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Questions and Answers
ما هي الأنواع الثلاثة الرئيسية للعضلات؟
ما هي الأنواع الثلاثة الرئيسية للعضلات؟
ما هي الوحدة الحركية؟
ما هي الوحدة الحركية؟
عصب حركي والعضلات التي يزودها بالأعصاب.
ما هو الـ sarcomere؟
ما هو الـ sarcomere؟
هو جزء من اللييف العضلي بين خطين Z متتاليين
يحتوي الجهاز sarcotubular على سائل خارج الخلية.
يحتوي الجهاز sarcotubular على سائل خارج الخلية.
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ما هو دور calmodulin في انقباض العضلات الملساء؟
ما هو دور calmodulin في انقباض العضلات الملساء؟
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ما هي العوامل المحلية التي يمكن أن تغير توتر العضلات الملساء؟
ما هي العوامل المحلية التي يمكن أن تغير توتر العضلات الملساء؟
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أي من العوامل التالية يُؤثر على انقباض العضلات الملساء؟
أي من العوامل التالية يُؤثر على انقباض العضلات الملساء؟
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خلال حالة التأمين latch state، يُستمر تحلل ATP بمعدل مرتفع.
خلال حالة التأمين latch state، يُستمر تحلل ATP بمعدل مرتفع.
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ما هي أنواع العضلات الملساء؟
ما هي أنواع العضلات الملساء؟
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ما هو الفرق الرئيسي بين انقباض smooth muscle وانقباض العضلات الهيكلية؟
ما هو الفرق الرئيسي بين انقباض smooth muscle وانقباض العضلات الهيكلية؟
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تُعد العضلات الملساء Smooth Muscle تحت سيطرة الإرادة.
تُعد العضلات الملساء Smooth Muscle تحت سيطرة الإرادة.
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ما الذي يُريح smooth muscle؟
ما الذي يُريح smooth muscle؟
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Study Notes
Excitable Tissue: Skeletal Muscle & Smooth Muscle
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Skeletal muscle makes up most of the somatic musculature
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Skeletal muscle has well-developed striations
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Skeletal muscle requires nervous stimulation to contract
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Skeletal muscle is under voluntary control
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Cardiac muscle has cross-striations
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Cardiac muscle is functionally syncytial
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Cardiac muscle can be modulated by the autonomic nervous system
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Cardiac muscle can contract rhythmically in the absence of external innervation
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Cardiac muscle contains pacemaker cells that discharge spontaneously
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Smooth muscle lacks cross-striations
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Smooth muscle is subdivided into unitary (visceral) and multiunit types
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Smooth muscle is not normally under direct voluntary control
Muscle Morphology
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Skeletal muscle is composed of individual muscle fibers, the "building blocks" of the muscular system
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Skeletal muscle fibers are arranged in parallel between tendinous ends
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Muscles refer to a number of muscle fibers bound together by connective tissue
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Skeletal muscle has a distinct striated appearance due to alternating light and dark bands when viewed under a microscope
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Smooth muscle is characterized by the lack of this striated appearance
The Sarcomere
- The sarcomere is the portion of the myofibril between two successive Z discs
- The sarcomere length is approximately 2 micrometers when the muscle fiber is contracted
- At this length, the actin filaments overlap the myosin filaments, enabling maximum force generation
The Sarcolemma
- Each muscle fiber is a single cell with multiple nuclei, surrounded by a cell membrane called the sarcolemma
- The sarcolemma fuses with tendon fibers, which collect to form muscle tendons that attach to bones
Myofibrils Composition
- Myofibrils are composed of about 1500 myosin filaments and 3000 actin filaments
- Myosin filaments are thick, and actin filaments are thin
- Myosin molecules consist of two large polypeptide heavy chains and four smaller light chains, forming cross-bridges
The Striations
- The myosin and actin filaments interdigitate to form striations, with light bands (I bands) and dark bands (A bands)
- The I bands are isotropic to polarized light, containing only actin filaments
- The A bands are anisotropic to polarized light, containing myosin
- The I bands are divided by a darker Z line
- The A band is divided by a lighter H band, with an M line in the center
The Sarcotubular System
- The sarcotubular system consists of transverse (T) tubules
- T tubules are continuous with the muscle fiber membrane and extend deep into the muscle fiber
- They contain extracellular fluid
- T tubules are responsible for spreading action potentials from the membrane to the interior of the muscle fiber, which causes muscle contraction
The Sarcoplasmic Reticulum
- The sarcoplasmic reticulum forms an irregular network of tubules surrounding the myofibrils
- It contains terminal cisterns, which are in close contact with the T-tubules, forming a triad
- The sarcoplasmic reticulum concentrates calcium ions in high concentrations
- Calcium release occurs when an action potential passes through the T-tubules, triggering muscle contraction
Skeletal Muscle Contraction
- Motor neurons innervate skeletal muscle fibers
- Motor neurons are myelinated, allowing rapid action potential propagation
- Axons of motor neurons branch, forming neuromuscular junctions with multiple muscle fibers
- Each muscle fiber is controlled by a branch from only one motor neuron
- The motor unit consists of a motor neuron and the muscle fibers it innervates
General Mechanism of Muscle Contraction
- An action potential traveling along a motor nerve stimulates muscle fibers
- Acetylcholine, a neurotransmitter, is released, activating acetylcholine-gated channels
- Sodium ions diffuse into the muscle fiber, causing depolarization, which initiates an action potential
- The action potential travels along the muscle fiber membrane and triggers Ca++ release from the SR
- Ca++ binding to troponin exposes myosin-binding sites on actin
- Myosin heads bind to actin, causing a cross-bridge cycle, leading to muscle contraction
Muscle Fatigue
- Prolonged and strong muscle contraction leads to muscle fatigue
- This can result from glycogen depletion, diminished neuromuscular junction transmission, or nutrient/O2 deficiency
Smooth Muscle
- Smooth muscle lacks cross-striations and is not under direct voluntary control
- Smooth muscle is classified as either multi-unit or unitary (visceral)
- Multi-unit smooth muscle is composed of separate fibers, each controlled independently by nerve signals
- Unitary (visceral) smooth muscle consists of sheets or bundles of fibers, joined by gap junctions, allowing action potentials to spread readily, and contract in unison
Smooth Muscle Contraction
- Smooth muscle contraction is controlled by Ca++-regulated phosphorylation of myosin, which binds to actin and triggers cross-bridge cycling
- The lack of troponin and tropomyosin means different mechanisms for control of contraction
Smooth Muscle Relaxation
- Relaxation occurs when cytosolic Ca++ concentration decreases, reduced myosin phosphorylation by myosin light-chain phosphatase, causing dephosphorylation of myosin and preventing its binding to actin
- Calcium pumps return calcium to the sarcoplasmic reticulum
Latch State
- In some smooth muscles, a latch state can maintain tension with low ATP consumption, useful in sphincter muscles
- This state occurs when stimulation persists and the cytosolic Ca++ remains elevated. Cross-bridges are held at relatively constant positions, generating tension without continuous ATP use.
Local Factors
- Oxygen, carbon dioxide, osmolarity, and ionic composition of extracellular fluid can affect smooth muscle tension
- Stretching smooth muscle can trigger contraction, as can chemical compounds like nitric oxide
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Description
تتناول هذه الاختبارات أنسجة العضلات المثيرة، بما في ذلك العضلات الهيكلية والملساء والقلبية. تستعرض الخصائص الفريدة لكل نوع من العضلات، وكيفية تنظيمها وعملها في الجسم. سيكون لديك فرصة لاختبار معرفتك حول وظائف العضلات وتكوينها.
