Exam 3 Focus of Study.docx

Peripheral Somatosensory System

• Types of Receptors

  • Mechanoreceptors

    • Detect mechanical deformation (touch, pressure, stretch, vibration)

    • Can be free nerve endings or specialized end-organs.

  • Chemoreceptors

    • Respond to exogenous chemicals or substances released by cells (e.g., in injury/infection)

    • Associated with free nerve endings.

  • Thermoreceptors

    • Respond to changes in temperature (heating or cooling)

    • Also associated with free nerve endings.

• Tonic vs Phasic Receptors

  • Tonic Receptors:

    • Respond continuously as long as the stimulus is present.

    • Example: Tonic stretch receptors in skin provide sustained input while holding a mug.

  • Phasic Receptors:

    • Adapt to constant stimuli and stop responding; alert about changes in stimuli.

    • Example: Skin pressure receptors may not respond after putting on a wristwatch until attention is drawn to it.

• Receptive Fields

  • Definition: Area of skin innervated by a single afferent neuron.

  • Trends:

    • Smaller distally (fingertips) and larger proximally (shoulders)

    • Greater receptor density distally allows for better stimulus distinction.

  • Example of Distal vs Proximal:

    • Distally, two points fall in separate receptive fields, perceived as two.

    • Proximally, they may fall within one receptive field, perceived as one.

• Peripheral Nerve vs Dermatome Innervation

  • Knowledge of lesion locations helps identify issues:

    • Dermatomes: Areas of skin innervated by a single spinal nerve root; used to diagnose spinal nerve root issues.

    • Peripheral Nerves: Connect end-organs with the CNS; deficits indicate peripheral nerve issues.

    • E.g., if the radial nerve is damaged, sensory impairment is localized to its territory.

• Musculoskeletal Innervation

  • Axons classified using Roman numerals (I-IV) convey sensory signals.

  • Types I and II: Large afferents innervate muscle spindles.

  • Types III and IV: Small afferents convey nociceptive information.

  • Normal proprioception needs input from muscle spindles, joint receptors, and cutaneous mechanoreceptors.

Central Somatosensory System

• Pathways for Somatosensory Information to the Brain

  • Conscious Relay Pathways:

    • Provide exact stimulation information to the cerebral cortex (e.g., light touch, proprioception).

  • Divergent Pathways:

    • Transmit information to many brain locations for conscious and nonconscious use.

  • Nonconscious Relay Pathways:

    • Relay proprioceptive information to the cerebellum.

• Dorsal Column Medial Lemniscus (DCML) Pathway

  • Responsible for transmitting light touch and conscious proprioception, essential for fine movement control and object recognition.

  • Pathway Details:

    • Three-neuron relay:

      • 1st Order: Receptor to medulla.

      • 2nd Order: Medulla to thalamus.

      • 3rd Order: Thalamus to cortex.

• Anterolateral Columns (Spinothalamic Pathway)

  • Carry nociceptive and temperature information.

  • Utilizes a three-neuron pathway similar to DCML but crosses midline in the spinal cord.

  • Important for detecting painful stimuli and temperature differentiation.

Pain and Its Classification

• Types of Pain:

  • Acute Pain: Short term; resolves with injury healing.

  • Chronic Pain: Persists beyond normal healing (three months or longer)

    • Chronic Primary Pain: No tissue damage.

    • Chronic Secondary Pain: Results from another condition.

• Mechanisms of Chronic Pain:

  • Central Sensitization: Increased responsiveness of nociceptive neurons following input.

  • Hyperalgesia: Increased pain response to a stimulus.

  • Allodynia: Innocuous stimuli cause pain due to neuroplasticity changes.

Treatments and Management in Chronic Pain

• Rehabilitation's Role:

  • Address factors contributing to chronic pain (e.g., disuse, distress, disability).

  • Interventions include education on pain perception and rehabilitation based on biopsychosocial models.

• TENS (Transcutaneous Electrical Nerve Stimulation):

  • Modulates pain by activating non-painful touch pathways, thus inhibiting nociceptive signals.

Motor System Overview

• Lower Motor Neurons (LMN):

  • Innervate muscles, affecting muscle contraction. Damage leads to decreased reflexes, paralysis, atrophy, and hypotonia.

• Upper Motor Neurons (UMN):

  • Control LMNs, impairments can cause paresis, abnormal reflex activity, and changes in muscle tone.

• Common Signs of UMN Damage:

  • Abnormal tone (spasticity, rigidity), hyperreflexia, and pathologic reflexes (e.g., Babinski).

Spinal Cord Anatomy and Function

• Ventral vs Dorsal Root:

  • Dorsal Root: Carries sensory information into the spinal cord.

  • Ventral Root: Contains motor neurons carrying signals to muscles.

• Withdrawal Reflex Anatomy:

  • Mediate quick responses to painful stimuli, with intricate interneuron connections to coordinate movements across different spinal segments.