Structure and Function of Bones and Muscles

00:01 Muscles and bones are interesting organs.

00:03 Sure, you could look at the obvious and say they provide structure, they provide movement, and that’s what’s right there in front of you.

00:10 But they’re also organs that make blood, make energy, and do a lot more for our body.

00:16 So the idea that I want to change here is not just looking at the structure of the musculoskeletal system, but look at the interaction of the musculoskeletal system with the whole body because the bone is an organ.

00:27 It’s made up of living tissue and it makes blood in the tip of the bone.

00:32 It stores calcium and phosphate which goes back and forth within the blood.

00:37 It helps regulate potassium.

00:39 It’s highly vascular and highly innervated so that we have a sense of what’s going on.

00:45 But when most people look at the bone, they say, “Yeah, it defines the structure of the body, the size of the body.” And we want to get past that and move forward.

00:56 When we talked about the ribs, we talked about it being a protective case.

00:59 The skull is also a protective case.

01:01 A lot of our bones protect the vasculature and the nerves underneath it and it does provide leverage for movement, activity, and other things.

01:11 The bone system—the skeletal system— develops neural crest cells early on in development—early on in embryology.

01:17 The 4th week is when it starts and by the 9th week it’s pretty much complete, and the bony skeleton has been set and it just needs to grow in size.

01:28 And when we look at where growth is occurring in bones, when we’re adults, it’s usually the metaphyseal plate.

01:37 So we’re going to look at epiphysis, the end which stores a lot of the blood and produces blood, the metaphysis which is right below it which holds the growth plate, and the diaphysis or the shaft, and each part of the bone has a different function in metabolism.

01:56 If there’s damage or disruption to the metaphyseal plate, then growth is going to be impaired.

02:04 And that’s why when you’re looking at x-rays, you want to make sure, particularly in pediatrics, particularly in young patients, that it’s intact and not separated and that there’s no lines through it or impairment of the metaphyseal plate.

02:20 Abnormal development can be from birth, from heredity.

02:25 It can be from differences in use, it can be from trauma, and some kind of deformities occur in each level.

02:32 Torsional deformities are when people walk wrong, use their limbs wrong, or have breaks.

02:39 Tibial torsion will cause toeing in and other changes in the foot.

02:45 So that’s something to be aware of.

02:49 Congenital deformities include limb length, limb size, limb symmetry, and also you can have differences in the number of fingers and toes, and the numbers of bones in the body.

03:01 So those are all things to keep in mind when we look at the body structure system and the skeletal system.

03:08 Some deformities are apparent and look different because they are different and they stand out.

03:15 Others may be unapparent, like the number of wrist bones or the number of bones in the hand or foot, may or may not be noted.

03:22 But those differences can cause contractures, dislocations, and distortions of bone that are going to effect functioning.

03:32 Hereditary deformities like osteogenesis imperfecta may lead to increased breaks and difficulty in bones’ functioning as efficiently as we would like.

03:44 You can also see a development of developmental dysplasia of the hip as a common bone deformity as well as club foot, or talipes is another term used to describe club foot.

03:56 One of the most common deformities we see is scoliosis and scoliosis could be a sidebending deformity with abnormal twisting or it could be a rotational deformity, and a lot of that is determined by heredity.

04:11 So always assess whether or not a scoliosis is something that is lateral or rotational and you also want to note if it goes away with motion.

04:21 A lot of early scoliosis is postural and that changes as someone gets older and as the bones solidify.

04:29 Some of it is structural and will not change with sidebending or motion.

04:35 We do classify scoliosis as being congenital, neuromuscular, or idiopathic.

04:42 Paget’s disease is a skeletal disorder that has excessive bone destruction and repair.

04:47 The bones are going to look different on x-ray and the bones will function differently, and may not be able to provide the same support to the body in terms of blood formation or mineral regulation without growing out of proportion to what we’d expect.

05:03 So you may have increased bony deposition and you may have increase in the size and shape of the bone in certain areas of the body.

