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SECTION 20 Proprioception

Definition

  • Proprioception, termed by Sherrington as the sixth sense, is "the sense by which the body knows itself, judges with perfect, automatic, instantaneous precision the position and motion of all of its movable parts, their relations to one another, and their alignment in space."

  • It enables the ability to sense body position in space.

Kinesthesia

  • Kinesthesia is the ability to sense one's body movement in space.

  • Essential for physical activity and coordination.

Systems Responsible for Proprioception

  1. Visual System

    • Utilizes visual cues to navigate the environment.

  2. Vestibular System

    • Located in the inner ear (semicircular canals) with liquid that provides constant feedback on head position.

    • Connects to the cerebellum for feedback regarding orientation.

  3. Proprioceptive System

    • Involves muscle spindles, Golgi tendon organs, and joint receptors.

    • Feedback/feedforward loop constantly providing information on body position.

Muscle Spindles (MS)

  • Sensory receptors in skeletal muscle that provide information about muscle length, tension, and load.

  • Function: Detect stretch in muscle and initiate counters to that stretch through reflex actions.

Types of Muscle Fibers

  1. Extrafusal Muscle Fibers

    • Make up the bulk of the muscle and are involved in muscle contraction.

  2. Intrafusal Muscle Fibers

    • Form the muscle spindles and are attached to extrafusal fibers.

Density of Muscle Spindles

  • Higher density in small muscles allows for finer motor control; low density in larger muscles.

Types of Intrafusal Fibers

  • Nuclear Bag Fibers: Respond to muscle length changes and stretch velocity.

  • Nuclear Chain Fibers: Respond only to static length changes.

Sensory Fibers from Muscle Spindles

  • Ia fibers (Primary Ending): Fast and respond to both rate of stretch and muscle length changes.

  • II fibers (Secondary Ending): Slow and respond only to length changes.

Sequence of Muscle Spindle Action

  • Upon muscle stretch:

  1. Intrafusal fibers stretch and activate Ia fibers.

  2. Ia fibers signal for both fast (phasic) responses and sustained (tonic) responses.

  3. II fibers activate, sending additional information on muscle length.

Proprioceptive Information Pathways

Proprioceptive Info Utilization

  • Transmits information to four targets:

  1. Alpha Motor Neuron of Agonist Muscle

    • Facilitates contraction of the muscle in response to stretch.

  2. Alpha Motor Neuron of Antagonist Muscle

    • Inhibits the antagonist muscle.

  3. Renshaw Cells

    • Modulates synergistic muscle actions to create refined movements.

  4. Cerebellum

    • Receives signals for monitoring muscle position and making adjustments.

SECTION 21 Disorders of Muscle Tone

Muscle Tone

  • Continuous contraction of muscle at rest aids in maintaining posture, regulated unconsciously by several mechanisms.

Mechanisms Mediating Tone

  1. Extrapyramidal Structures

    • Control pathways located outside the pyramidal system including vestibular and reticular nuclei.

  2. Basal Ganglia

    • Comprises structures critical for movement control such as caudate, putamen, globus pallidus, and others.

  3. Cerebellum

    • Works with sensory tracts to modulate muscle tone using afferent information.

  4. Motor Neurons (Alpha and Gamma)

    • Involved in signal transmission to skeletal muscles.

Tone Classifications

  • Hypotonicity

    • Decrease in muscle tone often seen in conditions like spinal cord injuries below L1.

  • Hypertonicity

    • Increase in muscle tone seen in upper motor neuron damage leading to spasticity, rigidity, or clasp-knife phenomenon.

Hypertonicity Types

  1. Spasticity: Velocity-dependent increase in muscle tone, common after CNS injury.

  2. Rigidity: Increased muscle tone that is independent of velocity,, often in conditions like Parkinsonian disorders.

  3. Clasp Knife Phenomenon: Sudden release of spasticity during sustained stretch.

Causes of Tone Disorders

  • Hyperactive Reflex Arcs: Symptoms resulting from disrupted communication between the cortex and motor neurons after UMN damage.

  • Reduced Reciprocal Inhibition: Loss of the ability of alpha motor neurons to inhibit antagonist/synergy muscle groups.

  • Cerebral Lesions: Impact tone regulation, often resulting in spasticity due to motor system disruptions.

SECTION 22 Motor Functions and Dysfunctions of the Central Nervous System

Cerebral Cortex

Cortical Mapping

  • Brodmann’s map featured 52 numbered areas reflecting various brain functions; boundaries are not absolute.

Functional Divisions

  • Archicortex, Paleocortex, Neocortex: Varied roles from memory (hippocampus) to sensory processing (neocortex).

Involvement in Motor Control

  • Primary Motor Area (M1): Initiates voluntary movement; impacted by lesions leading to contralateral motor loss.

Effects of Lesions

  • Premotor Area Lesions: Lead to apraxia, affecting motor planning skills.

Practice and Feedback in Motor Learning

  • Use it or lose it principle emphasizes reliance on practice and the brain's adaptation to sustained use of specific motor pathways.

Recommendations

  • Constraint-Induced Movement Therapy: Constraints are placed on unaffected limbs to encourage use of affected areas, promoting neuroplasticity.

  • Research and further studies target optimal methods for rehabilitation involving neuroplasticity.

Missing Chapters Note

It seems that the rest of the chapters are not included in the current notes. To address this:

  • Review the syllabus or table of contents for the course to identify which chapters are missing.

  • Check with peers or instructors for clarification on any chapter assignments or learning objectives that need attention.

  • Consider seeking additional resources or summaries for the chapters to supplement learning until the full content is available.