Trigeminal pathways PP

05. The Trigeminal System Somatic Sensation of the Face and Head

David A. Morton, Ph.D. Thursday February 7th, 2013

Objectives: 1.

Outline the two pathways for facial sensation from the head.

2.

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. 3.

Diagram the corneal reflex: the afferent and efferent limbs as well as nuclei involved in the brainstem.

4.

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?

5.

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?

Peripheral Receptors and Sensation • Structures served by trigeminal system

CN V-1

CN V-2

? Great auricular nerve (C2-C3) CN V-3

How many neurons in sensory pathway?

DCML/ALS

Trigeminal system

1. Peripheral ganglion (DRG)

1. Peripheral ganglion (Trig. gang.)

2. Spinal cord, medulla

2. 2 nuclei in brainstem (pons, medulla, sp cord)

3. VPL nucleus of the thalamus

3. VPM nucleus of the thalamus

II. Primary Sensory Neurons: Trigeminal ganglion

CN V-2

Trigeminal ganglion

Primary Sensory Neurons: Trigeminal ganglion

CN V-2

Primary sensory neuron

Second-Order Trigeminal Neurons Originate in two brain stem nuclei: • Principal (chief) trigeminal nucleus • Spinal (descending) trigeminal nucleus

Young, Young and Tolbert, 2008 Fig 11-10 

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 11-10 

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 11-10 

Second-Order Trigeminal Neurons C. Ascending Trigeminal Pathways • Axons of second-order neurons form the trigeminothalamic pathway to the

Secondary sensory neuron

VPM nucleus of the thalamus. Secondary sensory neuron

a. Axons from neurons in the chief sensory

nucleus carry sensations such as: _____

b. Axons from neurons in the spinal trigeminal nucleus carry sensations such

as: ____ Young, Young and Tolbert, 2008 Fig 11-10 

Second-Order Trigeminal Neurons

Secondary sensory neuron

Secondary sensory neuron

Young, Young and Tolbert, 2008 Fig 11-10 

Third-Order Trigeminal Neurons Project from VPM in the thalamus to the Postcentral gyrus (primary sensory cortex) • Axons course through the internal capsule

Pons

Chief trig nucleus

Medulla oblongata (rostral)

Spinal trigeminal tract & spinal trig nucleus

Med lem

ALS

The right side of the pons is lesioned. What sensory loss would you expect?

The right side of the pons is lesioned. What sensory loss would you expect? Below the lesion: • Loss of facial sensation on right • Loss of pain and temp from left side • Loss of proprioception/vibration from left side

L

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