chapter 9 sensory systems. announcements chapter 8a- extra credit (10 pts) chapter 8 online quiz-...

Chapter 9

Sensory Systems

Announcements

• Chapter 8a- Extra credit (10 pts)• Chapter 8 online quiz- Due Wednesday!• Quiz 7 Wednesday- Chapters 8, 9• Midterm grades updated

Chapter Outline

• 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

Figure 9.1

Step 1: A sensory receptor detects the stimulus from the external or internal environment.

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.

Stimulus

Sensory receptor

Nerve impulse carried by sensory nerves

Spinal cord Brain

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


• Receptors for the general senses are located throughout the body


• 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


Figure 9.2 (1 of 2)


Figure 9.2 (2 of 2)a


Figure 9.2 (2 of 2)b


• The special senses – Vision– Hearing– Equilibrium– Smell – Taste

Receptors for the General Senses

• Mechanoreceptors located in the skin perceive touch and pressure


• Free nerve endings in Merkel disks receive touch, as do the encapsulated nerve endings in Meissner’s corpuscles


Figure 9.2 (2 of 2)c


Figure 9.2 (2 of 2)d


• Pacinian corpuscles – Respond to pressure when it is first applied

• Ruffini corpuscles – Respond to continuous pressure


Figure 9.2 (2 of 2)e


Figure 9.2 (2 of 2)f


• Body and limb position are detected by – Muscle spindles responding to the stretch of a

muscle – Golgi tendon organs measuring muscle tension


• 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


Figure 9.3

Lungs anddiaphragm

Heart

Stomach

Liver andgallbladder

Small intestine

Colon

Appendix

Urinarybladder

Kidney

Testes

Ureter

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


Table 9.1 (2 of 4)


Table 9.1 (3 of 4)


Table 9.1 (4 of 4)


Figure 9.4

Retina

FoveaOptic disk(blind spot)

Optic nerve

Choroid

Sclera

Vitreous humor(fills the posteriorchamber)

Iris

Ciliary body

Pupil

Cornea

Aqueous humor(fills the anteriorchamber)

Sclera

Lens


• The choroid, ciliary body, and iris make up the middle layer

• The middle layer is vascular


• 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


• The cones are concentrated in the center of the retina (fovea) for focused vision


• 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


• 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


• Glaucoma – Results when pressure of the aqueous humor

reaches dangerous levels due to underabsorption or over–secretion of the fluid


• Light is bent (refracted) at 4 points when it enters the eye– The cornea– The aqueous humor– The lens – The vitreous humor


• 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


Figure 9.5


• A cataract – A lens that has become cloudy, usually due to

aging


• Depth perception and a focused image are accomplished by convergence– Keeps both eyes focused on the midline of an

object


• 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


Table 9.2


Figure 9.6a


Figure 9.6b


Figure 9.6c


Figure 9.6d


• Rods and cones are the two types of photoreceptors

• All photoreceptors respond to light with a neural message sent to the brain


Figure 9.7


Figure 9.8a

(a) Light enters the left eye and strikes the retina.

Light

Retina

Choroid

Sclera

Blind spot


Figure 9.8b

(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.

Ganglioncell layer

Bipolarcell layer

Retina

Photoreceptorcells

Pigment layer

Choroid

Sclera

Rod

Electricalsignals

Axons

Cone

Light

Vitreoushumor


Figure 9.8c

(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.

Retina

Light

Optic nerve

Visual cortex


• 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


• 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


Figure 9.9


Figure 9.9 (1 of 2)

Rod cell

Cone cell

Disks containingvisual pigments

Nuclei

Synapticendings

Rods function in black-and-white vision.

Cones function in color vision.


Figure 9.9 (2 of 2)

Rod cell

Cone cell

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


Figure 9.11a


Figure 9.11b


Figure 9.11c


• Three divisions of the ear – Outer ear – The middle ear – The inner 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


Figure 9.12 (1 of 2)

Outerear(receiver)

Middleear(amplifier)

Innerear(transmitter)



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.

Malleus(hammer)

Incus(anvil)

Stapes(stirrup)

Semicircular canals

Vestibular apparatus:

Auditory nerve

Cochlea

Oval window

Eardrum(tympanic membrane)

Round window

Auditory tube(Eustachiantube)

Outer ear(receiver)

Middle ear(amplifier)

Inner ear(transmitter)

External auditory canal

Vestibule


Table 9.3 (1 of 2)


Table 9.3 (2 of 2)


• 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


• The middle ear – Takes sound from the eardrum to the oval

window – Uses the malleus, incus, and stapes to amplify the

sound


• The inner ear – A transmitter – Consists of the cochlea and vestibular apparatus • The spiral organ is most directly responsible for the

sense of hearing



Hair cell

Tectorialmembrane


• 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


Figure 9.11a


Figure 9.11b


Figure 9.14

Spiral organ (of Corti)

Step 2: Movement of the oval window creates pressure waves in the cochlear fluid, causing the basilar membrane to vibrate.

Basilar membrane

Central compartment(cochlear duct)

Eardrum(tympanic

membrane)

Sound waves

Malleus(hammer)

Incus(anvil)

Stapes(stirrup)

CochleaUpper compartment (vestibular canal)

Lower compartment(tympanic canal)

Oval window

Roundwindow

Auditorytube

Step 1: Sound waves cause the eardrum to vibrate. These vibrations are transmitted through the bones of the middle ear to the oval window.

Tectorial membrane

Hair cell





Spiral organ (of Corti)

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.

Basilar membrane

Central compartment(cochlear duct)

Upper compartment (vestibular canal)

Lower compartment(tympanic canal)

Tectorial membrane

Hair cell


• Pitch is interpreted by the frequency of impulses in the auditory nerve

Figure 9.11c


• 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


Figure 9.16

Semicircularcanals

Dynamic equilibrium

Cochlea

Cochlear duct

Bony labyrinthAmpulla

Utricle

Saccule


Figure 9.16a (1 of 2)


Figure 9.16a (2 of 2)


Figure 9.16b (1 of 2)


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

chapter 9 sensory systems. announcements chapter 8a- extra credit (10 pts) chapter 8 online quiz-...

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stimuli receptors

sensory neurons