854
ensory mechanisms provide individuals with a con-
tinuous stream of information about their bodies,
the outside world, and the interactions between the two.
The somatosensory component of the nervous system
provides an awareness of pain, touch, temperature, and
position, as compared to the specialized senses of sight
and hearing (discussed in Chapter 38). Between 2 and
3 million nerve endings in the skin and deep body tis-
sues provide a steady stream of encoded somatosensory
information to the central nervous system. Only a small
portion of this information reaches awareness; most of
which provides input essential for the myriad of reflexes
and automatic mechanisms that keep us functioning.
This chapter is organized into two distinct parts.
The first part describes the organization and control of
somatosensory function, and the second focuses on pain
as a somatosensory modality.
Organization and Control
of Somatosensory Function
The somatosensory system provides the central nervous
system (CNS) with information related to deep and
superficial body structures. It includes three types of neu-
rons that vary in terms of distribution and type of sensa-
tion that is detected—general somatic, special somatic,
and general visceral.
General somatic afferent neurons
have branches with widespread distribution throughout
the body and with many distinct types of receptors that
result in sensations such as pain, touch, and temperature.
Special somatic afferent neurons
have receptors located
primarily in muscles, tendons, and joints. These recep-
tors sense position and movement of the body.
General
visceral afferent neurons
have receptors in various
visceral structures that sense fullness and discomfort.
Somatosensory Systems
Sensory systems can be conceptualized as a series of
first-order, second-order, and third-order neurons.
First-
order neurons
transmit sensory information from the
S
Somatosensory
Function, Pain,
and Headache
35
C h a p t e r
Organization and Control of Somatosensory
Function
Somatosensory Systems
The Sensory Unit
Dermatomal Pattern of Innervation
Spinal Circuitry and Ascending Neural
Pathways
Central Processing of Somatosensory
Information
Somatosensory Modalities
Tactile Sensation
Thermal Sensation
Position Sense
Pain Sensation
Pain Theories
Pain Mechanisms and Pathways
Pain Receptors and Primary Afferent Pathways
Spinal Cord Circuitry and Ascending
Pathways
Brain Centers and Pain Perception
Central Pathways for Pain Modulation
Endogenous Analgesic Mechanisms
Types of Pain
Cutaneous and Deep Somatic Pain
Visceral Pain
Referred Pain
Acute and Chronic Pain
Pain Management
Assessment
Nonpharmacologic Interventions
Pharmacologic Treatment
Surgical Interventions
Alterations in Pain Sensitivity and Special Types
of Pain
Alterations in Pain Sensitivity
Special Types of Pain
Neuropathic Pain
Neuralgia
Complex Regional Pain Syndrome
Phantom Limb Pain
Headache and Associated Pain
Headache
Migraine Headache
Cluster Headache
Tension-Type Headache
Chronic Daily Headache
Temporomandibular Joint Pain
Pain in Children and Older Adults
Pain in Children
Pain Assessment
Pain Management
Pain in Older Adults
Pain Assessment
Pain Management
