, depth, and shape are handled by different parts depth, and shape are handled by different parts of the occipital lobeof the occipital lobeThis speeds up the processing of the visual This speeds up the processing of the visual imageimage

Note that Note that images from images from the right eye the right eye are are interpreted interpreted on the left on the left side of the side of the occipital occipital lobelobe

12.3 - The Ear12.3 - The Ear

The ear carries out two functions – it is The ear carries out two functions – it is used for balance and for hearingused for balance and for hearing

Both of these senses use specialized hair Both of these senses use specialized hair cells that are very tiny and respond to the cells that are very tiny and respond to the movement of fluids in the earmovement of fluids in the ear

Anatomy of the EarAnatomy of the Ear

The Outer EarThe Outer Ear

The outer ear consists of:The outer ear consists of:

The pinna The pinna

The auditory canal The auditory canal

The Middle EarThe Middle Ear

The middle ear produces the sound nerve The middle ear produces the sound nerve impulses that are sent to the brainimpulses that are sent to the brain

It consists of several parts:It consists of several parts:

The tympanic membrane (tympanum) The tympanic membrane (tympanum)

The ossiclesThe ossicles

The oval windowThe oval window

The Eustachian tubeThe Eustachian tube

The Inner EarThe Inner Ear

The inner ear contains:The inner ear contains:

The cochleaThe cochlea

The semicircular canalsThe semicircular canals

The vestibuleThe vestibule

Hearing and SoundHearing and Sound

Our hearing can detect sound energy as Our hearing can detect sound energy as low as 1.0low as 1.0×10×10-12-12 Watts Watts

Sound travels as pressure waves through Sound travels as pressure waves through a material, and therefore will not pass a material, and therefore will not pass through a vacuumthrough a vacuum

Sounds travel most rapidly through solids, Sounds travel most rapidly through solids, and most slowly through gasesand most slowly through gases

The Organ of CortiThe Organ of Corti

The Organ of Corti consists of three The Organ of Corti consists of three structures:structures:

The basilar membrane, which contains The basilar membrane, which contains many hair cellsmany hair cells

The hair cells, which have many tiny The hair cells, which have many tiny projections known as stereociliaprojections known as stereocilia

The tectorial membrane, into which are The tectorial membrane, into which are embedded the ends of the stereociliaembedded the ends of the stereocilia

Production of a Sound ImpulseProduction of a Sound Impulse

1.1. The tympanic membrane vibrates as The tympanic membrane vibrates as pressure waves hit itpressure waves hit it

2.2. These vibrations are passed on to the These vibrations are passed on to the ossicles, which amplify the soundossicles, which amplify the sound

3.3. The vibrations of the ossicles move the The vibrations of the ossicles move the oval window; the round window moves oval window; the round window moves as well, producing waves of fluid in the as well, producing waves of fluid in the inner earinner ear

4.4. These waves of fluid travel through the These waves of fluid travel through the cochleacochlea

5.5. The movement of fluid causes a thin The movement of fluid causes a thin membrane known as the basilar membrane known as the basilar membrane to move. This membrane is membrane to move. This membrane is attached to hair cells located in the organ attached to hair cells located in the organ of Cortiof Corti

6.6. The movement of the cilia of the hair The movement of the cilia of the hair cells against the tectorial membrane cells against the tectorial membrane produces a nerve impulse which is sent produces a nerve impulse which is sent to the brainto the brain

Production of a Sound Impulse - Animation

Hearing and PitchHearing and Pitch

Different pitches of sound can be heard by Different pitches of sound can be heard by the human ear (a range of about 20 – the human ear (a range of about 20 – 20,000 cycles per second)20,000 cycles per second)

Low-pitched sounds stimulate the hair Low-pitched sounds stimulate the hair cells near the far end of the cochlea, while cells near the far end of the cochlea, while high-pitched sounds stimulate hair cells high-pitched sounds stimulate hair cells near to the oval windownear to the oval window

