Ch. 12 somatic & sensory

Somatosensory System Sensations

Pain (nociception), touch, temperature, body position (proprioception)

Nociceptive

Stimulus originates outside nervous system

Ex. Falling twisting your ankle playing beach volley ball

Neurogenic or neuropathic

Stimulus originates within nervous system

Ex. (MS patients)

Conduction of Pain Sensation

Stimulation of free nerve endings
Chemical, mechanical, or thermal stimuli

l

Transduction of noxious stimuli into a nerve impulse
l

Transmission from tissues to CNS
Type A (delta) and C fibers, Induction of autonomic & reflex responses C fibers

Conduction of pain sensation Modulation

Substances released during
impulse transmission, Slow the rate of impulse
transmission

Perception

Sensory (somatosensory cortex) and emotional (limbic system) involvement

General somatic afferent neurons

Wide distribution with branches throughout the body. Pain, touch temperature

Special somatic afferent neurons 

Muscles, tendons, and joints. Position and body movement 

General visceral afferent neurons

Visceral structures. Fullness and discomfort.

Somatosensory System

 Relay sensory information
from the periphery to the
CNS
 Sensory receptors
 Ascending pathways
 Processing centers

Mechanoreceptor 

tactile skin sensation, deep-tissue sensation, hearing and proprioception. Ex: Merkel cells

Photoreceptors

Vision, rods and cones

Chemoreceptors

Taste, smell

Nociceptor

Pain and itch. Free nerve endings

Somatosensory

Processing
 Awareness, recognition,
identification, and interpretation of
stimuli
 Primary processing in the thalamus

Myopia

Cant see far away

Hyperopia

Blurred vision for close objects

Astigmatism

Misshaped causing blurred vision

Presbyopia

affects the ability to focus on near objects

Taste process

Signal initiation
 Binding of dissolved substance with taste
receptor
 Signal transmitted along facial (VII) and
glossopharyngeal (IX) cranial nerves