Download The Special Senses

The General & Special Senses
Chapter 18
Introduction
• Senses – our perception of what is “out
there”
• 2 groups
– General senses
– Special senses
General Senses
• Includes senses that are skin or kinesthetic
– Temperature, pressure, touch, pain, vibration,
proprioception
• Pass information along the spinal nerves
and pathways to the somatosensory cortex
Special Senses
• Olfaction, gustation, equilibrium, hearing,
& vision
• Found within complex sense organs
• Pass information along the cranial nerves to
specific areas of the cerebral cortex.
Receptors
• Sensory receptors are transducers
– Change stimuli into electro-chemical impulses
– Specific receptors can transduce only certain
types of stimuli
• Two general types
– Exteroceptors
– Interoceptors
Interpretation of Sensory Information
• Occurs in cerebral cortex
• Depends on the area of the cerebral cortex
that receives the information
• Also depends on the sequence of neurons
carrying the information
Central Processing and Adaptation
• Adaptation – the loss of sensitivity after
continuous stimulation
– Tonic receptors are always active
– Phasic receptors only relay changes in the
conditions they are monitoring
• Role – prevents brain from being
overloaded with unimportant information
Receptors of the General Senses
• Nociceptors detect pain
– Referred pain
– Phantom pain
• Thermoreceptors detect changes in
temperature
Referred Pain
Figure 18-02
Receptors of the General Senses
• Mechanoreceptors respond to pressure &
touch
– Tactile receptors are found in the dermis
– Baroreceptors monitor changes in pressure
– Proprioceptors monitor positions of joints &
muscles
Tactile Receptors
Figure 18-03
Some Enteroreceptors
Figure 18-04
Receptors of the General Senses
• Chemoreceptors detect chemicals in
solution
– Smell
– Taste
– Blood composition
Chemoreceptors
Figure 18-05
The Special Senses
Olfaction (the nose)
• Olfactory receptors
– Can detect at least 50 different primary smell
– Located in the epithelium of roof of nasal cavity
– Molecules dissolve in the mucus or lipids of the
epithelium
– Olfactory neurons pass through the cribiform plate and
synapse in the olfactory bulb
– Olfactory tracts go directly to the cerebral cortex
Nasal Cavity
Figure 18-06a
Olfactory Receptors
Figure 18-06b
Gustation (the tongue)
• Taste receptors are in the taste buds
– Can detect 4 primary tastes
• Sweet, sour, salty, bitter
– Located in papillae or bumps on the surface of the
tongue (also on the walls of the pharynx & larynx)
• Taste buds contain the gustatory receptors
– Molecules dissolve in saliva
– 3 cranial nerves relay sensory impulses to the cerebral
cortex
• Facial, glossopharyngeal, vagus
• All pass through the medulla & thalamus
Tastes on the Tongue
Figure 18-07a
Taste Buds
Figure 18-07b
A Taste Bud
Figure 18-07c
Pathway of Gustatory Sense
Figure 18-08
Equilibrium & Hearing (the ear)
• External ear
– The auricle directs sound waves into the external
auditory meatus to the tympanic membrane
• Middle ear
– Located in the temporal bone
– Contains the auditory ossicles
• Malleus, incus, stapes
– Connected to throat by the eustachian tube
• Inner ear
– Located in the temporal bone
The Ear
Figure 18-09
The Middle Ear
Figure 18-10b
The Inner Ear
• Separated from the middle ear by the oval
window
• Consists of a series of canals called the
bony labyrinth
– Lined by a membranous labyrinth filled with
endolymph
– Perilymph flows between the bony and
membranous labyrinth
The Inner Ear
• The bony labyrinth is divided into 3 areas
– Vestibule
• Contains the saccule & utricle
– Involved in static equilibrium
– Semicircular canals
• Each has an ampulla which contains receptors for
head position
– Cochlea
• Contains the organ of Corti, the organ of hearing
The Semicircular Canals
Figure 18-12b
The Utricle & Saccule
• Detects static position
• Hair cells are embedded in a gelatinous
material
• Otoliths are balanced on top
– Slide when the head is tipped
– Bend hairs, generating a nerve impulse
The Utricle and Saccule
Figure 18-14a
Otoliths
Figure 18-14b
Otoliths at Work
Figure 18-14c
The Semicircular Canals
• Detects dynamic balance
• Arranged at right angles to each other
• In the ampula, hair cells are embedded in
gelatinous material (cupula) with fluid over
it
• Movement of the head bends the hairs,
creating nerve impulses
Ampulla
Figure 18-12c
Hair Cell
Figure 18-12d
Semicircular Canals at Work
Figure 18-13
The Cochlea
• Divided into 3 tunnels by the vestibular and
basilar membranes
– Scala vestibuli (top), ends in the oval window
– Cochlear duct (middle), contains the organ of
Corti
– Scala tympani (bottom), ends in the round
window
The Cochlea
Figure 18-16a
Cochlear Chambers
Figure 18-16d
The Organ of Corti
Figure 18-16e
The Organ of Corti
• Consists of hair cells on the basilar
membrane
• Tips of hairs touch the tectorial membrane
• When the basement membrane vibrates, the
hair cells are bent, sending a nerve impulse
Summary of Hearing
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Sound waves enter the external auditory meatus
Tympanic membrane vibrates
Auditory ossicles vibrate
Oval window vibrates
Perilymph in scala vestibuli & scala tympani
moves
• Basilar membrane moves
• Hairs rub against the tectorial membrane
• Nerve impulse is sent along the vestibulocochlear
nerve to the brain
Pathway of Auditory Sense
Figure 18-17
Vision (the eye)
• Accessory structures
– Eyelids protect the eye
• Conjunctiva lines the eyelid
– Lacrimal apparatus
• Lacrimal gland produces tears
• Lacrimal canals drain tears into lacrimal sacs
• Nasolacrimal duct drains into the nasal cavity
– Extrinsic muscles move the eyeball
The Eye
Figure 18-18b
Structure of the Eye
• Consists of 3 tunics (layers)
– Fibrous tunic – outermost layer
• Includes the cornea & sclera
– Vascular tunic – middle layer
• Includes the choroid coat, ciliary body, and lens, iris & pupil
– Neural tunic (retina) – inner layer
• Contains the rods & cones (photoreceptors)
• Includes the optic disc (blind spot), macula lutea & fovea
centralis
The Retina
Figure 18-20a
Sagittal Section of the Eye
Figure 18-20b
Photo of Posterior Eye
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 = pressure from too much aqueous humor
• Anterior chamber is in front of the iris
• Posterior chamber is behind the iris
– Posterior cavity behind the lens
• Contains vitreous humor
Figure 18-23
The Cavities of the Eye
Human Anatomy, 3rd edition
Prentice Hall, © 2001
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
The Retina
• Cones allow for sharp color vision in bright
light
– 3 types, each with a different pigment
– The macula lutea contains only cones
– Cones are most concentrated in the fovea
centralis
The Retina
• Rods provide for vision in dim light
– Most dense at the periphery of the retina
– Contain the pigment rhodopsin
The Retina
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
Pathway of Vision Sense
Figure 18-25b
Abnormal Vision
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Myopia
Hyperopia
Presbyopia
Astigmatism