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 Although Bones provide leverage and form the framework of the
body, they cannot move body parts by themselves. Motion result from
the alternating contraction and relaxation of muscles.
 Muscles constitute 40-50% of total body weight. Muscular strength
reflects the prime function of muscle i.e changing chemical energy into
mechanical energy to generate force, perform works and produce
movement.
 In addition, muscle tissue stabilizes the body’s position, regulates
organ volume and it also generates heat.
INTRODUCTION

CLASSIFICATION OF MUSCLES
• The basis of these classifications is as follows: :
1. DEPENDING UPON THE PRESENCE OR
ABSENCE OF STRIATIONS.
2. DEPENDING UPON THE CONTROL AND
3. DEPENDING UPON THE FUNCTION.
Basis of classification

DEPENDING UPON STRIATIONS
 Under this the muscles are divided into two groups namely
 STRIATED MUSCLE AND
 NON STRIATED MUSCLE
STRIATED MUSCLE:
 Under light microscope, in each muscle cell, a large number of
cross striations (transverse lines) are seen at regular interval.
 Skeletal and cardiac muscles are striated.
NON-STRIATED MUSCLE
 The muscle with out cross striations are called non striated muscle
or plain muscle.
 Eg. Smooth muscles.

DEPENDING UPON THE CONTROL
 These are classified into two types namely
 VOLUNTARY MUSCLE AND
 INVOLUNTARY MUSCLE
VOLUNTARY MUSCLE:
 These muscles can be controlled voluntarily.
 They are innervated by neurons that are part of the somatic
division of the nervous system.
E.g. Skeletal muscles.

INVOLUNTARY MUSCLE
 These muscles cannot be controlled voluntarily.
 Their action is involuntary either by anatomic nervous system or by
hormones selected by the endocrine system.
E.g. Cardiac and smooth muscles, and some skeletal muscles like
muscles, which cause contraction and relaxation of the diaphragm.

DEPENDING UPON THE FUNCTION
 They are classified into three types namely
 SKELETAL MUSCLE
 CARDIAC MUSCLE AND
 SMOOTH MUSCLE
SKELETAL MUSCLE:
 These muscles are in association with bones forming the skeletal
system.
 They constitute 40% of body mass.
 These are about 600 skeletal muscles identified.

CARDIAC MUSCLE
 This muscles form the musculature of the heart.
SMOOTH MUSCLE
 These are the muscle, which are in association with viscera.
 So they are also called visceral muscles.
 They form the contractile units of wall of the various visceral
organs and are present in the following structures like:

 Wall of organs of G.IT like oesophagus, stomach and intestine.
 Ducts of digestive glands.
 Trachea, bronchial tube and alveolar ducts of respiratory tract.
 Ureter, urinary bladder, urethra and genital ducts.
 Wall of the blood vessels.
 Arrector pilorum of skin
 Mammary glands.
 Iris and ciliary body of the eye.
 Prostate gland.

 Through sustained contraction or alternating contraction and
relaxation, muscle tissue has five key functions:
1. Producing Body Movements:
2. Stabilizing body positions
3. Regulating organ volume
4. Producing heat
5. Moving substances with in the body
FUNCTIONS OF MUSCLE TISSUE

 Total body movements such as walking and running, and localized
movements such as nodding the head, rely on the integrated function
of bones, joints and skeletal muscles.
PRODUCING BODY MOVEMENTS:
 Skeletal muscle contractions stabilize joints and help maintain body
positions like standing or sitting.
 Postural muscles contract continuously when a person is awake.
E.g. Sustained contractions in neck muscles hold the head upright.
STABILIZING BODY POSITION:

 Sustained contractions of ring like bands of smooth muscles
(sphincters) may prevents out flow of the contest of a hollow organ.
E.g. Temporary storage of food in the stomach or urine in the urinary
bladder.
REGULATING ORGAN VOLUME:
 As muscle tissue contracts, it also produces heat.
 Much of this heat is used to maintain body temperature.
PRODUCING HEAT:

 Cardiac muscle contractions pump blood through the blood vessels.
 Skeletal muscle contractions promote flow of lymph and aid the return
of blood to the heart.
 Smooth muscle contractions moves food and substances such as bile
and enzymes through the G.I.T.
 Contraction and relaxation of smooth muscle in the walls of blood
vessels help adjust this diameter and thus regulate the rate of blood
flow.
MOVING SUBSTANCES WITH IN THE BODY:

