Pons and Cerebellum
Terms in this set (38)
-Serves as connection between the midbrain and medulla
Divided into 2 regions
Basilar Pons (ventral)
- has 2 different groups of fibers and neurons
- One group is throughout the dorsoventral and rostrocaudal basilar pons - transverse pontine fibers (frontocerebellar) arise from neurons scattered throughout the basilar pons (deep pontine nuclei).
- The 2nd consists of corticospinal and corticobulbar fibers passing in a longitudinal manner and thus are perpendicular to the transverse pontine fibers.
- The sulcus in the midline of the basilar pons is called the basilar sulcus. It is formed by the basilar artery.
- The middle cerebellar peduncle, another massive fiber bundle found laterally is a continuation of the pontocerebellar fibers. Runs dorsolaterally into the cerebellum.
- Forms a bridge between the 2 structures
- Contain the corticospinal and corticobulbar tract which follow the longitudinal axis of the brainstem an perpendicular to the transverse pontine fibers
Corticonuclear (corticobulbar) fibers
- exit and terminate on interneurons of the reticular formation near cranial nerves motor nuclei such as the nuclei of the reticulospinal fibers
- forms the floor of the 4th ventricle and the roof of the pons.
- The facial colliculus, formed by the facial nerve (VII) as it passes over the dorsal region of the abducens nerve.
- The lateral walls of the 4th ventricle is formed by the superior cerebellar peduncles as they enter the brainstem from dorsolateral position at the level of the rostral pons
- Nuclei and fiber pathways can also be found in the tegmentum
- Nuclei associated with cranial nerves and other cranial nerves with sensory, motor, autonomic, and behavioral functions
- Fiber pathways are axons that may arise in the pons and run either dorsally or caudally.
- There are other ascending or descending fiber pathways which originate in the brainstem, spinal cord, other parts of the brainstem and forebrain
Pons- Fiber Pathways
Two of the most prominent ascending tracts include the - medial lemniscus
- medial longitudinal fasciculus (MLF)
-Other pathways including the spinothalamic and trigeminothalamic pathways that mediate somatosensory information from the body and head region to the ventral posterolateral and posteromedial nuclei of the thalamus.
-The are sandwiched between the medial and lateral lemniscus
- passes in a rostral direction within the pontine tegmentum and eventually synapse in the ventral posterolateral (VPL) of the thalamus
Medial Longitudinal Fasciculus (MLF)
- arises from the Vestibular nucleus (VN) and is thought to be involved in the maintenance of gaze
- Nuclei include the motor nuclei of the facial nerve (CN VII)
- Motor nuclei of the abducens nerve (CN VI),
the spinal nucleus of the trigeminal nerve (CN V)
- The superior olivary nucleus (relay nucleus of the auditory pathway)
- Raphe nucleus
- Pontine nucleus of the basilar pons
Main nucleus include
The main sensory, mesencephalic and motor nuclei of the CN V
The superior and lateral vestibular nuclei
The locus ceruleus
Other cell groups such as the pontine nuclei, and raphe nuclei are also present
The Locked-In Syndrome
- The is significant loss of function associated with both corticospinal and corticobulbar tracts when there is a large infarct of the basilar artery
There is paralysis of most motor function (limbs) and functions associated with motor cranial nerves other than the ability to blink one's eyes and display of vertical gaze.
Patient can only communicate by blinking or moving his or her eyes
The Medial Tegmental Syndrome
- Targets of medial pons lesions include the nucleus of CN VI, the fibers of the facial nerve which passes over the nucleus of CN VI and the medial lemniscus.
- Loss include ipsilateral facial paralysis,
loss of lateral gaze on the side ipsilateral to the lesion and contralateral loss of conscious proprioception and
Loss of discrimination touch if the lesion involve the medial lemniscus
The one and a half syndrome
- With a lesion of the dorsomedial tegmentum, the nucleus of CN VI, the pontine (lateral) gaze center of the paramedian pontine reticular formation and the MLF is affected
Combination of lateral gaze paralysis (CN VI) coupled with an internuclear ophthalamoplegia (an ability to gaze to the side of lesion)
Patient can't move the ipsilateral eye horizontally and contralateral eye can only be abducted
Pontine Tegmentun- Caudal Pons
- The abducens nucleus (CN VI) - Close to the floor of the 4th ventricle. Serves as a general somatic efferent (GSE-lower motor neuron) which innervates the lateral rectus muscle and lateral movement of the eye.
