Name: how motor units control muscle movement
Uploaded: 2025-10-23T11:49:15.000Z
Duration: 46 s
Channel: JoVE

الوحدة الحركية تشير إلى خلية عصبية حركية واحدة توجد في النخاع الشوكي و عدد ألياف العضلات التي تقويها في حين أن كل الألياف العضلية الهيكلية يتم تقويتها بواسطة خلية عصبية حركية واحدة فإن المحاور من كل خلية عصبية حركية يمكنها التفرع إلى عدد من النهايات وتشكل تقاطعات عصبية عضلية عبر العضلات نتيجة لذلك تحفيز الوحدة الحركية الفردية يؤدي إلى تقلص ضعيف في العضلات بأكملها إعتماداًعلى مستوى التحكم المطلوب يمكن لعدد الألياف لكل وحدة أن يختلف عن الآخر من عدد قليل من العضلات التي تتطلب حركة دقيقة إلى عدة مئات من العضلات أقل دقة في الوزن

ستيفاني ، نيكولاس. "الخلايا العصبية الحركية وتوليد تنوع الخلايا العصبية الحركية الشوكية". الحدود في علم الأعصاب الخلوي 8 (9 أكتوبر 2014). [<a href = "https://doi.org/10.3389/fncel.2014.00293" target = "__blank" >المصدر</a>]

الوحدات الحركية

Motor Units

تتكون الوحدة الحركية من مكونين رئيسيين: خلية عصبية حركية واحدة (أي خلية عصبية تحمل النبضات بعيداً عن الجهاز العصبي المركزي) وجميع الألياف العضلية التي تعصبها. قد تعصب الخلايا العصبية الحركية أليافاً عضلية متعددة ، وهي خلايا مفردة ، لكن عصبوناً حركياً واحداً فقط يعصب ليف عضلي واحد.

الخلايا العصبية الحركية السفلية هي خلايا عصبية مؤثرة تتحكم في العضلات الهيكلية ، وهي أكثر أنواع العضلات وفرة في الجسم. توجد أجسام الخلايا للخلايا العصبية الحركية السفلية في الحبل الشوكي أو جذع الدماغ. تلك الموجودة في جذع الدماغ تنقل الإشارات العصبية عبر العصب القحفي ، وتتحكم بشكل أساسي في عضلات الرأس والرقبة. ترسل الخلايا العصبية الحركية السفلية التي تنشأ في النخاع الشوكي إشارات على طول العصب الفقري ، وتتحكم بشكل أساسي في عضلات الأطراف وجذع الجسم.

تطلق الخلية العصبية الحركية السفلية جهود فعل التي تنقبض دفعة واحدة على جميع خلايا العضلات الهيكلية التي يعصبها العصبون. وبالتالي ، فإن الوحدات الحركية هي وحدات وظيفية للعضلات الهيكلية.

يختلف حجم الوحدة الحركية ، أو عدد الألياف العضلية التي يغذيها العصبون الحركي السفلي ، اعتماداً على حجم العضلات والسرعة والدقة التي تتطلبها الحركة. يتم التحكم في عضلات العين والأصابع ، والتي تتطلب تحكماً سريعاً ودقيقاً ، بشكل عام بواسطة وحدات حركية صغيرة. في هذه الوحدات ، تتصل الخلايا العصبية الحركية بعدد صغير من ألياف العضلات. على النقيض من ذلك ، فإن الوحدات الحركية الخاصة بحركات الأطراف والجذع كبيرة بشكل عام وتتكون من العديد من الألياف العضلية.

تتكون الوحدة الحركية من مكونين رئيسيين: خلية عصبية حركية صادرة واحدة (أي خلية عصبية تحمل نبضات بعيدا عن الجهاز العصبي المركزي) ...

Education

JoVE Core

Biology

علم الأحياء

Human Biology

بيولوجيا الإنسان

Musculoskeletal System

الجهاز العضلي الهيكلي

KEY TERMS AND CONCEPTS

المصطلحات والمفاهيم الأساسية

how motor units control muscle movement

Motor units control skeletal muscle movement. A motor unit includes one efferent motor neuron, which carries signals away from the central nervous system, and all of the muscle fibers it innervates. A single motor neuron can connect with multiple muscle fibers, but each muscle fiber is innervated by only one motor neuron.

Lower motor neurons are the efferent neurons that control skeletal muscle, the most abundant type of muscle in the body. Their cell bodies are found in the spinal cord or brain stem. Neurons in the brain stem send signals through cranial nerves and mainly control muscles in the head and neck.

Lower motor neurons in the spinal cord send signals through spinal nerves. These neurons mainly control muscles in the limbs and body trunk. When a lower motor neuron fires an action potential, all of the skeletal muscle cells it innervates contract at the same time.

Motor units are the functional units of skeletal muscle. Their size depends on the size of the muscle and on how fast and precise the movement must be. Muscles in the eyes and fingers usually have small motor units for rapid, precise control, while motor units for limb and trunk movement are generally large and contain many muscle fibers.

How Motor Units Control Muscle Movement

what is the skeletal system?

