Module 4 Flashcards
What is the best-known feature of skeletal muscle?
Its ability to contract and cause movement
How do muscles maintain skeletal stability and prevent skeletal structure damage or deformation?
By preventing excess movements of the bones and joints
What functions do skeletal muscles allow to be controlled voluntarily?
Swallowing, urination and defecation
How do skeletal muscles protect internal organs?
By acting as an external barrier or shield to external trauma and by supporting the weight of the organs.
How do skeletal muscles contribute to the maintenance of homeostasis?
By generating heat
What does muscle contraction require so that heat can be produced?
Energy
What are the three layers of connective tissue that a skeletal muscle has? What is its purpose?
Mysia; it encloses the skeletal muscle and provides structure to the muscle as a whole, and also compartmentalizes the muscle fibres within the muscle.
What is the purpose of epimysium?
It allows a muscle to contract and move powerfully while maintaining its structural integrity.
It also separates muscle from other tissues and organs in the area, allowing the muscle to move independently.
What is a fascicle?
Individual bundle of organized muscle fibers inside each skeletal muscle.
What is the middle layer of connective tissue inside a skeletal muscle?
Perimysium
What is the importance of the fascicular organization in the muscles of the limbs?
It allows the nervous system to trigger a specific movement of a muscle by activating a subset of muscle fibers within a bundle, or fascicle of the muscle
What is endomysium?
A thin connective tissue layer of collagen and reticular fibers in which each muscle fiber inside each fascicle is encased in.
What are skeletal muscle cells commonly referred to as? Why?
Muscle fibres because the skeletal muscle cells are long and cylindrical.
What is the plasma membrane of the muscle fibers?
Sarcolemma
What is the cytoplasm of muscle fibers called?
Sarcoplasm
What is the sarcoplasmic reticulum (SR)?
A specialized smooth endoplasmic reticulum which stores, releases, and retrieves calcium ions
What is the functional unit of skeletal muscle fiber?
Sarcomere
The sarcomere is a highly organized arrangement of the contractile of what two myofilaments?
Actin (thin filament) and myosin (thick filament)
What causes the striated appearance of skeletal muscle fibers?
The arrangement of the myofilaments of actin and myosin in sequential order from one end of the muscle fiber to the other.
What is each packet of microfilaments and their regulatory proteins, troponin and tropomyosin along with other proteins called?
Sarcomere
What happens to the entire muscle as myofibrils contract?
It ccontracts
What is another specialization of the skeletal muscle which is the site where a motor neuron’s terminal meets the muscle fiber called?
The neuromuscular junction (NMJ)
What is the neuromuscular junction (NMJ)?
This is where the muscle fiber first responds to signaling by the motor neruon.
What is the only way to functionally activate the fiber to contract?
Excitation signals from the neuron.
Both neurons and skeletal muscle cells are electrically excitable, what does this mean?
They are able to generate action potentials.
What is an action potential?
It is a special type of electrical signal that can travel along a cell membrane as a wave?
What must happen first for a skeletal muscle fiber to contract?
Its membrane must first be excited, i.e., it must be stimulated to fire an action potential
Explain the excitation-contraction coupling.
For a skeletal muscle fiber to contract, it must be first “excited” (stimulated to fire an action potential). The muscle fiber action potential, which sweeps along the sarcolemma as a wave, is “coupled” to the actual contraction through the release of calcium ions from the SR. Once released, the calcium ions interact with the shielding proteins, forcing them to move aside so that the actin-binding sites are available for attachment by the myosin head. The myosin then pulls the actin filaments toward the center, shortening te muscle fiber.
How does the excitation-contration coupling begin in skeletal muscle?
It begins with signals from the somatic motor division of the nervous system
Where do the motor neurons, that tell the skeletal muscle to contract, originate?
In the spinal cord with a smaller number located in the brainstem
What are the long processes that the motor neurons have? What is the function?
Axons are specialized to transmit action potentials long distances
What is a triad?
The arrangement of a T-tubule with the membranes of SR on either side.
What is the function of T-tubules?
They carry the action potential into the interior of the cell.
When does muscle contraction usually stop?
When signalling from motor neuron ends
When can a muscle also stop contracting (aside from signalling from motor neuron ends)?
When it runs out of ATP and becomes fatigued.
Why is the zone where thin and thick filaments overlap very important to muscle contraction?
As it is the site filament movement starts.
Myofibrils and muscle cells contract as the sarcomeres contract, why is that?
Because a myofibril is composed of many sarcomeres running along its length.
Describe the process known as the sliding filament model of muscle contraction.
When signalled by a motor neuron, a skeletal muscle fiber contracts as the thin filaments are pulled and then slide past the thick filaments within the fiber’s sarcomeres.
When can the sliding only occur?
When myosin-binding sites on the actin filaments are exposed by a series of steps that begins with calcium ions entry into the sarcoplasm.
What is a protein that winds around the chains of the actin filament and covers the myosin-binding sites to prevent actin from binding to myosin?
Tropomyosin
Tropomyosin binds to troponin to form what?
The troponin-tropomyosin complex
What is the importance of the troponin-tropomyosin complex?
It prevents the myosin “heads” from binding to the active sites on the actin microfilaments.
What does the tropomyosin have to do to initiate muscle contraction?
Tropomyosin has to expose the myosin-binding site on the actin filament to allow cross-bridge formation between the actin and myosin microfilaments.
What is the cross-bridge cycle?
The repeated movements of myosin head pulling the actin at the binding stes, detaching, re-cocking, and attaching to more binding sites during muscle contraction for thin filaments to continue to slide past thick filaments.
When does cross-bridge formation occur?
When the myosin head attaches to the actin while adenosine diphosphate (ADP) and inorganic phosphate are still bound to myosin.