 ELECTRICAL EXCITABILITY:
It is a property of both muscle cells and nerve cells, is the ability to
respond to certain stimuli by producing electrical signals called action
potentials.
 CONDUCTIVITY:
If is the ability of a cell, especially a muscle cell or neuron, to
propagate or conduct action potentials along the plasma membrane.
PROPERTIES OF MUSCLE TISSUE

 CONTRACTILITY:
It is the ability of the muscle to shorten and thicken when stimulated by
an action potential.
Thus it generates force to do work.
 EXTENSIBILITY:
This property of a muscle allows it to contract forcefully even it is
already stretched with being damaged.
 ELASTICITY:
The property helps the muscle tissue to return to its original length and
shape after contraction or extension. .

 Each skeletal muscle is a separate organ composed of hundreds to
thousands of cells called fibers because of their elongated shapes.
SKELETAL MUSCLES:

ANATOMY

 Connective tissue surrounds muscle fibers and whole muscles.
 Fascia sheet or broad band of fibrous connective tissue which is
deep to the skin and surrounds muscles and other organs.
 Superficial fascia or subcutaneous layer – separate muscle from skin.
 It is composed of areolar connective tissue and adipose tissue
 This provides a pathway for the nerves and blood vessels to enter and
exit muscles.
CONNECTIVE TISSUE COMPONENTS :

 DEEP FASCIA is a dense, irregular connective tissue which holds
muscles with similar functions together.
 Allows free movement of muscles at carrier nerves and blood and
lymphatic vessels and file the spaces between muscles.
 Three layers of connective tissue from deep fascia extend to further
protect and strengthen skeletal muscle.
 EPIMYSIUM it is the outermost layer encircling the whole muscle.
 PERIMYSIUM surrounds groups of 10 to 100 or more individual
muscle fibers, separating them into bundles called fascicles.
Epimysium and perimysium are dense irregular connective tissue.

 ENDOMYSIUM a thin sheath of areolar connective tissue which
penetrate the interior of each fascicle and separate the individual
fibers.
 All these three connective tissue layers may extend beyond the muscle
fibers to form a tendon.
 TENDON is a cord of dense regular connective tissue that attaches
a muscle to the periosteum of a bone.

MICROSCOPIC ANATOMY

 The plasma membrane of the muscle fiber is called as “sarcolemma”
 The multiple nuclei of a skeletal muscle fiber are located just beneath
the sarcolemma.
 Sarcolemma consists of thousands of tiny invaginations from the
surface towards the centre of each muscle fiber. Called as “T
(transverse) tubules”.
 T tubules are open to the outside the fiber and thus are filled with extra
cellular fluid.
 Muscle action potentials propagate along the sarcolemma and through
the T tubules spreading through out the muscle fiber.

 SARCOPLASM, the cytoplasm of a muscle fiber is present with in the
sarcolemma.
 Sarcoplasm consists of large amount of glycogen which is used or ATP
synthesis. At also contains myoglobin, a red colored oxygen binding
protein, found only in muscle fibers.
 MITOCHONDRIA lie in rows throughout the muscle fiber.
 MYOFIBRILS which are the contractile elements of the skeletal muscle
are present in the sarcoplasm and are seen under high magnification.
 Myofibrils are about 2 m in diameter and extend the entire length of
the muscle fiber.
 Prominent striations of these myofibrils gives the muscle its striated
appearance.

 SARCOPLASMIC RETICULUM or the fluid filled system of
membranous sacs encircles each myofibril.
 This is similar to endoplasmic reticulum in non muscle cells.
 Dilated end sacs of the sarcoplasmic reticulum are called terminal
cisternae butt against T tubule from both sides.
 This SR stores the ca2+ ions. Muscle contraction occurs if these ca2+
ions are released from the terminal cisternae.
 Within myofibrils are two types of even smaller structures called
filaments.
 They are only 1-2 m long

 When the muscle is in resting position the length of the sarcomeres is
2 m.
 Sarcomeres are separate from one another by a plate shaped regions
of dense material called Z –disc.
 Actin and myosin filaments are interdigitated partially thus filament
causes the myofibril to have alternate dark and light bands.

