Transcript Chapter 9

Chapter 9
Sensory Systems
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Chapter Outline
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Kinds of Sensory receptors
Vision and the eye
Hearing, balance, and the ear
Smell and taste
Perry joined the National Guard and was sent overseas
to a war zone. While on duty, an improvised explosive
device went off near him and he barely escaped
unharmed. What would be true of his nervous system?
• A) Parasympathetic impulses were increased.
• B) Most sympathetic impulses were reduced.
• C) The sympathetic neurons all released
acetylcholine.
• D) Norepinephrine and epinephrine were
released.
Sensory System
• Sensory receptors generate electrochemical
messages in response to stimuli
• Receptors are classified by the type of
stimulus to which they respond
• Receptors for the general senses are
distributed throughout the body
• Vision depends on the eye
• Hearing depends on the ear
Sensory Receptors Generate
Electrochemical Messages
• Sensory receptors respond to stimuli by
generating electrochemical messages
• All sensory receptors are selective, responding
best to one form of energy
Sensory Receptors Generate
Electrochemical Messages
Step 1: A sensory
receptor detects the
stimulus from the
external or internal
environment.
Stimulus
Sensory
receptor
Nerve impulse carried
by sensory nerves
Spinal cord
Brain
Step 2: Sensory
neurons conduct a
nerve impulse to
the spinal cord and
then to the brain, or
directly to the brain.
Step 3: The brain
interprets the
information from the
sensory receptor.
Step 4: The brain’s
interpretation of the
information is a
perception or
understanding of
the stimulus.
Figure 9.1
Sensory Receptors
• Continuous stimulation leads to sensory
adaptation, a decrease in the awareness of
the stimuli
Receptor Classification
• The body contains many specialized receptors
including
– Mechanoreceptors
– Thermoreceptors
– Photoreceptors
– Chemoreceptors
– Pain receptors
Receptor Classification
• Receptors for the general senses are located
throughout the body
Receptor Classification
• Receptors rely on either free nerve endings or
encapsulated nerve endings
– Free nerve endings are the tips of dendrites of
sensory neurons
– Encapsulated nerve endings are those in which a
connective tissue capsule encloses and protects
the tips of dendrites of sensory neurons
Receptor Classification
Figure 9.2 (1 of 2)
Receptor Classification
Figure 9.2 (2 of 2)a
Receptor Classification
Figure 9.2 (2 of 2)b
Receptor Classification
• The special senses
– Vision
– Hearing
– Equilibrium
– Smell
– Taste
Receptors for the General Senses
• Mechanoreceptors located in the skin
perceive touch and pressure
Receptors for the General Senses
• Free nerve endings in Merkel disks receive
touch, as do the encapsulated nerve endings
in Meissner’s corpuscles
Receptors for the General Senses
Figure 9.2 (2 of 2)c
Receptors for the General Senses
Figure 9.2 (2 of 2)d
Receptors for the General Senses
• Pacinian corpuscles
– Respond to pressure when it is first applied
• Ruffini corpuscles
– Respond to continuous pressure
Receptors for the General Senses
Figure 9.2 (2 of 2)e
Receptors for the General Senses
Figure 9.2 (2 of 2)f
Receptors for the General Senses
• Body and limb position are detected by
– Muscle spindles responding to the stretch of a
muscle
– Golgi tendon organs measuring muscle tension
Receptors for the General Senses
• Pain receptors are found in all tissues of the
body
• Referred pain
– Pain felt somewhere besides the site of the injury
– Common with damage to internal organs
Lungsfor
and the General Senses
Receptors
diaphragm
Heart
Stomach
Liver and
gallbladder
Small intestine
Appendix
Colon
Urinary
bladder
Ureter
Testes
Kidney
Figure 9.3
Vision Depends on the Eye
• The outer layer of the eye is made of
– The sclera
• Protects and shapes the eye
• Provides attachment for muscles
– The cornea
• Allows light to enter
Vision Depends on the Eye
Table 9.1 (2 of 4)
Vision Depends on the Eye
Table 9.1 (3 of 4)
Vision Depends on the Eye
Table 9.1 (4 of 4)
Vision Depends on the Eye
Optic nerve
Optic disk
(blind spot)
Fovea
Sclera
Choroid
Retina
Vitreous humor
(fills the posterior
chamber)
Lens
Ciliary body
Aqueous humor
(fills the anterior
chamber)
Cornea
Pupil
Iris
Sclera
Figure 9.4
Vision Depends on the Eye
• The choroid, ciliary body, and iris make up the
middle layer
• The middle layer is vascular
Vision Depends on the Eye
• The pupil
– An opening in the center of the iris
– Allows light to enter the eye and reach the
innermost layer, the retina, which contains
• Photoreceptors
• Rods
• Cones
Vision Depends on the Eye
• The cones are concentrated in the center of
the retina (fovea) for focused vision
Vision Depends on the Eye
• The optic nerve
– Cranial nerve II
– Carries visual information to the brain
– Forms a blind spot where it leaves the retina
