Brainstem and Cranial Nerves (No Eyes or Ears)

what is Cranial Nuclei?

• Collections of motor neuron cell bodies that perform similar function
• Collections of sensory neuron cell bodies (& dendrites) that receive similar sensory information

The nuclei of the first four cranial nerves (CN I-IV)and ( CN V-VIII) exist above the ?

pons (forebrain or midbrain)

?The last four nuclei of the cranial nerves (IX-XII) are located?

below the pons (medulla or spinal cord)

where is Olfactory Nucleus?

in the ventral Frontal Lobe

where is visual nucelus?

Lateral Geniculate Nucleus of the Thalamus

where is Oculomotor Nucleus located?

in Midbrain

• 4 Extraocular Muscles and Eyelids

what is part of Erdinger-Westphal Nucleus?

• Sphincter Pupillae of Iris

  • Pupillary Constriction

• Ciliary Muscles inside eye

  • Accommodation – change lens shape for focusing

where is trochlear nucleus?

in midbrain

where is trigeminal motor nucleus?

pons

where is trigeminal sensory nucleus?

Span the full length of brainstem

where is abducens nucleus?

pons

where is facial motor nuceli?

pons

where is facial motor nuceli?

• Pons and Medulla Oblongata
• Solitary Nucleus for taste

where is Vestibular and Cochlear Nuclei?

Both in Pons & Medulla

where is glossopharyngeal nuclei?

• motor (salivation) 

  • inf.salivary nucleus of pons 

• sensory 

  • solitary nucleus medulla - taste 

where is vagal nuclei?

• Motor (Throat & Viscera)

  • Medulla

  • Dorsal Vagal Nucleus and Nucleus Ambiguous

where is accessory nucleus located?

C1-C5 Cervical Spinal Cord

where is hypoglossal nucleus located?

medulla

what is Corticobulbar Tract?

• pathway of voluntary motor control to cranial nerves 

  • Except CN XI – the Corticospinal Tract is in charge of Voluntary Motor control of neck movement

where does corticobulbar tract descend through?

the Genu of the internal capsule

where does corticobulbar tract pass through?

Through the medial parts of the cerebral peduncles

where does the corticobulbar tract decussate?

• Decussate in Brainstem to synapse with nuclei on Contralateral side of brainstem

  • Some cranial Nuclei are innervated bilaterally

Motor nuclei receiving CBT innervation:

• Nuclei of oculomotor (CN III), trochlear (CN IV), and the abducens (CN VI) nerves

• Motor nuclei of the trigeminal nerve (CN V)

• Nuclei of facial nerve (CN VII)

• Nucleus Ambiguus of the glossopharyngeal (CN IX) and vagus (CN X) nerves

• Nucleus of hypoglossal nerve (CN XII)

• CN XI, the spinal accessory nerve has most of its motor neurons in the upper cervical spinal cord; it is supplied by the corticospinal tract

what does Nuclei of oculomotor (CN III), trochlear (CN IV), and the abducens (CN VI) nerves perform?

extraocular eye movements

what does Motor nuclei of the trigeminal nerve (CN V) perform?

muscles of mastication

what does Nuclei of facial nerve (CN VII)?

muscles of facial expression

what does Nucleus Ambiguus of the glossopharyngeal (CN IX) and vagus (CN X) nerves perform?

muscles of deglutition and phonation

what does Nucleus of hypoglossal nerve (CN XII) control?

tongue muscles

CN XI, the spinal accessory nerve has most of its motor neurons in the upper cervical spinal cord; it is supplied by the __

corticospinal tract

The facial motor nucleus has how many divisions?

two divisions ( upper & lower)

what is upper divisions?

• motor neurons to the upper half of the face

  • Orbicularis oculi musles

    • Close the eye

• Frontalis muscles

  • moves the eyebrows and forehead

Orbicularis oculi muscles function?

close the eye

Frontalis muscles function?

moves the eyebrows and forehead

what is the lower division of facial motor nucleus?

• Motor neurons that control the muscles of the lower half of the face

  • muscles that produce the nasolabial fold and move the mouth

The CBT provides bilateral innervation to:

• CNs III (Oculomotor) and IV (Trochlear)

•  Motor division of CN V (Trigeminal), CN VI (Abducens)

• Upper division of CN VII (Facial)

Most Motor Nuclei (except the lower division of VII):

• Receive bilateral innervation
• Lower Div of CNVII is only innervated contralaterally

Redundant bilateral innervation of the nuclei associated with control of:

• extraocular eye muscles

  • CBT lesions typically do not produce clinically observable deficits in eye movements

• eye-protective reflexes such as the corneal (blink) reflex

• i.e., one side of the brain has motor control over both eyes and both sets of muscles that close the eye

• However, the lower half of the face is only receives motor signals from the contralateral side of the brain

Central CBT Lesion (Upper mn injury)

Loss of crossed fiber innervation only to the lower face

Produces a Central Facial Palsy:

• Contralateral lower face paresis

  • Bilateral frontalis and orbicularis occuli function intact

Peripheral CN VII lesion (Lower mn injury) causes:

• ipsilateral paresis of both upper and lower facial muscles – Peripheral facial palsy

• A lesion above the upper facial division in CN VII motor nucleus will paralyze only the contralateral lower half of the face

• A lesion to the facial nerve can produce a complete ipsilateral facial paralysis

Reticular Formation of Brainstem

Virtually all ascending sensory, descending motor, and local circuit pathways interact with RF nuclei

what is Rostral Part?

related to consciousness, awareness, and arousal (the reticular activating system)

what is caudal part?

regulation of vital functions and patterned behaviors

what is Olfactory I?

