External and internal features of the pons Flashcards
(32 cards)
What is the pons and where is it located?
The pons is part of the brainstem that connects the medulla oblongata to the midbrain. It is located anterior to the cerebellum and is about 1 inch (2.5 mm) long.
What are the two main parts of the pons?
Tegmentum (older posterior/dorsal part) – contains cranial nerve nuclei and reticular formation.
Basal part (pons proper) – newer anterior/ventral part with pontine nuclei and transverse fibers.
Which cranial nerves are associated with the pons?
CN V (Trigeminal), CN VI (Abducent), CN VII (Facial), and CN VIII (Vestibulocochlear).
What is the function of the trapezoid body in the pons?
It is part of the auditory pathway where axons from the cochlear nucleus decussate (cross over) to the other side.
What is the role of the medial lemniscus in the pons?
It carries sensory information for discriminative touch, vibratory sense, and conscious muscle joint sense (part of the dorsal column-medial lemniscus pathway).
Why does a pontine hemorrhage cause facial paralysis on the same side of the lesion?
Because it affects the facial nucleus (CN VII) located in the pons.
Why does a pontine hemorrhage cause limb paralysis on the opposite side?
Because it damages the corticospinal tracts, which decussate (cross) in the medulla.
What are the respiratory centers in the pons, and what do they do?
Apneustic center: Increases depth and duration of inspiration.
Pneumotaxic center: Decreases depth and duration of inspiration.
What is the facial colliculus, and how is it formed?
An elevation on the floor of the fourth ventricle formed by the facial nerve fibers winding around the abducent nerve nucleus.
What is the blood supply to the pons?
Primarily the basilar artery.
What are the “Big Four” tracts in the pons?
Corticospinal tract
Medial lemniscus
Spinothalamic tract
(Note: Spinocerebellar tracts are not prominent in the pons.)
What is the significance of the locus coeruleus in the pons?
It contains pigmented nerve cells that secrete norepinephrine and is involved in stress, attention, and arousal.
What symptoms would a pontine tumor cause?
Ipsilateral cranial nerve deficits (e.g., facial weakness, hearing impairment).
Contralateral hemiparesis (due to corticospinal tract damage).
Sensory deficits (due to medial lemniscus/spinothalamic tract involvement).
What is the embryological origin of the pons?
The pons develops from the metencephalon, a subdivision of the rhombencephalon (hindbrain).
What structures form the floor of the fourth ventricle in the pons?
Median sulcus (midline groove).
Medial eminence (elongated elevation bounded by sulcus limitans).
Facial colliculus (inferior expansion of medial eminence).
Area vestibuli (lateral to sulcus limitans, overlying vestibular nuclei).
Why does damage to the pons cause paralysis of conjugate gaze?
Due to involvement of the abducent nerve nucleus (CN VI) and medial longitudinal fasciculus (MLF), which coordinate lateral eye movements.
What is the function of the medial longitudinal fasciculus (MLF) in the pons?
Coordinates eye movements (e.g., vestibulo-ocular reflex, saccades) by connecting vestibular/cochlear nuclei with oculomotor, trochlear, and abducent nuclei.
What are the pontine nuclei, and what is their role?
Small nerve cell groups in the basal pons that relay signals from the corticopontine fibers (cerebrum) to the cerebellum via transverse fibers (middle cerebellar peduncle).
What sensory pathways pass through the pons?
Medial lemniscus (fine touch, vibration, proprioception).
Spinothalamic tract (pain, temperature, light touch).
Trigeminal sensory pathways (face).
How does the pons link the cerebrum and cerebellum?
Through corticopontine fibers → pontine nuclei → transverse fibers → middle cerebellar peduncle → cerebellum.
What is the spinal nucleus of the trigeminal nerve, and where is it located in the pons?
A nucleus for pain/temperature sensation from the face. Located anteromedial to the inferior cerebellar peduncle in the caudal pons.
What is the difference between the caudal and cranial transverse sections of the pons?
Caudal pons: Contains facial colliculus, abducent nucleus, vestibular nuclei.
Cranial pons: Includes trigeminal motor/sensory nuclei and superior cerebellar peduncles.
What causes ipsilateral facial anesthesia to light touch but preserved pain sensation in pontine lesions?
Damage to the principal sensory nucleus of CN V (light touch) but sparing the spinal trigeminal nucleus (pain/temperature).
What is the role of the superior olivary nucleus in the pons?
Part of the auditory pathway; localizes sound by comparing input from both ears.
