properties & mechanism of muscular system, mechanism of contraction, biochemistry of muscles and neuromuscular junction.

1. MUSCULAR SYSTEM
Properties,
 Mechanism of contraction of muscles,
 Biochemistry of muscles,
 Neuro muscular junction
1

2. • Muscles are the active part of the motor
apparatus of higher animals. These
contribute most of the total weight of the
body.
• Muscular system is made up of over 600
muscles. It consists of thousands of
elongated fibres or cell organized in a
variety of ways and bound together by
connective tissue.
• Muscle receives their ability to move
through the nervous system.
2

3. • There are three types of muscles.
1) Striated muscles
These muscles are voluntary muscles, because
they show movement when we want.
These muscles are also called skeletal muscles.
It generate force and contract in order to support
respiration & locomotion.
2) Smooth muscles
Smooth muscle fibers are located in walls of hollow
visceral organs, except the heart, appear spindle-
shaped, and are also under involuntary control.
3) Cardiac muscles
Cardiac muscle tissue is only found in heart, where
it performs coordinated contractions that allow
heart to pump blood through circulatory system.
It is under involuntary control
3

4. PROPERTIES OF MUSCLES
1) EXCITABILITY
 The basic and most important functional property of all the
three types of muscle is excitability.
 They are capable of receiving stimulation and responding
to stimulation from the nerves.
2) CONTRACTIBILITY
 After receiving stimulation, they are capable of contracting
or shortening.
 when a muscle is contracted, it shortens and becomes
thicker but its total volume barely changes.
 contraction is stronger & faster in striated muscles
compared to other muscles.
4

5. 3) CONDUCTIBILITY
 Once a part of muscle fibre is stimulated by stimulus of
adequate strength, it is conducted within time to all its other
parts. This property is called conductibility.
 Conduction is much faster in striated muscles as
compared to other types of muscles.
4) TONICITY
 All the muscles in the body at the given time are never
found in perfectly relaxed state. Although not showing
outward signs of activity. They are in a state of mild contraction
which causes them to being stretched. This activity of muscle is
known as muscle tonus.
5) TENSILITY AND ELASTICITY
 All the muscle possess the property of tensility.
 A muscle is able to return to its original resting shape and
length after being extended or contracted.
5

6. 6) THRESHOLD, SUB-LIMINAL & SUPRA-LIMINAL STIMULI
 The lowest limit of stimulus capable to bring contraction
in muscle called the threshold or liminal stimulus.
 A stimulus weaker than the threshold is called subliminal
stimulus and stimulus which is stronger than the threshold is called
supra-liminal stimuli.
7) REFRACTORY PERIOD
 After stimulation there is a brief period during which the
muscle does not remain in excitable state, this period is called
refractory period or relaxation of muscles.
8) LATENT EXCITATION & CONTRACTION OF MUSCLES
 The period between the application of the stimulus and
beginning of the muscular contraction is called latent excitation
or latent period.
 The period during which muscle remains in contraction
state is called contraction of muscles.
6

7. MECHANISM OF CONTRACTION OF MUSCLES
SLIDING FILAMENT HYPOTHESIS
• It was introduced by Huxley & Hanson in 1955.
• This theory explains the mechanism of muscle
contraction based on muscle proteins that slide past
each other to generate movement.
• This theory is a widely accepted explanation of the
mechanism that underlies muscle contraction.
7

8. STRUCTURE
OF
MUSCLE
H zone
8

9. The I bands are composed of actin filaments,
and the A bands principally of myosin
filaments;
During contraction, the actin filaments move
into the A bands between the myosin
filaments.
The backbone of a muscle fibre is actin
filaments which extend from Z line up to one
end of H zone, where they are attached to an
elastic component.
Z line
Myosin filaments extend from one end of the A
band through the H zone up to the other end of
the A band
Myosin filaments remain in relatively constant
length during muscle stretch or contraction
If myosin filaments contract beyond the length
of the A band, their ends fold up to form
contraction bands
During stretching, only the I bands and H zone
increase in length, while A bands remain the
same
H zone
9