 The light band contains actin filaments and are called I bands because
they are isotropic to the polarized light.
 The dark band contains myosin filaments and ends of actin filaments,
where they overlap the myosin are called dark bands or A-bands.
 This band is anisotropic to polarized light.
 A narrow H zone in the centre of the each A band contains thick but not
thin filaments.
 M. line is present in the centre of the sarcomeres, holds the thick
filaments together with the help of supporting proteins.

MUSCLE PROTEINS
 Myofibrils are made up of three kinds of proteins.
 Contractile proteins
 Generates force during contraction.
 Regulatory proteins
 Regulates the process of contraction.
 Structural proteins
 Keeps the filaments in alignment, gives the myofibril elasticity
and extensibility, link the myofibrils to the sarcolemma and
extracellular matrix.

CONTRACTILE PROTEINS
Two contractile proteins are namely:
1. Myosin (thick filaments)
2. Actin (thin filaments).

 Functions as a motor protein in all the three types of muscles.
 300 molecular of myosin forms – single thick filament.
 The myosin molecules is composed of six polypeptide chains, two
heavy chains each with a molecular weight of about 200,000 and four
light chains with M.W of about 20,000 each.
 Two heavy chains wrap spirally around each other to form a double
helix, which is called the fail of the myosin molecule.
 One end of each of there chains in folded into a globular polypeptide
structure called the myosin head.
MYOSIN

 These head lie side by side at one end.
 The 4 light chains are also parts of the myosin heads, tow to each
head.
 Part of each myosin molecule hangs to the side along with the head,
thus providing an arm that extends the head outward from the body.
 The protruding arms and heads together are called cross bridges.
 Each cross – bridge is flexible attached to the myosin filament with the
help of hinges.
 This hinged arm allows the head to be extended for out wards from the
body of he myosin filament or to be brought close to the body.
 Thus it helps in contraction process.

ACTIN FILAMENT
 Actin is the main component of the thin filament.
 Actin filament is a double – stranded F-actin each protein molecule.
Which is 1 micrometer long.
 Each strand of F-actin helix is composed of polymerized G-actin
molecules with m.wt of about 42,000.
 There are 13 molecules in each revolution of each strand of helix.
 One molecule of ADP is attached to one G-actin molecule which is the
active site on actin myosin filament where the cross bridges of the
myosin filament interact to cause muscle contraction.

REGULATORY PROTEINS
 Tropomyosin Is regulatory protein present on the actin filament.
 Its mol.wt is 70,000 length is 40nm.
 Tropomyosin molecules are wrapped around the side of the F-actin
helix.
 When the muscle is resting, the tropomyosin molecules lie on top of
the active sites of the actin filament, and does not allow the myosin
filament to bind with the actin filament and thus not allowing the
contraction to occur.
Tropomyosin molecules

 Troponin molecules are attached along the sides of the tropomyosin
molecules.
 Troponin is made up of three subunits
 Troponin I – strong affinity for actin
 Troponin T – strong affinity for tropomyosin
 Troponin c – strong affinity for calcium ions.
 This complex helps in attachment of tropomyosin to actin.
 The affinity for ca2+ ions initiates the contraction process.
TROPONIN

STRUCTURAL PROTEINS
 These structural proteins helps in alignment, stability, elasticity and
extensibility of myofibrils.
TITIN
 It is the third most plentiful protein after action and myosin in skeletal
muscle
 Titin anchors a thick filament to both, Z disc and the M line, and helps
in stabilizing the position of the thick filament.
 It extends from Z disc to the beginning of thick filaments.
 It can stretch atleast 4 times its resting length and then spring back un
harmed.
 Thus it helps in elasticity and extensibility of myofibrils.

 This forms the M line in the middle of the sarcomeres.
 This binds to titin and also connect adjacent thick filaments to one
another.
MYOMESIN
 It is a large but in elastic protein and lies along side the thin filament.
 It is also attached to the Z disc.
 It helps maintain alignment of thin filaments in the sarcomeres.
NEBULIN

 It is a cyto-skeletal protein that links thin filaments of the sarcomeres to
integral membrane proteins of the sarcolemma.
 Dystrophin reinforce the sarcolemma and help transmit the tension
generated by sarcomeres to the tendon.
DYSTROPHIN

 Skeletal muscles are well supplied by nerves and blood vessels.
 Neurons that stimulate skeletal muscle to contract are the somatic
motor neurons.
 Blood capillaries bring in oxygen and nutrients and resolve heat and
the waste products of muscles metabolism.
NERVE AND BLOOD SUPPLY

