Muscular system Muscle cramps Flashcards
What are muscle cramps?
They are characterized by a sudden onset of painful, involuntary squeezing or contraction of muscles.
What does the observation of hard knots indicate?
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.
What happens during cramps?
→ High frequency of stimulation
→ Cumulation of cytosolic Ca++
→ Constant muscle contraction
What happens after cramps?
→ Cytosolic Ca++ remains high
→ Deficiency of sarco-endoplasmic
reticulum calcium ATPase (SERCA)
→ Lack of ATP
Whappens at the final stage of muscle contraction?
Myosin and actin are tightly attached to each other.
When does actin dissociates from myosin?
After the binding of ATP to myosin head.
What does the apperance of palpable hard knot indicate?
ATP depletion.
How can we speed up the relief of muscle cramp?
▪ Stretching the affected muscle.
▪ Contraction of its antagonist muscle.
What is the first of two leading hypothesis of muscle cramps?
Dehydration and electrolyte depletion hypothesis.
What are the triggering factors of dehydration and electrolyte depletion hypothesis?
Sweat losses that lead to:
- Dehydration and electrolyte disturbances.
- Redistribution between intracellular and extracellular fluid.
- pH disturbances
Thermal strain
What are the dehydration and
electrolyte depletion hypothesis sequence of events?
- 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.
What is the second of two leading hypothesis of muscle cramps?
Neuromuscular hypothesis.
- Increase in excitement of alpha motor neuron that
innervates extrafusal muscle fibers of the affected
muscle is observed during cramping.
What are muscle spindles?
They are stretch receptors that can be found in the capsules of the extrafusal muscle fiber.
What are extrafusal muscle fiber?
They are normal contractile fibers.
What innervate intrafusal fibers?
Gamma motor neurons from CNS.
What controls contraction in intrafusal fibers?
Gamma motor neurons from CNA.
What innervates extrafusal muscle fibers?
Alpha motor neuron.
What is required of the alpha motor neuron during onset muscle cramp?
Requires the alpha motor neuron to fire in high frequency.
What are the triggering factors of neuromuscular hypothesis?
→ Muscle fatigue.
→ Patients with motor neuron disease such
as amyotrophic lateral sclerosis (ALS).
→ Changes in electrolyte concentration or
mechanical effects around motor end-plates.
What are the sequence of events in neuromuscular hypothesis?
- 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
What is revealed when using EMG to monitor the electrical activity during the muscle cramp?
- 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.
What does EMG data strongly suggest?
That muscle twitch observed during muscle cramp are of peripheral nerve origin.
What is one of the signs in hypothyroid patients?
Cool extremities.
What can hypoadrenalism induce?
Electrolytes imbalance.
What could liver disease and cirrhosis associated with increased cramps be related to?
A decrease in intravascular volume and edema.
What decreased the frequency of cramps in some cirrhotic patients?
Infusion of human albumin compared with placebo infusions.
How can cramps be induced even after being abolished by nerve block?
By repetitive nerve stimulation distal to the anesthetic block.
When do motor units fire at unusually rapid rates?
When in idiopathic cramp an din cramp associate with chronic partial denervation.
What are muscle spindles?
Are tonically active and constantly firing even when muscle is relaxed.
What happens to impulses from sensory neuron originated from muslc espindle?
Will integrate with the signals from the brain at the level of spinal cord.
what has a high frequency impulse on the somatic motor neuron?
They have a higher frequency than that of the descending tract of the axons within the spinal cord.
What happens to muscle spindles in alpha activiation?
1- Alpha motor nueorns fores.
2- Muscle contracts.
3- Less stretch on center of intrafusal fibers.
4- Firing rate of spindle sensory neuron decreases.
How are contraction of the antagonist muscles or stretching mediated through?
Central inhibition.
Central mechanism cannot drive___?
motor neurons to discharge at a high frequency.
What does stretching induce?
Involuntary repetitive high frequency firings of the motor neuron that innervates the cramping motor unit.
What cause increase in frequency of sensory signals to spinal cord by the muscle spindle?
Stretching or contraction the antagonist muslces.
