Muscle Relaxers - Mechanisms, Indications, Side Effects

Summary

This video covers the topic of muscle relaxants, which reduce muscle tone and treat conditions like muscle spasms, hyperreflexia, and pain. Muscle relaxants are divided into neuromuscular blockers and spasmolytics. Neuromuscular blockers work peripherally to induce short-term paralysis during surgery, while spasmolytics act centrally in the brain or spinal cord. The video explains various drugs like diazepam, baclofen, tizanidine, and dantrolene, their mechanisms, and their use in conditions such as multiple sclerosis, cerebral palsy, and spinal cord injuries. It also emphasizes the potential side effects and precautions of these medications.

Takeaways

• 💊 Muscle relaxants decrease muscle tone and are used to treat symptoms such as muscle spasms, hyperreflexia, and pain.
• 🧠 Muscle relaxants are divided into two groups: neuromuscular blockers and spasmolytics. Neuromuscular blockers work at the neuromuscular junction, while spasmolytics act centrally in the brain or spinal cord.
• ⚡ Neuromuscular blockers are used for short-term flaccid paralysis during surgeries and procedures like intubation by blocking nicotinic 1 receptors.
• 💡 Spasmolytics, often referred to as muscle relaxants, are used to treat painful musculoskeletal conditions and disorders like multiple sclerosis and cerebral palsy.
• 🧬 Diazepam, a benzodiazepine, enhances GABA-A receptor activity, increasing chloride permeability in lower motor neurons, causing hyperpolarization and reducing muscle contraction.
• 🦴 Baclofen, used for spinal cord injuries, activates GABA-B receptors, increasing potassium conductance and reducing excitatory neurotransmitter release, leading to muscle relaxation.
• 🔗 Tizanidine is an alpha-2 agonist that decreases the release of excitatory neurotransmitters, used for managing spasms associated with multiple sclerosis.
• ⚙️ Dantrolene, a direct-acting muscle relaxant, blocks ryanodine receptors in skeletal muscles, preventing calcium release and muscle contraction, making it useful for conditions like malignant hyperthermia.
• 🚫 Muscle relaxants acting in the CNS can cause adverse effects like dizziness, fatigue, muscle weakness, and euphoria, with cautions against alcohol use and driving.
• ⚠️ Commonly prescribed muscle relaxants for local spasms include carisoprodol, cyclobenzaprine, and metaxalone, though their mechanisms are not well understood.

Q & A

What are the two major groups of muscle relaxants?

The two major groups of muscle relaxants are neuromuscular blockers and spasmolytics.

What is the primary function of neuromuscular blockers?

Neuromuscular blockers block nicotinic 1 receptors at the neuromuscular junction, preventing skeletal muscle contractions, often used during surgeries and intubation to induce short-term flaccid paralysis.

How do spasmolytics work in the body?

Spasmolytics work primarily in the central nervous system, either at the spinal cord or brain level, to reduce muscle tone and spasms.

What are some common indications for the use of muscle relaxants?

Muscle relaxants are indicated for treating painful musculoskeletal conditions such as muscle spasms, hyperreflexia, and conditions like multiple sclerosis and cerebral palsy.

How does diazepam work as a muscle relaxant?

Diazepam, a benzodiazepine, enhances the effect of GABA by increasing chloride permeability in the lower motor neurons, which hyperpolarizes the cell, reducing muscle spasms.

What is the mechanism of action for baclofen?

Baclofen activates GABA-B receptors, increasing potassium conductance and hyperpolarizing lower motor neurons. It also reduces excitatory neurotransmitter release by decreasing calcium influx in upper motor neurons.

What role does tizanidine play in muscle relaxation?

Tizanidine is an alpha-2 agonist that reduces excitatory neurotransmitter release, commonly used for managing muscle spasms in conditions like multiple sclerosis.

How does dantrolene differ from other muscle relaxants in terms of its mechanism?

Dantrolene acts directly on skeletal muscles by blocking ryanodine receptors, preventing calcium release from the sarcoplasmic reticulum, thereby inhibiting muscle contraction.

What is malignant hyperthermia, and how is it treated?

Malignant hyperthermia is a severe reaction to certain anesthetics, characterized by muscle rigidity and fever. It is treated with dantrolene, which prevents excessive calcium release in muscles.

What are common adverse effects associated with CNS-acting muscle relaxants?

Common adverse effects include euphoria, dizziness, fatigue, and muscle weakness. Patients should avoid alcohol and be cautious when operating machinery.

