Skeletal Muscle Mechanics

Question 1

What is a motor unit?

Answer 1

Single Neuron and all muscle fibers innervated by it

Question 2

What determines strength of muscle contraction?

Answer 2

• # Number of fibers
• Number motor units
• Frequency of stimulation
• Fiber length
• Fiber thickness

Question 3

How long is the lag phase of a muscle contraction?

Answer 3

2-4 ms

Question 4

How does tension and load resistance determine contraction?

Answer 4

If tension > load resistance, result is isotonic contraction

Tension

Question 5

How does summation play into contraction?

Answer 5

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

Question 6

What is the titanic fusion frequency?

Answer 6

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

Question 7

What is the role of the Golgi tendon organ?

Answer 7

Sends information to het CNA about muscle tension and rate of change of tension

Question 8

What are NM spindles?

Answer 8

• Stretch receptor organs in skeletal muscle

Question 9

What is the structure of a muscle spindle?

Answer 9

• 2-10 nifedipine skeletal muscle fibers (intrafusal) which are innervated by gamma motor neurons.
• Anulospiral an flower spray sensory neurons end information to CNA

Question 10

How is the hamstring an example of excitatory and inhibitory synaptic mediation of the stretch reflex?

Answer 10

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

Question 11

How are load and velocity related?

Answer 11

• 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

Question 12

What is phosphlamban?

Answer 12

• 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

Question 13

Describe pathology of Muscular dystrophy

Answer 13

• X-linked
• Muscle degeneration
• Defect or lack of dystrophin, a cytoskeleton Anchoring protein

Question 14

Describe pathology of malignant hyperthermia

Answer 14

• Autosomal dominant

- abnormal release of Ca from SR from anesthetics and strenuous exercise

Question 15

What is dantrolene sodium?

Answer 15

• Muscle relaxant which acts of Ryanodine channels to decrease excesssice contraction
• Mostly for malignant hyperthermia