Topic 11.2

Muscles and Movement

Human SkeletonAxial skeleton

Supports the axis, or trunk of the body.Consists of :

the skull, enclosing and protecting the brainthe vertebral column (backbone), enclosing the

spinal corda rib cage around the lungs and heart

Human SkeletonAppendicular skeleton

Made up of the bones of the appendages (arms and legs) and the bones that anchor the appendages to the axial skeleton.

Shoulder girdle and pelvic girdle provide a base of support for the bones of the forelimbs and hind limbs.

Human SkeletonDistinct features:

Housing our large brain, our skull is large and flat-faced; its rounded part is the largest braincase relative to body size in the animal kingdom.

The skull is balanced atop the backbone with the spinal cord exiting directly underneath.

Our backbone is S-shaped, which helps balance the body in the vertical plane.

Pelvic girdle is short, round, and oriented verticallyHuman hand is adapted for strong gripping and precise

manipulation.Our feet, with ground-touching heel, straight-facing big

toe for propulsion, and shock-absorbing arches, are specialized for supporting the entire body and for bipedal walking.

Our vertical backbone bears weight unevenly, and our lower back carries much of the load. The lower back is easily strained, especially when we bend over or

lift heavy objects.

Human movement requires…BonesLigamentsMusclesTendonsNerves

Role of BonesBones

provide rigid framework against which muscles attach and against which leverage can be produced, changing the size or direction of forces generated by muscles.

Role of LigamentsLigaments

connect bone to bone, restricting movement at joints and helping to prevent dislocation.

Made of strong fibrous connective tissues

Role of musclesMuscles

attach to bones via tendons, and when muscles contract, they create the forces that move bones; using leverage, small muscle contractions can produce large bone movements

Role of tendonsTendons

attach muscles to bone.

Role of nervesNerves

provide a communication network along which messages can be sent signaling muscles to contract at a precise time and extent, so that movement is coordinated.

Elbow joint

Human Skeleton Much of the versatility of the vertebrate skeleton comes from its

joints. Strong fibrous connective tissues called ligaments hold together the

bones of movable joints. Three kinds of joints:

1. ball-and-socket joints- HIP! Enables us to rotate our arms and legs and move them in several planes

Protraction/retraction: forward and backwards Abduction/adduction: sideways in and out Rotation: circular movement

For example, where the humerus joins the shoulder girdle and also where the femur joins the pelvic girdle

2. hinge joint- KNEE! Permits movement in a single plane But constrains movement from other two planes

For example, in the knee: Flexion bends the leg Extension straightens the leg

For example, found in the arm, elbow and also in the knee 3. pivot joint

Enable us to rotate the forearm at the elbow. Hinge and pivot joints in our wrists and hands enable us to make precise

manipulations.

Ball-and-socket joint

Hinge Joint- Elbow

Pivot Joint- Forearm

Human Elbow Joint

Functions of the structures of the Human ElbowCartilage: reduces friction between bones where they meet Synovial fluid: lubricates joint to reduce friction Joint capsule: seals the joint and holds in the synovial fluid Humerus: upper arm bone: attachment of biceps and

triceps Ulna & radius: forearm bones: attachment of biceps and

triceps Biceps: attaches from humerus to ulna & radius Triceps: attaches from humerus to ulna Antagonism: biceps and triceps attach across elbow joint;

while triceps contracts to to extend arm, biceps relaxes; conversely, while treceps relax and the biceps contract, flexing the arm

BoneBones are complex organs consisting of several

kinds of moist, living tissues.For example, Figure 30.4 a human humerus (upper

arm bone):Consists of a sheet of fibrous connective tissue that

covers most of the outside surface.(periosteum)Tissue helps form new bone in the event of a fracture.

A thin sheet of cartilage forms a cushion-like surface for joints, protecting the ends of bones as they move against one another.

Synovial membrane encloses the joint in synovial fluid.Synovial fluid is formed from blood plasma and is

secreted by the synovial membrane. It lubricates the joint as well as nourishing the cartilage.

BoneFor example, Figure 30.4 a human humerus

(upper arm bone) continued…:The bone itself contains living cells that

secrete a surrounding material, or matrix.Bone matrix consists of flexible fibers of the

protein collagen embedded in a hard mineral made of calcium and phosphate.

The collagen keeps the bone flexible and nonbrittle, while the hard mineral matrix resists compression

BoneFor example, Figure 30.4 a human humerus (upper

arm bone)continued…:The shaft of this long bone is made of compact bone,

so named because it has a dense structure.The compact bone surrounds a central cavity with

contains yellow bone marrow, which is mostly stored fat brought into the bone by the blood.

the ends, or heads, of the bone have an outer layer of compact bone and an inner layer of spongy bone, so named because it is honeycombed with small cavities.The cavities contain red bone marrow, a specialized tissue

that produces are blood cells.Blood vessels course through channels in the bone,

transporting nutrients and regulatory hormones to its cells.

Nerves paralleling the blood vessels help regulate the traffic of materials between the bone and the blood.

Bone

Diagram of a Human Elbow Joint

Skeleton and muscle interactionsMuscles interact with bones, which act as

levers, to produce movement.Muscles are connected to bones by tendons For example, one end of the biceps muscle

shown in figure 30.7 is attached by tendons to bones of the shoulder; the other end is attached across the hinge joint of the elbow—which acts as the point of support—to one of the bones in the forearm.

