Skeletal Muscle Anatomy lab
Introduction to Skeletal Muscle Tissue
Understanding the anatomy of skeletal muscle tissue is essential for physiology and helps in learning different muscle structures.
Properties of Muscle Tissue
Excitability: Ability to generate action potentials and change membrane potential. Unique to muscle cells and neurons.
Contractility: Muscles can shorten to produce power and force, unlike other cell types.
Elasticity: Muscles can stretch and recoil back to their original shape, similar to rubber bands.
Extensibility: Muscles can stretch or extend in length. Elasticity is about recoil.
Muscle Fibers (Muscle Cells)
Known as myoblasts, which are muscle-building cells. Myoblasts fuse to form muscle fibers, resulting in multiple nuclei per fiber.
Satellite Cells: These are muscle stem cells that remain outside fused muscle cells and help repair damaged muscle fibers.
Structure of Skeletal Muscle
Muscle is organized in layers:
Muscle: Composed of bundles of fascicles.
Fascicles: Made up of groups of muscle fibers (cells).
Muscle Fibers: Composed of myofibrils.
Connective Tissue Layers
Epimysium: Surrounds the entire muscle, separating it from neighboring muscles.
Perimysium: Surrounds individual fascicles within a muscle.
Endomysium: Surrounds individual muscle fibers.
Muscle Fiber Structure
Sarcoplasm: Cytoplasm of muscle cells.
Sarcoplasmic Reticulum: Specialized endoplasmic reticulum in muscle that surrounds myofibrils.
Transverse Tubules (T Tubules): Extensions of the sarcolemma; penetrate into the fiber and wrap around myofibrils.
Triad: Structure formed by a T tubule flanked by two terminal cisternae (lateral sacs of the sarcoplasmic reticulum).
Myofibrils and Myofilaments
Myofibrils: Composed of repeating units called sarcomeres.
Myofilaments: Two types:
Actin (Thin): Made of two strands of actin beads (G-actin) and associated with tropomyosin and troponin complexes.
Myosin (Thick): Composed of myosin molecules with heads; involved in muscle contraction.
Sarcomere Structure
Z Line: Points where actin myofilaments attach.
Titin: Elastic protein connecting myosin to the Z line, contributing to elasticity.
Muscle Fiber Types
Slow Fibers (Type I): Good for endurance, smaller with more capillaries, mitochondria, and myoglobin.
Fast Fibers (Type II): Larger, powerful, but fatigue quickly, with more glycogen and less myoglobin.
Intermediate Fibers: Between slow and fast fibers, adapted based on activity levels.
Motor Units
Defined as a motor neuron and all muscle fibers it innervates.
More fibers connected to a motor neuron means more force generated in contraction.
Muscle Fiber Arrangement Patterns
Parallel Muscles: Good for endurance. Example: Biceps.
Circular Muscles: Good for constricting openings. Example: Sphincters.
Convergent Muscles: Broad origin fibers converge at a single insertion. Example: Deltoid.
Pennate Muscles: Muscle fibers arranged at angles to a central tendon; they give more power.
Conclusion and Exam Preparation
Study the names of muscles, their relationships, and ensure to understand their structure and function.
Practice spatial orientation through muscle layers and arrangements.
Be prepared for questions regarding muscle classification, origination, and innervation in exams.
Muscle cells develop primarily during the embryonic stage of development. Myoblasts, the muscle-building cells, fuse to form muscle fibers, resulting in multi-nucleated structures. This process continues through childhood and adolescence as the body grows, and satellite cells assist in the repair and regeneration of muscle tissue following injury or stress.
29. In terms of relative amounts which do we have more and less of - ATP, CP or glycogen stores?
Glycogen stores are the most abundant, followed by creatine phosphate (CP), and ATP is present in the smallest amounts as it is used quickly in metabolic processes.
30. What are the different types of fuels (substrates) that can be used by the body to generate ATP?
The body can use carbohydrates (glucose), fats (fatty acids), and proteins (amino acids) as fuels to generate ATP.
31. What is the purpose for having creatine phosphate (CP)?
Creatine phosphate acts as a rapid source of energy; it donates a phosphate group to ADP to regenerate ATP quickly during high-intensity activities.
32. How do we generate more CP?
Did you think about the enzyme needed?
Yes, the enzyme creatine kinase is necessary for the production of CP.
Where in the muscle cell does this take place?
This reaction takes place in the sarcoplasm of the muscle cell.
Is this an aerobic or anaerobic process?
This is an anaerobic process.
33. During aerobic and anaerobic metabolism what are we using as “fuel” to produce ATP?
In aerobic metabolism, we primarily use glucose and fatty acids, while in anaerobic metabolism, glucose (from glycogen) is the main fuel source.
