Bones and Muscles

Details

Last Updated: Sunday, 21 June 2026 14:09

Published: Tuesday, 07 November 2023 02:35

Hits: 878

Bones and Muscles:

Very imp part of our body are bones and muscles. Muscles and bones work together, that's why they are referred as "Muscoskeletal system" and studied together.

Cartilage:

Cartilage is a type of connective tissue that is strong, flexible, and semi-rigid. It provides cushion where one bone moves against the other. There are synovial joints where one part of the body moves around other part of the body. Examples are shoulder joint, knee joint, hip joint, etc. All of these have one bone having an head, and the other bone having a groove (called as ball and pivot joint), and this allows the bones to move independently. To prevent friction b/w these 2 bones, the bones have a covering, which is called cartilage or articular cartilage (AC, since the surfaces are articulating). This covering can be seen in the thigh bone, where it meets the shin bone. When this AC breaks down, the condition is called osteoarthritis. There is also going to be fluid, aka synovial fluid, b/w the 2 joints (on top of the cartilage) that provides lubrication and reduces friction.

Unlike bone, cartilage does not contain blood vessels or nerves, making it less sensitive and slower to heal after injury.

Bones:

Childhood and adolescence is the period of greatest bone density. All through your life, your body is continually removing old bone and replacing it with fresh bone. This process is called remodeling. Until 30, we tend to gain more bone mass than we lose. After 30, reverse happens. Up until about age 40, all the bone removed is replaced. After age 40, however, less bone is replaced and we start losing bone mass. We lose about 1%-2% of bones every year (In space, people lose about 1%-2% of bones every month due to loss of gravity, most of it is reversible once they are back on earth). Once bones start getting brittle and weak, it can lead to disease like rickets and osteoporosis. it's very difficult to make them stronger again, so try to keep bones healthy in your young age. According to the American Academy of Orthopaedic Surgeons (AAOS), 50 percent of Americans over age 50 have weak bones. 80% of them are women, as their bones are smaller and thinner. Additionally, levels of the female hormone estrogen, which helps protect bones, declines sharply after menopause. No wonder, for women, we see so many more bone issues. So for women, protecting bones is even more important.

There are about 206 bones in human body. Bones get replaced every 7-10 years in our body.

Bone mass vs Bone density: Bone weight is about 15% of body weight, but that is not a useful metric. Bone density is more important metric for bone health. The DXA (central dual-energy X-ray absorptiometry) test measures your bone density compared to the bone density of a healthy young adult. Your score on the test is called your T-score. The normal healthy adult gets a T-Score of 0. If your T-score is more than one point (called a standard deviation) below 0, you may have weak bones, explains NIH. If your T score is between -1 and -2.5, you have low bone mass. If your score is -2.5 or lower, you have osteoporosis. Women are more prone to osteoporosis because of smaller bones.

Article from John Hopkins about bone maintenance => https://www.hopkinsmedicine.org/health/conditions-and-diseases/osteoporosis/osteoporosis-what-you-need-to-know-as-you-age

Few tips to keep bones healthy:

• Calcium + Vitamin D: Your bones store roughly 98 percent of the calcium in your body. Because calcium is important for many body functions, if you don't have enough, your body will take calcium out of your bone bank, thus weakening them. Take 1g of Calcium everyday (For people over 50, 1.2g is recommended). Foods like cheese, yougurt, milk, salmon, etc contain calcium. While calcium is the biggest bone-health player, your body also relies on Vitamin D, Vitamin K, Potassium and Magnesium to build strong bones. Vitamin D is needed to help calcium get absorbed into body. There are 2 sources of getting Vit D - one thru exposure to UV rays from sun, and other thru food. Very few foods (eggs, Orange Juice, cereals, salmon, etc) contain enough Vit D, so Vit D supplements are needed. Recommended amount is 1000 IU of Vit D every day. Upper safe limit is 4000 IU per day. 1000 IU is 25 microgram (0.025 mg or 25 mcg) of Vit D, so very small amount of Vit D is enough. Vit D helps with many other functions of our body too (helps build your immune system), so make sure you get enough. Indians in general have very low levels of Vit D (based on my family health results), so make sure you take supplements with 2000-5000 IU. I've myself taken 50,000 IU Vit D supplements (once a week, prescribed by Doctor), as Vit D levels have been too low. That barely got me into the acceptable range. Reason why Vit D levels don't rise in Indian, even after taking supplements may have to do with genetics, where Vit D doesn't get absorbed by the body as much as it should. Recommended range for Vit D is b/w 30-100 in your blood test.
  
