Muscles, Part 1 - Muscle Cells: Crash Course Anatomy & Physiology #21

We're kicking off our exploration of muscles with a look at the complex and important relationship between actin and myosin. Your smooth, cardiac, and skeletal muscles create movement by contracting and releasing in a process called the sliding filament model. Your skeletal muscles are constructed like a rope made of bundles of protein fibers, and the smallest strands are your actin and myosin myofilaments. It's their use of calcium and ATP that causes the binding and unbinding that makes sarcomeres contract and relax.

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

Chapters:
Introduction: Muscle Love 00:00
Smooth, Cardiac, and Skeletal Muscle Tissues 1:18
Structure of Skeletal Muscles 2:40
Protein Rules 3:25
Sarcomeres Are Made of Myofilaments: Actin & Myosin 3:54
Sliding Filament Model of Muscle Contraction 4:38
Review 9:17
Credits 9:57

***
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[Kenstoes]

NEVER STOP DOING WHAT YOU ARE DOING. YOU ARE SAVING MY WHOLE EXISTENCE. THANK YOU THANK YOU

[illblues]

The “chemistry” between myosin & actin makes my heart beat (:

[gmianosi]

Watched these videos to study for the MCAT. Crushed the exam and got into my top choice medical school. Now I'm using them to study for med school exams. The story keeps repeating itself! You're the best, Hank!

[morganstevens]

VIDEO NOTES:


MOVEMENT: 2 MAIN RULES

1. Proteins like to change shape when stuff binds to them
2. Changing shapes can allow proteins to bind or unbind with other things


SARCOMERE:
•contain 2 active proteins of actin and myosin
•Thin actin strands and thick myosin strands
•In a z shape, contract brings together
•When muscles are resting, actin and myosin do not touch, but want to


SLIDING FILAMENT MODEL: STEPS:
1. Actin wants to go to myosin but is trapped by tropomyosin and troponin
2. gaurds can move with ATP and calcium (sarcoplasmic reticulum loaded with calcium pumps)
3. eceptors on muscle cells release AcetylCoa and rush of sodium goes to cell, causing sodium channels to open in muscle cell
4. action potential goes to T-tubule
5. calcium stored inside t-tubule is released
6. troponin binds with calcium, causing the protein to change shape as it pulls trypomysoin away
7. ADP attaches to myosin and myosin goes into stretched position
8. myosin finally binds to actin and myosin releases stored energy and retracts whole muscle
9. ADP and phosphate unbind with myosin and ATP binds with myosin
10. myosin releases from actin
11. myosin then breaks down ATP to ADP and phosphate to get ready for next release of energy
12. calcium pumps grab calcium from tropomyosin back into place
~keeps replaying~

I hope some of these help you! If you are reading this, just know that you are such a beautiful, wonderful, and intelligent human being! I hope you all have a lovely day/night <3

[monj]

That myosin head ain't loyal tho. Switching actin binding sites all the damn time

[MessieXgirl]

Love the fault in our stars reference

[LizardaWizard]

When you reference your own brother's bestselling novel

[sonderingsong]

I lost it when he referred to his bro's book like,
"Okay?"
"Okay."

[simplymaci]

Dear Hank,

Thank you for saving me when I have an Anatomy test the next day.

Sincerely,
Everyone Subscribed to CrashCourse

[dennischiu]

Do you even -lift- attach and release your actin and myosin, bro? :D

[miluska]

one day I'll owe you my medical degreee

[izzypooley]

Favorite part: 9:00 "The whole drama plays itself over and over again, kind of like you'll have to replay this video over and over again to catch all the little steps." I had to laugh as I paused it for the 40+ time to take a note.

[speedstacker]

This stuff absolutely blows my mind.

On another note, my professor basically spent two 50 minute class periods on the sliding filament model and I only had to watch this video twice to learn what I needed to know. You guys do great stuff, thank you!

[clairefolkert]

Thank you Hank! I hope you know that your biology and anatomy/physiology videos are educating future nurses (me), doctors, surgeons, exercise scientists, physical therapists, etc. just trying to fumble through the undergrad years of college!

[Tremor]

What's fascinating to me is just how quickly all this happens

[mousumisaha]

I am a 34 yo adult who has recently decided to go back to school to study Medical Coding and Billing/Health Services Administration and currently I am studying Medical Terminology. These videos have been so helpful I am am so grateful that you and all of your wonderful people have taken the time to do these videos because it really does help. Not just learning the term and definitions but also the explanation of the terms or at least some of them. Now, how do I get you to be my professor? Because in all honesty, you make it all fun. Thanks again!

[ethanchang]

I love how Hank makes a reference to his brother's, John, book. "Okay? Okay".

[connorshipley]

"The mitochondria is the powerhouse of the cell"
-Said every biology book ever

[ehabjaradat]

I can't beleive I'm smiling while studing
Thank You !

[initialsCKN]

HANK, I DON'T NEED TO START HAVING FEELS ABOUT MY MUSCLES EVERY TIME I MOVE.