34. In what regions/parts of a cell do we find aerobic and anaerobic metabolism taking place?
Aerobic metabolism occurs in the mitochondria, whereas anaerobic metabolism takes place in the cytoplasm (sarcoplasm) of the cell.
35. What determines the metabolic pathway that a muscle cell uses to generate energy?
What are those different pathways?
The intensity and duration of activity, availability of oxygen, and type of fuel determine the metabolic pathway. Pathways include glycolysis, oxidative phosphorylation, and the Krebs cycle.
36. What do mitochondria use and produce as they make ATP?
Mitochondria use substrates (mainly glucose and fatty acids) and oxygen to produce ATP, carbon dioxide, and water as byproducts.
37. Define glycolysis
Glycolysis is the metabolic pathway that converts glucose into pyruvate, producing ATP and NADH.
What do you specifically get because of this process?
The process yields 2 ATP and 2 NADH per glucose molecule.
Is oxygen needed for this process?
No, glycolysis does not require oxygen.
How many total ATP are generated because of this process?
A total of 4 ATP are produced from glycolysis.
How many NET ATP do we get?
The net gain is 2 ATP.
38. During resting periods of muscle activity:
What is the “fate” of glucose (what does it become)?
Glucose is converted to glycogen for storage.
Are you using or producing ATP here?
ATP is being produced during this resting phase.
Are you producing or using CP?
CP is being produced during this time.
Are mitochondria making ATP and what happens to any “excess” ATP?
Yes, mitochondria are making ATP, and excess ATP is often used to regenerate creatine phosphate or is stored for future use.
What are the mitochondria using to produce ATP?
Mitochondria use fatty acids and glucose (from glycogen) to produce ATP.
What are the different ways to make ATP during this level of activity?
ATP can be generated via oxidative phosphorylation and substrate-level phosphorylation.
39. During moderate levels of activity
What happens to glycogen?
Glycogen is broken down into glucose for energy.
What does glucose become – what is its “fate?”
Glucose undergoes glycolysis to become pyruvic acid.
What do we call this process?
This process is called glycolysis.
What are the mitochondria using to produce ATP?
Mitochondria use the pyruvate derived from glycolysis and fatty acids to produce ATP.
Does glucose go directly into the mitochondria or is it cut (cleaved) into small parts?
Glucose is cleaved into smaller parts (pyruvate) before entering the mitochondria.
How many ATP are coming from glycolysis (glucose to pyruvic acid) directly?
Glycolysis directly produces 2 ATP.
How many ATP come from pyruvic acid being used by the mitochondria?
Each pyruvate generates approximately 15 ATP when fully oxidized in the mitochondria.
What are the different ways to make ATP during this level of activity?
ATP is made through glycolysis and oxidative phosphorylation.
40. During “peak” physical activity which metabolic pathway is our primary source of ATP production?
The primary source of ATP production during peak activity is anaerobic glycolysis.
Did you keep in mind the number of ATP generated and what was the fuel source for this?
Yes, anaerobic glycolysis generates 2 ATP from glucose.
What substance is not being used efficiently by the mitochondria?
Oxygen is not being used efficiently.
Why is this happening?
This occurs due to the high demand for ATP exceeding the oxygen supply.
What happens to this substance that is building up in the muscle cell?
Lactic acid builds up in the muscle cell.
How has the pH of the muscle changed?
The pH of the muscle decreases (becomes more acidic).
Why is this not a good change?
Decreased pH can lead to muscle fatigue and impair contraction.
Are you still using CP as a source of some ATP?
Yes, creatine phosphate (CP) is still used to produce ATP during peak activity.
What are the different ways to make ATP during this level of activity?
ATP can be generated through anaerobic glycolysis and the breakdown of CP.
41. Explain the Cori Cycle.
The Cori Cycle is the metabolic pathway that recycles lactic acid produced in muscles back to glucose in the liver.
What organs/cells are involved?
The liver and muscle cells are involved in the Cori Cycle.
What is not a part of the actual Cori cycle?
Glycolysis in muscle cells is not part of the Cori Cycle.
Why is this not a very efficient pathway?
It is not very efficient because it uses energy to convert lactic acid back to glucose, with some energy loss during the process.
42. What are the two different metabolic pathways for pyruvic acid?
The two pathways for pyruvic acid are:
Aerobic pathway – enters the Krebs cycle for complete oxidation with oxygen present.
Anaerobic pathway – converted to lactic acid when oxygen is limited.
43. Define gluconeogenesis and what are examples of this process?
Gluconeogenesis is the metabolic process of synthesizing glucose from non-carbohydrate precursors, such as lactate, amino acids, and glycerol.
Examples include the conversion of lactic acid from anaerobic metabolism and amino acids from protein breakdown into glucose.
44. Define hypertrophy and atrophy.
Hypertrophy: An increase in the size of muscle fibers due to resistance training and increased workload.
Atrophy: A decrease in muscle size and strength due to disuse, aging, or disease.