Skeletal Muscle Mechanics Flashcards
What is a motor unit?
Single Neuron and all muscle fibers innervated by it
What determines strength of muscle contraction?
- # Number of fibers
- Number motor units
- Frequency of stimulation
- Fiber length
- Fiber thickness
How long is the lag phase of a muscle contraction?
2-4 ms
How does tension and load resistance determine contraction?
If tension > load resistance, result is isotonic contraction
Tension
How does summation play into contraction?
The muscle can be activated again before it has fully relaxed
and if a second action potential occurs during relaxation, the
force it produces adds to that remaining from the first action
potential - this is called summation
What is the titanic fusion frequency?
the action potentials will occur so rapidly that no relaxation
occurs, this produces a smooth or fused rise in tension to a
plateau that is several (3-8) times that produced during a
single twitch
What is the role of the Golgi tendon organ?
Sends information to het CNA about muscle tension and rate of change of tension
What are NM spindles?
- Stretch receptor organs in skeletal muscle
What is the structure of a muscle spindle?
- 2-10 nifedipine skeletal muscle fibers (intrafusal) which are innervated by gamma motor neurons.
- Anulospiral an flower spray sensory neurons end information to CNA
How is the hamstring an example of excitatory and inhibitory synaptic mediation of the stretch reflex?
The stretch receptor sensor y neuron of the quadriceps muscle makes a monosynaptic excitator y connection with the extensor motor neuron of the same muscle and a disynaptic inhibitor y inter neuron projecting to flexor motor neurons supplying the antagonistic hamstring
How are load and velocity related?
• The Velocity of contraction depends on the load on the
muscle and is inversely propor tional to the amount of load
• Maximum velocity is achieved at zero load (no weight) and
corresponds to the maximal cross-bridge cycling rate which
is deter mined by the ATPase activity of the myosin present
What is phosphlamban?
- In unphosphorylated state, inhibits cardiac muscle SR Ca ATPase
- When phosphorylation, increases Ca uptake into SR contributing to lusitropic response elicited in heart by beta adrenergic agonists
- key regulator of diastolic function
Describe pathology of Muscular dystrophy
- X-linked
- Muscle degeneration
- Defect or lack of dystrophin, a cytoskeleton Anchoring protein
Describe pathology of malignant hyperthermia
- Autosomal dominant
- abnormal release of Ca from SR from anesthetics and strenuous exercise
What is dantrolene sodium?
- Muscle relaxant which acts of Ryanodine channels to decrease excesssice contraction
- Mostly for malignant hyperthermia