2. Somatic sensation

Crude touch receptors:

• Free nerve endings.

• Hair end organs.

Tactile localization:

It is the ability of the person to localize exactly the touched point with his eyes closed.

Tactile discrimination (two point discrimination):

It is the ability of the person to feel two points of the skin touched simultaneously as two separate points, provided that his eyes are closed and the distance between the two points is more than the threshold distance.

How does convergence effect two point discrimination?

↑ convergence = ↓ two-point discrimination

Pressure sense receptors:

*hint: P R

1- Pacinian corpuscles: rapidly adapting.

2- Raffini ending: slowly adapting.

Tension sense receptor:

Golgi tendon

Vibration sense receptors:

*hint: P M

Pacinian corpuscles for high frequency (200 - 800 C/sec)

Meissner’s corpuscles for low frequency (< 200 c/sec).

What are the largest represented areas in the somato-sensory areas?

Lips - Tongue - Fingers

Somatic sensory areas are:

area 1 ,2 ,3 + area 40

What is the somatic association area?

area 5 & 7

It is hypersensitivity to pain (non painful stimuli as touch become painful).

Hyperalgesia

Mechanism of 1ry hyperalgesia in injury area + redness area.

(what is released?)

Injury area: bradykinin & histamine

Redness area: substance P

Syringomyelia causes damage in?

Causes damage od spinothalamic senations (pain, temperature, & crude touch) in both sides

Incoordination of voluntary movements with normal cerebellar functions

Sensory ataxia

Romberg Sign:

Inability to maintain a balanced standing position with feet together and eyes closed