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The Muscular System

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There are four characteristics associated with muscle tissue:

A. Excitability

B. Contractility

C. Extensibility

D. Elasticity

- Tissue can receive & respond to stimulation

- Tissue can shorten & thicken

- Tissue can lengthen

- After contracting or lengthening, tissue always wants to return to its resting state

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The characteristics of muscle tissue enable it to perform some important functions, including:

I. Movement – both voluntary & involuntary

II. Maintaining posture

III. Supporting soft tissues within body cavities

IV. Guarding entrances & exits of the body

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Anatomy of the Muscular System

• Origin Muscle attachment that remains fixed

• Insertion Muscle attachment that moves

• Action What joint movement a muscle producesi.e. flexion, extension, abduction, etc.

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• Muscles in the body rarely work alone, & are usually

arranged in groups surrounding a joint.

• group of muscle that contracts to create an action in

same direction called agonist or prime mover

eg( flexor muscles )

• A muscle that helps the agonist is a synergist

• A muscle that act opposite to each other called

antagonist eg (flexor and extensor muscles)

Types of muscle

Skeletal Cardiac Smooth

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Skeletal muscle

• Look striped or striated

• Maintain posture

• Facilitate movement.

• Found in antagonistic pairs

• Joined to bones by tendons

Cardiac Muscle

• Cardiac muscle-found only in the heart

• Involuntary rhythmic contraction

• Striations, branched

• Contracts about 70 times a minute every day of your life.

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Smooth muscle

• Found in the viscera.

• Elongated, spindle shaped fiber with

single nucleus

• Involuntary movement of internal organs

• Found in longitudinal or circular

arrangement

• Muscles contract in circular and

longitudinal manner (peristalsis)

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Examples of Skeletal muscles

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Muscles of the facial expression

The platysma muscle lies in the superficial fascia.

• Its attach inferiorly to the fascia covering deltoid and pectoralis muscle

• Superiorly, the platysma muscle is attached to the mandible, skin of the cheek, angle of the mouth, and orbicularis oris muscle.

• It acts as depressor to the mandible.

Occipitofrontalis muscle lies in the scalp it consist of two parts frontal part lies in the fore head occipital part lies in the occipital region of the scalp it is action is to elevate eye brows and wrinkle the fore head

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Orbicularis oculi muscle is circular muscle that surround (encircle) the eye it close the eye

orbicularis oris it surround the mouth it lies in the lips It is the sphincter of the mouth ( it close the lips)

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Buccinator muscle it lies in the cheek It compresses the cheek against the teeth, keeping food close during chewing.( it return the food back to the oral cavity)

Buccinator

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Clinical CorrelationFacial Nerve

Bell's palsy is a sudden loss of control of the muscles of facial expression on one side of the face. The patient presents with drooping of the mouth and inability to close the eyelid on the affected side.

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MUSCLES OF MASTICATIONThere are four paired muscles of mastication:

1. Masseter

2. Temporalis

3. Medial pterygoid

4. Lateralpterygoid

they act together to open and close the mouth by elevating and depressing the mandible during mastication or chewing

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Masseter: Origin: Zygomatic Arch.

Insertion: Lateral surface of the ramus of the mandible.

Action: The masseter has two actions.:

elevation of the mandible combined with retrusion.

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Temporalis:Origin: fan-shaped on the side of the skull. It covers the majority of the temporal bone and lesser portions of the frontal and parietal bones.

Insertion: The temporal muscle inserts on the coronoid process of the mandible.

Action: The temporal muscle acts in unison with the masseter and medial pterygoid muscles to close the jaws. Very importantly, it also helps to retrude or pull back the mandible.

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Medial and lateral Pterygoid:Origin: from sphenoid bone.

Insertion: in to the mandible.

Action:

Fibers of medial pterygoid run upward downward so it pull the mandible up ward(elevation)

Fibers of lateral pterygoid run horizontal( transversely) so it pull the mandible forward.

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Sternocleidomastoid Muscle The Sternal head arises from the sternum.

The Clavicular head arises from the clavicle.

The muscle inserted into the mastoid process.

The function of this muscle is to rotate the head to the opposite side

When acting together it flexes the neck and extends the head..

Sternocleidomastoid

trapezius

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The Trapezius Muscle • Trapezius muscle is triangular it lies on the back.

• It has three parts, each of which has a distinctly different action:

1. Superior part of the trapezius muscle elevates the scapula.

2. Middle part of the trapezius muscle retracts the scapula.

3. Inferior part of the trapezius muscle depresses the scapula.

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The Deltoid Muscle• has large bulk and lies on

the lateral aspect of the shoulder

• it cover the shoulder• The deltoid muscle abducts

the arm• it is common site of

intramuscular injection

injection should be in the lower part of deltoid to avoid damage of axillary nerve that lies deep to the upper 3rd of the muscle

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Iliopsoas has two parts Psoas majorIliacus The two parts unit to form iliopsoas tendonThe iliopsoas muscle flexes the thigh at the hip joint

when the trunk is stabilized at erect position

flexes the trunk against gravity when the body is supine.

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• The quadratus lumborum muscles fill the space between 12th ribs and the iliac crest on both sides of the vertebral column.

• The muscles depress 12th rib and contribute to lateral flexion of the trunk.

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Intercostal Muscles• The interval between adjacent ribs is called the intercostal

space. • Three layers of muscle fill the intercostal space.• From superficial to deep, the three layers of muscle are • First layer: external intercostal muscle• 2nd layer internal intercostal muscle• 3rd layer innermost intercostal muscle ,tranversus and

subcostalis .• they produce the respiratory movement • external intercostal ( inspiration)• internal intercostal and inner most ,tranversus and subcostalis

(expiration)

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411111111

Subcostalis muscles

Transverse thoracic

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DIAPHRAGM • The diaphragm is a thin musculotendinous

structure that separates the thoracic cavity from the abdominal cavity

It is attached peripherally to:

1. the sternum;

2. the costal margin of the thoracic wall

3. vertebrae of the lumbar region.

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From these peripheral attachments, muscle fibers insert centrally into the central tendon

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action (function) of diaphragm

it is the main respiratory muscle 70%

it mainly inspiratory

it also compress the abdomen to increase intra-abdominal pressure for abdominal straining(defecation, urination, vomiting, sneezing, cough, labor and lifting heavy weights)

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Muscles Of Anterior Abdominal Wall

• Three flat muscles external oblique, internal oblique, and transversus abdominis form most of the anterolateral abdominal wall.

• The rectus abdominis muscle anteriorly. • their action is to compress the abdomen to

increase intra-abdominal pressure for abdominal straining and moving the trunk.

External Oblique Abdominis

(EOA)

Internal oblique abdominis

Transversus Abdominis

rectus abdominis