Muscles and Movement

Coordinating Movement Movement is controlled by a variety of things working together Bones: Support the body, facilitate movement, protect internal organs, site of blood cell formation and metabolism of calcium and other ions Muscles: attach to bones and provide forces necessary to change the position of the bones. Many muscles occur in antagonistic pairs Tendons: attach muscles and bones Ligaments: attach bones to other bones Nerves: Send and receive messages from the brain and aid in the control of movement

Joints Joints are points where the bones meet and are classified according to structure and function Structural classifications focus on materials and the presence of a joint cavity Can be fibrous, cartilaginous or synovial Functional classifications focus on the amount of movement allowed Synarthroses (immovable joints) Amphiarthroses (slightly moveable) Diarthroses (freely moveable) Most joints in the body are synovial

5 Distinguishing Features of Synovial Joints Articular cartilage – hyaline cartilage covers opposing bone surfaces Joint Cavity – a potential space that contains a small amount of synovial fluid Articular Capsule – encloses the joint cavity; strengthens the joint so it is not pulled apart Synovial Fluid – occupies all free spaces within the joint capsule; reduces friction; uses ‘weeping lubrication’ mechanism – fluids move in and out of area with compression of joint Reinforcing Ligaments – joint strengthened by ligaments (those that are ‘double jointed’ have more stretchy ligaments)

Types of Synovial Joints Plane Joints – articular surfaces are essentially flat; allow for gliding movements (intercarpal and intertarsal joints) Hinge Joints – a cylindrical projection of one bone fits into another a trough-shaped surface on another (elbow)*** Pivot Joints – the rounded end of one bone protrudes into a ‘sleeve’ or ring composed of bone (radius/ulna)*** Condyloid Joints – the oval articular surface of one bone fits into a complementary depression in another; both articulating surfaces are oval (wrist, knuckle and knee)*** Saddle Joints – similar to condyloid joints but allow for more freedom of movement; both bones have concave and convex areas (carpometacarpal joints of thumbs ) Ball-and-Socket Joints – the spherical or hemispherical head of one bone articulates with the cuplike socket of another (shoulder and hip)***

The Elbow Hinge joints limit the movement to a single plane Humerus-Ulna Pivot Joints limits movement to a rotation Humerus-Radius The movements are controlled by two antagonistic muscles: the biceps and the triceps

The Knee The knee is considered a complex, compound condyloid joint. This allows for greater range of motion when the joint is flexed than when it is extended.

The Hip The joint between the pelvis and the femur is considered a ball and socket joint. This allows the leg to both flex and extend as well as rotate and move sideways and back

There are 3 types of muscle Muscles There are 3 types of muscle Skeletal – move and support the skeleton Cardiac – found in the heart and composes the walls of the heart Action potentials are triggered without input from the nervous system Smooth – found mainly in the walls of hollow organs, such as blood vessels and digestive organs

Muscle Function Skeletal muscle is attached to the bone and is responsible for movement Muscles consist of bundles of fibers where each fiber is a single cell with multiple nuclei Running longitudinally across the fibers are myofibrils Thin (actin and regulatory protein) and thick filaments (myosin) composed of proteins The arrangement of fibers causes the muscle to be striated. Each repeat unit is a sarcomere, the basic contractile unit of the muscle

Sliding-Filament Model of Muscle Contraction As the sarcomere shortens, neither the thin or thick filaments change in length Filaments slide past each other, increasing the overlap of the thin and thick filaments Based on interaction between actin and myosin Myosin head is attached to head of ATP which it hydrolyzes to ADP, binding the myosin head to actin. This forms a cross-bridge. When a new ATP binds to the myosin, the cross-bridge is broken. The cycle can then begin anew

Muscle Contraction Calcium and regulatory proteins also play an intricate role in controlling muscle contracting and relaxation Regulatory proteins tropomyosin and troponin complex bind to actin in thin filaments. When muscles are at rest, tropomysin covers myosin bind sites, inhibiting interaction When calcium is present, it binds to troponin complex, causing the protein to shift position This allows cross-bridges to form Calcium will be removed via active transport by sarcoplasmic reticulums returning the cell to normal

Skeletal Systems 3 major types of skeletal systems Hydrostatic – fluid held under pressure in a closed body compartment; muscles change the shape of the compartment Cnidarians, flatworms, nematodes, annelids Exoskeleton – hard encasement on the animal’s surface Bivalves, arthropods Endoskeleton – hard supporting elements within the soft tissue Echinoderms, chordates