Download SMOOTH MUSCLE

MUSCLE
DR. AYISHA QURESHI
ASSISTANT PROFESSOR
MBBS, MPhil
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
TYPES of MUSCLE
(According to appearance or movement)
Muscle
Skeletal Muscle
Smooth Muscle
Cardiac Muscle
(Striated)
(Smooth)
(Striated)
(Voluntary)
(Involuntary)
(Involuntary)
SKELETAL MUSCLE:
Characteristics of
Skeletal Muscles:
 Attach to the
bone
 Move
appendages
 Support the
body
 Antagonistic
pairs: Flexors
& extensors
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 micrometres.
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)
Skeletal Muscle Organization
Whole Muscle (an organ)
↓
Muscle Fiber (a single cell)
↓
Myofibrils (a specialized structure)
↓
Thick & Thin filaments
↓
Myosin & Actin (protein molecules)
SKELETAL MUSCLE ORGANIZATION
PROTEINS OF MUSCLE:
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
Regulatory Proteins of the Muscles
TROPOMYOSIN
TROPONIN
• Rod-like protein
• 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
Binds to Ca2+
Inhibitory in function
Attached to Tropomyosin
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)
Binding sites on Myosin molecule:
The myosin molecule has 2 binding sites:
1. Binding site for ACTIN
2. ATPase site
A SARCOMERE:
• A myofibril displays alternating dark & light
bands.
Myofibril
Dark bands
Light bands
(A bands)
(I bands)
Anisotropic
Isotropic
Thick & thin filaments
Thin filaments only
A sarcomere model:
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
Sarcomere: Organization of Fibers
• 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.
THE SARCOTUBULAR SYSTEM
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
SARCOTUBULAR SYSTEM
Sarcoplasmic Reticulum
(SR)
Transverse System of Tubules
(T-Tubules)
• 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.