2. Introduction
Anatomically speaking, the somatosensory system is a
network of neurons that help humans recognize
objects, discriminate textures, generate sensory-
motor feedback and exchange social cues
In physiology, the somatosensory system is the
network of neural structures in the brain and body that
produce the perception of touch, as well as
temperature, body position, and pain. It is a subset of
the sensory nervous system.
3. 3
Receptors, Sensation,
and Perception
• Sensory receptors
•Specialized cells or multicellular structures that
collect information from the environment
•Stimulate neurons to send impulses along sensory
fibers to the brain
• Sensation
•A feeling that occurs when brain becomes aware of
sensory impulse
• Perception
•A person’s view of the stimulus; the way the brain
interprets the information
5. General
Senses
Senses associated with skin, muscles,
joints, and viscera
Three (3) groups:
Exteroceptive senses (exteroceptors)
Senses associated with body surfaces such as touch, pressure,
temperature, and pain
Visceroceptive senses (interoceptors)
Senses associated with changes in the viscera such as blood pressure
stretching blood vessels and ingestion of a meal
Proprioceptive senses
Senses associated with changes in muscles and tendons such
as at joints
13
6. 7
Sensory Impulses
• Stimulation of receptor causes local change in its receptor potential
•A graded electrical current is generated that reflects intensity of
stimulation
•If receptor is part of a neuron, the membrane potential may generate
an action potential
•If receptor is not part of a neuron, the receptor potential must be
transferred to a neuron to trigger an action potential
• Peripheral nerves transmit impulses to CNS where they are analyzed
and interpreted in the brain
7.
8. 14
Touch and Pressure Senses
Free nerve endings
• Common in epithelial tissues
• Simplest receptors
• Sense itching
Tactile (Meissner’s) corpuscles
• Abundant in hairless portions of
skin and lips
•Detect fine touch; distinguish
between two points on the skin
•Adapt rapidly
Lamellated (Pacinian) corpuscles
•Common in deeper
subcutaneous tissues, tendons
and ligaments
•Detect heavy pressure and
vibrations
Expanded Tip receptors (Merkel’s
discs---- Iggo dome receptors
•Initially strong but partially
adapting
•Localize touch and determine
texture
Hair end organ
•Adapts readily
•Touch (movement of object on
surface of body + initial contact)
Ruffini’s endings
• Slow adaptation
• found in joint capsules
13. • Fine touch
• Vibration
• Position
• Pressure
Dorsal column Medial lemniscal
system Anterolateral System
• Pain
• Temperature
• Crude touch
• Tickle and itch
• Sexual sensations
14.
15. Nociception
• Nocere – “to hurt”
• Nociceptors are nerve endings that give the sensation of pain.
• Types of nociceptors:
1. Aδ group: myelinated, dangerously intense mechanical/ both intense
mechanical and thermal stimuli, localized
2. C fiber group: unmyelinated slow, the majority respond to thermal, mechanical, and chemical stimuli
