Chapter 36 disorders of neuromuscular function
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Essentials of Pathophysiology. Chapter 36 Disorders of Neuromuscular Function. Paralysis refers to weakness or incomplete loss of muscle function.   Carpal tunnel syndrome is an example of a polyneuropathy . All levels of spinal cord injury will require assistance to maintain breathing.

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Chapter 36 Disorders of Neuromuscular Function

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Chapter 36 disorders of neuromuscular function

Essentials of Pathophysiology

Chapter 36Disorders of Neuromuscular Function

Pre lecture quiz true false

  • Paralysis refers to weakness or incomplete loss of muscle function.  

  • Carpal tunnel syndrome is an example of a polyneuropathy.

  • All levels of spinal cord injury will require assistance to maintain breathing.

  • Autonomic dysreflexia represents an acute episode of exaggerated sympathetic reflex responses that occur in persons with some types of spinal cord injuries.

  • The pathophysiology of multiple sclerosis involves the demyelination and subsequent degeneration of nerve fibers in the central nervous system.

Pre lecture quiz (True / false)






Pre lecture quiz

  • Myasthenia gravis, an autoimmune disorder, is caused by an antibody-mediated destruction of ______________________ receptors in the neuromuscular junction.

  • Guillain-Barré syndrome is characterized by progressive ascending muscle _____________________ of the limbs, producing a symmetric flaccid paralysis.

  • Parkinson disease is a degenerative disorder of the basal ___________________ that results in variable combinations of tremor, rigidity, and bradykinesia.

  • A __________________ is a an irregularly occurring, brief, repetitive movement such as winking, grimacing, or shoulder shrugging.

  • Muscular dystrophy is a term applied to a number of genetic disorders that produce progressive degeneration and necrosis of skeletal muscle __________________, which are eventually replaced with fat and connective tissue.

Pre lecture quiz

  • Acetylcholine

  • Fibers

  • Ganglia

  • Tic

  • Weakness

Upper motor neurons are in the brain and spinal cord

Upper motor neuron cell bodies are in the motor cortex

They send their axons down through the internal capsule

The axons then run down the white matter of the spinal cord

Upper Motor Neurons Are in the Brain and Spinal Cord

Two motor systems

  • Extrapyramidal

    • Most go to same side of body

  • Pyramidal

    • Most cross to other side of body

Two Motor Systems

Motor cortex neurons

Internal capsule



Pyramidal system


Motor unit

Lower motor neuron

Lower motor neuron’s axon running through peripheral nerves

The muscles it innervates

Motor Unit

Upper motor neurons

Send axons down

spinal cord tracts

Lower motor

neurons in spinal


Peripheral nerves



Which motor neurons are damaged in patients who have neuromuscular disorders that directly affect skeletal muscle?

  • Upper

  • Lower

  • Both upper and lower

  • Neither upper nor lower



  • Lower

    Rationale:The axons of lower motor neurons pass through peripheral nerves to effector tissue in skeletal muscle. Upper motor neurons’ axons travel down the spinal cord.


Muscle tone

Muscle stretches

Afferent neuron carries impulse to spinal cord

Motoneurons cause muscle to contract


Alterations in muscle tone





Alterations in Muscle Tone

Terms to describe motor dysfunction

-plegia = stroke or paralysis

Paralysis = loss of movement

-paresis = weakness

Mono- = one limb

Hemi- = both limbs on one side

Di- or para- = both upper limbs or both lower limbs

Quadri- or tetra- = all four limbs

Terms to Describe Motor Dysfunction


What would be the terms for the following?

  • A defect causing weakness in both arms

  • A weakness in the right arm and leg

  • Inability to move one leg


Upper vs lower motor neurons

  • Upper motor neurons

    • In the brain and spinal cord

  • Lower motor neurons

    • Send axons out of the spinal cord

Upper vs. Lower Motor Neurons

Upper motor neurons

Send axons down

spinal cord tracts

Lower motor

neurons in spinal


Peripheral nerves


Upper motor neuron damage

  • Weakness and loss of voluntary motion

  • Spinal reflexes remain intact but cannot be modulated by the brain

    • Increased muscle tone

    • Hyperreflexia

    • Spasticity

Upper Motor Neuron Damage

Lower motor neuron damage

  • Neurons directly innervating muscles are affected

  • Irritated neurons

    • Spontaneous muscle contractions: fasciculations

  • Death of neurons

    • Spinal reflexes are lost

    • Flaccid paralysis

    • Denervation atrophy of muscles

Lower Motor Neuron Damage

The motor unit

One lower motor neuron (motoneuron)

The neuromuscular junction

The muscle fibers it innervates

The Motor Unit


Tell whether the following statement is true or false.

To increase the strength of a contraction, more motor neurons must be recruited.




Rationale:A motor unit consists of branches of a neuron and the skeletal muscle fibers that they innervate. For stronger contractions, more motor units are required.


