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Differences between Nerve Cells and
Sensory Receptor Cells
Chapter 10 Outline
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Nerve Cells:
1. Action Potential
2. All or none response (like a rat trap)
Characteristics of Sensory Receptors
Cutaneous Sensations
Taste and Smell
Vestublar Apparatus and Equilibrium
The Ears and Hearing
Receptor Cells:
1. Receptor Potential (or Generator Potential)
2. “Graded Response” Increased stimulus causes
increased depolarization
Transduce energy of a stimulus into APs --
10-2
Sensory receptors are located throughout
the body
• Functional Classification by stimulus type:
Mechanorecptor - Thermoreceptor
Chemoreceptor - Photoreceptor
Nociceptors
• Classification by origin of stimulus
- Exteroceptors vs. Interoceptors
- Proprioceptors
• Classification by distribution in body
- General (somesthetic) senses – body
- Special senes; limited to head, cranial nerves -
Sensory Responses
• Tonic receptors
respond at constant
rate as long as
stimulus is applied
• e.g. pain
• Phasic receptors
respond with burst of
activity but quickly
reduce firing rate to
constant stimulation
(= adaptation)
– e.g. smell, touch
10-8
Generator (receptor) Potentials
• Are sensory
receptor equivalents
of EPSPs (1-4)
• Produced in
response to
adequate stimulus
• If threshold reached,
generates and
action potential (5)
Receptive Field
• Somatic sensory & visual neurons are activated by stimuli
that fall within a specific physical area.
• E.G. area of skin whose stimulation results in stimulating a
sensory neuron
– Sensitive areas have small receptive fields (i.e., lots of
neurons stimulated by the area
– Non-sensitive areas have large receptive fields
10-22
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Two-Point Touch Threshold
CNS Interprets APs
• Minimum distance at which 2 points of touch can be perceived
as separate
– Measure of tactile acuity or distance between receptive
fields
– Can have convergence (2 primary neurons converge to a
second order neuron)
• The CNS recieves a coded message
1. Modality – what type of neuron was stimulated
2. Location - Where are they coming from
– Different neural pathways go to different places in the
brain
3. Intensity - What freqency are they arriving
4. Duration – How long does it last
10-23
10-22
Somatic senses
• Include touch-pressure,
temperature, pain, &
proprioception
• Mediated by free and
encapsulated nerve endings
• Pacinian corpuscles:
vibrations
• Nociceptors: Use glutamate
and Substance P NTs
• Cold and Warm Receptors
Referred Pain
Liver and
gallbladder
Liver and
gallbladder
Lung and diaphragm
Heart
Stomach
Pancreas
Small intestine
Appendix
Ureter
Colon
Urinary
bladder
Kidney
Do you remember post-central gyrus?
Pathway: dorsal/lateral/anterior tracts – thalamus - postcentral gyrus
Chemoreceptors
Gustatory Sensation: Taste
• Taste requires dissolving
of substances
• Four classes of stimuli-sour, bitter, sweet, and
salty – Umami!!!
• Facial Nerve VII anterior
2/3
• Glossopharyngeal Nerve
IX
• 10,000 taste buds found on
tongue, soft palate &
larynx
• 3 cell types: supporting,
receptor & basal cells
• Taste sensory cells live
only 7-10 days
16-10
Phantom limb: Neuromas nodules?
Brain Reorganization??
Taste/Gustation
• Salty and sour do not have receptors; act by passing thru
channels
• Sweet and bitter have receptors; act thru G-proteins
10-29
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Smell (Olfaction)
• Receptor cells,
supporting cells and
basal cells
– Receptor cells are
bipolar neurons (axons
to olfactory bulb)
– Basal cells: stem cells
that produce new
receptor cells (1-2
months)
– Support cells contain
detoxifying enzymes
Smell (Olfaction)
• Odor molecules bind to receptors and act through G-proteins
• Up to 50 G-proteins may be assoc. with single receptor
• Dissoc.of G-proteins releases many G-protein subunits
• Amplifies affect many times/ extreme sensitivity of sense of smell
Fig.41.8
Macula
Vestibule
(Utricle &
Saccule)
Bony labyrinth
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Saccule and Utricle - macula
Gravity and speed
41-6
41.6
Endolymph
endolymph
Turning
Movements
Change
in direction
Vestibular apparatus
41.7
Vestibular Projection Pathways
Fig. 10.16
Central sulcus
Postcentral
gyrus
Vestibular
cortex
Awareness of spatial
orientation and movement
Thalamus
Compensatory
eye movements
Nuclei for
eye movement
Cerebellum
Motor coordination
Vestibulocochlear nerve
Vestibular
nuclei
Reticular
formation
Vestibular apparatus
Vestibulospinal
tracts
Postural reflexes
16-24
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Fig.41.8
Scala vestibuli
Vestibular
Membrane
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Scala tympani
Fig. 41.9
Potassium Gates
Fig. 10.21
Unstimulated
Stimulated
Tip link
Mechanically
gated K+
channel
Stereocilia
K+
Surface of
hair cell
K+
K+ gate
closed
K+ gate
open
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Vision
Neural Pathway for Hearing
• Vestibulocochlear nerve (XIII) - - medulla,- - Midbrain (inferior
colliculus), to thalamus - - auditory cortex
• Eyes transduce energy in small part of electromagnetic
spectrum
• Only wavelengths of 400 – 700 nm constitute visible light
Higher e
Lower e
10-59
Structure of Eye
10-63
Structure of Eye
• The iris (a pigmented muscle) controls size of pupil
• Pupil constricts by contraction of circular muscles
– What division of ANS?
