Transcript The Special Senses

The General & Special
Senses
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
smells
– 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
buds
receptors are in the taste
– 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
hearing
the organ of Corti, the organ of
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
 Cataract
focusing on near & distant objects
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