biology 105 lecture 11 chapter 9 - napa valley college 11 - sensory...fluid-filled cupulas at the...
TRANSCRIPT
Nervous System: Sensory Systems
Biology 105 Lecture 11 Chapter 9
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Outline
I. Senses II. Sensory receptors III. Touch IV. Vision V. Hearing and balance VI. Smell
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Senses
Major senses: touch, hearing, olfaction (smell), taste, and sight.
All the sensory nerves are routed through the thalamus, except the nerves for olfaction.
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Sensory Receptor Cells
Sensory receptors are specialized structures that detect specific stimuli (singular = stimulus).
Sensory receptor cells convert the original stimulus into an electrical response that is transmitted through the nerves.
If a sensory receptor is continuously stimulated, it will stop responding = sensory adaptation.
The Central Nervous System
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Touch
We can sense many different kinds of stimuli through touch:
Thermal Tactile Pain Vibration
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Figure 9.2 Sense receptors of the skin
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Types of Receptors in the Skin
Free nerve endings Merkel disks Meissner’s corpuscles Pacinian corpuscles Ruffini corpuscles Thermoreceptors
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Free Nerve Endings
Free nerve endings – tips of dendrites of sensory neurons (free nerve endings may be wrapped around hair); detect touch and pain
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Merkel Disks
Merkel disks – comprised of free nerve endings and Merkel cells; detect touch
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Meissner’s Corpuscles
Meissner’s corpuscles – encapsulated nerve endings; detect light touch, and tell us exactly where we were touched
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Pacinian Corpuscles
Pacinian corpuscles – layers of tissues surround the nerve ending; detects pressure when first applied, and important in sensing vibration
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Ruffini Corpuscles
Ruffini corpuscles – encapsulated nerve endings in deep layers that respond to continuous pressure
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Thermoreceptors
Thermoreceptors – specialized nerve endings; detect changes in temperature
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Vision
Sight is complex!
1. Light enters the eye and is focused… 2. Light has to be transformed into an electrical
signal… 3. That signal then has to be processed.
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Vision
Light enters the eye through the cornea.
The lens focuses it to the back of the eye.
The retina is a layer at the back of the eye where light is transformed into electrical signals.
Copyright © 2009 Pearson Education, Inc. Figure 9.4
Retina
Fovea Optic disk (blind spot)
Optic nerve
Choroid Sclera
Vitreous humor (fills the posterior chamber)
Iris
Ciliary body
Pupil
Cornea
Aqueous humor (fills the anterior chamber)
Sclera
Lens
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Layers of the Eye – Outer Layer
Sclera: Protects and shapes the eye Provides attachment for muscles
Cornea Allows light to enter
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Middle Layer of the Eye
The choroid:
Contains blood vessels that supply nutrients and oxygen. Contains melanin and absorbs light reflected from
the retina.
The ciliary body:
A ring of muscle that functions to control the shape of the lens so that light focuses on the retina.
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Middle Layer of the Eye
The iris:
The colored portion of the eye. Contains smooth muscle that dilates or constricts
to regulate the amount of light entering the eye.
The pupil:
The opening in the center of the iris that lets light into the eye.
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Middle Layer of the Eye
Table 9.1 (2 of 4)
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Inner Layer of the Eye
Contains: Retina Photoreceptors - Rods and Cones Fovea
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Inner Layer of the Eye - Retina
The retina contains photoreceptors: Rods Cones – detect color
The fovea is a pit in the retina with a high concentration of cones.
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Structures of the Eye
Optic Nerve Fluids: Aqueous humor Vitreous humor
Lens
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Optic Nerve
The optic nerve: Carries visual information to the brain. Forms a blind spot where it leaves the retina.
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(a) Light enters the left eye and strikes the retina.
Light
Retina
Choroid
Sclera
Blind spot
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Fluid in the Eye
There are two fluid-filled chambers in the eye: Aqueous humor: clear fluid in the anterior
chamber. Supplies nutrients and oxygen to the cornea
and lens, and removes waste. Creates pressure in the eye to maintain the
shape of the eye. Vitreous humor: jelly-like fluid in the posterior
chamber. Holds retina against the wall of the eye.
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Lens
The lens can change shape depending on whether you are viewing an object that is nearby or far away.
Focuses the light onto the retina.
Ciliary muscles are attached to the lens by ligaments.
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Vision Depends on the Eye!
Table 9.1 (4 of 4)
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Photoreceptors
Cones and rods contain pigments that absorb light: Cones work best in bright light and provide color
vision. Rods work in low light situations, but can only
provide black and white vision.
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Rods and Cones
Figure 9.9 (2 of 2)
Rod cell
Cone cell
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Photoreceptors
When there is no light coming in to the eye, cones and rods release neurotransmitters (note that this is opposite of most receptors!)
When they absorb light, they stop releasing neurotransmitters.
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Photoreceptors
The neurotransmitters are inhibitory.
When the neurotransmitters diminish, cells that process the information are stimulated.
The information from these cells (called bipolar and ganglion cells) is transmitted to the optic nerve, then to the thalamus, and then to the visual cortex.
Copyright © 2009 Pearson Education, Inc. Figure 9.8b
Ganglion cell layer
Bipolar cell layer
Retina
Photoreceptor cells
Pigment layer
Choroid
Sclera
Rod
Electrical signals
Axons
Cone
Light
Vitreous humor
Copyright © 2009 Pearson Education, Inc. 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
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Vision
Vision is much more complicated, because these signals have to be processed into a 3-D image.
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Which part of the human eye detects colored light?
