Nervous System Revision Sheet

1. 📌 Essentials

• Neurons are the fundamental units, comprising soma, dendrites, axon, and synapses.
• The CNS includes the brain (cerebrum, cerebellum, brainstem) and spinal cord.
• The PNS consists of cranial nerves (12 pairs) and spinal nerves (31 pairs).
• Major brain regions cerebral cortex (motor, sensory, association), diencephalon, brainstem cerebellum.
• Spinal cord gray matter: dorsal horn (sensory), ventral horn (motor), lateral horn (autonomic).
• Ascending pathways (sensory): dorsal columns, spinothalamic tract.
• Descending pathways (motor): corticospinal tract.
• Cranial nerves I-XII have specific sensory, motor, or mixed functions.
• Reflexes involve sensory receptor → afferent neuron → CNS → efferent neuron → effector.
• Typical neuron resting potential: ~ -70 mV; threshold: ~ -55 mV.
• Blood supply: carotid and vertebral arteries.

2. 🧩 Key Structures & Components

• Neuron / Nerve Cell — transmits electrical signals.
• Dendrites — receive incoming signals.
• Axon — conducts action potentials.
• Synapses — junctions for neuron communication.
• Cerebral Cortex — controls voluntary movement, sensation, reasoning.
• Thalamus — relay station for sensory info.
• Hypothalamus — regulates autonomic and endocrine functions.
• Brainstem — midbrain, pons, medulla; vital autonomic functions.
• Cerebellum — coordinates movement and balance.
• Gray Matter — neuron cell bodies.
• White Matter — myelinated axons connecting CNS regions.
• Spinal Cord Horns:
  • Dorsal horn: sensory processing.
  • Ventral horn: motor neurons.
  • Lateral horn: autonomic neurons.

3. 🔬 Functions, Mechanisms & Relationships

• Sensory signals travel via afferent neurons to dorsal horns of the spinal cord or brainstem.
• Motor commands originate from the motor cortex, descend via corticospinal tract.
• Dorsal columns carry fine touch and proprioception; spinothalamic transmits pain and temperature.
• Cranial nerves connect specific brainstem nuclei to peripheral targets.
• Reflex arcs bypass higher centers, providing rapid responses.
• Brain regions have specialized roles: frontal lobe (motor, reasoning), occipital (vision), temporal (auditory), parietal (sensory).
• Blood flow maintains neural function; disruptions cause strokes or ischemia.
• Hierarchical organization: neurons → nerve fibers → nerve bundles → CNS structures.

4. 📊 Comparative Table

5. 🗂️ Hierarchical Diagram (ASCII)

Nervous System
 ├─ Central Nervous System
 │    ├─ Brain
 │    │    ├─ Cerebrum
 │    │    ├─ Diencephalon
 │    │    ├─ Brainstem
 │    │    └─ Cerebellum
 │    └─ Spinal Cord
 └─ Peripheral Nervous System
      ├─ Cranial Nerves (I-XII)
      └─ Spinal Nerves

6. ⚠️ High-Yield Pitfalls & Confusions

• Confusing cranial nerves with similar functions (e.g., V and VII both involve facial sensation/movement).
• Mistaking dorsal horns for ventral horns in spinal cord anatomy.
• Overlooking the difference between ascending and descending pathways.
• Assuming all cranial nerves are purely sensory or motor; many are mixed.
• Misidentifying the function of brain lobes.
• Confusing gray matter (neuron bodies) with white matter (axons).
• Ignoring the clinical relevance of dermatomes in spinal injuries.
• Overgeneralizing reflex pathways without considering specific reflex types.

7. ✅ Final Exam Checklist

• Know neuron structure and function.
• Identify CNS and PNS components.
• Describe the main brain regions and their functions.
• Understand spinal cord organization: horns and funiculi.
• Differentiate between ascending and descending pathways.
• List the functions of cranial nerves I-XII.
• Explain the reflex arc components.
• Recognize the blood supply to the brain.
• Correlate clinical signs with brain or spinal cord lesions.
• Understand the hierarchical organization of neural pathways.
• Know the difference between gray and white matter.
• Be familiar with major neural pathways: dorsal columns, corticospinal.
• Understand the role of the cerebellum and hypothalamus.
• Recognize common pitfalls in neuroanatomy.
• Recall neuron resting potential and action potential threshold.
• Link neuroanatomy to clinical conditions like stroke and spinal injury.

This revision sheet provides a structured, high-yield overview of the nervous system, ideal for exam preparation.