11.2 Movement

KINESIOLOGY: The study of movement of the human body

What happens when somebody moves? Your brain sends an impulse (an action potential) through a nerve to a muscle to tell it to

contract. Muscles are connected to bones by tendons. When a muscle contracts, it will move the bone.

BONES

Rigid structures for anchoring muscles

They contain several different tissues and therefore are organs.

Functions: provide a hard framework to support the body Protect vulnerable softer tissues and organs Act as levers so that body movement can occur Form blood cells in bone marrow Storage of minerals (ex: calcium and phosphorus)

Exoskeletons Some animals do not have bones but have exoskeletons that provide a similar function. Exoskeletons are external skeletons that surround and protect most of the body surface of

crustaceans, insects, and spiders

Levers Bones and exoskeletons facilitate movement by anchoring muscles and acting as a lever. Muscles are attached to the outside of bones and the inside of exoskeletons A lever is a rigid rod (the bone) that turns about a pivot (usually a joint). Levers change the size and direction of forces.

MUSCLES & TENDONS

Skeletal Muscles are attached to bones

Tendons are what attach muscles to bones

Tendons are cords of dense connective tissue

Muscles provide the force necessary for movement by shortening the length of their fibres.

Antagonistic Muscle Action

Muscles work in antagonistic pairs to achieve movement When one muscle contracts, the other relaxes

When the biceps contract, the tendon pulls on the bone pulling the lower arm up. The triceps are relaxed

When the triceps contract, it causes the bones to straighten. The bicep

s are relaxed.

Antagonistic Muscle Pairs in Insect Legs

When the grasshopper prepares to jump:

FLEXING: The flexor muscles will contract bringing the tibia and tarsus in a “Z” position. The extensor muscles are relaxed.

EXTENDING: The extensor muscles contract to extend the tibia and produce a powerful

propelling force.

JOINT Also called an articulation or arthrosis

The point where 2 or more bones contact one another

Joints cause mobility and hold the body together

Most joints include: Bones Ligaments Muscles

Tendons nerves

Annotate a Human Elbow Joint

Elbow Joint Part Description

Spongy Bone

Cartilage

Joint Capsule

Synovial Fluid

Synovial Membrane

Ligaments

Biceps

Triceps

Humerus

Radius

Ulna

The elbow joint is called a synovial joint because of the presence of the synovial cavity. There is a rich supply of blood to joints. If blood vessels supplying the joint gets damaged and there is local bleeding, it may result in

swelling of the area

Joint Terms Flex and Extend = ex: movement that moves your leg back and forth (like a pendulum)

Flexion = decrease the angle between the connecting bones Extension = increase the angle between the connection bones

Abduction and adduction = moving your leg sideways (away from the center of the body) Abduction = bones moves away from body’s midline Adduction = bones move toward body’s midline

Rotation = bone moves along its own longitudinal axis

Hinge Joints Provides an opening-and-closing type of movement like the action of a

door This movement is in one direction – flex and extend Ex: the elbow joint, the knee joint

Ball and Socket Joints Allows for movement in several directions

Flex and extend Abduction and adduction Rotational movement

Ex: hip joint the head of the femur is ball shape and fits into a

cup like depression of the hip bone

Joints and Movement The structure of the joint (including the joint capsule and ligaments) determine the movements

that are possible.

Knee Joint Hip Joint

Type Synovial JointHinge Joint

Synovial JointBall and Socket

Role Involved in movement of the leg and required for walking

Involved in the movement of the leg and required for walking

Possible Motions

Flex and ExtendSmall amount of rotation

Flex and ExtendAbduction and AdductionRotation

Range of Movement

Movement in one direction Movement in many directions (multiaxial)

Types of Muscle Human body has 3 types of muscles: cardiac muscle, smoothe muscle, and skeletal muscle (also

known as striated muscle

Skeletal Muscle/Striated Muscle

Muscle associated with bones and therefore involved in movement Like all other body tissues, muscles are made up of cells. Muscle cells are called muscle fibres They are elongated in shape The arrangement of proteins within them create a banded appearance or stripes under a

microscope which is why is it called striated muscle

Parts of a Muscle Fibre Each muscle cell was originally many cells fused together, which is why a muscle cell has many

nuclei. Sarcolemma: membrane surrounding the muscle cell

Sarcoplasm: the cytoplasm of the muscle cell

Within the sarcoplasm there are multiple mitochondria for ATP production (because muscle contractions require a lot of energy)