  • Vit D: Vit D exists in 2 forms - Vit D2 and Vit D3. Vitamin D2, or ergocalciferol, is found in fungi (mushrooms) and yeasts. Vitamin D3, or cholecalciferol (koli-kal-ciferol) is produced by the body via sunlight (Thru sunlight, the skin converts 7-Dehydrocholesterol into Vit D3) or ingested via food. Liver converts this cholecalciferol into 25-Hydroxycholecalciferol, which the kidneys then convert into 1, 25-DiHydroxycholecalciferol. This is also called calcitriol, which is the active form of Vit D. This moves into the small intestine, which then increases the number of calcium binding proteins. That helps with calcium absorption. Vit D3 is more important than Vit D2. When we say Vit D, we always mean Vit D3. Video on Vit D: https://www.youtube.com/watch?v=iLDYbSX5MLA
  • For vegetarians, 1 glass of milk (250ml) has 25% calcium and 25% Vit D requirement of an adult. Here milk is fortified with Vit D (sold in USA). Even Orange Juice come with fortified Calcium and Vit D, so take those.
• Exercise: Higher bone density is needed for stronger bones, and exercise helps with that. Lifting weights, running, biking all make your bones stronger.

Important bones in Body:

Vid by Siebert Science shows all the bones => https://www.youtube.com/watch?v=0bzYIwVJreU

• Skull bone: It's not one bone, but many bones.  Frontal bone in front is attached to 2 bones on top of head called as parietal bones, which is attached to occipital bone in the back. From the bottom of this occipital bone is a opening, from where the spinal cord comes out. Then we have temporal bones on the side (near the ear), and facial bones on the face. The facial bones are maxilla near the nose, and mandible or jaw bone, which is the only movable bone in the body. There are many more bones, but these are the main ones.
  • There's a bone under the tongue called "hyoid bone", which helps stabilize the tongue.
• Vertebrae: This runs from the bottom of occipital bone in the skull and continues until the hip. It carries spinal cord inside it. Below are the bones in this vertebrae, starting from the top in the neck and going towards the bottom (total of 24 bones). This bone is in the back, and is also called backbone, and species having this bone are called vertebrats. At bottom of vertebrae is the sacrum, part of the hip bone, which is explained under "hip/pelvis bone" later.
  • Cervical Vetebrae (CV) (7): There are 7 cervical (circular) bones in the neck. 
  • Thoracic Vetebrae (TV) (12): There are 12 thoracic bones in the neck. Each of them connects to 1 rib, and since we have 12 ribs, there are 12 of these vertebrae. 
  • Lumbar vertebrae (LV) (5): There are 5 lumbar bones below the thoracic.
  • Cartilage disc (intervertebral disc): b/w each of the vertebrae of the spine, we have cartilage disc. They allow flexibility to spine.
  • Nerves: Each vertebrae ia circular ring with nerves going thru it in the center. These nerves come out from each vertebrae. There are 8 pairs of nerves coming out of CV (1 extra pair since there are only 7 CV), 12 pairs out of TV and 5 pairs out of LV.
• Scapula: It's the bone on your back below the shoulder. It's a triangular shaped bone one on each side (left and right) and is very thin, almost translucent. 
  • Dr Sam Webster's Link on Scapula => https://www.youtube.com/watch?v=zBbl8CYE9t8
  • Scapula is a special bone in the sense that it's not attached to any other bone. It's floating free. It's kind of attached loosely with only 2 bones:
    • Attached to humerus (upper arm bone): Scapula has a socket to allow the upper arm bone's ball to go into it to allow for hand movements. That socket is called Glenohumeral joint. This socket is very shallow. The scapula allows the direction of this socket to change so that arm can point in any dir, which gives incredible moving ability to the arm.
    • Attached to clavicle (collar bone): This is the bone on the shoulder that you can feel going from front of body to the back. The point where clavicle joins to the scapula is called a AC joint.
• Hip/Pelvis bone: It's the bone in your pelvis (buttock) area. It's connected to top half of body via the backbone. If you are naked, you may see and feel several of this hip bone landmarks on your body.
  • Dr Sam Webster's Link on Hip bone => https://www.youtube.com/watch?v=Iyz1Yyr-czQ
  • Another nice animated link => https://www.youtube.com/watch?v=qlCvKEOZtpo
  • This video shows how to find various landmarks on your hipbone => https://www.youtube.com/watch?v=hvfMsBe7vgs
  • Pelvis consists of 3 bones:
    • Right and Left hip bones (on sides and front): LEt's lok at 3 different parts of this hip bone:
      • Ilium: The top (superior) part of pelvic bone in the back (posterior) is called ilium. It's large and flat and curves to the front. The top part is what you can feel protruding out on the side of the body. If you follow that to the front of the body (near the pubic region), you will see a distinct line. If you feel it, it doesn't feel hard like a bone. This is a ligament known as inguinal ligament. The ilium posterior view show 3 lines running in the back, called as gluteal lines. The 3 gluteus muscles, called as Gluteus Maximus, Gluteus medius and Gluteus minimus connect to the bone, and these 3 lines help define the boundary of these 3 muscle connections. These 3 muscles connect the hip bone to the femur, and provide support to your bondy. These 3 muscles are very important, and a lot of exercises try strengthening these muscles.
        • Acetabulum: Ilium has a ball and socket joint (synovial joint)  to connect the thigh bone to the pelvis. The thigh bone is called femur, and it's a long bone. Towards the top of the femur, we have 2 notches (or sticking parts). The one towards the outside and on the top is called greater trochanter, and the one towards the inside and bottom is called lesser trochanter. That is followed by the rounded shape which is the socket. It has 2 parts => neck (flat part) and head (rounded part). Head of the femur fits in the socket in the pelvic bone which is called acetabulum. Articular cartilage and synovial fluids are there as expected for any synovial joints. Parts of acetabulum are also in ischium region (see below).
        • Pubofemoral / iliofemoral / ischiofemoral ligaments: There are lots of ligaments connecting the ilum, pubis and ischium with the femur to help stabilize the joint and to not allow thigh to extend too much in any direction. 
      • Pubis: The ilium starts curving and comes to the front of the body, near the pubic region. This part of the bone in the front (anterior) is called pubis. This pubis comes from both the left and right side and then the 2 parts connect in the front, with a cartilage called pubic symphysis. It's a cartllage and not a bone, to allow the two hip bones on left and right to move slightly independently. There are ligaments on top and bottom (superiot and anterior pubic ligaments) to reinforce this connection. The top and middle part of pubis is not possible to be felt as it's deeper inside the body. Only the bottom front part can be felt. This part in the front has a crest at top called pubic crest, which is where the rectus abdominis muscles (the so called 6 pack muscles) connect to 
      • Ischium: This is 3rd part which is still in the back, but is important, as this is the bone we rest on, when sitting. 
    • Sacrum (part in the back at the base of the spine): It connects to vertebrae of the spine on the top and to the coccyx (pronounced cok-six) on the bottom (coccyx is the just the final part where the back side ends).  
      • Sacro Iliac joint: The sacrum and ilium are joined by a very thin but strong cartilage. 
  • There's pelvic inlet which is a big hole around 12cm or so which is formed by a circular arc of these bones. Everything above is called greater pelvis, which houses small intestine and other organs. Everything below it is called lesser pelvis. which has bladder, reproductive organs and rectum.

