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Special senses

Special senses. Special senses. Taste, smell, sight, hearing, and balance Special sensory receptors Large complex organs (eyes, ears) Localized clusters of receptors (taste buds) confined to the head region. The eye and vision. eyes. Visual organs

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Special senses

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  1. Special senses

  2. Special senses • Taste, smell, sight, hearing, and balance • Special sensory receptors • Large complex organs (eyes, ears) • Localized clusters of receptors (taste buds) • confined to the head region

  3. The eye and vision

  4. eyes • Visual organs • 70% of all sensory receptors are in the eyes • 40% of the cerebral cortex is involved in processing visual information

  5. Accessory structures of the eyes Lacrimal apparatus – keeps the surface of the eye moist • Lacrimal gland – produces lacrimal fluid • Lacrimal sac – fluid empties into nasal cavity

  6. Accessory structures of the eyes, cont. • Eyelids- anterior protection • Eyelashes • Meibomian glands • Modified sebaceous glands at eyelid edges • Secrete oily lubricant for the eye • Ciliary glands • Between eyelashes • Modified sweat glands • Conjuctiva • Delicate membrane that lines eyelids and covers part of eye. • Fuses with corneal epithelium • Secretes mucus to keep eyes moist

  7. Eye movement • Controlled by 6 external muscles

  8. Internal structure of the eyes • Hollow sphere. • Fluid filled interior- helps maintain shape • Walls composed of 3 tunics • Fibrous tunic- outermost (white of the eye) • Thick connective tissue • Composed of two regions of connective tissue • Sclera – posterior five-sixths of the tunic • White, opaque region • Provides shape and an anchor for eye muscles • Cornea – anterior transparent window • Limbus – junction between sclera and cornea • Scleral venous sinus – allows aqueous humor to drain

  9. Internal eye structure cont. • Vascular tunic- middle coat • Composed of choroid, ciliary body, and iris • Choroid – vascular, darkly pigmented membrane • Brown color – from melanocytes • Prevents scattering of light rays within the eye • Choroid corresponds to the arachnoid and pia maters • Ciliary body- attachment to lens and iris • Iris- smooth muscle fibers that act like the diaphragm of a camera. • Pupil- opens to let light in

  10. Dilation of the pupil

  11. Internal eye structure cont. • Sensory tunic- innermost layer (retina) • Composed of two layers • Pigmented layer – single layer of melanocytes • Neural layer – sheet of nervous tissue • Contains three main types of neurons • Photoreceptor cells • Rod cells – more sensitive to light • Allow vision in dim light • Cone cells – operate best in bright light • Enable high-acuity, color vision • Bipolar cells • Ganglion cells

  12. Regional Specializations of the Retina • Macula lutea – contains mostly cones • Fovea centralis – contains only cones • Region of highest visual acuity • Optic disc – blind spot

  13. Medial View of the Eye

  14. Internal chambers and fluids • The lens and ciliaryzonules divide the eye • Posterior cavity • Filled with vitreous humor • Clear, jelly-like substance • Transmits light • Supports the posterior surface of the lens • Helps maintain intraocular pressure

  15. Internal Chambers and Fluids • Anterior cavity • Divided into anterior and posterior chambers • Anterior chamber – between the cornea and iris • Posterior chamber – between the iris and lens • Filled with aqueous humor • Renewed continuously • Formed as a blood filtrate • Supplies nutrients to the lens and cornea

  16. The Lens A thick, transparent, biconvex disc held in place by its ciliaryzonule.

  17. Homeostatic imbalance • Color Blindness • Lacking one type of cone • Cataracts • Lens becomes hard and opaque due to age • Glaucoma • Increased pressure in eyes due to lack of drainage for aqueos humor

  18. Light and focus • Structures in the eye bend light rays • Light rays converge on the retina at a single focal point • Light bending structures (refractory media) • The lens, cornea, and humors • Accommodation – curvature of the lens is adjustable • Allows for focusing on nearby objects

  19. Visual pathways to the brain Each side of the brain receives images from both eyes. Each eye sees a slightly different view, but visual fields overlap. This gives us binocular vision.

