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Sensory Systems – Chapter 22
1.
2.
3.
4.
5.
6.
7.
Sight
Hearing
Smell
Taste
Touch
Balance??
Pain??
Nerve Cells:
1. Action Potential
2. All or none response (like a rat trap)
Receptor Cells:
1. Receptor Potential
2. “Graded Response” Increased stimulus
causes increased depolarization
Sensory receptors are located throughout
the body – can be classified by:
1. Based on origin of stimuli:
•
•
•
2.
Differences between Nerve Cells and
Receptor Cells
Exteroceptors (external)
Interoceptors (within body organs)
Proprioceptors
Based on energy they respond to
(modality):
- Mechanorecptor - Thermoreceptor
- Chemoreceptor - Osmoreceptors
- Photoreceptor - Nociceptors
Classification of Receptors
3. by distribution
– general (somesthetic) senses - widely distributed
– special senses - limited to head
• vision, hearing, equilibrium, taste, and smell
• Some receptors are neurons
16-4
Receptors Transmit Four Kinds of
Information
Receptive Fields
1. Modality - type of stimulus or the sensation it produce
–
vision, hearing, taste
2. Location – encoded by which nerve fibers are issuing
1
2
3
signals to the brain
–
receptive field – area that detects stimuli for a sensory neuron
•
•
receptive fields vary in size – fingertip versus skin on back
two-point touch discrimination
Neuron 3
Neuron 2
Neuron
Neuron 1
(a) One large receptive field (arrow)
16-5
(b) Three small receptive
fields (arrows)
16-6
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Receptors Transmit Four Kinds of
Information
3. Intensity –
•
•
•
which fibers are sending signals
how many fibers are firing
how fast these fibers are firing
4. Duration – how long the stimulus lasts
1.
phasic receptor – generate a burst of action potentials when first
stimulated, then quickly adapt and sharply reduce or stop signaling
even though the stimulus continues
•
2.
smell, hair movement, and cutaneous pressure
tonic receptor - adapt slowly, generate nerve signals more steadily
•
proprioceptors - body position, muscle tension, and joint motion
Fig.41.8
16-7
Vestibule
(Utricle &
Saccule)
Bony labyrinth
Saccule and Utricle - macula
Macula
41.6
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Endolymph
Turning
Movements
Change
in direction
Gravity and speed
41-6
Vestibular apparatus
Another Mechanoreceptor
- Auditory receptors in the cochlea
endolymph
- Hair cells respond to pressure waves
(sound waves)
Vibrations
Fluid in cochlea
Basilar membrane vibrates
Hair cells are stimulated
Info. to brain
41.7
Fig.41.8
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scala vestibuli
Vestibular membrane
Cochlear
duct
scala tympani
Organ of corti
Fig.41.9
Scala vestibuli
Vestibular
Membrane
Scala tympani
Fig. 41.9
Cochlear nerve,
division of the
vestibulocochlear (VIII)
nerve
Oral
window
(a)
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Organ of
Corti
Vestibular canal
(contains perilymph)
Vestibular membrane
Cochlear duct (contains endolymph)
Vestibular canal
Tectorial membrane
Tectorial
membrane
Organ of Corti
Basilar membrane
(b)
Cochlear
duct
Cilia
Tympanic canal
(contains perilymph)
Force
Hair cell
Cochlear nerve
Basilar membrane
Fluid vibrations
Tympanic canal
(c)
Fig.41.08
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Gustatory Sensation: Taste
Chemoreceptors: Sesory receptors
that respond to chemicals
• Taste requires dissolving
of substances
• Four classes of stimuli-sour, bitter, sweet, and
salty
• 10,000 taste buds found on
tongue, soft palate &
larynx
• Found on sides of
circumvallate & fungiform
papillae
• 3 cell types: supporting,
receptor & basal cells
• Taste (gustation) (taste buds)
• Smell (olfaction) (olfactory cells)
Dad!!
