Download Cranial Nerve Locations CN I Olfactory ----------


Cranial Nerve Locations
o CN I Olfactory
o CN II Optic
o CN III Oculomotor
o CN IV Trochlear
o CN V Trigeminal
o CN VI Abducens
o CN VII Facial
o CN VIII Vestibulocochlear
o CN IX Glossopharyngeal
o CN X Vagus
o CN XI Spinal accessory
o CN XII Hypoglossal
--------------------Midbrain
Midbrain
Pons
Pons
Pons
Pons
Medulla
Medulla
Medulla
Medulla

Cerebellopontine Angle Syndrome (CPA)
o One of the most common neoplasms in the posterior fossa, accounting for 5-10%
of intracranial tumors
o Most CPA tumors are benign, with over 85% being vestibular schwannomas
 This neoplasm most often arises from the Schwann cells of CN VIII
 Also commonly called acoustic neuromas
o Signs and symptoms secondary to compression of nearby cranial nerves,
including CN V, CN VII, and CN VIII
o The most frequently associated symptom is asymmetric SNHL

Spinomedullary Junction
o Trigeminal nuclear complex
o Main subdivisions
 The principal sensory nucleus
 Discriminative touch with high spatial acuity
 The spinal trigeminal nucleus: pain & temperature

Rostral Medulla
o Vestibular nucleus (CRN VIII)
 Vestibular input from the semicircular canals and otolith organs is used to
maintain balance and to stabilize the visual image on the retina during
head movements

Vestibulospinal tract
 Lateral vestibulospinal tract
o Brings about postural changes to compensate for tilts
and movements of the body; balance
o ventral horn of entire spinal cord
 Medial vestibulospinal tract
o Stabilizes head and neck position as we walk around;
coordinating head movements with eye movements
o Bilateral projections to cervical, upper thoracic spinal
cord
o Solitary nucleus: related to autonomic regulation
o MLF = medial longitudinal fasciculus: helps to control direction of gaze
 MS can impact MLF

Caudal Pons
o Abducens nucleus: associated with CN VI - Coordination of eye movements
o Facial motor nucleus: nucleus associated with CN VII
 Related to Bell’s Palsy
 Lower motor neurons that innervate muscles of facial expression and the
stapedius (small muscle that stabilizes the stapes)

o Superior olive
 Role in hearing timing & intensity of sounds
Mid-Pons
o Further trigeminal nucleus subdivisions:
 Principal sensory nucleus
 Discriminative touch with high spatial acuity on the face
 Conscious proprioception of the jaw
 Motor nucleus
 Motor neurons that innervate muscles of mastication
o 2 Reticulospinal tracts one from the pons (pontine) and one from the medulla
(medullary)
 Fibers from the pons travel through the anterior funiculus in the spinal
cord
 Medullary projections descend bilaterally in the anterior part of the
lateral funiculus
 Major alternative route (to the corticospinal pathway) for controlling
spinal motor neurons directly and regulating spinal reflexes
 e.g., tonic inhibition of flexor reflexes allows only noxious stimuli
to produce this reflex (part of descending pathways influence
pain perception)


ARAS
 Reticular formations in midbrain and rostral pons collect
information from multiple sensory modalities and project to
(intralaminar nuclei of) thalamus, hypothalamus, basal ganglia,
cerebral cortex
 Control of inspiration, expiration, breathing rhythm, heart
rate, blood pressure
 Projections to widespread cortical areas causing heightened arousal
using acetylcholine/norepinephrine to modulate cortical activity
 These projections from the ascending reticular activating system
(ARAS) are essential for maintaining consciousness – bilateral
damage to midbrain reticular formation results in coma
 Modulation of ARAS has a role in sleep/wakefulness cycle
Rostral Pons
o Locus ceruleus
 Principal site for brain synthesis of norepinephrine
 Attention, alertness, stress, panic
o Pontine nuclei
 Modification of actions according to outcome - error correction, motor
learning
 Corticopontine fibers: M1 to the pontine nucleus
 Pontocerebellar fibers: pons to cerebellum

Caudal Midbrain
o PAG
 Pain suppression system
 Stimulating the PAG causes analgesia
 Lots of opiate receptors
o Inferior colliculus
 Inputs from auditory cortex
o Lateral lemniscus
 Carries auditory information from the cochlear nuclei to the superior olive
and the inferior colliculus

Rostral Midbrain
o Superior colliculus: orientation and saccades
o Edinger-Westphal nucleus
 Accessory parasympathetic nucleus of CN III
 Pupillary constriction, lens accommodation, and convergence of the eyes
o Oculomotor nucleus
 Controls many eye movements (as well as maintaining an open eyelid)
o Tectospinal Pathway
 Coordination of head and eye movements to enable orientation
behaviors
 Begins in a portion of the tectum (superior colliculus)
 Crosses at the dorsal tegmental decussation in the midbrain
 Terminates in the ventral (/anterior) horn of the cervical spinal cord
o Red nucleus – “the ruber”
 Appears to have a high iron content and is more vascular than the
surrounding tissue - in some brains is pinkish
 Inputs arise from motor areas of the brain and in particular the deep
cerebellar nuclei (via superior cerebellar peduncle; crossed projection) and
the motor cortex
 Outputs: rubrospinal pathway
 Movement of contralateral limbs
 Exerts control over tone of limb flexor muscles (excitatory to
motor neurons of these muscles)
 Terminate primarily in lateral parts of ventral horn, influencing
distal muscles
 Red nucleus receives afferent fibers from motor cortex, cerebellum
 Non-corticospinal route by which the motor cortex and cerebellum
can influence spinal motor activity
 Begins at the red nucleus (midbrain), decussates immediately:
at the ventral tegmental decussation
 Projects down rubrospinal tract to the spinal cord
o Substantia nigra
 Pars compacta
 Closely packed, pigmented neurons
 Widespread modulatory dopaminergic inputs to basal ganglia –
Parkinson’s Disease
 Pars reticulata
 Loosely packed, mostly non-pigmented
 Basal ganglia output

Brainstem Vascular Supply
o Vertebral arteries associated with the medulla
o Basilar artery associated with the pons
o Posterior cerebral artery associated with the midbrain

Spinocerebellar Tracts
o Info to cerebellum to coordinate movement
 2 divisions: anterior & posterior
o Fibers of the posterior spinocerebellar tract (blue)
 Mainly proprioceptive information from Aα fibers (muscle spindle
fibers and Golgi tendon organs) - trunk and lower limb
 Synapse on neurons of Clarke’s nucleus and axons ascend ipsilaterally as
the posterior spinocerebellar tract to enter cerebellum through inferior
cerebellar peduncle
 Clarke’s nucleus: group of interneurons found T1-L4,
associated with proprioception
o Fibers of the anterior spinocerebellar tract (green) decussate immediately
 Inputs not only from Golgi tendon organs, but also from cutaneous
receptors, spinal interneurons, etc.
 Lower limb information ascends on contralateral side of cord and enter
cerebellum via superior cerebellar peduncle
o Dx: Friedreich’s Ataxia
 An inherited degenerative disease involving the spinocerebellar tracts
 Part of the symptoms involve a wide-based, reeling gait (ataxia)