BIO 094 Chapter 8 Lecture

Special Senses : Special Senses

The Senses : The Senses General senses of touch Temperature Pressure Pain

The Senses : The Senses Special senses Smell Taste Sight Hearing Equilibrium

The Eye and Vision : 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 A cushion of fat surrounds most of the eye

Accessory Structures of the Eye : Accessory Structures of the Eye Eyelids and eyelashes Conjunctiva Lacrimal apparatus Extrinsic eye muscles

Accessory Structures of the Eye : Accessory Structures of the Eye Figure 8.1

Accessory Structures of the Eye : Accessory Structures of the Eye Conjunctiva Membrane that lines the eyelids Connects to the surface of the eye Secretes mucus to lubricate the eye

Accessory Structures of the Eye : Accessory Structures of the Eye Lacrimal apparatus Function of the lacrimal apparatus Protects, moistens, and lubricates the eye Empties into the nasal cavity Properties of lacrimal fluid Dilute salt solution (tears) Contains antibodies and lysozyme

Accessory Structures of the Eye : Accessory Structures of the Eye Figure 8.2b

Accessory Structures of the Eye : Accessory Structures of the Eye Extrinsic eye muscles Six muscles attach to the outer surface of the eye Produce eye movements These muscles have the finest motor control of any muscles in the body. (very small number of muscle cells per nerve ending)

Accessory Structures of the Eye : Accessory Structures of the Eye Figure 8.3a–b

Structure of the Eye : Structure of the Eye Layers forming the wall of the eyeball Fibrous layer Outside layer Vascular layer Middle layer Sensory layer Inside layer

Structure of the Eye : Structure of the Eye Figure 8.4a

Structure of the Eye: The Fibrous Layer : Structure of the Eye: The Fibrous Layer Sclera White connective tissue layer Seen anteriorly as the “white of the eye” Cornea Transparent, central anterior portion Allows for light to pass through Repairs itself easily The only human tissue that can be transplanted without fear of rejection

Structure of the Eye: Vascular Layer : Structure of the Eye: Vascular Layer Choroid is a blood-rich nutritive layer in the posterior of the eye Pigment prevents light from scattering Modified anteriorly into two structures Ciliary body—smooth muscle attached to lens Iris—regulates amount of light entering eye Pigmented layer that gives eye color Pupil—rounded opening in the iris

Lens : Lens Biconvex crystal-like structure Held in place by a suspensory ligament attached to the ciliary body

Lens : Lens Figure 8.4a

Lens : Lens Cataracts result when the lens becomes hard and opaque with age Vision becomes hazy and distorted Eventually causes blindness in affected eye

Two Segments, or Chambers, of the Eye : Two Segments, or Chambers, of the Eye Anterior (aqueous) segment Anterior to the lens Contains aqueous humor Posterior (vitreous) segment Posterior to the lens Contains vitreous humor

Anterior Segment : Anterior Segment Aqueous humor Watery fluid found between lens and cornea Similar to blood plasma Helps maintain intraocular pressure Provides nutrients for the lens and cornea Reabsorbed into venous blood through the scleral venous sinus, or canal of Schlemm

Posterior Segment : Posterior Segment Vitreous humor Gel-like substance posterior to the lens Prevents the eye from collapsing Helps maintain intraocular pressure

Structure of the Eye: Sensory Layer : Structure of the Eye: Sensory Layer Retina contains two layers Outer pigmented layer Inner neural layer Contains receptor cells (photoreceptors) Rods Cones Signals leave the retina toward the brain through the optic nerve Optic disc (blind spot) is where the optic nerve leaves the eyeball Cannot see images focused on the optic disc

Structure of the Eye: Sensory Layer : Structure of the Eye: Sensory Layer Figure 8.5a

Structure of the Eye: Sensory Layer : Structure of the Eye: Sensory Layer Figure 8.5b

Structure of the Eye: Sensory Layer : Structure of the Eye: Sensory Layer Neurons of the retina and vision Rods Most are found towards the edges of the retina Allow dim light vision and peripheral vision All perception is in gray tones

Structure of the Eye: Sensory Layer : Structure of the Eye: Sensory Layer 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 No photoreceptor cells are at the optic disc, or blind spot

Structure of the Eye: Sensory Layer : Structure of the Eye: Sensory Layer Cone sensitivity Three types of cones Different cones are sensitive to different wavelengths Color blindness is the result of the lack of one cone type

Sensitivities of Cones to Different Wavelengths : Sensitivities of Cones to Different Wavelengths Figure 8.6

Ophthalmoscope : Ophthalmoscope Instrument used to illuminate the interior of the eyeball Can detect diabetes, arteriosclerosis, degeneration of the optic nerve and retina

Posterior Wall of Retina as Seen with Ophthalmoscope : Posterior Wall of Retina as Seen with Ophthalmoscope Figure 8.8

Pathway of Light Through the Eye : Pathway of Light Through the Eye Light must be focused to a point on the retina for optimal vision The eye is set for distance vision (over 20 feet away) Accommodation—the lens must change shape to focus on closer objects (less than 20 feet away)

Pathway of Light Through the Eye : Pathway of Light Through the Eye Figure 8.9

Pathway of Light Through the Eye : Pathway of Light Through the Eye Image formed on the retina is a real image Real images are Reversed from left to right Upside down Smaller than the object

Images Formed on the Retina : Images Formed on the Retina Figure 8.10

Visual Fields and Visual Pathways : Visual Fields and Visual Pathways Optic chiasma Location where the optic nerves cross Fibers from the medial side of each eye cross over to the opposite side of the brain Optic tracts Contain fibers from the lateral side of the eye on the same side and the medial side of the opposite eye