• There are, in fact lots, of CN 1s

• Myelinated bundles of axons from the olfactory neurons

  • Ascend through the cribriform plate of ethmoid bone

  • Converge onto the olfactory bulb

  • make immediate connections within the olfactory tract

Olfactory tract goes bilaterally:

• Centrally (ipsilateral) via the medial pathway to the olfactory cortex and amygdala

• to contralateral olfactory structures via the anterior commissure

Tumors of the frontal lobe can lead to

unilateral anosmia

Bilateral anosmia often manifests as decreased taste and is most commonly caused by:

• damage to the delicate cribriform plate by head trauma

• viral infections

• neurodegenerative disease, including Parkinson's and Alzheimer's diseases

what is osmophobia?

• odor sensitivity

  • migrane symptom

what is Trigeminal V?

The somatosensory nerve of the face, oral cavity, and nasal cavity

what happens if the trigenminal V has a peripheral lesion?

• A peripheral lesion causes a band of paresthesia or numbness within the distribution of V1, V2, or V3
• A peripheral lesion of V3 paralyzes the ipsilateral muscles of mastication, producing weakness of bite and deviation toward the lesioned side, with mouth opening or protrusion

The masseter reflex, or jaw-jerk reflex, only seen under pathological conditions:

• presents as a sharp elevation of the mandible (bite) in response to a tap on the point of the chin.

• A large, exaggerated elevation of the mandible indicates a lesion of the upper motor neurons supplying the motor trigeminal nucleus

which nuclei is in Trigeminal V?

sensory and motor nuclei

what is masseter reflex loop?

• Signals from muscle spindles synapse with Secondary fibers which, in turn, synapse with motor neurons

• Forms the sensory part of the Corneal Blink reflex loop

what is Trigeminothalamic Tract?

• Touch, Proprioception, Temperature and pain from the face and, Nasal and Oral Cavities

• So All Somatosensation from the face, Cornea and, Nasal and Oral Cavities

• Sensations are not separated into different tracts like in the spinal cord

  • i.e. DC-ML vs STT

CN V's sensory pathway is a 

three-neuron sequence like that of the spinal cord

what is Trigeminal ganglion?

equivalent of DRG of spinal cord

what is Facial VII?

• Facial expression

• Parasym control of tears and saliva

• Bell's palsy is the most common cause of facial paralysis

• caused by a virus, possibly the herpes virus (HSV-1), or other source of irritation of the facial nerve.

• Usually resolves itself within three weeks

which palsy is associated with Facial VII?

• Bell's palsy is the most common cause of facial paralysis

• caused by a virus, possibly the herpes virus (HSV-1), or other source of irritation of the facial nerve.

• Usually resolves itself within three weeks

what is Glossopharyngeal IX

• Sensory component of Gag-reflex

• Saliva – Parotid gland – parasym.

• CO2 and O2

• Blood pressure

• Taste Post. 1/3 of tongue – bitterness

• Swallowing and speaking

  • Deglutition and Phonation

what is lesions in Vagus X?

• Choking when trying to swallow

• Loss of Taste in throat & epiglottis

• Neurogenic bladder. Loss of control of urinary storage/retention and volitional continence

  •  Lesions in the brainstem or spinal cord above T12 produce an upper motor neuron lesion and spastic bladder (also hyperactive)

    • unexpected and uncontrolled incontinence

• Lesions below T12, produce a lower motor neuron flaccid bladder

  • Catheterization needed

what is sexual function for vagus nerve?

• Mainly innervated parasympathetically by the sacral spinal cord

• SCI above lumbar levels:

  • Women – preserves sensation from Clitoris and Uterus

  • Men - priapism

Parasympathetic Control of Bladder and Sexual function comes from the

Sacral Spinal Cord

what is Taste?

Provided by 3 Cranial Nerves
• Facial
• Glossopharyngeal
• Vagus
• All taste signals synapse with the Solitary nucleus of the Pons

what is Accessory XI?

• vast majority of its motor neurons lie within the spinal accessory nucleus in the cervical spinal cord

• C1–2 supply the sternocleidomastoid

• C3–4 supply the trapezius

what is Hypoglossal XII?

• Emerges between pyramid and olive of medulla

• motor innervation to the tongue, supplying the muscles that assisting with chewing, drinking, and vocalization/phonation

• A lesion in the CBT will cause contralateral tongue weakness

A lesion to the hypoglossal nucleus or its nerve

• Ipsilateral paralysis of the tongue

• When a patient is asked to protrude the tongue, it deviates toward the lesioned side

• Dysarthria – slurred speech

what is locked in syndrome?

• Lesions of the ventral pons (basilar artery stroke) affecting bilateral corticospinal and corticobulbar tracts

  • Quadriplegia

  • loss of horizontal eye movements

  • weakness of the lower face

• reticular formation is spared, so the patient is fully aware

• most somatic sensation is also preserved, but all ability to move or communicate is lost – may communicate by blinking

• Oculomotor nucleus and nerve spare

what is Decorticate and Decerebrate posturing?

• Unilateral and bilateral brainstem injuries can produce pathological body posturing referred to as decerebrate and decorticate rigidity

  • Caused by a increases in pressure that compress CST fibers in the brainstem

  • Extrapyramidal tracts OK

  • Patient is comatose

  • Typical posture produced by applying noxious stimuli

what if there is a Lesion above the Red Nucleus?

Rubrospinal tract intact

Decorticate posture:

rigid extension and internal rotation of lower extremities with flexion of the upper extremities

what if theres a Lesions below the red nucleus?

interrupt rubrospinal output

Decerebrate posture:

extension generated by reticulospinal and vestibulospinal output

Reminder of Autonomic System Organization