The General & Special Senses
Chapter 18
Introduction
• Senses – our perception of what is “out
there”
– 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
General Senses
• Includes senses that are associated with skin
– Temperature, pressure, touch, pain, vibration,
proprioception
• Pass information along the spinal nerves
and pathways to specific areas of the
cerebral 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
Interpretation of Sensory Information
• Occurs in cerebral cortex
• Depends on the area of the cerebral cortex
that receives the information
Central Processing and Adaptation
• Sensory 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
Mechanoreceptors
• Respond to pressure & touch
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Tactile receptors
Baroreceptors
Proprioreceptors
Thermoreceptors
Tactile Receptors
• Found in the dermis
Baroreceptors
• Monitor changes in pressure
Chemoreceptors
• Detect chemicals in solution
– Blood composition
The Special Senses
Olfaction (the nose)
• Olfactory receptors
– Can detect at least 50 different primary smells
– Located in the epithelium of roof of nasal cavity
Olfactory Receptors
• Molecules dissolve in
the mucus of the
epithelium
• Olfactory neurons
pass through the roof
of the nasal cavity and
synapse in the
olfactory bulb
• Olfactory tracts go
directly to the cerebral
cortex
Gustation (the tongue)
• Taste receptors are
in the taste buds
• 6 primary tastes
– Sweet, sour,
salty, bitter,
water, umami
Gustatory Receptors
• Located in papillae
on the surface of
the tongue
• Contain the
gustatory
receptors
– Molecules dissolve
in saliva
Gustatory Receptors
Pathway of Gustatory Sense
• Cranial nerves relay
sensory impulses to
the cerebral cortex
– All pass through the
medulla & thalamus
Equilibrium & Hearing (the ear)
• External ear
– The auricle directs sound waves into the external
auditory meatus to the tympanic membrane
The Middle Ear
• Contains the auditory ossicles
• Separated from the external ear by the tympanic
membrane
– Malleus
– Incus
– Stapes
• Connected to
the throat by the
eustachian tube
The Inner Ear
• Separated from the middle ear by the oval window
The Inner Ear
• Consists of a series of
canals filled with fluid
The Inner Ear
• Consists of a series
of canals filled with
fluid
– Vestibule
– Semicircular
canals
– Cochlea contains
• Organ of
Corti
The Vestibule
• Detects static position
• Hair cells are
embedded in a
gelatinous material
Otoliths at Work
• Otoliths are
balanced on top
of gelatinous
material
– Slide when head
tips
– Bend hairs
– Generates nerve
impulse
The Semicircular Canals
• Detect dynamic
balance
• Arranged at right
angles to each other
• Hair cells are
embedded in
gelatinous material
with fluid over it
• Movement of head
– Bends the hairs
– Creates nerve
impulses
Semicircular Canals at Work
The Cochlea
• Divided into 3 tunnels
by membranes
– Tunnels connect with
the oval window and
round window
– Organ of Corti
Cochlear Chambers
The Organ of Corti
• Consists of hair cells
on a basement
membrane
• Tips of hairs touch the
tectorial membrane
• Basement membrane
vibrates
– Hair cells bend
– Sends a nerve
impulse
Pathway of Auditory Sense
Summary of Hearing
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Sound waves enter the external auditory meatus
Tympanic membrane vibrates
Auditory ossicles vibrate
Oval window vibrates
Fluid in cochlea moves
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 apparatus
– Lacrimal gland
produces tears
– Lacrimal canals
drain tears into
lacrimal sacs
– Nasolacrimal duct
drains into the nasal
cavity
• Extrinsic muscles
move the eyeball
Structure of the Eye – 3 Tunics
• Outer tunic
– Includes cornea &
sclera
• Middle tunic
– Includes choroid coat,
ciliary body, lens, iris
& pupil
• Inner tunic (retina)
– Contains
photoreceptors
• Rods & cones
– Includes optic disc,
macula lutea & fovea
centralis
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
• Contains aqueous
humor
• Glaucoma
– Posterior cavity
• Contains vitreous
humor
The Cavities of the Eye
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 Retina
• Cones allow for sharp
color vision in bright
light
– Contain pigments
– Macula lutea
– Fovea centralis
• Rods provide for
vision in dim light
– Contain the pigment
rhodopsin
– Most dense at
periphery of retina
Photo of Posterior Eye
Figure 18-22c
Pathway of Vision Sense
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
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Myopia
Hyperopia
Presbyopia
Astigmatism