05:12 So you’re going to have the increased structural changes that may be a tower skull, it may be long arms, but they’re going to look different.

05:20 Bones tend to grow and get reformed by themselves.

05:25 They have different mechanisms that tell many to be reformed.

05:29 So when somebody is active, their muscle use, their pressure they put on the bones, will say that the bone needs to be reformed.

05:37 Wolff’s law talks about the area of greatest bone growth is the area of greatest pressure.

05:43 So if you lift weights, you’re going to help grow bones.

05:47 The other force that’s involved is called piezoelectric forces, and those are the electric forces that come from the muscle that stimulate bone growth where the muscles are using the bones for leverage.

06:00 So it’s a nice feedback mechanism that determines how big, how long, and what size and shape the bone is going to be.

06:08 We also have some feedback from the vascular system in cytokines that will help reform the bone.

06:14 We do know that there are 4 types of cells involved in bony regrowth.

06:20 Most of the time we talk about osteoblasts and osteoclasts but there are also osteoprogenitor cells which are stem cells that can become either.

06:30 There are also osteocytes which is after laying down bone, the osteoblast gets caught in that area, and becomes more mature and helps maintain that area of bone.

06:42 And osteoclasts are the ones that remove the bone matrix and help stimulate reformation of bony tissue.

06:49 So every canaliculus, every blood supplied area of bone, can reform every 3 months.

06:55 Not everyone is doing it at the same time, so every 2 to 3 years, a bone is completely reformed and that maintains the structural integrity and maintains the strength of the bone.

07:07 When we talk about the bone, bones are an encased organ, and they’re encased by periosteum.

07:13 The periosteum has an outer fibrous layer where the muscles attach and an inner osteogenic layer which helps maintain the integrity, and the osteogenic layer also has osteoclasts and osteoblasts that are not caught like the osteocytes.

07:30 The vascular supply is critical for maintaining nutrition to the bone, making sure bones have what it needs, and giving feedback to the periosteal and the bone system.

07:42 When we talk about bone growth and bone structure, it’s important to know what the bones should look like, which ones are predetermined by hereditary—by genetics, which ones are going to be determined by your ethnic group, your sex, and basically your history of what size you are meant to be.

08:01 We also know that at different ages it changes even though the bone shape and structure is determined at about 9 weeks of gestation.

08:11 Bone growth in the first 4 years of life is critical.

08:14 That’s when arm length, leg length, and the length of the trunk versus the length of the extremities pretty much gets set.

08:22 We normally say that the ASIS to the shoulder should be equal to the distance of the ASIS to the medial malleolus as long as nutrition is good, proper sun exposure is obtained, and you get the minerals and nutrients you need to grow.

08:37 In areas where you do not have good nutrition, where people are sun sensitive—they stay inside—and don’t get proper activity, they’re going to have smaller leg length to trunk length.

08:51 The trunk will be longer than the legs.

08:53 You bring them from that environment to a healthy environment with a good diet and good nutrition, their legs— if it’s under 4 years of age—will grow longer.

09:01 And again, the nutrition is important whether or not they get calcium, magnesium, phosphorus, and the other nutrients necessary for growth.

09:09 Other issues that matter in terms of bone growth is physical activity.

09:14 People who are more sedentary are going to have smaller, weaker bones.

09:19 Weight, up until a certain level, matters.

09:22 If you’re underweight, you’re not going to have strong bones, and this is usually set by 25 years of age.

09:30 So people who are chronically thin, chronically malnourished, will not reach their predetermined bone mass activity that’s possible.

09:42 Other things we’re seeing in today’s modern society, is lifestyle choices are effecting bone growth.

09:49 People who try and maintain a low body mass, a low body weight tend not to reach it.

09:56 People who drink a lot of alcohol and caffeine, people who smoke tend not to reach peak muscle mass.

10:03 And we’re seeing supplements blanching bone and we’re seeing drugs like steroids and antiseizure medicines, also can effect the ability of the body to get to a particular body structure that is most efficient, most effective and strongest.

10:21 So those are all things we have to be aware of.