Physiology week 14 Flashcards
What is the sarcolemma
Muscle cell fiber membrane
What is the sarcolemma composed of
- Plasma membrane
-Outer coat of polysaccharides and collagen fibrils,(which fuses with tendons to connect muscle to bones)
What does muscle fiberes contain
- Thusands of myofibrils
What are myofibrils made up of
- Actin and mysoin filaments
Why does myofibrils have a striated apperance
- Due to alternating light and dark bands
When does the greatest force of attraction occur
- When the actin and mysoin filaments just being to overlap
Where is Titin located
In muscle fibers
What is the function of Titin
- Maintain alignment of myosin and actin filaments
-Act as a spring, helping the sacromere to contract and relax
What does the sarcoplasm surround
- Myofibrils
What does the sarcoplasm contain
- High amounts of potassium,magnesium,phosphate and enzymes
-And mitochondria , which produce ATP for muscle contraction
What is the function of Sarcoplasmic retciulul
- Surrounds myofibrils
-Stores,releases and reabsorbs calcium
Explain the mechanism of a mucle contraction starting from an action potential and then motor nerve
1.Action potential (AP) travels along a motor nerve
2.Nerve releases acetylcholine (ACh) at the neuromuscular junction.
3.ACh binds to receptors, opening ACh-gated cation channels.
4.Sodium (Na⁺) ions enter the muscle fiber, causing local depolarization.
5.Voltage-gated sodium channels open, generating an action potential in the muscle fiber.
6.Action potential spreads along the muscle membrane, reaching deep into the muscle.
7.Sarcoplasmic reticulum releases calcium (Ca²⁺) ions, triggering actin-myosin interaction.
8.Actin and myosin filaments slide past each other, leading to muscle contraction.
9.Calcium is pumped back into the sarcoplasmic reticulum, ending contraction until the next action potential.
What is myosin filaments composed of
-myosin molecules
What does each myosin molecule have and their function
- 2 heavy chains which form a double-helix tail and 2 globular heads
-4 Light chains : which help to regulate myosin head functiojn
What do myosin heads form
Crossbridges
Why do cross bridges have two hinges
- For flexibility, allowing head movement
What is the role of ATPase activity in the myosin heads
- Break down ATP to provide energy for contraction
What are Actin Filaments made of
- Actin
-Tropomyosin
-Troponin
Explain the structure of Actin backbone in actin filaments
- It is a double stranded F-actin helix made of G actin subunits
What does each G actin in Actin filaments have
ADP molecule that serves as an active site for myosin binding
What is the function of Tropomyosin
- Wraps around actin, blocking actin-myosin binding sites
What does troponin complex consits of and functions
- Troponin I: Binds to actin
-TnT: Binds to tropomyosin
-TnC: Binds to calcium ions , initiating contraction
The presence of what is required for actin to bind strongly to mysoin
- ATP and magnesium
What is the function of troponin-tropomyosin complex in inhibition
It blocks mysoin binding sites on actin, preventing contraction
Explain the process in which actin filaments are activated( contaction initiation) by clacium ions
-Calcium ions bind to troponin C, causing a conformational change.
-This shifts tropomyosin deeper into the actin groove, exposing myosin binding sites.
-This allows myosin cross-bridges to bind, initiating contraction.
Explain the walk-along (ratchet) theory
- Myosin heads attach to actin active sites.
-This causes a power stroke, where myosin tilts and pulls actin.
-The head then detaches, resets, and binds to a new site, repeating the process.
What does having more cross bridges mean..
- A greater contraction force
The muscle contraction cycle repeats until
- The z membrane reaches the myosin filaments
-The muscle load is too great for further contraction
Explain the step by step process of ATP driven contraction
-ATP binds to myosin head, and ATPase breaks it into ADP + phosphate, storing energy.
-Calcium ions bind to troponin, exposing actin binding sites.
-Myosin head attaches to actin, triggering a power stroke that pulls actin.
-ADP and phosphate are released, and new ATP binds, causing detachment from actin.
-ATP is cleaved again, resetting the myosin head for the next cycle.
What is the work equation
W=L x D ( work = load x Distance)
Name the three Energy sources
- Phosphocreatine
-Glycolysis
-Oxidative metabolism
Explain how phosphocreatine acts as an energy source
Provides instant ATP regeneration by transferring its high-energy phosphate bond
Explain how Glycolysis acts as an energy source:
What is dosent require
-What its faster than
Breaks down glycogen to Pyruvic acid/lactic acid producing ATP
-oxygen
- produces ATP faster than oxidative metabolism
How does Oxidative metabolism act as an energy source
Uses oxygen,glycolysis byproducts and foodstuffs(carbs,fat,proteins), to generate ATP
Name the types of muscle contraction
-Isometric contraction
-Isotonic contraction
Explain what happens to the muscles and tension in the 2 types of muscle contraction
Isometric: Muscle does not shorten ,but tension increase
Isotonic: Muscle shortens at constant tension , while lifting a load
Name the 2 systems used to record muscle contraction
-Isometric system
-Isotonic system
Explain what the 2 systems measure to record muscle contraction
Isometric system: Measures force changes without muscle shortening
Isotonic system: Measures muscle shortening while lifting a load
Name the types of muscle fibers
Fast and slow muscle fibers
Explain slow muscle fibers 4 (characteristics)
- Small
-Extensive blood supply and many capillaries for oxygen transport
-Contains large amounts of mitochondria to support oxidative metabolism - Contains myoglobin , which stores energy and gives a red colour
Explain fast muscle fibers (characteristics) 5
-They are large for strong contraction
-Have extensive sarcoplasmic reticulum for rapid calcium release
-High glycolysis enzyme content
-Has less blood supply and mitochondria
-Low myoglobin, which gives the muscle the white colour
What does a motor unit consist of
- All muscle fibers innervated by a single motonueron
What type of control does small muscles need
- fine control
What type of force does large muscles need
- High force
What is summation
- Adding individual twitch contractions to increase intensity
Name the 2 types of summation
- Multiple Fiber summation
- Frequency summation
When does tetanization occur
- When contraction frequency is high enoughh that twitches fuses into a smooth continous contraction
Prolonged contraction leads to fatigue mainly due to:
-Depletion of glycogen
-Reduced nerve signal transmission
- Loss of oxygen and nutrients
What happens in muscle Hypertrophy
- An increases in muscle mass due to more actin and myosin filaments
What does muscle hypertrophy require
- Forceful contractions
What happens in muscle atrophy
- Muscle mass decreases due to protein degredation
What causes an increased muscle length
- New sacromeres being added at the fiber ends
What acauses shortened muscle
- Sacromeres diappearing
What is muscle fiber hyperplasia
- Increases in fiber number undere extreme force conditions
What happens in muscle denervation
- Loss of nerve supply
What is contracture caused by
When fibrous tissue continues to shrink, leading to permeanent muscle shortening(contracture)
How can debilitating deformities be prevented
- Physical therapy and stretching
