Peripheral Nervous System

Introduction to the Nervous System

  • The nervous system is divided into two main parts:

    • Central Nervous System (CNS)

    • Peripheral Nervous System (PNS)

Peripheral Nervous System (PNS)

  • The PNS includes:

    • Cranial Nerves

    • Spinal Nerves

  • Functions of the PNS:

    • Detects sensory stimuli

    • Delivers information to the CNS

Divisions of the PNS

  • PNS is split into two divisions:

    1. Sensory Division

    • Somatic Sensory Division: Refers to the whole body

    • Visceral Sensory Division: Refers to internal organs

    1. Motor Division

    • Somatic Motor Division

    • Visceral Motor Division (Autonomic Nervous System - ANS)

      • Further divided into:

        • Sympathetic Nervous System: Associated with "fight or flight" response

        • Parasympathetic Nervous System: Associated with "rest and digest"

Motor and Sensory Functions

  • Somatic Motor Division:

    • Responsible for voluntary muscle movements, primarily affecting skeletal muscles.

  • Visceral Motor Division (ANS):

    • Responsible for involuntary control of cardiac and smooth muscles.

Neurons of the PNS

  • Sensory neurons play roles across multiple systems:

    • Involved in functions of muscles, bones, joints, and skin.

    • Visceral sensory neurons carry signals from internal organs to different cavities (e.g., thoracic and abdominal pelvic).

Mixed Nerves

  • Definition: Nerves that contain both sensory and motor fibers.

Cranial and Spinal Nerves

  • Cranial Nerves:

    • Attach to the brain, elongated through the head and neck.

  • Spinal Nerves:

    • Classified into two roots:

    • Anterior Root (Motor Neurons)

    • Posterior Root (Sensory Neurons)

    • Contains a posterior root ganglion housing sensory neurons.

Connective Tissue in Spinal Nerves

  • Spinal nerves consist of three connective tissue components:

    1. Epineurium

    2. Perineurium

    3. Endoneurium

Functions of the PNS

  • Sensory neurons detect stimuli at sensory receptors.

  • Stimuli are transmitted through spinal and cranial nerves to the CNS, particularly to the cerebral cortex for interpretation and integration.

  • Motor responses are initiated by the motor areas in the brain, sending impulses to relevant tissue via lower motor neurons of the PNS.

Cranial Nerve Breakdown

  • There are 12 pairs of cranial nerves, totaling 24 nerves.

  • Mnemonic: "Oh, once one takes the anatomy final, very good vacations are happening."

List of Cranial Nerves

  1. Olfactory (smell)

  2. Optic (vision)

  3. Oculomotor (eye movement)

  4. Trochlear (eye movement)

  5. Trigeminal (face sensation, motor functions like chewing)

  6. Abducens (eye movement)

  7. Facial (facial expressions)

  8. Vestibulocochlear (hearing and balance)

  9. Glossopharyngeal (salvation and taste)

  10. Vagus (control of the heart, lungs, and digestive tract)

  11. Accessory (head movement)

  12. Hypoglossal (tongue movement)

Nerve Functions Classification

  • Sensory Nerves: Olfactory, Optic, Vestibulocochlear

  • Motor Nerves: Oculomotor, Trochlear, Abducens, Accessory, Hypoglossal

  • Mixed Nerves: Trigeminal, Facial, Glossopharyngeal, Vagus

  • Mnemonic for functions: "Some say money matters, but my brother says big brains matter more."

Detailed Functions of Selected Cranial Nerves

  • Olfactory Nerve:

    • Function: Sense of smell

    • Origin: Unmyelinated axons in olfactory epithelium (located in the nasal cavity)

    • Destination: Olfactory tract

  • Optic Nerve:

    • Function: Vision (rapid input due to myelinated axons)

    • Origin: Myelinated axons, primary visual cortex

    • Destination: Axons from optic chiasma

  • Vestibulocochlear Nerve:

    • Function: Hearing and balance

    • Origin: Inner ear

    • Destination: Medulla oblongata

  • Trigeminal Nerve (mixed nerve):

    • Three branches: Ophthalmic, Maxillary (both sensory), Mandibular (motor)

    • Functions in chewing and sensation of the face.

    • Origin: Midbrain and pons

    • Destination: Somatosensory cortex, mandibular region, mastication muscles.

  • Facial Nerve:

    • Function: Facial expressions

    • Origin: Pons and Medulla

    • Destination: Different branches involved in facial movement.

  • Glossopharyngeal Nerve:

    • Function: Salivation, taste

    • Origin: Medulla

    • Destination: Tongue and throat.

  • Vagus Nerve:

    • Function: Voice box, swallowing

    • Origin: Medulla

    • Destination: Widely distributed throughout the body, including neck, thorax, and abdomen.

Disorders Related to Cranial Nerves

  • Trigeminal Neuralgia:

    • Chronic pain syndrome affecting branches of the trigeminal nerve.

    • Causes: Extreme pain upon stimuli (e.g., touch, breeze).

    • Treatment: Seizure medications.

  • Bell's Palsy:

    • Affects facial nerves, causing weakness or paralysis of facial muscles.

    • Causes: Viral infection, trauma.

    • Symptoms: Inability to make facial expressions.

    • Treatment: Anti-inflammatories, antiviral medications, physical therapy, surgical options.

  • Stroke Effects:

    • May affect facial nerve and lead to facial paralysis or droop.

    • Mnemonic for stroke symptoms: FAST (face drooping, arm weakness, speech difficulty).

Introduction to Spinal Nerves

  • Total of 31 pairs of spinal nerves:

    • 8 cervical pairs (C1-C8)

    • 12 thoracic pairs (T1-T12)

    • 5 lumbar pairs (L1-L5)

    • 5 sacral pairs (S1-S5)

    • 1 coccygeal pair (CO1)

Anatomy of Spinal Nerves

  • Each spinal nerve splits into:

    • Anterior Ramus: supplies anterior side, including limbs

    • Posterior Ramus: supplies posterior side of the body

  • Contains ramus communicantes involved in the sympathetic nervous system when discussing autonomics.

Plexuses

  1. Cervical Plexus (C1-C4):

    • Includes the phrenic nerve, which innervates the diaphragm muscle.

  2. Brachial Plexus (C5-T1):

    • Contains three trunks (superior, middle, inferior) and several critical nerves (e.g., ulnar, median).

  3. Lumbar Plexus (L1-L4):

    • Anterior division includes the obturator nerve; posterior division includes the femoral nerve.

  4. Sacral Plexus (L4-S4):

    • Contains the sciatic nerve, with branches to tibial and fibular nerves.

Summary of Major Nerves in Plexuses

  • Cervical Plexus:

    • Phrenic nerve: diaphragm ventilation.

  • Brachial Plexus:

    • Includes important upper limb nerves (e.g., radial, median).

  • Lumbar Plexus:

    • Femoral nerve: supplies leg and foot muscles.

  • Sacral Plexus:

    • Sciatic nerve: major nerve to lower limbs, splits into tibial and fibular nerves, influencing lower limb movements.

Review and Additional Resources

  • Suggested videos on cranial nerves available for further study

  • Reminder for students to utilize external resources for comprehension as additional learning aids.

Conclusion

  • Emphasis on cranial nerves over spinal nerves for examinations, but both systems remain fundamental to understanding the human nervous system.