Skeletal Muscular System 11.2 Muscles and Movement

Locomotion- swimming, crawling, running, hopping, and flying all result from muscles working against some type of skeleton.

The Skeleton Main functions of the skeleton are: Support- framework to maintain shape Protection- enclose vital organs and soft tissue. Movement- muscles attach to bone to form levers. Production of blood cells in marrow. Mineral storage- Calcium and Phosphorus

Human Skeleton 206 Bones

Types of Skeletons Hydrostatic Skeleton Soft bodied animals rely on pressurized fluid held in compartments within the body to act as a skeleton. (cnidarians, annelids and other phylum of worms) They use muscles surrounding these compartments to change shape and produce movement. (peristaltic movement)

Exoskeleton A hard external skeleton that covers all of the muscles and organs of some invertebrates. (Insect, crustacean, and spiders (arthropods) Composed of noncellular material (chitin, calcium salts) secreted by the epidermis. (light and strong)

Endoskeleton Skeleton found within the body for structure and support. Made up of hard supportive material buried within soft tissue. Found in chordates and echinoderms including cartilaginous fish

UNDERSTANDINGS Bones and exoskeletons provide anchorage for muscles and act as levers. Movement of the body requires muscles to work in antagonistic pairs. Synovial joints allow certain movements but not others. Skeletal muscle fibers are multinucleated and contain specialized endoplasmic reticulum. Muscle fibers contain man myofibrils.

Each myofibril is made up of contractile sarcomeres. The contraction of the skeletal muscle is achieved by the sliding of actin and myosin filaments. Calcium ions and the proteins tropomyosin and troponin control muscle contractions. ATP hydrolysis and cross bridge formation are necessary for the filaments to slide.

APPLICATIONS SKILLS NATURE OF SCIENCE Antagonistic pairs of muscles in an insect leg. SKILLS Annotate a drawing of the human elbow. Drawing labelled diagrams of the structure of a sarcomere. Analysis of electron micrograph to find state of contraction of muscle fibers. NATURE OF SCIENCE Fluorescence was used to study the cycle of muscle interactions in muscle contraction.

I. Movement and the Interaction of the Skeleton and Muscles. A. . Muscles attach to bones by tendons at the point of origin and then again to another bone at the insertion point. 1. Tendons are bands of connective tissue made up of strong protein fibers of collagen.

B. The force for movement is generated by the contraction (shortening) of muscle cells. 1. This contraction acts upon the skeleton to provide the leverage to either change the size or direction of the force. a. The bones act as levers to produce movement

2. Muscles can be found in antagonistic (opposite) pairs 2. Muscles can be found in antagonistic (opposite) pairs. (While one muscle is contracting the other muscle is relaxing.) a. One muscle extends the joint (extensor muscle) while the other muscle (flexor) in the pair flexes it or brings it closer to the body.

II. Joints- where bones meet A. Ligaments, made up of strong fibrous connective tissue, hold bone to bone to provide stability.

B. Bones at a joints fit together in a variety of different ways to allow for different ranges in motion. 1. Freely Movable Joints- Synovial Joints- where the bones meet are covered with smooth cartilage and lined with a synovial membrane that produces synovial fluid to provide lubrication and reduce friction.

a. Ball and Socket- hip/ shoulder the ball-shaped surface of one bone fits into the cuplike depression of another. Provides the greatest range in movement- rotation, forwards and backwards, and in and out. (3 planes of motion)

b. Hinge Joint- the knee / elbow Joint only moves forward and backwards allowing the knee to bend or straighten.(one plane of motion) Cartilage coverings of the bones, cartilage discs (meniscus), bursa, fat pads and synovial fluid all ease friction and aid in shock absorption.

Anatomy of the Elbow Joint

Anatomy of the Elbow Joint A. Humerus: upper arm bone B. Synovial Membrane: encloses the joint in synovial fluid. C. Synovial fluid: lubricates joint and provides supply of nutrients and oxygen. D. Radius and Ulna: forearm bones which act as levers in flexion and extension of arm. E. Cartilage: living tissue that covers ends of bones, reduces friction and absorbs shock F. Joint capsule- dense connective tissue that surrounds a joint that is lined with the synovial membrane that produces synovial fluid.

Antagonistic Muscle Pairing of Elbow: biceps: attaches from the humerus (ORIGIN) to radius(INSERTION) – the FLEXOR when contracted triceps: attaches from humerus (ORIGIN) to ulna (INSERTION)- the EXTENSOR when contracted.