Human Skeleton: Bones, Cells, and Disease

The human skeleton is a living framework made of 206 bones in adults. Bones connect with cartilage, tendons, and ligaments. This system gives the body support, protects organs, and helps with movement and locomotion. The skeleton has two main parts: the axial skeleton and the appendicular skeleton. The axial skeleton has 80 bones and includes the skull, the vertebral column, and the rib cage. The cranium, or upper skull, has eight bones that enclose the brain, while the lower part of the skull...

bone structure

Inside a Long Bone

Inside a long bone, osseous tissue is organized into two main types: cortical bone and cancellous bone. A femur is a clear example of this structure. The bone also includes outer coverings and inner spaces that support growth, repair, and blood cell production. Cortical bone, also called compact bone, forms the dense outer layer along the diaphysis, or shaft. It is covered by the periosteum, a membrane with connective tissue, capillaries, and nerves. Beneath the cortical layer is the medullary...

joints

Types of Joints in the Human Body

Joints are the places where adjacent bones connect. They are also called articulations or articular surfaces. Joints help the body move and stay stable. Joints can be classified by structure or by function. Structural classification depends on the material that forms the joint and whether there is a space between the bones. By structure, joints are fibrous, cartilaginous, or synovial. Fibrous joints are connected by fibrous tissue and have no cavity between the bones. Because of this, they do...

bone remodeling

How Hormones Control Bone Turnover

Bone turnover is a continuous process in which old bone is broken down and new bone is built. Osteoclasts carry out bone resorption, and osteoblasts carry out bone formation. In adults, this balanced cycle helps maintain bone mass and calcium homeostasis. Mechanical stress can also stimulate turnover as part of normal maintenance and repair. Parathyroid hormone, or PTH, helps control blood calcium levels by increasing bone resorption when calcium is low. It is released from the parathyroid...

skeletal muscle anatomy

Muscle Fibers, Tendons, and Contraction

Skeletal muscle moves the body by pulling on bones through tendons. Tendons are the connective tissue that attaches skeletal muscle to bones. When skeletal muscles contract, they create voluntary movement. Skeletal muscle is wrapped in layers of connective tissue. The outer layer is the epimysium, which helps protect the muscle. Beneath it, the perimysium surrounds and groups fasciculi, which are bundles of skeletal muscle cells called myocytes. These cells are also called skeletal muscle...

classification of skeletal muscle fibers

Skeletal Muscle Fiber Speed and Energy

Skeletal muscle fibers can be grouped by how fast they contract and how they make ATP, the energy cells use for movement. These differences also shape their physical features. Most human muscles contain all three fiber types, but in different amounts. Slow oxidative fibers, also called slow-twitch fibers, appear red because they have many capillaries and high levels of myoglobin, an oxygen-storing protein. They also contain more mitochondria, which make ATP through oxidative phosphorylation,...

muscle contraction

Nerve Signals That Trigger Muscle Contraction

Nerve signals trigger muscle contraction in both skeletal and smooth muscle, but the two muscle types use different control systems. In skeletal muscle, the signal begins at the motor end plate, which is the synapse between a motor neuron and a muscle fiber. In smooth muscle, contraction is controlled by the autonomic nervous system and happens without conscious control. In skeletal muscle, motor nerve terminals release acetylcholine. This neurotransmitter binds to receptors on the sarcolemma,...

cross-bridge cycle

Calcium Control in Muscle Contraction

Calcium control in muscle contraction depends on ATP, motor neurons, and the sliding action of actin and myosin. As a muscle contracts, the thin and thick filaments overlap more, and the sarcomere, which is the contractile unit of the muscle, becomes shorter. This process uses energy from ATP and happens in a repeating cycle at the molecular level. Myosin drives the movement of actin through a cross-bridge cycle. When ATP attached to the myosin head is hydrolyzed to ADP, myosin shifts into a...

motor units

Motor units control skeletal muscle movement. A motor unit includes one efferent motor neuron, which carries signals away from the central nervous system, and all of the muscle fibers it innervates. A single motor neuron can connect with multiple muscle fibers, but each muscle fiber is innervated by only one motor neuron. Lower motor neurons are the efferent neurons that control skeletal muscle, the most abundant type of muscle in the body. Their cell bodies are found in the spinal cord or...

the spinal cord

Spinal Cord Structure and Dermatomes

The spinal cord is the main nerve pathway of the central nervous system. It carries sensory signals from the body to the brain and motor signals from the brain to the body. It begins at the foramen magnum, the opening at the base of the skull, and extends to the level of the first or second lumbar vertebra. In cross-section, the spinal cord is cylindrical and contains both gray matter and white matter. The central canal lies in the middle and is a remnant of the lumen of the primitive neural...

nociception

Pain Signaling and Inflammation

Pain signaling begins when the body detects a harmful stimulus. Sharp objects, open flames, and corrosive chemicals can trigger this response. Sensory receptors called nociceptors, which sit on nerve endings, detect these noxious stimuli and use ion channels to turn them into electrical signals. Those electrical signals travel through sensory neurons to the brain, where they are experienced as pain. This warning system helps an organism avoid damage and stay safe. Pain is therefore an...

key terms and concepts

Learn how motor units link one motor neuron to many muscle fibers, and why small or large motor units help control precise or powerful movements.

How Motor Units Control Muscle Movement | JoVE K12

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How Motor Units Control Muscle Movement

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