Anatomy of the Brainstem and Cranial Nerve Flashcards
Name the components of the brainstem?
- Midbrain – First part of Brainstem
- Pons – Most anterior part of posterior cranial fossa
- Medulla Oblongata – Upper Roots of Cranial Nerves IX – XII attached here
Name the 3 parts of the midbrain?
- tectum
- periaqueductal grey matter
- tegmentum
Describe the tectum?
Location: Area dorsal to the aqueduct (of Sylvius)
Components: Has 4 dorsal prominences (corpora quadrigemina)
> Two superior colliculi – visual reflexes
> Two inferior colliculi – auditory reflexes
- Cranial nerve IV is attached between them
Function: preliminary processing of the visual or auditory stimuli before they reach their corresponding primary processing centers
Describe the periaqueductal grey matter?
Components: Contains nuclei of CN III (OCCULOMOTOR) and IV (TROCHLEAR)
Function: modulate pain by releasing endogenous opioids
- where distinction between the expected and actually perceived pain is made
Describe the tegmentum?
Location: Area ventral to the aqueduct
Components:
1. Has the red nucleus
> Passage of impulses to and from cerebral cortex from dentate nucleus through superior cerebellar peduncle to red nucleus (dentato-rubro-thalamic tract)
> Also connected to the spinal cord (rubrospinal, spinorubral tracts)
2. Has Substantia nigra (Latin: Black substance)
> dark area in the tegmentum; one of basal ganglia
> associated with Parkinson’s disease
Describe the pons?
Location: Where cerebellum and CN V are attached
Contents:
1. Contains nuclei of CN V, VI, VII, VIII
2. Locus coeruleus (latin: blue place) – pigmented area in the dorsal pons
> concerns with the limbic system and autonomic functions
> a focus for drug action
Describe the anterior aspect of the medulla?
4 swellings are visible: 2 on either side of the midline
1. Pyramid: medial swelling on each side
> Contains descending motor corticospinal tracts
2. Olive: lateral swelling on each side
> Contains the inferior olivary nucleus which like the red nucleus is an outpost of the cerebellum
Describe the posterior aspect of the medulla?
2 tubercles are visible on each side: concerned with sensation from the spinal cord
1. Gracile: medial tubercle
2. Cuneate: lateral tubercle
Note: Nuclei – Hypoglossal, vagus
What are the cerebellar peduncles?
3 paired cerebellur peduncles (bundles of nerve fibers)
> Connect cerebellum to brainstem
Describe the superior peduncle?
- Connects cerebellum with midbrain & pons
- Contains both afferent & efferent fibers eg:
> Trigeminocerebellar tract
> Cerebello – thalamic tract
Describe the middle peduncle?
- Connects cerebellum to pons
- Contains afferent fibers only
> e.g. Pontocerebellar fibers
What are the 12 cranial nerves?
I - olfactory (smell)
II - optic (sight)
III - oculomotor (motor/parasympathetic)
IV - trochlear (motor)
V - trigeminal (sensation/motor)
VI - abducent (motor)
VII - facial (motor/parasympathetic)
VIII - vestibulo-cochlear (balance/hearing)
IX - glossopharyngeal (sensation/parasympathetic)
X - vagus (parasympathetic/motor/sensory)
XI - accessory (motor)
XII - hypoglossal (motor)
Which parts of the brain do the cranial nerves directly attach to?
- cerebrum = I and II
- midbrain = III and IV
- pons = V, VI, VII, VIII
- medulla = IX, X, XI, XII
Which parts of the brain do the cranial nerves directly attach to?
- cerebrum = I and II
- midbrain = III and IV
- pons = V, VI, VII, VIII
- medulla = IX, X, XI, XII
Which parts of the brain do the cranial nerves directly attach to?
- cerebrum = I and II
- midbrain = III and IV
- pons = V, VI, VII, VIII
- medulla = IX, X, XI, XII
Where do cranial nerves exit the cranial cavity?
- olfactory = cribiform plate
- optic = optic canal
- Oculomotor, Trochlear, Trigeminal (V1 – Ophthalmic), Abducent = superior orbital fissure
- trigeminal (V2 - maxillary) = foramen rotundum
- trigeminal (V3 -mandibular) = foramen ovale
- facial + vestibulo-cochlear = internal acoustic meatus
- Glossopharyngeal, Vagus, Accessory = jugular foramen
- hypoglossal = hypoglossal canal
Describe the point of exit from/entry into skull, distribution/function and dysfunction in case of lesion for the olfactory nerve?
- foramen - cribriform plate
> 20 neurons from mucosa of upper part of nasal cavity pass via cribriform foramina amd end as olfactory bulb - function - smell
- dysfunction - anosmia > loss of olfaction
> leakage of CSF through nose (rhinorrhoea)
State the origin, course and function of optic nerve?
- origin - axons of ganglionic cells of retina
- course - optic canal
- function - vision + accomodation reflexes
State the foramen, distribution and dysfunction of the oculomotor nerve?
- foramen - enter orbit rhough superior orbital fissure
- distribution - extraocular muscles
> superior, inferior, medial recti, inferior oblique and levator palpebral superioris
> sphincter pupillary muscle of iris and ciliary muscle which Ck instructs pupil and accommodate lens - Dysfunction
•Eye deviation - down & out
(Lateral stabismus).
