Special Senses. Chapter 17

Transcription

1 Special Senses Chapter 17

2 Overview of Special Senses Special senses: Sense of smell.olfaction. Sense of taste.gustation. Sense of sight.vision. Sense of hearing and balance.auditory and equilibrium.

3 Visual Sense Involves eyes and accessory structures. Ophthalmology: study of eye, its disorders and treatment.

4 Visual Sense - Eyebrows Eyebrows: arch of hair superior to the eye. Protect the eye from foreign objects, sweat or sunrays falling directly on the eye surface.

5 Visual Sense - Eyelids Levator palpebrae superioris muscle Eyelids: also called palpebrae. Upper and lower palpebrae. Palpebral fissure: opening between the eyelids exposes anterior part of the eyeball. Orbicularis oculi muscle: circular muscle in the eyelids contract closes the eye. Levator palpebrae superioris muscle: muscle that raises the upper eyelid. Tarsal glands: sebaceous glands embedded along the edge of the eyelids oily secretion prevents eyelids from sticking to each other. Conjunctiva: a thin mucous membrane. Palpebral conjunctiva: lines the inner surface of the eyelids. Bulbar conjunctiva: lines the exposed white surface of the eyeball. Eyelashes: row of hair lining the eyelids...prevent foreign objects from falling on the eye.

6 Visual Sense - Eyelids Functions: Cover the eye during sleep. Protect the eye from dust and excessive light. Blink to spread tears over the exposed surface of the eyeball moist and clean. Cunjunctivitis/Pinkeye: inflammation of conjunctiva. Due to bacterial or viral infections or due to irritants such as dust, pollutants, smoke. Blood shot eyes: dilation of blood vessels in conjunctiva white part turns red. Treated with vasoconstrictors. Sty: infection of the eyelash follicle or tarsal glands.

7 Visual Sense Lacrimal Apparatus Opening of the nasolacrimal duct Lacrimal apparatus: consists of several components for secretion and flow of tears: Lacrimal glands: situated superior and anterolateral to the eyeball. Secrets lacrimal fluid (tears) that contains water, mucus, salt, and lysozymes (antibacterial enzyme) cleans, lubricates, moistens and protects the exposed eye surface. Lacrimal ducts: 6-15 ducts that drain the fluid from the gland to the eye surface. Lacrimal punctum: a pair of openings located at the medial edge of the eyelids drain lacrimal fluid. Lacrimal canals: take the lacrimal fluid from lacrimal punctum to the lacrimal sacs. Lacrimal sacs: a tiny sac fitted into the lacrimal fossa to collect the lacrimal fluid. Nasolacrimal duct: duct that drains fluid from lacrimal sac into the nasal cavity

8 Eyeball Fibrous tunic Vascular tunic Nervous tunic Lens Light Eyeball is a hollow ball about 2.5 cm or 1 inch in diameter. The wall is composed of 3 major layers: Fibrous tunic the outer layer. Vascular tunic/uvea the middle layer. Nervous tunic the inner layer.

9 Eyeball Fibrous Tunic Sclera Lens Cornea Light Fibrous tunic the outer layer..composed of: Sclera white part on the anterior, lateral and posterior part of the eye. Dense connective tissue for protection and attachment of eye muscles. Cornea transparent, avascular part on the anterior surface of the eyeball. - thin layer of epithelium overlaying dense connective tissue. - bends the light to focus image on the retina.

10 Eyeball Vascular Tunic Choroid Choroid Ciliary body Iris Ciliary body: muscle + processes Ciliary ligaments Iris Lens Light Lens Pupil Vascular tunic or Uvea the middle layer..composed of: Choroid Ciliary Body Iris

11 Eyeball Vascular Tunic Choroid Choroid Ciliary body Iris Ciliary body: muscle + processes Ciliary ligaments Iris Lens Light Lens Pupil Vascular tunic the middle layer..composed of: 1) Choroid thin, dark pigmented and vascularized layer. Absorbs light to prevent reflection of light and blurriness of the image 2) Ciliary Body 3) Iris

12 Eyeball Vascular Tunic Choroid Choroid Ciliary body Iris Ciliary body: muscle + processes Ciliary ligaments Iris Lens Light Lens Pupil aqueous humor Vascular tunic the middle layer..composed of: 2) Ciliary Body composed of: Ciliary ligaments: hold the lens. Ciliary muscles: smooth muscles contracts/relaxes regulate the shape of the lens for focusing. Ciliary processes: choroid plexus secrete fluid (aqueous humor) into the anterior cavity (between lens and cornea).

