1 - Internal Anatomy of Brainstem (Sensory)

Question 1

Midbrain Components

Answer 1

Base (basis peduncle)

tegmentum (ventral to cerebral aqueduct, dorsal to cerebral peduncle)

tectum (roof, dorsal to cerebral aqueduct)

Question 2

Major components of Pons

Answer 2

base

tegmentum

Corticospinal fibers, pontine nuclei in base

Question 3

Major components of Medulla

Answer 3

“base” (pyramids, inferior olivary nuclei)

tegmentum

Question 4

Tegmentum landmarks/functions?

Answer 4

Nuclei for CN III - XII (except XI)

Reticular formation

Ascending/Descending pathways

Question 5

Base landmark/function?

Answer 5

Mostly descending pathways (corticospinal, corticopontine, corticobulbar)

Question 6

Ventricular System landmarks/functions?

Answer 6

Cerebral aqueduct, 4th ventricles, foramina Magendie/Luschka, central canal

Question 7

Substantia Nigra

Answer 7

Pars Compacta

• Dopaminergic Neurons
• Adjacent to tegmentum

Parts Reticulata

- Adjacent to crus cerebri

Parkinson’s Disease

Question 8

Reticular Formation

Critical Functional Areas?

Answer 8

Diffuse network of loosely packed neurons w/out distinct boundaries forming central core of brainstem

Arousal, sleep/wake, pain, motor function, respiratory control and heart rate

Pattern generators for conjugate eye movement*(Pontine portion of pontine reticular formation), chewing, swallowing, vomting, breathing, locomotion

Lesion of midbrain reticular formation = “coma” or similar

Question 9

Ascending Sensory Pathways

Answer 9

*Dorsal (Posterior) Column/Medial Lemniscus System, Trigeminal Lemniscus

*Anterolateral System, Trigeminothalamic

Spinocerebellar

Other (taste, auditory, vestibular)

*Go across entire brainstem, major pathways for determining lesion level

Question 10

Descending Motor Pathways

Answer 10

Corticospinal, Corticbulbar, (Pyramidal System)

Corticopontine (travel with, not neccesarily part of)

Vestibulospinal, reticulospinal, rubrospinal (Coma and Posturing)

Sympathetic Pathways in lateral brainstem (Vulnerable to lesions that affect lateral brainstem) * Ipsilateral Horner Syndome

Only corticospinal go down to level of decussation

Question 11

What is the Descending Sympathetic Pathways vulnerable to?

Answer 11

Lesions of lateral brainstem

Ipsilateral Horner’s Syndrome

Question 12

Dorsal Column/Medial Lemniscus

Function?

Structure?

First Synapse?

Decussation?

Answer 12

Fine Touch (two point discrimination), Vibration, Conscious Proprioception (joint-position)

Large Diamete afferent fibers enter CNS, ascend Fasciculus Gracilus (medial), Fasciculus Cuneatus (lateral)

First Synapse: Caudal Medulla in dorsal column nuclei

2^o fibers decussate in caudal medulla and form medial lemniscus (extending entire brainstem)

Question 13

What occurs do the Dorsal Column/Medial Lemniscus as the fibers ascend?

Answer 13

Location and orientation shift w/ascension, orientation will begin to shift in pons

From bottom to top–goes superficial to deep, and vertical to horizontal

Question 14

What level does CN V enter the dorsal column?

Answer 14

Enters midpons

Fine touch, vibration, conscious proprioception are relayed by mesencephalic and main sensory nuclei of CN V

Most axons of 2⁰ neurons cross in mid pons and join medial lemniscus

Question 15

What occurs to the somatotopic representation of the Dorsal column as it ascends?

Answer 15

It rotates and moves deeper and to the right

Question 16

Where do second order neurons synapse in the Dorsal column pathway?

Answer 16

Ventral posterior nuclei of thalamus

Third order then relay to sensory cortex through internal capsule

Question 17

Anterolateral System

Functions?

Orientation?

Organization?

Answer 17

Function: Carriers sensory information about pain, temperature, crude touch

Orientation: Maintains lateral pistion while ascending brainstem

Organization: Small Diameter afferents from body enter CNS and synapse in dorsal (posterior) horn. 2^o neurons cross (decussate) and ascend in contralateral anterior/lateral white matter

Small diameter afferents from face enter CNS and synapse in spinal trigeminal nucleus; second order joining in pons

Question 18

Where do collaterals of second order neurons synapse in the anterolateral system?

What is their function?

Answer 18

Synapse occurs in the Reticular Formation of periaqueductal Grey

Important for modulation of pain

Question 19

What is the location of the Anterolateral System as it ascends the brain?

Answer 19

Orientation stays the same, moves from superficial to deep from a lateral position

Converges with Medial Lemniscus in midpons

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Anterolateral system will rotate to the posterior lateral position