Motor Function and Heat Related Illness

Chapter 15: Motor Function + Heat Related Illness

The Motor Cortex

• Functions of different body parts mapped onto the motor cortex

  • Little

  • Ring

  • Middle

  • Index

  • Thumb

  • Neck

  • Eyebrow

  • Eyelid and eyeball

  • Face

  • Lips

  • Jaw

  • Tongue

  • Swallowing

  • Hand

  • Elbow

  • Wrist

  • Trunk

  • Shoulder

  • Hip

  • Knee

  • Ankle

  • Toes

Organization of Movement

• Upper Motoneurons:

  • Project from the motor cortex to the brain stem or spinal cord.

  • Functionally innervate lower motoneurons or contracting muscles.

• Motor Unit:

  • Defined as a motor neuron and all muscle fibers it innervates.

• Sensory Feedback:

  • Continuously relayed to the cerebellum, basal ganglia, and sensory cortex.

• Neuromuscular Junction:

  • Critical for linking nervous system activity with muscle contraction.

Movement Planning

• Primary Motor Cortex:

  • Responsible for the execution of movement.

• Premotor Cortex:

  • Involved in generating a plan of movement.

• Supplemental Motor Cortex:

  • Responsible for rehearsing motor sequences of movement.

The Motor Unit & Neuromuscular Junction

• Motor Unit Definition:

  • Consists of a motor neuron and the muscle fibers it innervates.

• Components of Neuromuscular Junction:

  • Axon terminals of a motor neuron.

  • Specialized region of muscle membrane called the end plate.

• Neurotransmitter Release:

  • Transmission of impulses is mediated by release of the neurotransmitter acetylcholine (ACh).

• Muscle Contraction Mechanism:

  • Acetylcholine binds to receptors in the end plate region of the muscle fiber surface, causing muscle contraction.

Classifications of Muscles

• Flexors:

  • Muscles that decrease the angle of a joint.

• Extensors:

  • Muscles that increase the angle of a joint.

Golgi Tendon Organ

• Definition:

  • A sensory receptor located near the junction of muscle and tendon.

• Function:

  • Responds to muscle tension rather than muscle stretch, transmitting magnitude of contractile force during movement.

• Inhibition Mechanism:

  • If excessive muscle tension is detected, the Golgi tendon organ inhibits the muscle from creating additional force via a reflex arc.

Muscle Spindle

• Definition:

  • Stretch receptors that signal muscle length and changes in length.

• Location:

  • Lie within an independent capsule, parallel to the main muscle.

• Functional Mechanism:

  • Stretched when the muscle lengthens but shortens when the muscle contracts.

The Stretch Reflex and Muscle Tone

1. Stretch Reflex

   • Receptors:

     • Muscle spindle

     • Intrafusal muscle fiber

     • Primary sensory (Ia) nerve fiber

     • Extrafusal muscle fiber

2. Spinal Reflex Centers

   • Ascending fibers to brain centers.

   • Homonymous muscle Ia afferent to motor neuron.

3. Brain Center Connections

   • Intrafusal muscle fiber connections and descending fibers from brain centers.

   • Includes gamma motor neuron and alpha motor neuron pathways.

4. The Knee-Jerk Reflex

   • Involves muscle spindle and Ia afferent from quadriceps tendon to alpha motor neuron.

Disorders of Skeletal Muscle

• Muscular Atrophy:

  • Occurs if a normally innervated muscle is unused for extended periods, leading to shrinkage in diameter and loss of contractile protein.

Disorders of Skeletal Muscle: Muscular Dystrophy

• Overview:

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

Duchenne's Muscular Dystrophy

• Characteristics:

  • Progressive weakness and muscle wasting.

• Onset:

  • Occurs between ages 3-5.

• Genetic Basis:

  • Primarily affects males (X-linked inheritance).

• Clinical Manifestations:

  • Gower's sign, clumsiness, frequent falls, difficulty with stair climbing, running, tricycle riding, waddling gait with lordosis, and large calf muscles.

• Progression:

  • Ambulation often impossible by age 12; associated breathing issues lead to life-threatening infections and death typically by ages 15-18.

• Nursing Considerations:

  • Manage fatigue, frequent infections, mobility, psychological effects, and maintain function.

Disorders of the Neuromuscular Junction

• Impact of Drugs:

  • Certain drugs change neuromuscular function by altering release, inactivation, or receptor binding of acetylcholine.

  • Curare: Acts on postjunctional membrane of motor end plate, preventing ACh's depolarizing effect.

  • Clostridium botulinum: Blocks ACh, resulting in paralysis.

Myasthenia Gravis

• Definition:

  • Disorder of transmission at neuromuscular junction affecting communication between the motoneuron and muscle cell.

• Cause:

  • An autoimmune disease resulting from antibody-mediated loss of acetylcholine receptors in the junction.

