Vision: Crash Course Anatomy & Physiology #18

Next stop in our tour of your sensory systems? VISION. With a little help from an optical illusion, we take a look inside your eyes to try to figure out how your sense of vision works -- and how it can be tricked.

Pssst... we made flashcards to help you review the content in this episode! Find them on the free Crash Course App!

Chapters:
Introduction: Optical Illusions 00:00
How Does Light Work? 1:31
Structure of the Eye 2:31
Layers of the Eye: Fibrous, Vascular, and Inner Layers 3:33
The Retina 4:56
Rods and Cones 6:07
How do Optical Illusions Work? 7:15
Review 8:33
Credits 9:14

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[itsjusttravis]

I remember watching this video SO MANY TIMES for my high school biology tests because I couldn't get it. Now, I'm about to graduate university and start practicing as an optometrist. Thanks Hank 😬

[mercedeztinney]

hey guys you know what would make your videos even better?! if you could include the script in the video description, TO STUDY FROM! That would be amazing. LOOOOVE your videos

[aasthasharma]

Hank: that you don't want to google
Me: IMMEDIATELY googles it
extremely disgusted
goes back to video
Hank: I'll just sit here and wait for you to google it

[llawliet]

More info (not that anyone asked but here I go)
- there are more cones packed in the centre of the retina known s as the fovea. Each cone has a small receptive field (on centre off surround); conversely there's more rods scattered throughout the periphery with larger receptive fields
- due to the small receptive field, each cone can pick up information in their reference in great detail (high visual acuity) because each is focused on a small part of the visual field. Vice versa for Rods which is why they are better suited for movement and black and white imagery
- our visual field is represented as an image on the back of our retina due to retinotopic organization; this information is not altered
- cones attach to parvocellular retinal ganglion cells while rods attach to magnocellular retinal ganglion cells
- the optic nerve leaves the retina and travels to the thalamus which is responsible for relaying all incoming sensory information aside from olfaction. Visual information is relayed through the Lateral Geniculate Nucleus of the thalamus to PVC (primary visual cortex) of the occipital lobe
- magnocellular pathways in the LGN are relayed through layers 1&2 of the LGN while parvocellular pathways through 3, 4, 5&6
- when this information reaches the occipital lobe, magnocellular pathways are sent through the thick stripes of the striated cortex (through indirect and direct pathways)
- parvocellular pathways are sent through interstripes and thin stripes (visual acuity) of the striated cortex of the occipital lobe
- when we see an object we are familiar with, two general things are happening: the occipital lobe sends information through the dorsal and ventral streams to go to the parietal and temporal lobes respectively
- once the dorsal pathway reaches the posterior parietal cortex (PPC) this is where spatial recognition happens (exactly where in the visual field the object of focus is)
- when the ventral pathway reaches the Inferior temporal gurus (IT) it's responsible for object recognition- what exactly it is what we are looking at
- there's more to this than just what I've wrote but it's an extremely interesting sense to study; also easier to study in contrast to cognition because vision is localized to select discrete areas of the brain

[DuranmanX]

I didn't see the flag on the white screen, does that mean I'm unpatriotic?

[IIIUTUBEIII]

I resisted the temptation I didn't google it.

[crashcourse]

Pssst... we made flashcards to help you review the content in this episode! Find them on the free Crash Course App!

[chrisquisha]

I'm a nurse and even I started feeling woozy at those globe luxation pics omg... anyone who isn't in a medical profession, looked it up, and endured the images has my IMMEDIATE respect! Next time you're in emerg let your nurse know of your accomplishment and you'll have a new best friend

[mjocosta]

now i will hold my eyes every time i sneeze for my entire life XD

[Peanutker]

Hank:You really do not wanna goggle it
Me:* Immediately goggles it and cry’s because of the images*
Hank:I will just wait for you to goggle it
Me:*still crying*

[fiaa.]

Hank: ... called Globe Luxation--
*immedately googles*
*cries out in disgust and terror*
*Plays video*
Hank: That you really don't want to google!

[Buttocks]

Vision scientist here. That was a great video, I imagine I'll use that in some of my teaching in future. I really recommend adding a fixation cross to that flag at the start though in order to make it more effective, the illusion can be basically extinguished if people are moving their eyes all over the place.

[mongolianpearlove]

Thank you so much for this simple and fun breakdown of vision. So helpful in studying anatomy and physiology!

[zekeboy]

This was probably the most interesting of the first 18 A & P videos so far! Amazing stuff, our vision.

[christianjames]

You literally came back to rods & cones in a minute after you mentioned it (5:13 to 6:13)

[PER]

THANK YOU SO MUCH for these! I am currently taking an A&P course online and your videos really help tie everything together for me. Keep up the great work. I really appreciate it.

[chiedzamatowe]

Your lectures are full of energy and easy to follow. Thank you CrashCourse team.

[TriggerHappyRC]

Googled it, looked painful but nothing special. Got me curious about some of the common causes for it. Learned that globe luxation can be caused by Grave's Ophthalmopathy which is an autoimmune disease that attacks the fat cells around the eye which swell compressing veins and stopping the drainage of fluid from the eye.
Thanks Hank! Got to learn something extra.

[BoxofCarrots]

I have a psychology exam in two days. Praise this video for making studying pages upon pages of textbook info entertaining and amusing.

[Buddyb]

I GOOGLED IT!!!
OH GOD WHY?! WHY DID I GOOGLE IT?!!