Flavor Flav!!
Umami
Taste bud:
1. Support cells
2. Gustatory receptor cells
3. Basal cells
Meaty/savory
Adaptation????
Olfactory epithelium
tapetum lucidum
cilia
Fig. 41.6
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Tunics (Layers) of Eyeball
• Fibrous Tunic
(cornea, sclera)
• Vascular Tunic
(choroid, ciliary body, iris, pupil)
• Nervous Tunic
(Retina)
Fig.41.16
Rods = dim light
Cones = color
Red – green – blue cones
Layers of Retina
• Pigmented epithelium
– nonvisual portion
– absorbs stray light & helps
keep image clear
• 3 layers of neurons (outgrowth
of brain)
– photoreceptor layer
– bipolar neuron layer
– ganglion neuron layer
• 2 other cell types (modify the
signal)
– horizontal cells
– amacrine cells
Fig. 41-18
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Generating the Optic Nerve Signal
Rhodopsin Bleaching/Regeneration
In the dark
In response to light:
1. 11-cis converts to all-trans
2. it dissociates from opsin
3. This changes ion permeability
of rod plasma membrane
4. Nerve implulse in ganglion c.
In the light
Opsin
6 Opsin and cis-retinal
enzymatically combine
to regenerate rhodopsin
Disc
Cell membrane
1 Rhodopsin absorbs
photon of light
cis-retinal
Figure 16.37
(b)
5 Trans-retinal is
enzymatically
converted back
to cis-retinal
2 Cis-retinal
isomerizes to
trans-retinal
Pigment
molecule
CH3
C
H2C
C
(c)
Pigment
molecule
3 Opsin triggers reaction
cascade that breaks
down cGMP
(e)
CH3
H
C
C
H2C
C
CH
HC
O
Retinal
Cessation of dark current
H2C
C
H2C
C
C
C
H
CH3
H
C
C
H
H
C
C
C
H
C
H
O
C
CH3
H2 CH3
(a)
(d)
(f)
Visual cycle of retinal
16-37
CH3
H
C
C
Opsin
Signals created in optic nerve
Trans-retinal
(bleached)
16-38
Generating Visual Signals
1 Rhodopsin
absorbs no light
CH
C
H
C
CH3
H3C
H2 CH3
Cis-retinal
CH3
4 Trans-retinal
separates
from opsin
H
C
C
C
H
Electrical Activity of Retinal Cells
• Rods and cones contain many Na+ channels
that are open in dark
1 Rhodopsin
absorbs light
– This depolarizing Na+ influx is the dark current
– depolorized they release an inhibitory NT.
Rod cell
• Light cause Na+ channels to close
2 Rod cell releases
glutamate
3 Bipolar cell
inhibited
– cells become hyperpolarized!!!!!
– quit releasing inhibitory NT
– Bipolar cell no longer inhibited – released excitatory
NT
2 Glutamate
secretion
ceases
Bipolar cell
3 Bipolar cell
no longer
inhibited
4 Bipolar cell
releases
neurotransmitter
4 No synaptic
activity here
Ganglion cell
5 No signal in
optic nerve fiber
5 Signal in
optic nerve fiber
(a) In the dark
(b) In the light
16-39
10-82
Electrical Activity of Retinal Cells
Phototransduction
10-83
Figure 15.18
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Generating Visual Signals
1 Rhodopsin
absorbs no light
1 Rhodopsin
absorbs light
Rod cell
2 Rod cell releases
glutamate
3 Bipolar cell
inhibited
2 Glutamate
secretion
ceases
Bipolar cell
3 Bipolar cell
no longer
inhibited
4 Bipolar cell
releases
neurotransmitter
4 No synaptic
activity here
Ganglion cell
5 No signal in
optic nerve fiber
10-84
(a) In the dark
5 Signal in
optic nerve fiber
16-44
(b) In the light
Brain Pathways of Vision
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