Visual Fields and Visual Pathways : Figure 8.11 Visual Fields and Visual Pathways

Eye Reflexes : Eye Reflexes Internal muscles are controlled by the autonomic nervous system Bright light causes pupils to constrict through action of radial, circular, and ciliary muscles Viewing close objects causes accommodation External muscles control eye movement to follow objects Viewing close objects causes convergence (eyes moving medially)

A Closer Look : A Closer Look Myopia (nearsighted) Distant objects appear blurry Light from those objects fails to reach the retina and are focused in front of it Results from an eyeball that is too long Hyperopia (farsighted) Near objects are blurry while distant objects are clear Distant objects are focused behind the retina Results from an eyeball that is too short or from a “lazy lens”

Homeostatic Imbalances of the Eyes : Homeostatic Imbalances of the Eyes Astigmatism Images are blurry Results from light focusing as lines, not points, on the retina due to unequal curvatures of the cornea or lens Night blindness—inhibited rod function that hinders the ability to see at night Color blindness—genetic conditions that result in the inability to see certain colors Due to the lack of one type of cone (partial color blindness) Cataracts—when lens becomes hard and opaque, our vision becomes hazy and distorted

The Ear : The Ear Houses two senses Hearing Equilibrium (balance) Receptors are mechanoreceptors Different organs house receptors for each sense

Anatomy of the Ear : Anatomy of the Ear The ear is divided into three areas External (outer) ear Middle ear (tympanic cavity) Inner ear (bony labyrinth)

Anatomy of the Ear : Anatomy of the Ear Figure 8.12

The External Ear : The External Ear Involved in hearing only Structures of the external ear Auricle (pinna) External acoustic meatus (auditory canal) Narrow chamber in the temporal bone Lined with skin and ceruminous (wax) glands Ends at the tympanic membrane

The Middle Ear (Tympanic Cavity) : The Middle Ear (Tympanic Cavity) Two tubes are associated with the inner ear The opening from the auditory canal is covered by the tympanic membrane The auditory tube connecting the middle ear with the throat Allows for equalizing pressure during yawning or swallowing This tube is otherwise collapsed

Bones of the Middle Ear (Tympanic Cavity) : Bones of the Middle Ear (Tympanic Cavity) Three bones (ossicles) span the cavity Malleus (hammer) Incus (anvil) Stapes (stirrip) Function Vibrations from eardrum move the malleus ? anvil ? stirrup ? inner ear

Anatomy of the Ear : Anatomy of the Ear Figure 8.12

Inner Ear or Bony Labyrinth : Inner Ear or Bony Labyrinth Includes sense organs for hearing and balance Filled with perilymph A maze of bony chambers within the temporal bone Cochlea Vestibule Semicircular canals

Anatomy of the Ear : Anatomy of the Ear Figure 8.12

Organs of Hearing : Organs of Hearing Organ of Corti Located within the cochlea Receptors = hair cells on the basilar membrane Gel-like tectorial membrane is capable of bending hair cells Cochlear nerve attached to hair cells transmits nerve impulses to auditory cortex on temporal lobe

Organs of Hearing : Organs of Hearing Figure 8.15a

Organs of Hearing : Organs of Hearing Figure 8.15b

Mechanism of Hearing : Mechanism of Hearing Vibrations from sound waves move tectorial membrane Hair cells are bent by the membrane An action potential starts in the cochlear nerve Continued stimulation can lead to adaptation

Mechanism of Hearing : Mechanism of Hearing Figure 8.16a

Mechanism of Hearing : Mechanism of Hearing Figure 8.16b–c

Organs of Equilibrium : Organs of Equilibrium Equilibrium receptors of the inner ear are called the vestibular apparatus Vestibular apparatus has two functional parts Static equilibrium Dynamic equilibrium

Structure and Function of Maculae : Structure and Function of Maculae Figure 8.13b

Organs of Equilibrium : Organs of Equilibrium Figure 8.14a–b

Dynamic Equilibrium : Dynamic Equilibrium Figure 8.14c

Olfaction—The Sense of Smell : Olfaction—The Sense of Smell Olfactory receptors are in the roof of the nasal cavity Neurons with long cilia Chemicals must be dissolved in mucus for detection Impulses are transmitted via the olfactory nerve Interpretation of smells is made in the cortex

Olfactory Epithelium : Olfactory Epithelium Figure 8.17

The Sense of Taste : The Sense of Taste Taste buds house the receptor organs Location of taste buds Most are on the tongue Soft palate Cheeks

Taste Buds : Taste Buds Figure 8.18

The Tongue and Taste : The Tongue and Taste The tongue is covered with projections called papillae Filiform papillae—sharp with no taste buds Fungifiorm papillae—rounded with taste buds Circumvallate papillae—large papillae with taste buds Taste buds are found on the sides of papillae

Structure of Taste Buds : Structure of Taste Buds Gustatory cells are the receptors Have gustatory hairs (long microvilli) Hairs are stimulated by chemicals dissolved in saliva

Structure of Taste Buds : Structure of Taste Buds Impulses are carried to the gustatory complex by several cranial nerves because taste buds are found in different areas Facial nerve Glossopharyngeal nerve Vagus nerve

Taste Sensations : Taste Sensations Sweet receptors (sugars) Saccharine Some amino acids Sour receptors Acids Bitter receptors Alkaloids Salty receptors Metal ions

Chemical Senses: Taste and Smell : Chemical Senses: Taste and Smell Both senses use chemoreceptors Stimulated by chemicals in solution 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