Pons - Benifla Flashcards
Which cranial nerves are associated with the pons?
Where are they located?
Trigeminal (V, anterolateral surface), Abduscent, Facial and Vestibulocochlear (medial-lateral: VI, VII, VIII- inferior pontine sulcus)
Vestibulocochlear (4: lateral, superior, medial, and inferior)- beneath floor of fourth venricle lateral to abduscent nucleus and medial to inferior cerebellar peduncle.
Cochlear nuclei (2) - on lateral surface of inferior cerebellar peduncle.
Facial nucleus/nerve: Posterior to lateral part of medial lemniscus deep in reticular formation. Consists of 3 nuclei: motor, parasympathetic and sensory.
What are the boundaries of the pons?
Anterior: Basal occipital bone/clivus, basilar artery in midline in basilary groove
Posterior: Fourth ventricle and cerebellum
Superior: midbrain
Inferior: medulla oblongata
What is the tegmentum?
What does it include?
Dorsal part of pons containing cranial nuclei and the reticular formation (RF). Beneath lateral part of fourth ventricle.
Includes motor nucleus of trigeminal nerve (both ipsilateral and contralateral input) to muscles of mastication.
SVE: mastication, swallowing, movements of soft palette, auditory tube, tympanic membrane and ossicles.
Three sensory nuclei:
- Principle sensory nucleus: Tactile and pressure sense from 3 divisions of face and head.
- Mesencephalic nucleus: form upper pons to upper midbrain, runs with motor branches. Conveys proprioception impulses (organs in space).
- Spinal trigeminal nucleus and tract: Extends to upper cervical spine (C1/C2). Receives and conveys pain and temperature from all of head.
What are the fibers of the medial lemniscus and lateral lemniscus?
Medial lemniscus:
Fibers from the nuclei gracilis and cuneatus to the thalamus through arcuate fibers .
Lateral leminiscus:
Dorsolaterally to medial lemniscus. Principle ascending auditory pathway in brain stem. From cochlea to inferior colliculus. Impulses part of auditory system.
What longitudinal bundles course through the ventral (anterior) portion of the pons?
Which transverse fibers?
Longitudinal bundles:
- Corticospinal
- Corticobulbar
- Corticopontine (uncrossed)
Transverse fibers:
From cortex through cruz cerebri to pontine nuclei to synapse. From pontine nuclei they go through middle cerebellar peduncles to contralateral cerebellum.
Medial longitudinal Fasciculus (MLF)
What does it do?
What is the effect of injury?
Connects the vestibular nuclei via crossed and uncrossed fibers to the coculomotor nuclei (III), IV and VI and bring innervation of the extraocular muscles under vestibular (changes in balance) and cerebellar regulation.
Coordinates eye movement to move to the side of body movement.
Injury causes inability to coordinate eye movement.
What are the effects of the abduscent nuclei and nerve?
Where is it?
What is the clinical significance of when it is impaired?
Motor nucleus located beneath the floor of the fourth ventricle close to the midline and beneath the colliculus facialis.
Afferent fibers from both cerebral hemispheres form superior colliculus from MLF.
Innervates the lateral recutus. Merges out of anterior brainstem from inferior aspect along clivus towards cavernous sinus and to superior orbital fissure. Clinical significance: any pressure on the brainstem compresses the nerve and causes injury and impairment of the lateral recuts causing patient to be unable to move the eye externally-only medially. Abduscent nerve of VI nerve palsy. Often the first sign of increased cranial pressure.
What are the three branches of the facial nerve?
What is the effect of injury?
- Motor
Afferent fibers, part of nucleus supplies upper part of the face receiving fibers from precentral gyrus of both hemispheres and part of the nucleus that supplies the muscles of the lower part of the face receiving fibers from precentral gyrus of opposite side (superior: contralateral and ipsilateral- eye, inferior: contralateral- mouth). Muscles of facial expression.
Peripheral facial nerve palsy (distal to nucleus): Injury to whole nucleus causes paralysis of obribularis oculi and oris muscles.
Central facial nerve palsy will only cause missing contralateral input to the mouth so only contralateral mouth drooping. - Parasympathetic nucleus:
Afferent fibers form hypothalamus, olfactory system and nucleus of tractus solitarious.
Efferent fibers from superior salivatory nucleus to salivary glands (except parotid) and palatine and lacrimal glands. Increases saliva and sometimes tears. - Sensory nucleus (ascending fibers):
Upper part of nucleus tractus solitarius. Taste from anterior 2/3 of tongue, floor of mouth and soft palate (via geniculate ganglion). Motor and sensory roots form facial colliculus- bulge on floor of fourth ventricle.
What is the blood supply to the pons?
- Rostral pons:
Paramedian and long and short circumferential arteries from the basial artery. - Caudal Pons:
Paramedian from basilar cicumferential from the AICA.
What is Bell’s Palsy?
Peripheral facial nerve palsy.
Etiology unknown, but may be inflammatory process or virus affecting nerve.
Self limiting but some patients have palsy for life.
Mainly aesthetic issues with asymmetry of face but also functional problems with fluid and food through the mouth.
What is Locked In Syndrome?
Quadriplegia, aphonia, and sometimes VI nerve palsy.
Involves anterior part of pons usually due to infarct of vessels supplying this area due to thrombosis of basilar artery.
Ischemia of both sides of anterior pons.
Can’t move limbs on either side. No muscles involved in speech.
No sensory injury.
If involves CN VI nucleus, limited eye movement.
Usually injury to facial nerve as well.
Only thing left is eyelid.
Fully conscious, usually die of pneumonia because of aspiration. Generally need mechanical ventilation.
