13.1: Introduction to the Somatic Senses

Last updated
Save as PDF

Page ID: 63447

\( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \) \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)\(\newcommand{\AA}{\unicode[.8,0]{x212B}}\)

Chapter Learning Objectives

After studying this chapter, you will be able to:

Define general somatic sensation and special somatic sensation
Describe the structures and functions of general somatic senses
Explain how the structures of the eye modulate and assist with the detection of light by photoreceptors.
Explain how the structures of the ear modulate and assist with the detection of sound by hair cells.
Describe the structures of the vestibular apparatus and their role in equilibrium and balance.
Describe the receptors and supporting cells responsible for chemoreception in taste and in smell.
Trace the pathways from sensory receptors to their cerebral processing regions.

The somatic sensory system includes all the afferent, sensory receptors from the skin, skeletal muscles, joints and special senses which are responsible for our conscious perception of the environment.

Our somatic senses make us aware of our surroundings or state of our body through peripheral sensory receptors. These receptors send sensory information through cranial and spinal nerves to the central nervous system. The neurons of the central nervous system need to process the information, a step called integration. Once processed, if a motor response is required, the neurons of the central nervous system will send a signal to skeletal muscles to move. Let's take the example of touching a hot stove (Figure \(\PageIndex{1}\)). Sensory receptors in the skin sense extreme temperature and the early signs of tissue damage. This triggers an action potential (a change in electrical properties of a neuron) that travels along the sensory fiber from the skin through the posterior root to the spinal cord and directly activates an anterior horn motor neuron. That neuron sends a signal along its axon to excite the biceps brachii, causing contraction of the muscle and flexion of the forearm at the elbow to withdraw the hand from the hot stove. The basic withdrawal reflex explained above includes afferent somatosensory input (the painful stimulus), central processing (the synapse in the spinal cord), and efferent motor output (activation of a ventral motor neuron that causes contraction of the biceps brachii).

In this chapter, we will examine the sensory components of the somatic nervous system. For the sensory input, we will look at sensory receptors of general and special senses and how the sensory information is sent to the CNS.

Pot on blue flame of stove top — Figure \(\PageIndex{1}\): Too Hot to Touch. When high temperature is sensed in the skin, a withdrawal is initiated by the muscles of the arm. Sensory neurons are activated by a stimulus, which is sent to the central nervous system, and a motor response is sent out to the skeletal muscles that control this movement. (Image Credit: "Flame" by Steve Buissinne, Pixabay is in the Public Domain)

Contributors and Attributions

OpenStax Anatomy & Physiology (CC BY 4.0). Access for free at https://openstax.org/books/anatomy-and-physiology