Block 3: Muscular System - Lecture 3.2 Flashcards
What is an individual muscle cells called?
Myocytes or Muscle Cells
What are the steps to muscle growth?
More Exercise –> more nuclei –> more proteins –> more muscle growth!!
How many nuclei are in each myoblast prior to birth?
1
What causes the creation of an immature muscle fiber?
Fusion of myoblasts
What cells are considered stem cells for muscle and do not fuse with myoblasts?
Satellite cells
After an immature muscle fiber is formed, what becomes apparent?
Striations become visible and nuclei spread throughout the fiber
What are the 3 structural steps of making muscle fibers PRIOR TO BIRTH?
fusion of myoblasts with satellite cells on top –> immature muscle fiber forms –> mature muscle fiber forms with visible striations
What is the job of satellite cells?
Regenerate muscle after birth
What is a tendon?
Connects muscle to bone
What percentage of muscle is connective tissue?
10%
What are the names of the 3 different connective tissues that make up a muscle?
1) Epimysium (upon muscle)
2) Perimysium (around fascicles)
3) Endomysium (surrounds individual muscle fibers)
What are the two contractile proteins that make up a myofibril?
1) Actin
2) Myosin
From the subcellular level to the organ level, list all the layers that make up a muscle.
Subcellular Level
- myofibril
- muscle fiber
- endomysium
- fascicle
- perimysium
- muscle
- epimysium
Organ Level
What is the muscle cell membrane called?
Sarcolemma
- phospholipid bilayer of skeletal muscle cells
What connective tissue covers muscle fibers?
Endomysium
What connective tissue covers a fascicle?
Perimysium
What connective tissue covers a muscle?
Epimysium
What percentage of skeletal muscle is intramuscular connective tissue?
1 - 10%
As a person gets older, what happens to the Intramuscular CT?
Stiffens
What are the functions of Intramuscular CT?
1) Transmits forces
- to reach tendons
2) Spring-like properties
- tendons store and release energy
- more exercise = less energy needed
What is Fascia?
Connects groups of muscles together and separates them into compartments
- shows continuity (CT) throughout the body
What are the three units of subcellular organization that muscle activation relies on?
1) Sarcolemma
2) Sarcoplasmic Reticulum
3) Myofibrils
What is the job of the sarcolemma?
Conducts electrical signals
- muscle sheath
What is the job of the sarcoplasmic reticulum?
1) Control muscle contraction
2) Store calcium
What is the job of myofibrils?
Muscle contraction
How does conduction work in muscles?
T-tubules spread electrical signals to the center of muscle fibers
- surrounded by terminal cisterns, one on each side
Sarcolemma encloses cytoplasm of skeletal muscle fiber
How does control work in muscles?
Sarcoplasmic Reticulum (SR)
- organelle within muscle fiber that stores calcium
- surrounds myofibrils
What is included in the “Triad”?
1) Sarcoplasmic Reticulum (SR)
2) T-tubules
3) Terminal Cisterns
How does contraction work in muscles?
myofibrils arranged into bundles of protein filaments –> muscle shortening by actin & myosin –> actin & myosin are organized into muscle units called sarcomeres
Actin forms [thin/thick] filament.
Thin
Myosin forms [thin/thick] filament.
Thick
What are 3 basic characteristics of sarcomeres?
1) Repeating units within myofibril
- forms striations
2) Functional unit of muscle contraction
3) Basic structural unit of myofibrils
What is the function of longitudinal sarcomeres?
Force production
What is the function of cross sectional sarcomeres?
Individual muscle fibers
What are the 3 categories of muscle proteins?
1) Structural proteins
2) Contractile proteins
3) Regulatory proteins
What are the 5 structural proteins?
1) α-actinin
2) Nebulin
3) Titin
4) Dystrophin
5) Myomesin
What are the 2 contractile proteins?
1) Actin
2) Myosin
What are the 2 regulatory proteins?
1) Troponin
2) Tropomyosin
Why are structural proteins so important to skeletal muscle function?
mutations/disruptions can cause muscle disease
What structure do the two contractile proteins make up?
Sarcomere
What type of protein is α-actinin and what is its role?
Structural Protein
- makes up the z-disk
- binds to actin & tinin
What type of protein is Nebulin and what is its role?
Structural Protein
- “ruler” for thin filament
- anchors thin filament to z-disks
What type of protein is Myosin and what is its role?
Contractile Protein
- heads reach up to thin filament to bind to actin
- motor protein in thick filament
- forms crossbridge with thin filament
What type of protein is Actin and what is its role?
Contractile Protein
- wraps around Nebulin
- thin filaments with myosin binding sites
- forms crossbridge with thick filament
What type of protein is Myomesin and what is its role?
Structural Protein
- provides structural integrity in the M-line
What type of protein is Titin and what is its role?
Structural Protein
- stabilizes thick filaments
- spring-like to allow muscle to bring sarcomere back to resting length
What type of protein is Tropomyosin and what is its role?
Regulatory Protein
- protein on thin filaments
- covers myosin binding sites on actin when muscle is relaxed
- physically turns during muscle contraction to expose myosin binding sites
What type of protein is Troponin and what is its role?
Regulatory Protein
- protein on thin filaments and attached to tropomyosin
- turns when calcium is present to allow tropomyosin to bind to myosin binding sites
- controls position of tropomyosin
a. relaxed: troponin holds tropomyosin
b. contraction: calcium binds to troponin & causing conformation change to expose myosin binding sites
What type of protein is Dystrophin and what is its role?
Structural Protein
- relays force/tension from sarcomere to sarcolemma via CT around the muscle fiber and to the tendon
a. sarcomere links thin filament to sarcolemma then anchors to collagen fibers
What type of muscle tissue is Dystrophin not present?
Smooth muscle tissue
What happens when there is no Dystrophin present in the body?
weak muscles from not being able to contract
- ex: lose blood flow to cardiac muscle tissue because no dystrophin to allow contraction
What do actin molecules have that for crossbridges and actin helicies to form?
- globs of actin molecules with sites for myosin crossbridges
- actin helicies formed by two strands of connected actin molecules
What structure do actin/thin filaments attach to?
Z discs
What are the two main components of myosin/thick filaments?
Myosin heavy chain
- head & tail twisted together
- different forms give rise to different force and velocity production
Myosin ATPase site
- head = energy regulation uses ATP for conformation change of the protein, leading to muscle shortening
What two binding sites are on the myosin heads?
1) Actin-binding site
2) Myosin ATPase site
What structure do thick filaments overlap?
Zone of Overlap: overlap with thin filaments
a. may form crossbridges
How many molecules of thin filament surround one molecule of thick filament?
- 1 thick filament is surrounded by 6 thin filaments
- 1 thin filament is surrounded by 3 thick filaments
What are the basic steps to single muscle fiber contraction?
1) Myosin heads bind to actin & form crossbridges
2) Conformational change (energized by ATP hydrolysis) causes thin filaments to slide along thick filaments
3) Myosin head groups release and form new crossbridges
What are the results of basic single muscle fiber contraction?
1) Z-line move towards each other
2) Sarcomere decreases in length
3) Myofibril shortens
4) Muscle fibers shorten
