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SKELETAL MUSCLE

Smoking is injurious to health

Rakesh kumar

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Introduction Classification Microscopic structure Physiology Applied Anatomy References

Protocol

3 Introduction

MUSCULUS = LITTLE MOUSE

Muscle tissue is the one of the basic tissues of the body.

Responsible for movement .

Composed of differentiated cells containing contractile proteins(actin, myosin etc.)

4 Muscles – machines - chemical energy - mechanical energy.

40-50% of the body mass.

Attaches to bone, skin or fascia

Developed from MESODERM except a)Arrector pili b)Muscles of iris c)Myoepithelial cells of sweat ,salivary and lacrimal glands -

ECTODERM

5 Types of Muscle tissue Skeletal muscle

Smooth muscle

Cardiac muscle

6 Skeletal Muscles• Attached to skeleton

• Voluntary control of contraction & relaxation

• Each muscle cell = muscle Fiber

• Muscle fibers develop from the fusion of small, individual muscle cells called myoblast.

7 Microscopic structure shows light & dark bands –

Striations

Straight & Un-branched

Multinucleated Nuclei are located in the cytoplasm just beneath the

plasma membrane(sarcolemma)

LENGTH :- varies from few mm (stapedius) to many cm (sartorius)

SHAPE :- long and cylindrical

8Development of Skeletal muscle Myotomes of paraxial mesoderm

5Th week – spindle shape – myoblast- single nucleus- repeated mitosis.

join to form myotubes- single row nuclei in centre

Cross striations seen in 2nd month – myofibrils-periphery

Increase in no. of myofibril –nuclei pushed- periphery

Myotubes converted into muscle fibres.

9 Parts of Voluntary Muscle

10 Two parts of a muscle

1. Belly part:- Contractile part

2. Fibrous part:- Non contractile and non elastic

a) Tendon

b) Aponeurosis

11 Classification According to colour

According to Insertion of muscle

According to direction of muscle fibre - Parallel - Pennate - Spiral - Cruciate

121. Slow (or Red) Oxidative Fibers Type I Slow but continuous contraction for extended periods

Smaller diameter

contain myoglobin more capillaries more mitochondria

Does not fatigue as fast due to aerobic production of ATP Eg: Soleus.

132. Fast (Red) Oxidative Fibers Type IIaHave attributes in between fast and slow

types

143. Fast Glycolytic (white)Fibers Type IIb

Fast contraction after nervous stimulation Large diameter

Large glycogen reserve Fewer mitochondria Densely packed myofibrils

Fatigue fast due to mainly anaerobic respiration Eg. Biceps brachii, Gastrocnemius.

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16According to insertion of muscle

Insertion near the proximal end of bone Eg – biceps brachii, psoas major

Insertion towards the distal end of bone, away from the joint Eg- brachioradialis

Insertion at the middle of shaft of bone Eg- Coracobrachialis, pronator teres

17According to direction of muscle fibera) Parallel muscles

The muscle fibers are parallel to line of pull

The fibers are long, but their numbers are few

Functions: Range of movement . ↓ total force of contraction

18Sub divisions of parallel muscles Strap muscle- Sartorius, Rectus abdominis

Quadrate muscle- Quadratus lumborum

Fusiform muscle- Biceps brachii

19b) Pennate muscles Fibers are oblique to line of pull

20 Circumpennate The muscle is cylindrical Oblique fibers converge into central tendon

from all sides Eg- Tibialis anterior

c) Spiral muscle Muscles are twisted in arrangement

close to their insertion Eg- Pectoralis major & latissimus dorsi

21d) Cruciate muscle Fasciculi in the muscle are crossed Eg: Sternocliedomastoid, Masseter

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Circular: surrounds a bodyorifice, constricting it whencontracted Eg: Orbicularis occuli (closes the eyelids)

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24 Connective Tisssue

Epimysium = On top of the muscle

Perimysium = Around a bundle of myofibers

Endomysium = Surrounds each myofiber

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26 Vessels and nerves run in epimysium and perimysium

Branch in to arterioles and give off capillaries which are carried by endomysium

Each muscle fiber is accompanied by a set of parallel capillaries, which give off side branches at right angles to the fiber

27• Epimysium consists mainly type I collagen fibers

• Perimysium contain type I and III collagen fibers

• Endomysium contain type III and IV collagen fibers

• Collagen IV is associated with the basal lamina that invests each muscle fiber

• All these connective tissue layers extend beyond the muscle belly to form the tendons, aponeurosis and fascia.