Outlines

00:00

💊 Overview of Muscle Relaxants

This paragraph introduces muscle relaxants, explaining that they are used to decrease muscle tone and treat symptoms like spasms, hyperreflexia, and pain. Muscle relaxants are categorized into two main groups: neuromuscular blockers and spasmolytics. Neuromuscular blockers act at the neuromuscular junction, causing temporary paralysis, often used in surgeries or intubation. In contrast, spasmolytics act centrally in the brain or spinal cord and are the focus of this discussion. Muscle relaxants are mainly indicated for treating painful musculoskeletal conditions and chronic disorders such as multiple sclerosis and cerebral palsy, working best alongside physical therapy.

05:03

🧠 Mechanism of Muscle Relaxants

Here, the focus shifts to the mechanisms by which muscle relaxants function. It starts with a review of motor neuron synapses in the spinal cord. Voluntary muscle contraction involves upper motor neurons (UMNs) from the brain, which activate lower motor neurons (LMNs) to stimulate muscles. Inhibitory interneurons release GABA to dampen LMN excitation, preventing overactivity. Diazepam, a benzodiazepine, enhances GABA's inhibitory effect by increasing chloride ion permeability, further hyperpolarizing LMNs and reducing muscle contractions. The mechanisms of other muscle relaxants such as baclofen, tizanidine, and dantrolene, each with distinct actions on neurotransmitters and receptors, are also described in detail.

💉 Detailed Actions of Specific Muscle Relaxants

This paragraph elaborates on the specific functions of several muscle relaxants. Baclofen, for instance, activates GABA receptors, causing hyperpolarization of LMNs and reducing excitatory neurotransmitter release from UMNs, thus reducing muscle spasms. Tizanidine, used for multiple sclerosis, works as an alpha-2 agonist, decreasing the release of excitatory neurotransmitters. Dantrolene, a direct-acting relaxant, prevents muscle contractions by blocking calcium release in skeletal muscle. It’s particularly useful in treating conditions like malignant hyperthermia and other muscle-related disorders. Unlike other relaxants, dantrolene doesn’t act within the CNS but directly on muscles.

🩺 Common Uses and Side Effects of Muscle Relaxers

This paragraph discusses common muscle relaxants prescribed for local muscle spasms resulting from overexertion or injuries. Cyclobenzaprine, carisoprodol, and others are mentioned, though their exact mechanisms are not well understood. Muscle relaxants that act in the CNS generally share similar side effects such as euphoria, dizziness, fatigue, and muscle weakness. Patients taking these drugs should be monitored and advised not to mix them with alcohol or operate heavy machinery due to their CNS depressant effects.

Keywords

💡Muscle Relaxants

Muscle relaxants are a class of medications that reduce muscle tone and are used to treat conditions characterized by increased muscle tone, such as muscle spasms, hyperreflexia, and pain. In the video, they are divided into two major groups: neuromuscular blockers and spasmolytic agents. Muscle relaxants are indicated for the treatment of painful musculoskeletal conditions, and they are often used alongside physical therapy to enhance their effectiveness.

💡Neuromuscular Blockers

Neuromuscular blockers are a type of muscle relaxant that work peripherally by blocking nicotinic receptors at the neuromuscular junction, which stops skeletal muscle contractions. They are particularly useful during certain surgical procedures and for causing short-term flaccid paralysis, such as during intubation. This concept is critical for understanding how some muscle relaxants function at a physiological level to achieve their therapeutic effects.

💡Spasmolytic Agents

Spasmolytic agents are a category of muscle relaxants that act centrally, at the level of the spinal cord or brain, to reduce muscle spasms. The video emphasizes that the term 'muscle relaxants' is often used to refer specifically to these spasmolytic agents. They are used to treat conditions like muscle spasms associated with overexertion and spasticity in chronic disorders such as multiple sclerosis and cerebral palsy.

💡Diazepam

Diazepam is a benzodiazepine that is used to treat muscle spasms. It works by binding to the BZD binding site of GABA-A receptors on the cell bodies of lower motor neurons, which increases chloride permeability and hyperpolarizes the cell, reducing the frequency of action potentials that lead to muscle contractions. Diazepam is an example of how some muscle relaxants enhance the inhibitory action of GABA to achieve muscle relaxation.

