CHAPTER 5Muscular 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 terminologyPrefix myo refers to musclePrefix mys refers to musclePrefix sarco refers to muscle

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

Types of Muscle, cont.

Skeletal Muscle AttachmentsSkeletal Muscle Attachments

Slide 6.5Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

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

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 activityMuscles 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 This state is termed “muscle tone” Spinal reflexes continually activate an alternating

subset of motor neurons. No active movement produced but muscles are

kept firm, healthy, and ready to respond to stimulation.

Helps stabilize joints and maintain posture.

TYPES OF MUSCLE CONTRACTIONS

1-Isotonic contraction

Muscle length changes(shortens) and moves the load.Once tension is sufficient to move a load,

tension remains relatively constant.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

Try to lift your car or push against immovable object or trying to lift 400kg are examples.

Effect of exercise on Muscle 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 respiration3-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.Factors for this include an accumulation of

lactic acid, and the depletion of energy reserves.

Increased oxygen consumption is needed to recover from exercise (paying off an oxygen debt).

Naming Skeletal Muscle

Action

Origin&

Insertion

ShapeNumber

OfOrigins

Size

Location

Direction ofMuscleFibers

SkeletalMuscle

•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)

Triceps (contracted

Biceps (contracted)

Triceps (relaxed)

Types of body movements

Flexion – Movement that decreases angle between 2 bones.

Extension – movement that increases angle between 2 bones

Abduction – movement away from the midline of the body

Muscular System

Adduction – movement towards the midline of the body

Supination – occurs when palms rotate forward or upward

Opposition: moving the thumb to touch the tips of the other fingers

Pronation – occurs when palms rotate downward or posteriorly

Dorsiflexion – standing on heal

Plantar flexion – standing on toes

Axial and Appendicular Muscles

Figure 11–3a

Axial and Appendicular Muscles

Figure 11–3b

Divisions of the Muscular System

1. Axial muscles: position head and spinal column move rib cage 60% of skeletal muscles

2. Appendicular muscles: support pectoral and pelvic girdles support limbs 40% of skeletal muscles

Muscle of anterior abdominal wall RECTUS means parallel

to midline• Rectus Abdominus

TRANSVERSE means perpendicular to midline

• Transversus Abdominus

OBLIQUE means diagonal to midline

• External Oblique• Internal oblique

Muscles that Move the Arm

Figure 11–15a

Muscles that Move the Forearm and Hand

Figure 11–16a

Muscles that Move the Forearm and Hand

Figure 11–16b

The Intrinsic Muscles of the Hand

Figure 11–18b

Extensors of the Knee

the quadriceps femoris: 3 vastus musclesrectus femoris muscle

Flexors of the kneeThe hamstring groupo Semitendinosiso Semimembrenosiso Biceps femoris

Muscles that Move the Leg

Figure 11–20b, c

Muscles that Flex the Leg (hamstring)

Figure 11–20a

Muscles that Move the Foot and Toes

Figure 11–21a, b

Muscles that Move the Foot and Toes

Figure 11–21c, d

The Intrinsic Muscles of the Foot

Figure 11–22a

The Intrinsic Muscles of the Foot

Figure 11–22b, c

Effects of Aging on the Muscular System

1. Skeletal muscle fibers become smaller in diameter

2. Skeletal muscles become less elastic:

develop increasing amounts of fibrous tissue (fibrosis)

3. Decreased tolerance for exercise4. Decreased ability to recover from

muscular injuries