28Attachment of tendon to skeletal muscle

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Fascicles

Myofibrils

Myofilaments

Actin Myosin

It is important to remember the Heirarchy

30 Microscopic Structure

Some vocabulary:Skeletal muscle cell = fiber or myofiber Sarcolemma Sarcoplasm Sarcoplasmic reticulumMyofibrilMyofilamentsT-tubules

Muscle

Epimysium

Myofibrils

Sarcomere

Myofilament

Myofibrils

31 Muscle and Muscle fibre• Each muscle divides into several muscle bundles or fasciculi by perimysium

• Each fasciculus is composed of variable number of muscle fibers

• Individual muscles are separated by fascia, which also forms tendons and aponeurosis

32Muscle fibre(Cont..)

•Each muscle fiber is elongated,

multinucleated.

•Is essential for force transduction

33Muscle fibre(Cont..) sarcolemma- Plasma membrane sarcoplasm - Cytoplasm sarcoplasmic reticulum- Smooth endoplasmic reticulum

34 Light and dark bands

The cytoplasm or sarcoplasm shows alternate dark and light bands Dark band is called A-band Light band is called I-band

35Light and dark bands

36 Sarcomere The portion of myofibrils between every two Z-lines Z disc: filamentous network of protein. Serves as

attachment for actin myofilaments Titin filaments: elastic chains of amino acids; make

muscles extensible and elastic

37Myofibril Muscle fibers are filled with threads called

myofibrils, separated by SR (sarcoplasmic reticulum)

Myofilaments (thick & thin filaments) are the contractile proteins of muscle

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Transverse Tubules

T (transverse) tubules are invaginations of the sarcolemma into the center of the cell filled with extracellular fluid carry muscle action potentials down into cell

Mitochondria lie in rows throughout the cell near the muscle proteins that use ATP during contraction

Sarcoplasmic Reticulum (SR)

System of tubular sacs similar to smooth ER Placed horizontally between T-tubules Stores Ca2+ in a relaxed muscle Release of Ca2+ triggers muscle contraction

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40 Proteins of Muscle Myofibrils are built of 3 kinds of protein

Contractile proteins myosin and actin

Regulatory proteins which turn contraction on & off troponin and tropomyosin

Structural proteins which provide proper alignment, elasticity and extensibility

titin, myomesin, nebulin and dystrophin

41Neuromuscular Junction

SYNAPSE: axon terminal resting in an invagination of the sarcolemma

Neuromuscular junction (NMJ): Presynaptic terminal:

axon terminal with synaptic vesicles

Synaptic cleft: space Postsynaptic membrane

or motor end-plate

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43Sliding Filament Model

Actin myofilaments sliding over myosin myofilaments result shorten sarcomeres Actin and myosin do not change length during

sliding Shortening sarcomeres responsible for skeletal

muscle contraction

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45During relaxation:-

Sarcomeres lengthen because of some external force, like forces produced by other muscles (contraction of antagonistic muscles) or by gravity.

Agonist = muscle that accomplishes a certain movement, such as flexion.

Antagonist = muscle acting in opposition to agonist

Synergists= they prevent undesirable movement

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47 Energy Sources ATP provides immediate energy for muscle contractions. Produced from three sources Creatine phosphate

During resting conditions stores energy to synthesize ATP

ADP + Creatine phosphate------------------ Creatine + 1ATP

Anaerobic respiration Occurs in absence of oxygen and results in breakdown

of glucose to yield ATP and lactic acid Aerobic respiration

Requires oxygen and breaks down glucose to produce ATP, carbon dioxide and water

More efficient than anaerobic

(Creatine Kinase)

48Skeletal muscle: Nerve supply

Supplied by motor and sensory nerves Motor fibers: Two types

Alpha fibresThickly myelinated axons supply extrafusal

muscle fibresProduces movements(Contraction)

Gamma fibresThinly myelinated fibres which supply intrafusal

fibers of the muscle spindleMaintains the tone of the

muscle(Proprioception)Unmyelinated sympathetic fibers

Supply blood vessels

49Skeletal muscle: Nerve supply

Motor end plate : Motor neuron (efferent) axons originating in the spinal cord contact

muscle fibers via a structure known as the motor endplate.