Hearing LossHearing Loss

Hearing loss generally results from nerve Hearing loss generally results from nerve damage (generally damage to the hair damage (generally damage to the hair cells) or damage to the sound-conduction cells) or damage to the sound-conduction system of the outer and middle earsystem of the outer and middle ear

Repeated loud noise destroys stereociliaRepeated loud noise destroys stereocilia

Any noise over 80 dB can damage hair Any noise over 80 dB can damage hair cellscells

Hearing Loss TreatmentHearing Loss Treatment

For people who have conduction For people who have conduction deafness, hearing aids are often useddeafness, hearing aids are often usedHowever, patients with nerve deafness However, patients with nerve deafness can have a device implanted in the ear can have a device implanted in the ear that picks up sounds and transmits them that picks up sounds and transmits them directly to the auditory nervedirectly to the auditory nerveScientists have also been able to use Scientists have also been able to use viruses to insert genes that allow the viruses to insert genes that allow the growth of new stereocilia in guinea pigsgrowth of new stereocilia in guinea pigs

Perception of SoundPerception of Sound

Nerve transmissions from the ears Nerve transmissions from the ears eventually reach the temporal lobeseventually reach the temporal lobes

Depending on the neurons stimulated, the Depending on the neurons stimulated, the brain interprets the sounds as specific brain interprets the sounds as specific pitches and intensitiespitches and intensities

As well, neurons in our temporal lobes can As well, neurons in our temporal lobes can also generalize the area from which the also generalize the area from which the sound originatedsound originated

The Inner Ear – EquilibriumThe Inner Ear – Equilibrium

There are two types of equilibrium – static There are two types of equilibrium – static and dynamic equilibriumand dynamic equilibrium

Static equilibrium refers to the position of Static equilibrium refers to the position of the head, while dynamic equilibrium the head, while dynamic equilibrium provides information regarding the provides information regarding the direction of movementdirection of movement

The inner ear registers equilibrium for the The inner ear registers equilibrium for the bodybody

The Inner EarThe Inner Ear

http://oto.ucsd.edu

Gravitational EquilibriumGravitational Equilibrium

Gravitational equilibrium is maintained by Gravitational equilibrium is maintained by two fluid-filled sacs known as the utricle two fluid-filled sacs known as the utricle and the sacculeand the saccule

Inside these sacs are tiny hairs Inside these sacs are tiny hairs suspended in a jelly-like substance, which suspended in a jelly-like substance, which contains calcium carbonate granules contains calcium carbonate granules known as otolithsknown as otoliths

When the head is in When the head is in its normal position, its normal position, the otoliths do not the otoliths do not movemoveIf the head is tipped If the head is tipped sideways or sideways or backwards, the backwards, the otoliths are pulled by otoliths are pulled by the force of gravity, the force of gravity, and brush against the and brush against the ciliaciliaThe movement of the The movement of the cilia produce nerve cilia produce nerve impulses that are impulses that are sent to the brain, sent to the brain, indicating the position indicating the position of the headof the head

http://www.qmw.ac.uk

Rotational EquilibriumRotational Equilibrium

Rotational equilibrium is maintained by the Rotational equilibrium is maintained by the semicircular canals in the earsemicircular canals in the earEach canal contains a fluid-filled pocket known Each canal contains a fluid-filled pocket known as the ampullaas the ampullaRotational stimuli causes the fluid in the canals Rotational stimuli causes the fluid in the canals to moveto moveThis causes the ampulla to move, bending hair This causes the ampulla to move, bending hair cells that are attached to themcells that are attached to themThis produces a nerve impulse that is carried to This produces a nerve impulse that is carried to the brainthe brain

The AmpullaeThe Ampullae

http://geoanalyzer.britannica.com/eb/art-538

Motion SicknessMotion Sickness

Motion sickness is caused by contradictory Motion sickness is caused by contradictory messages being sent to the brainmessages being sent to the brain

