Post on 18-Jul-2016
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Kontraksi dan Eksitasi Otot Polos
Musculosceletal System for Nursing
Yulius TirandaPSIK STIKes Muhammadiyah Palembang
Karakteristik khusus OtotOtot mempunyai 4 fungsi utama yaitu, kontraktilitas, eksitabilitas, ekstensibilitas dan elastisitas.1. Contractility (kontraktilitas) adalah kemampuan otot untuk memendek dengan kekuatan tertentu. Ketika otot berkontraksi, hal tersebut menyebabkan pergerakan struktur internal otot (filamen otot) dan akan menngakibatkan tekanan pada organ dan pembuluh darah.2. Excitability (eksitabilitas) adalah kemampuan otot untuk merespon stimulus, dimana umumnya otot, khususnya otot rangka berkontraksi sebagai akibat stimulasi oleh saraf. Otot polos dan jantung dapat berkontraksi tanpa stimulus luar, tetapi keduanya juga berkontraksi akibat stimulus saraf dan hormon.3. Extensibility (ekstensibilitas) adalah dapat meregang pada panjang tertentu dengan derajat tertentu.4. Elasticity (elastisitas) adalah kemampuan otot untuk kembali ke kondisi semula setelah melakukan proses meregang.
SMOOTH MUSCLESmooth muscle tissue is nonstriated and involuntary and is classified into two types: visceral (single unit) smooth muscle (Figure 10.18a) and multiunit smooth muscle (Figure 10.18b).
▫Visceral (single unit) smooth muscle is found in the walls of hollow viscera and small blood vessels; the fibers are arranged in a network and function as a “single unit.”
▫Multiunit smooth muscle is found in large blood vessels, large airways, arrector pili muscles, and the iris of the eye. The fibers operate singly rather than as a unit.
Two Types of Smooth Muscle• Visceral (single-unit)
▫ in the walls of hollow viscera & small BV
▫ autorhythmic▫ gap junctions cause fibers
to contract in unison• Multiunit
▫ individual fibers with own motor neuron ending
▫ found in large arteries, large airways, arrector pili muscles,iris & ciliary body
Smooth Muscle•Fusiform cells•One nucleus per
cell•Nonstriated•Involuntary•Slow, wave-like
contractions
Smooth Muscle
• Cells are not striated• Fibers smaller than those in
skeletal muscle• Spindle-shaped; single, central
nucleus• More actin than myosin• No sarcomeres
▫ Not arranged as symmetrically as in skeletal muscle, thus NO striations.
• Caveolae: indentations in sarcolemma;▫ May act like T tubules
• Dense bodies instead of Z disks ▫ Have noncontractile intermediate
filaments
Smooth Muscle• Grouped into sheets in walls of hollow organs
Longitudinal layer – muscle fibers run parallel to organ’s long axis
Circular layer – muscle fibers run around circumference of the organ
Both layers participate in peristalsis
Microscopic Anatomy of the Smooth Muscle•Sarcoplasm of smooth muscle fibers
contains both thick and thin filaments which are not organized into sarcomeres.
•Smooth muscle fibers contain intermediate filaments which are attached to dense bodies. (Figure 10.19)
Microscopic Anatomy of Smooth Muscle
• Small, involuntary muscle cell -- tapering at ends
• Single, oval, centrally located nucleus• Lack T tubules & have little SR for Ca+2 storage
Microscopic Anatomy of Smooth Muscle
•Thick & thin myofilaments not orderly arranged so lacks sarcomeres
•Sliding of thick & thin filaments generates tension
•Transferred to intermediate filaments & dense bodies attached to sarcolemma
•Muscle fiber contracts and twists into a helix as it shortens -- relaxes by untwisting
Physiology of Smooth Muscle•Contraction starts slowly & lasts longer
▫no transverse tubules & very little SR▫Ca+2 must flows in from outside
•In smooth muscle, the regulator protein that binds calcium ions in the cytosol is calmodulin (in place of the role of troponin in striated muscle); ▫calmodulin activates the enzyme myosin
light chain kinase, which facilitates myosin-actin binding and allows contraction to occur at a relatively slow rate.
Smooth Muscle Tone•The prolonged presence of calcium ions
in the cytosol of smooth muscle fibers provides for smooth muscle tone, a state of continued partial contraction.
•Smooth muscle fibers can stretch considerably without developing tension; this phenomenon is termed the stress-relaxation response.
•Useful for maintaining blood pressure or a steady pressure on the contents of GI tract
DEVELOPMENT OF MUSCLE•With few exceptions, muscles develop
from mesoderm (Figure 6.13a)•Skeletal muscles of the head and
extremities develop from general mesoderm; the remainder of the skeletal muscles develop from mesoderm of somites (Figure 10.20a).
Fusion of Myoblasts into Muscle Fibers
• Mature muscle cells developed from 100 myoblasts that fuse together in the fetus. (multinucleated)
• Mature muscle cells are not known to divide.• Muscle growth is a result of cellular enlargement
(hypertrophy) & not cell division (hyperplasia)• Satellite cells retain the ability to regenerate new cells.
