Chapter 8 Special Senses Sensory system Sensory system

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Chapter 8 Special Senses

Chapter 8 Special Senses

Sensory system • Sensory system serves as a protective mechanism for an organism by

Sensory system • Sensory system serves as a protective mechanism for an organism by • • • detecting changes in the environment An environmental change becomes a stimulus and initiates nerve impulse to CNS by sensory neurons. The stimulus is then interpreted by cerebral cortex Senses are classified according to the distribution of the receptors as • • somatic (general) senses: touch, pain, pressure, temperature special senses : vision, taste, smell, hearing and balance

A special sense is located in a special sense organ e. g. Chemoreceptors: two

A special sense is located in a special sense organ e. g. Chemoreceptors: two types • • • Taste : receptors on tongue Smell : receptors in the upper nasal cavity Photoreceptors : • • Vision : receptors of eye Mechanoreceptors: • • Hearing and Equilibrium: receptors of internal ear

Chemical Senses – Taste and Smell l Both senses use chemoreceptors l Stimulated by

Chemical Senses – Taste and Smell l Both senses use chemoreceptors l Stimulated by chemicals in solution l Taste has four types of receptors l Smell can differentiate a large range of chemicals l Both senses complement each other and respond to many of the same stimuli

Sense of Smell: or olfaction l occurs in response to odors l The special

Sense of Smell: or olfaction l occurs in response to odors l The special nasal epithelium of nasal cavity is called olfactory epithelium l Airborne molecules enter nasal cavity and l stimulate chemo receptors present in olfactory epithelium

Sense of Smell: or olfaction l l Stimulation creates action potential sending impulses to

Sense of Smell: or olfaction l l Stimulation creates action potential sending impulses to brain through olfactory nerve (I) to cerebral cortex Between frontal and temporal lobe above hypothalamus These receptors degenerate with age

Sense of Smell: or olfaction l • • During common cold, nasal mucous producing

Sense of Smell: or olfaction l • • During common cold, nasal mucous producing cells is inflammated preventing the odor from reaching the olfactory neurons of nose and thus preventing the sense of smell

Sense of Taste l The sense structures that detect gustatory or taste stimuli are

Sense of Taste l The sense structures that detect gustatory or taste stimuli are called taste buds l Taste buds are oval structures embedded in the epithelium of tongue and mouth l Known as papillae

Sense of Taste • Food particles dissolved in saliva stimulate taste buds • And

Sense of Taste • Food particles dissolved in saliva stimulate taste buds • And send impulse to brain through • Medulla by facial nerve (VII) glassopharyngeal nerve (IX) vagus (X). • • •

Sense of Taste l There are four primary taste sensations detected by taste buds:

Sense of Taste l There are four primary taste sensations detected by taste buds: a. Bitter: e. g. coffee. Taste buds are at the back of the tongue b. Sour: due to acids. Taste buds are on either side of tongue c. Salty : salts like Na. Cl. Taste buds are on the sides and front of tongue d. Sweet : Sugars give sweet taste. Taste buds are in front of the tongue

The Eye and Vision 70% of all sensory receptors are in the eyes l

The Eye and Vision 70% of all sensory receptors are in the eyes l Each eye has over a million nerve fibers l Protection for the eye l l Most of the eye is enclosed in a bony orbit l A cushion of fat surrounds most of the eye

Accessory Structures of the Eyelids and eyelashes l Conjunctiva l Lacrimal apparatus l Extrinsic

Accessory Structures of the Eyelids and eyelashes l Conjunctiva l Lacrimal apparatus l Extrinsic eye muscles l

Accessory Structures of the Eye l Eyelids: Eyelids protect eye from foreign objects l

Accessory Structures of the Eye l Eyelids: Eyelids protect eye from foreign objects l Tarsal glands in eyelids lubricate the eye l Eyebrows: prevent sweat from entering eyes and help in shading eyes

Accessory Structures of the Eye l Conjunctiva l Delicate membrane that lines the eyelids

Accessory Structures of the Eye l Conjunctiva l Delicate membrane that lines the eyelids l Connects to the surface of the eye l Secretes mucus to lubricate the eye