💡Baclofen

Baclofen is a medication used for spasms associated with spinal cord injuries. It acts by activating gamma-B receptors in the postsynaptic membrane, which increases potassium conductance and causes hyperpolarization. Additionally, it can reduce the release of excitatory neurotransmitters from the upper motor neuron, thus decreasing muscle contractions. Baclofen exemplifies a drug that targets specific receptors to achieve muscle relaxation.

💡Tizanidine

Tizanidine is an alpha-2 agonist used for muscle spasms associated with conditions like multiple sclerosis. It binds to alpha-2 adrenergic receptors on axon terminals, leading to reduced release of excitatory neurotransmitters. This results in decreased muscle tone and spasms. Tizanidine illustrates the use of adrenergic receptor modulation as a strategy for muscle relaxation.

💡Dantrolene

Dantrolene is a direct-acting muscle relaxant that works by blocking ryanodine receptors in skeletal muscles, preventing the release of calcium from the sarcoplasmic reticulum, which is necessary for muscle contraction. It is used to treat muscle spasms associated with conditions like multiple sclerosis, cerebral palsy, spinal cord injuries, and malignant hyperthermia. Dantrolene is unique among muscle relaxants because it acts directly on muscle tissue rather than the central nervous system.

💡Malignant Hyperthermia (MH)

Malignant hyperthermia is a severe reaction characterized by fever, muscle rigidity, and tachycardia. It is a rare condition that occurs in susceptible individuals exposed to certain anesthetics or neuromuscular blockers. In the context of the video, MH is mentioned as a condition for which dantrolene is indicated, highlighting the importance of muscle relaxants in managing this life-threatening condition.

💡CNS Depressants

CNS depressants are substances that slow down the activity of the central nervous system. Most muscle relaxants, which act in the CNS, are considered CNS depressants. They can cause adverse effects such as euphoria, lightheadedness, dizziness, fatigue, and muscle weakness. The video advises caution with these effects, especially when operating machinery or driving, and warns against mixing muscle relaxants with alcohol.

💡Motor Neuron Synapses

Motor neuron synapses are the junctions where motor neurons connect with muscle fibers to facilitate muscle contraction. The video discusses how muscle relaxants work by affecting the excitatory and inhibitory neurotransmitters at these synapses. Understanding the role of motor neuron synapses is crucial for comprehending the mechanisms of action of muscle relaxants.

💡Hyperpolarization

Hyperpolarization is a physiological process where the membrane potential of a cell becomes more negative, making it less likely to generate an action potential. In the context of muscle relaxants, hyperpolarization of motor neurons reduces the likelihood of muscle contractions. The video explains how drugs like diazepam and baclofen induce hyperpolarization to achieve their muscle-relaxing effects.

Highlights

Muscle relaxants are divided into two groups: neuromuscular blockers and spasmolytics.

Neuromuscular blockers work peripherally by blocking nicotinic 1 receptors at the neuromuscular junction.

Neuromuscular blockers are used in surgeries and procedures like intubation to cause short-term flaccid paralysis.

Spasmolytics act centrally at the level of the spinal cord or brain.

The term 'muscle relaxants' typically refers to spasmolytics, which are used to treat painful musculoskeletal conditions.

Diazepam, a benzodiazepine, increases the action of GABA by binding to GABA-A receptors and enhancing chloride permeability.

Baclofen activates GABA-B receptors, increasing potassium conductance, which hyperpolarizes neurons and reduces muscle spasms.

Tizanidine, an alpha-2 agonist, reduces the release of excitatory neurotransmitters, helping manage muscle spasms.

Dantrolene is a direct-acting muscle relaxant that blocks ryanodine receptors in skeletal muscles, preventing calcium release.

Dantrolene is used to treat muscle spasms in conditions like multiple sclerosis, cerebral palsy, and malignant hyperthermia.

Malignant hyperthermia is a severe reaction to certain anesthetics and muscle relaxants, characterized by fever and muscle rigidity.

Dantrolene selectively targets skeletal muscle, sparing the heart due to the different types of ryanodine receptors.

Common muscle relaxers for local muscle spasms include carisoprodol, cyclobenzaprine, and metaxalone.

The mechanisms of most CNS-acting muscle relaxers are not fully understood but are thought to involve the brainstem.

Adverse effects of CNS-acting muscle relaxers include euphoria, dizziness, fatigue, and muscle weakness, requiring caution with tasks like driving.

