PSYB51H3 Lecture Notes - Lecture 11: Formant, Prefrontal Cortex, Coordinate System

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7 Sep 2013
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PSYB51- Lecture 11 Touch
What are formants? What are they good for?
Touch and more...
Touch: Mechanical displacements and other physical impacts on the skin.
Proprioception: Perception mediated by kinesthetic and vestibular receptors.
Somatosensation: A collective term for sensory signals from the body
Actions play a special role: haptics
Somatosensory Physiology
Receptors
Pathways to the brain
How we perceive pain.
Volunteers for demo?
Hold a pen. What do you feel?
=> subtracting (less interesting) sensation of the pen
Volunteers?
2 separate locations stimulated multiple times in quick succession feels like a rabbit,
hopping across the skin between the 2 locations
Investigated with fMRI
Middle location equally activated as stimulated locations
Touch receptors: Embedded in outer layer (epidermis) and underlying layer (dermis)
Multiple types of touch receptors
Touch receptors (& other somatosensory receptors) have three attributes:
1. Type of stimulation the receptor responds to
2. Size of the receptive field
3. Rate of adaptation
Tactile receptors (four): Mechanoreceptors- respond to mechanical stimulation or pressure
Meissner corpuscles (epidermis)
Merkel cell neurite complexes (epidermis)
Pacinian corpuscles (dermus, deeper down, less sensitive to smaller spaces on skin)
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Ruffini endings
* Know these 4 for final exam
FAI (fast adaptation): skin slip; low-frequency vibration (3-40Hz)
FAII: first contact with objects: high frequency vibration (50-700 Hz)
SAI (slow adapting): small receptive fields, fine spatial details, can sense textures, patterns,
persons who read Braille are trained to use them in an efficient way; sustained pressure, spatial
deformations (<5 Hz)
SAII: lateral stretch(e.g., grasping), hand shape; low sensitivity to vibration (have large receptive
fields)
Other types of mechanoreceptors within muscles, tendons, and joints:
Proprioceptive/kinesthetic receptors: Necessary to sense
Tells us where limbs are / posture
what kinds of movements are made
they signal stretching of muscles (ex. I‟m extending my elbow)
Spindles: Convey the rate at which the muscle fibers are changing in length
Receptors in tendons provide signals about tension in muscles attached to tendons
> if you work out too much and then flex your muslces, it‟s possible that you could hurt your
tendons
Receptors in joints react when joint is bent to an extreme angle
Proprioceptive illusion I: get a blindfolded person to hold chopsticks an touch and object and
guess what is it (in this case, it was a Rubic‟s cube)
Proprioceptive illusion II: tapping the ends of an arm and the person is supposed to feel that
there‟s some tapping all over her arm (like a rabbit hopping)
Proprioceptive illusion III (when person A tries to forcefully open person B‟s crossed arms and
then lets go to relax, person A‟s arms are automatically in a stiff position)
Demo = 2 volunteers
Thermoreceptors:
Sensory receptors that signal information about changes in skin temperature
Warmth fibers, cold fibers
Body is consistently regulating internal temperature
Thermoreceptors kick into gear when you make contact with object warmer or colder than your
skin
Nociceptors:
Sensory receptors that transmit information about noxious stimulation that causes damage or potential
damage to the skin
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A-delta fibers: strong pressure, heat; myelinated fast (basically, the greater the diameter of the
axon, the faster the transmission)
C fibers: pressure, heat, cold, chemicals; unmyelinated slow
2 phases of pain: When you hurt yourself, you experience two phases of pain; first is some sort of quick
sharp perception, and second is some sort of slower pain that comes later
Benefit of pain perception:
Sensing dangerous objects
Hansen‟s disease (Leper‟s disease): reduced ability to perceive pain-> you might cause damage to
your body because you can‟t feel the pain so you don‟t know that you‟re hurting your body
Pathways: up to 2 meters long
- Information must pass through spinal cord
- Axons of various tactile receptors combine into single nerve trunks
- Several nerve trunks from different areas of body
- Once in spinal cord, 2 major pathways: Spinothalamic (slower); dorsal (in the neck; at the back)
column- medial lemniscal (faster)-> KNOW THIS FOR FINAL EXAM
Spinothalamic pathway synapses multiple times within spinal cord: slow, nociception, thermal
information
Why is pain slow? (ex. why don‟t we burn our hands when we put it on a hot plate?) Shouldn‟t it be
fast?-> we have reflexes (operate at the level of the spinal cord-> from one sensory neuron directly to a
motor neuron)
Dorsal-column-medial- lemniscal (DCML) pathway: Fast
Synapse in medulla, near base of brain, then ventral posterior nucleus of thalamus, then
somatosensory area 1 (S1), somatosensory area 2 (S2)-> this is secondary
Patient with selective lesion in DCML pathway felt passive hand movements over surface why??
- as you move your arms around the air, you feel the resistance of the air and you feel that it‟s cool, but
it‟s actually processesity to the point that it‟s going in another pathway
Touch sensations are represented somatotopically: Analogous to retinotopy found in vision (look
at the diagram of the brain)
Adjacent areas on skin: Connected to adjacent areas in brain, called homunculus
The following image is a representation of the amount of neurons used and affected by S1
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