SENSORY PROCESSESSENSORY PROCESSES

SENSATIONSENSATION Every organism tries to adjust himself in Every organism tries to adjust himself in

the environment.the environment. For adjustment it is necessary that For adjustment it is necessary that

organism should be aware of the organism should be aware of the environment.environment.

This awareness is generated through sense This awareness is generated through sense organs of the organism.organs of the organism.

Sense organ is the tissue system senstive Sense organ is the tissue system senstive to energies generally adapted from the to energies generally adapted from the environment, but also sensitive to those environment, but also sensitive to those applied within the body.applied within the body.

Sensation is the combined activity of the Sensation is the combined activity of the sensory receptors and central nervous sensory receptors and central nervous system.system.

They receive, process and analyze They receive, process and analyze physical energy.physical energy.

Sensation occurs due to the Sensation occurs due to the impingement of the stimulus on the impingement of the stimulus on the sense organ then receptors, neural sense organ then receptors, neural transmitter, nerves and finally CNS. transmitter, nerves and finally CNS. It is a physiological process.It is a physiological process.

DEFINITIONSDEFINITIONS

Acc. To kendler and Kendler (1971) “ An Acc. To kendler and Kendler (1971) “ An organism is sensitive to the stimulus organism is sensitive to the stimulus when he can respond to it that is when when he can respond to it that is when he can discriminate it from other he can discriminate it from other stimulus .“stimulus .“

Acc to rathus et.al. (1986) “ sensation is Acc to rathus et.al. (1986) “ sensation is the stimulation of sensory receptors the stimulation of sensory receptors and the transmission of sensory and the transmission of sensory information to central nervous system.”information to central nervous system.”

In short sensation is that process by In short sensation is that process by which an organism gets aware of the which an organism gets aware of the presence of some stimulus in the presence of some stimulus in the environment. There are different environment. There are different stimuli for different sense organs stimuli for different sense organs such as photic stimulus will affect the such as photic stimulus will affect the eye and acoustic stimulus will affect eye and acoustic stimulus will affect the ear.the ear.

PROCESS OF SENSATIONPROCESS OF SENSATION

StimulusStimulus Sense organsSense organs nerve nerve impulseimpulse sensory nervessensory nerves Brain Brain perceptionperception motor nerves motor nerves taking the messagetaking the message Reaction Reaction towards the stimulustowards the stimulus

STIMULUSSTIMULUS Stimulus refers to the physical energy that Stimulus refers to the physical energy that

stimulates the receptors.stimulates the receptors. Some physical energies are weak and they Some physical energies are weak and they

do not stimulate the sense organs. These do not stimulate the sense organs. These physical energies are not termed as stimulus.physical energies are not termed as stimulus.

Stimulus can be adequate and inadequate.Stimulus can be adequate and inadequate. Stimulus can also be classified on basis of Stimulus can also be classified on basis of

external and internal environment.external and internal environment. Stimulus can also be classified into five types Stimulus can also be classified into five types

i.e. mechanical, thermal, chemical, acoustic, i.e. mechanical, thermal, chemical, acoustic, photic.photic.

RECEPTORSRECEPTORS

Receptor is a peripheral specialized Receptor is a peripheral specialized part of an analyzer that transforms part of an analyzer that transforms only specific forms of energy into only specific forms of energy into nervous excitation.nervous excitation.

Receptors work as transducers.Receptors work as transducers. Their basic function is to transform Their basic function is to transform

the physical energy impinging the the physical energy impinging the sense organ into nerve impulse.sense organ into nerve impulse.

