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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. - PowerPoint PPT Presentation
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CHAPTER 36DISORDERS OF NEUROMUSCULAR FUNCTION
Essentials of Pathophysiology
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.
F
F
F
T
T
PRE LECTURE QUIZ1. 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
Pyramidal Most cross to
other side of body
Motor cortex neurons
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. Upperb. Lowerc. Both upper and lowerd. Neither upper nor lower
ANSWER
b. 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
Hypotonia Hypertoni
a 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
TrueRationale: 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
FalseRationale: 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 gravisb. Multiple sclerosisc. Poliod. Tourette syndrome
ANSWER
d. Tourette syndromeRationale: The tics and hyperkinesia
that often accompany Tourette syndrome are typical of basal ganglia dysfunction (the function of the basal ganglia is movement control).
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. ALSb. MSc. Myasthenia gravisd. Parkinson disease
ANSWER
a. ALSRationale: 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 shockº Temporary complete loss of function
below injury Primary neurologic injury
º 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 of digestive enzymes from damaged cells
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-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