Pupil
Rods
Cones
Cornea
25% 25%25%25%1. Pupil 2. Rods 3. Cones 4. Cornea
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A ring of muscle that functions to change the shape of the lens is the:
Iris
Choro
id
Cilia
ry bod
y
Sclera
25% 25%25%25%
1. Iris 2. Choroid 3. Ciliary body 4. Sclera
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Hearing
Sound enters the ear canal and hits the tympanic membrane (ear drum).
The tympanic membrane vibrates.
This causes small bones in the ear to vibrate.
These bones focus and amplify the vibrations onto a small place (oval window) on the cochlea.
The cochlea is a fluid-filled, coiled membrane.
The vibrations shake the fluid in the cochlea.
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Three Regions of the Ear
1. Outer ear: receiver
2. Middle ear: amplifier
3. Inner ear: transmitter
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The Outer Ear
Consists of the:
Pinna – gathers the sound, acts like a funnel.
External auditory canal – brings the sound from the pinna to the tympanic membrane.
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Middle Ear
Consists of the:
Tympanic membrane separates the outer ear from the middle ear: vibrates when sound waves hit it.
Three auditory bones – amplify the vibrations: Malleus Incus Stapes
Auditory tube (eustachian tube) – equalizes pressure between outer and middle ear.
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Middle Ear
The tympanic membrane vibrates when sound waves hit it, and transmits the vibration to the malleus, incus, and stapes.
The vibrations are amplified by the three bones and transmitted to the oval window.
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Parts of the Inner Ear
Oval window – transmits sound from the stapes to the fluid in the cochlea.
Round window – relieves pressure.
Cochlea – contains the receptor cells that transform the signal from vibration to an electrochemical signal to the neurons.
Vestibular apparatus – monitors position of the head.
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Hearing Depends on the Ear
Figure 9.12 (2 of 2)
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 (Eustachian tube)
Outer ear (receiver)
Middle ear (amplifier)
Inner ear (transmitter)
External auditory canal
Vestibule
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Cochlea
The cochlea is where vibrations are transformed into electrical signals that can be sent by neurons.
When the fluid in the cochlea moves, it moves small “hair cells” against a membrane. This allows ion channels to open.
This leads to the release of neurotransmitters,
which trigger the neuron to send the message.
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Hearing Depends on the Ear
Figure 9.13 (1 of 2)
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Hearing Depends on the Ear
Figure 9.13 (2 of 2)
Hair cell
Tectorial membrane
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In the ear, the fluid-filled coiled membrane that is responsible for transforming the vibrations into electrical signals is called the:
Tymphan
ic mem
bran
e
Staples
Coch
lea In
cus
25% 25%25%25%1. Tympanic membrane 2. Stapes 3. Cochlea 4. Incus
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The tympanic membrane transmits the vibrations to the ___.
Stapes
Mall
eus
Incu
s
Ova
l window
25% 25%25%25% Stapes Malleus Incus Oval window
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The Vestibular Apparatus
Balance depends on the vestibular apparatus of the inner ear.
The vestibular apparatus is a fluid-filled maze of chambers and canals within the inner ear.
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The Vestibular Apparatus – Dynamic Equilibrium
Fluid-filled cupulas at the base of the semicircular canals have hair cells that are stimulated when the head moves. Hair cells send messages to the brain.
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Balance Depends on the Vestibular Apparatus
Figure 9.16a (1 of 2)
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Balance Depends on the Vestibular Apparatus
Figure 9.16a (2 of 2)
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The Vestibular Apparatus – Static Equilibrium
Otoliths are small chalk-like granules.
When the head is tilted, the otoliths move and stimulate hair cells that send messages to the brain.
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Balance Depends on the Vestibular Apparatus
Figure 9.16b (1 of 2)
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Balance Depends on the Vestibular Apparatus
Figure 9.16b (2 of 2)
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Smell – Olfaction
Sensory nerves for smell go directly to the cerebral cortex, the amygdala, and the hypothalamus.
They do not pass through the thalamus.
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Smell – Olfaction
Odor molecules bind to the receptors in the cilia of olfactory receptor cells.
The receptor cells send the message to the neurons in the olfactory bulb, which carry the message to the brain.
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Figure 9.17 Sense of Smell
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Taste
Taste and smell are very connected.
The tongue has taste buds on it. The taste buds have taste cells (receptor cells) in
them.
Food molecules bind to taste cells and stimulate them. The taste cells send the message to sensory
neurons, which send the message to the brain.
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Taste
Figure 9.18
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Read Chapter 9
What is the function of sensory receptor cells?
What is an example of sensory adaptation?
What are the different types of touch stimuli?
What are the types of sensory receptors in skin, and what type of touch do they detect? You should be able to describe their structure.
Important Concepts
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What are all of the layers and structures (including the fluids) of the eye, and what are their functions?
What is the blind spot?
How does the vision signal travel from the photoreceptors to the brain, and which part of the brain receives the signal? Be able to describe in detail this process, including the cells that transmit the messages.
Important Concepts
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What are all the parts of the ear, and are they part of the inner, middle or outer ear? What are their functions? Be able to describe the pathway that sound
waves and vibrations follow through the ear.
How does the ear detect head movement and position?
How do we detect odor? Which part of the brain receives the signal? Where are olfactory receptors found?
How do we detect tastes? What structures are responsible for taste?
Important Concepts
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Definitions
• Stimuli (stimulus), sensory adaptation, dilate, constrict, bipolar cell, ganglion cell, photoreceptors, transmit, amplify, otolith, cupula, taste bud