Special Senses

Special Senses Tubac, Cordella T. Dumaluan, Mary Gazelle L. Segovia, Cielo Maria Puzon, Camille Sarabia, Michael Anthony

THE FOUR TRADITIONAL SENSES  Vision  Hearing  Smell  Taste

Classification of Function (STIMULI) Mechanoreceptors – respond to touch, pressure, vibration, stretch, and itch  Thermoreceptors – sensitive to changes in temperature  Photoreceptors – respond to light energy (e.g., retina)  Chemoreceptors – respond to chemicals (e.g., smell, taste, changes in blood chemistry)  Nociceptors – sensitive to pain-causing stimuli 

Sensory Pathways Stimulus as physical energy  sensory receptor acts as a transducer  Stimulus > threshold  action potential to CNS  Integration in CNS  cerebral cortex or acted on subconsciously 

The Eye and Vision

The adult eye is a sphere that measures about 1 inch (2.5 cm) in diameter.  The accessory structures of the eye includes:    

Extrinsic eye muscle Eyelids Conjunctiva Lacrimal apparatus

 EYELIDS- the anterior protector of the eyes which meet at the medial and lateral canthus.  EYELASHES- Protects the border of each eyelid.  CONJUNCTIVA- lines the eyelids and covers part of the outer surface of the eyeball. It secretes the mucus, which lubricate the eyeball and keep it moist.

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LACRIMAL APPARATUS- consists of the lacrimal gland and ducts that drain the lacrimal secretions into the nasal cavity. ◦ Lacrimal glands, release a dilute salt solution (tears) onto the anterior surface of the eyeball through several small ducts. Lacrimal canals, where the tears flush across the eyeball then into the lacrimal sac and finally into the nasolacrimal duct, which empties into the nasal cavity.

• Lacrimal secretion contains antibodies called LYSOZYME, an enzyme that destroys bacteria. It cleanses and protects the eye surface as it moistens and lubricates it.  Six extrinsic or external eye muscles are attached to the outer surface of each eye. These muscles produce gross eye movements and makes it possible to follow a moving object. 

Four rectus muscles originate from the annular ring

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Two oblique muscles move the eye in the vertical plane

Names, actions, and cranial nerve innervation of the extrinsic eye

Internal Structures: The Eyeball The eye itself, commonly the eyeball, is a hollow sphere.  Its wall is composed of three tunics or coats.  Its interior is filled with fluids called humors that help to maintain the shape.  The lens, main focusing apparatus of the eye and is divided into two chambers.

INTERNAL STRUCTURE OF THE EYE

Tunics of Eyeball: Sclera The outermost tunic, is the thick white connective. Also called the fibrous tunic. It is seen anteriorly as the “white of the eye”.  Cornea- the transparent window through which the light passes through. It is well supplied with nerve endings. -The most exposed part of the eye and is vulnerable to damage. - The only tissue that can be transplanted from one person to another since it has no blood vessels.

Vascular Tunic The middle coat of the eyeball. 

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Choroid- a blood-rich nutritive tunic that contains a dark pigment. The pigment which prevents light from scattering in the eye. Ciliary Body- A thickened ring of tissue surrounding the lens. Anchors the suspensory ligament that holds the lens in place Iris- The colored part of the eye Pupil- central opening of the iris. Regulates the amount of light entering the eye during:  Close vision and bright light – pupils constrict  Distant vision and dim light – pupils dilate  Changes in emotional state – pupils dilate when the subject matter is appealing or requires problem-solving skills

SENSORY TUNIC: RETINA A delicate two-layered membrane

•Pigmented layer – the outer layer that absorbs light and prevents its scattering •Neural layer, which contains:  Photoreceptors that transduce light energy  Bipolar cells and ganglion cells  Amacrine and horizontal cells

PHOTORECEPTORS 

Rods: – Respond to dim light – Are used for peripheral vision

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Cones: – Respond to bright light – Have high-acuity color vision – Are found in the macula lutea – Are concentrated in the fovea centralis

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Electrical signals pass from the photoreceptors via a two-neuron chain: ◦ Bipolar cells and the ganglion cells before leaving via the optic nerve as nerve impulses that are transmitted to the optic cortex. The result is vision. ◦ Optic disc or blind spot, the site where the optic nerve leaves the eyeball.

Inner Chambers and Fluids 

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The lens separates the internal eye into anterior and posterior segments The posterior segment is filled with a clear gel called vitreous humor that: – Transmits light – Supports the posterior surface of the lens – Holds the neural retina firmly against the pigmented layer – Contributes to intraocular pressure

ANTERIOR & POSTERIOR SEGMENTS OF THE EYE ANTERIOR - between the cornea and the iris  Aqueous humor – A plasmalike fluid that fills the anterior segment – Drains via the canal of Schlemm POSTERIOR – between the iris and the lens  Vitreous Humor ◦ Gel-like substance that fills the posterior. It helps prevent the eyeball from collapsing inward by reinforcing it internally.

Lens – Image Formation 

Lens helps focus ◦ Light is refracted as it passes through lens ◦ Accommodation is the process by which the lens adjusts to focus images ◦ Normal visual acuity is 20/20

ACCOMODATION - Abillity of the eye to focus specifically for close objects (those less than 20 feet away).

