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Sensory Systems – Chapter 22
1.
2.
3.
4.
5.
6.
7.
Subdivisions of Nervous System
Central
nervous
system (CNS)
Sight
Hearing
Smell
Taste
Touch
Balance??
Pain??
Peripheral
nervous
system (PNS)
Br ain
Spinal
cord
Ner ves
Ganglia
12-2
Functional Classes of Neurons
Peripheral nervous system
Central nervous system
1 Sensory (afferent)
neurons conduct
signals from
receptors to the CNS.
2 Interneurons
(association
neurons) are
confined to
the CNS.
3 Motor (efferent)
neurons conduct
signals from the CNS
to effectors such as
muscles and glands.
Differences between Nerve Cells and
Receptor Cells
Nervous System:
1) Detect stimuli and send to brain (sensory)
2) Interpret the information received
3) Respond to information (motor)
Nerve Cells:
- Action Potential
- Electrical current runs down the cell
- Triggers release of neurotransmitters
12-3
Sensory receptors are located throughout
the body – can be classified by:
1. Based on origin of stimuli:
•
•
•
2.
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
16-6
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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
•
•
Neur on 3
receptive fields vary in size – fingertip versus skin on back
two-point touch discrimination
Neur on 2
Neur on
Neur on 1
(a) One lar ge r eceptive field (ar r ow)
16-7
(b) Thr ee sm all r eceptive
fields (ar r ows)
16-8
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
16-9
Vestibule
(Utricle &
Saccule)
Bony labyrinth
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Saccule and Utricle - macula
Macula
41.6
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
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Fig.41.8
scala vestibuli
Vestibular membrane
Cochlear
duct
scala tympani
Organ of corti
Fig.41.9
Scala vestibuli
Vestibular
Membrane
Scala tympani
Fig. 41.9
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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)
Co c h l e a r
duc t
Cilia
Tympanic canal
(contains perilymph)
Forc e
Hair cell
Cochlear nerve
Basilar membrane
Fluid vibrations
Tympanic canal
(c)
Fig.41.08
Gustatory Sensation: Taste
Chemoreceptors: Sesory receptors
that respond to chemicals
•
•
• Taste (gustation) (taste buds)
•
• Smell (olfaction) (olfactory cells)
•
•
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
Dad!!
Flavor Flav!!
Taste bud:
1. Support cells
2. Gustatory receptor cells
3. Basal cells
Umami
Meaty/savory
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Adaptation????
Olfactory epithelium
tapetum lucidum
cilia
Fig. 41.6
retina
• The human eye
sclera
ligaments
(a) Normal eye
Distant object:
the lens thins
to focus light
on the retina
Close object: the
lens fattens to focus
light on the retina
choroid
iris
retina
fovea
eyelash
vitreous
humor
blood
vessels
lens
pupil
Distant object:
light is focused
in front of the retina
(b) Nearsighted eye (long eyeball)
Concave lens diverges
light rays, so the object
is focused on the retina
cornea
optic
nerve
aqueous
humor
Lens muscle
(ciliary body)
Close object:
light is focused
behind the retina
(c) Farsighted eye (short eyeball)
Convex lens converges
light rays, so the object
is focused on the retina
Fig. 24-19
Red – green – blue cones
Fig.41.16
Rods = dim light
Cones = color
Fig. 41-18
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Layers of Retina
•
•
•
Brain Pathways of Vision
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
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