Muscular System in brief Types of muscle fibres Muscles of limbs Muscles of trunk Neuro Muscular Junction

1. MUSCULAR SYSTEM
- CHAITRA CHINMAYEE M K

2. MUSCLE
•Muscle is a contractile tissue which brings about body
movements by contraction and relaxation of its fibers.
• PARTS OF A MUSCLE:-
i. Two ends:
 Origin – the end of the muscle which remains fixed
during its contraction.
 Insertion – the end which moves during its
contraction.
ii. Two parts:
 Fleshy part - contractile, and is called the 'belly'.
 Fibrous part - non-contractile and inelastic. It is
called TENDON.

3. PROPERTIES OF MUSCLE FIBRES
•CONTRACTABILITY: the muscle fibers contract
lengthwise, to bring body movements when stimulated.
•EXCITABILITY: the muscle fibers are sensitive and
respond to stimulus.
• EXTENSIBILITY: the muscle fibers return to their original
length on removing the stimulus.
• ELASTICITY: the muscle fibers are elastic and can be
stretched.

4. Types of Muscles
• There are three types
of muscles:
i. Skeletal/Striated
Muscle – the
muscles attached to
skeleton
ii. Smooth/Non-
striated Muscle –
the muscles attaches
to viscera (abdominal
organs)
iii. Cardiac Muscle – the
muscle of the heart

5. SKELETAL MUSCLE
• The most abundant
muscle in our body.
• They are voluntary, that is
under our control and
striated.
• Located superficially and
mostly attached to the
skeleton.
• They are unbranched,
cylindrical, multinucleated
muscle fibers.

6. Functions
i. Body Movement – contraction of these muscle fibers cause
body movement.
ii. Heat Production – metabolism within the muscle cells
releases heat as end product, which increases during
strenuous exercises.
iii. Posture and Body support – These muscles maintain body
posture by providing support around flexible joints.
Types of skeletal muscle fibres
Red Fibres White Fibres
Their speed of contraction is
less but more sustained. They
are fatigue resistant hence
present in postural muscles
and long muscles of the back.
Their speed of contraction is
fast but less sustained. They
are easily fatigued hence
present in the muscles of the
eyeball, etc.

7. SARCOMERE
• The structural and functional unit
of a striated muscle fibre, and it is
due to the presence of this the
muscle appears striated.
• It is the basic unit of contraction,
that is it is the contraction of this,
which brings about the
contraction of a muscle fibre.
• it comprises of two types of
filaments, called myofilaments:-
i. Thick filaments: it is
composed of a protein called
myosin
ii. Thin filaments: it is
composed of protein called
actin
• The sliding of thin filament
over the thick filament brings
about the contraction of
sarcomere, and hence the
contraction of muscle fibre.

8. Smooth Muscle
• They are present in the walls
of the hollow organs, blood
vessels, glands and skin.
• They are involuntary,
unstriated muscle fibres.
• They have unbranched,
spindle shaped muscle fibres.
• Functions:
i. Movement of organs to
facilitate proper mixing of
food
ii. Regulation of blood flow.
iii. Propulsion of urine

9. Cardiac Muscle
• It is also called myocardium.
• It is present only in the walls
of the heart.
• Its major function is pumping
of blood from the heart
• It is involuntary and striated
muscle.
• It has branched, cylindrical
fibres with intercalated discs
and they are uninucleated.
• It is auto-rhythmic, that is it
generates its own contractions
and does not require an
external stimulus for its activity.

10. Muscles of the Upper Limb
Muscles of Arm:-
Anterior: (Flexion of Arm) Posterior: (Extension of Arm)
• Biceps Brachii Triceps Brachii
• Coraco-brachialis
• Brachialis
Muscles of Forearm:-
Anterior: (Flexion of Forearm) Posterior: (Extension of Forearm)
• Pronator Teres Anconeus
• Flexor carpi radialis Brachio-radialis
• Palmaris longus superficial Extensor carpi radialis longus
• Flexor digitorum superficialis Extensor carpi radialis brevis
• Flexor carpi ulnaris Extensor digitorum
• Flexor digitorum profundus Extensor digiti minimi
• Flexor pollicis longus deep Extensor carpi ulnaris
• Pronator quadrus Supinator
Abductor pollicis longus
Extensor pollicis brevis deep
Extensor pollicis longus
Extensor indices
Superficial

