1. Somatic Sensation of the Face and Head
04. The Trigeminal System
Somatic Sensation of the Face and Head

2. Objectives:
Outline the two pathways for facial sensation from the head.
Contrast facial sensation from the head and somatic sensation from the body. In what ways are they similar? Different? Try drawing this on the Haines atlas diagram at the end of the lecture.
Diagram the corneal reflex: the afferent and efferent limbs as well as nuclei involved in the brainstem.
If a person does not blink, how would you determine if the problem were in the sensory (afferent) limb, motor (efferent) limb, or brainstem interconnections for the corneal reflex?
Explain how a single, small medullary vascular lesion could abolish pain and temperature from the face on the right side and pain and temperature from the body on the left side. What vessel is most likely occluded?

3. Peripheral Receptors and Sensation
Structures served by trigeminal system
CN V-1
CN V-2
CN V-3 ?
Great auricular nerve (C2-C3)

4. How many neurons in sensory pathway?
DCML/ALS
Peripheral ganglion (DRG)
Spinal cord, medulla
VPL nucleus of the thalamus
Trigeminal system
Peripheral ganglion (Trig. gang.)
2 nuclei in brainstem (pons, medulla, sp cord)
VPM nucleus of the thalamus

5. Primary Sensory Neurons: Trigeminal ganglion
CN V-1
CN V-2
CN V-3
Trigeminal ganglion

6. Primary Sensory Neurons: Trigeminal ganglion
CN V-1
CN V-2
CN V-3
Primary sensory neuron

7. Second-Order Trigeminal Neurons
Originate in two brain stem nuclei:
Principal (chief) trigeminal nucleus
Spinal (descending) trigeminal nucleus
Young, Young and Tolbert, 2008 Fig 

8. III. Second-Order Trigeminal Neurons
A. Principal (chief) trigeminal nucleus
Mediates fine touch, joint position, vibration.
Located in pons lateral to motor nucleus of CN V.
This would be equivalent to what nucleus of the brainstem? _____________
Young, Young and Tolbert, 2008 Fig 

9. III. Second-Order Trigeminal Neurons
B. Spinal (descending) trigeminal nucleus
Mediates pain and temperature.
Spinal (descending) trigeminal tract
Descends caudally as far as C2-C3 and is continuous with dorsal horn.
This would be equivalent to what region in the spinal cord? _____________
Young, Young and Tolbert, 2008 Fig 

10. III. Second-Order Trigeminal Neurons
C. Ascending Trigeminal Pathways
Axons of second-order neurons form the trigeminothalamic pathway to the VPM nucleus of the thalamus.
Axons from neurons in the chief sensory nucleus carry sensations such as: _____
Axons from neurons in the spinal trigeminal nucleus carry sensations such as: ____
Secondary sensory neuron
Secondary sensory neuron
Young, Young and Tolbert, 2008 Fig 

11. IV. Third Order Neurons
Project from VPM in the thalamus to the Postcentral gyrus (primary sensory cortex)
Axons course through the internal capsule

12. V. Primary Somatosensory Cortex, Postcentral Gyrus
There are four different body maps to help extract texture, form, and motion that come from the head and body.
Name them:
1. DCML (vibration, fine touch, proprioception)
2. ALS (pain, temperature)
3. Trigeminal system (vibration, fine touch)
4. Trigeminal system (pain, temperature)

13. VI. Association Somatosensory Cortex
Posterior Superior Parietal Areas 5 and 7 of Brodmann.

14. Self-assessment: When you think you have mastered the pathways, select 2 colors in both a dark and light shade. Use the dark color for the body and the lighter color for the face pathways.
e.g. Light blue-Trigeminothalamic (ventral)
Dark blue – ALS
Pink – trigeminothalamic (dorsal) from chief
Red – DCML
Animation