Structure and Function Flashcards
What are the 2 multiaxial joints?
Shoulder and hip; ball and socket joints that allow movement about all 3 perpendicular axes
How many neuromuscular junctions are there in a muscle cell?
One
What is a motor neuron and the muscle fibers it innervates called?
Motor unit
What is sarcoplasm?
Cytoplasm of the muscle cell
Two types of myofilaments that make up a myofibril in the muscle cell?
Myosin and actin
Which myofilament forms the crossbridge in the muscle cell?
Myosin
What is the smallest contractile unit of skeletal muscle?
Sarcomere; repeated the entire length of the muscle fiber
A band
Corresponds to the alignment of myosin filaments
I band
Light area; corresponds to the area of 2 adjacent sarcomeres that only contain actin
Z line
Thin dark line in the middle of the I band
H zone
Area in the center of the sarcomere where only myosin is present
What mineral is released into the muscle cell when an action potential is discharged?
Calcium
Sliding Filament Theory of Muscle Contraction
Calcium binds to troponin (on actin); the myosin crossbridges attach to actin and pull the actin towards the center of the sarcomere
Steps of Muscle Contaction
- ATP binds to myosin head and is split by myosin ATPase which puts the myosin head in an energized state and allows it to bind to move into position and bind with actin
- Release of phosphate from ATP causes the myosin filament to change shape and shift
- This pulls the actin filament towards the center of the sarcomere and is referred to as the power stroke; ADP is then released
- A new ATP must bind to myosin in order for it to detach from actin; move back to its original position; and repeat the process
- Cycle continues as long as ATP and ATPase are present and calcium is bound to troponin
What determines the force production of a muscle?
The number of crossbridges that are formed between actin and myosin at any instant in time
What neurotransmitter is released when an action potential arrives at the neuromuscular junction?
Acetylcholine; excites the sarcolemma which stimulates the release of calcium which produces muscle contraction
What is the maximal amount of force that a muscle can develop called?
Tetanus; occurs when the time between muscle twitches decreases so that the twitches begin to merge and eventually fuse together
Type 1 muscle fiber
slow twitch; efficient and fatigue resistant; high capacity for aerobic energy supply; limited force production; low myosin ATPase activity
Type 2 muscle fiber
fast twitch; inefficient and fatigable; low aerobic power; rapid force development; high myosin activity and high anaerobic power
What two variables can change the amount of muscular force produced?
1) Frequency at which motor units are activated 2) Number of motor units activated
Muscle spindle
Proprioceptor located deep inside the muscle fibers
What happens when the muscle is lengthened (stretched) and the muscle spindle is activated?
Activates the muscle and causes it to contract
Golgi Tendon Organ
Proprioceptor located in tendons
What happens when a tendon (and muscle) is stretched and the Golgi tendon organ is activated?
Inhibits muscle activation and reduces tension in the muscle (brain motor cortex can override this inhibition however)
What node is the pacemaker of the heart?
SA node
Bradycardia
Less than 60 bpm
Tachycardia
More than 100 bpm
What does the P-wave represent?
Depolarization of the atria which results in atrial contraction
What does the QRS complex represent?
Depolarization of the ventricles which causes the ventricles to contract
What does the T wave represent?
Re-polarization of the ventricles
What is hemoglobin?
The iron-protein molecule attached to red blood cells that transports oxygen in the blood
What percentage of total energy expended by the body is used for normal respiration?
3-5%
What percentage of total energy expended by the body is used for respiration during heavy exercise?
8-15%