 In the mid-1950 Jean Hanson and Hurdey had a revolutionary insight
in to the the mechanism of muscle contraction.
 They examined the first electron micrographs of skeletal muscle and
found that the length of the thick and thin filaments were the same in
both relaxed and the contracted muscle.
 Later on, the researches discovered that skeletal muscle shortens
during contraction because the thick and thin filaments slide past one
another.
 This model, which describes the contraction of muscle, is known as the
sliding filament mechanism.
CONTRACTION AND RELAXATION OF
SKELETAL MUSCLES

 In the relaxed state, the ends of the action filaments derived from two
successive discs barely begin to overlap one another, while at the
same time lying adjacent to the myosin filaments.
 Conversely in the contracted state, actin filaments have been pulled
inward among the myosin filaments, so that their ends overlap one
another to a major extent.
 Z Discs have been pulled by the actin filaments up to the ends of the
myosin filaments.
 Thus the muscle contractions occurs by the sliding filament
mechanism.
SLIDING MECHANISM OF CONTRACTION

 At the onset of contraction the sarcoplasmic reticulum releases ca2+
ions which bind to Troponin.
 This moves the Troponin, tropomyosin complexes away from the
myosin binding sites on actin. When these sites are free, the
contraction cycle that causes the filaments to slide.
 This contractions cycle occurs in four steps
THE CONTRACTION CYCLE

 The myosin head induces an ATP binding pocket and an ATP
ase, an enzyme that hydrolyzes ATP into ADP (adenosine
diphosphate) and a phosphate group.
 This hydrolysis reaction energies the myosin head.
ATP HYDROLYSIS
 The energized myosin head attaches to the myosin-binding site on
actin and then releases the hydrolyzed phosphate group.
ATTACHMENT OF MYOSIN TO ACTIN TO FORM CROSS
BRIDGES

 The release of the phosphate group triggers the power stroke of
contraction.
 During power stroke, the pocket on the myosin head where ADP is
bound opens, which rotates the myosin head and releases the ADP.
The myosin head generates force as it rotates toward the centre of
the sarcomere, sliding the thin filament part the thick filament
towards the M line.
POWER STROKE
 At the end of the power stroke, the myosin head remains firmly
attached to actin until it binds another molecule of ATP.
DETACHMENT OF MYOSIN FROM ACTIN

 As ATP binds to the ATP - binding pocket on myosin head, the
myosin head detaches from actin.
 Thus the contraction cycle repeats as the myosin ATP-ase again
hydrolyses ATP. Contraction cycle repeat over and over, as long as
ATP is available and the ca2+ level nears the thin filament is
sufficiently high.
 600 Myosin heads in one thick filament attach and detach about five
times per second.
 The continual movement of the myosin head applies the force that
draws the discs toward each other, and the sarcomere shortens.
 During a maximal muscle contraction, the distance between Z discs
can decrease to half the resting length.

 An increase in ca2+ concentration in the cytosol starts muscle
contraction, where as a decrease stops it.
 When a muscle fiber is relaxed the concentration of ca2+ in its cytosol
is very low, only about 0.1 millimole / liter (10-7 M). But where as in the
sarcoplasmic reticulum. It is 10,000 times higher that is cytosol.
 As muscle action potential propagates.
 Along the sarcolemma and into the tubules it causes Ca2+ release
channels in the SR membrane to open
EXCITATION – CONTRACTION COUPLING

 This permits Ca2+ to diffuse across the SR membrane.
 As a result Ca2+ ions flood from the SR into the cytosol around the
thick and thin filaments. By this, the Ca2+ ion concentration rises
tenfold or more.
 This released Ca2+ ions combine with troponin, causing it to change
its shape and moves troponin – tropomyosin complex away from the
myosin – binding sites on actin.
 Once these binding sites are free, myosin heads bind to them, and the
contraction cycle begins.
 The SR membrane also contains Ca2+ active transport pumps that
hydrolyze ATP as they continually move Ca2+ from the cytosol into the
SR. Ca2+ ions diffuse more rapidly into the cytosol than they are
transported back by the pumps.

 Ca2+ ions diffuse more rapidly into the cytosol than they are
transported back by the pumps.
 After the last action potential has propagated throughout the T
tubules, the Ca2+ release channels close.
 As the pumps move Ca2+ back into the SR, the concentration of
Ca2+ ions in cytosol quickly decrease.
 Inside the SR molecules of a Ca2+ binding protein, called
calsequestrin, bind to the Ca2+ to be sequestrated within the SR.
 As the Ca2+ level drops in the cytosol, the troponin – tropomyosin
complexes slide back over and cover the myosin-binding sites, and
the muscle fiber relaxes.

