Human Physiology - Muscles and Movement

• Muscles- Provide the force needed for movement by contracting, muscles can only pull and therefore need to be found in pairs that move bones in opposite directions (called antagonistic pair)
• Tendons-Attach muscles to bones
• Bones- Provide a firm anchorage for muscles, act as levers, changing the size or direction of forces generated by muscles
• Ligaments- Connecting bone to bone, restricting movement at joints and helping to prevent dislocation
• Nerves- Stimulate muscles to contract at a precise time and extent, so that movement is coordinated

• Cartilage: a layer of smooth and tough tissue that covers the ends of the bones where they meet to reduce friction
• Synovial Fluid: lubricates the joint to reduce friction
• Joint Capsule: seals the joint
• Radius: bone that transmits forces from the biceps through the forearm
• Ulna: bone that transmits forces from the triceps through the forearm
• Humerus Bone: provides a firm anchorage for the muscles
• Biceps: the flexor muscle, used to bend the arm at the elbow
• Triceps: the extensor muscles, used to straighten the arm
• Tendons: attaches muscle to bones

• Similarities:
• • Both are joints where there is a junctions between bones
• • Both have muscles attached to bones by tendons and generate a force that pulls on the bones to produce movement in the joint
• • Both are synovial joints in which the ends of the bones are covered with cartilage the joint is enclosed in a tough fibrous capsule, the inner surface on the capsule is lined with synovial membrane that secretes a lubrication synovial fluid
• • Both carry out flexion and extension movements

• Differences:
• • Knee is hinge joint
• • Hip is ball and socket joint where the femur has a ball at the end of it that fits into a socket like cavity in the pelvis

• Knee allows for movement in only one plane:
• 1. Flexion and extension
• • Bending of the joints is called flexion and I achieved by the hamstring muscle contacting and pulling on the fibula bone of the lower leg
• • Straightening of the joints is called extension and is achieved by the quadriceps pulling on the patella and tibia

• The hip has movement in three planes
• 1. Flexion and Extension
• • femur can move up towards the pelvis (flexion) and can move downwards away from the pelvis (extension)
• 2. Adduction and Abduction
• • Femur can move sideways in toward the medial (center) line of the body (adduction) and can move sideways out from the medial line (abduction)
• 3. Rotational
• • Femur can move in a circular motion around a longitudinal plane of the bone

• • Skeletal muscle is composed of large multinucleate cells called muscle fibers.
• • Surrounding each muscle fiber is its plasma membrane called the sarcolemma
• •The numerous nuclei are usually located at the peripheries of the cell near the sarcolemma.
• • Inside each muscle fiber are cylinders called myofibrils that consist of repeating units called sarcomeres.
• • The sarcomeres have a light and dark banding pattern created by the arrangement of the myofilaments (filaments) actin and myosin.
• • Actin- protein that makes up the thin filaments and has binding sites where myosin can bind
• • Myosin-protein that makes up thick filaments and has heads that are able to bind to the myosin binding sites on the actin
• • Part of the sarcomere containing myosin is the dark band and the part containing only actin is the light band.
• • This banding pattern repeats across all the myofibrils in a muscle fiber giving it a striped or striated type of endoplasmic reticulum called the sarcoplasmic reticulum.
• • Many mitochondria are also found in the narrowband of cytoplasm between the myofibrils.

• 1. A nerve impulse or action potential arrives at the terminal of a motor neuron causing the release of acetylocholine (ACH)
• 2. Ach diffuses across the synaptic cleft and binds to Ach receptors on the sarcolemma (plasma membrane of the muscle cell) which produces an action potential in the sarcolemma
• 3. The action potential is propagated along the sarcolemma and down into the T-tubules (infoldings of the sarcolemma into the cytoplasm)
• 4. The T-tubule touches the sarcoplasmic reticulum and whan an action potential passes down the T-tubule and contacts the sarcoplasmic reticulum (SR), it causes the SR to release Ca2+ ions into the cytoplasm
• 5. Ca2+ ions bind to troponin causing a conformational change that makes troponin pull on tropomyosin exposing the myosin binding sites on the actin
• 6. The myosin heads can now bind to the actin forming cross-bridges. This binding causes ADP and Pi bound to the myosin head to be released. The myosin head now relaxes to its lower energy state pulling the actin filament, to which it is attached, toward the center of the sarcomere. In this way the actin filament slides across the surface of the myosin filament. This is called the power stroke
• 7. ATP now binds to the myosin head causing it to release from the myosin binding site on the actin
• 8. ATP is hydrolyzed ADP and Pi by the myosin head. This causes the myosin head to become upright into its higher energy configuration
• 9. The myosin head will now bind to the actin further toward the Z band than before and the process will repeat again pulling on the actin until Ca2+ is removed from the cytoplasm
• 10. When the action potential ends Ca2+ is removed by active transport back into the SR. Ca2+ will drop off of the troponin which changes shape pulling the tropomyosin back over the myosin head binding sites on the actin. Now cross-bridges cannot be formed and muscle contraction ceases.

To determine if a muscle is fully relaxed, slightly contracted, moderately contracted or fully contracted look at the light and dark bands as well as comparing the size of the sarcomere if comparative photos are shown 

If the light band is gone completely or the H band is gone then the muscle is fully contracted, if part of the light band is present a comparison must be done.