The Special Senses. Taste Smell Vision Hearing & Balance Special sensory receptors Localized –...
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The Special Senses
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The Special Senses• Taste• Smell• Vision• Hearing & Balance• Special sensory receptors• Localized – confined to the head region• Receptors are not free endings of sensory
neurons• Special receptor cells
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The Chemical Senses: Taste and Smell
• Taste – gustation • Smell – olfaction• Receptors are chemoreceptors • Respond to chemicals
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Taste Buds• Most are found on surface of the tongue
located within the tongue papillae• Collection of 50-100 epithelial cells• Contain three major cell types• Supporting cells• Gustatory cells• Basal cells
• Contain long microvilli – extend through a taste pore
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Taste Buds
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Taste Sensation and the Gustatory Pathway• Four basic qualities of taste• Sweet, sour, salty, and bitter• A fifth taste – umami – “deliciousness”
• No structural difference among taste buds• 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
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Gustatory Pathway from Taste Buds
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Smell (Olfaction)• Receptors are part of the olfactory epithelium• Olfactory epithelium composed of:• Cell bodies of olfactory receptor cells• Supporting cells – columnar cells• Basal cells – form new olfactory receptor cells
• Axons of olfactory epithelium• Gather into bundles – filaments of the
olfactory nerve• Pass through the cribriform plate of the
ethmoid bone • Attach to the olfactory bulbs
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Olfactory Receptors
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The Eye and Vision• Visual organ – the eye• 70% of all sensory receptors are in the eyes• 40% of the cerebral cortex is involved in
processing visual information
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Medial View of the Eye
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Posterior View of the Anterior Half of the Eye
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Accessory Structures of the Eye
• Lacrimal apparatus – keeps the surface of the eye moist• Lacrimal gland:
produces lacrimal fluid • Lacrimal sac: fluid
empties into nasal cavity
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The Fibrous Tunic• Most external layer of the eyeball• 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 one-sixth of the fibrous tunic• Limbus – junction between sclera and cornea• Scleral venous sinus – allows aqueous humor to
drain
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The Vascular Tunic• The middle coat of the eyeball• Composed of choroid, ciliary body, and iris • Choroid – vascular, darkly pigmented membrane• Forms posterior five-sixths of the vascular tunic• Brown color – from melanocytes• Prevents scattering of light rays within the eye
• Choroid corresponds to the arachnoid and pia maters• Ciliary body – thickened ring of tissue – encircles the lens• Composed of ciliary muscle• Ciliary processes – posterior surface of the ciliary body• Ciliary zonule (suspensory ligament) • Attached around entire circumference of the lens
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The Vascular Tunic
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The Iris
• Visible colored part of the eye• Attached to the ciliary body• Composed of smooth muscle• Pupil – the round, central opening• Sphincter pupillae muscle (constrictor or
circular)• Dilator pupillae muscle (dilator or radial)• Act to vary the size of the pupil
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Pupillary dilation and constriction
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The Sensory Tunic (Retina)
• Retina – the deepest tunic• Composed of two layers• Pigmented layer – single layer of
melanocytes • Neural layer – sheet of nervous tissue• Contains three main types of neurons• Photoreceptor cells• Bipolar cells• Ganglion cells
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Microscopic Anatomy of the Retina
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Photoreceptors
• Two main types:• Rod cells – more
sensitive to light • Allow vision in dim
light• Cone cells – operate best
in bright light• Enable high-acuity,
color vision• Considered neurons
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Specializations & Blood Supply of the Retina• Macula lutea – contains
mostly cones• Fovea centralis – contains
only cones• Region of highest visual
acuity • Optic disc – blind spot• Retina receives blood from
two sources• Outer third of the retina –
supplied by capillaries in the choroid• Inner two-thirds of the
retina – supplied by central artery and vein of the retina
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Medial View of the Eye
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Internal Chambers and Fluids• The lens and ciliary zonules divide the eye • Posterior segment (cavity)• Filled with vitreous humor• Clear, jelly-like substance• Transmits light• Supports the posterior surface of the lens• Helps maintain intraocular pressure
• Anterior segment• 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
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Internal Chambers and Fluids
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The Lens• A thick, transparent, biconvex disc• Held in place by its ciliary zonule
http://sam.ntpi.spcollege.edu/spjc/default.jhtml
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Lens, Zonule Fibers, & Ciliary Muscles
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Lens Epithelium
capsule
epithelium
fibers
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The Eye as an Optical Device• 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
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Visual Pathways• Most visual information travels to the cerebral cortex• Responsible for conscious “seeing”• Other pathways travel to nuclei in the midbrain and
