Transcript Sensory Systems - Cedar Crest College

Sensory Systems
Dr. Audrey Ettinger
April 10, 2006
Neuronal signaling
Axon: electrical
signal
Synapse:
Chemical
signal
Receptors
Figure 39-10
Page 755
Examples of the Variety of Neurons
Found in the Human Nervous System
Examples of the Variety of Neurons
Found in the Human Nervous System
Human (and animal) senses
•
•
•
•
•
Vision
Hearing
Touch
Taste
Smell
• Proprioception (the secret sixth sense)
What is the purpose of having
senses?
Answer:
Senses bring information about the outside
world into the body
Sensory systems
• Convert sensory information into neural
signals
• Process is called sensory transduction
What kind of information should
the sensory system transduce for
the rest of the nervous system?
Transduction process must
include two kinds of information
• What kind of signal?
– Red or blue sweater?
– Salty or sweet taste?
– More generally: a taste or a color?
• How much signal?
– Loud or soft music?
General principles of sensation
• “What kind” information is transmitted by
which neurons respond to the signal
• “How much” information is transmitted by
the number of action potentials sent
– The action potential is an “all or none” signal
Characteristics of sensory neurons
• Shape suited to function
• Receptor type (molecule) specific to sense
– Chemoreceptors, mechanoreceptors,
photoreceptors
• GRADED receptor potential
– Not all-or-nothing action potential
• Synapse onto neuron that fires regular
action potentials
Taste
• Chemoreceptors are similar to
neurotransmitter receptors
• Only four (or five) tastes recognized by
humans
– Sweet, salty, bitter, sour, “umami” (MSG)
• One kind of receptor for each taste
Taste (Gustation)
Epithelial cells
Taste pore
Taste receptor cell
Papillae
Fig. 41-10a,b
Page 797
Taste bud
50 µm
Sugar binds to a taste receptor
Sugar molecule
1
Receptor
K+ channel
open
2
3
G protein
Adenylyl
cyclase
GTP
4
activates
Figure 41-10c
Page 797
5
Protein
kinase A
6
K+ channel
closes
Taste
• “Stronger” taste results from more sugar
molecules binding
• Closing potassium channels depolarizes cell
• Gustatory neuron synapses onto another
neuron to carry information into the brain
Smell
• Chemoreceptors are similar to
neurotransmitter receptors
• 10,000 odorants recognized by humans
• 1,000 kinds of odorant receptors
• Each odorant activates a subset of receptors
• Pattern of receptors bound indicates odorant
Olfactory receptors
Sinuses
Olfactory
bulb
Olfactory tract to
brain centers for smell
Neurons of the
olfactory bulb
Olfactory
bulb
Receptor
cells
Nonsensory
epithelium
Cilia
Wall of
nasal cavity
Fig. 41-11a,b Page 798
Odorant binding to a receptor
Odor molecule
1
2
G protein
Receptor
3
Adenylyl
cyclase
Na+ channel
closed
GTP
4
5
Figure 41-11c Page 798
Na+ channel
opens
Smell
• “Stronger” smell results from more odorant
molecules binding
• Opening sodium channels depolarizes cell
• Olfactory neuron synapses onto another
neuron to carry information into the brain
Touch (and pressure, and pain)
• Six kinds of mechanoreceptors
• Respond to different types of input
• Different adaptation patterns
Free nerve
endings
(pain)
Hair
Meissner
corpuscle
(touch, pressure)
Epidermis
Ruffini
corpuscle
(pressure)
Subcutaneous
tissue
Dermis
Merkel disc
(touch, pressure)
Hair follicle
receptor
(hair displacement)
Pacinian
corpuscle
(deep pressure,
touch)
Mechanoreceptors
500 µm
Figure 41-2a,b
Page 790
Pressure directly opens sodium
channels in the Pacinian corpuscle
Pressure
Sodium
channel
closed
Sodium
channel
opens
Figure 41-2c
Page 790
Touch, pressure, pain
• Opening sodium channels depolarizes cell
• Mechanoreceptor neurons synapse onto
another neuron to carry information into the
brain
Vision
•
•
•
•
Best understood of all the senses
Retina contains light-sensitive cells
Four types of photoreceptors : 3 cones, 1 rod
Four additional types of neurons are present
in the retina
The human eye
Figure 41-14
Page 801
Retina
Iris
Lens
Pathway
of light
Pupil
Optic nerve
Cornea
“Blind
spot”
Fovea
Ganglion cell
Bipolar cell
Retina
The retina
Light rays
Figure 41-16a
Page 802
Optic nerve
fibers
Cone cell
Rod cell
Pigmented
epithelium
Electron microscopy of rods and cones
10 µm
Cone cell
Rod cell
Figure 41-16b
Page 802
Vision
• Photoreceptor types are responsive to
different light signals
• Brighter light causes bigger response
• More photoreceptors are recruited to see
bigger objects
Discs
Light REDUCES signaling
from the rods
Na+
channel
open
Plasma
membrane
of rod
Na+
channel
closes
Photon
Plasma
membrane
of disc
Rod
Esterase G protein Rhodopsin
Disc interior
Figure 41-18
Page 803
In the dark, the rod cell is
depolarized
In the light, the rod cell becomes
hyperpolarized
Cone
Rod
Discs
Cells of the retina
Horizontal cell
Bipolar cell
Amacrine cell
Figure 41-17
Page 802
Ganglion cell
To optic nerve
Light
The light signal travels into the brain
Optic chiasm
Lateral geniculate nucleus
of the thalamus
Right primary
visual cortex
Optic
nerves
Left primary
visual cortex
Figure 41-19
Page 804
Vision
• Several neuron types process vision in the
retina
• Visual information crosses to the opposite
side of the brain
• Visual information travels to the thalamus
(lateral geniculate nucleus) and then to
primary visual cortex
Hearing
• Auditory receptors are complex
mechanoreceptors
• Pitch and loudness signals are transduced
by the same receptors
The Organ of Corti lies within the ear
Cochlear nerve, division
of the vestibulocochlear
(VIII) nerve
Oval
window
Figure 41-9a
Page 795
Organ of
Corti
Auditory
receptors
Tectorial membrane
Organ of Corti
Basilar membrane
Tectorial
membrane
Stereocilia
Force
Hair cell
Cochlear nerve
Basilar membrane
Figure 41-9b,c
Page 795
Fluid vibrations
Auditory
receptors
Tectorial membrane
Organ of Corti
Basilar membrane
Tectorial
membrane
Stereocilia
Force
Hair cell
Cochlear nerve
Basilar membrane
Figure 41-9b,c
Page 795
Fluid vibrations
Hearing
• Receptors responsive to different
wavelengths are arranged spatially
• Louder sounds move the stereocilia farther
• Ion channels are mechanically opened to
depolarize the hair cells
If this material interests you...
• NEU/PSY/BIO 220 Sensation and
Perception (Spring course; required for
Neuroscience major, Biopsych
concentration, elective for Biology majors)
• NEU 200: Introduction to Neuroscience
(Spring course)
• Neuroscience Club!