Motor point: The site where the motor nerve enters the muscle

50Skeletal muscle: Nerve supply Motor unit/functional

unit A single motor neuron

together with the muscle fibers supplied by it.

The size of the unit depends on the precision of the movement

Large & Small

51 Sensory fibers

Arises from specialized endings

Muscle spindle/tendon spindle

Essential for muscle tone and body posture

Essential for coordinated voluntary movements

52Deep Tendon Reflex

53 Blood Supply

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Movement

Posture & Body

position

Support to Soft tissues

Joint stabilizatio

n

Body Temperatur

e

Skeletal Muscles

Functions

Facial Expression

Protection

55Properties of Muscle Tissue

Excitability Respond to chemicals released from nerve cells

Conductivity Ability to propagate electrical signals over

membrane Contractility

Ability to shorten and generate force Extensibility

Ability to be stretched without damaging the tissue

Elasticity Ability to return to original shape after being

stretched

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APPLIED ANATOMY

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Muscle Disorders

Trauma

Compartment syndrome

Carpal tunnelsyndromeBruises or tear

Infection

Myositis Trichinosis Fibromyalgia Tetanus

Inherited disorders

Muscular dystrophies

Tumors

MyomasSarcomas

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Secondary Disorders

Immune problems:

Myasthenia gravisGuilliain Barre

syndrome

Nervous system:

Botulism Poliomyelitis

Cardiovascular system:

AnemiaHeart failure

Metabolic problems:

HypercalcemiaHypocalcemia

59Fatigue Decreased capacity to work and reduced

efficiency of performance Cause - Exhaustion of Ach in motor endplate Accumulation of metabolites like lactic

acid and phosphoric acid Lack of nutrients like glucose Lack of oxygen

60Spasticity -Tone is increased (Eg- stroke)

Flaccidity -Tone is decreased (Eg -spinal shock)

Atrophy- (wasting of muscles)

(Eg- Poliomyelitis)

61 Hypertrophy - New muscle fibers are not

formed, Enlargement due to production of more myofibrils and cell organelles Hyperplasia –

increase in number Damage of skeletal

muscle – replaced by fibrous scar tissue

62Myasthenia gravis Autoimmune disorder - blocks the ACh receptors-

NMJ

The more receptors are damaged the weaker the muscle.

More common in women 20 to 40 with possible line

to thymus gland tumors

Symptoms

Treatment includes steroids that reduce antibodies that bind to ACh receptors and inhibitors of acetylcholinesterase

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65Muscular Dystrophies Inherited, muscle-destroying diseases Sarcolemma tears during muscle

contraction X linked disease - male Appears by age 5 in males and by 12 may

be unable to walk Degeneration of individual muscle fibers

produces atrophy of the skeletal muscle

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67Poliomyelitis

Poliovirus

Under the age of 3

Poliovirus destroys motor neuron in the AHC.

Muscle of leg more affected than arm but paralysis can spread to the muscle of the thorax and abdomen

68Sports Injuries 5 year study of college football players

indicate:• Mild – 73.5%• Moderate – 21.5%• Severe – 11.6%

A study of 1650 joggers running 27 miles a week reported 1819 injuries in a single year.

69Sports related conditions Bone bruise: bleeding within the periosteum

Bursitis: an inflammation of bursae

Muscle cramps: prolonged,involuntary,and painful muscular contraction

Sprains: tear or break in ligaments or tendons

Strains: tears in muscles

Tendinitis: an inflammation of connective tissue surrounding a tendon

70Muscle Memory

Muscle memory is not a memory stored in your muscles,but memories stored in your brain.

Motor Learning.

Muscle Encoding.

Muscle Re-education or Rehabilitaion.

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72 Electromyography

To test the action of muscle

EMG helps in testing the efficiency of lower motor neuron

REFERENCES1. Gray’s Anatomy- Susan Standring. 40th Edition. 2. Inderbir singh. Textbook of human histology with color atlas,

2006, 5th edition3. DiFiore’s , Atlas of histology, 12th edition4. Vander’s Human physiology, 12th edition5. Manipal manual of physiology,1st edition6. Principal of general anatomy A.k.datta,7th edition7. General anatomy,B D Chaurasia,4th edition8. Principles of Human Anatomy,Gerard J.Tortora/Mark T.Nielsen,

13th edition9. Gross Anatomy,Kyung Won Chung/Harold M. chung, 6th edition10. A&P ,Applications Manual ,Martini &Welch

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