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The Senses

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Monica Helseth

on 9 March 2016

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Transcript of The Senses

The Senses
I. Vision
A. Vision begins with light entering the eye
1. Human photoreceptors in the eye are sensetive to wavelengths of light energy called the visible spectrum
2. The visible spectrum ranges from red to violet

B. Structures of the eye

1. Sclera: mostly "white part" of the eye that provides protection and structure

2. Cornea: specialized, transparent portion of the sclera through which light enters

3. The iris is the pigmented muscle that gives the eye its color and regulate the size of the pupil. The muscles of the iris control the amount of light entering the eye.

4. Pupil: opening in the iris

5. The lens is the transparent, shape changing convex structure that focuses images on the retina. The lens must accommodate in order to focus on a specific object. The ciliary muscles relax for objects in the distance and constrict, which thickens the lens, for close items

6. Retina: layer containing two types of photoreceptors - rods and cones - that transduce light energy to electrochemical energy.

a. rods
i. Located primarily in the retina's periphery

ii. Capable of receiving light energy in low light

iii. Not involved in color perception

b. cones
i. Concentrated in the middle of the retina in the fovea

ii. involved with color perception in bright light

c. both rods and cones synapse with bipolar cells, which synapse with ganglion cells, which form the optic nerve.

d. The blind spot is where the optic nerve connects to the eye and contains neither rods nor cones.
C. Coding information in the retina

1. A receptive field is an area in the retina to which a particular neuron is sensitive. Receptor fields are made up of only rod or cone receptors, which send visual signals to a ganglion cell in the retina

2. In the retina, there are sets of receptor cells connected to ganglion cells. There are two general types of receptor cells:

a.On-center, off surround

b.Off-center, on surround

c.Receptive fields are described by their response properties

d.The existence of these types of cell organization makes the visual system more sensitive to changes in amount of light - which correspondingly helps us to distinguish objects from the background
D. Visual pathways from the eye

1. The optic chiasm is the junction of the two optic nerves where fibers from the nasal sides of the two retinas cross. The nerve fibers from the peripheral sides of the retinas do not cross to the other side of the brain. The result is that the left half of the world is represented in the right hemisphere of the brain and vice versa

2. Visual Cortex: located in the occipital lobe of both hemispheres and contains the many specialized cells for visual perception.
E. Color Theories

1. Young-Helmholtz trichromatic theory

a. The retinas contain three types of cone cells, each responding to a particular wavelength of light. One type of cone cell responds best to short wavelengths (blue light), a second type responds best to medium wavelengths (green light), and a third type responds best to long wavelengths (red light).

b. "Other colors" are perceived through the mixing of signals from the cones.
2. Opponent Process theory

a. Two-color processes, one for red versus green perception, and one for yellow versus blue perception

b. In the thalamus, some neurons are turned on by red but off by green, for example, which helps explain after images.

3. How we perceive color is informed by types of color blindness.

a. In monochromatic color blindness, the person cannot see any color at all.

b. In dichromatic color blindness, the person perceives only two of the three visual pigments.
F. Common problems with vision

1. Cataracts: clouding of the lens of the eye; affects acuity and color vision

2. Retinopathy: damage to the small blood vessels; begins to leak and may cause blurred vision, blind spots, or floaters

3. Glaucoma: fluid pressure builds up inside the eye; damaging the optic nerve; blurred vision and loss of peripheral vision

4. Macular degeneration: inability to see objects clearly; distorted vision and dark spots in the center of vision

5. Hyperopia (farsightedness): focusing the image behind the retina; difficulty seeing objects close up

6. Myopia (nearsightedness): focusing the image in front of the retina; difficulty seeing objects far away.
II. Audition

A. Begins with sound entering the ear

1. Sound is mechanical energy typically caused by vibrating objects

2. Vibrations produce movement of air molecules (sound waves)

3. Moving one's head helps in detecting the source of a sound.
B. Structures

1. Pinna: external (visible flap of skin and cartilage

2. Auditory canal: part of outer ear along pinna, leads to tympanic membrane

3. Tympanic membrane: also called the eardrum, separates outer ear from middle ear and vibrates with recption of sound

4. Ossicles: three bones in middle ear (malleus/incus/stapes or hammer/anvil/stirrup) set in motion by ear drum that transmit sound vibrations to the cochlea

5. Cochlea: a part of the inner ear, contains fluid and receptors

a. Basilar membrane: subject to pressure changes in cochlear fluid; contains the organ of Corit, an organ that contains auditory sensory (hair) cells

b. Hair cells: Hair cells of the organ of Corti deflected by fluid movement trigger neural impulses to the brain via the auditory nerve.

C. Characteristics of sound

1. Frequency corresponds to the perceptual term pitch. Frequency is measured in hertz (Hz)

2. Amplitude corresponds to the perceptual term loudness (volume). Amplitude is measured in decibels (dB). The decibel scale is logarithmic, so a small change is dB is actually a large change in intensity. Exposure to intense sounds can cause hearing loss.

