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Muscular System
| Question | Answer |
|---|---|
| What are myofibrils? | Structures that contain microfilaments divided into sarcomeres. |
| What are sarcomeres? | Individual contractile units separated by a border called the Z-line. |
| What does the sarcoplasmic reticulum do? | Stores Ca²⁺ and surrounds myofibrils. |
| What is the sarcoplasm? | The same thing as cytoplasm, but referred to as sarcoplasm in muscles. |
| What is the sarcolemma? | The plasma membrane of muscle cells that can propagate action potentials; it is invaginated by T-tubules, which are channels for ion flow. |
| Why are mitochondria important in muscle fibers? | They are present in large amounts in myofibrils to support energy demands. |
| What are the two filament types in a sarcomere? | Thin filaments (made of actin polymers) and thick filaments (made of the protein myosin). |
| What is the A band? | The dark band that contains thick (myosin) filaments. |
| What is the I band? | The light band that contains thin (actin) filaments only. |
| What is the H zone? | The region in the center of the A band containing only thick filaments (no actin overlap). |
| What is the M line? | The midline of the sarcomere that anchors the thick filaments. |
| What is the Z disc/Z line? | The border that defines the edges of each sarcomere; thin filaments attach here. |
| What type of response does muscle activation follow? | An "all or nothing" response, just like an action potential. |
| What are the 5 steps of the neuromuscular pathway? | 1. AP releases ACh at NMJ. 2. AP spreads along sarcolemma/T-tubules. 3. SR releases Ca²⁺. 4. Ca²⁺ binds troponin, exposing actin sites. 5. Myosin binds actin; sliding filament model causes contraction. |
| What does ACh do at the neuromuscular junction? | It binds to receptors and opens sodium ion channels, leading to an action potential in the sarcolemma. |
| What is Step 1 of the Sliding Filament Model? | Ca²⁺ exposes binding sites on actin — Ca²⁺ binds to troponin, which pulls back tropomyosin, exposing attachment sites on actin. |
| What is Step 2 of the Sliding Filament Model? | The myosin head attaches to the actin filament, forming a cross-bridge. |
| What is Step 3 of the Sliding Filament Model? | Inorganic phosphate is released from the myosin head, initiating the power stroke. The muscle contracts, bringing the Z-lines together. After the power stroke, ADP is released and myosin remains bound to actin. |
| What is Step 4 of the Sliding Filament Model? | New ATP attaches to the myosin head, causing cross-bridges to unbind. If no ATP is available, the muscle stays stuck in contraction (ex: rigor mortis). |
| What is Step 5 of the Sliding Filament Model? | When ATP is converted to ADP + Pᵢ, the myosin head is cocked back (energized), and the cycle is ready to repeat. |
| What happens if no ATP is available during muscle contraction? | Myosin stays bound to actin and the muscle is stuck in contraction — this is called rigor mortis. |
| What is a motor unit? | A single motor neuron and all the muscle fibers it stimulates. |
| Why don't all muscle fibers contract at once when we use a muscle? | This is beneficial — it allows us to use just a single muscle with controlled force rather than full contraction every time. |
| How does force increase in a muscle? | More force needed → more motor units recruited → more fibers used to generate force. |
| What happens as submaximal stimulus increases? | Motor unit recruitment increases. |
| What happens when a maximum stimulus is reached? | All motor units are recruited. |
| What are the key features of cardiac muscle? | Striated appearance; one or two central nuclei; cells separated by intercalated discs that have gap junctions; contains a lot of mitochondria. |
| What is the function of intercalated discs in cardiac muscle? | They connect cardiac muscle cells and contain gap junctions that allow electrical signals to pass between cells. |
| Can cardiac muscle contract without nerve stimuli? | Yes — cardiac muscle is capable of contracting without nerve stimuli. |
| What are the key features of smooth muscle? | Lacks striation; contains one central nucleus; stimulated by the autonomic nervous system; does not utilize sarcomeres. |
| Can smooth muscle contract without nerve stimuli? | Yes — smooth muscle is capable of contracting without nerve stimuli. |
| What nervous system controls smooth muscle? | The autonomic nervous system. |
| What is a sarcomere? | The structural unit of a myofibril in striated muscle; composed of thin filaments (actin polymers) and thick filaments (myosin). |
| How does skeletal muscle contraction aid circulation? | Contraction squeezes blood and lymph vessels, and skeletal muscles act as a muscular pump that contracts and relaxes to aid circulation. |
| What are satellite cells? | Stem cells located on the outer surface of muscle fibers (beneath the sarcolemma) that are involved in muscle repair and regeneration. They are found in skeletal muscle and smooth muscle. |
| Where are satellite cells found across muscle types? | They are present in skeletal muscle (on the surface of muscle fibers near the sarcolemma) and in smooth muscle (alongside autonomic neurons and muscle fibers). |
Created by:
smurtab