pons

CN V (Trigeminal) Functional Type

Mixed cranial nerve containing both general somatic sensory and branchial motor (SVE) fibers.

CN V Brainstem Exit Point

Exits from the ventro-lateral surface of the mid-pons.

CN V Ophthalmic Division (V1) Foramen

Exits the cranium via the Superior Orbital Fissure (SOF).

CN V Maxillary Division (V2) Foramen

Exits the cranium via the Foramen Rotundum.

CN V Mandibular Division (V3) Foramen

Exits/enters the cranium via the Foramen Ovale.

CN V Motor Innervation (V3 Branch)

Innervates muscles of mastication (masseter, temporalis, medial and lateral pterygoids), tensor tympani, mylohyoid, and anterior belly of digastric.

Unilateral Pterygoid Weakness Jaw Deviation

Causes the jaw to deviate TOWARD the weak (ipsilateral) side upon opening.

CN V General Sensory Innervation

Provides sensory innervation to the skin of the face, oral cavity, teeth, anterior 2/3 of tongue, nasal sinuses, and supratentorial dura.

Trigeminal Mesencephalic Nucleus Location & Function

Located along the periaqueductal gray in midbrain; processes proprioception for the jaw, tongue, and muscles of mastication.

Jaw Jerk Reflex Circuit

Monosynaptic stretch reflex: Tapping chin -> mesencephalic nucleus -> trigeminal motor nucleus -> jaw closure.

Chief (Primary) Trigeminal Sensory Nucleus Location

Located in the lateral pons; receives primary afferents for fine discriminative touch and dental pressure.

Ventral Trigeminothalamic Tract (VTTT)

Carries decussated fine touch and pain/temperature fibers from trigeminal sensory nuclei to the contralateral VPM of thalamus.

Dorsal Trigeminothalamic Tract (DTTT)

Carries uncrossed (ipsilateral) fine touch fibers from the chief sensory nucleus to the ipsilateral VPM of thalamus.

Spinal Trigeminal Nucleus Location & Extension

Located in the lateral pons and medulla, extending down into the upper cervical spinal cord (C2/C3).

Spinal Trigeminal Nucleus Function

Processes crude touch, fast pain, and temperature sensation from the face and head.

Spinal Trigeminal Tract

Descending tract in the lateral brainstem carrying primary afferent pain and temperature fibers to the spinal trigeminal nucleus.

Trigeminal Neuralgia (Tic Douloureux) Definition

Dysfunction of CN V causing severe, sharp, stabbing facial pain triggered by non-noxious stimuli (eating, talking, light touch).

Trigeminal Neuralgia Episode Duration

Brief, intense paroxysms of pain typically lasting up to 2 minutes.

CN VI (Abducens Nerve) Functional Type & Target

Pure somatic motor nerve innervating the Lateral Rectus muscle.

CN VI Lateral Rectus Muscle Action

Abduction of the eye (moving pupil laterally away from the nose).

Abducens Nucleus Location

Located in the caudal pontine tegmentum near the floor of the fourth ventricle.

CN VI Brainstem Exit Point

Exits ventrally at the pontomedullary junction.

CN VI Cranial Exit Foramen

Exits the skull through the Superior Orbital Fissure (SOF) into the orbit.

CN VI Abducens Lesion Presentation

Ipsilateral deficit in eye abduction (medial strabismus) resulting in horizontal diplopia.

CN VII (Facial Nerve) Functional Type

Mixed cranial nerve carrying motor (SVE), parasympathetic (GVE), special sensory taste (SVA), and general sensory (GSA) fibers.

Facial Nucleus Location

Located in the caudal pontine tegmentum.

Facial Colliculus Formation

Formed by motor axons of CN VII looping dorsally around the abducens (CN VI) nucleus on the floor of the 4th ventricle.

CN VII Brainstem Exit Point

Exits ventrolaterally at the pontomedullary junction (cerebellopontine angle).

