Muscular system Muscle cramps

Question 1

What are muscle cramps?

Answer 1

They are characterized by a sudden onset of painful, involuntary squeezing or contraction of muscles.

Question 2

What does the observation of hard knots indicate?

Answer 2

Hard knots of the affected muscle after the termination of cramp could be an indication of a deficiency in muscle relaxation.
* Could be related to the cytosolic Ca+ or ATP concentration.

Question 3

What happens during cramps?

Answer 3

→ High frequency of stimulation
→ Cumulation of cytosolic Ca++
→ Constant muscle contraction

Question 4

What happens after cramps?

Answer 4

→ Cytosolic Ca++ remains high
→ Deficiency of sarco-endoplasmic
reticulum calcium ATPase (SERCA)
→ Lack of ATP

Question 5

Whappens at the final stage of muscle contraction?

Answer 5

Myosin and actin are tightly attached to each other.

Question 6

When does actin dissociates from myosin?

Answer 6

After the binding of ATP to myosin head.

Question 7

What does the apperance of palpable hard knot indicate?

Answer 7

ATP depletion.

Question 8

How can we speed up the relief of muscle cramp?

Answer 8

▪ Stretching the affected muscle.
▪ Contraction of its antagonist muscle.

Question 9

What is the first of two leading hypothesis of muscle cramps?

Answer 9

Dehydration and electrolyte depletion hypothesis.

Question 10

What are the triggering factors of dehydration and electrolyte depletion hypothesis?

Answer 10

Sweat losses that lead to:
- Dehydration and electrolyte disturbances.
- Redistribution between intracellular and extracellular fluid.
- pH disturbances
Thermal strain

Question 11

What are the dehydration and
electrolyte depletion hypothesis sequence of events?

Answer 11

• Massive sweating causes depletion of fluid and electrolyte
• increase osmolarity of the extracellular fluid
• Shifting of the fluid towards the
  extracellular space
  Interstitial space is progressively
  expanded
• Cause an increasing of pressure on
  specific nerve pathways
• Altered excitability leading to muscle cramp.

Question 12

What is the second of two leading hypothesis of muscle cramps?

Answer 12

Neuromuscular hypothesis.
- Increase in excitement of alpha motor neuron that
innervates extrafusal muscle fibers of the affected
muscle is observed during cramping.

Question 13

What are muscle spindles?

Answer 13

They are stretch receptors that can be found in the capsules of the extrafusal muscle fiber.

Question 14

What are extrafusal muscle fiber?

Answer 14

They are normal contractile fibers.

Question 15

What innervate intrafusal fibers?

Answer 15

Gamma motor neurons from CNS.

Question 16

What controls contraction in intrafusal fibers?

Answer 16

Gamma motor neurons from CNA.

Question 17

What innervates extrafusal muscle fibers?

Answer 17

Alpha motor neuron.

Question 18

What is required of the alpha motor neuron during onset muscle cramp?

Answer 18

Requires the alpha motor neuron to fire in high frequency.

Question 19

What are the triggering factors of neuromuscular hypothesis?

Answer 19

→ Muscle fatigue.

→ Patients with motor neuron disease such
as amyotrophic lateral sclerosis (ALS).

→ Changes in electrolyte concentration or
mechanical effects around motor end-plates.

Question 20

What are the sequence of events in neuromuscular hypothesis?

Answer 20

• Triggering factors such as muscle fatigue and neural damage.
• Increase afferent sensory neuron excitability.
• Increase alpha motor neuron firing frequency.
• Increase frequency of muscle contraction.
• Leading to onset of muscle cramp

Question 21

What is revealed when using EMG to monitor the electrical activity during the muscle cramp?

Answer 21

• There are involuntary repetitive high frequency firings of the motor neuron that innervates the cramping motor unit.
• These high frequency involuntary repetitive
  firing pattern is not a representation of a normal spontaneous muscle activity.

Question 22

What does EMG data strongly suggest?

Answer 22

That muscle twitch observed during muscle cramp are of peripheral nerve origin.

Question 23

What is one of the signs in hypothyroid patients?

Answer 23

Cool extremities.

Question 24

What can hypoadrenalism induce?

Answer 24

Electrolytes imbalance.

Question 25

What could liver disease and cirrhosis associated with increased cramps be related to?

Answer 25

A decrease in intravascular volume and edema.

Question 26

What decreased the frequency of cramps in some cirrhotic patients?

Answer 26

Infusion of human albumin compared with placebo infusions.

Question 27

How can cramps be induced even after being abolished by nerve block?

Answer 27

By repetitive nerve stimulation distal to the anesthetic block.

Question 28

When do motor units fire at unusually rapid rates?

Answer 28

When in idiopathic cramp an din cramp associate with chronic partial denervation.

Question 29

What are muscle spindles?

Answer 29

Are tonically active and constantly firing even when muscle is relaxed.

Question 30

What happens to impulses from sensory neuron originated from muslc espindle?

Answer 30

Will integrate with the signals from the brain at the level of spinal cord.

Question 31

what has a high frequency impulse on the somatic motor neuron?

Answer 31

They have a higher frequency than that of the descending tract of the axons within the spinal cord.

Question 32

What happens to muscle spindles in alpha activiation?

Answer 32

1- Alpha motor nueorns fores.
2- Muscle contracts.
3- Less stretch on center of intrafusal fibers.
4- Firing rate of spindle sensory neuron decreases.

Question 33

How are contraction of the antagonist muscles or stretching mediated through?

Answer 33

Central inhibition.

Question 34

Central mechanism cannot drive___?

Answer 34

motor neurons to discharge at a high frequency.

Question 35

What does stretching induce?

Answer 35

Involuntary repetitive high frequency firings of the motor neuron that innervates the cramping motor unit.

Question 36

What cause increase in frequency of sensory signals to spinal cord by the muscle spindle?

Answer 36

Stretching or contraction the antagonist muslces.