chapter 45 sensory systems

Chapter 45: Sensory Systems

CHAPTER 45Sensory Systems


Chapter 45: Sensory SystemsSensory Cells, Sensory Organs, and TranSensory Cells, Sensory Organs, and Transductionsduction

ChemoreceptorsChemoreceptors: Responding to Specific Molecules: Responding to Specific Molecules

Mechanoreceptors: Detecting Stimuli thaMechanoreceptors: Detecting Stimuli that Distort Membranest Distort Membranes


Chapter 45: Sensory SystemsPhotoreceptors and Visual Systems: ResPhotoreceptors and Visual Systems: Responding to Lightponding to Light

Sensory Worlds Beyond Our ExperienceSensory Worlds Beyond Our Experience


Sensory Cells, Sensory Organs, and Transduction• Sensory cells transduce information Sensory cells transduce information

about an animal’s external and about an animal’s external and internal environment into action internal environment into action potentials.potentials.

Review Figures Review Figures 45.145.1, , 45.245.2

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Figure 45.1 – Part 1

Figure 45.1 – Part 1Figure 45.1 – Part 1

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Figure 45.2

Figure 45.2Figure 45.2

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Sensory Cells, Sensory Organs, and Transduction• The interpretation of action potentials The interpretation of action potentials

as particular sensations depends on as particular sensations depends on which neurons in the CNS receive which neurons in the CNS receive them.them.

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Sensory Cells, Sensory Organs, and Transduction• Membrane receptor proteins of sensory Membrane receptor proteins of sensory

cells cause ion channels to open or cells cause ion channels to open or close, generating receptor potentials. close, generating receptor potentials.

• Receptor potentials can spread to Receptor potentials can spread to regions of the sensory cell plasma regions of the sensory cell plasma membrane that generate action membrane that generate action potentials, or influence release of potentials, or influence release of neurotransmitter from the sensory cell. neurotransmitter from the sensory cell.

Review Figure Review Figure 45.345.3

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Figure 45.3


figure 45-03.jpg


Sensory Cells, Sensory Organs, and Transduction • Adaptation enables the nervous Adaptation enables the nervous

system to ignore irrelevant stimuli system to ignore irrelevant stimuli while remaining responsive to relevant while remaining responsive to relevant or to new stimuli.or to new stimuli.

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Chemoreceptors: Responding to Specific Molecules• Smell, taste, and the sensing of Smell, taste, and the sensing of

pheromones are examples of pheromones are examples of chemosensation. chemosensation.

• Chemoreceptor cells have receptor Chemoreceptor cells have receptor proteins that can bind to specific proteins that can bind to specific molecules that come into contact with molecules that come into contact with the sensory cell membrane. the sensory cell membrane.

Review Figures Review Figures 45.545.5, , 45.645.6

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Figure 45.5


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Chemoreceptors: Responding to Specific Molecules • Binding of an odorant molecule to a Binding of an odorant molecule to a

receptor protein causes production of receptor protein causes production of a second messenger in the a second messenger in the chemoreceptor cell. chemoreceptor cell.

• The second messenger alters ion The second messenger alters ion channels and creates a receptor channels and creates a receptor potential.potential.

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Chemoreceptors: Responding to Specific Molecules • Chemoreceptors in the mouth cavities Chemoreceptors in the mouth cavities

of vertebrates are responsible for the of vertebrates are responsible for the sense of taste. sense of taste.

Review Figure 45.6Review Figure 45.6

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Figure 45.6


figure 45-06.jpg


Mechanoreceptors: Detecting Stimuli that Distort Membranes• The skin has a diversity of The skin has a diversity of

mechanoreceptors that respond to mechanoreceptors that respond to touch and pressure. touch and pressure.

• The density of mechanoreceptors in The density of mechanoreceptors in any skin area determines the any skin area determines the sensitivity of that area. sensitivity of that area.


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Figure 45.7


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Mechanoreceptors: Detecting Stimuli that Distort Membranes • Stretch receptors in muscles, tendons, Stretch receptors in muscles, tendons,

and ligaments inform the CNS of the and ligaments inform the CNS of the positions of and the loads on parts of positions of and the loads on parts of the body. the body.


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Figure 45.8


figure 45-08.jpg


Mechanoreceptors: Detecting Stimuli that Distort Membranes • Hair cells are mechanoreceptors that Hair cells are mechanoreceptors that

are not neurons. are not neurons. • Bending of their stereocilia alters their Bending of their stereocilia alters their

membrane proteins and therefore their membrane proteins and therefore their receptor potentials. receptor potentials.

• Hair cells are found in organs of Hair cells are found in organs of equilibrium and orientation. equilibrium and orientation.

Review Figures Review Figures 45.9, 45.10, 45.1145.9, 45.10, 45.11

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Figure 45.9


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Figure 45.10


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figure 45-11a.jpg




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Mechanoreceptors: Detecting Stimuli that Distort Membranes • Hair cells are responsible for Hair cells are responsible for

mammalian auditory sensitivity. mammalian auditory sensitivity. • Ear pinnae collect and direct sound Ear pinnae collect and direct sound

waves to the tympanic membrane, waves to the tympanic membrane, which vibrates in response to sound which vibrates in response to sound waves. waves.

• The vibrations are amplified through a The vibrations are amplified through a chain of ossicles that conduct them to chain of ossicles that conduct them to the oval window. the oval window.

