BMS2-21 Special Senses PDF

12/29/20 The Senses • General senses of touch (tactile) Special Senses Assist. Prof. Dr. Cenk Serhan Özverel [email protected] The Eye and Vision • 70% of all sensory receptors are in the eyes. • Each eye has over a million nerve fibers • Protection for the eye • Most of the eye is en...

12/29/20 The Senses • General senses of touch (tactile) Special Senses Assist. Prof. Dr. Cenk Serhan Özverel [email protected] The Eye and Vision • 70% of all sensory receptors are in the eyes. • Each eye has over a million nerve fibers • Protection for the eye • Most of the eye is enclosed in a bony orbit made up of the lacrimal (medial), ethmoid (posterior), sphenoid (lateral), frontal (superior), and zygomatic and maxilla (inferior) • A cushion of fat surrounds most of the eye • Temperature- thermoreceptors (heat) • Pressure- mechanoreceptors (movement) • Pain- mechanoreceptors • Special senses • • • • • Smell- chemoreceptors (chemicals) Taste- chemoreceptors Sight- photoreceptors (light) Hearing- mechanoreceptors Equilibrium- (balance) mechanoreceptors Accessory Structures of the Eye • Eyelids- brush particles out of eye or cover eye • Eyelashes- trap particles and keep them out of the eye 1 12/29/20 Accessory Structures of the Eye Accessory Structures of the Eye • Conjunctiva • Ciliary glands – • • Membrane that lines the eyelids • Connects to the surface of the eye- forms a seal modified sweat glands between the eyelashes • Secretes mucus to lubricate the eye • secrete acidic sweat to kill bacteria, • lubricate eyelashes Accessory Structures of the Eye CONJUNCTIVITIS - Inflammation of the conjunctiva • Lacrimal apparatus - Caused by bacterial or viral infection • Lacrimal gland – produces lacrimal fluid • Lacrimal canals – drains lacrimal fluid from eyes - Highly contagious 2 12/29/20 Accessory Structures of the Eye • Function of the Lacrimal Apparatus Lacrimal sac – provides passage of lacrimal fluid towards nasal cavity • Properties of lacrimal fluid • Dilute salt solution (tears) • Contains antibodies (fight antigens- foreign substance) and lysozyme (enzyme that destroys bacteria) • Protects, moistens, and lubricates the eye • Empties into the nasal cavity • Nasolacrimal duct – empties lacrimal fluid into the nasal cavity Extrinsic Eye Muscles • Muscles attach to the outer surface of the eye • Produce eye movements When Extrinsic Eye Muscles Contract • Superior oblique- eyes look out and down • Medial rectus- eyes look inward • Superior rectus- eyes looks up • Inferior rectus- eyes looks down • Lateral rectus- eyes look outward • Inferior oblique- eyes look in and up 3 12/29/20 Structure of the Eye • The wall is composed of three tunics • Fibrous tunic – outside layer • Choroid – middle layer • Sensory tunic – inside layer The Fibrous Tunic • Sclera • White connective tissue layer • • Seen anteriorly as the “white of the eye” Semi-transparent The Fibrous Tunic • Cornea • Transparent, central anterior portion • Allows for light to pass through (refracts, or bends, light slightly) • Repairs itself easily • The only human tissue that can be transplanted without fear of rejection 4 12/29/20 Choroid Layer Choroid Layer Modified interiorly into two structures • Blood-rich nutritive tunic • Pigment prevents light from scattering (opaqueblocks light from getting in, has melanin) Cilliary body – smooth muscle (contracts to adjust the shape of the lens) Iris- pigmented layer that gives eye color (contracts to adjust the size of the pupil- regulates entry of light into the eye) Pupil – rounded opening in the iris Sensory Tunic (Retina) • Contains receptor cells (photoreceptors) • Rods • Cones Sensory Tunic (Retina) • Signals pass from photoreceptors via a two-neuron chain • Bipolar neurons and Ganglion cells • Signals leave the retina toward the brain through the optic nerve 5 12/29/20 Neurons of the Retina and Vision ROD CELLS • Rods • Most are found towards the edges of the retina • Allow dim light vision and peripheral vision (more sensitive to light, do not respond in bright light) • Perception is all in gray tones Neurons of the Retina and Vision • Cones • Allow for detailed color vision • Densest in the center of the retina • Fovea centralis – area of the retina with only cones • Respond best in bright light • No photoreceptor cells are at the optic disk, or blind spot 6 12/29/20 Cone Sensitivity • There are three types of cones • Different cones are sensitive