Special Senses – Part I

Chapter 8BIO 160

Kelly Trainor

The Senses General senses of touch

Temperature Pressure Pain

Special senses Smell Taste Sight Hearing Equilibrium

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

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

The Sense of Taste Taste buds house the receptor organs Location of taste buds

Most are on the tongue Soft palate Cheeks

The tongue is covered with projections called papillae Taste buds are found on the sides of papillae Gustatory cells are the receptors

Have gustatory hairs (long microvilli) Hairs are stimulated by chemicals dissolved in saliva

Taste Buds

Figure 8.18

Taste Sensations Sweet receptors (sugars)

Saccharine Some amino acids

Sour receptors Acids

Bitter receptors Alkaloids

Salty receptors Metal ions

Special Senses – Part II

Chapter 8BIO 160

Kelly Trainor

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 Eyelids and eyelashes Conjunctiva Lacrimal apparatus Extrinsic eye muscles

Accessory Structures of the Eye Eyelids and eyelashes

Tarsal glands lubricate the eye Ciliary glands are located between the eyelashes

Conjunctiva Membrane that lines the eyelids Connects to the surface of the eye Secretes mucus to lubricate the eye

Accessory Structures of the Eye 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 Extrinsic eye muscles

Six muscles attach to the outer surface of the eye Produce eye movements

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

Figure 8.4a

Structure of the Eye

Figure 8.4b

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 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

Structure of the Eye: Sensory Layer Retina contains two layers

Outer pigmented layer Inner neural layer

Contains receptor cells (photoreceptors) Rods Cones

Structure of the Eye: Sensory Layer Signals pass from photoreceptors via a two-neuron chain 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

Figure 8.5b

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

Cones Allow for detailed color vision Densest in the center of the retina Fovea centralis—area of the retina with only cones

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

No photoreceptor cells are at the optic disc, or blind spot

Structure of the Eye: Sensory Layer

Lens Biconvex crystal-like structure Held in place by a suspensory ligament attached to the ciliary body Cataracts result when the lens becomes hard and opaque with age

Vision becomes hazy and distorted Eventually causes blindness in affected eye

Lens

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 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 Vitreous humor

Gel-like substance posterior to the lens Prevents the eye from collapsing Helps maintain intraocular pressure

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 Image formed on the retina is a real image Real images are

Reversed from left to right Upside down Smaller than the object

A Closer Look Emmetropia—eye focuses images correctly on the retina 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”

Astigmatism Images are blurry Results from light focusing as lines, not points, on the retina due

to unequal curvatures of the cornea or lens

Homeostatic Imbalances of the Eyes 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

Glaucoma—can cause blindness due to increasing pressure within the eye

Special Senses – Part III

Chapter 8BIO 160

Kelly Trainor

The Ear Houses two senses

Hearing Equilibrium (balance)

Receptors are mechanoreceptors Different organs house receptors for each sense

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

Figure 8.12

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) Air-filled cavity within the temporal bone Only involved in the sense of hearing 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) 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

Figure 8.12

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

Figure 8.12

Organs of Equilibrium Equilibrium receptors of the inner ear are called the vestibular

apparatus Vestibular apparatus has two functional parts

Static equilibrium Dynamic equilibrium

Static Equilibrium Maculae—receptors in the vestibule

Report on the position of the head Hair cells are embedded in the otolithic membrane Otoliths (tiny stones) float in a gel around the hair cells Movements cause otoliths to bend the hair cells

Structure and Function of Maculae

Figure 8.13a

Dynamic Equilibrium Crista ampullaris—receptors in the

semicircular canals Tuft of hair cells Cupula (gelatinous cap) covers the

hair cells Action of angular head movements

The cupula stimulates the hair cells An impulse is sent via the vestibular

nerve to the cerebellum Action of angular head movements

The cupula stimulates the hair cells An impulse is sent via the vestibular

nerve to the cerebellum

Organs of Equilibrium

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

Figure 8.15a

Organs of Hearing

Figure 8.15b

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

Figure 8.16a

Figure 8.16b–c