Muscle Physiology Pt. 2 Flashcards
It is the force generated by muscle fiber in order to oppose a force (load) exerted on the muscle by an object
Tension
It is the mechanical response of a muscle fiber to a single action potential
Twitch
What are the three phases of twitch contraction?
- Latent Period
- Contraction Period
- Relaxation Period
This period is the time from action potential to the onset of contraction
Latent period
This period is the time that tension is developing due to cross-bridge cycling of actin and myosin filaments
Contraction period
This period is the time the tension is decreasing due to the time it takes to receive all Ca2+
Relaxation period
What are the two types of twitch contraction?
Isometric and Isotonic Twitch
This twitch generates tension but does not shorten muscle; tension is high, but there is not much change in the muscle
Isometric twitch
This twitch shortens the muscle; tension is not as high, but the muscle contracts
Isotonic twitch
This relationship indicates that:
- The lighter the load, the less shortening of muscle, the bigger the distance, while
- The heavier the load, the shorter the time a person is able to carry it, the smaller the distance
Load-Velocity Relationship
This relationships is when single action potentials lasts only 1-2 ms; twitch may last for 100 ms
Frequency-Tension Relationship
Increase in muscle tension from successive action potentials occurring during the phase of mechanical activity
Summation
Maintained contraction in response to repetitive stimulation
Tetanus
This occurs when skeletal muscle fiber is repeatedly stimulated, causing tension to eventually decrease even if stimulation continues
Muscle fatigue
In muscle fatigue, velocity __________ and rate of relaxation __________
Shortens; Slows down
What are the three potential causes of muscle fatigue?
- Conduction failure
- Lactic acid build-up
- Inhibition of cross-bridge recycling
This is a result from build-up of K+ in T-tubule during repolarization of repetitive action potentials
Conduction failure
Acidification of muscle by lactic acid may change muscle proteins, causing __________
Lactic Acid Build-up
Build-up of ADP + PI within muscle fibers during intense activity may inhibit cross-bridge
Inhibition of Cross-Bridge Recycling
Classification of muscle fibers:
- Oxidative fibers
- Glycolytic fibers
Type of muscle fiber that has combined low myosin-ATPase activity with high oxidative capacity
Slow-oxidative fibers (Type I)
Type of muscle fiber that has combines high myosin-ATPase activity within high glycolytic capacity
Fast-glycolytic fibers (Type IIB)
Type of muscle fiber with combined high myosin-ATPase activity within high oxidative capacity and intermediate glycolytic capacity
Fast-oxidative-glycolytic fibers (Type IIA)
Fourth possibility of muscle fiber that is generally not found
Slow-glycolytic fibers
Muscle tension is affected by two factors. What are they?
- Amount of tension developed by each fiber
- Number of fibers contracting at any time
Two types of muscle atrophy
- Disuse atrophy
- Denervation atrophy
Type of atrophy in which nerves are intact and appearance becomes small if not used in a long time
Disuse atrophy
Type of atrophy that causes muscles to become smaller in diameter and decreases in the number of contractile proteins
Denervation atrophy
Muscle disorder with involuntary tetanic contraction of skeletal muscles and action potentials fire at abnormally high rates
Muscle cramps
Muscle disorder with involuntary tetanic contraction of skeletal muscles, in which extracellular Ca2+ concentration falls to +- 40% of normal value
Hypocalcemic Tetany
Muscle disorder that is also referred to as “Polio”; It is a viral disease that destroys motor neurons and leads to the paralysis of skeletal muscles
Poliomyelitis
Muscle disorder with progressive degeneration of skeletal and cardiac muscle fibers
Muscular dystrophy
It is a sex-linked recessive disorder (X chromosome) that is often seen in children
Duchenne Muscular Dystrophy (DMD)
This is due to the destruction of nicotinic ACh receptor proteins of the motor end plate due to autoimmunity
Myasthenia gravis
This type of muscle is spindle/fusiform-shaped with thick myosin-containing filaments and thin actin-containing filaments and tropomyosin
Smooth muscle
What are the two sources of Ca2+ in smooth muscles?
- Sarcoplasmic reticulum
- Extracellular Ca2+ entering the cell through plasma membrane Ca2+ channels
This is done by Myosin Light Chain Kinase (MLCK)
Cross-bridge activation
This is influenced by autonomic neuron endings and does not have a specialized motor end plate region
Neural and hormonal control
Membrane potential change occurring during the spontaneous depolarization to threshold
Pacemaker potential
Membrane potential drifts up and down due to regular variation in ion influx across the membrane
Slow waves
This type of smooth muscle responds to stimuli as a single unit because cells are connected by gap junctions
Single-unit
This type of smooth muscle contains cells that respond to stimuli independently and contain few gap junctions
Multi-unit
This type of muscle is striated and uses sliding filament to contract
Cardiac muscle
This prevents tetanic contraction in cardiac muscles
Absolute Refractory Period (250 ms)