Possible problems with the motor unit

Lower motor neuron lesions or infections; peripheral nerve injury

Neuromuscular junction disorders

Muscle atrophy or dystrophy

Possible Problems With the Motor Unit

Skeletal muscle problems

  • Disuse atrophy

  • Denervation atrophy

  • Muscular dystrophy

    • Contractile proteins not properly attached to cytoskeleton of muscle cell

    • Protein movement does not effectively contract muscle cell

Skeletal Muscle Problems

Neuromuscular junction problems

  • Decreased acetylcholine release

    • Botulism

  • Decreased acetylcholine effects on muscle cell

    • Curare

    • Myasthenia gravis

  • Decreased acetylcholinesterase activity; acetylcholine has a stronger effect on the muscle cell

    • Organophosphates

Neuromuscular Junction Problems


Tell whether the following statement is true or false.

Acetylcholinesterase stimulates the release of acetylcholine (ACh).




Rationale:Acetylcholinesterase breaks down ACh, resulting in relaxation of the skeletal muscle.


Myasthenia gravis

  • Autoimmune disease

    • Gradual destruction of acetylcholine receptors

    • Associated with thymus tumor or hyperplasia

  • Gradual development of weakness

    • From proximal to distal portions of body

  • Myasthenia crisis: respiration compromised

Myasthenia Gravis

Peripheral nerve injuries

Damage to LMN cell bodies in the spinal cord

Damage to axons in the spinal or peripheral nerves

Damage to myelin sheath (demyelination)

Peripheral Nerve Injuries

Peripheral nerve injuries cont

  • Mononeuropathies

    • Damage to one peripheral nerve

    • E.g., carpal tunnel syndrome

  • Polyneuropathies

    • Damage to many peripheral nerves

    • E.g., Guillain-Barré syndrome

Peripheral Nerve Injuries (cont.)

Back pain

Peripheral nerve injury at the spinal nerve roots

Often due to compression of nerve root by vertebrae or vertebral disk


Motor impulses are modulated by the basal ganglia

Upper motor neuron cell bodies are in the motor cortex

They send their axons down through the internal capsule

The basalganglia inhibit and modulate movement patterns

Motor Impulses Are Modulated by the Basal Ganglia

Basal ganglia dysfunction can increase patterned movement

  • Tremors

  • Tics

  • Hyperkinesia

    • Choreiform: jerky movements

    • Athetoid: continuous twisting movements

    • Ballismus: violent flinging movements

    • Dystonia: rigidity

Basal Ganglia Dysfunction Can Increase Patterned Movement


Which disease is a result of basal ganglia dysfunction?

  • Myasthenia gravis

  • Multiple sclerosis

  • Polio

  • Tourette syndrome



  • Tourette syndrome

    Rationale:The tics and hyperkinesia that often accompany Tourette syndrome are typical of basal ganglia dysfunction (the function of the basal ganglia is movement control).





Bradykinesia (slow movement)

Loss of postural reflexes

Autonomic system dysfunction



Cerebellum damage

  • Vestibulocerebellar disorders

    • Difficulty maintaining posture

  • Cerebellar ataxia

    • Movements divided into separate components

  • Cerebellar tremor

Cerebellum Damage

Amyotrophic lateral sclerosis

  • Damages both upper and lower motor neurons

  • UMN damage  weakness, lack of motor control

    • Loss of control over spinal reflexes  stiffness, spasticity

  • LMN damage

    • Irritation  fasciculations

    • Decreased neuron firing  weakness, denervation atrophy, hyporeflexia

Amyotrophic Lateral Sclerosis

Multiple sclerosis

Destruction of myelin coating on axons

Demyelinated or sclerotic patches develop through white matter of CNS

Decreased conduction velocity

Multiple Sclerosis


Which disorder causes damage to both upper and lower motor neurons?

  • ALS

  • MS

  • Myasthenia gravis

  • Parkinson disease



  • ALS

    Rationale:Also known as Lou Gehrig disease, ALS destroys both upper and lower motor neurons. Typical S/S include weakness, lack of motor control, denervation atrophy, and hyporeflexia.


Spinal cord injury

  • Immediate damage causes:

    • Spinal cord shock

      • Temporary complete loss of function below injury

    • Primary neurologic injury

      • Irreversible damage to neurons

Spinal Cord Injury

Secondary injury to the spinal cord

  • Neurons and white matter in area of initial damage are affected

  • Possible causes include:

    • Damage to blood vessels supplying the area

    • Decreased vasomotor tone decreasing blood supply

    • Local release of substances that cause vasospasm

    • Release of digestive enzymes from damaged cells

Secondary Injury to the Spinal Cord

Partial spinal cord injury

  • Central cord syndrome: damage to axons near the gray matter

    • Arms more affected than legs

  • Anterior cord syndrome: damage to anterior section of cord

    • Motor functions affected; touch sensation not affected

  • Brown-Séquardsyndrome: damage to one side of cord

    • Motor function lost on that side; pain/temperature sensation lost from other side

Partial Spinal Cord Injury

Complete spinal cord injury

  • To upper motor neurons (T12 and above)

    • Spinal reflexes still work

    • No longer modulated by brain

    • Hypertonia, spastic paralysis

  • To lower motor neurons (T12 and below)

    • Cells in spinal reflex arcs damaged

    • Flaccid paralysis

Complete Spinal Cord Injury

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