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Ted Petit (310)
Lecture 5

Lecture Five-psyb65.docx

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University of Toronto Scarborough
Ted Petit

Lecture Five-PSYB65 Petit Mall Epilepsy  Very small compared to grand mall epilepsy  No true behaviour convulsions  Ex. Rolling up of eyes, twitches, loss of awareness  Twitching or rolling back of the eyes 5-20 seconds  They do not have after depression  50-75% of the times is occurs by itself; but It can occur in patients with other kinds of epilepsy  EEG 3 cycle per second activity –broad waves with little spikes Sensory and motor functions and dysfunctions  Visual system o We are very visually oriented o So much is dependent upon on its anatomy o It is involved with seeing/recognizing o Our retina is divided right down the center of each eye o Our visual world is divided right down the center –two visual half fields (right visual field and left visual field. o The part of your retina toward the outside portion of your head is referred to as your temporal portion of your retina. Temporal means on the side. The portion closest to your nose is your nasal portion. Their anatomy is very different. o The information from the retina leaves from the optic nerve. Your retina is part of your brain that grows away from your brain. o Optic nerve is what we call it as it leaves the retina. Then the two nerves cross and that is known as the optic chiasm. The point where the nerves from the back of your eyes, going toward your brain come together. Potions of it cross and some meet and then they go back away from each other. When they pull away from each other, it is called the optic tract. o The part of your retina from the temporal portion; the outside portion of each retina as it continues to the back, it comes to the optic chiasm and it stays on the same side of the brain. Does not cross. o The nasal portion of each retina (close to your nose), that half, whenever they go toward the optic chiasm, they cross over to the opposite side of the brain. o This creates a system: everything in the left and right have to go through the iris (the very small opening in your eye) o Everything in the right visual field hits the nasal portion of the right eye and the temporal portion of the left eye. And vice versa with the left side. Behind the eyes...Everything from the temporal potion stays on the same side while everything on the nasal crosses over. o Bottom line is that everything that hits your right visual field ends up in your left cortex. o Before doing a CAT scan, you can tell exactly where a tumor is by asking patients where they ca o and cannot see. o Damage:  a person’s visual field not their retina  close one eye at a time normal: your right eye is open and you look straight. You can see a lot on the right and some on the left and vice versa with the left eye.  Monocular blindness: If you severe the optic nerve on the right eye, the left eye is not affected; everything is normal. You will see nothing through your right eye.  Bitemporal hemianopia: if you slice vertically through the optic chiasm. You're cutting out the fibres that cross over. The ones on the same side are fine. The nasal portion of both eyes will be blind. The right hand side will be blind on the right side and the left hand side on the left will be blind.  Right nasal hemianopia: (number 4) right eye (near optic chiasm) very outside portion. Destroys right portion of right eye. So you won’t be able to see from the inner (left) portion of the right eye. Everything else will be fine.  Homonymous hemianopia: if you cut the optic tract on the right you're losing the nasal portion on the left and the temporal potion on the right. Visual field: left on the left and left on the right.  Quadranticanopia:  Macular sparing: if you go all the way to the cortex and you have damage there, it will be quite similar to (number 5) where you lose sight on the left of each side. However, this is little portion in the middle where you have some “sparing”. Functional damage  The neurons at the retina are able to detect a single spot of light in a particular receptive field.  At the level of the retina all that you can tell “is light shining on this particular spot?”  As you move towards the cortex, each neuron builds upon the information of the neuron beneath it  Once you get to area 17, which is the bottom of this image (primary receptive area for vision) neurons respond to bars of light oriented in a particular direction (orientation). They will not respond to bars of light in a different orientation, it has to be a specific orientation.  They have put together all the information from the neurons which are little dots of light and only when these little dots of light connect in this particular orientation then will the neurons fire.  So it’s built in from all this information from the retina so now its responding to bars of light oriented in a specific orientation.  When you get to association cortex (posterior portion of the temporal area) the neurons respond to complex images.
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