CHAPTER 5 Muscular System Muscles are responsible for

CHAPTER 5 Muscular System ¢ ¢ Muscles are responsible for all types of movement Characteristics of Muscle -All Muscle cells are elongated (muscle cell = muscle fiber) -All can contract due to the movement of microfilaments -All muscles share some terminology Prefix myo refers to muscle l Prefix mys refers to muscle l Prefix sarco refers to muscle l

Types of Muscle Three basic muscle types are found Skeletal muscle Cardiac muscle Smooth muscle

Types of Muscle, cont.

Skeletal Muscle Attachments · Sites of muscle attachment · Bones · Cartilages · Connective tissue coverings as skin · Muscles end into a connective tissue attachment which may be: · Tendon – cord-like structure · Aponeuroses – sheet-like structure Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 6. 5

Neuromuscular junction(myoneural junction): the point where a motor neuron joins muscle fibers. Motor unit is a motor neuron and all the muscle fibers it innervates(may be few or hundreds). All or none law : with adequate stimulation, a muscle fiber (cell) will contract to its fullest extent or not at all. So there is no partial contraction of muscle fiber.

Skeletal muscle activity Muscles have two special functions: 1 -Irritability : the ability to receive and respond to stimulus. 2 -Contractility : the ability to shorten -Muscle cell must be stimulated by nerve impulse to contract. -There is a gap (synaptic cleft) between the nerve &muscle cell ¢ This gap is crossed by a chemical transmitter called Acetylcholine (Ach). ¢ Sarcolemma becomes temporarily permeable to sodium which enter the cell so leads to depolarization of the cell. ¢ This upset generates an electric current called action potentiual which is unstoppable leading to muscle fiber contraction.

MUSCLE TONE ¢ Relaxed skeletal muscles are always slightly contracted l This state is termed “muscle tone” l Spinal reflexes continually activate an alternating subset of motor neurons. l No active movement produced but muscles are kept firm, healthy, and ready to respond to stimulation. l Helps stabilize joints and maintain posture.

TYPES OF MUSCLE CONTRACTIONS 1 -Isotonic contraction Muscle length changes(shortens) and moves the load. l Once tension is sufficient to move a load, tension remains relatively constant. l Bending the knee, rotating the arms and smiling are examples

2 -ISOMETRIC CONTRACTIONS ¢ Muscle length remains constant Muscle attempts to move a load greater than the force the muscle is able to develop l Try to lift your car or push against immovable object or trying to lift 400 kg are examples. l

Effect of exercise on Muscles are no exceptions to the saying –use it or lose it¢ Regular exercise increases muscle size, strength and endurance - Isotonic contraction (Aerobic exercise) results in stronger muscle with greater resistance to fatigue. No increase in size but better heart &lungs. -Isometric(Resistance)contraction: Require little time. No special equipment. Leads to enlargement of muscle cell without increase in their number (physiologic hypertrophy) ¢

Energy for muscle contraction ATP store in the muscle supplies energy ONLY for 4 -6 seconds ¢ ATP then comes from 1 -direct phosphorylation of ADP ¢ 2 -Anaerobic respiration 3 -aerobic mechanism (oxidative phosphorylation

Muscle fatigue. ¢ Muscle fatigue occurs when an exercising muscle can no longer respond to the same degree of stimulation with the same degree of contractile activity. l Factors for this include an accumulation of lactic acid, and the depletion of energy reserves. l Increased oxygen consumption is needed to recover from exercise (paying off an oxygen debt).

Naming Skeletal Muscle Direction of Muscle Fibers Location Action Skeletal Muscle Origin & Insertion Size Shape Number Of Origins

• Naming Skeletal Muscles According to Function NAME ACTION EXAMPLE FLEXOR Decrease angle at a joint Flexor Carpi Radialis EXTENSOR Increase angle at a joint Extensor Carpi Ulnaris ABDUCTOR Move bone away from midline Abductor Pollicis Longus ADDUCTOR Move bone toward midline Adductor magnus LEVATOR Produces upward movement Levator Scapulae DEPRESSOR Produces downward movement Depressor Labii Inferioris SUPINATOR Turn palm upward/anteriorly Supinator PRONATOR Turn palm downward/posteriorly Pronator Teres

Types of Skeletal Muscle ¢ ¢ Prime mover (Agonist) – muscle with the major responsibility for a certain movement Antagonist – muscle that opposes or reverses a prime mover Synergist – muscle that aids a prime mover in a movement and helps prevent rotation Fixator – stabilizes the origin of a prime mover

Biceps (relaxed) Biceps (contracted) Triceps (contracted Triceps (relaxed)

Types of body movements l Flexion – Movement that decreases angle between 2 bones.

l Extension – movement that increases angle between 2 bones

l Abduction – movement away from the midline of the body

Muscular System l Adduction – movement towards the midline of the body

l Supination – occurs when palms rotate forward or upward

Opposition: moving the thumb to touch the tips of the other fingers l Pronation – occurs when palms rotate downward or posteriorly

l Dorsiflexion – standing on heal l Plantar flexion – standing on toes

Axial and Appendicular Muscles Figure 11– 3 a

Axial and Appendicular Muscles Figure 11– 3 b

Divisions of the Muscular System 1. Axial muscles: l l l 2. position head and spinal column move rib cage 60% of skeletal muscles Appendicular muscles: l l l support pectoral and pelvic girdles support limbs 40% of skeletal muscles

Muscle of anterior abdominal wall l RECTUS means parallel to midline • Rectus Abdominus l TRANSVERSE means perpendicular to midline • Transversus Abdominus l OBLIQUE means diagonal to midline • External Oblique • Internal oblique

Muscles that Move the Arm Figure 11– 15 a

Muscles that Move the Forearm and Hand Figure 11– 16 a

Muscles that Move the Forearm and Hand Figure 11– 16 b

The Intrinsic Muscles of the Hand Figure 11– 18 b

Extensors of the Knee the quadriceps femoris: 3 vastus muscles l rectus femoris muscle l Flexors of the knee The hamstring group o Semitendinosis o Semimembrenosis o Biceps femoris

Muscles that Move the Leg Figure 11– 20 b, c

Muscles that Flex the Leg (hamstring) Figure 11– 20 a

Muscles that Move the Foot and Toes Figure 11– 21 a, b

Muscles that Move the Foot and Toes Figure 11– 21 c, d

The Intrinsic Muscles of the Foot Figure 11– 22 a

The Intrinsic Muscles of the Foot Figure 11– 22 b, c

Effects of Aging on the Muscular System 1. 2. Skeletal muscle fibers become smaller in diameter Skeletal muscles become less elastic: l 3. 4. develop increasing amounts of fibrous tissue (fibrosis) Decreased tolerance for exercise Decreased ability to recover from muscular injuries