This document discusses muscle relaxants and their use and mechanisms. It covers different types of spinal reflexes and fibers that control muscle movement. Muscle spasm and spasticity are described as being caused by changes in the central nervous system. Most muscle relaxants work in the brain and spinal cord by interfering with reflexes causing spasm. Direct-acting relaxants enter muscle fibers and interfere with calcium release and contraction. Centrally-acting relaxants are absorbed and metabolized quickly while direct-acting ones have a longer half-life. Common side effects and drug interactions are provided. Nursing considerations for the different types of relaxants are also mentioned.

1. Muscle Relaxants
Chapter 25
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2. Regulation of Movement and Control of
Muscles
• Spinal Reflexes
• Influences from Upper-level CNS Areas
– Basal ganglia
– Cerebellum
– Cerebral cortex
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3. Types of Spinal Reflexes
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• Simple
– Involving an incoming sensory neuron and an
outgoing motor neuron
• Complex
– Involving interneurons which communicate with the
related centers in the brain

4. Reflex Arc Showing Pathway of Impulses
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5. Fibers in the CNS Controlling Different
Types of Movements
• Pyramidal Tract
– Controls precise intentional movements
• Extrapyramidal Tract
– Modulates unconsciously controlled muscle activity
– Allows the body to make automatic adjustments in
posture, position, and balance
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6. Neuromuscular Abnormalities
• Muscle Spasm
– Often results from injury to the musculoskeletal
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system
– Caused by the flood of sensory impulses coming to
the spinal cord from the injured area
• Muscle Spasticity
– Result of damage to neurons within the CNS
– May result from an increase in excitatory influences
or a decrease in inhibitory influences within the CNS

7. Action of Skeletal Muscle Relaxants
• Most Relaxants
– Work in the brain and spinal cord
– Interfere with cycle of muscle spasm and pain
• Botulinum Toxins and Dantrolene
– Enter muscle fibers directly
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8. Action of Centrally Acting Skeletal Muscle
Relaxants
• Work in the upper levels of the CNS to interfere with the
reflexes causing the muscle spasm
– Possible depression anticipated with their use
• Lyse or Destroy Spasm
– Often referred to as spasmolytics
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9. Question
Which of the following may result in muscle spasticity?
A. A decrease in inhibitions
B. An increase in excitatory influences
C. An increase in inhibitory influences
D. A decrease in excitatory influences
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10. Answer
B. An increase in excitatory influences
Rationale: Muscle spasticity may result from an increase in
excitatory influences or a decrease in inhibitory
influences within the CNS.
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11. Centrally-Acting Skeletal Muscle
Relaxants
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• Actions
– Exact mechanism of action is not known
– Thought to involve action in the upper or spinal
interneurons
• Indications
– Alleviation of signs and symptoms of spasticity; use in
spinal cord injuries or diseases
• Pharmacokinetics
– Rapidly absorbed and metabolized in the liver
– Excreted in the urine

12. Centrally-Acting Skeletal Muscle Relaxants
(cont.)
• Contraindications
– Known allergy
– Rheumatic disorders
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• Cautions
– Epilepsy
– Cardiac dysfunction
– Conditions marked by muscle weakness

13. Centrally-Acting Skeletal Muscle
Relaxants (cont.)
• Adverse Reactions
– Drowsiness
– Fatigue
– Weakness
– Confusion
– Headache
– Nausea
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14. Centrally-Acting Skeletal Muscle
Relaxants (cont.)
• Adverse Reactions (cont.)
– Dry mouth
– Hypotension
• Drug-to-Drug Interactions
– CNS depressants
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15. Direct-Acting Skeletal Muscle Relaxants
• Actions
– Interfering with the release of calcium from the
muscle tubules
– This prevents the fibers from contracting
– Does not interfere with neuromuscular transmission
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• Indications
– Treatment of spasticity directly affecting peripheral
muscle contraction
– Management of spasticity associated with
neuromuscular diseases

16. Direct-Acting Skeletal Muscle Relaxants
(cont.)
• Pharmacokinetics
– Slowly absorbed from the GI tract
– Metabolized in the liver
– T ½ 4-8 hours
– Excreted in the urine
• Contraindications
– Known allergy
– Spasticity
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17. Direct-Acting Skeletal Muscle Relaxants
(cont.)
• Contraindications (cont.)
– Hepatic disease
– Lactation
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• Cautions
– Women
– All patients older than 35 years
– Cardiac disease

18. Direct-Acting Skeletal Muscle Relaxants
(cont.)
• Adverse Reactions
– Fatigue
– Weakness
– Confusion
– GI irritation
– Enuresis
• Drug-to-Drug Interactions
– Estrogen
– Neuromuscular junction blockers
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19. Mechanisms of Muscle Relaxants
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20. Use of Muscle Relaxants Across the
Lifespan
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21. Prototype Centrally Acting Skeletal Muscle
Relaxants
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22. Prototype Direct-Acting Skeletal Muscle
Relaxants
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23. Nursing Considerations for Centrally-
Acting Skeletal Muscle Relaxants
• Assessment: History and Physical Exam
• Nursing Diagnosis
• Implementation
• Evaluation
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24. Nursing Considerations for Direct-Acting
Skeletal Muscle Relaxants
• Assessment: History and Physical Exam
• Nursing Diagnosis
• Implementation
• Evaluation
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25. Question
A patient experienced a musculoskeletal injury resulting in
a great deal of pain in his lower back. How can the nurse
augment the drugs to aid in pain relief?
A. Moist cold
B. NSAIDs
C. Passive exercise
D. Active exercise
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26. Answer
B. NSAIDs
Rationale: Provide additional measures to relieve
discomfort—heat, rest for the muscle, NSAIDs,
positioning— to augment the effects of the drug at
relieving the musculoskeletal discomfort.
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