lecture recording on 13 March 2025 at 10.22.19 AM

Breakdown of the Nervous System

• The nervous system can be divided into two main parts:

  • Somatic Nervous System: Controls voluntary body functions.

    • Responsible for skeletal muscle movements.

    • Functions primarily through motor (efferent) and sensory (afferent) nerves.

      • Acronym to remember: SAME (Sensory Afferent, Motor Efferent).

  • Autonomic Nervous System: Controls involuntary functions.

    • Regulates organs, heart rate, salivary glands, and sweat glands.

    • Divided into:

      • Sympathetic Division: Activates the fight or flight response.

      • Parasympathetic Division: Promotes rest and digest functions.

Somatic vs. Autonomic Functions

• Somatic Nervous System:

  • Responsible for voluntary movements of muscles.

  • Sensory nerves detect sensations like touch and pain, while motor nerves control muscle contractions.

• Autonomic Nervous System:

  • Involuntary control of bodily functions.

  • Viscera receptors sense conditions within the organs (e.g., pain signals from the appendix).

  • Motor component regulates activities such as heart rate, digestion, and secretion from glands.

Sympathetic and Parasympathetic Systems

• Sympathetic Nervous System:

  • Prepares the body for stressful or emergency situations.

  • Symptoms include increased heart rate, rapid breathing, and dilated pupils (e.g., during fear).

• Parasympathetic Nervous System:

  • Restores body functions after a stressful event (rest and digest).

  • Promotes activities like saliva production and reduced heart rate.

Peripheral Nervous System Structures

• Contains Cranial Nerves and Spinal Nerves:

  • Cranial Nerves: 12 pairs emerge from the brain and control functions primarily in the head and neck. They can be sensory, motor, or mixed.

  • Spinal Nerves: 31 pairs that extend from the spinal cord to the rest of the body.

  • Each cranial nerve is assigned a Roman numeral from I to XII based on its position.

Mnemonic Devices for Cranial Nerves

• Cranial Nerve Names: Mnemonic for order: "Oh, Oh, Oh, To Touch And Feel Very Green Vegetables, AH"

  • Function Designation Mnemonic: "Some Say Marry Money, But My Brother Says Big Brains Matter More"

Functions of Individual Cranial Nerves:

• Cranial Nerve I: Olfactory (1)

  • Function: Smell.

• Cranial Nerve II: Optic (2)

  • Function: Vision.

• Cranial Nerve III: Oculomotor (3)

  • Function: Eye movement, pupil size.

• Cranial Nerve IV: Trochlear (4)

  • Function: Eye movement.

• Cranial Nerve V: Trigeminal (5)

  • Function: Facial sensation, chewing.

• Cranial Nerve VI: Abducens (6)

  • Function: Eye movement.

• Cranial Nerve VII: Facial (7)

  • Function: Facial expression, taste (anterior 2/3 of tongue).

• Cranial Nerve VIII: Vestibulocochlear (8)

  • Function: Hearing and balance.

• Cranial Nerve IX: Glossopharyngeal (9)

  • Function: Taste (posterior 1/3 of tongue), swallowing.

• Cranial Nerve X: Vagus (10)

  • Function: Controls autonomic functions like heart rate, digestion, taste in the throat.

• Cranial Nerve XI: Accessory (11)

  • Function: Shoulder movement, head rotation.

• Cranial Nerve XII: Hypoglossal (12)

  • Function: Tongue movements.

Spinal Nerve Plexuses

• Cervical Plexus: Controls neck and diaphragm functions (breathing).

• Brachial Plexus: Controls arm movement (despite being located in the neck).

• Lumbar Plexus: Controls lower back and anterior leg.

• Sacral Plexus: Controls lower extremities and pelvic organs.

Reflexes

• Reflex Actions: Involuntary responses to stimuli.

• Works through simple pathways involving sensory and motor neurons.

  • Monosynaptic Reflex: Involves a single synapse, like the knee-jerk reflex.

  • Polysynaptic Reflex: Involves interneurons and allows for more complex responses.

Types of Reflexes:

• Deep Tendon Reflexes: Include biceps, patellar, and Achilles reflexes (test at clinics).

• Withdrawal Reflex: Complex reflex to move away from pain.

Key Takeaways for Exam Preparation

• Understand the names, functions, and classifications (sensory, motor, mixed) of all cranial nerves.

• Familiarize with the visceral and motor functions of the autonomic nervous system.

• Be able to identify and explain the nerve plexuses.

• Know types of reflexes, their mechanisms, and examples for clinical scenarios.