Structure of the Brain Stem

Question 1

Which cranial nerves exit the brainstem to innervate peripheral targets?

Answer 1

CNIII-XII

Question 2

Which of the CNs exiting the brainstem (to the PNS) are purely motor?

Answer 2

CNIV, VI, XI and XII

Question 3

Which of the CNs exiting the brainstem (to PNS) are mixed motor AND sensory?

Answer 3

CNV, VII, IX and X

Question 4

Which of the CNs exiting brainsten to PNS also have a PNSN component?

Answer 4

CNIII, VII, IX and X

Question 5

What is the obex?

Answer 5

Point at which the 4th ventricle narrows to become continuous with the central canal of the SC

Question 6

Where are the sensory tracts located in the brainstem? (where do they run?)

Answer 6

Dorsal Root Ganglia (DRG)

or Cranial Ganglia

Question 7

What are the key structures, in the brainstem, that are related to the cerebellum. What is their general function (shared)?

Answer 7

Inferior Olivary Nucleus
Pontine Nuclei
Spinocerebellar Tracts

All contribute to the co-ordination of movement

Question 8

FUnctions of the reticular formation? Where is it located?

Answer 8

Throughout the brainstem

1. Reticular Activating System (maintaining consciousness)
2. Processing of some Noxious Stimuli (sensory)
3. Maintenance of muscle tone and posture (motor)
4. Visceral Functions (autonomic centres)

Question 9

What are the dorsal funiculi?

What are the 2 different ones & their location

Answer 9

Dorsal columns on the SC, also visible on caudal medulla. Contain sensory axons (DRGs)

Fasciculis Gracilis -> sensory information below T6-leg *Central - either side of the posterior median sulcus

Fasciculis Cuneatus -> sensory information above T6-arm *lateral to Fasciculis Gracilis

Question 10

What type of sensory information to the dorsal fasciculi carry?

Answer 10

proprioception
vibration
finet tactile sensation

Question 11

Where do primary sensory axons of the dorsal fasciculi synapse?

Answer 11

In caudal medulla

In the Nucleus Gracilis and Nucleus Cuneatus

Question 12

Where do sensory fibres go after synapsing in the nucleus gracilis and nucleus cuneatus?

Answer 12

They cross over
Ascend, as the Medial Lemniscus, to the Ventroposterolateral Nucleus (VPL) - tertiary sensory nucleus - of the Thalamus -> on to Postcentral Gyrus -> Primary Somatosensory Cortex

Question 13

Where to primary pain and temperature sensory neurons from the body synapse in the SC? Then where to?

Answer 13

Dorsal horn of the SC

Cross over at/near to level of entry

Then ascend in the Spinothalamic Tract (Part of the Anterolateral Pathway System)

The STT passes through the brainstem without synapsing -> Synapses in VPL of Thalamus -> then on to somatosensory cortex

Question 14

Pathway of pain and temperature modalities from the face

Answer 14

Primary sensory fibres enter Pons as part of CNV ->
Primary SN cell bodies in Trigminal Ganglion ->
Axons descend to the Upper Spinal cord as the Spinal Trigeminal Tract to synapse in the Spinal Trigeminal Nucleus.

Secondary fibers cross the midline
Then ascend to thalamus in the Trigeminothalamic tract
-> to the VPN of the Thalamus -> on to somatosensory cortex

Question 15

Which Nuclei in the Caudal Medulla give rise to CNXI and XII?

Answer 15

Spinal Accessory Nucleus and Hypoglossal Nucleus

Question 16

Where does Spinal Accessory Nucleus extend?

Answer 16

Extends from caudal medulla into cervical spinal cord

Question 17

Describe the course of the Descending Corticospinal tract (containing UMN axons) from precentral gyrus (and associated areas) through the brainstem

Answer 17

Descends in the Pyramids of the Medulla
Cross over at the Decussation of the Pyramids
Then continue in the Lateral Corticospinal Tract of the SC
These UMNs then synapse with either interneurons, or directly onto LMNs