Accessory Structures of the Eye l l Lacrimal apparatus: Consists of lacrimal gland l

Accessory Structures of the Eye l l Lacrimal apparatus: Consists of lacrimal gland l l Lacrimal gland— produces lacrimal fluid, located above the lateral end of eye Properties of lacrimal fluid l l Dilute salt solution (tears) Contains antibodies and lysozyme l Protects, moistens, and lubricates the eye l Empties into the nasal cavity

Accessory Structures of the Eye l Extrinsic eye muscles l l Six muscles attach

Accessory Structures of the Eye l Extrinsic eye muscles l l Six muscles attach to the outer surface of the eye Produce eye movements

Structure of the Eye l Eye is enclosed in three layers or tunics l

Structure of the Eye l Eye is enclosed in three layers or tunics l Fibrous layer l l Vascular layer l l Outside layer Middle layer Sensory layer l Inside layer

Structure of the Eye: The Fibrous Layer l Sclera l l l White connective

Structure of the Eye: The Fibrous Layer l Sclera l l l White connective tissue layer Seen anteriorly as the “white of the eye” Cornea l l Transparent, central anterior portion Allows for light to pass through Repairs itself easily The only human tissue that can be transplanted without fear of rejection

Structure of the Eye: Vascular Layer l Choroid is a blood-rich nutritive layer in

Structure of the Eye: Vascular Layer l Choroid is a blood-rich nutritive layer in the posterior of the eye contains a dark pigment l l Light is focused by choroid pigment onto retina thus preventing scattering of the light Modified anteriorly into two structures l l Ciliary body— smooth muscle attached to lens Iris— regulates amount of light entering eye l Pigmented layer that gives eye color l Pupil— rounded opening in the iris

Structure of the Eye: Vascular Layer Iris is regulated by: a. sympathetic nervous system

Structure of the Eye: Vascular Layer Iris is regulated by: a. sympathetic nervous system by dilating it b. parasympathetic nervous system by constricting it

Structure of the Eye: Sensory Layer l Retina contains two layers l l l

Structure of the Eye: Sensory Layer l Retina contains two layers l l l Outer pigmented layer They contain photosensitive pigments Involved in the conversion of light into nerve impulses l Inner neural layer l l l Contains receptor cells Biopolar cells Ganglion cells

Structure of the Eye: Sensory Layer l Light sensitive pigments are l Rods: contain

Structure of the Eye: Sensory Layer l Light sensitive pigments are l Rods: contain rhodopsin pigment differentiates between light and darkness l Cones: detect colors (red, blue and green) of the visual light.

Cone Sensitivity There are three types of cones l Different cones are sensitive to

Cone Sensitivity There are three types of cones l Different cones are sensitive to different wavelengths l Color blindness is the result of lack of one cone type l

Structure of the Eye: Sensory Layer l Fovea centralis: region where there are more

Structure of the Eye: Sensory Layer l Fovea centralis: region where there are more cones l Blind spot: region where the optic nerve exits the eye

o Lens is present behind the pupil o Lens focuses the light on the

o Lens is present behind the pupil o Lens focuses the light on the retina o Lens is made of transparent intercellular material It is suspended by ligaments Lens regulates the focusing with the help of suspensory ligaments o o Lens

o o o Lens divides the eye cavity into Anterior cavity or aqueous humor

o o o Lens divides the eye cavity into Anterior cavity or aqueous humor Posterior cavity or vitreous humor It is made of water and mucoprotein. It maintains the pressure to support retina Lens

Physiology of vision · Light reflected from the object enters cornea towards lens to

Physiology of vision · Light reflected from the object enters cornea towards lens to retina. · Retina has cones, which detect colors (red, blue and green), and rods detect tone of object and night vision. · Photoreceptors of rods and cones send impulse to brain through bipolar cells to optic nerves

l optic nerve pass through thalamus cross path at ( optic chiasma), connecting to

l optic nerve pass through thalamus cross path at ( optic chiasma), connecting to occipital lobe of the cerebral cortex Thus responding to light stimulation And visual interpretation, or seeing occurs Human vision is binocular l Provides depth perception l l l

