export_brainstem Flashcards
The midbrain is comprised of what structures?
The tectum, tegmentum and crus cerebri
What are the structures found in the midbrain at the level of the superior colliculus?
- Superior colliculus
- Oculomotor nucleus
- Red nucleus
- Superior cerebellar peduncle
- Substantia nigra
Unilateral damage to the superior colliculus produces:
Contralateral visual field neglect.
Impaired tracking, but with no deficit in eye movements.
Stimulation of the superior colliculus produces what?
Contralateral conjugate deviation
- Stimulates rostral interstitial nucleus of the MLF to excite the ipsilateral 3rd cranial nerve.
- Contralateral CN 6 via the PPRF
Input to the superior colliculus
- Contralateral retina
- Cortex - frontal, parietal, temporal and occipital
- Brainstem nuclei
- Spinal cord
Output of the superior colliculus
Parabigeminal nucleus
Pulvinar
LBG
PPRF
RiMLF - rostral interstitial nucleus of the MLF
Reticular formation
Spinal cord
What are the three portions of the oculomotor nucleus.
- Lateral part
- Medial part
- Central part
Lateral portion of the CN3 nucleus
Ipsilateral cell columns for inferior rectus, inferior oblique, and medial rectus muscles
Medial part of the CN 3 nucleus
Contralateral cell columns for the superior rectus muscle
Central part of the CN 3 nucleus
Cell columns for the levator palpebrae superioris and the Edinger-Westphal nucleus.
Input to the CN3 nucleus
Nucleus of Cajal
Contralateral abducens nucleus
Perihypoglossal nucleus
RiMLF
Pretectal olivary nucleus
Flocculus via the nucleus prepositus to control vertical eye movements.
The PPRF projects to
The abducens nucleus (conjugate horizontal gaze center) and the RiMLF (conjugate vertical gaze center)
The RiMLF input and output
Input: Superior vestibular nucleus and PPRF
Output: Oculomotor complex/inferior rectus portion.
Role of the interstitial nucleus of Cajal
Function: vertical eye movements, pursuit, head movements and posture.
Input: Superior and medial vestibular nuclei, pretectum, FEF and fastigial nuclei.
Output: Ipsilateral medial vestibular nuclei and spinal cord. Trochlear nuclei. Contralateral oculomotor nuclei.
What are the subcommissural organs
Modified ependymal cells in the aqueduct below the posterior commissure which lack a BBB.
What is the posterior commissure
White matter tract which lies posterior to the aqueduct at the junction of the midbrain/diencephalon. It is involved with the light reflex. Contains fibers from the pretectal nuclei, nucleus of the posterior commissure, interstitial nuclei and Darkshevich’s nucleus.
Nuclei in the pretectal region are involved with..
Pupillary light reflexes.
Role of the inferior colliculus
The inferior colliculus is responsible for the tonotopic organization of auditory information and projects via the brachium of the inferior colliculus to the MGB.
Key structures in the midbrain at the level of the inferior colliculus include
- Inferior colliculus
- Parabigeminal area
- Periaqueductal gray
- Interpeduncular nucleus
Role of the parabigeminal area
Connects to the visual system via the superior colliculus.
Located ventrolateral to the inferior colliculus.
Components of the periaqueductal gray
- Mesencephalic nucleus of 5.
- Locus ceruleus
- Ventral and dorsal tegmental nuclei
- Dorsal nucleus of the raphe
- Medial nucleus of the raphe
Function and connections of the periaqueductal gray
Function: Central analgesia, vocalization, control of reproductive behavior, aggressive behavior and upward gaze.
Connections: Hypothalamus, spinal cord, locus ceruleus, raphe nucleus, reticular formation.
Features of the interpeduncular nucleus
- Located just dorsal to the interpeduncular fossa.
- Input: habenular nucleus via the fasciculus retroflexus
- Output: diffuse cholinergic fibers to the CNS.
What is the midbrain tegmentum
This is the ventral surface of the midbrain, containing the reticular formation and tracts, periaqueductal gray(surrounding the cerebral aqueduct), substantia nigra, red nucleus, CN3 and CN4 nuclei.
Where is the red nucleus located and what fibers run through it?
It is located in the reticular formation.
Fibers of CN3 and the superior cerebellar peduncle run through it.
Input to the red nucleus
- Deep cerebellar nuclei: rostral 1/3 from the dentate and cadual 2/3 from the interposed. These fibers exit via the SCP and cross to the contralateral side in the midbrain to get to the red nucleus.
- Motor Cortex: Pre-central, pre-motor, supplementary motor and motor cortex
Output of the red nucleus
- Contralateral cervical and lumbar spine via the rubrospinal tract
- Contralateral nucleus interpositus, facial nucleus and medulla via the ventral tegmental tract.
- Ipsilateral inferior olivary nucleus via uncrossed central tegmental tract
Role of the red nucleus
Maintains flexor muscle tone
Key components of the pons
- Reticular formation
- Isthmus rhobencephali
- Locus ceruleus
Role, input and output of the pedunculopontine nuclei.
Located in the lateral tegmentum ventral to the inferior colliculus. Controls locomotion and walking movements.
