5.7.3 Peripheral Nervous System

The peripheral nervous system (PNS) consists of the nerves that branch out from the central nervous system and connect it to other body parts. It can be subdivided into the somatic and autonomic nervous systems. The autonomic nervous system is further divided into the sympathetic and parasympathetic divisions.

Definition

Peripheral Nervous System (PNS): The peripheral nervous system consists of the nerves that branch out from the central nervous system and connect it to other body parts.

Somatic Nervous System: The somatic nervous system consists of the cranial and spinal nerve fibres that connect the CNS to the skin and skeletal muscles; it is involved in conscious activities.

Autonomic Nervous System: The autonomic nervous system includes those fibres that connect the CNS to the visceral organs, such as the heart, stomach, intestines and various glands. It is concerned with unconscious activities.

Main Idea

• The peripheral nervous system can be subdivided into:
• Somatic nervous system connects the CNS to the skin and skeletal muscles; involved in conscious activities.
• Autonomic nervous system connects the CNS to the visceral organs; concerned with unconscious activities.
• The autonomic system is divided into:

Core Concept

• PNS = nerves that branch out from CNS
• Somatic nervous system = connects CNS to skin and skeletal muscles; conscious activities
• Autonomic nervous system = connects CNS to visceral organs; unconscious activities
• Sympathetic division = controls autonomic functions during emergency; fight or flight response
• Parasympathetic division = controls autonomic functions during rest; returns body functions to normal

Detailed Explanation

Peripheral Nervous System

- The peripheral nervous system can also be subdivided into the somatic and autonomic nervous systems.

Somatic Nervous System

• Generally, the somatic nervous system consists of the cranial and spinal nerve fibres that connect the CNS to the skin and skeletal muscles.
• It is involved in conscious activities.

Autonomic Nervous System

• The autonomic nervous system includes those fibres that connect the CNS to the visceral organs, such as the heart, stomach, intestines and various glands.
• It is concerned with unconscious activities.
• The autonomic system is divided into sympathetic and parasympathetic system.
• Both of these systems function automatically and usually subconsciously in an involuntary manner.

Sympathetic Division

• The sympathetic division controls various autonomic functions during the state of emergency.
• It prepares the body for fight or flight response.
• It consists of only spinal nerves.
• These nerves arise from first thoracic segment to second lumbar segment of the spinal cord.

Parasympathetic Division

• A few cranial nerves, including the vagus nerve, together with nerves that arise from the sacral portion of the spinal cord, form the parasympathetic division.
• It controls various autonomic functions during the state of rest.
• In short, the parasympathetic system returns the body functions to normal after they have been altered by sympathetic stimulation.
• In times of danger, the sympathetic system prepares the body for violent activity.
• The parasympathetic system reverses these changes when the danger is over.

Summary Table of Peripheral Nervous System

Comparison of Sympathetic and Parasympathetic Divisions

Intermediate Level

Peripheral Nervous System

Somatic Nervous System

Autonomic Nervous System

Sympathetic Division

Parasympathetic Division

Formula / Mathematical Form

Not applicable to this topic.

Solved Example

Not applicable to this topic (descriptive topic).

Important Points

• 1. PNS consists of nerves that branch out from CNS.
• 2. PNS is subdivided into somatic and autonomic nervous systems.
• 3. Somatic nervous system connects CNS to skin and skeletal muscles.
• 4. Somatic nervous system is involved in conscious activities.
• 5. Autonomic nervous system connects CNS to visceral organs.
• 6. Autonomic nervous system is concerned with unconscious activities.
• 7. Autonomic system is divided into sympathetic and parasympathetic.
• 8. Sympathetic division controls functions during emergency.
• 9. Sympathetic division prepares body for fight or flight.
• 10. Sympathetic division consists of spinal nerves.
• 11. Sympathetic nerves arise from first thoracic to second lumbar.
• 12. Parasympathetic division controls functions during rest.
• 13. Parasympathetic division returns body functions to normal.
• 14. Parasympathetic division includes cranial nerves (vagus) and sacral nerves.
• 15. In times of danger, sympathetic system prepares body for violent activity.
• 16. Parasympathetic system reverses changes when danger is over.
• 17. Both systems function automatically and involuntarily.
• 18. Somatic nervous system controls voluntary movements.
• 19. Autonomic nervous system controls involuntary functions.
• 20. The balance between sympathetic and parasympathetic is essential.

Remember

• - PNS = nerves that branch out from CNS
• - Somatic nervous system = connects CNS to skin and skeletal muscles; conscious activities
• - Autonomic nervous system = connects CNS to visceral organs; unconscious activities
• - Sympathetic division = emergency; fight or flight response
• - Parasympathetic division = rest; returns body functions to normal
• - Sympathetic nerves = first thoracic to second lumbar
• - Parasympathetic nerves = cranial (vagus) and sacral
• - Both systems = automatic and involuntary

Common Mistakes

• 1. Confusing somatic and autonomic nervous systems — Somatic = conscious; autonomic = unconscious.
• 2. Mixing up sympathetic and parasympathetic — Sympathetic = emergency; parasympathetic = rest.
• 3. Forgetting the nerve origins — Sympathetic: first thoracic to second lumbar; parasympathetic: cranial and sacral.
• 4. Thinking the autonomic nervous system is voluntary — It is involuntary.
• 5. Confusing the effects — Sympathetic increases heart rate; parasympathetic decreases it.
• 6. Forgetting the role of the vagus nerve — It is part of the parasympathetic division.
• 7. Mixing up the functions — Somatic = movement; autonomic = organ function.
• 8. Believing the sympathetic system is always active — It is active during emergency.
• 9. Thinking the parasympathetic system is not important — It is essential for rest and recovery.
• 10. Confusing the neurotransmitters — Sympathetic = norepinephrine; parasympathetic = acetylcholine.

Quick Revision

The peripheral nervous system can also be subdivided into the somatic and autonomic nervous systems. Generally, the somatic nervous system consists of the cranial and spinal nerve fibres that connect the CNS to the skin and skeletal muscles; it is involved in conscious activities. The autonomic nervous system includes those fibres that connect the CNS to the visceral organs, such as the heart, stomach, intestines and various glands. It is concerned with unconscious activities. The autonomic system is divided into sympathetic and parasympathetic system. Both of these systems function automatically and usually subconsciously in an involuntary manner. The sympathetic division controls various autonomic functions during the state of emergency. It prepares the body for fight or flight response. It consists of only spinal nerves. These nerves arise from first thoracic segment to second lumbar segment of the spinal cord. A few cranial nerves, including the vagus nerve, together with nerves that arise from the sacral portion of the spinal cord, form the parasympathetic division. It controls various autonomic functions during the state of rest. In short, the parasympathetic system returns the body functions to normal after they have been altered by sympathetic stimulation. In times of danger, the sympathetic system prepares the body for violent activity. The parasympathetic system reverses these changes when the danger is over.

60-Second Revision

• PNS = nerves that branch out from CNS
• Somatic nervous system = connects CNS to skin and skeletal muscles; conscious activities
• Autonomic nervous system = connects CNS to visceral organs; unconscious activities
• Sympathetic division = emergency; fight or flight response
• Parasympathetic division = rest; returns body functions to normal
• Sympathetic nerves = first thoracic to second lumbar
• Parasympathetic nerves = cranial (vagus) and sacral
• Both systems = automatic and involuntary
• Warning: Sympathetic = emergency; parasympathetic = rest

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• 5. Nervous System of Man

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• 5.7.4 SENSORY RECEPTORS AND THEIR WORKING

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