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Introduction to Muscular System
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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