• An image that strikes the blind spot can not be
seen
Vision Depends on the Eye
• The eyeball is divided into two fluid filled
cavities
– The posterior cavity
• The main cavity of the eye
• Contains vitreous humor, the jelly–like fluid
– The anterior cavity
• The cavity in front of the eye between the cornea and
the lens
• Contains aqueous humor, the watery fluid
Vision Depends on the Eye
• Glaucoma
– Results when pressure of the aqueous humor
reaches dangerous levels due to underabsorption
or over–secretion of the fluid
Vision Depends on the Eye
• Light is bent (refracted) at 4 points when it
enters the eye
– The cornea
– The aqueous humor
– The lens
– The vitreous humor
Vision Depends on the Eye
• The ciliary muscle can change the shape of the
lens, allowing the image to be focused on the
retina
• The elasticity of the lens provides for the
process of accommodation
– The changing the shape of the lens to change the
bending of light
Vision Depends on the Eye
Figure 9.5
Vision Depends on the Eye
• A cataract
– A lens that has become cloudy, usually due to
aging
Vision Depends on the Eye
• Depth perception and a focused image are
accomplished by convergence
– Keeps both eyes focused on the midline of an
object
Vision Depends on the Eye
• Farsightedness, nearsightedness, and
astigmatism are the three most common
visual problems and are due to refractive
problems
• These refractive disorders may be caused by
discrepancies in the lens or the shape of the
eye
• Normal vision can be restored with corrective
lenses
Vision Depends on the Eye
Table 9.2
Vision Depends on the Eye
Figure 9.6a
Vision Depends on the Eye
Figure 9.6b
Vision Depends on the Eye
Figure 9.6c
Vision Depends on the Eye
Figure 9.6d
Vision Depends on the Eye
• Rods and cones are the two types of
photoreceptors
• All photoreceptors respond to light with a
neural message sent to the brain
Vision Depends on the Eye
Figure 9.7
Vision Depends on the Eye
Light
Choroid
Sclera
Retina
Blind spot
(a) Light enters the left eye
and strikes the retina.
Figure 9.8a
Vision Depends on the Eye
Light
Vitreous
humor
Ganglion
cell layer
Electrical
signals
Bipolar
cell layer
Retina
Cone
Rod
Axons
Photoreceptor
cells
Pigment layer
Choroid
Sclera
(b) When light is focused on the retina, it passes through the ganglion
cell layer and bipolar cell layer before reaching the rods and
cones. In response to light, the rods and cones generate electrical
signals that are sent to bipolar cells and then to ganglion cells.
These cells begin the processing of visual information.
Figure 9.8b
Vision Depends on the Eye
Light
Retina
Optic nerve
Visual cortex
(c) The axons of the ganglion cells leave the eye at the blind spot,
carrying nerve impulses to the brain (viewed from below) by means
of the optic nerve.
Figure 9.8c
Vision Depends on the Eye
• Rods allow us to see in dim light, seeing black
and white
– They contain the pigment rhodopsin, which is
broken down in bright light
– They are more numerous than cones
Vision Depends on the Eye
• Color vision depends on cones
• Three types of cones—red, blue, and green—
allow us to see color
• Produce sharp images
• A reduced number or lack of one of the types
of cones results in color blindness
Vision Depends on the Eye
Figure 9.9
Vision Depends on the Eye
Cones function in
color vision.
Rods function in
black-and-white vision.
Disks containing
visual pigments
Rod cell
Cone cell
Nuclei
Synaptic
endings
Figure 9.9 (1 of 2)
Vision Depends on the Eye
Rod cell
Cone cell
Figure 9.9 (2 of 2)
Hearing Depends on the Ear
• In order to hear, the ear collects and amplifies
sound waves
– Converts them to neural messages
• The sound waves are produced by vibrations
Hearing Depends on the Ear
Figure 9.11a
Hearing Depends on the Ear
Figure 9.11b
Hearing Depends on the Ear
Figure 9.11c
Hearing Depends on the Ear
• Three divisions of the ear
– Outer ear
– The middle ear
– The inner ear
Hearing Depends on the Ear
• Outer ear
– The receiver
• Consists of the pinna and external auditory canal
• Receives the waves
• The middle ear
– The amplifier
• The inner ear
– The transmitter
Hearing Depends
on
the Ear
Outer
Inner
Middle
ear
ear
ear
(receiver) (amplifier) (transmitter)
Figure 9.12 (1 of 2)
Hearing Depends on the Ear
Outer ear
(receiver)
Middle ear
(amplifier)
Inner ear
(transmitter)
Eardrum
Malleus Incus Stapes
(tympanic membrane) (hammer) (anvil) (stirrup)
Vestibular apparatus:
Semicircular canals
Vestibule
Auditory nerve
Oval window
Cochlea
Round window
External auditory canal
Auditory tube
(Eustachian
tube)
The pinna gathers sound and
funnels it into the external
auditory canal to the tympanic
membrane (eardrum).
The eardrum vibrates
synchronously with sound
waves, causing the bones
of the middle ear to move.
The three bones of the middle
ear amplify the pressure waves
and convey the vibrations of
the eardrum to the inner ear.
