Podcast
Questions and Answers
Which enzyme breaks down acetylcholine (ACh) to permit skeletal muscle relaxation?
Which enzyme breaks down acetylcholine (ACh) to permit skeletal muscle relaxation?
- Cholinesterase
- Acetylcholinase (ACh)
- Carboxylase
- Acetylcholinesterase (AChE) (correct)
What prevents cross-bridge formation during muscle relaxation?
What prevents cross-bridge formation during muscle relaxation?
- Tropomyosin-troponin complexes covering the myosin binding sites on actin (correct)
- Binding of Ca2+ to actin
- Inhibition of acetylcholinesterase
- Low ATP levels
When does a muscle fiber develop its greatest tension?
When does a muscle fiber develop its greatest tension?
- When there is an optimal overlap between thick and thin filaments (correct)
- When thick filaments outnumber thin filaments
- When Ca2+ concentration is zero
- When there is no overlap between thick and thin filaments
Which factor does NOT affect maximum muscle tension (force)?
Which factor does NOT affect maximum muscle tension (force)?
Approximately how many muscle fibers are in a motor unit that controls eye movements?
Approximately how many muscle fibers are in a motor unit that controls eye movements?
What term refers to the brief contraction in response to a single action potential?
What term refers to the brief contraction in response to a single action potential?
Which phenomenon describes larger contractions resulting from stimuli arriving at different times?
Which phenomenon describes larger contractions resulting from stimuli arriving at different times?
How long is the refractory period for skeletal muscle?
How long is the refractory period for skeletal muscle?
What do smooth muscle filaments attach to and stretch from one to another?
What do smooth muscle filaments attach to and stretch from one to another?
What functions like Z discs in smooth muscle?
What functions like Z discs in smooth muscle?
What activates myosin light chain kinase (MLCK) during smooth muscle contraction?
What activates myosin light chain kinase (MLCK) during smooth muscle contraction?
Which of the following causes relaxation of smooth muscle in airways and some blood vessel walls?
Which of the following causes relaxation of smooth muscle in airways and some blood vessel walls?
What type of invaginations contain Ca2+ in smooth muscle?
What type of invaginations contain Ca2+ in smooth muscle?
Which of the following is NOT a typical response trigger for smooth muscle fibers?
Which of the following is NOT a typical response trigger for smooth muscle fibers?
Which proteins prevent myosin from binding to actin in a relaxed muscle?
Which proteins prevent myosin from binding to actin in a relaxed muscle?
What role does myosin play in muscle contraction?
What role does myosin play in muscle contraction?
During the contraction cycle, which step is associated with the detachment of myosin from actin?
During the contraction cycle, which step is associated with the detachment of myosin from actin?
Which process enables the release of more Ca2+ into the sarcoplasmic reticulum (SR)?
Which process enables the release of more Ca2+ into the sarcoplasmic reticulum (SR)?
What triggers the removal of tropomyosin from myosin-binding sites on actin?
What triggers the removal of tropomyosin from myosin-binding sites on actin?
What is the primary factor that allows muscle contraction to occur?
What is the primary factor that allows muscle contraction to occur?
Which of the following is correctly associated with the 'power stroke' phase of the contraction cycle?
Which of the following is correctly associated with the 'power stroke' phase of the contraction cycle?
Which bands form the striations visible in skeletal muscle fibers?
Which bands form the striations visible in skeletal muscle fibers?
What occurs during a concentric isotonic contraction?
What occurs during a concentric isotonic contraction?
Which type of muscle fiber is characterized by high myoglobin content and numerous mitochondria?
Which type of muscle fiber is characterized by high myoglobin content and numerous mitochondria?
Which muscles have a high proportion of fast glycolytic fibers?
Which muscles have a high proportion of fast glycolytic fibers?
What happens to fast glycolytic fibers during aerobic exercise?
What happens to fast glycolytic fibers during aerobic exercise?
What is the primary function of connexins in cardiac muscle?
What is the primary function of connexins in cardiac muscle?
Where is visceral (single unit) smooth muscle commonly found?
Where is visceral (single unit) smooth muscle commonly found?
Which type of skeletal muscle fiber is predominant in postural muscles of the neck, back, and legs?
Which type of skeletal muscle fiber is predominant in postural muscles of the neck, back, and legs?
What characteristic is associated with isometric contraction?
What characteristic is associated with isometric contraction?
Which type of muscle has long cylindrical fibers with multiple peripherally located nuclei?
Which type of muscle has long cylindrical fibers with multiple peripherally located nuclei?
What regulates the contraction of cardiac muscle?
What regulates the contraction of cardiac muscle?
Which type of muscle tissue can regenerate via pericytes?
Which type of muscle tissue can regenerate via pericytes?
Where are intercalated discs found?
Where are intercalated discs found?
Which muscle type is voluntary and controlled by the somatic nervous system?
