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Skeletal System and Muscular System

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  1. 0:06 Skeletal System and Muscular System
  2. 0:35 Skeletal System
  3. 2:20 Types of Muscle
  4. 5:20 Musculoskeletal System
  5. 8:11 Lesson Summary
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Taught by

Zachary Pino

Do you know how many bones are in the human body? Check out this video lesson to uncover the answer, as well as understand the role and importance of the skeletal and muscular systems.

Skeletal System and Muscular System

People have skeletal systems made up of over 200 bones. Actually, the exact number in adults is 206 if you were wondering. In this lesson, we'll talk about how these bones and other connective tissues are organized into a skeletal system to give the body its form and protect vital organs. We'll also talk about the muscular system and how the skeletal and muscular systems work together to allow a wide range of movements and physical capabilities in humans.

The skeletal and muscular systems work together to allow movement.
skeletal 1

Skeletal System

Humans have an endoskeleton, which is located inside the body. Most of the human skeleton is made of bone, which you may recall is composed of mineralized calcium phosphate that is secreted into the extracellular matrix by bone cells called osteocytes. The human skeleton also contains quite a lot of cartilage too. Bones are hard and inflexible, but cartilage is rubbery and flexible, which makes it very useful in parts of the skeleton where movements require flexibility of the skeleton or padding is needed between bones that would otherwise rub against each other. Ligaments made of collagen make flexible connections between bones that keep the bones in their proper places while allowing a wide range of motion.

The most basic function of the skeletal system is to support and provide structure for the body. Without our skeletal systems, we wouldn't be able to hold our shape, and we definitely would not be able to stand upright. A second major function of the skeletal system is to provide protection for vital organs like the brain, heart and lungs, which are protected by the skull and rib cage.

The last basic function of the skeletal system is to facilitate movement. Part of this function is a direct result of providing support for the body, but beyond support, bones also function as levers that the muscles can manipulate to run, jump, lift, grab, or basically move in almost any way you can think of.

Bones serve as levers so we can run, jump, lift, and grab
Skeletal 2

In addition to acting as levers, the positioning of bones and the way that they are attached to each other and to muscles define the kinds of movements that the body can make.

Types of Muscle

So now that we've talked about the skeletal system and its functions, let's talk about the muscular system and how it contributes to the form and movement of the human body. Muscle tissue is one of the four major tissue types found in the human body, and all muscle cells function in the same basic way; they contract or get shorter and pull whatever they are attached to closer together.

Muscles only do work when they contract, they do not actively push things further apart when they stretch back out. Instead, muscle cells are said to relax when they stretch back out because it is a passive action that does not result in any force being applied by the cell. In contrast, contraction requires energy and results in a force being exerted by the cell.

Some muscles in our bodies are under our conscious control and allow us to control our movements. These muscles are said to be voluntary muscle or muscle that can be contracted consciously by an animal. In contrast, the body also contains muscle that is not under our conscious control. This involuntary muscle is muscle that cannot be consciously contracted by the animal. There are three types of muscle cells, two that are involuntary and one that is voluntary. These three muscle types are cardiac muscle, smooth muscle and skeletal muscle.

Cardiac muscle cells are involuntary muscle cells that make up the heart. Cardiac muscle is only found in the heart and a key difference between cardiac muscle and other muscle types is that cardiac muscle cells pass electrical signals to each other. In this way, when one cardiac muscle cell gets a signal to contract, it passes that signal along to all its neighbors. The electrical signal is quickly passed to all of the muscle cells of the heart chamber and they contract in unison.

Smooth muscle cells are involuntary muscle cells that are found throughout the body, except for the heart.

Smooth muscles are located throughout the body
Skeletal 3

Unlike cardiac and skeletal muscle, smooth muscle does not have visible stripes, or striations, when viewed under a microscope. This is actually the reason why it's called smooth muscle. Smooth muscle is found in many places throughout the body like blood vessel walls, the stomach, the small intestine, the large intestine and the bladder.

Skeletal muscle cells are voluntary striated muscle cells that control body movements. These are the muscles that people are generally most familiar with because many of them are visible and we actively control them all the time in our every day lives An interesting feature of skeletal muscle is that each skeletal muscle cell contains lots of nuclei. This is because each mature skeletal muscle cell is actually formed from lots of immature muscle cells that fuse together to form one large cell.

Musculoskeletal System

So I mentioned earlier that bones can function as levers that the muscles manipulate to move in almost any way you can think of. I also mentioned that the positioning of bones and the way that they are attached to each other and to muscles define the kinds of movements that the body can make. For example, let's look at a few movements that your arms can make.

Hold your hand out in front of you, palm up. Go ahead we'll leave the screen blank while you do this. Now turn your palm down. Did you see how easily you flipped your hand over by twisting just your forearm? Now try twisting your upper arm the same way. Maybe you can twist it some, but not nearly to the extent that you can twist your forearm.

Okay, we're back to showing visuals again. The reason why you can twist your forearm so much easier than your upper arm is because you have two long bones in your forearm, the radius and ulna, which can be twisted around each other and allow you to twist your forearm. In contrast, you have only one long bone in your upper arm, so there is no second bone to twist around. This limits the amount that you can twist your upper arm.

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