4. ut_sensation_lecture

Sensation: involves the detection and reception of sensory signals
from the environment, and the transduction of those signals into
neural information.
Vision: all light is electromagnetic radiation; detectable
wavelengths range from 400 - 750 nanometers.
There are two characteristics of these wavelengths:
1. Amplitude: intensity or brightness
2. Saturation: purity of the color
Major structures of the Eye Involved in Light Detection
1. cornea: protective layer
2. pupil: takes in light
3. iris: eye color, regulates amount of light that enters pupil
4. lens: focuses light (accommodation) , projects image
5. retina: where the image is projected, contains lightreceptors
Vision (continued)
Photoreception: the retina has photoreceptors that produce special
light sensitive pigments.
There are two types of photoreceptors:
1. rods: night vision
2. cones: color perception
Photorectors activate bipolar cells that connect to ganglion cells of
the optic nerves from the retina directly to the brain.
bipolar cells: information about light & dark contrasts
ganglion cells: information about features such as edges
and lines; comprised of cells that have center-surround
receptive fields.
The Visual Pathway Through the Brain
1. The optic nerves from each eye join at the optic chiasm.
2. The outermost field of vision goes to the corresponding
hemisphere, while the nasal field of vision crosses to the
opposite hemisphere.
3. Information goes to the thalamus, then the visual cortex.
Vision (continued)
Two theories of color perception:
1. Trichromatic Theory
2. Opponent Process Theory
Color Blindness
1. monochromats
2. dichromats
3. anomalous trichromats
Hearing: the repetitive vibrations of objects produce fluctuations in
air pressure and create soundwaves.
Soundwaves move through the air in three dimensions, and have
three descriptive characteristics:
1. Amplitude: intensity
2. Wavelength: frequency
3. timbre: purity
Major Structures Involved in Auditory Transduction
1. pinna (outer ear)
2. ear Canal
3. tympanic membrane (ear drum)
4. the malleus, incus, and stapes
5. oval window
6. cochlea
7. basilar membrane: the movement of hairs on the basilar
membrane stimulates activity of the auditory nerve ...
Two theories of pitch perception:
1. Place Theory
2. Frequency Matching Theory
Taste & Smell: Gustation &Olfaction
Gustation: receptors in the tongue, mouth & throat (taste buds)
detect sweet, sour, bitter, and salt. Our perception of flavor is a
combination of the smell, taste, temperature, and texture of foods.
Olfaction: airborne molecules are detected by receptors in the nose
and stimulate the olfactory bulb
Vestibular Sense: Information about the position of the body in
space. Tiny sacs in the ear contain fluid moves with the head.
Fluid movement moves hair cells. Connects to cerebellum to
coordinate balanced movement.
Kinesthetic Sense: Information from joints and muscles that
indicates where your body parts are in relation to one another.
Somatosensory Sensation
The perception of weight, texture, and vibration is based on the
number and frequency of nerves in the skin that are stimulated by
The perception of temperature is based on the activation of
specific warm or cold nerve fibers in the skin called
Firing rate corresponds with the magnitude of cold or hot.
Pain receptors are called nocireceptors or free nerve endings
Gate Control Theory of Pain
Free Nerve Endings -------> Spinal Cord -------> Substance P
Substance P (neurotransmitter)
Provides the information interpreted by the brain as "pain"
The "gate" is "opened" when substance P release is triggered by
noxious or harmful stimuli.
The "gate" is "closed" when endorphins bind to receptors on
neurons that store Substance P, and inhibit its release.