Transcripts

our pharmacology topic today is muscle

relaxants muscle relaxants decrease

muscle tone they are used to treat

symptoms associated with increased

muscle tone such as muscle spasms

hyperreflexia and pain technically the

term muscle relaxants can be subdivided

into two major groups including

neuromuscular blockers and spasmolytic

s' neuromuscular blockers work in the

periphery neuromuscular blockers block

nicotinic 1 receptors in the

neuromuscular Junction to stop skeletal

muscle contractions they are useful

during certain types of surgery and for

procedures such as intubation to cause

short-term flaccid paralysis most

spasmolytic centrally at the level of

the spinal cord or brain the term muscle

relaxants is most often used to refer

just to spasmolytic s' and these are the

topic of this video remember that an

indication is the reason the drug is

used as mentioned muscle relaxants are

often indicated for the treatment of

painful musculoskeletal conditions

some examples include treating muscle

spasms associated with over exertion and

helping manage the spasticity of severe

chronic disorders like multiple

sclerosis and cerebral palsy these drugs

usually work best when used alongside

physical therapy to understand the

mechanisms for the muscle relaxers

diazepam tizen adeana baclofen let's

review a cross-section of the spinal

cord and zoom in on the motor neuron

synapses

for voluntary muscle contraction of

limbs the upper motor neuron or a umn is

activated in the cerebral cortex and

action potentials travel down the spinal

cord or they synapse with lower motor

neurons or elements at the level of exit

inhibitory interneurons regulate the

excitation of the element an action

potential traveling down the upper motor

neuron will cause the release of

excitatory neurotransmitters like

norepinephrine or glutamate onto the lmn

which will then activate the skeletal

muscle the inhibitory neurotransmitter

gaba is released from the inhibitory

neuron and acts to decrease the

excitation of the element by increasing

chloride permeability in the element

diazepam a benzodiazepine used for

muscle spasms will bind to the BZD

binding site of gaba-a receptors located

on cell bodies of the lower motor

neurons to increase the permeability of

chloride even more

thus the action of diazepam augments or

increases the action of GABA and

hyperpolarizes the cell even more the

hyper-polarization decreases the

frequency of action potentials traveling

through the element to the muscle

baclofen is a drug used for spasms

associated with spinal cord injuries

baclofen activates gamma b receptors in

the postsynaptic membrane to cause an

increase in potassium conductance in the

alamin which also causes

hyper-polarization there are also gamma

B receptors in the presynaptic membrane

of the upper motor neuron activation of

these receptors leads to less release of

calcium ions and consequently less

release of excitatory neurotransmitters

like norepinephrine and glutamate from

the umn onto the element consequently

less action potentials travel down the

lmn to reach the muscle ties Anna Dean

is one of the drugs used for spasms

associated with multiple sclerosis this

drug is an alpha-2 agonist and binds to

um

and axon terminals and causes less

release of excitatory neurotransmitter

another muscle relaxer dantrolene is a

direct acting muscle relaxant that

blocks ryanodine receptors in skeletal

muscles therefore unlike the other

muscle relaxants it doesn't act in the

CNS dantrolene is indicated for the

treatment of muscle spasms associated

with multiple sclerosis cerebral palsy

spinal cord injuries and malignant

hyperthermia or mhm mhm is a severe

reaction characterized by fever muscle

rigidity tachycardia although rare mhm

occurs in susceptible individuals that

are exposed to volatile general

anesthetics like halothane and

depolarizing neuromuscular blockers like

succinylcholine dantrolene binds to the

ryanodine channel and prevents it from

opening when the action potential

reaches the D HPR this prevents release

of calcium from the sarcoplasmic

reticulum and prevents muscle

contraction dantrolene is more selective

for skeletal muscle because the heart

has ryouta dean type 2 receptors instead

of type 1 that is in skeletal muscle

several muscle relaxers are used for

local muscle spasms associated with over

exertion or injuries manual laborers or

those in car accidents are examples of

individuals who may have these drugs

prescribed by a physician common muscle

relaxers that fit this category are car

sore / doll cyclobenzaprine Mattacks

alone Clorox is owned and orphan adrene

the mechanism for these drugs is not

well understood but is believed that

they are to act in the brain stem

most relaxers that act in the cns have

the following adverse effects in common

euphoria lightheadedness or dizziness

fatigue and muscle weakness due to these

effects it is important to advise

patience and monitor them while taking

these medications also since most muscle

relaxers are CNS depressants don't mix

with alcohol and use caution when

driving and operating machinery here is

a summary of the mechanisms of action

for muscle relaxers pause the video now

for review here now is a practice

problem to test your knowledge pause the

video and think of your answer

if you answered age then you are correct

thanks for watching