MUSCLE

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MUSCLE

• DR. AYISHA QURESHI
• ASSISTANT PROFESSOR
• MBBS, MPhil

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MUSCLE

• (1) purposeful movement of the whole body or
  parts of the body (such as walking or waving your
  hand),
• (2) manipulation of external objects (such as
  driving a car or moving a piece of furniture),
• (3) propulsion of contents through various hollow
  internal organs (such as circulation of blood or
  movement of a meal through the digestive tract),
  and
• (4) emptying the contents of certain organs to
  the external environment (such as urination or
  giving birth).

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MUSCLE

• Chemical energy
• ?Muscle
• Mechanical energy
• Muscle forms about 50 of the total body weight
• 40 skeletal muscle
• 10 smooth cardiac muscle
• Simply put, Muscles perform the following
  functions
• They contract
• They generate heat
• They generate motion
• They generate force
• They provide support

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TYPES of MUSCLE (According to appearance or
movement)
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Types of Muscle
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Skeletal muscle
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Characteristics of Skeletal Muscles

• Attach to the bone
• Move appendages
• Support the body
• Antagonistic pairs Flexors extensors

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Skeletal muscle anatomy
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SKELETAL MUSCLE CELL STRUCTURE

• A single skeletal muscle cell is also called a
  MUSCLE FIBER b/c of its greater length than
  width.
• LENGTH upto 75,000 µm or 2.5 feet.
• DIAMETER from 10 to 100 micrometers.
• SHAPE elongated cylindrical.
• OUTER MEMBRANE called sarcolemma.
• Nucleus Organelles present. Mitochondria,
  microsomes ER
• What is the chemical composition of the muscle?
• Proteins (20) (either as enzymes or for muscle
  Cont.)
• Lactic Acid (in muscle that has undergone
  fatigue)
• ATP, ADP
• Myoglobin (stores O2 gives colour to the muscle)

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Skeletal Muscle Organization

• Whole Muscle (an organ)
• ?
• Muscle Fiber (a single cell)
• ?
• Myofibrils (a specialized structure)
• ?
• Thin Thick filaments
• ?
• Actin Myosin (protein molecules)

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Skeletal Muscle Organization
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A single muscle fiber
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LAYERS COVERING A MUSCLE

• The skeletal muscle has the following layers
  covering it
• Epimysium
• Perimysium
• Endomysium

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PROTEINS OF MUSCLE
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ACTIN THIN FILAMENTS

• G-actin is the monomer which will form the thin
  filament. It is a protein with a molecular weight
  of 43,000. It has a prominent site for
  cross-linkage with myosin.
• G-actin
• ?
• F-actin
• (6-7 nm long polymerized G-actin, double
  stranded in structure)
• ?
• Thin filaments

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Regulatory Proteins of the Muscles

• TROPOMYOSIN

• TROPONIN

• Rod-like protein
• Mol. Weight 70,000
• 2 chains alpha beta chains
• Under resting conditions, it covers the site for
  myosin attachment on F-actin molecule.
• Forms part of Thin filaments

• Globular protein complex made of 3 polypeptides
• Forms part of thin filaments

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THIN FILAMENTS

• Length 1 µm
• Diameter 5-8 nm
• No. of G-Actin mol 300-400
• Other Proteins
• - Nebulin provides elasticity to the sarcomere.
  
• - Titin is the largest known protein in the
  body. It connects the Z-line to the M-line in the
  sarcomere contributes to the contraction of
  skeletal muscle.

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MYOSIN THICK FILAMENTS

• Thick filaments consist of 2 symmetrical halves
  that are mirror images of each other.
• Chief constituent is MYOSIN, with a mol. weight
  of 480,000.
• Its molecule has 2 ends, a globular end having 2
  heads a rod-like tail.
• It has 6 peptide chains
• - 2 identical heavy chains (200,000 each)
• - 4 light chains ( 20,000 each)

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Binding sites on Myosin molecule

• The myosin molecule has 2 binding sites
• Binding site for ACTIN
• ATPase sit e

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A SARCOMERE
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• A myofibril displays alternating dark light
  bands.

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A sarcomere model
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A SARCOMERE

• The area between 2 consecutive Z discs/ lines is
  called A Sarcomere. It is the functional unit of
  a muscle.
• It has a length of 2.3 µm.
• It has the following important features
• Z-disc
• M-line
• I-band
• A-band
• H-zone
• Titin
• Nebulin

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Sarcomere Organization of Fibers

• Z disks
• I band
• A band
• H Zone
• M line
• Titin
• Nebulin

Figure 12-5 The two- and three-dimensional
organization of a sarcomere
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• Z-disc are dense thin membranes made up of
  special lattice-like proteins present
  transversely.
• Dark or A-band Thick filaments present
  overlapped by the thin filaments at the ends
  only.
• Light or I band area present b/w the ends of the
  2 thick filaments. It consists of thin filaments
  only.
• H-Zone The lighter area in the middle of the
  A-band, where the thin filaments do not reach. It
  consists of thick filaments only.
• M-Line A line that extends vertically down the
  middle of the A-band in the center of the H-zone.
  
• Pseudo H-zone M-line H-zone.

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THE SARCOTUBULAR SYSTEM
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Sarcotubular System

• The sarcoplasm of the myofibril is filled with a
  system of membranes, vesicles and tubules which
  are collectively termed as The Sarcotubular
  system.
• It is made up of
• T-Tubules Sarcoplasmic
  Reticulum

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SARCOTUBULAR SYSTEM

• Transverse System of Tubules
• (T-Tubules)

• Sarcoplasmic Reticulum
• (SR)

• It is a fine network of interconnected
  compartments which run in the longitudinal axis
  of a myofibril embedded in the I and A bands,
  surround them.
• They are surrounded by the sarcoplasm are NOT
  connected to the outside of the cell.
• At their both ends they show dilated ends called
  as Terminal cisterns or sacs.
• They contain a protein called as Calsequestrin,
  which binds and holds CALCIUM.

• It is a system of tubules that runs transverse to
  the long axis of the muscle.
• They enter the myofibrils at the junction b/w the
  A and I bands.
• The T-tubules open onto the sarcolemma. It is an
  invagination of the cell membrane thus
  communicates with the ECF.
• It functions to rapidly transmit the AP from the
  sarcolemma to all the myofibrils.

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THE TRIAD

• The cisterns of the SR the central portion of
  the T-tubules give rise to a characteristic
  pattern called the TRIAD.
• Each TRIAD consists of 2 terminal sacs of SR 1
  central t-tubule.
• There is no physical communication between each
  component of the triad.
• In the triad, the cisterns of the SR have the
  Ryanodine receptors which are complimentary to
  the Dihydropyridine receptors on the t-tubule.
  They are both involved in excitation-contraction
  coupling.

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