1 - Internal Anatomy of Brainstem (Cerebellum, Olfactory, Eye Movement, Respiration) Flashcards
Cerebella Peduncles functions?
Inferior
Middle
Superior
Inferior Cerebellar Peduncle (Restiform body): Medulla
- Major input pathway for most ascending somatosensory information, input form inerior olive
Middle Cerebellar Peduncle (brachium pontis): Pons
- Input from pontine nuclei
Superior Cerebellar Peduncle (brachium conjunctivum): Pons, Midbrain
- Output pathways from cerebellum
Dorsal (posterior) Spinocerebellar Tract
Function?
Route?
Function: Somatic sensation (uncoiscious proprioceptions) from lower limbs, trunk
Route: Primary (sensory) acons ascend gracile fasciculus, synapse in Clark’s Nucleus, 2o fibers run in dorsal spinocerebellar tract (lateral funiculus), remain lateral through medulla to inferior cerebellar peduncle
Cuneocerebellar Tract
Function?
Upper limb equivalent of dorsal spinocerebellar pathways
Uncrossed pathway, ascend Cuneate Fasciculus, Synapse in accessory cuneate nucleus, 2o fibers enter inferior cerebellar peduncle
Ventral (anterior) Spinocerebellar Tract
“Double Crossed” Pathway (Double Decussation)
Origin: Spinal interneurons (intermediate grey) - lumbar, lower thoracic level
Axons cross in ventral commissure, ascene in ventral spinocerebellar tract
Enter superior cerebellar peduncle and cross AGAIN to reach ipsilateral cerebellum
Olivocerebellar Pathway
Origin: Inferior Olivary Nuclei
Fibers cross, enter cerebellum through inferior cerebellar peduncles
Vestibulocerebellar pathway
Origin: Primary vestibular afferents and acons of secondary vestibular neurons
Enter cerebellum through inferior cerebellar peduncles (juxtarestiform body)
Corticopontine Pathway
Function?
Origin?
Function: Major input from motor, somatosensory, visual cortex–from most of cerebral cortex
Coordination of movements that we are conscious to
Pontocerebellar fibers cross and enter contralateral middle cerebellar peduncle to reach cerebellum
Cerebellar Output
Mostly occurs through the superior cerebellar peduncle
Fibers cross at inferior colliculi, project to red nuclei, and ventrolateral thalamus (VL)
**Some output from vestibular cerebellum goes through inferior peduncles
Clinical: Lesion of Cerebellar Peduncle
Produce signs/symptoms similar to cerebellar injury
Ataxia: Uncoordinated movements w/disordered contraction of agonist / antagonist muscles
Dysmetria: Over or under shooting of intended movements
Vertigo / Nausea if vestibular nuclei or vestubular connection to cerebellum affected
Gustatory Pathway
Afferents from CN VII, IX, X project to rostral solitary nucleus
2o fibers provide input to autonomic nervous system by projecting to:
Dorsal motor nucleus of X
Reticular formation/preganglionic sympathetic neurons in spinal cord
Ascending Pathway to Primary Gustatory Cortex
Pathway?
Conscious sensation in Gustatory Pathway
Pathway:
Central Tegmental Tract
Thalamus (VPM)
Insula, frontal operculum
Gustatory information also reaches hypothalamus (metabolic regulation, hunger, satiety) amygdala (emotional response to food)
Location of LMNs for extraocular muscles?
Types of eye movements?
Saccade
Smooth Pursuit
VErgence
Reflexive
Oculomotor, Trochlear, and Abducens Nuclei
Saccade: Very rapid (700 deg/s), voluntary movements to direct vision to objects of interest
Smooth Pursuit: Rapid (100 deg/s), non-voluntary to allow stable vision of moving objects
Vergence: Slower (20 deg/s) maintain vision for objects moving towards or away
Reflexive (OKR, VOR): Triggered by object movement (OKR) or head movement (VOR)
Generation of Horizontal eye movements?
How are conjugate eye movements accomplished?
What acts as the control center for horizontal gaze?
Horizontal movements are generated by Lateral Rectus (abducens nucleus) and medial rectus (oculomotor nucleus)
Medial Longitudinal Fasciculus (MLS) connects these nuclei to allow conjugate movements
Abducens functions as control center for horizontal gaze
Paramedian Pontine Reticular Formation (PPRF)
Location?