Developmental Anatomy of the Muscular System
•Develops from mesoderm•Somite formation
▫blocks of mesoderm give rise to vertebrae and skeletal muscles of the back
•Muscles of head & limbs develop from general mesoderm
Regeneration of Muscle•Skeletal muscle fibers cannot divide after 1st year
▫growth is enlargement of existing cells▫repair
satellite cells & bone marrow produce some new cells
if not enough numbers---fibrosis occurs most often
•Cardiac muscle fibers cannot divide or regenerate▫all healing is done by fibrosis (scar formation)
•Smooth muscle fibers (regeneration is possible)▫cells can grow in size (hypertrophy)▫some cells (uterus) can divide (hyperplasia)▫new fibers can form from stem cells in BV walls
Aging and Muscle Tissue•Skeletal muscle starts to be replaced by fat
beginning at 30 ▫“use it or lose it”
•Slowing of reflexes & decrease in maximal strength•Change in fiber type to slow oxidative fibers may be
due to lack of use or may be result of aging
Regulation of Contraction by Calcium Ions • For skeletal muscle, calcium ions initiate contraction • Smooth muscle has no troponine but does contain the thin
filament protein tropomyosin and other notable proteins - caldesmon and calponin.
• Combination of calcium ions with calmodulin in smooth muscle
• Calmodulin: a special protein that reacts with four calcium ions.
• Three steps for activation and contraction by calmoduline 1. Calcium ions bind with calmodulin 2. Calmodulin-calcium conbination then joins with and
activates myosin kinase, an enzyme 3. One of the light chains of each myosin head becomes
phosphrelated by myosin kinase. The head binds with the actin filament (less clacum, reverse phosphorylation due to myosin phosphatase, then cessation of contractoin)
•No neuromuscular junctions of the highly structured type in smooth muscle, unlike skeletal muscles
•Instead the autonomic nerve fibers innervate smooth muscle
Mekanisme Kontraksi pada Otot Polos 1. Pada saat sebuah hormon berikatan pada reseptor di membran
maka akan mengaktifkan sebuah molekul G protein akibat terjadinya mekanisme depolarisasi membran plasma.
2. Akibat depolarisasi membran plasma akan membuka kanal Ca2+ di permukaan membran plasma dan memicu proses difusi Ca2+ melalui kanal Ca2+ yang kemudian akan berkombinasi dengan calmodulin.
3. Calmodulin dengan Ca2+ yang telah membentuk ikatan kemudian melekat pada miosin kinase dan mengaktivasi protein kinase ini.
4. Aktivasi miosin kinase menempelkan phosphat dari ATP pada kepala miosin untuk mengaktifkan proses kontraktil.
5. Kemudian terjadilah sebuah siklus cross-bridge formation, pergerakan, dan pelepasan ikatan protein kontraktil yang terlibat.
6. Relaksasi pada otot polos terjadi ketika miosin phosphatase memindahkan phosphat dari miosin.
Properties of Single-Unit Smooth Muscle▫Gap junctions▫Pacemaker cells
with spontaneous depolarizations
▫Innervation to few cells
▫Tone = level of contraction without stimulation
▫Increases/decreases in tension
▫Graded Contractions No recruitment Vary intracellular
calcium▫Stretch Reflex
Relaxation in response to sudden or prolonged stretch
Release and uptake of calcium by the sarcoplasmic reticulum during contraction and relaxation of a skeletal muscle fiber.
Comparison of smooth muscle contraction with skeletal muscle contraction •Most skeletal muscles contact and relax rapidly •Smooth muscle contraction is prolonged,
lasting hours or even days. •Some of the differences 1. Slow cycling of the myosin cross-bridges Attachment to actin and release from actin is
much slower. As little as 1/10 to 1/300 the frequency
Yet the fraction of time that the cross-bridges remain attached to the actin is greater in smooth muscl
2. Energy required to sustain smooth muscle contraction Only 1/10 to 1/300 as much energy is required to
sustain the same tension of contraction in smooth muscle
Explains in tension in intestines, urinary bladder, gallbladder (tonic muscle contaction of these. Energy saving)
3. Slowness of onset of contraction and relaxation of smooth muscle Total contraction time of 1 to 3 seconds 30 times as long as a single contraction of a skeletal
muscle Slow attachement and detachement Initiation of contraction due to calcium is much
slower to
4. Force of smooth muscle contraction Max. force of contraction of smooth muscle is
greater than that of skeletal muscle, as great as 4 to 6 kg/cm2 in comparison to 3 to 4 kg for skeletal muscle
This great force results from the prolonged attachment of the myosin cross-bridges to actin
5. Latch mechanism After full contraction, actin-myosin continue to
be attached (latched) continuously generating tension without using ATP. (a very low affinity for ATP)
This mechanism is called the latch mechanism and saves the smooth muscle cell a great deal of ATP