  20. Homeostatic imbalance • Age-related macular degeneration (AMD) • Involves the buildup of visual pigments in the retina Wet

  21. Homeostatic imbalance • Retinopathy in diabetes • Vessels have weak walls – causes hemorrhaging and blindness

  22. The ear: hearing and balance

  23. Anatomy of the ear • receptor organ for hearing and equilibrium • Composed of three main regions • Outer ear – functions in hearing • Middle ear – functions in hearing • Inner ear – functions in both hearing and equilibrium

  24. The Outer (External) Ear • The part we think of as the ear. • The auricle (pinna) • Helps direct sounds • External acoustic meatus • Canal lined with skin • Contains hairs, sebaceous glands, and ceruminous glands (secrete yellow wax) • Tympanic membrane • Forms the boundary between the external and middle ear

  25. The Middle Ear • The tympanic cavity • A small, air-filled space • Located within the petrous portion of the temporal bone • Contains ossicles that transmit vibration from eardrum to fluids of inner ear. • Malleus (hammer) • Incus (anvil) • Stapes (stirrup) • Medial wall is penetrated by: • Oval window • Round window • Pharyngotympanic tube (auditory or eustachian tube) • Links the middle ear and pharynx

  26. The Inner (Internal) Ear • Inner ear – also called the bony labyrinth • Lies within the petrous portion of the temporal bone behind the eye socket • cavity consisting of three parts • Semicircular canals • Vestibule • Cochlea

  27. The Inner Ear, cont. • Membranous labyrinth • Series of membrane-walled sacs and ducts within the bony laryrinth. • Consists of three main parts • Semicircular ducts • Utricle and saccule • Cochlear duct • Filled with a clear fluid – endolymph • Confined to the membranous labyrinth • Bony labyrinth is filled with perilymph • Continuous with cerebrospinal fluid

  28. The Membranous Labyrinth Figure 16.20

  29. The Vestibule • The central part of the bony labyrinth (actually a cavity) • Lies medial to the middle ear • Utricle and saccule – suspended in perilymph • Two egg-shaped parts of the membranous labyrinth • House the macula – a spot of sensory epithelium that contains receptor cells • Monitor the position of the head when the head is still • Contains columnar supporting cells • Receptor cells – called hair cells • Synapse with the vestibular nerve

  30. The Semicircular Canals • Lie posterior and lateral to the vestibule • Anterior and posterior semicircular canals • Lie in the vertical plane at right angles • Lateral semicircular canal • Lies in the horizontal plane

  31. The Semicircular Canals

  32. The Semicircular Canals • Semicircular duct – snakes through each semicircular canal • Membranous ampulla – located within bony ampulla • Houses a structure called a cristaampullaris • Responsible for maintaining static equilibrium.

  33. Structure and Function of the Crista Ampullaris Figure 16.22

  34. The Cochlea • A spiraling chamber in the bony labyrinth • contains receptors for hearing

  35. Equilibrium and Auditory Pathways • The equilibrium pathway • Transmits information on the position and movement of the head • Most information goes to lower brain centers (reflex centers) • The ascending auditory pathway • Transmits information from cochlear receptors to the cerebral cortex

  36. Disorders of Equilibrium and Hearing: Motion Sickness • Motion sickness – carsickness, seasickness • Popular theory for a cause – a mismatch of sensory inputs

  37. Disorders of Equilibrium and Hearing: Meniere’s Syndrome • Meniere’s syndrome – equilibrium is greatly disturbed • Excessive amounts of endolymph in the membranous labyrinth Meniere’s Normal

  38. Disorders of Equilibrium and Hearing • Deafness • Conduction deafness • Sound vibrations cannot be conducted to the inner ear • Ruptured tympanic membrane, otitis media, otosclerosis Otitis media Normal tympanic membrane Ruptured tympanic membrane

  39. Disorders of Equilibrium and Hearing: • Deafness • Sensorineural deafness • Results from damage to any part of the auditory pathway mild severe

  40. The Chemical Senses: Taste and Smell

  41. Taste – Gustation • Taste receptors • Occur in taste buds • Most are found on the surface of the tongue • Located within tongue papillae (circumvallate and fungiform) • Collection of 50-100 epithelial cells • Contain three major cell types • Supporting cells • Gustatory cells-respond to chemicals in saliva • Contain long microvilli – extend through a taste pore • Basal cells

  42. Taste Buds

  43. Taste Sensation and the Gustatory Pathway • Four basic qualities of taste • Sweet (responds to sugars and amino acids) • Sour (respond to hydrogen ions or acidity) • Salty (respond to metals) • Bitter (responds to alkaloids) • No structural difference among taste buds

  44. Gustatory Pathway • Taste information reaches the cerebral cortex • Primarily through the facial (VII) and glossopharyngeal (IX) nerves • Some taste information through the vagus nerve (X) • Sensory neurons synapse in the medulla • Located in the solitary nucleus

  45. Smell (Olfaction) • Receptors occupy a postage-stamp sixe area in the roof of each nasal cavity. • Olfactory receptor cells • Neurons with olfactory hairs that transmit to the olfactory nerve.

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