The Skin
Light touch
Pressure
Vibration
Temperature
Pain
Hair movement
Example Skin Receptors: Free nerve ending; Pacinian corpuscles;
Ruffini endings; Hair follicle ending; Meissner corpuscle;
Merkel’s disk
The Skin
Example Skin Receptors: Free nerve ending; Pacinian corpuscles;
Ruffini endings; Hair follicle ending; Meissner corpuscle; Merkel’s disk
Different types of skin receptors
Spinal Cord
Spinal Cord
1. Sensory neurons
Monosynaptic Reflex
2. Neurons in the spinal
cord
3. Motor neurons which
control muscle contraction
Disynaptic Reflex
Why does the reflex occur before
perception takes place? Answer:
• The sensation of heat reaches our perception only after the reflexive
withdrawal took place, because the somatosensory information can
travel very quickly to the spinal cord and then back down to the motor
neurons, whereas it takes a longer time for this information to reach
the higher areas of the brain, where it yields to perception.
Spinal Cord  Brain
BRAIN
SKIN
Somatosensory pathway
Spinal Cord  Brain
Cerebral Cortex
Thalamus
Medulla
Note crossing!
Spinal Cord
The Thalamus: Anatomy
The thalamus: Functions
The major role of thalamus is to
gate and otherwise modulate the
flow of sensory information to
cortex.
The Thalamus: Functions
The thalamus also play an important
role in regulating states of sleep and
wakefulness.
Sensory processing hierarchy
Cortex
Thalamus
Sensor
Sensory processing is different areas of
the brain
The full
somatosensory
pathway
Touch on left finger
Heat on right finger
The “Homunculus”
The cortical representation of sensory information is not uniform, but
emphasizes certain sensory parts of the body, such as the lips and fingers.
Somatosensory - Brain
CNS preserves the peripheral body map.
Amount of CNS tissue is proportional to the distribution
of peripheral receptors.
Homunculus: Other Animals
Brain Mapping
Finding out what each part of the brain does
Brain Areas are Specialized for Different Functions
Demo: how many picks?
• Use a fork for the following experiment.
• Gently pressure your neighbor’s fingertip with 1, 2, or 3 of
the fork’s picks. Can he tell (without looking) how many
picks are touching his fingertip?
• Now do the same on other body area, such as inside the
arm, on the legs, on the lips, or on the back of the body.
Can you still tell how many picks? Where?
Somatosensory discrimination varies
throughout the body surface
Somatosensory - Brain
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Somatosensory - Brain
Site
Fingers
Upper Lip
Cheek
Nose
Palm
Forehead
Foot
Belly
Forearm
Upper arm
Back
Shoulder
Thigh
Calf
Threshold Distance
2-3 mm
5 mm
6 mm
Influence of:
7 mm
Ice
10 mm
Distraction
15 mm
Sound
20 mm
30 mm
35 mm
39 mm
39 mm
41 mm
42 mm
45 mm
Pain!
Gate Control Theory
Proprioception
1
2
3
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