Peripheral Nervous System

PERIPHERAL NERVOUS SYSTEM (PNS)

TOPICS TO BE COVERED

• Purpose of the PNS

• Nerve Coverings

• Sensory Receptors

• Spinal Nerves, Dermatomes, Cutaneous Nerves

• Referred vs. Radicular Pain

• Brachial Plexus and Named Nerves

• Lumbosacral Plexus and Named Nerves

• Motor Reflexes

PURPOSE OF THE PNS

• Transmits Information:

  • From the outside world to the CNS (sensory)

  • From the CNS to the outside world (motor)

• Functions:

  • Innervates skin (touch, pressure, vibration, temperature, chemicals)

  • Innervates muscles (movement)

  • CNS makes decisions; PNS executes orders and relays information back to CNS

NERVE COVERINGS

• CNS Coverings:

  • Dura Mater

  • Arachnoid Mater

  • Pia Mater

• PNS Coverings:

  • Epineurium (covers entire nerve)

  • Perineurium (covers bundles of axons)

  • Endoneurium (covers individual axons)

• Muscle Coverings:

  • Epimysium (covers entire muscle)

  • Perimysium (covers fascicles)

  • Endomysium (covers individual fibers)

SENSORY RECEPTORS

• Convey specific information to specific areas in brain:

  • Types of Receptors:

    • Extero-receptors (external information)

    • Intero-receptors (internal information)

• Classes of Extero-receptors:

  • Chemoreceptors, Thermoreceptors, Mechanoreceptors, Nociceptors

• Classes of Intero-receptors:

  • Baroreceptors, Proprioceptors

SPINAL NERVES & DERMATOMES

• Spinal Nerves:

  • Cervical: C1-C8, Thoracic: T1-T12, Lumbar: L1-L5, Sacral: S1-S5

• Dermatome:

  • Area of skin associated with a specific spinal nerve root

  • Important for diagnosing musculoskeletal conditions.

CUTANEOUS NERVES

• Areas of skin innervated by specific cutaneous nerves, branches of named nerves.

REFERRED VS. RADICULAR PAIN

• Referred Pain:

  • Pain felt in a location different from its source (e.g., left arm pain with heart attack)

• Radicular Pain:

  • Pain traveling along a specific spinal nerve root.

BRACHIAL PLEXUS

• Purpose: Motor and sensory innervation for arm and lower neck.

• Components:

  • Spinal Nerve Roots: C5-T1

  • Divisions: Anterior, Posterior

  • Terminal Nerves: Musculocutaneous, Median, Radial, Ulnar, Axillary

LUMBOSACRAL PLEXUS

• Purpose: Motor and sensory innervation for leg and pelvis.

• Components: Ventral Rami (L1-L5) and major trunks (e.g., iliohypogastric, femoral, sciatic).

MOTOR REFLEXES

• Definition: Involuntary response to a sensory stimulus.

• Specifically assesses health of the peripheral nervous system.

• Types include deep tendon reflexes, muscle spindle reflexes, and withdrawal reflexes.

SENSORY – MOTOR - REFLEX

• Clinical Assessment:

  • Sensory pathways (dermatomes)

  • Motor pathways (myotomes)

  • Reflex arcs (DTRs)

  • Consider overall health and presentation.