Neuromuscular Physiology II Flashcards
What is a muscle twitch?
Contractile response of a muscle fiber to a single muscle AP
What happens if all muscle fibers within a muscle were activated?
Whole muscle twitch
Latent Period
delay between the arrival of the AP and initiation of contraction
Contraction period
When CA2+ binds to troponin and the actin-myosin cross-bridges are formed
Relaxation period
When Ca2+ is actively pumped back into the SR, myosin head detaches from actin and muscle tension decreases
Refractory period
the period of time when the muscle tissue is unable to respond to a subsequent AP
Wave summation
occurs when a second AP triggers muscle contraction before the first contraction has finished
Wave summation - result
stronger contraction; b/c the muscle fiber hasn’t had enough time to completely reset its self
What is tetanus
when repeated stimuli are sent in short durations that they can lead to an even greater summation of contraction force
Unfused (incomplete) tetanus
occurs when muscle fibers are stimulated at a rate where they don’t completely relax between stimuli
Fused (complete) tetanus
occurs when muscle fibers are stimulated at a rate where they don’t relax AT ALL between stimuli
Henneman’s size prinicple
- not all MN have same excitability threshold
- smaller, fatigue-resistant MU’s recruited first
What is fatigue?
reduction in the force output (or capacity) of a muscle in response to a voluntary effort
Where does peripheral fatigue occur?
at or below the level of the NMJ
Where does central fatigue occur?
above the level of the NMJ; motor cortex, spinal cord
Motor unit rotation
some MU’s deactivate and others become active, maintaining contraction strength
Muscle and tendon proprioceptor role
send info to CNS about changes in length, tension, and joint angles
Muscle spindle location
within muscle body
golgi tendon organ location
within the tendon
Names of muscle and tendon proprioceptors
- muscle spindles
- golgi tendons
What affects the force produced by a muscle?
sarcomere length
Passive tension
as you stretch the muscle beyond resting length it produces a force (non-contracting)
Active tension
force produced by contractile mechanisms
Optimum length (Lo)
maximum active force
- optimal overlap of actin-myosin cross-bridge produces greatest tension development
Force-velocity relationship - concentric
as velocity of a concentric muscle action is increased, less force is capable of being generated
Force-velocity relationship - eccentric
as the velocity of an eccentric muscle action is increases, more force is capable of being generated during that contraction
Force-velocity relationship - eccentric - why?
greater strain placed on the myosin heads, facilitates the attatchment of the second head more frequently
Force-velocity relationship - concentric - why?
takes time for cross-bridges to attach/detach
- number of total cross-bridges becomes limited as contraction velocity increases
Ways to improve maximal power output of a muscle
- increasing the maximal force we can move
- increasing our movement velocity
What dictates the amount of force generated by a muscle?
the number of attached cross-bridges
Does force production increase or decrease when contraction velocity increases?
Force production decrease
equation: power =
Power = force x velocity
What is power maximized at?
maximized at a combination of submaximal force and velocity values
What affects the force-velocity properties of a muscle?
affected by the fibre type contribution to the whole muscle area
What muscle fiber has the fastest velocity?
Type IIx; 5.6 fiber lengths/second
Power and velocity continuum of muscle fiber types
IIx > IIa > I