11. ANTERIOR POSTERIORARM

12. FOREARM
ANTERIOR POSTERIOR

13. Muscles of the hand
• Abductor pollicis brevis
• Flexor pollicis brevis
•Opponens pollicis
• Adductor pollicis
• Palmaris brevis
• Abductor digiti minimi
• Flexor digiti minimi
• Opponens digiti minimi
• Lumbricals(4)
• Palmar interossei(4)
• Dorsal Interossei(4)
F

14. Muscles of lower limb
Muscles of thigh:-
Anterior: (Extension of thigh)
• Sartorius
• Quadriceps Femoris- it has,
Rectus Femoris
Vastus lateralis
Vastus intermedius
Vastus medialis
• Articularis genu
• Tensor fascia lata
Medial: (Adduction of thigh)
• Adductor brevis
• Adductor longus
• Adductor magnus

15. Muscles of thigh(cont’d)
Posterior:- (Flexion of thigh)
HAMSRTING MUSCLES:
• Semi-tendinosus
• Semi-membranosus
• Short head of biceps
femoris
• Ischial fibres of Adductor
magnus
NON-HAMSTRING
MUSCLES:
• Long head of biceps
femoris

16. MUSCLES OF FRONT OF TRUNK
•Pectoralis Major
• Pectoralis minor Pectoral Region
• Subclavius
• Deltoid
• External Intercostal
• Internal intercostal
• Transversus thoracis
Subcostalis Thorax
Intercostalis intimi
Sternocostalis
deltoid

17. MUSCLES OF BACK OF TRUNK
• Trapezius
• Lattisimus dorsi
• Levator scapulae Back
• Rhombois major
• Rhomboid minor
• Supraspinatous
• Infraspinatus
• Subscapularis Scapular
• Teres minor Muscles
• Teres major

18. Nerve-Muscle Junction (NMJ)
• Neuromuscular junction (NMJ)
refers to the intimate contact of
the nerve endings with the muscle
fibre to which they innervate.
• It is a microstructure through
which the process of contraction is
initiated or halted in the muscles
by the neurons.
• Components of a NMJ are:-
i) Pre - synaptic terminal (Axon
terminal)
ii) Synaptic Cleft
iii) Post - synaptic terminal

19. COMPONENTS OF NMJ
Presynaptic Terminal: The presynaptic terminal is an axonal
terminal of a motor neuron. The axonal terminal contains a
number of synaptic vesicles. These vesicles contain the
neurotransmitters that are released upon receiving a nerve
impulse.
Synaptic Cleft: It is the space between the presynaptic terminal
and the postsynaptic cell. It is roughly the size of 30 nm. The
synaptic cleft allows the neurotransmitters to diffuse and reach
the other side of the synapse or the neuromuscular junction. It
also contains enzymes for the degradation of the excess or extra
neurotransmitters.
Post Synaptic Cell: The postsynaptic cell is the skeletal muscle
fiber. The motor neurons make synapse on the membrane of the
skeletal muscle fibers, whose membrane has receptors for
binding to the released neurotransmitters.

20. Mechanism of Contraction
• When a nerve impulse reaches the presynaptic
axonal terminal, it causes depolarization. As a result,
the voltage-gated calcium channels open. The
calcium ions from the surrounding environment
diffuse into the presynaptic axon.
• These calcium ions activate the membrane proteins.
These proteins mediate the fusion of synaptic
vesicles to the cell membrane of the neuron,
resulting in the release of neurotransmitters into the
synaptic cleft.
• They diffuses across the synaptic cleft and binds to
the receptors. This results in the opening of the
cation channels. These channels are open to both
sodium and potassium ions.

21. • As the concentration of sodium ions is
higher in the extracellular space, the sodium
ions enter through these open cation
channels. As a result, depolarization of the
skeletal muscle increases..
The depolarization of post – synaptic
membrane results in the opening of
voltage-gated calcium channels locate on
the membrane as well as the membrane of
the smooth endoplasmic reticulum.
• As the calcium ions enter the cell, it
initiates the cycle of skeletal muscle
contraction. The actin-myosin bridges of the
sarcomere are formed, and the result in
contraction of the skeletal muscles.
Mechanism of Contraction CONT’D

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