MUSCLE METABOLISM
 Contraction of muscle requires a tremendous amount of ATP for
powering the contraction cycle, for pumping Ca2+ in to the SR to
achieve muscle relaxation, and for other metabolic reactions.
 The ATP present inside muscle fibers is enough to power contraction
for only a few seconds.
 If strenuous exercise is to continue for more than a few seconds,
additional ATP must be synthesized.

 Muscle fibers have three sources for ATP production.
 They are:
1. Creatine phosphate
2. Anaerobic cellular respiration
3. Aerobic Cellular respiration

TYPES OF SKELETAL
MUSCLES:
 Skeletal muscle fibers contract and relax with different
velocities.
 A fiber is categorized as either slow or fast depending on
how rapidly the ATPase in its myosin heads hydrolyzes
ATP.
 Skeletal muscle fibers vary in the metabolic reactions
they use to generate ATP and in how quickly they fatigue.

• Based on these structural and functional characteristics, skeletal
muscle fibers are classified into three main types.
• They are:
1. Slow oxidative fibers (SO)
2. Fast oxidative glycolytic fibers (FOG)
3. Fast glycolytic fibers (FG)
 Most skeletal muscles are a mixture of all these types of
muscles, about half of which are so fibers.
 Even though they compromise of all the three types of skeletal
muscles fibres, the skeletal muscle fibers of any give motor unit are
all of same type.

Structural
Characteristic
Slow Oxidative
(SO) Fibers
Fast Oxidative-
Glycolytic (FOG)
Fibers
Fast Glycolytic
(FG) Fibers
Fiber Diameter Smallest Intermediate Largest
Myoglobin
Content
Large Amount Large Amount Small Amount
Mitochondria Many Many Few
Capillaries Many Many Few
Colour Red Red to Pink White (Pale)
CHARACTERISTICS OF THE THREE TYPES OF
SKELETAL MUSCLE FIBERS

Functional
Characteristics
Slow Oxidative (SO)
Fibers
Fast Oxidative-
Glycolytic (FOG) Fibers
Fast Glycolytic (FG)
Fibers
Capacity of generating ATP
and m,method used
High capacity, by aerobic
(oxygen – requiring)
cellular respiration
Intermediate capacity, by
both aerobic (oxygen-
requiring) cellular
respiration and glycolysis
(anaerobic)
Low capacity, by
anaerobic cellular
respiration (Glycolysis)
Rate of ATP hydrolysis by
myosin ATPase
Slow Fast Fast
Contraction velocity Slow Fast Fast
Fatigue resistance High Intermediate Low
Glycogen stores Low Intermediate High
Order of recruitment First Second Third
Location where fibers are
abundant
Postural muscles such
as those of the neck
Leg muscles Arm muscles
Primary functions of fibers
Maintaining posture and
endurance – type –
activities
Walking, sprinting
Rapid, intense
movements of short
duration
CHARACTERISTICS OF THE THREE TYPES OF
SKELETAL MUSCLE FIBERS
Contn…

 Once an action potential has been elicited at any point on the
membrane of a normal fiber, the depolarization process travels over
the entire membrane if conditions are right, or it might not.
 It applies to all normal excitable tissues.
ALL OR NONE LAW

ISOTONIC AND ISOMETRIC CONTRACTIONS
 Contraction of a muscle is described as isotonic when a muscle
length is altered during contraction with the tension on the muscle
remaining constant.
 Isotonic contractions are of two types:
1. Concentric isotonic contraction.
2. Eccentric isotonic contraction.

 If a muscle shortens and pulls on another structure, such as a
tendon, to produce movement and reduces the angle at a joint then it
is said to be concentric contraction.
E.g. Picking a book up off a table involves concentric isotonic
contractions of the biceps brachial muscle in the arm.
CONCENTRIC ISOTONIC CONTRACTION
 When the overall length of a muscle increases during a contraction,
it is called as an eccentric contraction.
E.g. While placing the book back on the table, the previously
shortened biceps gradually lengthens while it continuous to contract.
ECCENTRIC ISOTONIC CONTRACTION

ISOMETRIC CONTRACTION
 Contraction of muscle is described as isometric if tension is
generated in the muscle with out any change in the length of the
muscle.
E.g: Holding a book steady using an out starched arm.
 Contraction and stretching applied in opposite directions create the
tension.

