The Musculoskeletal System

• Rigor

  A state at the beginning of the cycle, when myosin is tightly bound to actin and noATPis bound tomyosin.
• Describe the key stages of the cross-bridge cycle.

  Cross-Bridge Formation:Myosin heads bind to actin, forming cross-bridges.Power Stroke:Myosin heads pivot, pulling actin filaments toward the center of the sarcomere.Cross-Bridge Detachment:ATP binds to myosin, causing detachment from actin.Cocking of Myosin Head:ATP is hydrolyzed, resetting the myosin head for the next cycle.
• Myosin converts...

  the chemical bond energy of ATP into mechanical energy.
• Describe the process of excitation contraction coupling.

  Nerve Signal:Action potential travels down a motor neuron to reach the neuromuscular junction.Acetylcholine Release:Nerve signal triggers the release of acetylcholine, a neurotransmitter.Muscle Fiber Excitation:Acetylcholine binds to receptors on the sarcolemma, initiating an action potential.Calcium Release:Action potential travels along T-tubules, causing the release of calcium ions from the sarcoplasmic reticulum.Cross-Bridge Formation:Calcium binds to troponin, allowing myosin heads to bind to actin, initiating muscle contraction.
• Myosin crossbridges

  In skeletal muscle, two F-actin polymer twist together to form a double stranded light filament.

  Each G-actin contains a myosin binding site, and each myosin head has an actin binding site

  
• F-actin


  A fibrous protein made of a long chain of G actin molecules twisted into a helix; main protein of the thin myofilament

  
• Microfilament


  Actin
• Regulatory proteins


  tropomyosin and troponin
• Thin filaments


  Actin, troponin, tropomyosin
• Myosin


  A thick filament. Each myosin molecule contains two identical protein chains, each with onelargeheavy and two light chains. ​
• T-tubules


  Tubular invaginations of the sarcolemma, aiding in the transmission of nerve signals.
• Sarcomeres


  The functional unit of muscle contraction, composed of overlapping actin and myosin filaments.
• Sarcoplasmic Reticulum


  Specialized endoplasmic reticulum that stores calcium ions, crucial for muscle contraction.
• Sarcoplasm


  Cytoplasm of a muscle cell
• Sarcolemma


  The membrane of the muscle fibre
• Myofibrils


  Thread-like structures within muscle fibers, containing contractile units (sarcomeres).
• Describe the structure of skeletal muscle fibres.

  Make up the skeletal muscle. Each fibre is along,cylindricalcell arranged in parallel and containmultiple nuclei.The membrane of the muscle fibre is thesarcolemma. The cytoplasm is thesarcoplasm,that contains manymitochondria. Composed ofmyofibrilsthat are responsible for thestriatedappearance. Thesarcoplasmic reticulumis a form of endoplasmic reticulum (stores Ca2+ required for muscle contraction).
• Describe the functions of skeletal muscle.

  Locomotion (movement)Static support(muscle tension to keep you upright when still).Heat generation(contractions generate heat)Metabolism(insulin-dependent glucose absorption)

  Humans have approx. 639 skeletal muscles, which accounts for 30-40% of body weight.
• Cardiac muscle


  Found only in the heart and moves blood through the circulatory system. The heart wall is composed of three layers. The middle layer, themyocardium, is responsible for the heart’s pumping action. Cardiac muscle contracts in response to signals from the cardiac conduction system to make the heart beat. Like skeletal muscle cells, cardiac muscle have astriatedappearance, but their overall structure is shorter and thicker.
• Smooth muscle


  Found in the walls ofhollow organsthroughout the body. Smooth muscle contractions areinvoluntarymovements triggered by impulses that travel through theautonomic nervous systemto the smooth muscle tissue. The arrangement of cells within smooth muscle tissue allows for contraction and relaxation with greatelasticity.

  The smooth muscle in the walls of organs like the urinary bladder and the uterus allow those organs to expand and relax as needed. The smooth muscle of the digestive tract facilitates the peristaltic waves that move swallowed food and nutrients. In the eye, smooth muscle changes the shape of the lens to bring objects into focus. Artery walls include smooth muscle that relaxes and contracts to move blood through the body.
• Skeletal muscles


  Attach to and move bones bycontractingandrelaxingin response tovoluntarymessages from the nervous system. Skeletal muscle tissue is composed oflong cellscalledmuscle fibresthat have astriatedappearance. Muscle fibres are organised into bundles supplied by blood vessels and innervated bymotor neurons.
• Describe the three types of muscle tissues.