13 Eyeball Vascular Tunic Choroi d Lens Choroid Ciliary body Iris Light Lens Ciliary body: muscle + processes Ciliary Iris ligaments Pupil Vascular tunic the middle layer..composed of: 3) Iris extends in front of the lens.behind the cornea. Doughnut shaped structure with a hole in the middle called the pupil. Gives color to the eye.blue, green, hazel or brown. Has circular and radial smooth muscles contract/relax regulate the size of the pupil regulate the amount of light entering the eye.

14 Eyeball Nervous Tunic Retina Light Optic nerve Nervous tunic the inner layer..also called the retina. -Light-sensitive layer of the eye, where the image is formed. - Has photoreceptors that detect light and convert into neural signals which is in turn sent to the brain.

15 Eyeball Nervous Tunic- Retina Photoreceptors specialized neurons. Receive light stimulus generate impulses. Two type: Rod cells Cone cells Rod cells - Rod shaped. - Do not discriminate different colors of light. - Forms black & white image. - More sensitive to light and function well in dim light. - Enables night vision. - Image is not very sharp. - Contains light sensitive pigment called rhodopsin. - There are about 125 million rods in each eye-located at the periphery of retina. Cone cells - Cone shaped. - Responsible for color vision in relatively bright light. - Image is very sharp. - Contains light sensitive pigments called photopsins. - 3 types of cone cells: specialize in red, green, blue (RGB) colors. - Roughly 6 million cones at the center of retina.

16 Eyeball Nervous Tunic Macula/ Fovea Retina Optic disc/ Blind spot Light Optic nerve Rods and cones are unequally distributed in retina. Blind Spot / Optic Disc place in the back of the eyeball where the optic nerve and blood vessels exit. No retina.no rods and cones present.no image is formed here. Macula / Fovea Centralis area on the retina just superior to blind spot and directly at the end of the light pathway. Highest concentration of cones provides sharp central vision.

17 Eyeball Lens Lens Choroid Ciliary body Iris Light Posterior Vitreous Cavity Ciliary ligaments Ciliary muscle Lens Anterior Cavity Lens: Posterior to cornea. - transparent sac filled with protein crystallins. - held in place by ciliary ligaments. - focus the light entering eyes and helps to form a visual image on the retina by changing the shape of the lens (by the contraction/relaxation of ciliary muscles). - separates eye into anterior cavity and posterior vitreous cavity.

18 Eyeball Cavities & Fluids Lens divides the interior of the eye into cavities: Anterior cavity: cavity in front of the lens. Divided into anterior & posterior chamber. Anterior chamber- space between iris and cornea. Posterior chamber- space between lens and iris. Contains a clear, watery fluid called aqueous humor that is constantly replaced and circulated: Allows light to pass. Provides nutrients, O2 to the tissues present in front of the eye such as cornea. Pick up waste products and CO2. Maintains proper pressure in the anterior cavity to maintain position of iris and lens. Posterior/ Vitreous Cavity Lens I r i s Anterior Cavity: Posterior Chamber Anterior Chamber C o r n e a Pupil Posterior/Vitreous cavity: cavity behind the lens up to retina. Contains a clear, jelly-like liquid called vitreous humor: Helps to maintain shape of the eyeball. Allows light to pass to retina. It is permanent (not replaced). Ciliary processes Sclera venous sinus

19 Eyeball Aqueous Humor Aqueous humor is the fluid found in the anterior cavity of the eyeball. 1. Formation of aqueous humor: Ciliary body present around the lens has choroid plexus (blood capillaries + epithelial tissue) filters blood to form aqueous humor. 2. Circulation of aqueous humor: Aqueous humor is secreted in the posterior chamber of the anterior cavity goes through the pupil to circulate in the anterior chamber of anterior cavity. The purpose is to provide nutrients and O2 to the tissues and pick up waste and CO2. 3. Reabsorption of aqueous humor: Aqueous humor is reabsorbed and returned to blood by sclera venous sinus located at the junction of cornea and sclera. Posterior Vitreous Cavity Lens I r i s Ciliary processes Anterior Cavity: Posterior Chamber Anterior Chamber C o r n e a Sclera venous sinus Pupil

20 Eyeball Pathway of Vision Cornea Anterior cavity Optic nerve Lens Light Posterior cavity Fovea region of retina Light is refracted through transparent cornea passes through aqueous humor in the anterior cavity passes through pupil refracted through the lens passes through vitreous humor in the posterior cavity forms an image on retina photoreceptors (rods and cones) in retina absorb light get stimulated generate impulses impulses exit through optic nerve optic nerve fibers cross (optic chiasm) before entering the brain optic tracts travel to thalamus then to vision center in occipital lobe of cerebrum interpretation of image.