- Facial nucleus (CN VII) - Lies in the ventrolateral tegmentum and has axons (special visceral efferent-SVE) which pass over the abducens nucleus and forming the facial colliculus.
-They then exit the brain to innervate the muscle that control the ipsilateral facial expression
Pontine Tegmentum- Dorsolateral
- Superior and lateral vestibular nuclei
- Receives direct inputs from the vestibular apparatus and contribute fibers to the MLF.
- Axons of the lateral vestibular nuclei form the lateral vestibulospinal tract
Auditory relay structures - trapezoid body (and nucleus of trapezoid body), superior olivary nucleus, and lateral lemniscus
- These nuclei are in the ventral region.
- The nucleus of the trapezoid body and the superior olivary nucleus receive auditory inputs primarily from the cochlear nuclei and transmit signals to high centers of the brainstem
- The trapezoid body is made up of commissural fibers which originate from either the ventral cochlear nucleus or superior olivary nucleus.
- The lateral lemniscus are fibers of the cochlear nuclei and superior olivary nucleus that transmit auditory signals to the inferior colliculus
Superior salivatory nucleus (GVE)
-is ventrolateral to the abducens nucleus
-Give rise to preganglionic parasympathetic axons of CN VII which innervate submandibular, submaxillary and pterygopalatine ganglia
- Serves to mediate lacrimation, salivation and vasodilation
Nuclei and fibers of the reticular formation
- Midline region contains the raphe nuclei (large-celled and small-celled regions) which produce serotonin.
- The cells project to many areas of the CNS.
- The large-celled regions give rise to ascending and descending fibers that extend to the central tegmental tract and the small-celled region serves as a source of inputs to the reticular formation
Rostral Pons structures
-Main sensory (trigeminal CN V) - This is a general sensory afferent (GSA) is large and in the dorsolateral region.
- Contains 2nd order neurons for the transmission of somatosensory information from the head region as its axons project to the ventral posteromedial nucleus of the thalamus
- Motor nucleus (CN V) - SVE projects axons to the muscles of mastication and plays a major role in closing the jaw
Nucleus locus ceruleus
- Contains norepinephrine -containing neurons which project to different cell groups in the brainstem, cerebellum and forebrain, including the cerebral cortex
Mesencephalic nucleus of CN V
- extends to the midbrain.
In the ventrolateral gray matter surrounding the rostral end of the 4th ventricle and the beginning of the cerebral aqueduct
Receives mainly muscle spindle afferents from the jaw and related areas of the face which serve as afferents for reflex closing of the jaw
Superior cerebellar peduncle
- Contain large majority of cerebellar efferent fibers to the midbrain and thalamus
Forms the lateral walls of the 4th ventricle
- Either side is attached by the superior medullary velum which forms the roof of the 4th ventricle
Rostrally, the superior cerebellar peduncle enters the pons and course towards the midline and in the caudal midbrain crosses over to the opposite side of the brainstem
- Most of the volume of the cerebellum is occupied by the laminated cerebellar cortex and its accompanying white matter
- In the mediolateral dimension, the cerebellum is divided into
the midline vermis ("worm")
the lateral cerebellar hemispheres
-Plays a major role in the integration of motor functions
Attached to the brainstem by the 3 cerebellar peduncles
- Inferior cerebellar peduncle
- Middle cerebellar peduncle
- Gyri of the cerebellar cortex
- extends from near the brainstem at its superior end, wrapping most of the way around the cerebellum in the sagittal plane, to end near the brainstem at its inferior end involved in coordination of the body midline (gait and balance)
- are involved in coordination of the most lateral body parts (arms and hands)
Damage to the Cerebellum
-causes deficits such as loss of balance, tremors, lack of coordination of muscles and reduced muscle tone
Inferior cerebellar peduncle
- Extends from the dorsolateral upper medulla to the brainstem. Carries most of the output of the cerebellar hemisphere
-generally contain cerebellar afferents fibers and superior peduncle has cerebellar efferent fibers.