  Skeletal Muscle Tissue:Attached to bones, responsible for voluntary movements.Smooth Muscle Tissue:Found in walls of internal organs, involuntary movements like digestion.Cardiac Muscle Tissue:Forms the heart, involuntary contractions to pump blood.
• Wormian (Sutural) Bones


  small extra bones that sometimes appear within the joints of certain cranial (skull) sutures. Sutures are the joints between the bones of the skull, and these extra bones can be like little puzzle pieces in those joints.
• Examples of sesamoid bones


  mostly found in the (patella) knee, thumb, and big toe.
• Sesamoid bones


  Small, round bones that act like helpers for tendons, making it easier for your joints to move.
• Examples of irregular bones

  Vertebrae:These are the bones that make up your spine, and they have a unique, irregular shape that allows them to stack together and protect your spinal cord.Facial Bones:Bones in your face, like the ones around your eyes (zygomatic bones) and nose (nasal bones), are irregular because they need to form the specific structure of your face.Pelvic Bones:The bones that make up your pelvis, like the ilium, ischium, and pubis, are irregular in shape to provide stability and support to your body.
• Irregular Bones


  A bit like puzzle pieces - they don't have a regular or predictable shape. Instead, they come in various shapes and sizes, often with unique contours. These bones usually serve special purposes, fitting into specific spots in the body where a standard shape wouldn't work well.
• Examples of flat bones


  Skull Bones (Parietal and Frontal):The skull has several flat bones that protect your brain.Scapula (Shoulder Blade):This flat bone helps form the shoulder joint and provides a surface for muscle attachment.Ribs:The ribcage is made up of flat bones that protect the organs in your chest.Sternum (Breastbone):A flat bone in the center of your chest that connects to your ribs.
• Flat Bones


  Flat and thin. protect internal organs such as the brain (skull), heart (thoracic cage - sternum and ribs), and pelvic organs (pelvis).
• Examples of short bones

  Carpals:These are the small, cube-like bones in your wrist.Tarsals:Found in your ankle, these are another set of short bones.Metacarpals:These are the palm bones of your hand, connecting your fingers to your wrist.Metatarsals:Similar to metacarpals, these are in the mid-foot, connecting your toes to your ankle.
• Short Bones

  Relatively small and cube-shaped. Unlike long bones, they're not elongated; instead, they're more equal in length, width, and thickness (are shaped roughly as a cube (cuboidal)). Contain mostlyspongy bone. The outside surface is comprised of a thin layer ofcompact bone.These bones are primarily found in places where you need a little bit of flexibility combined with strength.
• Examples of long bones

  Femur:This is the thigh bone, the longest bone in the body;Humerus:Found in the upper arm, between the shoulder and elbow.Radius and Ulna:These are in the forearm, between your elbow and wrist.Tibia and Fibula:These are in the lower leg, between your knee and ankle.

  
• Long bones


  A type of bone that is long and slender. They are mostly found in the limbs, like arms and legs
• Name the six different types of bones and give examples

  Long Bones:Examples include the femur, humerus, and phalanges.Short Bones:Examples include the carpal bones and tarsals.Flat Bones:Examples include the skull bones (parietal, frontal) and ribs.Irregular Bones:Examples include the vertebrae and facial bones.Sesamoid Bones:Examples include the patella (kneecap).Wormian (Sutural) Bones:Small bones found within sutures of some cranial bones.
• Yellow marrow


  Made mostly of fat.
• Red marrow

  Contains blood stem cells that can become red blood cells, white blood cells, or platelets.
• Types of bone marrow

  Red marrow and yellow marrow
• Periosteum


  The dense, tough outer shell that contains blood vessels and nerves. Essential for bone growth, repair, and nutrition.
• Bone Marrow


  The jelly-like substance found inside the cavities of most bones.
• Spongy (Cancellous) bone


  The porous material found inside most bones, which allows the bone to be strong yet lightweight.