Part 6
The Sensory Function of CNS
Senses
 Somatic
senses
Mechanoreceptive
 Tactile
and position
Thermoreceptive
Pain
sense
 Special
somatic senses
senses
senses
Five basic types of sensory receptors

Mechanoreceptors

Thermoreceptors

Nociceptors (Pain receptors)

Electromagnetic receptors

Chemoreceptors
The somatosensory system includes multiple
types of sensation from the body--- light touch,
pain, pressure, temperature, joint and muscle
position sense (also called proprioception).

Sensory pathways: Spinal cordBrainstem 
Thalamus  Cerebral cortex
Spinal cord
Sensory pathways in spinal cord

Two alternative pathways:
 The

Fine touch, two-point discrimination, phasic or
position sensation  dorsal column  cross in
medulla  medial lemniscal system  thalamus
 The

dorsal column-medial lemniscal system
anterolateral system
Pain, warmth, cold, crude tactile, tickle and itch,
sexual sensation  dorsal spinal roots  cross in
spinal cord  brain stem and thalamus
1.The dorsal
column-medial
lemniscal system
2. The
anterolateral
system
Structure of Thalamus
Function of thalamus
A
relay station to the cerebrum
for all varieties of sensory input
except olfaction
1. Specific sensory relay nuclei

Somatosensoryventral-posterior (VP
thalamus)  somatosensory area I

Visual signal  lateral geniculate body
visual cortex

Auditory signal  medial geniculate body 
auditory cortex
Nuclei of Thalamus
2. Associated nuclei

Association nuclei
receive their driving
inputs from other
cortical areas
 Anterior
nucleus
 ventral-lateral
nucleus
 Pulvinar
nucleus
3. Nonspecific projection nuclei
“Nonspecific nuclei" connect to association areas
of cortex

Medial nucleus

Nuclei in lamina
Specific projection system of thalamus

The projecting system of
thalamic relay nuclei
receives fibers from
ascending somatosensory
pathways and projects
mostly to a localized
(discrete) region of the
cortex - focal projection
Nonspecific projection system of
thalamus

Nonspecific thalamic nuclei
receive afferent fibers from
reticular formation and send
fibers to very broad regions
of cortex - diffuse projection
A: cut the specific projection pathway
B: cut the nonspecific projection pathway
Sensory areas of cerebral cortex
Somatosensory cortex
 Somatosensory
Brodmann’s
area I
areas: 3-1-2
 Somatosensory
area II
Pain

The purpose of pain
A

main protective mechanism for the body
Types of pain
 Fast
pain: sharp pain
 Slow
pain: burning pain-- associated with tissue
destruction
Pain receptors and their stimulation

Pain receptors: nociceptors
 Free

nerve endings in skin and internal tissue
Stimulation
 Mechanical
 Thermal
 Chemical

Bradykinin, 5-HT, histamine, K+, acids, Ach, PG
Dual transmission of pain signals
into the central nervous system
 Fast-sharp

pain pathway
A fiber (6-30m/sec)
 Slow-chronic pain

pathway
Type C fiber (0.5-2m/sec)
Visceral pain

True visceral pain
 Causes:

Ischemia

Chemical stimuli

Spasm of a hollow viscus

Overdistention

Parietal pain

Referred pain
Surface areas of referred pain
Mechanism of referred pain

1. Convergence theory

2. Facilitation theory
General Questions
 Specific
projection system
 Non-specific projection
 Referred

system
pain
What is the sensory area of cerebral cortex? Please
describe its details.