Muscles:

Muscles are just as important as bones, as weak muscles put more stress on bones, and make it harder to ppl to carry out daily routines like sitting, walking, etc. Skeletal muscle fibers are cells, but unlike many cells in the body, they don’t divide. They bulk up by joining together. Not using your muscles causes them to atrophy or shrink as the muscle fibers get smaller. Starting at age 30, adults lose about 0.8% of their muscle mass each year, mostly due to a lack of physical activity and changes in metabolism that lead to less protein reaching the muscle. Basically by age 80, you'll have only half of your muscle mass left as compared to age 30, which is going to be insufficient to carry your body around.

3 ways to get stronger muscles:

1. Diet: Have a balanced diet with lots of fruits and veg. Incorporate atleast 1.g of protein per kg of your body weith per day. See in diet and supplements section.
2. Exercise: Strength training is the most effective exercise in regaining muscles. It involves stressing the body's muscles repeatedly by lefting weights, squats, pull ups, push ups, etc.
3. Medications: Supplements as Vit D or amino acids and Omega-3 fatty acids all help with muscle recovery.

Few terms for diff kinds of muscles/connective tissues (even though not strictly muscles as they don't have nerve cells ??):

• Ligaments => Soft tissue structures that connect bone to bone.
• Tendons => These are much like Ligaments except that they connect bones to muscles. Muscles move the bones by pulling on the Tendons

Knee Basics:

Knees are the most important part of the bone structure and the most fragile. They are the first ones to give up due to old age, or plain wear and tear. It's important to consider knees in it's own section.

Knee bone basics: https://www.youtube.com/watch?v=_q-Jxj5sT0g

Meniscus tear: This is one the common tears that you can get very easily. Once you get it, it's very difficult to fix by itself. Doctors will want to do surgery, but don't fall for it.

Good advice on this link: https://kingbrand.com/Meniscus-Information.php?msclkid=fb0a365fb9521e7e41d353ed1bb57eaa

 Parts of Knee:

• Meniscus: These are C shaped shock absorbers between the thigh bone and shin bone, and help with the impact when the 2 bones are moving against each other. It's made of cartilage, and hence has a poor blood supply. A tear in meniscus can cause lockup, giving out, pain when squatting, lifting weight, etc. Lock up or giving out is when you cannot straigten your knee completely while running. The torn parts of meniscus get in between the 2 bones, and cause pain. A Surgery is done to shave off these lose parts, and get them out of your body, which relives the pain. But then you have less of miniscus left, which may increase your chances of getting  arthritis down the line.

Knee Surgery: This is one of the most violent surgeries that is done in a human body. IHA has good video on this: https://www.youtube.com/watch?v=2mqZnJJNU5s

ACL Repair: Good animation on repair of ACL => https://www.youtube.com/watch?v=Xsq0sQp6DwU