Transcript Chapter 17 Special Senses

Special Senses
The Special Senses
– Olfaction (smell)
– Gustatory (taste)
– Vision
– Hearing and Equilibrium
Olfaction
• 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
Physiology of Olfaction
• Many different combinations of receptors produces the
possibility for thousands of different odor sensations.
• Low threshold, only few molecules needed.
• Adaptation - rapid
Olfactory Pathway
1. Olfactory receptors
2. Olfactory (I) nerves
3. Olfactory tract
4. Temporal lobe (primary olfactory
area)
Olfactory Pathway
Gustation
• Sweet (sugars)
– Saccharine
– Some amino
acids
• Sour
– Acids
• Bitter
– Alkaloids
• Salty receptors
– Metal ions
• Umami
– Meaty/savory
Anatomy of Taste Buds and Papillae
• The tongue is covered with projections called
papillae
– Filiform papillae—sharp with no taste buds
– Fungiform papillae—rounded with taste buds
– Circumvallate papillae—large papillae with taste
buds
• Taste buds are found on the sides of papillae
Anatomy of Taste Buds and Papillae
Physiology of Gustation
• Gustatory cells are the receptors
– Have gustatory hairs (long microvilli)
– Hairs are stimulated by chemicals dissolved in saliva
• 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
• Impulse travels from receptors to medulla→ thalamus→
primary gustatory area of the cerebrum
Accessory Structures of Eye
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Eyelids and eyelashes
Conjunctiva
Lacrimal apparatus
Extrinsic eye muscles
Vision
Accessory Structures of the Eye
• Eyelids
– Meet at the medial and lateral commissure (canthus)
• Eyelashes
– Tarsal glands produce an oily secretion that lubricates
the eye
– Ciliary glands are located between the eyelashes
• Conjunctiva
– Membrane that lines the eyelids
– Connects to the outer surface of the eye
– Secretes mucus to lubricate the eye and keep it moist
Accessory Structures of the Eye
• Lacrimal apparatus = lacrimal gland + ducts
– Lacrimal gland—produces lacrimal fluid;
situated on lateral aspect of each eye
– Lacrimal canaliculi—drain lacrimal fluid from
eyes medially
– Lacrimal sac—provides passage of lacrimal
fluid towards nasal cavity
– Nasolacrimal duct—empties lacrimal fluid into
the nasal cavity
Lacrimal Apparatus
Accessory Structures of the Eye
• Function of the lacrimal apparatus
– Protects, moistens, and lubricates the eye
– Empties into the nasal cavity
• Lacrimal secretions (tears) contain:
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Dilute salt solution
Mucus
Antibodies
Lysozyme (enzyme that destroys bacteria)
Accessory Structures of the Eye
• Extrinsic eye muscles
– Six muscles attach to the outer surface of the eye
– Produce eye movements
Muscles of the Eye
Muscles of the Eye
Structure of the Eye
• Three layers:
– Fibrous tunic- outer layer
• Sclera “white” of the eye
• Cornea-transparent coat
– Vascular tunic or uvea- middle layer
• Choroid
• Ciliary body consists of ciliary processes and ciliary
muscle
• Iris
– Retina- inner layer
• Optic disc
• Macula lutea- fovea centralis
Structure of the Eye
Structure of the Eye
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
– The only human tissue that can be transplanted
without fear of rejection
Structure of the Eye: The 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
Muscles of Iris
Structure of the Eye: The Sensory Layer
• Retina contains two layers
– Outer pigmented layer
– Inner neural layer
• Contains receptor cells (photoreceptors)
– Rods
– Cones
Structure of the Eye: The Sensory Layer
• Signals pass from photoreceptors via a twoneuron chain
– Bipolar neurons
– Ganglion cells
• 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
Retina
View with Ophthalmoscope
Retina
Interior of the Eyeball
• Lens
– lack blood vessels, consists of a capsule with
proteins (crystallins) in layers; transparent.
– held in place by a suspensory ligament attached to
the ciliary body
– divides the eyeball into two cavities: anterior and
posterior.
- Anterior cavity- further divided into anterior and
posterior chambers. Both are filled with aqueous humor.
- Posterior cavity (vitreous chamber)-filled with vitreous
body.
Chambers of the Eye
Cavities of the Interior of Eyeball
• Anterior cavity (anterior to lens)
– filled with aqueous humor
• produced by ciliary body
• continually drained
• replaced every 90 minutes
– 2 chambers
• anterior chamber between cornea and iris
• posterior chamber between iris and lens
• Posterior cavity (posterior to lens)
– filled with vitreous body (jellylike)
– formed once during embryonic life
– floaters are debris in vitreous
Lens - Cataract
Image Formation
• Refraction: Bending of light as
it passes from one substance
(air) into a 2nd substance with a
different density (cornea)
• In the eye, light is refracted by
the anterior & posterior surfaces
of the cornea and the lens
Vision
• 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”
Vision Correction
Visual
Pathway
Anatomy of Ear
Middle Ear
Inner Ear
Cochlea
and
Cranial
Nerve VIII
One Turn
of
Cochlea
and
Organ of
Corti
Physiology of Hearing
Auditory Pathway
Balance and Position
Crista and Rotational Movement