뒤로Somatic and Autonomic Nervous Systems: Structure and Function
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Somatic vs. Autonomic Nervous System
Overview of the Peripheral Nervous System
The peripheral nervous system (PNS) is divided into two major subsystems: the somatic nervous system and the autonomic nervous system. Each subsystem has distinct roles in controlling body functions.
Somatic Nervous System (SNS): Innervates skeletal muscle.
Autonomic Nervous System (ANS): Innervates smooth muscle, cardiac muscle, and glands.
Somatic Nervous System
The somatic nervous system is responsible for voluntary movements and conscious control of skeletal muscles.
Controls: Voluntary movement.
Efferent pathway consists of: 1 neuron from the CNS to the effector muscle.
Example: Moving your arm to pick up an object.
Autonomic Nervous System
The autonomic nervous system regulates involuntary functions, such as heart rate, digestion, and glandular activity.
Controls: Involuntary functions.
Efferent pathway consists of: 2 neurons (a preganglionic and a postganglionic neuron).
Example: Increasing heart rate during exercise.
Comparison Table: Somatic vs. Autonomic Nervous System
Feature | Somatic Nervous System | Autonomic Nervous System |
|---|---|---|
Effector Organs | Skeletal muscle | Cardiac muscle, smooth muscle, glands |
Control | Voluntary | Involuntary |
Number of Neurons in Efferent Pathway | 1 | 2 |
Functional Differences
SNS: Controls voluntary muscle movements.
ANS: Controls involuntary functions such as gland secretion, heart rate, and smooth muscle contraction.
Practice Example
Heart rate increasing: Autonomic
Pupils dilating: Autonomic
Knee jerk reflex: Somatic
Secreting insulin: Autonomic
Sudden jump in response to a loud noise: Somatic
Throwing a ball: Somatic
Divisions of the Autonomic Nervous System (ANS)
Sympathetic and Parasympathetic Divisions
The autonomic nervous system is further divided into two branches: the sympathetic division and the parasympathetic division. These divisions often have opposing effects on target organs.
Sympathetic Division: Activated during stress, excitement, or danger ("fight or flight").
Parasympathetic Division: Activated during rest and relaxation ("rest and digest").
Sympathetic Division
Prepares the body for physical activity.
Increases heart rate, dilates pupils, inhibits digestion.
Example: Running from danger.
Parasympathetic Division
Promotes rest and recovery.
Decreases heart rate, stimulates digestion, constricts pupils.
Example: Relaxing after a meal.
Comparison Table: Sympathetic vs. Parasympathetic Division
Feature | Sympathetic Division | Parasympathetic Division |
|---|---|---|
Activation | Stress, excitement, danger | Rest, relaxation |
Effect on Heart Rate | Increases | Decreases |
Effect on Digestion | Inhibits | Stimulates |
Dual Innervation and Effects
Most organs receive input from both divisions, which usually have opposite effects.
If one division stimulates an effector, the other usually inhibits it.
Effects are typically small and finely regulated.
Practice Example
Sympathetic division increases heart rate.
Parasympathetic division decreases heart rate.
Watching a horror movie activates the sympathetic division, increasing heart rate and sweat gland activity.
Key Terms
Somatic Nervous System (SNS): Controls voluntary movements of skeletal muscles.
Autonomic Nervous System (ANS): Regulates involuntary functions of smooth muscle, cardiac muscle, and glands.
Sympathetic Division: Prepares the body for action.
Parasympathetic Division: Promotes rest and recovery.
Additional info: The notes include diagrams and practice questions to reinforce understanding of the differences between the somatic and autonomic nervous systems, as well as the sympathetic and parasympathetic divisions.