 Many hormones that have effects on skeletal muscles are Many
hormones that have effects on skeletal muscles are:
1. GROWTH HORMONE: is administrate to a person if causes
increase in the bulk of the But this increase in bulk is not due to
the increment in contractile element but increments of non-
contractile proteins of the muscle cells. Here the muscles
become voluminous but are weak.
ROLE OF HORMONES IN MUSCLE
CONTRACTION

2. CORTICOSTEROIDS (CORTISOL) administration promote
break down of muscle proteins (endogens proteolysis) and the
extra amino acid thus available are utilize to form glucose.
(Glyconeogenesis).
2. ANDROGEN administration to a person increase the contractile
elements of protein and thus the strength of the muscle is
increased.
2. INSULIN lack as in untreated diabetes mellitus, can cause
muscle wasting due to endogenous proteolysis –
gluconeogenesis.

LENGTH – TENSION RELATIONSHIP
 At a Sarcomere Length of About 2.0 –2.4 µM, the zone of overlap in
each sarcomere is optimal, and the muscle fiber can develop
maximum tension.
 Maximum tension occurs when the zone of overlap between a thick
and thin filament extends from the edge of the H zone to one end of
a thick filament.
 As the sarcomeres of a muscle fiber are stretched to longer
length, the zone of overlap is shorter. Fewer myosin heads can
make contact with thin filament.
 Consequently, the tension, the fiber can produce decrease.

 When a skeletal muscle fiber is stretched to 170% of its optimal
length, these is no overlap between the actin and myosin filaments.
And the tension generated is zero.
 As the sarcomeres length becomes increasingly shorter than the
optimum, the tension that can develop again decreases.
 This is because thick filament crumple as they are compressed by Z
discs, resulting in fewer myosin heads making contact with thin
filaments.
 But the resting muscle length is held very close to the optimum by
firm attachments of skeletal muscles to bones and to other in elastic
tissues, so that overstretching does not occur.

ACTIVE AND PASSIVE TENSION
 As thin filaments start to slide past thick filaments, they pull on the Z
discs, which in turn pull on neighboring sarcomeres. Eventually,
whole muscle cells pull on their surrounding connective tissue
layers.
 The elastic components of a muscle are titin molecules,
endomysium, perimysium, epimysium and tendons.
 These elastic components stretch slightly before they transfer the
tension generated by the sliding filaments.
 Muscle tension that is generated by the contractile components i.e
thin end thick filaments is called active tension.

 Muscle tension generated by the elastic components is called
passive tension.
 Within limits, the more the elastic component of a muscle are
stretched, the greater the passive tension.
 As a skeletal muscle start to shorten, it first pulls on its connective
tissue covering and tendons.
 The covering and tendons stretch and then become taut, and the
tension Passed through the tendons pulls on the bone to which they
are attached.
 Thus the movement of a part of a body occurs.

THE NEUROMUSCULAR JUCNTION
 The junction between the terminal branch of the nerve fiber and
muscle fiber is called Neuro Muscular Junction (NMJ).
 All the muscle fibers innervated by a single motor nerve fiber are
called a motor unit.
 A muscle fiber contracts in response to action potentials.
 These action potentials arise at the neuromuscular junction, the
synapse between a motor neuron and a skeletal muscle fiber.
 The terminal branch of the nerve fiber is called axon terminal.
 While approaching close to the muscle fiber, the axon loses the
myelin sheath and the axis cylinder is exposed.

 This expands like a bulb called the motor end plate.
 The membrane of the muscle fiber below the end plate is thickened,
and invaginates inside the muscle fiber forming a depression known
as synaptic trough or synaptic gutter into which the motor end plate
fits.
 The membrane of the nerve ending is called the pre synaptic
membrane.
 The membrane of the muscle fiber is called post synaptic
membrane.
 The space between these two is called synaptic cleft.
 Axon terminal contains synaptic vesicles in the which the
neurotransmitter substance acetylcholine present.
 The Ach is synthesized by mitochondria present in the axon terminal
and stored in the vesicles.www.indiandentalacademy.com

 Synaptic cleft contains basal lamina which is a thin layer of spongy
reticular fiber through which the extra cellular fluid diffuses
 Large quantity of the enzyme, acetyl cholinesterase is attached to
the matrix of basal lamina.
 The postsynaptic membrane is thrown into numerous folds called
sub neural clefts.
 The post synaptic membrane contains the receptor proteins called
nicotinic acetylcholine receptors to which the Ach binds forming Ach-
receptor complex.