A. Skeletal Muscle Organization II. Movement by Muscles A. Skeletal Muscle Organization 1. Skeletal muscles consist of bundles of long fibers that run parallel to each other. a. Each fiber is a fused single cell which is multinucleated. Striated Muscle Fibers

2. Each muscle fiber is a bundle of myofibrils made up of two types of specialized protein myofilaments. a. thin filament: two strands of ACTIN and two strands of tropomyosin with troponin, (regulatory proteins) coiled around each other. b. THICK FILAMENT: arrangements of MYOSIN with globular heads.

3. The myofibrils are arranged in repeating units called SARCOMERES- basic contractile unit of the muscle.

a. Each sarcomere goes from Z Line to Z line. b. Thin filaments (actin) are attached to the Z lines and project towards the center of the sarcomere. c. Thick filaments (myosin) are centered in the sarcomere. d. The overlapping or lack of overlapping form the light and dark banded appearance of the striations.

4. Microanatomy of Muscle Fibers a. Sarcolemma- plasma membrane of a muscle fiber that conducts the action potential. b. Sarcoplasm- cytoplasm c. T-tubules- transverse tubules- narrow tubules that form passageways through the muscle fiber. d. Sarcoplasmic Reticulum- specialized smooth ER that surrounds the myofibrils- stores and releases large amounts of Calcium ions.

Ample supply of ATP provided by MITOCHONDRIA throughout the myofibril.

Electron Microscope images Note: •large number of mitochondria •Diagonal myofibrils •Sarcoplasmic reticulum

5. The Nervous System Control of Muscle Fiber Contraction a. Impulses from motor neurons control the contraction of skeletal muscles at neuromuscular junctions

b. The neurotransmitter acetylcholine is released into the synaptic cleft which stimulates an action potential (nerve impulse) in the sarcolemma of the muscle fibers. c. This impulse spreads quickly over the sarcolemma and through the fibers through the T-tubules. d. Large amounts of calcium are released by the sacroplasmic reticulum into the myofibrils. e. The calcium will allow for the interaction of actin and myosin to cause a contraction. TUTORIAL

6. The Sliding Filament Theory of Muscle Contraction a. The THICK filaments are comprised of MYOSIN molecules made up of a “tail” and a “globular head”. These extension have a molecule of ADP and a phosphate group attached as well as the stored energy released from ATP.

b. These myosin heads attach to ACTIN molecules (thin filaments) during a muscle contraction to pull the Z- lines of the sarcomere closer. Filaments do not change size. Filaments “slide” past each other

c. Myosin heads cannot attach to the actin until the active sites on the actin are exposed. The calcium released by the sarcoplasmic reticulum binds to the troponin and causes the tropomyosin to expose the myosin binding sites.

d. The myosin heads can now attach to the exposed active site on the actin filament forming cross bridges. e. The attached myosin heads pivot towards the center of the sarcomere and the ADP and phosphate group are released. f. The attachment of a new molecule of ATP causes the cross bridge to release and detach allowing it to reattach further along.

Cross Bridge Cycle If the electron micrographs of a relaxed and contracted myofibril are compared it can be seen that: •These show that each sarcomere gets shorter when the muscle contracts, so the whole muscle gets shorter. •But the dark band, which represents the thick filament, does not change in length. •This shows that the filaments don’t contract themselves, but instead they slide past each other.

Sliding Filament theory The cross bridge swings out from the thick filament and attaches to the thin filament. 2. The cross bridge changes shape and rotates through 45°, causing the filaments to slide. The energy from ATP splitting is used for this “power stroke” step, and the products (ADP + Pi) are released. 3. A new ATP molecule binds to myosin and the cross bridge detaches from the thin filament. 4. The cross bridge changes back to its original shape, while detached (so as not to push the filaments back again). It is now ready to start a new cycle, but further along the thin filament. This model is for one myosin molecule cross bridging to one actin. Looking at some of the diagrams above we can see that there must be many cross bridges formed but not quite together.

The movements your muscles make are coordinated and controlled by the brain and nervous system. The involuntary muscles are controlled by structures deep within the brain and the upper part of the spinal cord called the brain stem. The voluntary muscles are regulated by the parts of the brain known as the cerebral motor cortex and the cerebellum