Sarcoplasmic Reticulum: membrane found within the sarcoplasm (similar to the ER) Stores and releases calcium ions into the sarcoplasm which will trigger a muscle

contraction Myofibrils:

Thin fibres inside the muscle cell

There are many myofibrils in a muscle fibre Create the striated (striped) pattern of light and dark skeletal muscles Contain 2 types of myofilaments: myosin and actin which are made of proteins Each myofibril is made up of contractile sarcomeres

Sarcomere: a functional unit of the muscle (a segment of a myofibril)

Sarcromere

A sarcomere is found between two Z-lines Thin actin filaments form the I band They are attached to the Z line Thick myosin filaments are found in the A band In the dark regions, myosin and actin overlap In the gray H zone, only myosin is present

Myofilaments - Myosin Myosin filaments contain several myosin strands

bundled together Each myosin strand has a “hook” or a “head” that

binds to actin. The ends without “heads” are the “tails” and they

are found within the H zone

Myofilaments - Actin Actin filaments contain strands of actin and 2 proteins: TROPOMYOSIN and TROPONIN 2 strands of tropomyosin wind around the actin filament covering the binding site for the

myosin hooks This prevents the muscle from contracting

Sliding Filament Theory Actin and myosin slide over each other to make the muscle shorter (actin and myosin stay the

same size!) Little “hooks” on the myosin filaments attach to the actin and

pull them closer to the center of the sarcomere This shortens the sarcomere and the overall length of the

muscle fibre muscle contraction Myosin then releases the actin and repeats the hooking and

pulling action further down the actin. This is done with ATP energy (from the mitochondria!) As the filaments slide over each other, the H bands

disappears and the I band shortens

Which of the following diagrams shows a relaxed muscle and which shows a contracting muscle?

Muscle Contraction1. When you want to start a muscle contraction, a nerve impulse arrives at the muscle2. The action potential causes the sarcoplasmic reticulum to release calcium ions into the

sarcoplasm3. The Ca2+ attach to troponin (which is attached to tropomyosin) causing tropomyosin to uncover

the binding sites for the myosin hooks.

4. The myosin hooks will have an ATP molecule bonded to it already. The ATP will hydrolyse into ADP and Pi (but will still be attached to the myosin hook)

5. The myosin hooks can now bind to the binding sites on the actin filament, forming cross-bridges.

6. The ADP and Pi dissociate from the cross-bridge and the myosin hooks bend, pulling the actin filaments toward the M line. This is called the power stroke. It causes the myofilaments to slide over each thus the muscle fibre contracts

7. A new ATP molecule will attach to the myosin hook and the myosin will detach from the binding site.

8. The process may repeat with the hooks attaching to binding sites further down the actin filament.

Muscle Relaxation Contraction cycles will continue as long as ATP is available and Ca2+ is present in the sarcoplasm When the nerve impulse stops, Ca2+ move back into the vesicle of the sarcoplasmic reticulum by

active transport This causes the binding sites on the actin to be covered again (so myosin cannot bind) The muscle will relax.

Cardiac Muscle Cells (p 685) The structure of cardiac muscle cells allows for propagation of stimuli through the heart wall. Remember, cardiac muscle tissue is unique. It is also striated in appearance, and the arrangement of myofilaments is similar to skeletal

muscle.

How do they differ from skeletal muscle fibres?

The cells are Y-shaped. There is a specialized junction called an intercalated disc where the end of one cell meets the

end of another cell The intercalated disc consists of a double membrane containing gap junctions which are

channels that provide a connection between the cytoplasm of adjacent cells. This allows for the rapid movement of ions from one cardiac cell to the next, with low electrical

resistance.

So, their Y-shape and gap junctions allows them to be electrically connected This means a wave of depolarization can easily pass form one cell to a network of other cells

leading to synchronization of muscle contraction allowing for both atria or both ventricles to contract simultaneously as if it was one large cell.