Page 2 Flashcards
What do smooth muscle fibers contain?
Smooth muscle fibers contain intermediate filaments and dense bodies; the function of dense bodies is similar to that of the Z discs in striated muscle.
How does the duration of contraction and relaxation in smooth muscle compare to skeletal muscle?
The duration of contraction and relaxation of smooth muscle is longer than in skeletal muscle since it takes longer for Ca to reach the filaments.
What stimulates smooth muscle fibers to contract?
Smooth muscle fibers contract in response to nerve impulses, hormones, and local factors.
What is a characteristic of smooth muscle fibers?
Smooth muscle fibers can stretch considerably and still maintain their contractile function.
Where is visceral smooth muscle found?
Visceral smooth muscle is found in the walls of hollow viscera and of small blood vessels. Many fibers form a network that contracts in unison.
Where is multiunit smooth muscle found?
Multiunit smooth muscle is found in large blood vessels, large airways to the lungs, arrector pili muscles, and the eye, where it adjusts pupil diameter and lens focus.
What is the contraction cycle in skeletal muscle?
The contraction cycle is a repeating sequence of events that causes sliding of the filaments.
What initiates filament sliding in muscle contraction?
An increase in Ca2 concentration in the cytosol starts filament sliding; a decrease turns off the sliding process.
What triggers a muscle action potential?
Acetylcholine released at the neuromuscular junction triggers a muscle action potential, which leads to muscle contraction.
What is the first step in the muscle contraction process?
Nerve impulse arrives at axon terminal of motor neuron and triggers release of acetylcholine (ACh).
What happens after acetylcholine diffuses across the synaptic cleft?
ACh binds to its receptors in the motor end plate, and triggers a muscle action potential (AP).
What role does acetylcholinesterase play in muscle contraction?
Acetylcholinesterase in synaptic cleft destroys ACh so another muscle action potential does not arise unless more ACh is released from motor neuron.
What occurs when the muscle action potential travels along the transverse tubule?
It opens Ca2+ release channels in the sarcoplasmic reticulum (SR) membrane, allowing calcium ions to flood into the sarcoplasm.
What happens when calcium binds to troponin?
Ca binds to troponin on the thin filament, exposing the binding sites for myosin.
What is the process of muscle contraction?
Power strokes use ATP; myosin heads bind to actin, swivel, and release; thin filaments are pulled toward center of sarcomere.
What happens after contraction in muscle relaxation?
Ca release channels in SR close and active transport pumps use ATP to restore low level of Ca2+ in sarcoplasm.
What is the role of the troponin-tropomyosin complex during relaxation?
It slides back into position where it blocks the myosin binding sites on actin.
What are the three sources for ATP production in muscle fibers?
Muscle fibers have three sources for ATP production: creatine, anaerobic glycolysis, and aerobic respiration.
What is the role of creatine kinase?
Creatine kinase catalyzes the transfer of a high-energy phosphate group from creatine phosphate to ADP to form new ATP molecules.
How long can creatine phosphate and ATP provide energy for maximal muscle contraction?
They provide enough energy for muscles to contract maximally for about 15 seconds.
How long can anaerobic glycolysis provide energy for muscle activity?
It can provide enough energy for 2 minutes of maximal muscle activity.
What does aerobic respiration depend on?
Muscular activity that occurs over a prolonged time depends on mitochondrial reactions that require oxygen to produce ATP.
What is muscular fatigue?
Muscular fatigue is the inability of a muscle to contract forcefully after prolonged activity.
What is recovery oxygen uptake?
Recovery oxygen uptake is elevated oxygen use after exercise.
What is a motor unit?
A motor unit is composed of a motor neuron and the muscle fibers it stimulates.
What is recruitment in muscle physiology?
Recruitment is the process of increasing the number of active motor units.
What is unfused tetanus?
Unfused tetanus is produced by repeated stimuli; it is an incomplete, sustained muscle contraction with partial relaxation between stimuli.
What is fused tetanus?
Fused tetanus is produced by rapidly repeated stimuli; it is a sustained contraction without relaxation.
What is an eccentric isotonic contraction?
An eccentric isotonic contraction is when the muscle lengthens.
What are isotonic contractions?
Isotonic contractions are when tension is generated without muscle lengthening.
What is the regeneration capacity of skeletal muscle fibers?
Skeletal muscle fibers cannot divide and have limited powers of regeneration.
What is the regeneration capacity of cardiac muscle fibers?
Cardiac muscle fibers can regenerate under limited circumstances.
Which muscle fibers have the best capacity for division and regeneration?
Smooth muscle fibers have the best capacity for division and regeneration.
What happens to skeletal muscle mass with aging?
With aging, there is a slow, progressive loss of skeletal muscle mass, which is replaced by fibrous connective tissue and fat.
What are some effects of aging on muscles?
Aging results in a decrease in muscle strength, slower muscle reflexes, and loss of flexibility.
What is fibromyalgia?
Fibromyalgia is a chronic, painful, nonarticular rheumatic disorder that affects the fibrous connective tissue components of muscles, tendons, and ligaments.
What is a striking sign of fibromyalgia?
A striking sign is pain that results from gentle pressure at specific ‘tender points.’
What are some treatments for fibromyalgia?
Treatment consists of stress reduction, regular exercise, application of heat, gentle massage, physical therapy, medication for pain, and a low-dose antidepressant to help improve sleep.
What is muscular hypertrophy?
Muscular hypertrophy is muscle growth that occurs after birth by enlargement of existing muscle fibers.