• Movements of the oval window create Movements of the oval window create pressure waves in the fluid-filled pressure waves in the fluid-filled cochlea. Review Figure cochlea. Review Figure 45.12, 45.1345.12, 45.13

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figure 45-12a.jpg




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Mechanoreceptors: Detecting Stimuli that Distort Membranes • The basilar membrane running down the The basilar membrane running down the

center of the cochlea is distorted at specific center of the cochlea is distorted at specific locations depending on the frequency of the locations depending on the frequency of the pressure wave. pressure wave.

• These distortions cause bending of hair cells These distortions cause bending of hair cells in the organ of Corti, which rests on the in the organ of Corti, which rests on the basilar membrane. basilar membrane.

• Changes in hair cell receptor potentials Changes in hair cell receptor potentials create action potentials in the auditory create action potentials in the auditory nerve, which conducts the information to the nerve, which conducts the information to the CNS. CNS.


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Figure 45.13


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Photoreceptors and Visual Systems: Responding to Light• Photosensitivity depends on the capture Photosensitivity depends on the capture

of photons of light by rhodopsin.of photons of light by rhodopsin.• Rhodopsin is a photoreceptor molecule Rhodopsin is a photoreceptor molecule

consisting of opsin and retinal. consisting of opsin and retinal. • Absorption of light by retinal is the first Absorption of light by retinal is the first

step in a cascade of intracellular events step in a cascade of intracellular events leading to a change in the receptor leading to a change in the receptor potential of the photoreceptor cell. potential of the photoreceptor cell.



Figure 45.14


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Figure 45.15


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Photoreceptors and Visual Systems: Responding to Light • When excited by light, vertebrate When excited by light, vertebrate

photoreceptor cells hyperpolarize and photoreceptor cells hyperpolarize and release less neurotransmitter onto release less neurotransmitter onto neurons with which they form neurons with which they form synapses. synapses.

• They do not fire action potentials. They do not fire action potentials.

Review Figures Review Figures 45.1645.16, , 45.1745.17, , 45.1845.18

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Figure 45.16


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Photoreceptors and Visual Systems: Responding to Light • Vision results when eyes focus Vision results when eyes focus

patterns of light onto layers of patterns of light onto layers of photoreceptors. photoreceptors.

• The simple eye cups of flatworms can The simple eye cups of flatworms can sense the direction of a light sourcesense the direction of a light source

• The compound eyes of arthropods can The compound eyes of arthropods can detect shapes and patterns detect shapes and patterns

• The eyes of cephalopods and The eyes of cephalopods and vertebrates have lenses. vertebrates have lenses.

Review Figures Review Figures 45.18, 45.1945.18, 45.19, , 45.2045.204040


Figure 45.18


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Figure 45.19


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Figure 45.20


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Photoreceptors and Visual Systems: Responding to Light • The eyes of vertebrates and The eyes of vertebrates and

cephalopods focus detailed images of cephalopods focus detailed images of the visual field onto dense arrays of the visual field onto dense arrays of photoreceptors that transduce the photoreceptors that transduce the visual image into neural signals. visual image into neural signals.


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Figure 45.21


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Photoreceptors and Visual Systems: Responding to Light • The vertebrate photoreceptors are rod The vertebrate photoreceptors are rod

and cone cells. and cone cells. • Rod cells are responsible for dim light Rod cells are responsible for dim light

and black-and-white visionand black-and-white vision• Cone cells are responsible for color Cone cells are responsible for color

vision by virtue of their spectral vision by virtue of their spectral sensitivities. sensitivities.


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Photoreceptors and Visual Systems: Responding to Light • The vertebrate retina is a dense array of The vertebrate retina is a dense array of

neurons lining the back of the eyeball. neurons lining the back of the eyeball. • It consists of five layers of cells. It consists of five layers of cells. • The outermost layer consists of rods and The outermost layer consists of rods and

cones. cones. • The innermost layer consists of ganglion The innermost layer consists of ganglion

cells, which send their axons in the optic cells, which send their axons in the optic nerve to the brain. nerve to the brain.

• Between the photoreceptors and ganglion Between the photoreceptors and ganglion cells are neurons that process information cells are neurons that process information from the photoreceptors. from the photoreceptors.


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Figure 45.24


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Photoreceptors and Visual Systems: Responding to Light • The area of the retina that receives The area of the retina that receives

light from the center of the visual field, light from the center of the visual field, the fovea, has the greatest density of the fovea, has the greatest density of photoreceptors. photoreceptors.

• In humans it contains almost In humans it contains almost exclusively cone cells, which are exclusively cone cells, which are responsible for color vision but not responsible for color vision but not very sensitive in dim light.very sensitive in dim light.

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Photoreceptors and Visual Systems: Responding to Light • Each ganglion cell is stimulated by Each ganglion cell is stimulated by

light falling on a small circular patch of light falling on a small circular patch of photoreceptors called a receptive field. photoreceptors called a receptive field.

• Receptive fields have a center and a Receptive fields have a center and a surround, which have opposing effects surround, which have opposing effects on the ganglion cell. on the ganglion cell.

• If the center is excitatory, the surround If the center is excitatory, the surround is inhibitory, and vice versa. is inhibitory, and vice versa.

See fig.45.25See fig.45.255151




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Sensory Worlds Beyond Our Experience• Many animals have sensory abilities Many animals have sensory abilities

that we do not share. that we do not share. • Bats echolocateBats echolocate• Insects see ultraviolet radiationInsects see ultraviolet radiation• Pit vipers “see” infrared radiation Pit vipers “see” infrared radiation • Fish sense electric fields.Fish sense electric fields.

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chapter 45 sensory systems

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