• Dilation is via contraction of radial muscles (Div. of ANS?)
• The sclera (white of eyes)
is outermost layer
• The transparent cornea is
continuous with sclera
– Light passes thru it into
anterior chamber
• thru pupil which
– thru lens
– thru vitreous
chamber
– retina!
10-64
• Refraction: light bends when it passes through medium
into a medium of different density (it bends)
• Visual Field: Image projected onto retina is upside down
and backward
and
lens focus right
part of visual
field on left half
of retina
Left half of
visual field
focuses on
right half of
each retina
10-65
Refraction and Lenses
Cornea
10-69
Figure 15.12a, b
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Accommodation
Focusing for Distant Vision
• Light from a
distance needs little
adjustment for
proper focusing
• Ability of eyes to keep
image focused on
retina as distance
between eyes and
object varies
• Results from
contraction of ciliary
muscle
•
Ciliary muscles
relax – lens fibers
tighten and lens is
pulled flat
10-71
Focusing for Close Vision
Focusing for Close Vision <20 ft
• Close vision requires:
1. Accommodation – changing the lens shape by
ciliary muscles – lens bulges
2. Constriction – pupils constrict to prevent divergent
light rays from entering eye
3. Convergence – medial rotation of the eyeballs
Muscles contract – loosens
Fibers – lens more rounded
– Near point: minimum distance we can focus
Figure 15.13b
Retina
•
•
•
•
Rods and Cones
Bipolar cells
Ganglion cells (optic n.)
Horizontal cells and
amacrine cells are
interneurons involved
in visual processing in
retina
• Pigmented epithelium
Rhodopsin
– Absorbs light
– Suppresses immune
attack on retina
– Phagocitizes old discs
10-76
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Generating the Optic Nerve Signal
Rhodopsin Bleaching/Regeneration
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 impulse in ganglion c.
In the dark
In the light
Opsin
Disc
6 Opsin and cis-retinal
enzymatically combine
to regenerate rhodopsin
Cell membrane
1 Rhodopsin absorbs
photon of light
cis-retinal
Figure 16.37
(b)
Pigment
molecule
CH3
C
H2C
H2C
(c)
Pigment
molecule
(e)
CH3
H
C
5 Trans-retinal is
enzymatically
converted back
to cis-retinal
H
C
C
C
C
C
H
H
C
C
CH3
H3C
H2 CH3
Cis-retinal
2 Cis-retinal
isomerizes to
trans-retinal
CH
C
CH
HC
3 Opsin triggers reaction
cascade that breaks
down cGMP
O
Retinal
CH3
C
H2C
Opsin
H2C
(a)
(d)
(f)
CH3
H
C
C
C
C
CH3
H2 CH3
C
C
H
CH3
H
C
C
H
C
C
H
4 Trans-retinal
separates
from opsin
H
C
C
H
O
Cessation of dark current
Signals created in optic nerve
Trans-retinal
(bleached)
Visual cycle of retinal
16-43
Generating Visual Signals
Electrical Activity of Retinal Cells
• Ganglion and amacrine cells produce APs
• Rods, cones, bipolar and horizontal cells produce graded
potential changes
• Visual transduction is inverse of other sensory systems
– In dark, photoreceptors release inhibitory NT that
hyperpolarizes bipolar cells
– Light inhibits photoreceptors from releasing inhibitory
NT, thus stimulating bipolars cells!
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
5 Signal in
optic nerve fiber
(a) In the dark
(b) In the light
16-46
10-81
Electrical Activity of Retinal Cells
Electrical Activity of Retinal Cells
• Rods and cones contain many Na+ channels that are open
in dark
– This depolarizing Na+ influx is the dark current
– deporised they release an inhibitory NT.
• Light cause Na+ channels to close
– cells become hyperpolarized!!!!!
– quit releasing inhibitory NT
– Bipolar cell no longer inhibited – released excitatory NT
10-82
10-83
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Phototransduction
Figure 15.18
Cones and Color Vision
10-84
Visual Acuity and Sensitivity
• Humans have
trichromatic color
vision
• All colors created by
stimulation of 3 types of
cones
– Blue, green, red
• Instead of opsin, cones
have photopsins
– A different photopsin
for each type of cone
• Eyes oriented so that
object of attention is
focused on fovea
centralis
– Pin-sized pit
within yellow
macula lutea
– Contain only
cones
– Neural layers
displaced to sides
so light strikes
cones directly
10-86
Visual Acuity and Sensitivity continued
10-88
Neural Pathways from Retina
• In fovea each cone
supplies 1 ganglion
cell
– Allows high acuity
• Peripheral regions
contain both rods and
cones
– Degree of
convergence of
rods on ganglions
is much greater
• Allows high
sensitivity, low
acuity
• Right half of visual field
projects to left half of
retina
• Left half of visual field
projects to right half of
retina
• Left lateral geniculate
nucleus receives input
from right half of visual
field of both eyes
• Right Lateral geniculate
body receives input from
both eyes from left half of
visual field
10-89
10-90
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