Unit 3 – Your muscles and your skeleton We will start with the muscular system. You have, on average, 320 pairs of muscle groups. These pairs oppose one another. An example of this would be the bicep / tricep pairing on the arm. The biceps contract the arm (like when you scratch your nose), and the triceps act to straighten the arm out. We have 3 different types of muscle tissue: Striated – this muscle type is under voluntary control

Muscles continued As noted in the previous slide, striated muscle is made of thin strands of protein called myofibrils. These bundles of myofibrils are grouped into sarcomeres and these are separated by dark regions called z-bands. Actin is interspersed with the myofibrils in a stacked arrangement. When the muscle is stimulated, the actin pulls the z bands toward one another – resulting in a contraction. This contraction can be weak or strong – depending on the level of stimulation. (TENS unit demo right away).

Muscles continued. NOTE: - Just like neurons, muscle contractions are all or nothing. The second type of muscle tissue is SMOOTH muscle. Smooth muscle is found in various internal organ systems – like the digestive system – and the contractions of smooth muscles are involuntary. Smooth muscle is also composed on myofibril strands and actin fibers, but they are not arranged like striated tissue. Smooth muscle fibres are tapered at both ends. These muscle fibres contract very rhythmically, and you may not even notice them.

Muscles continued. The third type of muscle tissue is cardiac muscle. It is found only in the heart (hence the name cardiac). Cardiac tissue is very similar to striated tissue but much shorter in length. It also has an incredibly high number of mitochondria (5000 per cell compared to 200 per cell of bicep muscle). Your heart needs this large number of mitochondria because it contracts and relaxes approx. 70 times per minute – all day, every day for, on average, 72 years. That’s 70x60x24x365.25x72 = 2.65 x 10 9 beats ! Your heart rests in between beats and the lowest resting heart rate documented was 27bpm.

Muscles continued Muscles are connected at both ends by tendons, and these tendons are attached to neighboring bones (like the humerus and the ulna/radius). Muscular contractions will move the bone up or down (depending on which of the antagonist pair is working). An example is when you flex your bicep, the tricep will relax. When the tricep flexes, the bicep will relax.

The Skeletal system Now we come to the framework that ties all body systems together – your skeleton. The human body has 270 bones at birth, but this number goes down to 207 in adulthood as some bones fuse together. You have the greatest bone density at around age 30, but this can vary according to diet in younger years (it’s important to lay down a good foundation early, as you will need all that density later on in life).

The skeleton continued. Your skeleton has 6 major functions: – Support – Movement – Production of blood cells – in the marrow – Endocrine regulation – osteocalcin regulates blood sugar – Storage – calcium and iron – Protection Skull protects brain, eyes, and middle/inner ears The vertebrae protect the spinal cord Rib cage, spine, and sternum protects heart, lungs, and other major blood vessels. Clavicle and scapula protects the shoulder Patella and ulna protects the knee and elbow Ilium and spine protects the urogenital systems and the digestive system Carpals and tarsals protect the wrists and ankles

The skeleton continued The bones of the skeleton are held together by tough bands of flexible tissue called ligaments – Muscles, on the other hand, attach to bone through tendons. The ends of bones are covered in a thin layer of cartilage that allows smooth movement of the joints. The joint spaces are bathed in synovial fluid that acts as a lubricant for the joints.

The skeleton continued We have several different types of joints: – Pivotal joints (Neck and elbow) – Ball and socket joints (shoulder and hip) – Gliding joint (ankles, spine, and ribs) – Hinge joint (fingers, knees, and elbow) – Why would a ball and socket joint not work for a knee joint? – How does osteoarthritis and rheumatoid arthritis play a role in joint pain? – If a tree falls in a forest and hits a mime, does the mime make a sound?