B 3.3 Muscle and Motility PDF

## B 3.3 Muscle and motility ### HL * Locomotion: the movement of an organism from one place to another. * Skeletal muscles: * Voluntary muscles * Striated muscles * Muscle fibres are made up of smaller myofibrils #### Skeletal Muscle Fibre Diagram: A diagram of a single muscle fibre s...

## B 3.3 Muscle and motility ### HL * Locomotion: the movement of an organism from one place to another. * Skeletal muscles: * Voluntary muscles * Striated muscles * Muscle fibres are made up of smaller myofibrils #### Skeletal Muscle Fibre Diagram: A diagram of a single muscle fibre shows: * **Muscle fibre** * **Cell membrane (sarcolemma)** * **Myofibril** * **Nucleus** * **Fibre (multinucleate)** * **SER (sarcoplasmic reticulum)** * **Dark protein (myosin)** * **Light protein (actin)** * **Z-line** * **Binding sites** * **Sarcomere** #### Diagram of Sarcomere A diagram of a single sarcomere (the functional unit of a muscle fibre) shows: * **Myosin** * **Actin** * **Z-line** ## Two types of protein filaments * Thin actin filaments: attached to a Z-line at one end. * Thick myosin filaments: occupy the centre of the sarcomere and interlock like fingers with the actin filaments at both ends. Each myosin filament is surrounded by six actin filaments and form cross-bridges with them. ## Skeletal Muscles contract when actin and myosin filaments slide over each other. * Myosin causes the sliding when "heads" form cross-bridges with actin through binding sites found on actin filaments. * Contraction causes the actin filaments to slide towards the centre of the sarcomere causing actin and filaments to overlap and resulting in shorter sarcomere * In each sarcomere actin moves a short distance towards the centre of sarcomere (8-10nm), but due to large numbers of sarcomeres in a muscle fibre → causes very powerful force. ## Figures 5 and 6 page 295 * Study figure 7 carefully on page 269 ## Titin: largest polypeptide that is elastic and can act as a molecular spring, that stores potential energy when it stretches and releases this energy when it recoils. * Titin connects the end of myosin to the Z-line (Z-disc). See figure 9 page 297 * Prevents overstretching of sarcomere. * Helps with the force of contraction when it recoils. * Holds myosin filaments in their position. ## Muscles working antagonistically helps in returning titin into position as the muscle relaxes. ## Skeletal muscles contract when stimulated by motor neurons using acetylcholine as a neurotransmitter (neuromuscular junctions) * One motor unit can stimulate hundreds of muscle fibres. ## Skeleton * Exoskeleton → Outside of the body → spiders, crustaceans and insects → consists of tough plates made up of chitin. * Endoskeleton → Inside of the body → Vertebrates → consists of bones. ## Muscles attach to 2 parts of the skeleton: * Insertion: Causes movement when muscles contract. * Origin: Fixed ## Joints: Where bones meet and movement is facilitated. ## Types of joints: * Fixed joints (Non-movable): e.g. skull * Slightly movable joints: e.g. vertebral column (cartilage between vertebrae) * Freely movable joints (synovial joints) * Hinge joints → Move only in one direction → e.g. Elbow and knee * Ball and socket joints → move in many directions → e.g. Pelvis and shoulder joints ## Hinge joint (elbow joint) → flexion and extension (bending and straightening) only. * Diagram of an elbow joint shows: * Radius * Ulna * Humerus * Ligaments * Cartilage * Synovial membrane * Synovial fluid ## Ball and socket joint (hip joint) → Figure 15 Page 299 * Diagram of a hip joint shows: * Pelvis * Femur * Study definition of all the parts from the book page 299 * Bones * Cartilage * Synovial fluid * Ligaments * Tendons * Pro tract * Retract * Abduct * Adduct * Rotate * See figure 17 page 300 ## Measuring range of movement using goniometer. * Read page 301 related to figure 18 ## Muscles and joints work as levers. * Pivot joint (fulcrum) * Effort (force) → Muscles contracting * Load → body weight or something carried ## Example: * A diagram shows a bicep muscle as an example of a lever system shows: * Effort * Load * Fulcrum (elbow joint) ## Example of antagonistic muscle action is the action of intercostal muscles between ribs. * **During inhalation:** External intercostal muscles contract while internal intercostal muscles relax → results in expanding the rib cage. * **During exhalation:** External intercostal muscles relax while internal intercostal muscles contract → results in decreasing volume of ribcage. * See figure 19 page 301 ## Reasons for locomotion: * Foraging for food * Escaping from danger * Searching for a mate * Migration ## Adaptations for swimming in marine Mammals: * Streamlining * Adaptations for locomotion → study from book page 303 * Airways to allow ventilation → study from book page 303 * Study figures 24 and 25 page 303