21 Eye Disorders Glaucoma: increased aqueous humor in the anterior cavity increased pressure: Projects cornea forward light refraction is affected vision is affected. Pushes lens inwards pressure on retina photoreceptors die vision lost. Prevented with eye drops and treated with laser surgery. Colorblindness: inability to see certain colors due to nonfunctioning of specific cone cells. Sex linked disorder.gene on X chromosome more often expressed in males. Macular degeneration: degeneration of macula/fovea centralis loss of acute central vision. Due to heredity, infections, trauma, tumors or aging. Retinal holes and detachment: retina becomes separated from choroid blood supply is cut off to retina photoreceptors degenerate permanent black spot is visible. Small areas of detachment (holes) becomes bigger most of retina separates total loss of vision. Cataract: opacification of the transparent crystalline lens-lens becomes cloudy light passage is affected blurry vision. Surgery to replace natural lens with artificial lens. Diabetic Retinopathy: is due to diabetes blockage of small retinal blood vessels/excessive growth of abnormal blood vessels retina is affected damage to photoreceptors vision is lost with time. With age: Number of rods goes down loss of night vision; retinal detachment; cataract; weakening of ciliary muscles difficulty/delayed focusing; macular degeneration.

22 Auditory & Equilibrium Sense Ear is involved in: Auditory sense. Sense of equilibrium balance.

23 Ear Major Parts External Ear Middle Ear Internal Ear Ear is composed of: External ear Middle ear Internal ear

24 Ear - External External Ear Middle Ear Internal Ear Pinna/ Auricle External auditory meatus Tympanic membrane External ear is composed of: Pinna/Auricle (ear flap) attached to the head cartilage mold covered by skin collects & directs sound waves into the auditory canal. External auditory canal a canal that goes through external auditory meatus of the temporal bone.passage of sound waves. Cartilaginous with skin lining the inner surface of the canal: Hair near the opening trap debris and provide touch sensation. Ceruminous glands secrete cerumen trap water & insects, prevent growth of microorganisms reduces chances of infection. Tympanic membrane (eardrum) thin, semitransparent, fibrous connective tissue membrane separates outer from middle ear; vibrates when sound waves hit.

25 Ear - Middle Middle ear: An air-filled cavity located behind the tympanic membrane. Ossicles: 3 smallest bones in the middle ear cavity.held by ligaments & muscles: Malleus connected to tympanic membrane. Incus connected to malleus. Stapes (smallest bone in human body) connected to incus at one end and oval window (connective tissue membrane that connects the middle ear to inner ear) membrane at the other end. Function: ossicles amplify vibrations of tympanic membrane pass on to the oval window. Pharyngotympanic/Eustachian/Auditory tube: connects middle ear cavity to nasopharynx (throat). Function: allows pressure in the middle ear to equilibrate with outside atmospheric pressure. Otitis media-middle ear infection- microorganisms can travel from nasopharynx into middle ear.

26 Ear - Internal External Ear Middle Ear Internal Ear Labyrinth Internal ear: Located in the temporal bone. A complex structure called labyrinth. Labyrinth is like a tube inside another tube! It is composed of: Outer tube - bony labyrinth (made of dense bone) Inner tube - membranous labyrinth There is fluid in labyrinth: Perilymph is the outer compartment. between bony labyrinth and membranous labyrinth. Endolymph in the inner compartment. inside membranous labyrinth. Bony labyrinth Membranous labyrinth Section through the labyrinth Perilymph Bony labyrinth Endolymph Membranous labyrinth

27 Labyrinth Semicircular canals Vestibule Cochlea Labyrinth can be subdivided into 3 parts: Cochlea Vestibule Semicircular canals

28 Labyrinth - Cochlea Spiral organ/organ of Corti stereocilia Cochlea Cochlear duct cochlear nerve Cochlea: spiral, snail shaped part of labyrinth-responsible for auditory sense. Cochlear duct: a membranous duct located in the center of the spiraling cochlea. Contains endolymph and Organ of corti. Spiral organ/organ of Corti: a complex structure located in the cochlear duct that contains the sound receptors. Hair cells with stereocilia: auditory receptor cells located in the Organ of Corti that converts sound waves to nerve impulses, which is carried by the cochlear nerve to brain.