CHARACTERISTICS OF CHARACTERISTICS OF RECEPTORSRECEPTORS

Extra senstivityExtra senstivity SelectivitySelectivity Prolonged responseProlonged response

CLASSIFICATION OF CLASSIFICATION OF RECEPTORSRECEPTORS

CLASSCLASS SENSES INVOLVEDSENSES INVOLVED BASIS OF BASIS OF CLASSIFICATIONCLASSIFICATION

ExtroceptoExtroceptorsrs

Cutaneous pressure, Cutaneous pressure, pain, warmth, vision, pain, warmth, vision, olfaction, gustationolfaction, gustation

They mainly interact They mainly interact with the stimulus that with the stimulus that occur near the occur near the surface of the body surface of the body and are involved in and are involved in bodily movementsbodily movements

IntroceptorIntroceptorss

Organic pain, pressure, Organic pain, pressure, organic warmth, organic organic warmth, organic cold, olfaction, gustationcold, olfaction, gustation

These receptors are These receptors are involved in digestion involved in digestion and they interact and they interact with the internal with the internal bodily movement due bodily movement due to change in the to change in the internal environment. internal environment.

ProprioceptoProprioceptorsrs

Muscle, Kinesthesis, joint Muscle, Kinesthesis, joint kinesthesis etc.kinesthesis etc.

These receptors are These receptors are found in muscles, found in muscles, tendons and joints tendons and joints and non- auditory and non- auditory inner ear.inner ear.

NociceptorsNociceptors Cutaneous pain, organic Cutaneous pain, organic pain, kinesthetic painpain, kinesthetic pain

These receptors are These receptors are involved when we involved when we are interacting with are interacting with injurious stimulus injurious stimulus and they show their and they show their movement by flexionmovement by flexion

ATTRIBUTES OF SENSATIONATTRIBUTES OF SENSATION Quality- It is due to the structural difference of Quality- It is due to the structural difference of

sensation due to different sense organs.sensation due to different sense organs. Intensity – It refers to the strength of the Intensity – It refers to the strength of the

sensation. It depends on the intensity of the sensation. It depends on the intensity of the stimulus and effeciency of the sense organ.stimulus and effeciency of the sense organ.

Duration – It refers to the period during which a Duration – It refers to the period during which a sensation is experienced. It depends on for that sensation is experienced. It depends on for that period the stimulus has operated on the sense period the stimulus has operated on the sense organ.organ.

Vividness or clarity – Clarity of the sensation Vividness or clarity – Clarity of the sensation depends on the intensity and duration of stimulus depends on the intensity and duration of stimulus and also on the functional efficiency of the sense and also on the functional efficiency of the sense organ.organ.

Extensity – It refers to the area of the Extensity – It refers to the area of the sense organ stimulated by the sense organ stimulated by the stimulus e.g. touch of pin is different stimulus e.g. touch of pin is different from the touch of block. So the from the touch of block. So the extensity of the sensation depends extensity of the sensation depends on the area of the sense organ being on the area of the sense organ being stimulated.stimulated.

Localization – It means to detect the Localization – It means to detect the point of the object or stimulus. The point of the object or stimulus. The attribution is mainly related to attribution is mainly related to tactual sensation.tactual sensation.

STRUCTURE OF HUMAN EYESTRUCTURE OF HUMAN EYE

STRUCTURE OF HUMAN EYESTRUCTURE OF HUMAN EYE

Eye is the sense organ meant for visual Eye is the sense organ meant for visual sensation.sensation.

It is necessary to know the functions and It is necessary to know the functions and structure of human eye if we want to know structure of human eye if we want to know about the visual sensation.about the visual sensation.

The eyeball is almost spherical and the The eyeball is almost spherical and the common analogy is that eyeball resembles common analogy is that eyeball resembles a camera.a camera.

It has 25 mm of diameter and 7gms weight.It has 25 mm of diameter and 7gms weight.

Eyeball has three important parts -:Eyeball has three important parts -:1. 1. SCLERA or SCLEROTIC COAT SCLERA or SCLEROTIC COAT – – The outermost cover is called sclera The outermost cover is called sclera which maintains shape of the eye and which maintains shape of the eye and protects delicate structure of the eye. It protects delicate structure of the eye. It is tough white opaque coat that forms is tough white opaque coat that forms white of the eye in front with the a white of the eye in front with the a transparent window membrane the transparent window membrane the cornea.cornea.2. 2. CHOROIDCHOROID- It is attached to sclera. It - It is attached to sclera. It consist of blood vessels and provides consist of blood vessels and provides major source of nutrition to the eye. It major source of nutrition to the eye. It obstacles extra light coming to the eye.obstacles extra light coming to the eye.