10. For a muscle in action, energy is required. This
energy is released by ATP molecules. The
energy binds with active site of actin filament
to contract.
During contraction, actin filaments move into
the A bands and the H zone is filled up, the I
bands shorten, the Z line comes in contact
with the A bands;
The possible driving force of contraction is the
actin-myosin linkages which depend on ATP
hydrolysis by the myosin.
Filament sliding occurs by cyclic attachment
and detachment of myosin on actin filaments.
Contraction occurs when the myosin pulls the
actin filament towards the centre of the A
band, detaches from actin and creates a
force to bind to the next actin molecule. This is
known as the cross-bridge cycle.
10

11. BIO CHEMISTRY OF MUSCLES
ATP (Adenosine triphosphate )
• The mechanism of muscular contraction is based
upon the interaction between ATP.
• The ATP is the ultimate source of energy for:
 The contractile process.
 The pumping of calcium back into the
sarcoplasmic reticulum during relaxation.
 Maintaining the sodium/potassium ion gradients
across the sarcolema.
PHOSPHOCREATINE
It is also known as creatine phosphate or Pcr,
that is an important energy stored in the skeletal
muscle.
Creatine is synthesized in the liver and
transported to the muscle cells, where it is
phosphorylated by creatine kinase to creatine
phosphate.
Phosphocreatine is subject to depletion during
extended periods of contraction.
Rephosphorylation of creatine occurs at the
mitochondrial membrane.
•The contractile proteins are myosin and actin.
•The role of calcium ions through the sarcoplasmic
reticulum and the calcium-receptive protein are
troponin–tropomyosin complex.
11

12. NEURO MUSCULAR JUNCTION
• It is also called as myoneural
junction/ motor end plate.
• It is a synaptic connection
between the terminal end of
a motor nerve and a muscle.
• It is the site for the
transmission of action
potential from nerve to the
muscle.
12

13.  It is a microstructure through which
the process of contraction is
initiated or halted in the muscles by
the neurons.
 Any changes in the neuromuscular
junction can result in
impaired contractions of the
skeletal muscles.
 In the neuromuscular system nerves
from the central nervous system
and the peripheral nervous system
are linked and work together with
muscles.
13

14. It consists of three mechanism
Presynaptic terminal
Synaptic cleft
Post synaptic membrane
14

15. 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.
The presynaptic terminal also has calcium
channels.
These channels are voltage-gated calcium
channels which open when a nerve impulse
reaches the presynaptic axonal terminal.
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.
15

16. POST SYNAPTIC CELL OR MEMBRANE
• The postsynaptic cell in case of
neuromuscular junction is the skeletal
muscle fiber.
• The motor neurons make synapse on
the sarcolemma or membrane of the
skeletal muscle fibers.
• At the neuromuscular junction, the
sarcolemma of the skeletal muscle
shows a number of invaginations called
postjunctional folds.
• These folds greatly increase the surface
area for the neurotransmitters to act.
• The walls of these folds
have acetylcholine receptors.
• These receptors are the most important
functional part of the neuromuscular
junction.
16

17. ACETYLCHOLINE RECEPTORS
• Acetylcholine is the neurotransmitter
used in neuromuscular junction.
• The acetylcholine receptors are
present in the walls of postjunctional
folds. These receptors are also called
cholinergic receptors.
• The receptor can also be activated by
nicotine, thus called nicotinic receptors.
• The acetylcholine receptors are the
ionotropic receptors linked to ion
channels.
• It is made up of two α, one β, one ɛ,
and one δ subunit.
• The acetylcholine binds to the alpha
subunit.
• When a single acetylcholine
molecule binds to the alpha subunit, it
induces a conformational change
resulting in the increased affinity of the
second subunit.
• When both the subunits are occupied
by acetylcholine, it results in
the opening of the cation channels,
resulting in the inward diffusion of
sodium and potassium ions.
NERVE TERMINAL
ACETYLCHOLINE
NICOTINIC
RECEPTORS
17

18. THANK YOU
18