The cochlea converts pressure
waves to neural messages that
are sent to the brain for
interpretation as sound.
Figure 9.12 (2 of 2)
Hearing Depends on the Ear
Table 9.3 (1 of 2)
Hearing Depends on the Ear
Table 9.3 (2 of 2)
Hearing Depends on the Ear
• The tympanic membrane separates the outer
ear from the middle ear
• The middle ear consists of an air-filled cavity
within the temporal bone of the skull and the
three auditory bones
– Malleus
– Incus
– Stapes
Hearing Depends on the Ear
• The middle ear
– Takes sound from the eardrum to the oval
window
– Uses the malleus, incus, and stapes to amplify the
sound
Hearing Depends on the Ear
• The inner ear
– A transmitter
– Consists of the cochlea and vestibular apparatus
• The spiral organ is most directly responsible for the
sense of hearing
Hearing Depends on the Ear
Figure 9.13 (1 of 2)
Hearing Depends on the Ear
Tectorial
membrane
Hair cell
Figure 9.13 (2 of 2)
Hearing Depends on the Ear
• Vibrations
– Transmitted from the middle ear to the fluid
within the cochlea
– Activate hair cells that stimulate the nerves that
carry the impulse to the brain
– The more hair cells stimulated, the louder the
sound
Hearing Depends on the Ear
Figure 9.11a
Hearing Depends on the Ear
Figure 9.11b
Hearing Depends on the Ear
Figure 9.14
Hearing Depends on the Ear
Round
window
Cochlea
Upper compartment
(vestibular canal)
Oval
window
Central compartment
(cochlear duct)
Stapes
(stirrup)
Incus
(anvil)
Malleus
(hammer)
Spiral organ (of Corti)
Eardrum
(tympanic
membrane)
Tectorial membrane
Hair cell
Sound waves
Basilar membrane
Step 1: Sound waves cause
the eardrum to vibrate. These
vibrations are transmitted
through the bones of the
middle ear to the oval window.
Step 2: Movement of the oval
window creates pressure waves
in the cochlear fluid, causing the
basilar membrane to vibrate.
Lower compartment
(tympanic canal)
Auditory
tube
Figure 9.14 (1 of 2)
Hearing Depends on the Ear
Upper compartment
(vestibular canal)
Central compartment
(cochlear duct)
Spiral organ (of Corti)
Tectorial membrane
Hair cell
Basilar membrane
Lower compartment
(tympanic canal)
Step 3: When the basilar membrane
vibrates, the hairlike projections on the
hair cell receptors are pushed against the
overhanging tectorial membrane,
resulting in nerve impulses that are
carried to the brain by the auditory nerve.
Figure 9.14 (2 of 2)
Hearing Depends on the Ear
• Pitch is interpreted by the frequency of
impulses in the auditory nerve
Figure 9.11c
Hearing Depends on the Ear
• There are two types of hearing loss
– Conductive
• Involves an obstruction along the route that sound
follows to the inner ear
– Sensorineural
• Caused by damage to the hair cells or the nerve supply
of the inner ear
Balance Depends on the Vestibular
Apparatus
• Balance
– Depends on the vestibular apparatus of the inner
ear
• A fluid-filled maze of chambers and canals within the
inner ear
Balance Depends on the Vestibular
Apparatus
Dynamic equilibrium
Bony labyrinth
Ampulla
Utricle
Semicircular
canals
Saccule
Cochlea
Cochlear duct
Figure 9.16
Balance Depends on the Vestibular
Apparatus
Figure 9.16a (1 of 2)
Balance Depends on the Vestibular
Apparatus
Figure 9.16a (2 of 2)
Balance Depends on the Vestibular
Apparatus
Figure 9.16b (1 of 2)
Balance Depends on the Vestibular
Apparatus
Figure 9.16b (2 of 2)
Balance
• The semicircular canals and the vestibule
make up the vestibular apparatus
Balance
• The semicircular canals
– Contain sensory receptors that monitor
movement
• The vestibule
– Monitors balance when we are not moving
Smell and Taste Are the Chemical
Senses
• Olfactory receptors
– Neurons with long cilia covered by mucus
– Located in the roof of the nasal cavity
• There are about 1000 types of olfactory
receptors
Smell and Taste Are the Chemical
Senses
Figure 9.17
Smell and Taste
• Odor molecules
– Dissolve in the mucus and bind to the receptors
• Causes a stimulation that is relayed to the olfactory
bulb in the brain
Smell and Taste
• Taste
– Perceived by taste buds
• Located on the tongue and inner surfaces of the mouth
Smell and Taste
Figure 9.18
Smell and Taste
Figure 9.18a–b
Smell and Taste
Figure 9.18b–c
Smell and Taste
Figure 9.18d
Smell and Taste
• Taste cells have taste hairs
– They project into a pore at the tip of the taste bud
• When food molecules are dissolved in water,
they enter the pore and stimulate the taste
hairs
Smell and Taste
• Taste buds sense the five basic tastes
– Sweet
– Salty
– Sour
– Bitter
– Umami