3. Complexity corresponds to the perceptual term timbre (quality). Complexity is measured by looking at the shape of the sound waveform. This can be assessed by looking at how much the sound wave deviates from a sine wave (a waveform with a variation) or by decomposing the sound into its sine wave components in Fourier analysis.
D. Auditory theories

1. Place theory: Differences in pitch result from stimulation of different areas of the basilar membrane

2. Frequency theory: Differences in pitch are due to rate of neural impulses traveling up the auditory nerve
E. Hearing deficits

1. Conductive deafness: This is when sound waves are unable to be transferred from outer to inner ear; causes include tumors, objects in ear canal, inflections, otosclerosis (genetic degeneration of the inner ear bones). Other than treating the infection and swelling, metal bones can serve as replacements.
2. Sensorineural deafness: This is damage to the inner ear or auditory nerve leading to the brain. Causes include infections, genetic defects, exposure to loud noises, trauma, high blood pressure, diabetes, MS. Treatments include hearing aids and cochlear implants.
3. Perception and attention change to make other incoming information more important with the lack of auditory input. For example, deaf people focus more on mouth movement, which change the nature of how they process information. The same is true for deficits in other senses.
Gustation (Taste)
III. Gustation (taste)

A. Taste cells are chemical-sensitive receptors located in taste bud clusters

1. Taste buds and papillae are located on the tongue, in the throat, and on the soft palate

2. For a stimulus to be tasted, it must be disolved

B. Receptors are sensitive to five basic taste qualities

1. Sweetness
2. Saltiness
3. Sourness
4. Bitterness
5. Umami - glutamates
C. Other influences on taste: Smell, touch, and temperatures can influence taste. It is possible to demonstrate how the flavor of food can be changed by the food's texture or the aroma it exudes.

D. Types of tasters: This is based primarily on the work of Linda Bartoshuk, who differentiated different types of tasters based on the density of taste buds on their tongues. Bartoshuk distinguished three types of tasters based on their sensitivity to differnt tastes. This can lead to a great discussion of food preferences and "picky" eaters.

1. Non-tasters are people who are unable to taste the chemical propylthiouracil (PROP), a bitter compound.

2. Medium tasters are people with an average number of taste buds, they taste the bitter PROP at an average or medium level

3. Supertasters are people who are extremely sensitive to some tastes, have a high number of taste buds, and are highly sensitive to PROP, women are more likely than men to be supertasters.
Olfaction (smell)
IV. Olfaction (smell)

A. Receptors for smell are located of the olfactory epithelium, a thin membrane found in the upper nasal cavity

1. Olfactory cells carry information to the olfactory bulb. The olfactory bulb activates the prefrontal cortex.

2. Olfactory receptor neurons have a life cycle of about 30 days and are continually created.

3. Olfactory cells in the olfactory epithelium are stimulated by gases dissolved in the fluid covering the membrane.

4. For a stimulus to be smelled, it must be disolved

C. Pheromones: same-species odors, used as a form of chemical communication

D. Anosmia is the loss or lack of sense of smell. Specific anosmia is the inability to smell a single chemical
Somesthesis - the mechanical senses
V. Somesthesis - the mechanical senses

A. Somesthesis refers to the mechanical senses, including kinesthesis, vestibular sensation, and the skin senses

B. Kinesthesis

1. Communicates information about movement and location of body parts

2. Receptors found in joints and ligaments

C. Vestibular Sense

1. This is also called equilibratory sense

2. Receptors are in semicircular canals and vestibular sacs found in the inner ear

3. This is concerned with the sense of balance and knowledge of body position.

4. The vestibular organ monitors head movement and movement of the eyes

5. The semicircular canals are filled with a jelly-like substance lined with hair cells
D. Skin senses

1. Basic skin sensations include cold, warmth, pressure, and pain

2. Current research does not support the belief that specialized receptor cells for each of the four skin sensations exist.

E. Touch plasticity - when an area of skin is used a lot, it becomes more sensitive, and the receptors actually take over more brain space in the corresponding sensory region of the brain. Physical experience changes the brain directly.

F. Pain

1. Pain: the experience evoked by a harmful stimulus; directs our attention toward danger and holds our attention.

2. Basics of pain

a. Pain is not triggered by one stimulus and at certain intensities other stimuli can cause pain.

b. Pain circuit: Sensory receptors respond to potentially damaging stimuli by sending an impulse to the spinal cord, which sends the message to the brain, which interprets the signal as pain

c. Thicker and faster axons convey sharp pain, and thinner ones convey dull pain. These axons enter the spinal cord, where they release two neurotransmitters depending on the severity of the pain:

i. Mild pain releases glutamate

ii. Severe pain releases both glutamate and Substance P, a neuromodulator

iii. Pain receptors can also react to chemicals

3. Pain relief: Endorphins block the release of Substance P in the spinal cord and brain stem
4. Gate control theory of pain: The brain can only focus on one pain stimulus at a time

a. Pain messages from the body travel along a set of spinal cord nerve fibers, and all other sensory messages travel along another set. These pain messages are an exaple of bottom up processing

b. fibers carrying pain messages have pain gates, which open during a powerful experience

c. The non-pain fibers, can sometimes close the pain gates if there is competing stimuliation to larger nerve fibers.

5. Top-down processing can also occur during the pain experience because your brain plays an important role in whether or not you will perceive pain and how that perception will occur.

6. Phantom limb pain: The person feels pain in the area of an amputated limb

a. Phantom limb sensations suggest that the brain can misinterpret spontaneous central nervous system activity that still occurs even when normal sensory input is not there
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