•Ptosis (drooping of eyelid)
•Mydriasis (fully dilated pupil)
•Loss of power of accommodation
•Diplopia
What is Horners syndrome?
Damage to sympathetic (“Fight or Flight” response) chain fibres before join oculomotor nerve
- leads to
> Droopy eyelid
> Pupillary constriction
> Absence of sweating
State the foramen, distribution and dysfunction of the trochlear nerve?
Trochlear Nerve (IV)
• Passes through superior orbital fissure
Distribution: Superior oblique
Dysfunction: Rarely paralysed alone
• Diplopia (double vision) on looking down &
Extorsion
What are the 3 divisions of the trigeminal nerve?
Ophthalmic Division (V1 ) - superior orbital fissure
Maxillary Division (V2 ) - foramen rotundum
Mandibular Division (V3 ) - foramen ovale
Describe the sensory distribution of the trigeminal nerve?
• Sensory
- Periodontal ligaments of teeth
- Reflex control of force of bite
- Discriminative tactile: from skin of face, mucous membrane of middle ear, pharygotympanic tube, pharynx, larynx
Describe the motor distribution of the trigeminal nerve?
• Motor
- Muscles of mastication
- Tensor tympani
- Tensor veli palatine
- Mylohyoid
- Anterior belly of digastric
Describe the consequences of trigeminal nerve dysfunction?
• Trigeminal Nerve dysfunction
• Trigeminal neuralgia - pain in distribution of maxillary and/or mandibular nerve.
• Decreased forehead pain and touch, corneal reflex (1st sign of lesion of ophthalmic nerve), cheek touch & pain, jaw touch & pain & jerk, and
Weakness of muscles of mastication
State the foremen, distribution and dysfunction of the abducens nerve?
Enters orbit through superior orbital fissure
Distribution: Supplies Lateral rectus
Dysfunction: Medial deviation & diplopia. Cannot look outwards
Describe the course of the facial nerve?
Course: Internal acoustic meatus to facial canal
• Exits skull through the
Stylomastoid foramen to supply muscles including those of facial expression
Describe the distribution of the facial nerve?
• Taste from anterior 2/3 of tongue
• Skin of external acoustic meatus
• Mucous membrane of nasopharynx & palate
• Lacrimal, nasal, palatine, submandibular & sublingual glands.
Describe the dysfunction of the facial nerve?
• Most frequently paralysed of all
cranial nerves
• Infranuclear lesion (LMN) - Bell’s palsy (most common):
- facial muscles
paralysis/weakness with asymmetry of corner of mouth
- Inability to close eye or wrinkle forehead on affected side
- excessive acuteness of hearing (hyperacusis)
• Decreased tearing, salivation & taste
State the foremen, functions and dysfunction of the vestibulo-cochlear nerve?
• Both pass with CN VII through internal acoustic meatus
.
Functions:
- Vestbular part for balance and posture (Semicircular canals, utricle & saccule).
- Cochlear for Hearing
• Dysfunction
.
Vestibular nerve: Dysequilibrium & vertigo
• Decreased hearing (nerve deafness) - cochlear lesion
• Conduction deafness - external or middle ear
• Tinnitus (noise in ear)
State the course, distribution and dysfunction of the glossopharyngeal nerve?
• Course: Passes through jugular foramen
• Distribution: Stylopharyngeus, Parotid gland (parasympathetic & sensation), carotid body & sinus, pharynx & middle ear, Taste posterior 1/3 of tongue, Tonsil & palate, Sensation from external ear
• Dysfunction: Decreased Salivation, sensation to back of ear, gag reflex (closure of glottis), taste
What is the foremen of the vagus nerve?
Jugular foremen
Describe the distribution of the vagus nerve?
Motor: Pharyngeal constrictor muscles, intrinsic muscles of larynx, muscles of palate.
• Parasympathetic: Smooth muscles of trachea, bronchi, Gl tract, heart
• Sensory: Tongue, pharynx, larynx, thoraco-abdominal viscera, auricle, external auditory meatus, meninges of post cranial fossa.
Describe the dysfunction of the vagus nerve?
Dysfunction:
.
Recurrent laryngeal nerye palsies are common, from malignant diseases & surgical damage during surgery
heart & lung
on thyroid gland, heck, oesophagus,
. •
Hoarseness and Dysphagia
Decreased gag reflex, sensation in external auditory meatus, pharynx, tachycardia
State the foremen, distribution and dysfunction of the accessory nerve?
Foremen
Jugular foremen
Distribution
Sternocleidomastoid & Trapezius
muscles
• Dysfunction:
• Wry neck
• Decreased ability to shrug shoulders or turn neck to opposite side
State the foramen, distribution and dysfunction of the hypoglossal nerve?
Leaves skull through hypoglossal canal
• Distribution: Intrinsic and extrinsic muscles of tonque
.
Dysfunction
Vicarness of tongue movement
.
. On attempted protrusion, tongue deviates
towards affected side
Moderate dysarthria
What causes the paralysis of the hypoglossal nerve?
• fracture of the occipital condyle
• tumor near the hypoglossal canal
What is the consequence paralysis of the hypoglossal nerve?
The tongue will deviate towards the side of a peripheral lesion therefore, this is right CN XII paralysis
How do you test cranial nerve lesions?