CILIARY BODY- It is the ring of muscles CILIARY BODY- It is the ring of muscles that are joined with the lens with the help that are joined with the lens with the help of suspensory ligaments.of suspensory ligaments.

IRIS- Front of choroid is modified to form IRIS- Front of choroid is modified to form Iris. Iris originates from ciliary body. Iris is Iris. Iris originates from ciliary body. Iris is a structure of smooth muscles that a structure of smooth muscles that surrounds the pupil. The pigmented layer surrounds the pupil. The pigmented layer behind the iris gives colour to the eye.behind the iris gives colour to the eye.

PUPIL - The opening in the iris is called PUPIL - The opening in the iris is called pupil. Pupil size adjusts automatically to pupil. Pupil size adjusts automatically to the amount of light. When lighting the amount of light. When lighting conditions are poor (dim light) the iris conditions are poor (dim light) the iris opens to increase the size of or dilate the opens to increase the size of or dilate the pupil. When light is bright the iris closes pupil. When light is bright the iris closes thereby contracting the pupil.thereby contracting the pupil.

RETINARETINA- it is like the film or image surface of - it is like the film or image surface of the camera. Retina is a multilayered screen the camera. Retina is a multilayered screen that arises at the back surface of the eyeball that arises at the back surface of the eyeball and contains specialized sensory neurons. The and contains specialized sensory neurons. The retina consists of photosensitive cells called retina consists of photosensitive cells called rods and cones, bipolar cells and rods and cones, bipolar cells and ganglion cellsganglion cells..

FOVEAFOVEA- it is a pit in front of the pupil. There - it is a pit in front of the pupil. There are no rods on fovea, only cones are present. are no rods on fovea, only cones are present. This is the point of most clear vision. Receptors This is the point of most clear vision. Receptors are located on fovea or around fovea.are located on fovea or around fovea.

There is a point on retina called There is a point on retina called blind blind spotspot. This point is located near fovea. . This point is located near fovea. No image is formed on this point. There No image is formed on this point. There are no rods and cones on this point so no are no rods and cones on this point so no colour vision occurs on this point.colour vision occurs on this point.

Optic nerve leaves for brain from this Optic nerve leaves for brain from this point.point.

Aqueous humor and vitreous humor- Aqueous humor and vitreous humor- these are two types of liquids present in these are two types of liquids present in the eye. These liquids absorbs some the eye. These liquids absorbs some amount of light while scatter the rest of amount of light while scatter the rest of light.light.

RODS AND CONESRODS AND CONES

Cones are responsible for sensation Cones are responsible for sensation of hues and brightness.of hues and brightness.

Cones are activated only in light.Cones are activated only in light. Cones contain an chemical pigment Cones contain an chemical pigment

called iodopsincalled iodopsin Light acts upon iodopsin and converts Light acts upon iodopsin and converts

it into intermediate compounds it into intermediate compounds Intermediate compounds breaks it Intermediate compounds breaks it

into vitamin A and conopsin.into vitamin A and conopsin.

Rods are sensitive only to brightness.Rods are sensitive only to brightness.

Rods have sensation of grey and different Rods have sensation of grey and different shades of grey.shades of grey.

Rods are activated in the dark. That is why Rods are activated in the dark. That is why we do not perceive colours in the dark.we do not perceive colours in the dark.

A chemical component called A chemical component called rhodopsinrhodopsin is is present in the rods.present in the rods.

Light is converted to intermediate Light is converted to intermediate compounds which excite the rods. These compounds which excite the rods. These then break down to rhodopsin and vitamin then break down to rhodopsin and vitamin A.A.

FUNCTIONS OF EYEFUNCTIONS OF EYE

Light enters through the cornea.Light enters through the cornea. Light passes through the aqueous humor Light passes through the aqueous humor

to pupil.to pupil. The amount of light that enters in is The amount of light that enters in is

determined by the iris.determined by the iris. Light reaches the lens.Light reaches the lens. Lens adjusts the light on retina.Lens adjusts the light on retina. Light rays pass through the viterous Light rays pass through the viterous

humor and image is formed on retina.humor and image is formed on retina.

