NURS 260 Pathophysiology Study Notes


Components of the Neuromuscular System

  • Neuromuscular unit containing motoneurons

  • Myoneural junction

  • Muscle fibers

  • Spinal cord

  • Descending pathways from the brain stem circuits

The Motor Control System

  • The final common pathway transmits all central nervous system (CNS) commands to the skeletal muscles.

  • This path is influenced by sensory input from the muscle spindles and tendon organs as well as descending signals from the cerebral cortex and brain stem.

  • The cerebellum and basal ganglia influence motor function indirectly via the brain stem.

Motor Homunculus

  • Representation of the areas of the brain responsible for motor control of different body parts:

    • Little

    • Ring

    • Middle

    • Index

    • Thumb

    • Neck

    • Eyebrow

    • Eyelid and eyeball

    • Face

    • Lips

    • Jaw

    • Tongue

    • Swallowing

    • Hand

    • Wrist

    • Elbow

    • Trunk

    • Shoulder

    • Hip

    • Knee

    • Ankle

    • Toes

Motor Systems

  • Pyramidal Motor System

    • Originates in the motor cortex.

    • Provides control of delicate muscle movements.

  • Extrapyramidal System

    • Originates in the basal ganglia.

    • Provides background for more crude, supportive movement patterns.

Disorders of Motor Function

  • Upper Motoneuron Lesions

    • Can affect the motor cortex, internal capsule, or brain structures through which the corticospinal or corticobulbar tracts descend, or the spinal cord.

  • Lower Motoneuron Lesions

    • Disrupt communication between the muscle and all neural input from spinal cord reflexes, including the stretch reflex, which maintains muscle tone.

Disorders of Skeletal Muscle Groups

  • Muscular Atrophy

    • If a normally innervated muscle is not used for long periods, the muscle cells shrink in diameter, lose contractile protein, and weaken.

  • Muscular Dystrophy

    • Genetic disorders that result in progressive deterioration of skeletal muscles due to mixed muscle cell hypertrophy, atrophy, and necrosis.

Muscular Dystrophy

  • Characteristics:

    • Normal fibers

    • Overcontracted fibers

    • Endomysial collagen

    • Regenerating fibers

    • Macrophages in degenerated fiber (myophagocytosis)

Alterations of Neuromuscular Function

  • Drugs and agents can alter neuromuscular function by changing the release, inactivation, or receptor binding of acetylcholine.

  • Curare

    • Acts on the postjunctional membrane of the motor end plate to prevent the depolarizing effect of the neurotransmitter.

    • Commonly used during various surgical procedures.

Myasthenia Gravis

  • Definition

    • A disorder of transmission at the neuromuscular junction affecting communication between the motoneuron and the innervated muscle cell.

  • Cause

    • An autoimmune disease causing antibody-mediated loss of acetylcholine receptors at the neuromuscular junction.

Components of the Peripheral Nervous System

  • Motor and sensory branches of the cranial and spinal nerves.

  • The peripheral parts of the autonomic nervous system.

  • Peripheral ganglia.

Peripheral Neuropathies

  • Mononeuropathies

    • Caused by localized conditions such as trauma, compression, or infections affecting a single spinal nerve, plexus, or peripheral nerve trunk.

    • Examples:

    • Fractured bones may lacerate or compress nerves.

    • Excessively tight tourniquets may directly injure nerves or produce severe effects.

  • Polyneuropathies

    • Involves demyelination or axonal degeneration of multiple peripheral nerves, leading to symmetric sensory, motor, or mixed sensorimotor deficits.

    • Typically, the longest axons are involved first, with symptoms beginning in the distal parts of the extremities.

Carpal Tunnel Syndrome

  • Caused by compression of the median nerve due to repetitive use of the wrist.

  • Characterized by areas of numbness in the carpal tunnel regions (depicted in shaded green).

Guillain-Barre Syndrome

  • Characteristics

    • Acute, immune-mediated condition.

    • Often preceded by an acute influenza-like illness prior to the onset of symptoms.

Nerve Root Injuries

  • A common cause of back pain due to trauma, aging, or degenerative processes affecting nerve roots at L4, L5, S1 levels.

Disorders of the Cerebellum

  • The cerebellum is responsible for:

    • Coordination of motor movement.

  • Cerebellum-associated movement disorders

    • Causes: congenital defects, vascular accidents, or tumors.

    • Types of disorders include:

    • Vestibulocerebellar ataxia

    • Decomposition of movement

Basal Ganglia

  • A group of deep, interrelated subcortical nuclei that play an essential role in movement control.

  • Receive:

    • Indirect input from the cerebellum and all sensory systems (including vision).

    • Direct input from the motor cortex.

  • Function in organizing inherited and learned automatic movement programs.

  • Key pathways include:

    • A dopamine pathway from the substantia nigra to the striatum.

    • A γ-aminobutyric acid (GABA) pathway from the striatum to the globus pallidus and substantia nigra.

    • Acetylcholine-secreting neurons involved in network functions within the neostriatum.

    • Several pathways from the brain stem secreting norepinephrine and serotonin.

Characteristics of Basal Ganglia-Associated Movement Disorders

  • Movement Disorder Characteristics:

    • Tremor: Involuntary, oscillating contractions of opposing muscle groups around a joint.

    • Hypokinetic disorders: Slowness in initiating movement and reduced range and force (bradykinesia).

    • Chorea: Irregular wriggling and writhing movements, accentuated by movement and environmental stimuli.

    • Athetosis: Continuous wormlike, twisting, and turning motions of a limb or body.

    • Ballismus: Violent, sweeping, flinging motions of one side of the body (hemiballismus).

    • Dystonia: Abnormal maintenance of a posture due to simultaneous contraction of antagonist and agonist muscles.

    • Dyskinesias: Bizarre wriggling and writhing movements often affecting facial regions.

Definition of Parkinson's Disease

  • A degenerative disorder of basal ganglia function characterized by tremor, rigidity, and bradykinesia.

  • Characteristics:

    • Progressive destruction of the nigrostriatal pathway, leading to reduced striatal dopamine concentrations.

Amyotrophic Lateral Sclerosis (ALS)

  • A devastating neurologic disorder affecting motor function, typically following a progressive course with a mean survival period of 2 to 5 years from the onset of symptoms.

  • Motor Neurons affected:

    • Anterior horn cells of the spinal cord.

    • Motor nuclei of the brain stem, particularly hyoglossal nuclei.

    • UMNs of the cerebral cortex.

  • Death of LMNs leads to denervation, resulting in musculature shrinkage and muscle fiber atrophy.

Multiple Sclerosis (MS)

  • A demyelinating disease of the CNS, it is the most common nontraumatic cause of neurologic disability among young and middle-aged adults.

  • Characterized by exacerbations and remissions over many years, affecting multiple sites in the CNS.

  • Initially, individuals may have normal or near-normal neurologic function between exacerbations.

  • As the disease progresses, there is less improvement between exacerbations.

Spinal Cord Injury (SCI)

  • Definition: Damage to the neural elements of the spinal cord.

  • Causes: Motor vehicle crashes, falls, violence, and sporting activities.

  • Involvement: Most SCIs involve damage to the vertebral column and/or supporting ligaments in addition to the spinal cord.

  • Commonly affect:

    • Sensory and motor functions, spinal reflexes, the autonomic nervous system, temperature regulation, sensorimotor function, skin integrity, pain reception, bladder and bowel function, and sexual functions.