IV. Movement Types:
Angular Movements:
Flexion: decrease in the angle of a joint.
Example: the flexion of the elbow moves the forearm towards the upper arm.
Dorsiflexion: flexion of the foot upwards
Example: standing on the heels of your feet.
Plantar flexion: flexion of the foot downwards.
Example: standing on your toes.
Extension: increasing the angle of a joint.
a. Example: the extension of the flexed elbow moves the forearm away from the upper arm.
3. Abduction: movement of a body part laterally away from the midline.
4. Adduction: movement of a body part medially towards the midline.
a. Example: moving your legs together.
B. Circular Movements:
1. rotation: the movement of a body part on its own axis.
1) Example: shaking your head “no”
a. Supination: rotation of the lower arm so that the palm is upward.
b. pronation: rotation of the lower arm so that the palm is downward.
2. circumduction: movement of a body part in a wide circle
a. Example: moving the arm in a circle
3. Inversion: turning the foot such that the sole is inward and towards the midline.
4. Eversion: turning the foot such that the sole is outward.
5. Elevation: to lift a body part up.
a. Example: shrugging your shoulders
6. Depression: lowering a body part down
a. Example: opening the mouth.
V. Muscle Functions:
A. There are 4 functions of muscle in the human body:
1. Muscle contractions oppose the force of gravity
2. Muscle contractions produce movements, allowing us to carry out life functions.
(Examples: breathing, pumping blood, communicating, etc.)
3. Muscles control the body entrances and passages.
4. Muscles generate heat, maintaining body temperature.
IV. Anatomy of a Skeletal Muscle:
Connective tissue (Fascia): extends beyond the muscle to form the tendon.
Epimysium: fascia surrounding the entire muscle.
Deep Fascia: surrounds the epimysium and forms the outer layer of the tendon.
Perimysium: fascia surrounding bundles of muscle fibers. (fascicles)
Endomysium: fascia surrounding/separating individual muscle fibers.
Muscle Fibers:
Myofibril: the contractile unit of a muscle.
Each runs the entire length of the muscle, which may contain thousands of them.
Myofibrils are made of Sarcomeres.
Sarcomere: these are the structures in a muscle cell which contract.
Each sarcomere is separated by a z-line.
Myofilaments: these are responsible for the striations found in muscle cells, and make up sarcomeres.
Actin: the thin filament
Myosin: the thick filament. It contains ‘heads which can bind the actin filament.
VII. Muscle Contraction:
The sliding Filament Model
Normally the actin filament is bound by Troponin and Tropomyosin proteins.
A signal from a nerve comes into the Neuromuscular Junction (NMJ). This signal is transmitted to the muscle cell.
This signal is transmitted through the Sarcolemma, which is the plasma membrane of the muscle cell.
The signal enters the tubes in the sarcolemma, known as the T system. This then comes into contact with the sarcoplasmic reticulum. (SR)
The signal triggers the SR to release Ca+2 into the cell.
The Ca+2 removes Troponin and Tropomyosin from the actin filament.
This allows the myosin heads to bind to actin.
ATP is ‘drained of energy to tightly bind the myosin heads to the actin filament.
As the drained ATP leaves, the myosin heads move, pulling the actin filament to the myosin filament.
The binding of another ATP allows the myosin heads to let go of the actin and be ready to bind actin further down the filament.
Physiology of Muscle Contraction:
All-or-None Law:
When a muscle fiber is stimulated, it either contracts or stays relaxed.
The muscle itself does NOT obey the law. For a strong muscle contraction, many fibers will contract. For a weak one, few muscle fibers will contract.
In extreme circumstances, all the fibers can contract at once. However, this usually permanently damages the muscle.
All of the muscle fibers stimulated by one nerve cell are called a Motor Unit.
The period of time after a stimulus has been received, but before the muscle contracts, has been known as the Latent Period.
This is followed by the contraction and relaxation period.
Muscle twitch: when a single stimulus causes a muscle to contract and then relax.
Summation: when a muscle receives many signals in rapid succession until the muscle reaches tetanus.
Tetanus: the maximal sustained contraction.
Fatigue: when the muscle relaxes even in the presence of a signal. Usually caused by a shortage of ATP.
Oxygen Debt: Exercise quickly uses up ATP. It can be replaced in presence of oxygen. If oxygen is unavailable, the cell undergoes lactic acid fermentation.

This changes the pH, resulting in feeling muscles “burn”.
Once oxygen levels are restored, the lactic acid is converted back into pyruvate.
Rigor Mortis: after death, oxygen and ATP are quickly broken down. Without ATP, the muscles lock in place, resulting in the stiffening of a corpse.
Myoglobin: this heme protein stores oxygen for use in muscle cells. It helps account for the difference between ‘red and ‘white meat.
VIII. Human muscle Action
The origin of the muscle is where the muscle attaches to the stationary bone. The insertion of a muscle is where the muscle attaches to the bone that moves.

Prime Mover: a muscle within a muscle group which does most of the work.
Synergist: muscle which assists the prime mover.
Antagonist: pairs of muscles which work against each other.
Example: biceps brachii and triceps brachii.
Fixor: a muscle which prevents movement and stabilizes the body.
Isotonic contractions result in limb or body movement. Isometric contractions do not result in movement.

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V. Muscle Functions And Functions Of Muscle. (May 31, 2021). Retrieved from