Rods and cones transmit the neural Rods and cones transmit the neural message to bipolar cells and ganglion message to bipolar cells and ganglion cells.cells.

Optic nerve is generated by axons in Optic nerve is generated by axons in the ganglion cells.the ganglion cells.

Sensory input reaches the brain.Sensory input reaches the brain.

This neural message reaches the This neural message reaches the occipital lobe where visual sensation occipital lobe where visual sensation occurs.occurs.

STRUCTURE OF HUMAN EARSTRUCTURE OF HUMAN EAR

STRUCTURE OF HUMAN EARSTRUCTURE OF HUMAN EAR

The ear is divided into three main The ear is divided into three main areas: areas:

Outer (external) ear Outer (external) ear Middle ear Middle ear Inner ear Inner ear

OUTER EAROUTER EAR

Outer ear is divided into three partsOuter ear is divided into three parts PinnaPinna Auditory canalAuditory canal Eardrum Eardrum

The first step in hearing is the entrance The first step in hearing is the entrance of sound waves into the of sound waves into the external external auditory canalauditory canal. .

The outer ear consists of an outer, The outer ear consists of an outer, funnel-like structure called the funnel-like structure called the auricle(or auricle(or pinnapinna) and an S-shaped tube, ) and an S-shaped tube, the external auditory meatus. the external auditory meatus.

The shapes of the outer ear (the auricle) The shapes of the outer ear (the auricle) and the external auditory canal can help and the external auditory canal can help amplify and direct the sound.  amplify and direct the sound. 

The sound waves reverberate from the The sound waves reverberate from the sides and end of the external auditory sides and end of the external auditory canal, filling it with the continuous canal, filling it with the continuous vibrations of pressure waves. vibrations of pressure waves.

The auricle of the ear helps to collect sound The auricle of the ear helps to collect sound waves travelling through air and directs them waves travelling through air and directs them into the auditory meatus. into the auditory meatus.

Sound waves entering the external auditory Sound waves entering the external auditory canal eventually hit the canal eventually hit the tympanic membranetympanic membrane, , or eardrum (tympanum = drum), the boundary or eardrum (tympanum = drum), the boundary between the outer and middle ears.  between the outer and middle ears. 

The eardrum is a thin, translucent, connective The eardrum is a thin, translucent, connective tissue membrane, covered by skin on its tissue membrane, covered by skin on its external face and by a mucosa internally.  external face and by a mucosa internally. 

It is shaped like a flattened cone, with its apex It is shaped like a flattened cone, with its apex protruding medially into the middle ear.  protruding medially into the middle ear. 

Sound waves make the eardrum vibrate; the Sound waves make the eardrum vibrate; the eardrum, in turn, transfers the sound energy to eardrum, in turn, transfers the sound energy to the tiny bones of the middle ear and sets them the tiny bones of the middle ear and sets them into vibration. into vibration.

THE MIDDLE EAR THE MIDDLE EAR

It consists of an air-filled space in the It consists of an air-filled space in the temporal bone called the tympanic cavity temporal bone called the tympanic cavity that separates the external and inner ears, that separates the external and inner ears, an eardrum or tympanum (tympanic an eardrum or tympanum (tympanic membrane), and three small bones called membrane), and three small bones called auditory ossicles.  auditory ossicles. 

The tympanic membrane is the first The tympanic membrane is the first structure to respond to sound by vibrating structure to respond to sound by vibrating sympathetically with the airborne waves.  sympathetically with the airborne waves. 

The tympanic membrane is stretched across The tympanic membrane is stretched across the end of the external auditory canal, and the end of the external auditory canal, and air molecules push against the membrane, air molecules push against the membrane, causing it to vibrate at the same frequency causing it to vibrate at the same frequency as the sound wave. as the sound wave.

It has an oval margin and is cone-shaped, It has an oval margin and is cone-shaped, with the apex of the cone directed inward.  with the apex of the cone directed inward. 