VISUAL ABNORMALITIES

Emmetropia (harmonious vision)- eye that focuses images correctly on the retina.  Myopia (Nearsightedness) or short visiondistant objects become blurry because parallel light rays from distant objects fail to reach the retina and instead are focused in front of it.  Hyperopia (Farsightedness) or far visionparallel light rays from distant objects are focused behind the retina but they can clearly see distant objects.  Astigmatism- caused by unequal curvatures in different parts of the cornea or lens. Blurry images occur because points of light are focused not as points but as lines. (Astigma which means not a point) 

THE EAR: HEARING AND BALANCE 

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The three parts of the ear are the inner, outer, and middle ear The outer and middle ear are involved with hearing The inner ear functions in both hearing and equilibrium Receptors for hearing and balance: – Respond to separate stimuli – Are activated independently

OUTER EAR 

The auricle (pinna) is composed of: – The helix (rim) – The lobule (earlobe)

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External auditory canal – Short, curved tube filled with ceruminous glands

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Tympanic membrane (eardrum) – Thin connective tissue membrane that vibrates in response to sound – Transfers sound energy to the middle ear ossicles – Boundary between outer and middle ears

MIDDLE EAR 

A small, air-filled, mucosa-lined cavity – Flanked laterally by the eardrum – Flanked medially by the oval and round windows

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Epitympanic recess – superior portion of the middle ear Pharyngotympanic tube – connects the middle ear to the nasopharynx – Equalizes pressure in the middle ear cavity with the external air pressure

EAR OSSICLES 

The tympanic cavity contains three small bones: the malleus, incus, and stapes – Transmit vibratory motion of the eardrum to the oval window – Dampened by the tensor tympani and stapedius muscles

MIDDLE EAR (TYMPANIC CAVITY)

INNER EAR 

Bony labyrinth

– Tortuous channels worming their way through the temporal bone – Contains the vestibule, the cochlea, and the semicircular canals – Filled with perilymph

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Membranous labyrinth

– Series of membranous sacs within the bony labyrinth – Filled with a potassium-rich fluid

COCHLEA  

The scala tympani terminates at the round window The scalas tympani and vestibuli: – Are filled with perilymph – Are continuous with each other via the helicotrema

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The scala media is filled with endolymph The “floor” of the cochlear duct is composed of: – The bony spiral lamina – The basilar membrane, which supports the organ of Corti

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The cochlear branch of nerve VIII runs from the organ of Corti to the brain

MECHANICS OF EQUILIBRIUM Vestibular apparatus- the equilibrium receptors of the inner ear. TWO FUNCTIONAL ARMS Static Equilibrium ( AT REST) Dynamic Equilibrium (ROTATORY MOVEMENTS)

Static Equilibrium Maculae- sacs of vestibule within the membrane.  The maculae report on the position of the head with respect to the pull of gravity when the body is at rest.  Each macula is a patch of receptor cells with their hairs embedded in otolithic membrane, a gel or jellylike material containing otoliths, tiny stones made of calcium salts.  The events that activates the hair cells sends impulses along the vestibular nerve to the cerebellum of the brain.

Dynamic Equilibrium Semicircular canals (each about ½ inch or 1.3 cm around) responds to rotatory movements of the head. They are oriented in the three planes of space. With each receptor region called a crista ampullaris which consists of a tuft of hair cells covered with a gelatinous cap called the cupula.

Transmission of Sound to the Inner Ear 

The route of sound to the inner ear follows this pathway: – Outer ear – pinna, auditory canal, eardrum – Middle ear – malleus, incus, and stapes to the oval window – Inner ear – scalas vestibuli and tympani to the cochlear duct  Stimulation of the organ of Corti  Generation of impulses in the cochlear nerve

OLFACTORY SENSES Smell receptors Olfactory receptors Chemoreceptors Respond to changes in chemical concentrations Chemicals must be dissolved in the mucus of the nose to activate smell receptors

Smell Sensation

Smell Sensation Smell undergoes sensory adaptation Same chemical can only stimulate smell receptors for a limited amount of time Smell receptors no longer respond to the chemical and you can no longer smell You smell perfume when you first encounter it but in a few minutes, you no longer smell it.

Apply Your Knowledge You notice an odor coming from a patient when you enter the exam room. Why would the patient not be able to smell After a fewit? minutes, smell receptors no longer respond to the chemical and the patient can no longer smell the odor.

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GUSTATORY SENSES  Taste or gustatory receptors –taste buds  Found on "the bumps" of the tongue (papillae)  Taste buds are microscopic  Also on roof of your mouth and walls of your throat

Taste Sensation  Four types of taste cells - activated by a particular group of chemicals     

Sweet - tip of the tongue. Sour - sides of the tongue. Salty - tip and sides of the tongue. Bitter - back of the tongue Umami- elicited by the amino acids glutamate

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Taste buds are monitored by cranial nerves ◦ Synapse within the solitary nucleus of the medulla oblongata ◦ Then on to the thalamus and the primary sensory cortex

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Primary taste sensations ◦ Sweet, sour, salty, bitter ◦ Receptors also exist for umami and water

Taste sensitivity shows significant individual differences, some of which are inherited  The number of taste buds declines with age 

Gracias! 