ACTION POTENTIAL THROUGH MOTOR NERVE FIBER
AXON TERMINAL
Opening of voltage gated calcium channels
Entry of calcium ions from ECF
Opening of vesicles and release of Ach
SYNAPTIC CLEFT
Passage of Ach

POSTSYNAPTIC MEMBRANE
Binding of Ach with receptor and formation of Ach
– Receptor complex
Opening of ligand gated sodium channels and
entry of sodium ions from ECF
Development of end plate potential
MUSCLE FIBER
Generation of action potential
Excitation contraction coupling
Muscular contraction

 Involuntary activation of small number of motor units causes
sustained, small contractions that give firmness to a relaxed skeletal
muscle.
 This firmness is known as muscle tone.
MUSCLE TONE

MUSCLE FATIGUE AND TETANY
 The inability of a muscle to contract forcefully after prolonged activity
is called muscle fatigue.
 Fatigue results mainly from changes within muscle fibers.
 Several factors are thought to contribute for muscle fatigue.
 The one important factor is inadequate release of Ca2+ ions from
the SR, resulting in a decline of Ca2+ concentration in the
sarcoplasm.

 Depletion of creatine phosphate also is associated with fatigue.
 Other factors are
1. In sufficient oxygen
2. Depletion of glycogen and other nutrients build up of lactic acid
and ADP and failure of action potentials in the motor neuron to
release enough acetylcholine.

TETANY
 With rapidly repeated stimulation, activation of the contractive
mechanism occurs repeatedly before any relaxation has occurred.
 The individual responses fuse into one continuous contraction. Such
a response is called a tetanus (tetanic contraction).
 It is a complete tetanus when there is no relaxation between stimuli.
 When there are periods of incomplete relaxation between the
summated stimuli it is called incomplete tetanus.
 During a complete tetanus, the tension developed is about four times
that of the individual twitch contraction.

ELECTROMYOGRAPHY
 Activation of motor units can be studied by electromyography, the
process of recording the electrical activity of muscle on a cathode-
ray oscilloscope.
 This may be done in un-anaesthetized humans by using small metal
discs on the skin overlying the muscle as the pick-up electrodes.
 It can also be done by using hypodermic needle electrodes.
 The record obtained with such electrodes is the electromyogram

 Used to determine the cause of muscular weakness or paralysis.
 To evaluate involuntary muscle twitching.
 To determine the abnormal levels of muscles enzymes that appear in
blood.

MYOTACTIC REFLEX OR STRETCH REFLEX
 The stimulus of the stretch reflex is the stretch of the muscle.
 The stretch reflex when elicited causes sustained contraction of the
stretched muscle.
 Functional significance of this reflex is that it serves as a mechanism
for upright posture or standing.
 The same stretch reflex is also useful in functional appliance therapy
as the forces elicited by this reflex results in tooth movement and
bone remodeling and may prevent further forward adaptation of the
maxillary dentoalveolar process.

 If one attempts to flex the spastic limb of a patient forcibly, resistance
is encountered as soon as the muscle is stretched throughout the
initial part of the bending.
 This resistance is due to hyperactive reflex contraction of the muscle
in response to stretch reflex.
 If the flexion is forcibly carried further a point is reached at which all
resistance to additional flexion seems to melt, and the previously
rigid limb collapses readily.
 Thus the muscle first resists and then relaxes.
 This is called clasp-knife reflex.
CLASP – KNIFE REFLEX

 The stimulus necessary to elicit this reflex is excessive stretch
and, when elicited, it inhibits muscular contraction, thus causing the
muscle to relax.
 The functional significance of the clasp-knife reflex is, it protects the
overloaded muscle by preventing damaging contraction against
strong stretching forces.

CONCLUSION
 The treatment of dento-facial mal-relations requires considerable
insight into the modalities of craniofacial growth and muscle
physiology.
 The goal of modern orthodontics is to make the appliances
subservient to the achievable goals.
 So, it is necessary for an orthodontist to know the mechanism of
muscle physiology as the success of the functional appliance
therapy depends on the neuromuscular response.

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