The auditory ossicles being the smallest bones in The auditory ossicles being the smallest bones in the body are named according to their shapethe body are named according to their shape

MalleusMalleus (hammer) (hammer) Incus Incus (anvil)(anvil) Stapes Stapes (stirrup).  (stirrup).  The handle of the malleus  is secured to the The handle of the malleus  is secured to the

eardrum, and the base of the stapes fits into the eardrum, and the base of the stapes fits into the oval window.  oval window. 

tiny ligaments suspend the ossicles, and tiny ligaments suspend the ossicles, and minisynovial joints link them together into a chain minisynovial joints link them together into a chain that spans the middle ear cavity.  that spans the middle ear cavity. 

The ossicles  transmit the vibratory motion of the The ossicles  transmit the vibratory motion of the eardrum  to the oval window, which in turn sets eardrum  to the oval window, which in turn sets the fluids of the inner ear into motion, eventually the fluids of the inner ear into motion, eventually exciting the hearing receptors. exciting the hearing receptors.

The middle ear chamber, though The middle ear chamber, though sealed off from outside atmospheric sealed off from outside atmospheric pressure changes connects with the pressure changes connects with the back of the mouth cavity through back of the mouth cavity through Eustachian tube.Eustachian tube.

THE INNER EARTHE INNER EAR The inner ear is small tubular structure about 25 The inner ear is small tubular structure about 25

to 35 mm in length resembling a small shell.to 35 mm in length resembling a small shell. That is why it is called cochlea ( latin form snail)That is why it is called cochlea ( latin form snail) Cochlea is coiled on itself about three turns.Cochlea is coiled on itself about three turns. The cochlea contains three chambers on canals. The cochlea contains three chambers on canals.

Most of its length is divided by its central canal, Most of its length is divided by its central canal, the cochlear duct.the cochlear duct.

This is also called scala media.This is also called scala media. The upper canal the scala vestibuli starts at the The upper canal the scala vestibuli starts at the

oval window and connects at the lower canal.oval window and connects at the lower canal.

Within the cochlear duct is the Within the cochlear duct is the structure called organ of corti.structure called organ of corti.

It contains columns of hair cells.It contains columns of hair cells. They are divided by arch of corti.They are divided by arch of corti. The inner hair cells and the outer hair The inner hair cells and the outer hair

cells.cells. The sensory hair cells are ultimate The sensory hair cells are ultimate

transducers of mechanical vibrations transducers of mechanical vibrations into nerve impulses.into nerve impulses.

The nerve impulse then reaches the The nerve impulse then reaches the brain.brain.

This is how we hear.This is how we hear.

THANK YOUTHANK YOU

AN EUSTACHIAN TUBE (AN EUSTACHIAN TUBE (AUDITORY TUBEAUDITORY TUBE)) It connects each middle ear to the throat.  It connects each middle ear to the throat.  This tube allows air to pass between the tympanic This tube allows air to pass between the tympanic

cavity and the outside of the body by way of the cavity and the outside of the body by way of the throat and mouth.  throat and mouth. 

It is important in maintaining equal air pressure on It is important in maintaining equal air pressure on both sides of the eardrum, which is important for both sides of the eardrum, which is important for normal hearing. normal hearing.

The function of the Eustachian tube can be The function of the Eustachian tube can be experienced during rapid altitude change.  For experienced during rapid altitude change.  For example, as a person moves from a high altitude example, as a person moves from a high altitude to a lower one, the air pressure on the outside of to a lower one, the air pressure on the outside of the membrane becomes greater and greater.  The the membrane becomes greater and greater.  The eardrum may be pushed inward, out of its normal eardrum may be pushed inward, out of its normal position, and hearing may be impaired. When the position, and hearing may be impaired. When the air pressure difference is great some air may force air pressure difference is great some air may force its way up through the eustachian tube into the its way up through the eustachian tube into the middle ear.  middle ear. 

THE INNER EARTHE INNER EAR

The second step in hearing is the transmission of sound The second step in hearing is the transmission of sound energy from the tympanic membrane through the energy from the tympanic membrane through the middle-middle-ear cavity ear cavity to the inner ear. to the inner ear. 

