Somatic Nervous System (SNS): Often called the voluntary nervous system, it allows conscious control of skeletal muscles. It consists of motor neurons that conduct impulses from the CNS directly to the target muscle.
Autonomic Nervous System (ANS): Known as the involuntary nervous system, it regulates the activity of smooth muscles, cardiac muscles, and glands. It maintains internal homeostasis without conscious effort.
Structural Difference: The Somatic system typically involves a single neuron from the CNS to the effector, whereas the Autonomic system involves a two-neuron chain (preganglionic and postganglionic).
Sympathetic Division: This division mobilizes body systems during activity, often referred to as the "fight-or-flight" response. It increases heart rate, dilates pupils, and redirects blood flow to muscles.
Parasympathetic Division: This division promotes house-keeping functions and conserves energy, known as the "rest-and-digest" system. It slows heart rate and stimulates digestive processes.
Dynamic Balance: Most visceral organs receive dual innervation, meaning they are served by both divisions. They act in opposition to one another to maintain a stable internal environment.
| Feature | Somatic Nervous System | Autonomic Nervous System |
|---|---|---|
| Control | Voluntary | Involuntary |
| Effectors | Skeletal Muscles | Cardiac/Smooth Muscle, Glands |
| Neurotransmitter | Always Acetylcholine (ACh) | ACh or Norepinephrine (NE) |
| Pathway | Single neuron from CNS | Two-neuron chain with ganglion |
Afferent vs. Efferent: Afferent is input (arriving at CNS); Efferent is output (exiting CNS).
Sympathetic vs. Parasympathetic: Sympathetic is for arousal/expenditure; Parasympathetic is for recovery/storage.
Directional Logic: When identifying a division, always ask: "Is the signal going to the brain or away from it?" This distinguishes the primary functional divisions immediately.
Target Organ Identification: If the effector is a skeletal muscle, it must be Somatic. If it is a gland or internal organ, it must be Autonomic.
Homeostatic Context: In scenario-based questions, look for keywords like "stress," "emergency," or "exercise" to identify Sympathetic activity, and "relaxation" or "digestion" for Parasympathetic.
Terminology Precision: Do not confuse nerves (PNS) with tracts (CNS). They are functionally similar but geographically distinct.
