




audition
vision
olfaction
taste
smell

some addtl senses
◦ vestibular
◦ organ
◦ muscular tension

sensory transduction
◦ - conversion of physical energy from the
environment into changes in electrical potential

sensory coding◦ Making sense of that input

vision - light waves -

taste – chemicals in fluid –
hearing – sound wavestouch- pressure, temperature changes,

smell- chemical in air



vision

taste hearing -

touch

smell

- rods and cones in
retina
- taste buds on tongue
- hair cells in inner ear
(cochlea)
- specialized receptors
under skin
- hair cells in olfactory
epithelium

Receptors show adaptation
◦ most sensitive to changes rather than constant
stimulation
◦ why is this important?

General pathway for most sensory
information:

General pathway for most sensory
information:
◦ sensory neurons – sensory nerves
 spinal tracts –
 thalamus –
 primary cortex –
 higher association cortex
Certain sensory neurons have a
spontaneous firing rate.
For these cells any change in their firing
rate will convey important info (i.e. color
vision)
Different rhythms of firing also can convey
different information
* most highly developed sense in humans
optic nerve for one eye - 1,000,000 axons
auditory nerve contains about 30,000
axons
adaptability and plasticity of visual system
- make sense out of nonsense

iris
◦ largely a muscle that expands and contracts pupil
in response to light
◦ phenotypically unique –
 iris scan

sclera
◦ tough opaque tissue

pupil
◦ often used to determine neurological function

light waves along the visual spectrum
1.
2.
inverted image on retina
region important for transduction is at very
back of the eye
retina - structure of eye important for
transduction
- retina contains neurons, glial cells and two
types of photoreceptors


responsible for transduction
numerous differences between rods and
cones





rods
shaped like a rod
insensitive to color
work well under low
illumination




cones
shaped like a cone
sensitive to color
work best in bright
light







rods
shaped like a rod
insensitive to color
work well under low
illumination
20,000,000/eye
location: found around the
periphery of the retina






cones
shaped like a cone
sensitive to color
work best in bright light
5,000,000/eye
location – found
around the fovea of
the retina
◦ responsible for
sharp images and
vision

a low ratio of synaptic connections between
neurons ensures higher definition and
sharpness compared to a higher ratio
sharp, acute
vision
less sharp focused
visual input
sharp, acute
vision
less sharp focused
visual input







rods
shaped like a rod
insensitive to color
work well under low
illumination
20,000,000/eye
location: found around the
periphery of the retina
requires extended time until
optimal function








cones
shaped like a cone
sensitive to color
work best in bright light
5,000,000/eye
location – found around
the fovea of the retina
responsible for sharp
images and vision
works optimally very
quickly

there are at least two levels of communication
within the neural cells of the eye
◦ rods and cones – bipolar cells – ganglion cells
(axons make up the optic nerve) to CNS

there are at least two levels of communication
within the neural cells of the eye
◦ rods and cones – bipolar cells – ganglion cells
(axons make up the optic nerve) to CNS
◦ across a single layer (rods and cones communicate
with each other; bipolar cells communicate with
each other; etc)
optic nerve (ganglion cell axons) – make a
blind spot on each eye!

component (trichromatic ) or YoungHelmholz
◦ occurs at level of cones
 3 different cones more sensitive to different
wavelengths (ie colors)

trichromatic or Young-Helmholz
◦ occurs at level of cones

explains major type of color blindness
◦ deficits in certain types of cones can explain major
type of color blindness


At level of cones- GREAT!
◦ there are different cones that produce greater changes in
electrical potentials depending on the color (wave)
◦ abnormalities in cones can explain red/green color
blindness

Very rare to see complete color blindness - only
usually seen with brain injury

~ 7% of US males (10,000,000) compared to 0.4%
women - red/green

X-linked phenomenon
X
Y
X
XX
XY
Xb
XXb
XbY
What happens in hereditary
color deficiency?
 Red or green cone peak sensitivity is shifted.
 Red or green cones absent.
40
437 nm
B
533 nm
564 nm
G
R
41
5% of
Males
437 nm
B
564 nm
G
R
(green shifted toward red)
42
1% of Males (there is no green
curve)
437 nm
B
564 nm
R
(no green cones; only red and blue)
43
1% of Males (there is no red
curve)
533 nm
437 nm
B
G
(no red cones; only green and blue)
44

At level of cones- GREAT!

negative afterimage –
◦ phenomenon that occurs as a result of overactivity
or inhibition of neurons (due to color stimulation)

opponent process theory
◦ occurs at level of bipolar cells and higher
 black/white, red/green; yellow/blue; one color excites
bipolar cell; other color inhibits it


says nothing about complexity as information
reaches occipital lobe –
says nothing about color constancy
◦ color constancy and the retinex theory- occurs at
the level of the cortex……

prestriate – primary occipital cortex; multiple
layers of higher association cortex
Copyright © 2006 by Allyn and
Bacon




Touch (mechanical stimuli)
Temperature (thermal stimuli)
Pain (nociceptive stimuli)
Specialized receptors respond to the various
stimuli
Copyright © 2006 by Allyn and
Bacon
Ruffini ending

Merkel’s disks
Free nerve endings
Figure 7.15
Copyright © 2006 by Allyn and Bacon
Pacinian corpuscles



a necessary sense
too little or too much – yikes!
No obvious cortical representation (although
there are regions that appear to be involved
in the emotional component)

Substance P◦ Most pain is a result of substances released by
damaged tissues including substance P

What else causes substance P release?


Substance P is a large peptide and synthesis
can take time SO
Release of large amounts of substance P
results in a brief time (when more is being
synthesized) that is “pain-free”

Substance P

Endogenous opioids
◦ endorphins – endogenous morphine-like
substances
 may explain acupuncture, placebo effects


Descending pain control – pain can be
suppressed by cognitive and emotional
factors
PAG – periaqueductal gray
Copyright © 2006 by Allyn and
Bacon

3 discoveries made this possible
◦ Electrical stimulation of the PAG has analgesic
(pain-blocking) effects
◦ PAG and other brain areas have large amounts of
opiate receptors
◦ Existence of endogenous opiates (natural
analgesics) - endorphins
Copyright © 2006 by Allyn and
Bacon
MIDBRAIN

Congenital insensitivity to pain
Extremely rare – less than 100 cases currently in the U.S.
Inability to thermoregulate (through skin) or feel pain



types: cancers, debilitating arthritis, back
pain, undiagnosed, migraine
Approximately 80 million people in the
United States suffer
Chronic pain consumes approximately $70
billion per year
Chronic low back pain affects nearly 31 million Americans and
represents the most common cause of disability in persons less than
45 years of age

drugs – morphine derivatives
◦ oxycontin

ESB
periaqueductal gray

drugs – morphine derivatives
◦ oxycontin



ESB
periaqueductal gray
acupuncture
pain management


types: cancers, debilitating arthritis, back
pain, undiagnosed
phantom limb

drugs – antidepressants; antiseizure meds

cutting dorsal roots

anesthetizing stump