Download Muscle tissue

Kharkov National Medical University
Muscle tissue
• Lecture N 7
Department of histology, cytology and
embryology
Types of movement in nature and
in the human body
• - by movement of cilia and flagella
• - by contraction of cells of the body
• Muscle cells satisfy requirement of the body
in movement.
Classification –
3 types of muscle tissue:
1. skeletal muscle
• groups:
• Striated
2. cardiac muscle
3. smooth muscle
• Smooth
Why do muscles contract?
• Muscle cells have contractile proteins actin and myosin, troponin, tropomyosin
and some another .
The interaction of actin and myosin mediates
the contraction of muscle cells.
Why do muscles contract?
•
•
•
•
Actin and myosin form myofilaments:
Myosin - thick, dark and Anisotropic (A)
Actin – thin, light and Isotropic (I)
Actin and myosin myofilaments are
arranged parallel to the direction of cellular
contraction,
• and form special organelles – myofibrils,
responsible for muscle contraction.
SMOOTH MUSCLE
• Locations: walls of visceral hollow organs
(stomach, uterus, ureter, blood vessels, eye)
Functions: involuntary movement -changes of lumen of hollow organs, movement of its
contens , i.e.:
- churning of food - peristalsis,
- movement of urine from the kidney to the bladder,
- parturition,
- blood pressure,
- accomodation and adaptation of the eye
(The innervation -- by autonomic nervous system)
• Unit – myocyte (cell)
• Cells are spindle-shaped.
•
Individual cells are
organized in sheaths
• In hollow organs they
form layers:
- longitudinal,
- circular,
- oblique.
Contraction is usually slow
and may take minutes to
develop.
SMOOTH
MUSCLE
Origin of smooth muscle
• 1. Smooth muscle cells arise from
mesenchymal cells.
• 2. These cells differentiate first into
mitotically active cells, myoblasts,
which contain a few myofilaments.
• 3. Myoblasts differentiate into mature
smooth muscle cells.
• Very good regenerates!
Striated muscles
See: regular organization of the myofibrils
gives rise to the cross-striations, which
characterize skeletal and cardiac muscle.
CARDIAC MUSCLE
• Location: the heart
• Function: involuntary,
rhythmic contraction
• Unit – cardiomyocyte
(cell)
Cardiac muscle cells:
3 types:
• Contractile,
• Conducting,
• Secretory.
• Regeneration - intracellular
CARDIAC MUSCLE
• cardiac muscle cells are
cylindrical,
• connected end-by-end,
• and form “functional
fiber”, which
• often branches at acute
angles.
CARDIAC MUSCLE
• They are connected by special junction intercalated discs – that consist of gap junctions and
desmosomes.
Excitation in cardiac muscle
A special system of modified cardiac muscle
cells –
conducting myocytes –
they form conducting system - Purkinje fibers.
Excitation in cardiac muscle
• Modified nodal muscle cells, which are
called P-cells (pacemaker or pale-staining),
generate rhythm of the heart contraction
• The rhythm can be modified by the
autonomic nervous system, which
accelerates (sympathetic) or decelerates
(parasympathetic) heart rate.
SKELETAL MUSCLE
Location
• Muscles which are
associated with the
skeleton (are
connected to bones
by tendons).
• Platysma and
mimic muscles
• Voluntary
sphincters of inner
organs
SKELETAL MUSCLE
• --- is innervated by the somatic
nervous system – voluntary!!
• ---- consists of very long tubular cells
(also called muscle fibres).
Nuclei
• Skeletal muscle
fibres contain many
nuclei
(up to several
hundred )
placed beneath the
plasma membrane
(sarcolemma)
Myofibrils
Mechanism of contraction:
Sliding filaments theory
•
• Myofibrils has some bands and lines depending on the
distribution and interconnection of myofilaments -- :
• I-band - actin filaments,
• A-band - myosin filaments which may overlap with
actin filaments
• Z-line -- band of connections between actin
filaments; zone of apposition of actin filaments
belonging to two neighbouring sarcomeres;
• M-line - band of connections between myosin
filaments.
• H-zone - zone of myosin filaments only (no overlap
with actin filaments) within the A-band
Sarcomeres
• are smallest
contractile units of
myofibrils.
• Sarcomere formula:
• S=½I+A+½I
Sarcomere after contraction
• S=A
• (- ½ I, - ½ I, - H)
Mechanism of contraction
• Skeletal muscles (C) are stimulated
by nerve impulses carried by axons
(A) of motor neurons.
• Axon forms synapse – motor end
plate (B).
• The excitatory transmitter is
acetylcholine.
Invaginations of the sarcolemma form the T-tubule
system which "leads" the excitation into the muscle
fiber.
Close to the border between A- and I-bands of the
myofibrils T-tubules are in close apposition with
cisternae of sarcoplasmatic reticulum.
This association is called a triad.
Origin of skeletal muscle
• The myoblasts of all skeletal muscle fibers
originate from the paraxial mesoderm myotome.
• 1. Myoblasts undergo frequent divisions
and coalesce with the formation of a
multinucleated, syncytial muscle fiber or
myotube. The nuclei of the myotube are
still located centrally in the muscle fiber.
• 2. In the course of the synthesis of the
myofilaments and myofibrils, the nuclei are
gradually displaced to the periphery of the
cell.
Regeneration. Satellite cells
• Satellite cells are small cells which are
closely apposed to muscle fibers within the
basal lamina which surrounds the muscle
fiber.
• Satellite cells are believed to represent
persistent myoblasts. They may regenerate
muscle fibers in case of damage.
Muscle as an organ
• Muscle fibers
in skeletal
muscle occur
in bundles,
fascicles,
which make
up the muscle.
Muscle
• The muscle is
surrounded by
a layer of
connective
tissue, the
epimysium,
which is
continuous with
the muscle
fascia.
• Connective tissue
from epimysium
extends into the
muscle to surround
individual fascicles
(perimysium)
from which a
delicate network of
reticular fibers
surrounds each
individual muscle
fiber
(endomysium).
Tendons join muscle with bone
• The dense regular connective tissue of
tendon transduces the force generated by
the muscle fibers to the bone.
Red and white
• Red muscle fibers are comparatively thin and
contain large amounts of myoglobin and
mitochondria.
• Red fibers contain an isoform of myosin with low
ATPase activity, i.e. the speed with which
myosin is able to use up ATP.
• Contraction is therefore slow.
• Red muscles are used when sustained production
of force is necessary, e.g. in the control of posture.
Red and white
• White muscle cells, which are
predominantly found in the white muscles,
are thicker and contain less myoglobin.
ATPase activity of the myosin isoform in
white fibres is high, and contraction is fast.
Motor units
• Motor units - groups of muscle fibers
innervated by one motor neuron and its
branches.
• All muscle fibers of a motor unit are of the
same type.
• Skeletal muscle fibers do not contract
spontaneously.