Which muscle type is voluntary and controlled by the somatic nervous system?
What is the primary function of the skeletal muscle pump?
What is the primary function of the skeletal muscle pump?
What feature is unique to skeletal muscle under microscopic examination?
What feature is unique to skeletal muscle under microscopic examination?
Which layer of connective tissue surrounds individual muscle fibers?
Which layer of connective tissue surrounds individual muscle fibers?
Which part of the sarcomere contains only thick filaments?
Which part of the sarcomere contains only thick filaments?
What is the role of somatic motor neurons in skeletal muscle?
What is the role of somatic motor neurons in skeletal muscle?
Study Notes
Skeletal Muscle Relaxation
- Two processes permit skeletal muscle relaxation:
- ACh is broken down by acetylcholinesterase (AChE)
- Ca2+ active transport pumps
- As Ca2+ levels drop, tropomyosin-troponin complexes slide back over the myosin binding sites on actin, preventing cross-bridge formation.
Length Tension Relationship
- The graph displays how tension developed varies with different sarcomere lengths.
- A muscle fiber develops its greatest tension when there is an optimal overlap between thick and thin filaments.
Control of Muscle Tension
- Maximum tension (force) is dependent on:
- Rate of nerve impulses at NMJ (frequency of stimulation)
- Amount of stretch before contraction
- Nutrient and O2 availability
- Number of muscle fibers that are contracting (motor unit size)
Motor Units
- A motor unit consists of a somatic motor neuron and all the skeletal muscle fibers it stimulates.
- Motor unit size varies:
- Voice production: 2-3 muscle fibers/motor unit
- Eye movements: 10-20 muscle fibers/motor unit
- Limbs: 2000-3000 muscle fibers/motor unit
Twitch Contraction - Myogram
- A brief contraction in response to a single action potential
- Refractory Period: period of lost excitability, muscle cannot be excited again during this time
- Skeletal muscle: 5 ms
- Cardiac muscle: 300 ms
Frequency of Stimulation
- The phenomenon in which stimuli arrive at different times causing larger contractions is called wave summation.
- This occurs when additional Ca2+ is released from SR and levels of sarcoplasmic Ca2+ are still high from the previous stimulus.
Zones and Bands of a Sarcomere
- The striations of skeletal muscle are formed by alternating darker A bands and lighter I bands.
Skeletal Muscle Proteins
- Myofibrils are built from three kinds of proteins:
- Contractile proteins
- Regulatory proteins
- Structural proteins
Structure of Thick and Thin Filaments
- Contractile proteins:
- Myosin (thick filaments): convert ATP to energy of motion
- Actin (thin filaments): site where a myosin head attaches
Regulatory Proteins
- Troponin and Tropomyosin:
- In relaxed muscle, myosin is blocked from binding to actin
- Calcium ion binding to troponin moves tropomyosin away from myosin-binding sites, allowing muscle contraction
The Sliding Filament Mechanism
- With exposure of the myosin binding sites on actin (thin filaments) - in the presence of Ca2+ and ATP - the thick and thin filaments "slide" on one another and the sarcomere is shortened.
The Contraction (Cross-Bridge) Cycle
- Consists of 4 steps:
- ATP hydrolysis: myosin heads hydrolyze ATP and become reoriented and energized
- Detachment of myosin from actin
- Formation of cross-bridges: myosin heads bind to actin, forming crossbridges
- Power stroke: myosin crossbridges rotate toward center of the sarcomere (power stroke)
Calcium is Key to Muscle Contraction
- Inside SR, a calcium binding protein called calsequestrin binds Ca2+, enabling more Ca2+ to be taken up into the SR
- Ca2+ release channels: open and closed
Muscle Tissue
- Types of Muscle:
- Skeletal
- Cardiac
- Smooth
- Properties of Muscle:
- Microscopic appearance and features
- Location
- Fiber diameter
- Fiber length
- Nervous control
- Contraction regulated by
- Capacity for regeneration
Muscle Pump and Connective Tissues
- Skeletal Muscle Pump: aids the heart in venous return and relies on the presence of valves in veins
- Fascia: dense sheet or broad band of irregular connective tissue that surrounds muscles and other organs of the body
- Tendon: cord that attaches a muscle to a bone
Within Myofibrils are Filaments and Sarcomeres
- Filaments: thick and thin
- Sarcomeres: compartments of arranged filaments - basic functional unit of a myofibril
- Z discs: separate one sarcomere from the next
- A band: darker middle part of the sarcomere, thick and thin filaments overlap
- I band: lighter, contains only thin filaments
- H zone: center of each A band which contains only thick filaments
- M line: supporting proteins that hold the thick filaments together in the H zone
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Description
Learn about the zones and bands of a sarcomere, the types of skeletal muscle proteins, and the structure of thick and thin filaments. Understand the roles of contractile, regulatory, and structural proteins.