Skeleton and muscle interactionsThe action of a muscle is always to contract, or

shorten.A muscle’s relaxation to an extended position is a

passive process.The ability to move an arm in opposite directions

requires that muscles be attached to the arm bones in antagonistic pairs.

In the arm: contraction of the biceps muscle raises the forearm. The triceps muscle is the biceps’s antagonist.The upper end of the triceps attaches to the shoulder,

while its lower end attaches to the elbow. The contraction of the triceps lowers the forearm,

extending the biceps in the process.

Skeleton and muscle interactions

Muscle tissue Muscle tissue

Consists of bundles of long cells called muscle fibers and is the most abundant tissue in most animals.

Skeletal muscleAttached to bones by tendons and is responsible for voluntary

movements of the body.The arrangement of the contractile units along the length of

muscle cells gives them a striped or striated appearance. Cardiac muscle

Forms the contractile tissue of the heart. It is striated like skeletal muscle, but its cells are branched,

interconnecting at specialized junctions that rapidly relay the signal to contract from cell to cell during the heartbeat.

Smooth muscleGets its name from its lack of striations.Type of muscle is found in the walls of the digestive tract, urinary

bladder, arteries, and other internal organs. The cells (fibers) are shaped like spindles. They contract more

slowly than skeletal muscles, but they can sustain contractions for a longer period of time.

Muscle Tissue

Skeletal muscleSkeletal muscle, which is attached to the skeleton

and produces body movements, is made up of a hierarchy of smaller and smaller parallel strands. A muscle consists of bundles of parallel muscle fibers,

and each muscle fiber is a single cell with many nuclei. Each muscle fiber is itself a bundle of smaller myofibrils.A myofibril consists of repeating units called sarcomeres. Skeletal muscle is called striated (striped) muscle because

the sarcomeres produce alternating light and dark bands when viewed with a microscope.

Structurally, a sarcomere is the region between the two dark, narrow lines, called Z lines, in the myofibril.

Functionally, the sarcomere is the contractile apparatus in a myofibril—the muscle fiber’s fundamental unit of action.

Skeletal muscleSarcomere

Composed of regular arrangements of two kinds of filaments:Thin filament

Consists of two strands of the protein actin an two strands of a regulatory protein, coiled around each other.

Light bands at the edge of the sarcomere, within light band are the Z lines that consist of proteins that connect adjuacent thin filaments

Thick filamentContains a staggered array of multiple strands of the protein

myosin. Broad, dark band centered in the sarcomere; they are interspersed

with thin filaments that project toward the center of the sarcomere.

*The specific arrangement of repeating units of thin and thick filaments is directly related to the mechanics of muscle contraction.

Sarcomere

Sliding Filament Model

Sliding-Filament model of muscle contraction:A sarcomere contracts (shortens) when its thin

filaments slide across its thick filaments. In a contracting sarcomere:

The Z lines and the thin filaments have moved toward the middle of the sarcomere.

When the muscle is fully contracted, the thin filaments overlap in the middle of the sarcomere.

Contraction only shortens the sarcomere; it does not change the lengths of the thick and thin filaments.

A whole muscle can shorten about 35% of its resting length when all its sarcomeres contract.

http://www.lab.anhb.uwa.edu.au/mb140/CorePages/Muscle/Images/Mus1ani.gif

Sliding Filament ModelWhat makes the thin filaments slide when a

sarcomere contracts?The key events are energy-consuming interactions

between the myosin molecules of the thick filaments and the actin of the thin filaments.

Parts of the myosin, called heads, bind with specific sites on actin molecules located on the thin filaments.

In a muscle fiber at rest, these sites are covered by a regulatory protein complex of two molecules: tropomyosin and troponin

Stimulation by a motor neuron causes the binding sites to be exposed so that actin and myosis can interact.

Muscle contraction requires calcium ions (Ca2+) and energy (ATP) in order for thick and thin filaments to slide past each other.

Sliding Filament Model Steps: 1. The binding sites on the actin molecule (to which

myosin “heads” will locate) are blocked by a complex of two molecules: tropomyosin and troponin.

2.Prior to muscle contraction, ATP binds to the heads of the myosin molecules, priming them in an erect high energy state. Arrival of an action potential causes a release of

Ca2+ from the sarcoplasmic reticulum. The Ca2+ binds to the troponin and causes the

blocking molecules to move so that the myosin binding sites on the actin filament become exposed.

3.The heads of the cross-bridging myosin molecules attach to the binding sites on the actin filament. Release of energy from the hydrolysis of ATP

accompanies the cross bridge formation.

Sliding Filament Model

Steps (continued…)4. The energy release from ATP hydrolysis causes a

change in shape of the myosin cross bridge, resulting in a bending action (the power stroke). This causes the actin filaments to slide past the

myosin filaments towards the center of the sarcomere.5.Fresh ATP attaches to the myosin molecules,

releasing them from the binding sites and repriming them for a repeat movement. They become attached further along the actin chain (closer to the Z line) as long as ATP and Ca2+ are available.

Sliding Filament ModelThis sequence—detach, extend, attach, pull—

occurs again and again in a contracting muscle.Though we are only looking at one myosin head

in action, a typical thick filament has about 350 heads, each of which can bind and unbind to a thin filament about five times per second.

Some myosin heads hold the thin filaments in position, while others are reaching for new binding sites.

As long as sufficient ATP is present, the process continues until the muscle is fully contracted or until the signal to contract stops.

Animationhttp://www.blackwellpublishing.com/

matthews/myosin.html