to different wavelengths http://www.yorku.ca/eye/rod-cone.gif h ttp ://www.secretb ey o n d matter.co m/o u rb rain s/th ewo rld in o u rb rain s_ files/1 1 -1.jp g • - red- long • - green- medium • - blue- short • Color blindness is the result of lack of one or more cone type How do we see colors? Colorblindness • To see any color, the brain must compare the input from different kinds of cone cells—and then make many other comparisons as well. - An inherited trait that is transferred on the sex chromosomes (23rd pair)sex-linked trait • The lightning-fast work of judging a color begins in the retina, • Retina has three layers of cells. • Signals from the red and green cones in the first layer are compared by specialized red-green "opponent" cells in the second layer. • These opponent cells compute the balance between red and green light coming from a particular part of the visual field. • Other opponent cells then compare signals from blue cones with the combined signals from red and green cones. - Occurs more often in males - Can not be cured or corrected •Comes from a lack of one or more types of color receptors. •Most are green or red or both and that is due to a lack of red receptors. •Another possibility is to have the color receptors missing entirely, which would result in black and white vision. 7 12/29/20 COLORBLINDNESS TEST PLATES Lens · Biconvex crystal-like structure · Held in place by a suspensory ligament attached to the ciliary body · Refracts light greatly Internal Eye Chamber Fluids Internal Eye Chamber Fluids • Vitreous humor • Aqueous humor • Watery fluid found in chamber between the lens and cornea • Similar to blood plasma Refracts light slightly • Gel-like substance behind the lens Refracts light slightly Holds lens and retina in place • Keeps the eye from collapsing • Lasts a lifetime and is not replaced • Helps maintain intraocular pressure • Provides nutrients for the lens and cornea • Reabsorbed into venous blood through the canal of Schlemm 8 12/29/20 Lens Accommodation • Light must be focused to a point on the retina for optimal vision MYOPIA Nearsightedness, or myopia is the difficulty of seeing objects at a distance. Myopia occurs when the eyeball is slightly longer than usual from front to back. This causes light rays to focus at a point in front of the retina, rather than directly on its surface. Concave lenses are used to correct the problem. • The eye is set for distance vision (over 20 ft away) • The lens must change shape to focus for closer objects HYPEROPIA Images Formed on the Retina Hyperopia, or farsightedness, is when light entering the eye focuses behind the retina. Hyperoptic eyes are shorter than normal. Hyperopia is treated using a convex lens. • If the image is focused at the spot where the optic disk is located, nothing will be seen. This is known as the blind spot. • There are no photoreceptors there, as nerves and blood vessels pass through this point. 9 12/29/20 Visual Pathway Visual Pathway • Photoreceptors of the retina • Optic tracts • Optic nerve • Thalamus (axons form optic radiation) • Optic nerve crosses at the optic chiasma • Visual cortex of the occipital lobe Eye Reflexes • The Ear Internal muscles are controlled by the autonomic nervous system • Bright light causes pupils to constrict through action of radial (iris) and ciliary muscles • Viewing close objects causes accommodation • External muscles control eye movement to follow objects- voluntary, controlled at the frontal eye field • Viewing close objects causes convergence (eyes moving medially) • • Responsible for two senses!! • Hearing (interpreted in the auditory cortex of the temporal lobe) • Equilibrium (balance) (interpreted in the cerebellum) Receptors are mechanoreceptors 10 12/29/20 Anatomy of the Ear • The ear is divided into three areas • Outer (external) ear The External Ear • Involved in hearing only • Structures of the external ear • Pinna (auricle)- collects sound • External auditory canalchannels sound inward • Middle ear • Inner ear The External Auditory Canal The Middle Ear or Tympanic Cavity • Narrow chamber in the temporal bone- through the external auditory meatus • Air-filled cavity within the temporal bone • Lined with skin • Only involved in the sense of hearing • Ceruminous (wax) glands are present • Ends at the tympanic membrane (eardrum) 11 12/29/20 The Middle Ear or Tympanic Cavity • Two tubes are associated with the inner ear • The