It is often caused by the balance centers It is often caused by the balance centers of the ears sending a different message of the ears sending a different message than what is perceived by the eyesthan what is perceived by the eyes

This results in a nervous system response This results in a nervous system response that often includes nauseathat often includes nausea

Preventing Motion SicknessPreventing Motion Sickness

One way of preventing motion sickness is One way of preventing motion sickness is to ensure that the eyes and the ears to ensure that the eyes and the ears receive the same information – you should receive the same information – you should be able to register the motion visuallybe able to register the motion visually

Certain drugs may be used to combat Certain drugs may be used to combat motion sicknessmotion sickness

TasteTaste

Our sense of taste Our sense of taste enables us to enables us to differentiate differentiate between edible and between edible and non-edible matternon-edible matterOur taste buds are Our taste buds are arranged into arranged into sections on our sections on our tonguetongue http://www.diwinetaste.com

Our individual taste buds act in a similar manner Our individual taste buds act in a similar manner to other selective receptors in the bodyto other selective receptors in the bodyTherefore, for a chemical to activate a nerve Therefore, for a chemical to activate a nerve impulse from a taste bud, it must correctly fit impulse from a taste bud, it must correctly fit into the receptor (the ‘lock & key’ principle)into the receptor (the ‘lock & key’ principle)

Unlike other stimuli, taste requires water to Unlike other stimuli, taste requires water to operateoperate

The chemicals must be dissolved to enter The chemicals must be dissolved to enter the taste budsthe taste buds

Therefore, saliva also plays a role in Therefore, saliva also plays a role in whether or not we can taste something whether or not we can taste something that is put in our mouththat is put in our mouth

SmellSmell

Our sense of smell is similar to our sense Our sense of smell is similar to our sense of tasteof taste

Receptor sites on olfactory cells in our Receptor sites on olfactory cells in our nose are designed to combine with nose are designed to combine with molecules of a certain geometrymolecules of a certain geometry

The messages that are produced by the The messages that are produced by the receptors are then sent to the olfactory receptors are then sent to the olfactory bulb of the brainbulb of the brain

Smell and Taste TogetherSmell and Taste Together

You may be familiar with the fact that both You may be familiar with the fact that both taste and smell work togethertaste and smell work together

For instance, when you have a cold, the For instance, when you have a cold, the olfactory receptors in your nose do not olfactory receptors in your nose do not work as effectively, and therefore you work as effectively, and therefore you have a diminished sense of tastehave a diminished sense of taste

People such as wine tasters use both of People such as wine tasters use both of these senses togetherthese senses together

TouchTouch

Mechanoreceptors for touch are located Mechanoreceptors for touch are located throughout the bodythroughout the bodyDifferent receptors are sensitive to stimuli Different receptors are sensitive to stimuli such as light touch, pain, and high and low such as light touch, pain, and high and low temperaturestemperaturesThe receptors that release pain signals, as The receptors that release pain signals, as we have seen, release impulses to the we have seen, release impulses to the brain which can be blocked by pain brain which can be blocked by pain medicationsmedications

Sensation and HomeostasisSensation and Homeostasis

Our senses allow our bodies to maintain Our senses allow our bodies to maintain homeostasishomeostasis

Our senses of sight, touch, taste, smell, Our senses of sight, touch, taste, smell, and hearing give us information on which and hearing give us information on which to actto act

Neurotoxin PainkillersNeurotoxin Painkillers

Many animals (such as frogs, puffer fish, and Many animals (such as frogs, puffer fish, and cone snails) produce neurotoxinscone snails) produce neurotoxinsMany of these neurotoxins work by preventing Many of these neurotoxins work by preventing the transmission of an impulse through a neural the transmission of an impulse through a neural pathwaypathwayScientists are currently studying whether or not Scientists are currently studying whether or not many of these compounds could be used to many of these compounds could be used to prevent the transmission of pain messages prevent the transmission of pain messages without the side-effects of morphine and other without the side-effects of morphine and other opiate-based drugsopiate-based drugs