Tracts of the brain stem Flashcards
I. Basics
1. What are tracts?
Axons coursing in the white matter of the spinal cord form bundles of fibers with similar origins, courses and destinations.
=> These bundles are called tracts
I. Basics
2. How should tracts be characterized?
Tracts should be characterized by the location of their perikarya, the course and termination of the axon
I. Basics
3. What are the 3 types of tracts?
Can be subdivided into long ascending, long descending and intraspinal (intersegmental) tracts
II. Descending tracts of the brainstem
1. What are the 4 descending tracts of the brainstem?
- Corticospinal tract (Pyramidal tract)
- Corticobulbar (corticonuclear) tract (part of the pyramidal tract)
- Rubrospinal tract
- Medial longitudinal fasciculus
II. Descending tracts of the brainstem
2. Describe Corticospinal tract (Pyramidal tract)
- Goes through the brainstem and terminates in the spinal cord as anterior and lateral corticospinal tracts
- Most of the axons cross to the opposite side (pyramidal decussation) at the level of the pyramids (lateral corticospinal tract). The rest of the fibers do this at the level of the spinal cord
- Axons arise from large pyramidal neurons of the primary motor cortex and terminate on or near alpha-motoneurons in the ventral horn of the spinal cord
II. Descending tracts of the brainstem
3. Describe Corticobulbar (corticonuclear) tract (part of the pyramidal tract)
- Originate from the motor cortex and descend down to cranial nerve nuclei, most importantly the motor cranial nerve nuclei
1. Bilateral for: trigeminal motor nucleus (CN-V), facial motor nucleus (CN-VII, for forehead muscles) and nucleus ambiguus (CN-IX + X)
2. Contralateral (crossed) for: abducent motor nucleus (CN-VI), facial motor nucleus (CN-VII, for lower face muscles) and hypoglossal motor nucleus (CN-XII)
3. Ipsilateral for: accessory motor nucleus (CN-XI) innervates SCM, a separate spinal nucleus
II. Descending tracts of the brainstem
4. Describe Rubrospinal tract
Arises from the red nucleus in the brainstem and goes to the spinal cord
II. Descending tracts of the brainstem
5. Describe Medial longitudinal fasciculus:
- Found in the midline of the brainstem
- Arises near the lateral geniculate body
- Mainly a descending tract, but also has some ascending fibers
- Has a lot to do with eye movements and visual information
III. Ascending tracts of the brainstem
1. What are the 3 types of Ascending tracts of the brainstem?
- Fasciculus cuneatus and gracilis = posterior funiculus / dorsal column system EPICRITIC
- Lateral lemniscus
- Lateral spinothalamic tract
III. Ascending tracts of the brainstem
2. What are the characteristics of Fasciculus cuneatus and gracilis?
- The fasciculus gracilis (medial) and fasciculus cuneatus (lateral) arise from the spinal cord and terminate in the gracile and cuneate nucleus
- From the nuclei, arcuate fibers emerge and decussate (lemniscal decussation), continuing as the medial lemniscus - the most important ascending epicritic system
- Ends in the thalamus
III. Ascending tracts of the brainstem
3. What are the characteristics of Lateral lemniscus?
- Arises from the superior olive and trapezoid body
- The main auditory pathway
III. Ascending tracts of the brainstem
4. What are the characteristics of Lateral spinothalamic tract?
- Arises from the spinal cord and goes to the thalamus
- Has protopathic modality (crude touch, pain, heat)
IV. Cerebellar connections of the brainstem
1. What are the characteristics of Cerebellar connections of the brainstem?
The cerebellar fibers cross to the cerebellum through 3 peduncles which are
1. Inferior cerebellar peduncle
2. Middle cerebellar peduncle
3. superior cerebellar peduncle
IV. Cerebellar connections of the brainstem
2. What are the characteristics of Inferior cerebellar peduncle?
- Posterior spinocerebellar tract: arises from the spinal cord and goes through the inferior cerebellar peduncle to the cerebellum
- Olivocerebellar tract: goes from the olive through to the inferior cerebellar peduncle and then to the cerebellum
IV. Cerebellar connections of the brainstem
3. What are the characteristics of Middle cerebellar peduncle?
- Pontocerebellar fibers pass here. They have direct input from the cortex to corticopontine tract
- The tract descends to the basis of the pons, where we can find the pontine nuclei
- The pontocerebellar fibers after that reach the cerebellum through the superior cerebellar peduncle
IV. Cerebellar connections of the brainstem
4. What are the characteristics of Superior cerebellar peduncle?
- Anterior spinocerebellar tract enters the cerebellum through the superior cerebellar peduncle