29 Cochlea Process of Hearing Malleus Incus Stapes Oval window 6 Cochlear branch of cranial nerve VIII Movement of sound waves Cochlear duct (contains Organ of Corti with hair cells) 5 4 Spiral organ/organ of Corti External auditory canal Tympanic membrane Round window Sound waves are collected by pinna, travel through external auditory canal to arrive at tympanic membrane. Sound waves hit tympanic membrane set it into vibrations which causes ossicles to vibrate vibrations are amplified. Vibration of stapes vibration of the oval window which then sends out pressure waves in perilymph surrounding cochlear duct inside cochlea. The pressure waves cause stereocilia of hair cells (in Organ of Corti located in cochlear duct) to move hair cells are stimulated. Hair cells generate impulses. Impulses travel through the cochlear nerve which eventually takes impulses to the temporal lobe cerebrum for auditory sensation.

30 Labyrinth Semicircular canals Vestibule Cochlea Labyrinth can be subdivided into 3 parts: Cochlea for sense of hearing (auditory sense) Vestibule Semicircular canals

31 Labyrinth - Vestibule Vestibule Hair cells Wall of vestibule Gelatinous layer Otoliths Vestibule: a sac like structure. Part of the labyrinth that is responsible for sense of static equilibrium. respond to gravity and linear changes in the position of the head. Otoliths (ear stones): calcium carbonate crystals embedded in the gelatinous layer lining the inner surface of the vestibular wall. Hair cells: epithelial receptor cells located in the wall of the vestibule. Have stereocilia that are stimulated by the pull of gravity that causes shifting of otoliths in the gelatinous layer. When head is in upright position otoliths sit on top of stereocilia vestibular nerve takes impulses to inform cerebellum the equilibrium center of the brain! When head is tilted otoliths move in response to gravity stereocilia are pulled hair cells are stimulated impulses inform cerebellum of the changing position.

32 Labyrinth Semicircular canals Vestibule Cochlea Labyrinth can be subdivided into 3 parts: Cochlea for sense of hearing (auditory sense) Vestibule for sense of static equilibrium Semicircular canals

33 Labyrinth Semicircular canals Semicircular canals Ampulla Ampulla Cupula Hair cells Stereocilia Hair cells Sensory neuron Semicircular canals: 3 tubes that are positioned in 3 planes. Part of the labyrinth that is responsible for sense of dynamic equilibrium.respond to angular acceleration (rotation of head nodding of head, tilting from side to side). Ampulla: swollen base of each canal that contains the receptors. Hair cells: epithelial receptor cells located in the ampulla of semicircular canals. Have stereocilia that are embedded in gelatinous mass called the cupula. When the body moves/rotates endolymph in semicircular canals moves that causes cupula in the ampulla to bend stimulates plasma membrane of stereocilia impulses are generated vestibular nerve takes impulses to inform cerebellum the equilibrium center of the brain!

34 Ear Pathways External Ear Middle Ear Internal Ear Vestibulocochlear nerve (VIII) Cochlea Vestibule Semicircular canals Sound stimulus converted to vibrations by tympanic membrane amplified by ossicles oval window causes pressure waves in cochlea stimulates hair cells in Organ of Corti located in cochlear duct impulses are generated passed on by cochlear nerve. Equilibrium change (static or dynamic) stimulates hair cells in vestibule (static) or ampullae of semicircular canals (dynamic) impulses are generated passed on by vestibular nerve. Cochlear branch Vestibular branch Vestibulocochlear nerve (VIII) Cochlear nerve and vestibular nerve combine to form vestibulocochlear nerve (N VIII) takes impulses to inform: Auditory center in temporal lobe of cerebrum. Equilibrium center in cerebellum.

35 Ear Disorders External Ear Middle Ear Internal Ear Otitis media- middle ear infection-infection and mucus in the pharynx spreads into eustachian/auditory tube into middle ear cavity pain, pressure and limits vibration of the ossicles affects hearing. Deafness: loss of hearing. Due to: Damage of vestibulocochlear nerve. Damage of middle or internal ear components. Motion sickness: sickness due to travelling in cars, boat or planes. Symptoms: headache, sweating, nausea, and vomiting. Causes: due to conflicting sensory inputs from eyes and inner ear to the brain. Vertigo: sensation of spinning. Could be due to infection of inner ear, increased endolymph fluid accumulation, conflict in brain processing.

36 Overview of Special Senses Special senses: Sense of smell.olfaction. Sense of taste.gustation. Sense of sight.vision. Sense of hearing and balance.auditory and equilibrium.

37 Olfactory Sense Olfactory epithelium Nose is involved in olfactory sense.sense of smell. Olfaction is a chemical sense- sensations arise from the interaction of molecules with smell receptors.