Myasthenia Gravis Mechanism

• Components:

  • Synaptic vesicle, nerve cell, ACh receptors, ACh antibodies, blocked receptors, leading to reduced muscle contraction.

Peripheral Neuropathy

• Definition:

  • Primary disorder affecting peripheral nerves.

• Results:

  • Causes muscle weakness (with or without atrophy) and sensory changes.

• Involvement Types:

  • Can affect single nerve (mononeuropathy) or multiple nerves (polyneuropathy).

Axon Degeneration and Regeneration

• Process:

  • In neuropathies and crushing injuries where the endoneurial tube remains intact, fibers can grow back to their original target.

Parkinson's Disease

• Definition:

  • Degenerative disorder of basal ganglia function resulting in tremor, rigidity, and bradykinesia.

• Characteristics:

  • Progressive destruction of nigrostriatal pathway reducing striatal dopamine levels.

• Clinical Syndrome:

  • Known as Parkinsonism.

Parkison’s Disease Manifestations

• Onset:

  • Usually gradual, after age 50, and progresses slowly.

• Symptoms:

  • Mask-like expression, stooped posture, pill-rolling tremors, bradykinesia, loss of arm swing, blinking issues, difficulty swallowing, shuffling gait, possible mental deterioration, and depression.

• Tremors:

  • Commonly in hands and arms, increases during rest and under stress.

REM Behavior Disorder (RBD)

• Definition:

  • Parasomnia characterized by dream-enactment behaviors during loss of REM sleep atonia.

• Statistics:

  • 80-90% of individuals with RBD eventually develop Parkinson's disease or dementia.

Amyotrophic Lateral Sclerosis (ALS)

• Definition:

  • A severe neurological disorder affecting motor function, typically following a progressive course.

• Survival Rate:

  • Mean survival is 2-5 years from symptom onset.

• Manifestations:

  • Weakness in upper extremities, dysarthria, dysphagia.

• Nicknamed:

  • Lou Gehrig's Disease, due to the famous baseball player affected by it.

• Onset:

  • Age range of 40 - 70 years, with death occurring within 2-6 years of diagnosis.

• Demographic Distribution:

  • More common in men than women (ratio of 2:1).

ALS Nursing Measures

• Facilitate patient communication.

• Manage risk of aspiration.

• Address pain secondary to muscle weakness.

• Prevent injuries related to falls.

• Promote diversional activities and companionship.

• Assist patients and families in managing disease and grief processes.

Multiple Sclerosis (MS)

• Definition:

  • A demyelinating disease affecting the central nervous system (CNS).

• Epidemiology:

  • Most common nontraumatic cause of neurologic disability in young and middle-aged adults.

• Characteristics:

  • Exhibits exacerbations and remissions, often with normal function interspersed between episodes. Over time, neurologic dysfunction typically increases and there is less recovery between episodes.

MS Symptoms

• Autoimmune basis, often familial.

• Symptoms include tinnitus, urinary retention, spastic bladder, constipation, nystagmus, blurred vision, dysarthria, dysphagia, intention tremors, weakness that can progress to paralysis, muscle spasticity, ataxia, and vertigo.

• Onset:

  • Commonly occurs between ages 20-40, characterized by episodes of exacerbation and remission.

Case Study

John (63 years old)

• Care Situation:

  • Receives occupational therapy for joint flexibility and balance; exhibits resting tremor.

• Therapeutic Techniques:

  • Occupational therapist works on adaptive techniques for tasks such as writing and cooking, while his wife assists with mobility.

Questions:

1. What motor disease does John demonstrate based on his resting tremor? What is the difference between a resting tremor and an intention tremor?

2. Discuss the advantage of combining levodopa with carbidopa and the role of anticholinergic drugs in Parkinson’s management.

3. Explain the masklike facial expression seen in Parkinson's disease and how it affects facial movements, specifically the eyes, mouth, and laryngopharynx.

Types of Injuries to the Vertebral Column

• Injury Types:

  • Fractures, Dislocations, Subluxations.

• Force Displacement:

  • Includes mechanisms leading to fractured vertebral bodies and ruptured posterior ligament complex.

Heat Illness

• Heat Cramps:

  • Slow, painful skeletal muscle cramps and spasms; last 1-3 minutes; caused by salt depletion from sweat.

• Heat Exhaustion:

  • Moist skin; rectal temperature from 37.8°C (100°F) to 40°C (104°F); elevated heart rate.

• Heat Stroke:

  • Failure of thermoregulatory mechanisms resulting in core temperature greater than 40°C (104°F); symptoms include hot, dry skin, absence of sweating, possible CNS abnormalities like delirium, convulsions, and loss of consciousness.

Heat Warning Signs

• Advisory against hiking in extreme heat and considerable elevation changes, emphasizing fitness and preparedness.

Questions?

• Contact for further information or clarification on motor function and heat-related illnesses.