The inner ear consists of a fluid, called perilymph, that is The inner ear consists of a fluid, called perilymph, that is secreted by cells in the wall of the bony canal. secreted by cells in the wall of the bony canal.

The membranous labyrinth contains another fluid, called  The membranous labyrinth contains another fluid, called  endolymph, whose composition is slightly different. endolymph, whose composition is slightly different. 

These fluids serve the dual purpose of cushioning the soft These fluids serve the dual purpose of cushioning the soft structures and conducting waves from the middle ear to the structures and conducting waves from the middle ear to the Organ of Corti, the actual receptor of sound. Organ of Corti, the actual receptor of sound.

The inner ear includes cochlea that functions in hearing, and The inner ear includes cochlea that functions in hearing, and three three semicircular canals semicircular canals (anterior, posterior and lateral) (anterior, posterior and lateral) that function in providing a sense of equilibrium.  that function in providing a sense of equilibrium. 

A bony chamber, called the vestibule, which is located A bony chamber, called the vestibule, which is located between the cochlea and the semicircular canals, contains between the cochlea and the semicircular canals, contains membranous structures that serves both hearing and membranous structures that serves both hearing and equilibrium. equilibrium.

It lies between the two bony compartments and It lies between the two bony compartments and ends as a closed sac at the apex of the cochlea.  The ends as a closed sac at the apex of the cochlea.  The cochlear duct is separated from the scala vestibuli cochlear duct is separated from the scala vestibuli by a vestibular membrane (Reissner’s membrane) by a vestibular membrane (Reissner’s membrane) and from the scala tympani by a basilar membrane. and from the scala tympani by a basilar membrane.

The basilar membrane extends from the bony shelf The basilar membrane extends from the bony shelf of the cochlea and forms the floor of the cochlear of the cochlea and forms the floor of the cochlear duct.  duct.  

It contains many thousands of stiff, elastic fibres, It contains many thousands of stiff, elastic fibres, whose lengths vary becoming progressively longer whose lengths vary becoming progressively longer from the base of the cochlea to its apex. from the base of the cochlea to its apex. 

Vibrations entering the perilymph  at the oval Vibrations entering the perilymph  at the oval window travel along the scala vestibuli and pass window travel along the scala vestibuli and pass through the vestibular membrane to enter the  through the vestibular membrane to enter the  endolymph of the cochlear duct, where they cause endolymph of the cochlear duct, where they cause movements in the basilar membrane. movements in the basilar membrane.

After passing through the basilar membrane, the After passing through the basilar membrane, the sound vibrations enter the perilymph of the scala sound vibrations enter the perilymph of the scala tympani, and their forces are dissipated to the air in tympani, and their forces are dissipated to the air in the tympanic cavity by movement of the membrane the tympanic cavity by movement of the membrane covering the round window. covering the round window.

The Organ of Corti which contains the hearing The Organ of Corti which contains the hearing receptors, is located on the upper surface of the receptors, is located on the upper surface of the basliar membrane and stretches from the apex to basliar membrane and stretches from the apex to the base of the cochlea. the base of the cochlea.

Its receptor cells, which are called hair cells, are Its receptor cells, which are called hair cells, are arranged in rows and they possess numerous hair arranged in rows and they possess numerous hair like processes that extend into the endolymph of like processes that extend into the endolymph of the cochlear duct.the cochlear duct.

As sound vibrations pass through the inner ear, the As sound vibrations pass through the inner ear, the hairs shear back and forth against the tectorial hairs shear back and forth against the tectorial membrane, and the mechanical deformation of the membrane, and the mechanical deformation of the hairs stimulates the receptor cells. hairs stimulates the receptor cells.

Various receptor cells, however, have Various receptor cells, however, have slightly different sensitivities to such slightly different sensitivities to such deformation of the hairs. Thus, a deformation of the hairs. Thus, a sound that produces a particular sound that produces a particular frequency of vibration will excite frequency of vibration will excite certain receptor cells, while a sound certain receptor cells, while a sound involving another frequency will involving another frequency will stimulate a different set of cells. stimulate a different set of cells.