opening from the auditory canal is covered by the tympanic membrane (eardrum) • The auditory tube c onnecting the middle ear with the throat (also know as the eustacian tube) Bones of the Tympanic Cavity • Three bones span the cavity • Malleus (hammer) • Incus (anvil) • Allows for equalizing pressure during yawning or swallowing • Stapes (stirrip) • This tube is otherwise collapsed Bones of the Tympanic Cavity • Vibrations from eardrum move the malleus • These bones transfer sound to the inner ear Inner Ear or Bony Labyrinth · Also known as osseous labyrinth- twisted bony tubes · Includes sense organs hearing and balance for · Filled with perilymph 12 12/29/20 Organs of Hearing Organ of Corti • • Located within the cochlea • Receptors = hair cells on the basilar membrane Scala vestibuli Scala tympani Mechanisms of Hearing • Vibrations from sound waves move tectorial membrane (pass through the endolymph fluid filling the membranous labyrinth in the cochlear duct) Hair cells membrane are bent • Cochlear nerve attached to hair cells transmits nerve impulses to auditory cortex on temporal lobe Scala vestibuli Scala tympani • Organ of Corti by the Mechanisms of Hearing · An action potential starts in the cochlear nerve · The signal is transmitted to the midbrain (for auditory reflexes and then directed to the auditory cortex of the temporal lobe) 13 12/29/20 Mechanisms of Hearing Organs of Equilibrium • Receptor cells are in two structures • Continued stimulation can lead to adaptation (over stimulation to the brain makes it stop interpreting the sounds) • Vestibule • Semicircular canals Organs of Equilibrium Static Equilibrium • Equilibrium has two functional parts • Static equilibrium- in the vestibule • Dynamic equilibrium- in the semicircular canals • Maculae – receptors in the vestibule • Report on the position of the head • Send information via the vestibular nerve 14 12/29/20 Function of Maculae • Movements cause otoliths to bend the hair cells (gravity moves the “rocks” over and pulls the hairs) http://neuromedia.neurob io.ucla .edu/ca mpbel l/eyean dear/ wp_i mages /17 7_mac ula_HP. gif Dynamic Equilibrium • Whole structure is the ampulla • Crista ampullaris – receptors in the semicircular canals • Tuft of hair cells • Cupula (gelatinous cap) covers the hair cells Dynamic Equilibrium · Action of angular head movements ·The cupula stimulates the hair cells ·Movement of endolymph pushes the cupula over and pulls the hairs ·An impulse is sent via the vestibular nerve to the cerebellum 15 12/29/20 DYNAMIC EQUILIBRIUM STRUCTURES http://www.faculty.une.edu/com /abell /his to /Cris ta Amp. jpg Chemical Senses – Taste and Smell http://neuromedia.neurob io.ucla .edu/ca mpbel l/eyean dear/ wp_i mages /17 7_mac ula_c ris ta.gi f Olfaction – The Sense of Smell • Olfactory receptors are in the roof of the nasal cavity • Neurons with long cilia • Both senses use chemoreceptors • Stimulated by chemicals in solution • Chemicals must be dissolved in mucus for detection • Taste has four types of receptors • Smell can differentiate a large range of chemicals • Both senses complement each other and respond to many of the same stimuli 16 12/29/20 Olfaction – The Sense of Smell · Impulses are transmitted via the olfactory nerve · Interpretation of smells is made in the cortex (olfactory area of temporal lobe) http://as b.aecom.yu.edu/his tology/labs/images/s lides/A74_OlfactoryEpith_40X.jpg The Sense of Taste • Taste buds house the receptor organs Structure of Taste Buds • Gustatory cells are the receptors • Have gustatory hairs (long microvilli) • Hairs are stimulated by chemicals dissolved in saliva • Location of taste buds • Most are on the tongue • Soft palate • Cheeks 17 12/29/20 Structure of Taste Buds · Impulses are carried to the gustatory complex (pareital lobe) by several cranial nerves because taste buds are found in different areas ·Facial nerve ·Glossopharyngeal nerve ·Vagus nerve http://www.bios ci.ohiou.edu/introbios lab/Bios171/images /lab6/Tas tebuds.JPG Taste Sensations • Sweet receptors • Sugars • Saccharine • Some amino acids • Sour receptors • Acids • Bitter receptors • Alkaloids • Salty receptors • Metal ions Developmental Aspects of the Special Senses • Formed early in embryonic development • • Eyes are outgrowths of the brain All special senses are functional at birth http://ins truct1.cit.cornell.edu/cours es /ps ych431/s tudent2000/mle6/tonguebig.gif 18 12/29/20 The End 19