MUSCLEDr. Seyed Morteza Mahmoudi,

MBBS

For the students of Gulf Medical University, Ajman, PharmD

LECTURE 21

MUSCULAR SYSTEM

Dr. Seyed Morteza Mahmoudi, MBBSGulf Medical University, Ajman

LEARNING OBJECTIVE

• Define muscle

• Understand the gross and microscopic structure of muscle

• What are the various classifications of muscles?

•What are muscles?•What are the types of muscles?•What are their functions?

• There are approximately 639 skeletal muscles in the human body.

Functions of skeletal muscle 1. Movement:

2. Support and posture maintain a constant state of slight contraction – muscle tonus.

3. Heat production: The contraction of skeletal muscle involves the production of energy, the by-product of which is heat.

Functions

•Prime movers- chief muscle for primary movement

•Antagonists-opposing action of prime mover

•Fixators (increase tone but not movement) eg shoulder girdle to trunk muscles for deltoid to act.

•Synergists –acting on intermediate joints to prevent unwanted movements eg.. Flexor and extensors of carpus on wrist to facilitate efficient movement of digits.

Visceral muscles are smooth and without banding.

They have short fibres and single cell nuclei.

These are involuntary muscles

Sites •Walls of blood vessels and viscera (organs in the abdominal cavity).

•Sphincter & dilator pupillae

•Orbitalis muscle in orbit and Muller’s muscle in upper eyelid

•Dartos muscle in scrotum

•Arrector pilorum of hair follicle.

•Myoepithelial cells in glands

A muscle has 2 attachments•Origin- the attachment that moves the least•Insertion- the attachment that moves the most•Belly- fleshy part of a muscle•Tendon- end of a muscle that is attached to bones, cartilage or ligaments•Aponeuroses- a flattened tendon•Raphe- interdigitation of tendinous ends of a flat muscle

MUSCLES• The red flesh of the body that are the

specialized contractile cells

• The parts of a muscle are its:

OriginMuscle attachment that remains

fixed

InsertionMuscle attachment that moves

Belly

Fleshy and contractile part of a muscle

ActionWhat joint movement a muscle produces i.e. flexion, extension, abduction etc.

origin

belly

insertion

• Muscles are joined to bone by tough connective tissue called TENDON

CLASSIFIED

i)Voluntary muscle-under one’s control and Involuntary muscles-not under willful control

ii)Striated muscle-appears striated under microscope; Smooth/unstriated- appears unstriped/unstriated

iii)Somatic muscle- makes up the body wall and limbs.Visceral muscles- muscular component of hallow organs and blood vessels.

Type I slow fibers of skeletal muscle

Type II fast fibers of skeletal muscle

Intermediate fibers of skeletal muscle

Slow tonic specially designed for postural muscles, red in colour due to high concentration of myoglobin and rich in mitochondria and oxidative enzymes

Fast tonic contractions needed for body movement, pale colour rich in glycogen and phosphorylases

Varient of Type II

Highly resistance to fatigue due to well-developed in aerobic respiration

Easily fatigue Resistant to fatigue

Flat :eg: external oblique.The muscle fibers will run paralle to the line of pull.

Quadrilateral:eg: thryohyoid

Strap like:eg: sartorius

Strap like with tendinous insertion:eg: rectus abdominus

Fusiform:eg: biceps brachi

Pennate: are oblique placed faciculi, feather like in arrangement of the fasicles in relation to a tendon

i. Unipennate: eg: extensor digitorum longus

ii. Bipennate: eg: gastronimeus

iii. Multipenate: eg: deltoid

Classified based on shape

• Spiral fasciculi : spiral or twisted fibers are seen as seen in trapezius pectoralis major

• Circular: muscle surrounds a body orifices, constricting when contracted

eg: orbicularis oculi

Prime mover: A muscle that is chiefly responsible for a particular movement

Antagonist: A muscle that opposes the action of a prime mover

Synergist: A muscle that prevents unwanted movements in an intermediate joint where the another muscle crosses that joint. To prevent unwanted movements and stabilizes the intermediate joints.

Fixator: A muscle that contracts isometrically, to stabilize the origin of the prime mover so that it can act efficiently

Classified based on movement

Concentric action: the muscle length shortens to produce a movementIsometric action :the muscle length remains constant on producing a movementExcentric action: the muscle lengthens when active

• Passive insufficiency: the opposing muscle unable to stretch beyond a certain length to allow full range of movement is Passive insufficiency.

• Active insufficiency: normally muscles contract 40%of its fully stretched state. This limitation in the range affects all muscles that act on several joints simultaneously, thus unable to shorten to produce full range of movement is Active insufficiency

Range of contraction

Muscles

Skeletal muscles are striated (have distinct bands) made up of fibres (long cells). – 30cm!!!!

The cells are multinucleated (many cell nuclei) and contract and relax quickly.

These are voluntary muscles attached to the skeleton that help to move the bones.

There are nearly 700 skeletal muscles spread all over the body.

Ends attached to bones, cartilage or ligaments by tendons, aponeuroses

Muscles Types

Structure of a muscle

Properties of skeletal muscle

1. Extensibility – the ability of muscle tissue to lengthen when contracting

2. Elasticity – the ability of muscle tissue to return to its normal resting length after being stretched, allowing repeated contractions

3. Contractility – the capacity of a muscle to contract or shorten forcibly when stimulated by nerves or hormones (excitability).

4. Controlled by nerve stimuli.

5. Will atrophy (waste) –inadequate blood supply

6. Will hypertrophy -overworked

•Raphe is between 2 flat muscles serving as an attachment

Aponeuroses – thin sheet of fibrous tissue attached to flat muscles

Different forms

Rhomboid

Strap muscles

Fusiform Rectus

Bipennate; Flat Unipennate

Lumbricoid Multipennate