Input from the cortex, mGP, and SNpr.
Output to the thalamus and SNpc (ACH output)
Where is the substantia nigra located?
Between the crus cerebri and the midbrain tegmentum
Features of the SNpc and SNpr
SNpc -> contains large cells, and its neurotransmitters are dopamine and CCK.
SNpr - > contains fewer cells, lies ventral to the SNpc and its neurotransmitters are GABA and 5HT.
Input to the substantia nigra
- Caudate
- Putamen
- Lateral GP
- Subthalamus
- Dorsal raphe nucleus
- Pedunculopontine nucleus
Output of the substantia nigra
- SNpc -> striatum
- SNpr -> VA and MD thalamus
- SNpr -> Superior colliculus and pedunculopontine nucleus
The crus cerebri contain the….
Corticospinal, corticobulbar and corticopontine tracts.
Lower extremities located laterally.
Extreme medial and lateral ends of the crus cerebri contain the corticopontine tracts.
What are the key components of the pons
- Pontine reticular formation
- Isthmus rhombencephali
- Locus ceruleus
Where is the reticular formation located?
Pons and the medulla
What is the role of the reticular formation
It is involved with wakefulness, muscle tone, respiration, blood pressure regulation, and sensory transmission.
What are the four zones of the reticular formation?
- Median zone
- Paramedian zone
- Medial zone
- Lateral zone.
Median zone of the reticular formation
- Contains the raphe nucleus
The dorsal and median raphe nuclei send fibers to the ventral tegmental tract -> median forebrain bundle-> hypothalamus, striatum, thalamus, amygdala, hippocampus, cortex and olfactory bulb.
Paramedian zone of the reticular formation
Input: cortex
Output: cerebellum
The medial zone of the reticular formation
The effector zone with ascending and descending fibers.
Features of the locus ceruleus
It is pigmented by melanin.
It uses norepinephrine as its neurotransmitter and projects widely.
It controls cortical activation and paradoxical/rapid eye movement sleep.
Major structures in the medulla at the level of the olivary nuclei
- Floor of the fourth ventricle
- Inferior olivary complex
- Medullary reticular formation
- Raphe nuclei
- Tracts
- Inferior cerebellar peduncles.
Features of the floor of the fourth ventricle. (The eminences)
Contains three eminences
1. Hypoglossal eminence over the CN12 nucleus
- Intermediate eminence over the dorsal motor nucleus of 10.
- Lateral eminence over the area vestibularis
The roof of the fourth ventricle contains…?
The roof of the fourth ventricle contains the tela choridea, and the choroid plexus which lie in the inferior medullary velum.
Features of the inferior olivary complex
- Contains the principal olivary nucleus which sends efferents to the cerebellar hemispheres.
- Contains the medial and dorsal accessory olivary nuclei which send fibers to the vermis.
- Contains the olivocerebellar fibers which cross to the inferior cerebellar peduncles.
Features of the medullary reticular formation
Afferent fibers from the cortex, deep cerebellar nuclei and cranial nerves.
Output to the gigantocellular reticular nucleus.
What do the rostral and caudal fibers of the reticulospinal tract do
- Rostral fibers: stimulate lower motor neurons.
2. Caudal fibers: inhibit lower motor neurons.
Features of the raphe nucleus
It extends from the midbrain to medulla and uses serotonin, CCK and enkephalin as neurotransmitters.
Provides endogenous analgesia via the substantia gelatinosa and controls deep sleep, mood and aggression.
Nucleus magnus projects to layers 1 and II of the spinal cord to inhibit pain. Less firing of the nucleus magnus = less arousal, destruction of the nucleus magnus -> insomnia.
What tracts run in the medulla at the level of the olivary nuclei
- Medial lemniscus
- Spinothalamic tract
- Dorsal spinocerebellar tract -> inferior peduncle
- Ventral spinocerebellar tract -> superior cerebellar peduncle, MLF, rubrospinal, rubrobulbar and vestibulospinal tracts.
Inferior cerebellar peduncles
Carries fibers from the spinal cord and medulla to the cerebellum.
The majority of these fibers are crossed olivocerebellar fibers and some uncrossed dorsal spinocerebellar tracts.
What are the four features of the spinomedullary junction
- Decussation of the pyramids
- Termination of the fasciculi gracilis and cuneatus
- Replacement of Lissauer’s zone by the spinal trigeminal tract
- Replacement of the spinal gray by the reticular formation and cranial nerve nuclei
What is the area postrema
Area in the floor of the fourth ventricle above the obex.
It is a chemoreceptor, sensitive to apomorphine, and digitalis with afferent fibers from the spinal cord and nucleus solitarius
The spinal trigeminal tract and nucleus receives input from which cranial nerves
5,7,9, and 10
Features of the corticospinal decussation
Anterior corticospinal tract travels in the anterior fasciculus uncrossed.
Lateral corticospinal tract travels in the dorsolateral fasciculus, crossed.
Relationship of the posterior circulation arteries to the lower cranial nerves
- SCA -> passes under CN 3, and 4. Passes above CN 5.
- AICA -> passes CN 6, 7, and 8.
- PICA -> Passes CN 9, 10, 11 and 12.
