Presentation on theme: "CHAPTER 36 DISORDERS OF NEUROMUSCULAR FUNCTION Essentials of Pathophysiology."— Presentation transcript:
CHAPTER 36 DISORDERS 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 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 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. Upper b. Lower c. Both upper and lower d. 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 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
QUESTION Which disease is a result of basal ganglia dysfunction? a. Myasthenia gravis b. Multiple sclerosis c. Polio d. Tourette syndrome
ANSWER d. 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).
PARKINSONISM Tremor Rigidity Bradykinesia (slow movement) Loss of postural reflexes Autonomic system dysfunction Dementia
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 a. 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 º 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