Internal Anatomy of the Brainstem 1

Question 1

What is the reticular formation?

Answer 1

Diffuse network of loosely packed neurons without distinct boundaries, forming central core of brainstem

Question 2

What critical functional areas does the reticular formation contain?

Answer 2

Arousal

Sleep/wake cycle

Pain

Motor function

Respiratory/Cardiovascular

Question 3

What pattern generator circuits does the reticular formation contain?

Answer 3

Conjugate eye movements

Chewing

Swallowing

Vomiting

Breathing

Locomotion

Question 4

What kind of information is carried in the dorsal column/medial lemniscus pathway?

Answer 4

Fine touch (two-point discrimination)

Vibration

Conscious propioception

Question 5

Where is the first central synapse in the medial lemniscal pathway?

Answer 5

Afferents traveling in the fasciculus gracilus synapse in the nucleus gracilus

Afferents traveling in the fasciculus cuneatus synapse in the nucleus cuneatus

Question 6

Describe the pathway of second order neurons from the medial lemniscal pathway

Answer 6

Travel ventrally and decussate at the level of the nuclei, then they ascend, forming the medial lemniscus

Question 7

How do somatosensory afferents from the face join the medial lemniscal pathway?

Answer 7

They enter through the chief sensory nucleus

From there, second order neurons cross in the mid-pons and join the medial lemniscus

Question 8

What is the trigeminal lemniscus?

Answer 8

Second order sensory fibers from the face

Question 9

How does the orientation of the medial lemniscus shift?

Answer 9

Dorsal to ventral in the lower medulla

Medial to lateral orientation in the mid-pons

Ventromedial orientation in the midbrain

Question 10

What type of information does the anterolateral system carry?

Answer 10

Pain, temperature, and crude touch

Question 11

Where does the anterolateral pathway decussate?

Answer 11

Level of entry in the spinal cord

Question 12

What is the pathway of anterolateral nerves from the face?

Answer 12

Enter the brainstem through the trigeminal nerve

Descen ipsilaterally through the spinal trigeminal tract to the appropriate somatotopic level, then synapse on second order neurons

Question 13

Describe the corticospinal pathway

Answer 13

Originates in the motor cortical areas

Travels through the internal capsule into the crus cerebri, through the basal pons and then forms the pyramids with the corticobulbar pathway

Question 14

Where do the corticobulbar fibers terminate?

Answer 14

One of the brainstem motor nuclei to regulate LMNs for CNs V, VII, IX, X, or XII

Question 15

What are the two exceptions to bilateral corticobulbar innervation?

Answer 15

LMNs for the lower half of the face only receive contralateral input

LMNs innervating the genioglossus muscle only receive contralateral input

Question 16

What results from a unilateral lesion of UMNs targeting the facial motor nucleus?

Answer 16

Weakness of the lower half of the face on the contralateral side

Question 17

What results from a unilateral lesion of UMNs targeting the hypoglossal nucleus?

Answer 17

Contralateral weakness of the genioglossus

Tongue deviates tot he weak side, contralateral to the lesion

Question 18

Describe the pathway of corticopontine fibers

Answer 18

Originate from all four lobes of the cerebral hemispheres

Fibers descend to the level of the pons where they synapse on neurons in the grey matter of the basal pons

Pontine nuclei axons cross the midline and reach the contralateral cerebellum

Question 19

What is the medial longitudinal fasciculus?

Answer 19

Well defined pathway that links nuclei controlling the extraocular muscles with horizontal and vertical gaze centers, the vestibular nuclei, and the spinal cord

Question 20

What functions does the medial longitudinal fasciculus support?

Answer 20

Cinjugate horizontal eye movements

Vestibulo-ocular reflexes

Vestibulo-spinal reflexes

Question 21

What are the functions of the two vestibulospinal pathways?

Answer 21

Maintain posture against gravity, reflexive adjustments in motor function in response to vestibular signals

Question 22

What is the pathway and function of the medial vestibulospinal pathway?

Answer 22

Originates in the medial vestibular nucleus and descends bilaterally in the medial longitudinal fasciculus

Facilitates reflexes and tone for muscles of the neck

Question 23

What is the pathway and function of the lateral vestibulospinal pathway?

Answer 23

Originates in the lateral vestibular nucleus and descends uncrossed in the anterior funiculus to all levels of the spinal cord

Facilitates reflexes and tone for extensor muscles

Question 24

What is the pathway and function of the pontine reticulospinal pathway?

Answer 24

Descends uncrossed in the medial longitudinal fasciculus, then enters the anterior funiculus and innervates all spinal levels

Facilitates voluntary and reflexive activity of axial and limb muscles

Question 25

What is the pathway and function of the medullary reticulospinal pathway?

Answer 25

Descends uncrossed posterior to the inferior olives, enters the anterior funiculus of the spinal cord, innervating all spinal levels

Inhibits voluntary and reflex activity of axial and limb muscles

Question 26

What is the pathway and function of the tectospinal pathway?

Answer 26

Originates in the superior colliculi, decussate and descends anterior to the medial longitudinal fasiculus

Functions thought to be coordination of head and eye movements, stimulation of reflex movements in response to visual stimuli

Question 27

What is the pathway and function of the rubrospinal pathway/

Answer 27

Originates in the red nucleus located in the midbrain tegmentum

Fibers decussate and descen through the lateral medulla into the lateral funiculus

Projects to the cervical and thoracic levels, facilitates flexor muscles and inhibits extensors for the upper limbs

Question 28

What is the cause and result of decorticate posturing?

Answer 28

Typically caused by a large lesion of cerebral hemispheres that causes a loss of cortical input.

Results in upper limb flexion and lower limb extenstion

Question 29

What is the cause and result of decerebrate posturing?

Answer 29

Large lesion of the cerebral hemispheres that expand into the midbrain, and rostral pons

Loss of activity of rubrospinal pathway

Upper and lower limb extension

Question 30

Why do lesions affecting the anterolateral system also tend to cause horner’s syndrome?

Answer 30

The descending sympathetic pathway has a lateral location in the brains stem, close to the anterolateral system