Lecture 12-Midbrain Flashcards
What is the unique pathway of the trochlear nucleus in the brainstem?
The trochlear nucleus features a distinctive pathway where its fascicles leave laterally, wrap around the periaqueductal gray (PAG) matter, decussate, and exit below the inferior colliculus in the rostral pons or caudal midbrain.
Which cranial nerve has the only dorsal exit?
The trochlear nerve (CN IV) is the only cranial nerve with a dorsal exit.
What is the primary muscle innervated by the trochlear nucleus, and what kind of eye movement does it control?
The trochlear nucleus primarily innervates the superior oblique muscle of the eye, leading to a “down and out” turning movement.
What is the pathway of efferent projections to the eyes?
Efferent projections to the eyes rise through the Medial Longitudinal Fasciculus (MLF) to reach the oculomotor nuclear complex
Oculomotor Nuclear Complex
Includes the oculomotor nuclei and Edinger-Westphal nuclei.
How do the oculomotor nuclei project and where do they exit?
The oculomotor nuclei project ventrally and exit at the ventral boundary of the pons and midbrain.
Which extraocular muscles do the oculomotor nuclei project to?
The oculomotor nuclei project to four out of the six extraocular muscles: superior, inferior, and medial rectus muscles, as well as the inferior oblique muscle. They also project to the levator palpebrae muscle.
What muscles does the oculomotor nuclei not project to?
The muscles they do not innervate are the lateral rectus muscle and the superior oblique muscle. These muscles are primarily controlled by the abducens nerve (CN VI) and the trochlear nerve (CN IV), respectively
What are the two distinct populations of neurons in the Edinger-Westphal (EW) nuclei?
Consist of two distinct populations of neurons: EW preganglionic parasympathetic (EWpg) neurons and EW centrally-projecting (EWcp) neurons.
What is the primary function of EW preganglionic parasympathetic (EWpg) neurons?
EWpg neurons follow the oculomotor nerve to innervate the sphincter pupillae and ciliary muscles, controlling pupil dilation and accommodation.
Where do EW centrally-projecting (EWcp) neurons project?
EW centrally-projecting (EWcp) neurons project to various nuclei in the brain and spinal cord, playing a role in a range of fdiplpunctions beyond pupillary and ciliary muscle control.
What information does the superior colliculus receive?
1) afferent fibres from retina,
2)corticotectal fibres from FEF (tracking moving object)
3) Corticotectal fibres from visual cortex (accommodation)
4) Auditory information from inferior colliculus (audiovisual reflexes)
Which structure in the auditory system is associated with dorsal nuclei and commissure?
The inferior colliculus is associated with dorsal nuclei and commissure in the auditory system.
Where do the efferent projections from the brachium of the inferior colliculus extend to?
The efferent projections from the brachium of the inferior colliculus extend to the superior colliculus and the medial geniculate nucleus in the thalamus.
What is the pathway of afferent projections to the inferior colliculus in the auditory system?
Afferent projections to the inferior colliculus originate from various auditory nuclei in the pons and medulla and travel up the lateral lemniscus.
What is the general role of the tectum across different species?
The tectum is involved in localizing and responding to stimuli in body-centered space.
Where do cerebellorubral fibers originate and terminate?
Cerebellorubral fibers come from the superior cerebellar peduncle and terminate in the red nucleus.
Do the superior cerebellar peduncles decussate as they move from the rostral pons to the caudal midbrain?
Superior cerebellar peduncles decussate as they move from rostral pons to caudal midbrain
What areas are damaged by Medial medullary syndrome?
Damage to corticospinal tract, medial lemniscus
What areas are damaged by Ataxic hemiparesis syndrome?
Damage to corticospinal tract, pontine nuclei
Medial midbrain syndrome damages which areas?
damage to oculomotor nerve
Medial Medullary Syndrome Effects
Contralateral effects: Damage to the corticospinal tract results in weakness or paralysis on the opposite (contralateral) side of the body.
Ipsilateral effects: Damage to the medial lemniscus can cause loss of tactile and proprioceptive sensations on the same (ipsilateral) side of the body.
Ataxic Hemiparesis Syndrome Effects:
1)Contralateral effects: Damage to the corticospinal tract leads to weakness or paralysis on the opposite (contralateral) side of the body.
2) Ipsilateral effects: Damage to the pontine nuclei may cause coordination and balance problems on the same (ipsilateral) side of the body.
Medial Midbrain Syndrome Effects:
Ipsilateral effects: Damage to the oculomotor nerve typically leads to eye movement problems on the same (ipsilateral) side of the body. For example, if the right oculomotor nerve is affected, the right eye may have difficulty moving.
What is the location of the tectum in the brainstem?
The tectum is located from the dorsal surface to approximately the cerebral aqueduct.
What part of the brainstem is situated between the cerebral aqueduct and the substantia nigra?
The tegmentum occupies the space between the cerebral aqueduct and the substantia nigra.
What does the basis pendunculi comprise, and what larger structure does it contribute to?
The basis pendunculi consists of the substantia nigra and the crus cerebri. Together with the tegmentum, it forms the cerebral peduncle.
Which structures make up the tectum in the brainstem?
Superior and interior colliculus
What is the primary function of the substantia nigra in the brain?
The substantia nigra is responsible for subconscious control of movement.
What tracts are associated with the crus cerebri in the brainstem?
The crus cerebri contains the descending tracts, including the corticospinal, corticonuclear, and corticopontine tracts.
Where is the Medial Longitudinal Fasciculus (MLF) typically located within the midbrain?
The MLF is typically located dorsally within the midbra
What role does the Medial Longitudinal Fasciculus (MLF) play in the midbrain?
The MLF plays a crucial role in coordinating eye movements and is involved in maintaining stable visual focus during head and body movements.
What type of sensory information does the Medial Lemniscus (ML) carry?
The Medial Lemniscus (ML) carries sensory information related to touch and proprioception.
Where is the Medial Lemniscus (ML) positioned in relation to the Medial Longitudinal Fasciculus (MLF) within the midbrain?
The Medial Lemniscus (ML) is positioned below the MLF within the midbrain.
What is the primary function of the Spinothalamic Tract (ALS) within the midbrain?
The Spinothalamic Tract (ALS) is responsible for transmitting pain and temperature sensations.
Brachium of Inferior Colliculus:
Branches of white matter that carry auditory information from the inferior colliculus to the medial geniculate nucleus in the thalamus.
Mesencephalic Trigeminal Tract/Nucleus
It conveys proprioceptive information from the face, particularly the jaw and teeth.
Dorsal Trigeminothalamic Tract
It transmits sensory information related to touch, pressure, and proprioception from the face to the thalamus.
Ventral Trigeminothalamic Tract:
It carries pain and temperature sensations from the face to the thalamus.
Why is there a swelling at the tubercuelum gracilis? what causes it?
The swelling at the tuberculum gracilis is due to the concentration of sensory nerve fibers entering the medulla to relay sensory information to the brain
