Skeletal muscle Flashcards
What are the properties of skeletal muscle?
- Cross striations2. Voluntary control3. Individual muscle fibers NOT connected by gap junctions / electrical synapses
What are the properties of cardiac muscle?
- Cross striations2. Can be modified by ANS but beats independently via pacemaker cells3. Gap junctions / electrical synapses are part of intercalated discs between cardiac cells
What are the properties of smooth muscle?
- Lack cross striations2. Unitary - functionally syncytial and contains pacemaker cells3. Multiunit - stimulated to contract by NTs
What constitutes a muscle fiber?
- Myofibrils2. Sarcoplasm
What is a myofibril?
Cylindrical structure made up of an end to end chain of repeating units - sarcomeres
What is a sarcomere?
- Functional unit of muscle 2. Contain thick and thin filaments (myofilaments)
What are the features of the sarcoplasm?
Contains mitochondria, nuclei, and other cellular constituents including an extensive ER (SR)
What is the sarcolemma?
Cell membrane of muscle fiber made up of plasma membrane and outer coat
What makes up the outer coat of the sarcolemma?
- Thin layer of material that contains many thing collagen fibers2. At the end this layer fuses with tendon fiber
What is the Z disc?
- Where one end of actin filaments attach2. Attach myofibrils to each other all the way across muscle fiber
What is titin?
- Large proteins that acts as a framework to hold myosin and actin filaments in place2. One end is attached to Z disc and the other to myosin thick filaments 3. Acts as a spring that can change its length as the sarcomere contracts and relaxes
What are the properties of the sarcotubular system?
- Made up of T tubule sysem and SR2. Transmits APs generated near end plate3. SR stores calcium, releases it into myscle cytosol in response to AP and resequesters it to end contraction4. Triad of sarcoplasmic cisterns on either side of a central T tubule
What is the dystrophin-glycoprotein complex?
Dystrophin - forms a rod that connects thin actin filament to a transmembrane protein
What makes up the troponin complex?
- TnI - affinity to actin2. TnT - affinity to tropoyosin3. TnC - affinity for calcium ions
What is the role of calcium in muscle contraction?
- When Ca binds to TnC is causes tropomyosin to move, exposing active site on actin where myosin can bind2. When Ca is pumped back into SR tropomyosin can move back to cover active site on actin 3. ATP must be present to detach myosin heads from actin active sites
What are the steps of the cross bridge cycle?
- ATP binds to and detaches from myosin head2. Due to calcium, binding site on actin is exposed and myosin-ADP+Pi complex binds to a new position on actin 3. Release of Pi triggers power stroke - pulls actin filament 4. ADP release completes cycle - myosin stays bound to actin untila nother ATP binds to myosin head
How does muscle relax?
- ATP binds to myosin head and detaches it from actin2. ATP pumps calcium back into SR - tropomyosin covers active site
What are the characteristics of muscle contraction - excitation?
- AP occurs via EPP2. L type Ca channels in T tubules act as voltage sensors - coupled to Ca release channels (ryanodine)3. Ca rapidly leaves SR via ryanodine receptors and spreads into myofibrils4. Ca pumped back into SR via Ca-ATPase 5. Calsequestrin ensures high functionality of Ca-ATPase pump
What regulates cross bridge cycling?
- Calcium concentrations in myofibrils 2. ATP is responsible for maintaining cycling as long as active site on actin is exposed
How is energy regenerated in muscle?
- Phosphocreatine and creatine kinase rephosphorylate ADP to ATP using high energy bond from phosphocreatine2. Glycogen can be metabolized to pyruvate with rapid production of ATP
What is a motor unit?
- Smallest unit that the nervous system can turn on 2. Has one neuron and several muscle fibers 3. Muscles with fine control have very small motor units (a few muscle cells)4. Large muscles have large motor units (still only one alpha motor neuron but over a thousand fibers)
How is graded muscle contraction produced?
- Multiple motor unit summation - increase number of motor units contracting at a given time 2. Increase rate of stimulation of a single motor unit
The strength of muscle contraction depends on what?
Rate of stimulation of APs in the muscle cell
What is isotonic contraction?
Muscle shortens during contraction but the tension remains constant