Middle cerebellar peduncle
- Lateral pons. Carries input that is relayed from the cerebral cortex to the cerebellum via the gray matter of the pons
-generally contain cerebellar afferents fibers and superior peduncle has cerebellar efferent fibers
Superior cerebellar peduncle
- Enters brainstem at the level of the upper pons. Carries connections of the cerebellum to and from the medulla and spinal cord
- includes the nodule, which is the most anterior folium at the inferior end of the vermis
its two lateral appendages, which form the flocculi
flocculonodular lobe is involved in
Three arteries supply blood to the cerebellum
- the superior cerebellar artery (SCA)
- anterior inferior cerebellar artery (AICA)
-posterior inferior cerebellar artery (PICA)
Superior Cerebellar Artery
- The SCA branches off the lateral portion of the basilar artery, just inferior to its bifurcation into the posterior cerebral artery.
- Here it wraps posteriorly around the pons (to which it also supplies blood) before reaching the cerebellum.
- The SCA supplies blood to most of the cerebellar cortex, the cerebellar nuclei, and the middle and superior cerebellar peduncles
Anterior Inferior Cerebellar Artery
-The AICA branches off the lateral portion of the basilar artery, just superior to the junction of the vertebral arteries.
- From its origin, it branches along the inferior portion of the pons at the cerebellopontine angle before reaching the cerebellum.
- This artery supplies blood to the anterior portion of the inferior cerebellum, and to the facial (CN VII) and vestibulocochlear nerves (CN VIII).
- Obstruction of the AICA can cause paresis, paralysis, and loss of sensation in the face; it can also cause hearing impairment.
Posterior Inferior Cerebellar Artery
- The PICA branches off the lateral portion of the vertebral arteries just inferior to their junction with the basilar artery.
- Before reaching the inferior surface of the cerebellum, the PICA sends branches into the medulla, supplying blood to several cranial nerve nuclei.
- In the cerebellum, the PICA supplies blood to the posterior inferior portion of the cerebellum, the inferior cerebellar peduncle, the nucleus ambiguus, the vagus motor nucleus, the spinal trigeminal nucleus, the solitary nucleus, and the vestibulocochlear nuclei
Caudal Tegmental Pontine Syndrome
- occlusion of circumference branches of the basilar artery. Major structures affected include
MLF, motor nuclei of CN VI and CN VII, spinal nucleus of CN V, spinothalamic tracts and descending pathways of hypothalamus
Deficits include ipsilateral facial nerve palsy (CN VII), lateral gaze palsy (CN VI) and Horner's syndrome (loss of descending sympathetic input to the lower brainstem)
Caudal Basal Pontine Syndrome
- associated with the paramedian branches of the basilar artery.
Affects the descending corticospinal tract and root fibers of CN VI
Effects produce a contralateral hemiplegia and signs of a paralysis of CN VI (loss of lateral gaze in the eye on the ipsilateral side of the lesion)
Rostral Basal Pontine Syndrome
- Occlusions of portions of the paramedian branches of the basilar artery which affects the rostral half of the basilar pons.
Affect axons of sensory and motor components of the trigeminal nerve and corticospinal tract
Deficits include a contralateral hemiplegia (corticospinal tract) and ipsilateral loss of facial sensation and ability to chew (CN V deficit)
Rostral Pontine Tegmental Syndrome
- Associated with occlusion of long circumferential branches of the basilar artery
Structural affected include the sensory and motor nuclei of CN V, medial lemniscus, spinothalamic tracts, reticular formation, and depending on the extension of the lesion, the cerebellar afferent fibers contained in the middle cerebellar peduncle
Deficits include ipsilateral loss of sensation to the face and the ability to chew (CN V), contralateral loss of pain, temperature, Horner's syndrome and conscious proprioception from the body (spinothalamic and medial lemniscus), and ataxia of movement (due to disruption of cerebellar afferent fibers)