Chapter 9 - Part 2 Flashcards
The force exerted on the load
Contraction produces this
Muscle tension
Load is greater than maximum tension muscle can generate, no shortening of muscle
Isometric contraction
Muscle changes length and moves load
Actin filaments move towards center of sarcomere and cause movement
Concentric: muscle shortens, work done
Eccentric: muscle lengthens and generates force
Isotonic contraction
Each muscle is served by at least one _____
Motor nerve
As a motor neuron axon enters muscle, it branches into many _____
Endings
Each ending forms a ______ with a single muscle fiber
Neuromuscular junction
Consists of motor neuron and all of the muscle fibers it innervates (supplies)
Motor unit
Smaller the number of muscle fibers innervated _______
Greater fine control
More precise
Simplest form of contraction resulting from a muscle fiber’s response to a single action potential from motor neuron
Muscle twitch
Twitch recorded and observed as _____
Myogram
Line recording of myogram
Tracing
First phase of muscle twitch; events of excitation-contraction coupling
No muscle tension seen
Latent Period
Second phase of muscle twitch; cross bridge formation
Tension increases
Period of Contraction
Third phase in muscle twitch; Ca2+ reentry into SR
Tension declines to zero
Period of Relaxation
Differences in muscle strength and duration of twitches are due to variations in metabolic properties and ________
Enzymes
Muscle responses are graded by:
- Change in frequency of stimulation
- Change in strength of stimulation
Results if two stimuli are received by a muscle in rapid succession
Muscle fibers do not have time to completely relax between stimuli, so twitches increase in force with each stimulus
Wave (temporal) summation
Single stimulus results in single contractile response
Individual twitches
If stimuli frequency, muscle tension reaches near maximum
Produces smooth, continuous contractions that add up (summation)
Quivering contraction
Unfused tetanus
Stimuli frequency increases, muscle tension reaches maximum
Contractions “fuse” into one smooth sustained contraction
Leads to muscle fatigue
Fused tetanus
Stimulus send to more muscle fibers, leading to more precise control
Recruitment
Stimulus not strong enough, so no contractions seen
Subthreshold stimulus
Stimulus strong enough to cause a first observable contraction
Threshold stimulus
Strongest stimulus that increases maximum contractile force
All motor units have been recruited
Maximal stimulus
Recruitment works on ____
Motor units with smallest muscle fibers are recruited first
Largest motor units are activated only for most powerful contractions
Size principle
Some fibers contract while others rest
Asynchronous contraction
Constant, slightly contracted state of all muscles; Due to spinal reflexes
Keeps muscles firm, healthy, and ready to respond
Stabilizes joints and maintains posture
Muscle tone
- Moves and detaches cross bridges
- Pumps calcium back into SR
- Pumps Na+ out and K+ back into cell after EC coupling
ATP
Unique molecule located in muscle fibers that donates a phosphate to ADP to instantly form ATP
Creatine phosphate
Enzyme that carries out transfer of phosphate
Creatine kinase
Breaking down and using energy stored in nutrient molecules
Muscles use glucose from blood or glucose produces by first breaking down glycogen
1. Anaerobic respiration
2. Aerobic respiration
Cellular respiration
Glycolysis and lactic acid formation
Anaerobic respiration
First step in glucose breakdown
Broken into pyruvic acid
2 ATPs generated for each glucose
Glycolysis
High intensity activities ______ oxygen availability
Bulging muscles compresses blood vessels, impairing oxygen delivery
Decreases
Product of pyruvic acid break down in absence of oxygen
Lactic acid
Which organ cells can convert lactic acid back into pyruvic acid?
Liver cells
When oxygen is available, pyruvic acid enters mitochondria to start process
Produces 95% of ATP during rest and light to moderate exercise
Slower than anaerobic pathways
32 ATP per glucose
Aerobic respiration
Physiological inability to contract despite continued stimulation;
Usually occurs when there are ionic imbalances (K+, Ca2+, P)
Lack of ATP rarely a reason for fatigue, except in severely stressed muscles
Muscle fatigue
_____ of contraction depends on number of cross bridges attached
Force
The more motor units recruited, the greater the force
Number of muscle fibers stimulated
The bulkier the muscle, the more tension it can develop
Hypertrophy occurs with regular exercise
Relative size of fibers
The higher the frequency, the greater the force
Stimuli are added together
Frequency of stimulation
Muscle fibers with sarcomeres that are 80-120% their normal resting length generate more force (not stretched or shortened more)
Degree of stretch
Exercise using oxygen, such as swimming, jogging, biking
More muscle capillaries, number of mitochondria, myoglobin synthesis
Results in increased muscle metabolism endurance, strength, resistance to fatigue
Aerobic endurance exercise
Exercise such as weight lifting, isometric movements
Typically anaerobic
Muscle hypertrophy occurs, increased mitochondria, myofilaments, glycogen stores, and connective tissue
Results in muscle strength and size
Resistance training
Muscle degeneration and loss of mass
Due to immobilization of muscle or loss of neural stimulation
Can begin almost immediately
Can decline 5% per day
Disuse atrophy
Paralyzed muscles can shrink to 1/4th initial size
Fibrous connective tissue replaces lost muscle tissue
Muscle atrophy
Variants of male sex hormone
testosterone
Involved in increasing muscle and bone mass during male puberty
Originally used to treat anemia
Corticosteroids (steroids)
Side effects of steroids
Found in walls of most hollow organs, except heart; Spindle-shaped fibers with one nucleus; Only connective tissue sheath is endomysium; No sarcomeres, myofibrils, T tubules; SR less developed than skeletal muscle
Smooth muscle
Pouchlike infoldings of sarcolemma; Contain numerous Ca2+ channels that open to allow rapid influx of extracellular Ca2+
Caveolae
Thick and thin filaments arranged _____
Diagonally
Myofilaments arranged _______, allowing smooth muscle to contract like a corkscrew
Spirally
Lattice like arrangement of noncontractile intermediate filaments that resist tension
Intermediate filament-dense body network
Connect adjacent fibers; helps cells “talk” to one another
Gap junctions
Proteins that anchor filaments to sarcolemma at regular intervals
Dense bodies
Is tropomyosin involved in smooth muscle?
Yes
Is troponin involved in smooth muscle?
No
Protein that will bind to Ca2+ instead of troponin
Calmodulin
Bulbous swellings on nerve fibers
Located on autonomic nerve fibers that innervate smooth muscle
Store and release neurotransmitters into a wide synaptic cleft
Varicosities
Synaptic cleft in smooth muscle
Diffuse junction
True or false; some smooth muscle cells have no nerve supply
(Some respond to both neural and chemical stimuli)
True
Ca2+ binds to calmodulin, not troponin
Activated calmodulin then activates myosin kinase
Stopping smooth muscle contraction requires more steps than skeletal muscle
Differences between Smooth and Skeletal muscle contraction
First (outermost) layer in smooth muscle; Fibers are parallel to long axis of organ
Contraction causes organ to shorten
Longitudinal layer
Alternating contractions and relaxations of layers
Mixes and squeezes substances through lumen of hollow organs
Peristalsis
Second layer in smooth muscle; Fibers run around circumference of organ
Circular layer
