The Skin

Example Skin Receptors: Free nerve ending; Pacinian corpuscles; Ruffini endings; Hair follicle ending; Meissner corpuscle; Merkel’s disk

Light touchPressureVibrationTemperaturePainHair movement

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

Monosynaptic Reflex

Disynaptic Reflex

1. Sensory neurons

2. Neurons in the spinal cord

3. Motor neurons which control muscle contraction

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.

SKIN

Spinal Cord Brain

BRAIN

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

Thalamus

Cortex

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 MappingFinding 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| |

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Site Threshold DistanceFingers 2-3 mm

Upper Lip 5 mmCheek 6 mmNose 7 mmPalm 10 mm

Forehead 15 mmFoot 20 mmBelly 30 mm

Forearm 35 mmUpper arm 39 mm

Back 39 mmShoulder 41 mm

Thigh 42 mmCalf 45 mm

Influence of:IceDistractionSound

Pain!

Gate Control Theory

Proprioception

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