diencephalon • Pathway begins at the retina• Light activates photoreceptors • Photoreceptors signal bipolar cells• Bipolar cells signal ganglion cells • Axons of ganglion cells exit eye as the optic nerve
• Optic tracts send axons to:• Lateral geniculate nucleus of the thalamus • Synapse with thalamic neurons • Fibers of the optic radiation reach the primary visual
cortex
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Visual Pathways to the Brain and Visual Fields
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Visual Pathways to Other Parts of the Brain
• Some axons from the optic tracts• Branch to midbrain• Superior colliculi• Pretectal nuclei
• Other branches from the optic tracts• Branch to the suprachiasmatic nucleus
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Disorders of the Eye and Vision: Macular Degeneration
• Age-related macular degeneration (AMD)• Involves the buildup of visual pigments in the retina
Dry Wet
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Macular Degeneration Simulation
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Disorders of the Eye and Vision: Retinopathy
• Retinopathy in diabetes • Vessels have weak walls – causes hemorrhaging and
blindness
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Disorders of the Eye and Vision: Trachoma
• Trachoma – contagious infection of the conjunctiva
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The Ear: Hearing and Equilibrium
• 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
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The Outer (External) Ear• Composed of:• The auricle (pinna)• Helps direct sounds
• External acoustic meatus• Lined with skin • Contains hairs, sebaceous glands, and
ceruminous glands • Tympanic membrane• Forms the boundary between the external and
middle ear
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The Outer (External) Ear
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The Middle Ear• The tympanic cavity • A small, air-filled space • Located within the petrous portion of the
temporal bone• Medial wall is penetrated by:• Oval window • Round window
• Pharyngotympanic tube (auditory or eustachian tube) • Links the middle ear and pharynx
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Structures of the Middle Ear
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The Middle Ear• Ear ossicles – smallest
bones in the body• Malleus – attaches to
the eardrum • Incus – between the
malleus and stapes• Stapes – vibrates
against the oval window
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The Inner (Internal) Ear• Inner ear – also called the labyrinth• Lies within the petrous portion of the temporal
bone• Bony labyrinth – a cavity consisting of three parts• Semicircular canals• Vestibule• Cochlea
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The Inner (Internal) Ear
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The Inner (Internal) Ear II• Membranous labyrinth • Series of membrane-walled sacs and ducts• Fit within the bony labyrinth• 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
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The Membranous Labyrinth
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The Vestibule• The central part of the bony labyrinth• 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
• Macula – 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
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Anatomy and Function of the Maculae
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Anatomy and Function of the Maculae
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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 planeSemicircular duct –
snakes through each semicircular canal• Membranous ampulla – located within bony
ampulla• Houses a structure called a crista ampullaris • Cristae contain receptor cells of rotational
acceleration• Epithelium contains supporting cells and
receptor hair cells
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The Semicircular Canals
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Structure and Function of the Crista Ampullaris
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The Cochlea• A spiraling chamber in the bony labyrinth• The cochlear duct (scala media) – contains receptors for
hearing• Lies between two chambers• The scala vestibuli • The scala tympani
• The vestibular membrane – the roof of the cochlear duct• The basilar membrane – the floor of the cochlear duct
• The cochlear duct (scala media) – contains receptors for hearing• Organ of Corti – the receptor epithelium for hearing • Consists of: • Supporting cells• Inner and outer hair cells (receptor cells)
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The Cochlea
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The Anatomy of the Cochlea
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The Role of the Cochlea in Hearing
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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
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Auditory Pathway from the Organ of Corti
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Disorders of Equilibrium and Hearing: Motion Sickness
• Motion sickness – carsickness, seasickness• Popular theory for a cause – a mismatch of
sensory inputs
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Disorders of Equilibrium and Hearing: Meniere’s Syndrome
• Meniere’s syndrome – equilibrium is greatly disturbed• Excessive amounts of endolymph in the membranous
labyrinth
Normal Meniere’s
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Disorders of Equilibrium and Hearing: Conduction Deafness
• Deafness • Conduction deafness • Sound vibrations cannot be conducted to the inner ear• Ruptured tympanic membrane, otitis media,
otosclerosis
Normal tympanicmembrane
Otitis mediaRuptured tympanicmembrane
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Disorders of Equilibrium and Hearing: Sensorineural Deafness
• Deafness • Sensorineural deafness • Results from damage to any part of the auditory
pathway
mild severe