Difference Between Somatic and Visceral Reflex

The key difference between somatic and visceral reflex is that the somatic reflex occurs in the skeletal muscles while the visceral reflex occurs in the soft tissue organs.

A reflex arc is a neural pathway that controls a reflex action. A typical reflex arc has five different components namely sensory receptor, afferent neuron (sensory neuron), interneuron, efferent neuron (motor neuron), and effector organ (muscle or organ). Furthermore, there are two main types of reflex arc namely autonomic reflex arc and somatic reflex arc. Autonomic reflex arc targets cardiac and smooth muscles, as well as glandular tissue (basically inner organs) while somatic arc targets skeletal muscles.

CONTENTS

1. Overview and Key Difference
2. What is Somatic Reflex
3. What is Visceral Reflex
4. Similarities Between Somatic and Visceral Reflex
5. Side by Side Comparison – Somatic vs Visceral Reflex in Tabular Form
6. Summary

What is Somatic Reflex?

The somatic nervous system is a part of the peripheral nervous system. The somatic reflex is a reflex that occurs in the skeletal muscles. Therefore, these reflexes involve the skeletal muscle contractions in response to stimuli. The spinal cord is the part of the central nervous system that controls somatic reflexes. Hence, these reflexes take place before information is reaching the brain. Some examples of the somatic reflexes are blinking or knee-jerk arc, etc.

There are several major events of a somatic reflex. Somatic reflex initiates with the stimulation of somatic receptors. Then, the afferent fibres carry this signal to the dorsal horn of the spinal cord. There, interneurons integrate the information and handover to efferent fibres. Next, the efferent fibres carry the information to skeletal muscles — finally, skeletal muscles contract giving a somatic response.

What is Visceral Reflex?

Visceral reflex is an autonomic reflex which occurs in the soft tissue organs of the body. Basically, it involves the reflex actions of internal organs such as the heart, reproductive system and digestive system, etc. Autonomic nervous system (ANS) is responsible for the visceral reflexes. Hence, they are mostly involuntary reflexes.

Unlike somatic reflex, the visceral reflex is a polysynaptic reflex. Furthermore, the efferent pathway has two nerve fibres from the central nervous system to effector organ in visceral reflex.  For example; some of the visceral reflexes are dilation of the pupils, defecation, vomiting, blood pressure, heart rate, body temperature, digestion, energy metabolism, respiratory airflow and urination.

What are the Similarities Between Somatic and Visceral Reflex?

• Somatic and Visceral Reflex are neural pathways from a stimulus to response.
• Both somatic and visceral reflexes have the same components.
• Furthermore, often they have a similar afferent pathway.

What is the Difference Between Somatic and Visceral Reflex?

Somatic and visceral reflex are two types of reflex actions. Somatic reflex occurs in the skeletal muscles while visceral reflex occurs in the smooth muscles of the inner organs. This is the key difference between somatic and visceral reflex. A further difference between somatic and visceral reflex is that the efferent pathway of visceral reflex involves two efferent nerve fibres but that of somatic reflex involves only one efferent fibre between the central nervous system and the effector. Also, the somatic nervous system controls somatic reflexes while the autonomic nervous system controls visceral reflexes. Hence, a difference between somatic and visceral reflex based on this is that most of the somatic reflexes are voluntary while visceral reflexes are usually involuntary.

The below infographic on difference between somatic and visceral reflex tabulates these differences.

Summary – Somatic vs Visceral Reflex

Somatic reflex targets skeletal muscles while visceral reflex targets soft tissue organs. Furthermore, somatic reflexes are mostly voluntary while visceral reflexes are autonomic and involuntary. Unlike somatic reflexes, visceral reflexes are polysynaptic, and they have two efferent nerve fibres between the central nervous system and the effector organ. Thus, this summarizes the difference between somatic and visceral reflex.

Reference:

1.“Reflex Arc.” NeuroImage, Academic Press. Available here 

Image Courtesy:

1.”Patellar-knee-reflex”By Christina (CC BY-SA 3.0) via Commons Wikimedia  
2.”1505 Comparison of Somatic and Visceral Reflexes”By OpenStax College – Anatomy & Physiology, Connexions Web site, Jun 19, 2013., (CC BY 3.0) via Commons Wikimedia