CN VII Cranial Pathway

Enters the Internal Auditory Meatus (IAM), traverses the facial canal, and motor fibers exit via the Stylomastoid Foramen.

CN VII Motor Branches

Five terminal branches: Temporal, Zygomatic, Buccal, Mandibular, and Cervical.

CN VII Motor Innervation Scope

Innervates all muscles of facial expression (wrinkling forehead, eye closure, smiling, puffing cheeks, puckering).

Upper Face Corticobulbar Innervation

Upper facial motor neurons receive BILATERAL Upper Motor Neuron (UMN) input from the motor cortex.

Lower Face Corticobulbar Innervation

Lower facial motor neurons receive CONTRALATERAL Upper Motor Neuron (UMN) input only from the motor cortex.

Facial UMN Lesion Sign

Causes contralateral facial weakness/droop of the LOWER face only (forehead is spared due to bilateral innervation).

Facial LMN Lesion Sign

Causes ipsilateral facial paralysis of the ENTIRE face (both upper and lower face affected).

CN VII Special Sensory Function (Taste)

Carries taste sensation from the anterior 2/3 of the tongue.

Geniculate Ganglion

Contains primary sensory cell bodies for taste carried by the facial nerve (CN VII).

Rostral Solitary Nucleus

Brainstem nucleus that receives gustatory (taste) afferents from CN VII, IX, and X.

CN VII Taste Central Pathway

Geniculate ganglion -> Rostral Solitary Nucleus -> VPM nucleus of thalamus -> Primary Somatosensory/Gustatory Cortex.

CN VII General Somatic Sensory Distribution

Conveys general touch/pain from a small patch of skin near the external auditory meatus to the Spinal Trigeminal Nucleus.

CN VII Parasympathetic Innervation Scope

Innervates lacrimal glands, sublingual glands, submandibular glands, and nasal mucosa (EXCEPT parotid gland).

Superior Salivatory Nucleus

Pontine parasympathetic nucleus providing pre-ganglionic fibers for CN VII to the pterygopalatine and submandibular ganglia.

Corneal Reflex Afferent & Efferent Arms

Afferent arm: CN V1 (Ophthalmic division via chief/spinal trigeminal nucleus); Efferent arm: CN VII (Facial nerve to orbicularis oculi).

Corneal Reflex Normal Response

Bilateral eye blink triggered by lightly touching the cornea with a cotton swab.

Bell's Palsy Definition

Sudden, idiopathic acute peripheral (LMN) facial nerve paralysis affecting all branches of CN VII on one side.

Bell's Palsy Key Symptoms

Ipsilateral full facial droop, inability to close eye, dry eye/tearing, dry mouth or drooling, hyperacusis, and loss of taste on anterior 2/3 tongue.

Synkinesis in Bell's Palsy Recovery

Abnormal involuntary facial movements (e.g., eye winking when smiling) caused by misdirected axon regeneration.

Medial Pontine Syndrome Vascular Etiology

Ischemia caused by occlusion of paramedian branches of the Basilar Artery.

Medial Pontine Syndrome Motor & Sensory Deficits

Contralateral hemiplegia of limbs/trunk (Corticospinal tract) and contralateral loss of vibration/proprioception (Medial Lemniscus).

Medial Pontine Syndrome Ocular Deficit

Ipsilateral abducens palsy (CN VI nerve/nucleus) or internuclear ophthalmoplegia (MLF damage).

Lateral Pontine Syndrome Vascular Etiology

Ischemia caused by occlusion of the Anterior Inferior Cerebellar Artery (AICA).

Lateral Pontine Syndrome Cerebellar & Auditory Deficits

Ataxia, unsteady gait, and falls toward lesion (MCP/cerebellum) + vertigo, nystagmus, and hearing loss (Vestibulocochlear CN VIII).

Lateral Pontine Syndrome Facial & Sensory Deficits

Ipsilateral facial paralysis (CN VII nucleus), ipsilateral facial pain/temp loss (Spinal CN V), and contralateral body pain/temp loss (ALS).