Internal Anatomy of the Brainstem 1 Flashcards
What is the reticular formation?
Diffuse network of loosely packed neurons without distinct boundaries, forming central core of brainstem
What critical functional areas does the reticular formation contain?
Arousal
Sleep/wake cycle
Pain
Motor function
Respiratory/Cardiovascular
What pattern generator circuits does the reticular formation contain?
Conjugate eye movements
Chewing
Swallowing
Vomiting
Breathing
Locomotion
What kind of information is carried in the dorsal column/medial lemniscus pathway?
Fine touch (two-point discrimination)
Vibration
Conscious propioception
Where is the first central synapse in the medial lemniscal pathway?
Afferents traveling in the fasciculus gracilus synapse in the nucleus gracilus
Afferents traveling in the fasciculus cuneatus synapse in the nucleus cuneatus
Describe the pathway of second order neurons from the medial lemniscal pathway
Travel ventrally and decussate at the level of the nuclei, then they ascend, forming the medial lemniscus
How do somatosensory afferents from the face join the medial lemniscal pathway?
They enter through the chief sensory nucleus
From there, second order neurons cross in the mid-pons and join the medial lemniscus
What is the trigeminal lemniscus?
Second order sensory fibers from the face
How does the orientation of the medial lemniscus shift?
Dorsal to ventral in the lower medulla
Medial to lateral orientation in the mid-pons
Ventromedial orientation in the midbrain
What type of information does the anterolateral system carry?
Pain, temperature, and crude touch
Where does the anterolateral pathway decussate?
Level of entry in the spinal cord
What is the pathway of anterolateral nerves from the face?
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
Describe the corticospinal pathway
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
Where do the corticobulbar fibers terminate?
One of the brainstem motor nuclei to regulate LMNs for CNs V, VII, IX, X, or XII
What are the two exceptions to bilateral corticobulbar innervation?
LMNs for the lower half of the face only receive contralateral input
LMNs innervating the genioglossus muscle only receive contralateral input
What results from a unilateral lesion of UMNs targeting the facial motor nucleus?
Weakness of the lower half of the face on the contralateral side
What results from a unilateral lesion of UMNs targeting the hypoglossal nucleus?
Contralateral weakness of the genioglossus
Tongue deviates tot he weak side, contralateral to the lesion
Describe the pathway of corticopontine fibers
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
What is the medial longitudinal fasciculus?
Well defined pathway that links nuclei controlling the extraocular muscles with horizontal and vertical gaze centers, the vestibular nuclei, and the spinal cord
What functions does the medial longitudinal fasciculus support?
Cinjugate horizontal eye movements
Vestibulo-ocular reflexes
Vestibulo-spinal reflexes
What are the functions of the two vestibulospinal pathways?
Maintain posture against gravity, reflexive adjustments in motor function in response to vestibular signals
What is the pathway and function of the medial vestibulospinal pathway?
Originates in the medial vestibular nucleus and descends bilaterally in the medial longitudinal fasciculus
Facilitates reflexes and tone for muscles of the neck
What is the pathway and function of the lateral vestibulospinal pathway?
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
What is the pathway and function of the pontine reticulospinal pathway?
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
What is the pathway and function of the medullary reticulospinal pathway?
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
What is the pathway and function of the tectospinal pathway?
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
What is the pathway and function of the rubrospinal pathway/
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
What is the cause and result of decorticate posturing?
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
What is the cause and result of decerebrate posturing?
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
Why do lesions affecting the anterolateral system also tend to cause horner’s syndrome?
The descending sympathetic pathway has a lateral location in the brains stem, close to the anterolateral system
