Topic 11.2 – Muscles & Movement

Human movement requires that several

different organs and structures work

together.

Bones provide a rigid structure to

support the body and act as levers for

movement. They also allow storage of

minerals (Ca & P) for use in the body.

Blood cells are formed in the bone

marrow.

Joints, or arthrosis, are points where two

or bones contact each other. They are

connected by ligaments.11.2.1

Muscles are bundles of fibers

that create the force necessary

for movement. They are

attached to two bones and

contract.

Tendons are cords of dense

connective tissue that anchor

muscles to bones.

Nerves provide the impulses

that result in muscle

contractions in addition to

sensing limb position.11.2.1

11.2.1

Hinge joints are joints that only allow motion in one place (like

a door opening and closing). The elbow joint is an example

of this.

11.2.2

Joint Part Function

Cartilage Reduces friction at joints

Synovial FluidLubricant that reduces friction and

provides nutrients to cartilage cells

Joint CapsuleEncloses synovial cavity, surrounds

joint and connects the two bones

Biceps Contracts to bend arm (flexion)

Triceps Contracts to straighten arm (extension)

Humerus Upper arm bone

Radius Lever bone for bicep

Ulna Lever bone for tricep

Elbow joint structures

11.2.3

11.2.2

Joints that contain a synovial cavity are referred to as synovial

joint.

11.2.3

Antagonistic pairs of muscles

are muscles that produce

movement in different

directions.

Flexor muscles bend the limb at

the joint. Extensor muscles

straighten limbs at the joint.

In an elbow, the biceps is the

flexor and the tricep is the

extensor.

11.2.3

Exercise:

• Bend your arm in a flexion. Point your elbow upwards

vertically. Raise your hand vertically above your head. This

is a true concentric contraction of the Triceps

• Pick up a heavy object in concentric Biceps flexion. Now

lower and straighten your arm. You should feel your

Biceps contracted but Triceps relaxed. That an eccentric

contraction of the Biceps This just shows how complex

movement can be!

11.2.3

Ball and socket joints are diarthrotic joints (free moving) that

allow movement in many directions, including rotation. The

hip joint is an example of this.

The hip joint acts as

the fulcrum while

the femur is the

lever.

Quadriceps are the

flexor and the

hamstring is the

extensor.

11.2.4

Ball and socket joints are diarthrotic joints (free moving) that

allow movement in many directions, including rotation. The

hip joint is an example of this.

11.2.4

Elbow vs. Knee Joint

11.2.4

Elbow vs. Knee Joint

HIP JOINT KNEE JOINT

Free moving Free moving

Angular motions in many

directions and rotational

movements (ball and

socket)

Angular motion in one

direction (hinge joint)

Flexion, extension,

abduction, adduction,

circumduction and rotation

Flexion and extension

Ball-like structure fits into a

cup-like depression

Convex surface fits into

a concave surface

11.2.4

Striated muscles (skeletal muscle) are responsible for voluntary

skeletal movement. They are made up of bundles of muscle

fibers (cells) that contain multiple nuclei and mitochondria.

11.2.5

The plasma membrane of a muscle fiber is called the

sarcolemma and the cytoplasm called the sarcoplasm.

Myofibrils within the sarcoplasm are surrounded by a fluid-

filled system of sacs called the sarcoplasmic reticulum.11.2.5

Myofibrils are rod-shaped bodies that run parallel along the

length of muscle fiber cells. They give striated muscles their

banded pattern and consist of sarcomeres.

11.2.5

11.2.5

Sarcomeres are the units that allow for muscle movement and

are made of actin and myosin filaments.

• Thick myosin filaments (red) have heads and are located

between thin actin filaments. Myosin and actin alternate.

• The overlapping pattern of actin and filament results in the

light/dark banding seen in striated muscle.

11.2.6

Sarcomere Banding

• A band = extend the entire length of myosin filaments

• H band = only myosin, no actin (within A band)

• M line = supporting protein that holds myosin together

• I band = only actin, no myosin

• Z lines = edges of sarcomeres

11.2.6

11.2.6

Sarcomere Banding

Z line Z lineM line

A

H II

11.2.6

Actin is thin filament whose molecules form a helical

structure. It contains myosin-binding sites that are regulated

by two regulatory proteins, tropomyosin and troponin.

11.2.6

Myosin is thick filament with myosin heads containing actin-

binding sites. The heads are called cross-bridges and contain

ATP-binding sites and ATPase enzymes.

11.2.6

11.2.6

Sliding filament theory explains that muscles contract when

actin filaments slide over myosin filaments. The filaments

themselves do not shorten, but sliding causes the sarcomere to

change length. Occurs in many steps.

11.2.7

Sliding Filament Theory

1. A motor neuron carries an action potential to the

neuromuscular junction.

2. Motor neuron releases acetylcholine (Ach) into the

synapse (space between neuron and sarcolemma).

3. Ach binds to

sarcolemma

receptors, which

triggers opening

of sodium ion

channels.

11.2.7

Sliding Filament Theory

4. Na+ ions move into sarcoplasm and generate a muscle

action potential.

5. Muscle action potential is carried along the sarcoplasm by

the T tubules (ivaginations in the surface).

11.2.7

Sliding Filament Theory

6. After muscle potential has been generated,

acetylcholinesterase breaks down Ach to prevent another

potential from being formed (one signal = one potential)

11.2.7

11.2.7

Sliding Filament Theory

6. After muscle potential has been generated,

acetylcholinesterase breaks down Ach to prevent another

potential from being formed (one signal = one potential)

11.2.7

Sliding Filament Theory

7. Muscle action potential results in release of Ca+ ions from

the sarcoplasmic reticulum into the sarcoplasm.

8. Ca+ ions bind to actin-bound troponin, which exposes the

myosin-binding site.

11.2.7

Sliding Filament Theory

9. ATPase bound to myosin head splits ATP and releases

energy. This causes the myosin heads to ‘cock.’

10. With the help of tropomyosin, the myosin heads bind to

the binding-sites on the actin, which promotes

disassociation of ADP.

11.2.7

Sliding Filament Theory

11. Loss of energy causes the myosin heads to stroke towards

the center of the sarcomere. This moves the actin inwards.

12. ATP binds to the myosin resulting in the detachment of

myosin to actin.

13. If no additional action

potentials are received, the

Ca+ levels in the sarcoplasm

and the troponin-tropomyosin

moves to its original

position, blocking

the myosin binding

sites. Muscle relaxes.

11.2.7

11.2.7

11.2.7

11.2.7

11.2.7

Post-mortem, cells lose the ability to

produce ATP so myosin heads lose the

ability to detach from the actin filaments.

11.2.7

In electromicrographs, band size can be used to determine

whether a muscle is in a relaxed or contracted state.

Notice that the size of the A band does not change. The

myosin and actin filaments are sliding past each other, but

neither is shortening. The sarcomere DOES shorten, though.

11.2.8

11.2.8