Function?
Location: Pontine tegmentum (reticular formation) near abducens nucleus
Higher level horizontal gaze center, receives input from higher level eye movement control centers
Projects to ipsilateral abducens
Triggers ipsilateral horizonal gaze
Clinical: Lesion of Abducens Nerve
Impaired abduction of ipsilateral eye
- Looking straight ahead with ipsilateral eye when attempting to look towards lesion
Clinical: Lesion of Abducens Nucleus
Ipsilateral gaze palsy (both eyes affected)
Cause: Loss of connection (via MLF) by contralateral oculomotor nucleus
Both eyes look straight ahead when attempting to look toward lesion
Clinical: Lesion of Paramedian Pontine Reticular Formation (PPRF)
Causes ipsilateral gaze palsy (both eyes affected)
Prevents gaze toward lesion in both eyes (same as Abducens NUCLEUS)
Clinical: Lesion of Medial Longitudinal Fasciculus (MLF)
Faiure of adduction in ipsilateral eye
Abduction in contralateral accompanied by nystagmus (rhythmic oscillating eye movement)
Intranuclear Ophthalmoplegia (INO)
***MLF = Nystagmus (INO) contralateral of lesion***
Clinical: What may be spared in lesions of MLF?
Eye adduction may be spared during convergence
LMNs for medial rectus are intact
These movements are “programmed” by control center in midbrain
Clinical: Lesion of Abducens (or PPRF) + MLF
Combinaytion of ipsilateral lateral gaze palsy + INO
One-and-a-half Syndrome
Symptoms:
- Ipsilateral eye can’t move horizontal (loses ALL horizontal movement, “one”)
-
Contralateral eye can only abduct (the “half”)
- - -
Contralateral eye may have Nystagmus when looking away from lesion
***Key difference is IPSILATERAL eye can’t move horizontal AT ALL***
Brainstem circuits for vertical eye movements:
Mediated by what regions/muscles?
Muscles: Superior / Inferior Rectus, Superior / Inferior Oblique
Regions: Midbrain Reticular Formation, Pretectal Area
Clinical: Lesion of dorsal midbrain
Clinical: Lesion of ventral midbrain
Dorsal - May impair upgaze
Ventral - May impair downgaze
Ex: Pineal Tumor, Hydrocephalus
Frontal Eye Fields
Project to?
Movements generated?
Clinical: Lesion?
Project to contralateral PPRF
Movements: Saccades in contralateral direction
Lesion: Gaze Preference towards side of lesion
Receive input from visual cortical areas
Parietal-Occipital-Temporal Area
Connect to?
Movements Generated?
Connect to: PPRF, other eye movement control centers
Movements Generated: Smooth Pursuit in ipsilateral direction
Receive input from visual cortical areas
Respiratory Control (not in brainstem)
Medulla
Pons/Midbrain
Forebrain
Caudal Solitary Nucleus
Pre-Bötzinger Complex
Medulla: Automatic g_eneration of respiratory rhythms_ (inspiration/expiration); project to cervical and thoracic spinal levels to LMNs
Rostral Pons/Midbrain: Respiratory rhythm modulation
Forebrain: Can override, and exert voluntary control
Caudal Solitary Nucleus: Receives visceral sensory input (O2, pH in blood)
Pre-Bötzinger Complex: Pacemaker center for respiration; ventro-lateral medullary reticular formation
Clinical: Damage to medulla and respiration
Damage to medulla may disrupt respiration
Respiratory Arrest (central apnea) and death
Ataxic respiration (irregular breathing), may progress to respiratory arrest
Clinical: Lesions of Kölliker-Fuse Area
Apneustic Respiration (breif respiratory pauses at full inspiration)
Respiration:
Inpspiration Centers
Expiration Centers
Modulation Centers
Inspiration: Pre-Bötzinger Complex, Rostral Ventral Respiratory Group, Phrenic Nerve, Thoracic Inpspiratory Nerve, Dorsal Respiratory Group
Expiration: Bötzinger Complex, Caudal Ventral Respiratory Group, Thoracic Expiratory Nerve
Modulation: Kölliker-Fuse Area, Nucelus Solitarius
Clinical: What can be compressed in tonsillar herniation?
Respiratory centers in medulla
Inspiration, Expiration, and Modulation all at risk