Lens Accommodation l Light must be focused to a point on the retina for

Lens Accommodation l Light must be focused to a point on the retina for optimal vision l The eye is set for distance vision (over 20 ft away) l The lens must change shape to focus for closer objects

 • Short sight or near sightedness: Eye ball is stretched in length thus

• Short sight or near sightedness: Eye ball is stretched in length thus focusing the object in front of retina rather than on retina. concave lens correct the mistake

 • Long Sight or far sightedness: Eye ball is compressed such that the

• Long Sight or far sightedness: Eye ball is compressed such that the light is focused behind the retina instead of on the retina Convex lens fixes the mistake

Ear l Is the sense organ important for hearing and balance The ear is

Ear l Is the sense organ important for hearing and balance The ear is divided into three parts: l l l Outer ear Middle ear Inner ear

a. Outer ear : Is composed of l Auricle (pinna) which directs sound waves

a. Outer ear : Is composed of l Auricle (pinna) which directs sound waves into ear l And External auditory maetus (canal) lined with epithelial cells of skin called ceruminous glands, l They produce wax l Wax collects the dust particles

a. Outer ear : l Tympanic membrane (or eardrum) connects outer ear to middle

a. Outer ear : l Tympanic membrane (or eardrum) connects outer ear to middle ear l Sound waves reach tympanic membrane through pinna and l cause it to vibrate

b. Middle ear: v v v Connects the outer ear to inner ear Filled

b. Middle ear: v v v Connects the outer ear to inner ear Filled with air cavity within the temporal bone Consists of two passages: One passage opens into Mastoid air cells of temporal bone and Second passage opens into pharynx through auditory or Eustachian tubes Auditory tube equalizes air pressure between outside air and middle air cavity

b. Middle ear: • • • Is made of three small bones called auditory

b. Middle ear: • • • Is made of three small bones called auditory ossicles Malleus (hammer) Incus (anvil) and Stapes (stirrup) These bones are connected to the inner ear They amplify the vibrations from tympanic membrane and transfer the vibration to malleus anvil stirrup inner ear

l l l l Inner ear Includes sense organs for hearing and balance consists

l l l l Inner ear Includes sense organs for hearing and balance consists of bony labyrinth: vestibule cochlea (snail like structure) and 3 semicircular canals And filled with perilymph (plasma like fluid)

Organs of Hearing l Organ of Corti l Located within the cochlea l Cochlea

Organs of Hearing l Organ of Corti l Located within the cochlea l Cochlea is a bony structure l Has modified cells forming a structure called spiral organs or organ of corti. l Organ of corti is specialized sensory haircells and filled with endolymph.

Physiology of hearing l l Vibrations of air medium generate sound waves. The sound

Physiology of hearing l l Vibrations of air medium generate sound waves. The sound waves are collected by pinna and directed to external auditory maetus.

Physiology of hearing l The sound waves cause vibrations of tympanic membrane, l which

Physiology of hearing l The sound waves cause vibrations of tympanic membrane, l which moves ossicles l resulting sound waves being amplified. l Amplified sound waves create waves in endolymph of the cochlea l and activate haircells of spiral organ

l l This creates action potential, which is transmitted through vestibulocochlear nerve to pons(

l l This creates action potential, which is transmitted through vestibulocochlear nerve to pons( of brain stem) l to thalamus. l From thalamus , impulse is directed to auditory cortex of temporal lobe l and sound is perceived

Sound is measured in decibels

Sound is measured in decibels

Diseases related to sensory system Sensory disease Specific Function function structure affected Sense of

Diseases related to sensory system Sensory disease Specific Function function structure affected Sense of smell Common cold Nasal epithelium Cannot smell visual glaucoma Build up of aqueous fluid due to blockage of ducts in the choroid Blindness caused due to damage to nerves vision Macular degeneration Degeneration of fova Blind spot, faded centralis( cones) due colors to age advancement vision Color blindness Cone proteins not made Cannot distinguish red, blue and green auditory Conduction deafness Fused middle ear bones Cannot hear from birth auditory Nerve deafness Cochlear cilia of nerve cell receptors degenerate due to age advancement Cannot hear