HL Papers 1 and 2 Muscles and Movement

Responding to stimuli is one of the six life functions Movement is responding to stimuli Movement from point A to point B is called locomotion Done by the coordination of the nervous system with the muscles and bones

Muscles and Movement You need: Nerves (went over previous topic) Carry impulses to and from the brain to co-ordinate muscular activity Motor neuron impulses stimulate the muscles to contract Nerve impulses control timing and speed of muscular contraction Muscles Contain receptors that send information via sensory neurons to the brain about the position of the muscle Contract to bring movement to the joint Work in muscles pairs on each side of a joint

Muscles and Movement Muscles have a belly (gaster) and a tendon Belly - fleshy portion of the muscle between the tendons. Tendon - a white fibrous cord of dense, regularly arranged connective tissue that attaches muscle to bone. They have the tensile strength of steel.

Muscles and Movement – Belly and Tendon

Muscles and Movement Each muscle has an origin and an insertion. Insertion is the attachment of the muscle tendon to the moveable bone Origin is the attachment of the other muscle tendon to the stationary bone.

Muscles and Movement Bones Bones meet at a joint and act as levers Different types to joints between bones control the range of movement Provide rigid anchorage for muscles through tendons Form blood cells in the bone marrow Provide a hard framework to support the body Allow protection of vulnerable softer tissue and organs Allow for the storage of minerals, especially calcium and phosphorus Connected by ligaments Ligaments fibrous tissue run from one bone to another, across joints connect bones together, and give the joint strength.

Muscles and Movement – Bones and Ligaments

Muscles and Movement - Joints Consist of two or more bones, connected by ligaments and muscles, connected to bones by tendons, to facilitate movement. Joints contain the following: Cartilage – smooth, strong covering on articulating surfaces of a joint Synovial Fluid – lubricates articulating surfaces of cartilage; acts like a shock absorber. Contains nutrients and Oxygen for the cartilage.

Muscles and Movement - Joints Spongy Bone – end of bones that are light and strong. Band Ligaments – tough elastic structures holding bones of a joint together. Capsular Ligaments – encloses joint to protect it.

Example – Elbow Joint

Movement – A comparison The knee is similar to the elbow. both are hinge joints Freely movable are also called diarthrotic joints. The hip is also a diarthrotic joint, but is a ball and socket joint.

Movement – A comparison Hip Joint Knee Joint

Muscle Structure – Striated Muscle Muscles are made up of various strands, like rope A skeletal muscle is made up of bundles muscle fibers, or muscle cells. Each muscle fiber is surrounded by a sarcolemma, the muscle fiber’s cell membrane. Each muscle fibers contains many myofibrils The cytoplasm, called sarcoplasm, contains mitochondria packed between the myofibrils. In between the myofibrils is a transverse tubular endoplasmic reticulum, called the sarcoplasmic reticulum.

Muscle Structure – Striated Muscle In the myofibrils, there are two protein myofilaments called myosin and actin. The myosin is the thick filament, that appears darker. The actin is the thin filament, that appears light. The stripes are caused by the alternating light and dark bands.

Muscle Structure – Striated Muscle

Structure and Contraction of Skeletal Muscle Sarcomere – section between the z – lines Actin filaments are held together by transverse bands called Z line. Where the actin partially overlaps the myosin filaments and from end to end of the myosin filament, is called the A band The area where only myosin is seen is called the H band or zone. This is between the two Z lines.

Structure and Contraction of Skeletal Muscle Across the fibers there are transverse tubules, or T – tubules Tubules touch the sarcolemma and associated with vesicles which are part of the sarcoplasmic reticulum A T-tubule with a pair of vesicles is called a triad. The vesicles are important. Regulate the movement of calcium ions to and from the sarcoplasm. The Ca +2 concentration determines the activity of ATPase

Structure and Contraction of Skeletal Muscle

Sliding Filament Theory The actin slides across the myosin, powered by ATP On the actin filament are binding sites for the heads of the myosin Actin filaments contain actin as well as tropomyosin and troponin. Tropomyosin forms two strands which wind around the actin filament, covering the binding site. The tropomyosin is held in place by the troponin. This is how the actin filament remains at rest.

Sliding Filament Theory The thick filaments are composed of myosin molecules Each has a bulbous head The head protrudes from the length of the myosin filament. The head, binds to the site on the actin filament. This is what causes movement of the filaments, and eventually the movement of the whole muscle.

Actin, Myosin, Tropomyosin, and Troponin

Contraction – Sliding Filament 4 Steps 1. The myofibril is stimulated to contract by the arrival of an action potential Triggers the release of calcium ions from the sarcoplasmic reticulum, to surround the actin molecules. The calcium ions react with the troponin. When the troponin is activated, it triggers the removal of the blocking molecule, tropomyosin. The binding sites are now exposed.

Contraction – Sliding Filament 2. Each bulbous head has an ADP and Phosphate group attached to it (called a charged bulbous head). It reacts with a binding site on the actin molecule beside it. The phosphate group detaches. This is called Attachment 3. The ADP molecule is then released from the head This is a trigger for the rowing movement of the head. The head tilts 45 o and pushes the actin filament along. This step is called the power stroke and the myofibril contracts.

Contraction – Sliding Filament 4. A molecule of ATP binds to the head. The protein, ATPase, catalyses the hydrolysis of ATP. The result is ADP and Phosphate is attached to the bulbous head It is said to be charged again The charged head detaches from the binding site and straightens. With more ATP and calcium, the head attaches again, step 2, to shorten more. Another power stroke is acheived. When no more impulses arrive, calcium ions are moved back into the vesicles of the sarcoplasmic reticulum binding sites are covered by the tropomysin and the muscle relaxes.

Exposure of Binding Sites

Sliding Filament Theory ( Animation)Animation

Extensions – Muscle Disorders Multiple Sclerosis Muscular Dystrophy