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Essentials of Pathophysiology
CHAPTER 36
DISORDERS OF NEUROMUSCULAR
FUNCTION
PRE LECTURE QUIZ (TRUE / FALSE)
F

F

F

T

T

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
1.
Myasthenia gravis, an autoimmune disorder, is caused by an
antibody-mediated destruction of ______________________
receptors in the neuromuscular junction.
2.
Guillain-Barré syndrome is characterized by progressive
ascending muscle _____________________ of the limbs,
producing a symmetric flaccid paralysis.
3.
Parkinson disease is a degenerative disorder of the basal
___________________ that results in variable combinations
of tremor, rigidity, and bradykinesia.
4.
A __________________ is a an irregularly occurring, brief,
repetitive movement such as winking, grimacing, or shoulder
shrugging.
5.
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.
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
TWO MOTOR SYSTEMS

Extrapyramidal
 Most
go to same
side of body

Motor cortex neurons
Pyramidal
 Most
cross to
other side of
body
Internal capsule
Pons
Extrapyramidal
system
Pyramidal system
MOTOR UNIT
Lower motor neuron
 Lower motor neuron’s
axon running through
peripheral nerves
 The muscles it
innervates

Upper motor neurons
Send axons down
spinal cord tracts
Lower motor
neurons in spinal
cord
Peripheral nerves
Muscles
QUESTION
Which motor neurons are damaged in patients
who have neuromuscular disorders that
directly affect skeletal muscle?
a. Upper
b. Lower
c. Both upper and lower
d. Neither upper nor lower
ANSWER
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.
b.
MUSCLE TONE



Muscle stretches
Afferent neuron
carries impulse
to spinal cord
Motoneurons
cause muscle to
contract
ALTERATIONS IN MUSCLE TONE

Hypotonia

Hypertonia

Rigidity

Clonus
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
DISCUSSION
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 motor neurons
Send axons down
spinal cord tracts
Lower motor
neurons in spinal
cord
Peripheral nerves
Muscles
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
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
THE MOTOR UNIT

One lower
motor neuron
(motoneuron)

The
neuromuscular
junction

The muscle
fibers it
innervates
QUESTION
Tell whether the following statement is true or
false.
To increase the strength of a contraction, more
motor neurons must be recruited.
ANSWER
True
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
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
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
QUESTION
Tell whether the following statement is true or
false.
Acetylcholinesterase stimulates the release of
acetylcholine (ACh).
ANSWER
False
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
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 (CONT.)


Mononeuropathies
 Damage to one peripheral nerve
 E.g., carpal tunnel syndrome
Polyneuropathies
 Damage to many peripheral nerves
 E.g., Guillain-Barré syndrome
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 basal ganglia
inhibit and modulate
movement patterns

BASAL GANGLIA DYSFUNCTION CAN INCREASE
PATTERNED MOVEMENT



Tremors
Tics
Hyperkinesia
 Choreiform: jerky movements
 Athetoid: continuous twisting movements
 Ballismus: violent flinging movements
 Dystonia: rigidity
QUESTION
Which disease is a result of basal ganglia
dysfunction?
a. Myasthenia gravis
b. Multiple sclerosis
c. Polio
d. Tourette syndrome
ANSWER
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).
d.
PARKINSONISM

Tremor

Rigidity

Bradykinesia (slow movement)

Loss of postural reflexes

Autonomic system dysfunction

Dementia
CEREBELLUM DAMAGE

Vestibulocerebellar disorders
 Difficulty

maintaining posture
Cerebellar ataxia
 Movements

divided into separate components
Cerebellar tremor
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

MULTIPLE SCLEROSIS

Destruction of myelin coating on axons

Demyelinated or sclerotic patches develop
through white matter of CNS

Decreased conduction velocity
QUESTION
Which disorder causes damage to both upper
and lower motor neurons?
a. ALS
b. MS
c. Myasthenia gravis
d. Parkinson disease
ANSWER
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.
a.
SPINAL CORD INJURY

Immediate damage causes:
 Spinal
º
cord shock
Temporary complete loss of function below
injury
 Primary
º
neurologic injury
Irreversible damage to neurons
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
cells
of digestive enzymes from damaged
PARTIAL SPINAL CORD INJURY

Central cord syndrome: damage to axons near
the gray matter


Anterior cord syndrome: damage to anterior
section of cord


Arms more affected than legs
Motor functions affected; touch sensation not
affected
Brown-Séquard syndrome: damage to one side of
cord

Motor function lost on that side; pain/temperature
sensation lost from other side
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