Download The Special Senses

The General & Special Senses
Chapter 18
Introduction
• Senses – our perception of what is “out there”
• 2 groups
– General senses
• Includes senses that are not specific
• Pass information through spinal nerves
– Special senses
• Found within complex sense organs to cerebral cortex
• Pass information through cranial nerves to cerebral cortex
Receptors
• Sensory receptors are transducers
– Change stimuli into electro-chemical impulses
– Specific receptors can transduce only certain
types of stimuli
Receptors
Figure 18-01
Interpretation of Sensory Information
• Occurs in cerebral cortex
• Depends on the area of the cerebral cortex
that receives the information
Central Processing and Sensory Adaptation
• Sensory adaptation – the loss of sensitivity
after continuous stimulation
– Occurs in some types of receptors
• Role – prevents brain from being
overloaded with unimportant information
Receptors of the General Senses
• Pain
– Referred pain
– Phantom pain
• Thermoreceptors detect changes in temperature
• Mechanoreceptors respond to pressure & touch
• Chemoreceptors detect chemicals in solution
– Blood composition
– (Smell)
– (Taste)
Referred Pain
Figure 18-02
The Special Senses
Olfaction (the nose)
• Olfactory receptors
– Can detect at least 50 different primary smell
– Located in the roof of nasal cavity
– Molecules dissolve in the mucus or lipids of the
epithelium
– Olfactory neurons pass through the roof of the
nasal cavity and synapse in the olfactory nerve
– Olfactory tracts go directly to the cerebral
cortex
Olfactory Receptors
Figure 18-06a
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Olfactory Receptors
Figure 18-06b
Taste (the tongue)
• Taste receptors are in the taste buds
– Can detect 4 primary tastes
• Sweet, sour, salty, bitter
–
–
–
–
Located in papillae on the surface of the tongue
Taste buds contain the taste receptors
Molecules dissolve in saliva
Cranial nerves relay sensory impulses to the
cerebral cortex
Taste Areas of the Tongue
Figure 18-07a
Taste Buds
Figure 18-07b
Taste Bud
Figure 18-07c
Equilibrium & Hearing (the ear)
• External ear
– The auricle directs sound waves into the external
auditory meatus to the tympanic membrane
• Middle ear
– Contains the auditory ossicles
• Malleus, incus, stapes
– Connected to throat by the eustachian tube
• Inner ear
The Ear
Figure 18-09
Human Anatomy, 3rd edition
Prentice Hall, © 2001
The Middle Ear
Figure 18-10b
The Inner Ear
• Separated from the middle ear by the oval
window
• Consists of a series of canals filled with
fluid
The Inner Ear
– Semicircular canals
• Contains receptors for head position
– Cochlea
• Contains the organ of Corti, the organ of hearing
The Inner Ear
Figure 18-12b
The Semicircular Canals
• Detects balance
• Arranged at right angles to each other
• Contain hair cells are embedded in
gelatinous material with fluid over it
• Detect movement of the head
– Bends the hairs, creating nerve impulses
Hair Cells in the Semicircular
Canals
Figure 18-12c
The Organ of Corti
• Detects sound waves
• Consists of hair cells on a basement
membrane
• Tips of hairs touch the tectorial membrane
• When the basement membrane vibrates, the
hair cells are bent, sending a nerve impulse
Organ of Corti
Figure 18-16d
Organ of Corti
Figure 18-16e
Summary of Hearing
•
•
•
•
•
•
•
•
Sound waves enter the external auditory meatus
Tympanic membrane vibrates
Auditory ossicles vibrate
Oval window vibrates
Fluid in inner ear vibrates
Basement membrane moves
Hairs rub against the tectorial membrane
Nerve impulse is sent along the auditory nerve to
the brain
Vision (the eye)
• Accessory structures
– Eyelids protect the eye
• Conjunctiva lines the eyelid
• Lacrimal gland produces tears
– Extrinsic muscles move the eyeball
The Eye
Figure 18-18b
Structure of the Eye
• Consists of 3 tunics (layers)
– Outer tunic – outermost layer
• Includes the cornea & sclera
– Middle tunic
• Includes the choroid coat, ciliary body, and lens,
iris & pupil
– Inner tunic (retina) – inner layer
• Contains the rods & cones (photoreceptors)
• Includes the optic disc (blind spot),
The Eye
Figure 18-20b
Tunics of the Eye
Figure 18-20a
Inner Tunic
Figure 18-22c
The Cavities of the Eye
• The lens separates the interior of the eye
into 2 cavities
– Anterior cavity in front of the lens
• Contains aqueous humor
– Glaucoma
– Posterior cavity behind the lens
• Contains vitreous humor
Cavities of the Eye
Figure 18-23
The Vascular Tunic
• Contains many blood vessels & nerves
• The iris controls the size of the pupil
• Suspensory ligaments attach the lens to the
ciliary body
– Controls the shape of the lens
• Allows focusing on near & distant objects
• Cataract
The Pupil
Figure 18-20c
The Retina
• Cones allow for sharp color vision in bright
light
– 3 types, each with a different pigment
The Retina
• Rods provide for vision in dim light
– Most dense at the periphery of the retina
– Contain the pigment rhodopsin
Visual Receptors
Figure 18-22a1
Summary of Vision
• Light rays enters through the pupil
• Light rays cross in the lens
• Retina receives reversed & upside down
image
• Rods & cones are stimulated
• Optic nerve carries impulse to the brain
Abnormal Vision
•
•
•
•
Myopia
Hyperopia
Presbyopia
Astigmatism