38 Olfactory Sense To Olfactory bulb Cribriform plate Olfactory gland Basal cell Olfactory nerve fibers Olfactory receptor cell Olfactory dendrites Mucous layer Substance being smelled Olfactory epithelium: tissue located in the roof of nasal cavity.lining the inferior surface of cribriform plate of ethmoid bone. Composed of: Olfactory receptor cells bipolar neurons with olfactory dendrites embedded in the mucus lining the nasal cavity can distinguish thousands of different odors. Supporting cells simple columnar epithelial cells that support receptors. Basal cells helps in turnover of olfactory receptors replace damaged or worn-out olfactory receptor cells and supporting cells. Olfactory glands exocrine glands secrete mucus lines the inner surface of nasal cavity.

39 Olfactory Sense - Receptor To Olfactory bulb Olfactory epithelium Cribriform plate Olfactory gland Basal cell Olfactory nerve fibers Olfactory receptor cell Olfactory dendrites Mucous layer Substance being smelled Olfactory receptors are: Bipolar neurons.with sensory olfactory hair embedded in mucus lining the nasal cavity. Exception: replaceable as compared to neurons in CNS and PNS. Chemoreceptors.stimulated by chemicals present in the air. Have low threshold value.require only a small amount of chemical to stimulate them. Rapidly adapting receptors.threshold value may increase temporarily once they are exposed to the chemical making them less sensitive odors don t seem as strong after a few minutes. Olfactory receptor population changes over time..affects the way you perceive smells. Number of receptors goes down with age. Threshold of receptors increases with age.making them less sensitive.decline in smelling.

40 Olfactory Sense - Pathway To Olfactory bulb Cribriform plate Olfactory gland Basal cell Olfactory nerve fibers Olfactory receptor cell Olfactory dendrites Mucous layer Substance being smelled Chemicals in the air dissolve in mucus lining the nasal cavity stimulate the olfactory dendrites of bipolar receptor neurons an impulse is generated impulse travels along olfactory nerve fibers that pass through porous cribriform plate of ethmoid bone to olfactory bulb located just below the frontal lobe of cerebrum through olfactory tract directly to primary olfactory cortex in temporal lobe of cerebrum for integration.

41 Overview of Special Senses Special senses: Sense of smell.olfaction. Sense of taste.gustation. Sense of sight.vision. Sense of hearing and balance.auditory and equilibrium.

42 Gustatory Sense Tongue and upper pharynx are involved in gustatory sense.sense of taste. Gustation is a chemical sense- detect chemicals from food dissolved in saliva.

43 Gustatory Sense Tongue is covered with different shaped bumps called the papillae composed of: Stratified squamous epithelium covering the surface. Have taste buds located on their lateral walls. Taste bud is a compact structure with an opening called the taste pore. Each bud is composed of: Gustatory receptor cells columnar epithelial cells with microvilli called the gustatory hair project into the taste pore and communicate with the dissolved solutes on the surface of the tongue. Supporting cells simple columnar epithelial cells support receptors. Basal cells replace damaged or worn-out gustatory receptor cells and supporting cells. Sensory nerve fibers at the base of the taste buds take impulses to the brain.

44 Gustatory Sense - Receptor Nerve fibers Gustatory hair Papillae Taste buds Papilla Basal cell Gustatory cell Supporting cell Taste pore Gustatory receptors are: Columnar epithelial cells.with gustatory hair hanging out in the taste pore. Chemoreceptors.stimulated by chemicals present in the food mixed in the saliva. Have low threshold value.require only a small amount of chemical to stimulate them. Rapidly adapting receptors.threshold value may increase temporarily once they are exposed to the chemical making them less sensitive.food does not taste as strong after the first bite!

45 Gustatory Sense - Pathway Nerve fibers Gustatory hair Papillae Taste buds Papilla Basal cell Gustatory cell Supporting cell Taste pore Chemicals in the food dissolve in the saliva stimulate the gustatory hair of gustatory receptor cells an impulse is generated impulse travels along nerve fibers that are located at the base of the taste bud through cranial nerves VII, IX and X that innervate with different regions of the tongue through thalamus to cerebrum for integration. Total taste sensation = gustatory sense + olfactory sense. Also influenced by food texture, vision, memory and moods!

46 Gustatory Sense - Chemical Discrimination Nerve fibers Gustatory hair Papillae Taste buds Papilla Basal cell Gustatory cell Supporting cell Taste pore There are 4 primary taste sensations: Sweet, salty, sour, bitter. Now 2 more added: Umami: tasting of flavors of beef broth, chicken broth and parmesan cheese! Water: is tasted with its own receptor located in the pharynx take impulses to hypothalamus affects hormonal regulation of water level in the body. Gustatory receptor population changes over time..affects liking/disliking of certain tastes. Number of receptors goes down with age. Threshold of receptors increases with age.making them less sensitive.decline in tasting.