Download The Special Senses

The General & Special Senses
Chapter 10
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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–
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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
– Sends a nerve
impulse
– Hair cells bend
Pathway of Auditory Sense
Summary of Hearing
• 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
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