THE MUSCULAR SYSTEM

Dr Idara

Muscular System

Muscles are responsible for all types of body movement

3 basic muscle types are found in the body. They are:

Skeletal muscle Cardiac muscle Smooth muscle

Characteristics of Muscles

Muscle cells are elongated (muscle cell = muscle fiber)

Contraction of muscles is due to the movement of microfilaments

All muscles share some terminology Prefix myo refers to muscle Prefix mys refers to muscle Prefix sarco refers to flesh

Muscle histology (cont.)

Scaterred throughout the sarcoplasm is the sarcoplasmic reticulum

It stores Calcium ions The sarcoplasm contains myoglobin

Red pigmented protein related to Hemoglobin that carries oxygen

Along entire length are myofibrils Myofibrils made of protein filaments

Come in thick and thin filaments

Comparison of Types of Muscle

Types of Muscle, cont

Skeletal Muscle Characteristics

Most attach to bones by tendon

Cells are multinucleate

Striated—have visible binding

Voluntary Cells surrounded &

bundled by connective tissue

Smooth Muscle Characteristics

Picture sub A Has no striations Spindle-shaped

cells Single Nucleus Involuntary—no

conscious control Found mainly in

the walls of hollow organs

Characteristics of Cardiac Muscle

Picture sub B Has striations Usually has a

single nucleus Joined to another

cardiac muscle cell Involuntary Found only in the

heart

Functions of Skeletal Muscle

Produce Movement Maintain posture Stabilize joints Generate Heat

Sites of Muscle Attachment

Bones Cartilage Connective tissue

coverings

Muscle Fibers blend into a connective tissue attachment

Tendon—cordlike structure Aponeurosis—sheet-like

structure Properties of Muscle

Irritability – ability to receive and respond to a stimulus

Contractibility – ability to shorten when an adequate stimulus is received

Extensibility – ability to lengthen when an adequate stimulus is received

Elasticity – ability to return to normal shape

To Note:

A muscle cell is also called a muscle Fiber

A discrete bundle of muscle cells is called a Fascicle

The thin connective tissue that surrounds each muscle cell is called Endomysium

The connective tissue that surrounds each Fascicle is called Perimysium

The connective tissue surrounding the entire muscle is called Epimysium

Anatomy of a Muscle Cell

Naming Skeletal Muscles

Direction of Muscle Fibers

Location Structure near which

muscle is found FRONTALIS = near

FRONTAL bone OCCIPITALIS =

near OCCIPITAL bone

Size Relative Size of Muscle and

location MAXIMUS = largest

Gluteus Maximus MEDIUS = middle

Gluteus Medius MINIMUS = smallest

Gluteus Minimus LONGUS = longest

Fibularis Longus BREVIS = short

Fibularis Brevis TERTIUS = shortest

Fibularis Tertius

Number of Origins Number of tendons

of origin BICEPS = Two

Biceps Brachii Biceps Femoris

TRICEPS = Three Triceps Brachii

QUADRICEPS = Four

Quadriceps Femoris

Shape Relative Shape of

the Muscle DELTOID =

triangular shape Δ TRAPEZIUS =

trapezoid shape SERRATUS = saw-

toothed ♒ RHOMBOIDEUS =

rhomboid shape TERES = round ○

Origin & Insertion Origin –

attachment to an immoveable bone

Insertion – attachment to a movable bone

ILIO COSTALIS= attaches to the ilium & ribs (costal = ribs)

Types of Muscle--Actions

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

Head & Neck Muscles

Key Muscles of Facial Expression

Smiling Muscles Orbicularis Oculi Nasalis Levator Labii

Superioris Levator Anguli

Superioris Zygomaticus Risorius

Frowning Muscles Frontalis Orbicularis Oris Depressor Anguli

Oris Depressor Labii

Inferioris Mentalis Platysma

Frontalis - Used in frowning

Orbicularis Oculi – Surrounds the eye, eyelid and orbit. Used to close the eyes

Zygomaticus - Used in smiling

Buccinator- A flat muscle of the cheek, draws in

the cheek and puffs up the cheeks. Called the Trumpeter’s Muscle.

Orbicularis Oris- surrounds the mouth, closes the lips when contracted and used for whistling and kissing.

Masseter- Is the Prime mover for jaw closure. Also used for chewing.

Temporalis - is the synergist for jaw closure and assists with chewing.

Muscles of the Axial Skeleton

Muscles of the Axial Skeleton

Intrinsic Muscles Erector Spinae:

maintain posture of back/extension

Spinalis Longissimus Iliocostalis

Oblique Muscles: rotation of the vertebrae

Semispinalis Multifidus Rotatores

Muscles of Quiet Respiration

Diaphragm External Intercostals Internal Intercostals—

deep breaths Abdominal Muscles

External Obliques Internal Obliques Transverse Abdominus Rectus Abdominus

Quadratus Lumborum – Fixes the lower rib during respiration and cause lateral flexion of the vertebral column.

Diseases and Disorders of the Muscular System

Cerebral Palsy: This disorder is characterized by paralysis and or weakened muscles due to loss of muscle tone.

It can be caused due to lack of oxygen to the region of the motor region of the cerebrum of the brain which controls conscious control of muscles.

This is often attributed to complication during birth.

Others Myalgia: Muscle pain due to strain, tearing

of muscle fibers. It also is a symptom of an immune response along with a fever.

Myositis: Inflammation of muscle tissue due to injury or disease.

Charley Horse (fibromyositis): Inflamation of muscle tissue and the tendons associated with that muscle due to injury (tear or severe bruising- contusion).

Cramps: Painful, involuntary muscle contraction, typically caused by fatigue or strain.

Muscular Dystrophy

A Series of genetic disorders characterized by the atrophy or wasting away of skeletal muscle.

Duchenne Muscular Dystrophy is the most common and affects primarily males.

X- linked recessive mutation i.e. mother’s transmit disease to their sons.

Onset before 5 years of age.Deletion of the dystrophin gene

Becker’s Muscular Dystrophy

Onset in adolesence or early adulthood.

Mutated dystrophin gene