Brainstem Flashcards
Which cranial nerves are different?
Olfactory cranial
Optic nerve
Direct outgrowth of brain, share same structure as CNS, myelinated so not similar to peripheral nerves
Describe the Oculomotor nerve function (3)
Motor
oculomotor nucleus in midbrain (LMN), innervates most extra-ocular muscles
Parasympathetic motor
arise from Edinger-Westphal nucleus and pass to the ciliary ganglion. Post-ganglionic fibres innervate the pupil (constrict).
What are the consequences of damage to the oculomotor nerve?
Damage results in the ipsilateral eye being deviated downward and laterally (“down and out”), ptosis (eyelid droops), and a fixed dilated pupil (no parasympathetic innervation)
May be damaged in raised intracranial pressure with tentorial herniation, or disorders involving the cavernous sinus. Trauma around orbit
What are the muscles involved in eye movement control?
- Superior and inferior oblique
- Superior, inferior, lateral and medial rectus
Which eye muscles does the oculomotor nerve not innervate?
- Superior oblique
- Lateral rectus
Where are the oculomotor nerves in the brainstem?
LMN = Close to periaqueductal grey matter Parasympathetic= Edinger-Westphal nucleus
Describe the Trochlear nerve function (4)
Only cranial nerve to arise from the dorsal surface of the brainstem.
Motor
Supplies the superior oblique muscle
What is the consequence of damage to the trochlear nerve?
Damage results in diplopia (double vision) when looking downward and medially (direction globe moves when sup. oblique contracts).
Where does the Trochlear nerve arise?
Trochlear nucleus
Describe the Abducens nerve function (6)
Motor
supplies the lateral rectus muscle
What are the consequences of damage to the abducens nerve?
Damage results in diplopia when looking laterally.
Where do the abducens fibres arise?
Upper pons
Describe the Trigeminal nerve motor function (5)
Motor supply
Supplies the skeletal muscles of mastication which all develop from the first branchial arch. Fibres arise from the trigeminal motor nucleus and join the mandibular division of the trigeminal nerve
Describe the Trigeminal nerve sensory function
the trigeminal ganglion is the equivalent of a dorsal root ganglion and receives sensory input from three branches; ophthalmic, maxillary and mandibular. There are three sensory nuclei;
mesencephalic; proprioception from jaw
chief sensory nucleus and spinal nucleus
Fibres decussate and pass to thalamus.
Describe the trigeminothalamic pathway
- Pressure and temperature and pain pass into the brainstem trigeminal nuclei
- Proprioception= mesencephalic nucleus
- Head to ventral posterior nuclei of thalamus
What is the Cavernous sinus?
This is a dural venous sinus in the middle cranial fossa.
The III, IV, V (ophthalmic and maxillary) and VI nerves all lie in relation to the sinus.
Either side of the pituitary fossa
What is cavernous sinus syndrome?
The “cavernous sinus syndrome” will give rise to variable ocular palsies and upper trigeminal sensory loss.
Caused by trauma, neoplasia, thrombosis, inflammatory conditions.
Describe the motor functions of the facial nerve (7)
supplies the muscles of facial expression which develop from the second branchial arch, and stapedius, stylohyoid and part of digastric
Describe the parasympathetic motor functions of the facial nerve
pre-ganglionic fibres arise in the sup. salivatory nucleus and pass to; pterygopalatine ganglion (lacrimal gland) submandibular ganglion (submandibular and sublingual salivary glands)
Describe the sensory functions of the facial nerve
cutaneous sensory information from the external ear. 1st order neurones lie in the geniculate ganglion (middle ear) and axons pass to the spinal trigeminal nucleus.
Describe the special sensory functions of the facial nerve
the chorda tympani nerve innervates (taste) the anterior 2/3rds of the tongue. 1st order neurones lie in the geniculate ganglion (middle ear) and pass to the nucleus solitarius (also receives fibres from IX and X).
What are the consequences of damage to the facial nerve?
Conditions affecting VIIth nerve include;
Bell’s palsy; unilateral facial paralysis
Geniculate herpes zoster (vesicles in ear drum)
UMN lesion- upper facial muscles are relatively well preserved due to bilateral innervation of the facial nucleus.
LMN lesion- paralysis of both upper and lower facial muscles.
Where do facial nerve fibres arise?
- Facial nucleus
- Pons
Describe the special sensory functions of the vestibulocochlear nerve (8)
sensory information relating to hearing (cochlear nerve) and balance (vestibular nerve). 1st order neurones in the vestibular and cochlear ganglia pass to vestibular (4) and cochlear nuclei (2) in the medulla.
What are the symptoms of vestibulocochlear nerve damage?
deafness, tinnitus
dizziness, vertigo
What are the conditions involving the vestibulocochlear nerve?
Acoustic schwannoma
labyrinthitis
Meniere’s disease
Describe the motor functions of the glossopharyngeal nerve (9)
fibres arise from the nucleus ambiguus and innervate a single pharyngeal muscle which arises from the third and fourth branchial arches (stylopharyngeus).
Describe the parasympathetic motor functions of the glossopharyngeal nerve
fibres arise from the inf. salivatory nucleus and pass to the otic ganglion, from where post-ganglionic fibres innervate the parotid gland
Describe the sensory functions of the glossopharyngeal nerve
provides sensory information from the pharynx, posterior 1/3rd of the tongue and the middle ear. 1st order neurones lie in the ganglion and pass to the trigeminal sensory nucleus. Important in the gag reflex.
Describe the special sensory functions of the glossopharyngeal nerve
taste information passes from posterior 1/3rd of the tongue and the pharynx to the nucleus solitarius.
information from the carotid body and carotid sinus passes to the nucleus solitarius.
Describe the motor functions of the vagus nerve (10)
fibres arise from the nucleus ambiguus and innervate muscles of the soft palate, pharynx, larynx and oesophagus which arises from the third and fourth branchial arches . Important in swallowing and speech
Describe the parasympathetic functions of the vagus nerve
fibres arise from the dorsal motor nucleus and pass to a number of ganglia within the cardiovascular, respiratory and gastrointestinal systems.
Describe the sensory functions of the vagus nerve
provides sensory information from the pharynx, larynx, tympanic membrane and part of outer ear. 1st order neurones lie in the ganglion and pass to the trigeminal sensory nucleus. Important in the gag reflex.
Describe the special sensory functions of the vagus nerve
taste information passes from the pharynx to the nucleus solitarius.
information from the aortic body and aortic arch passes to the nucleus solitarius.
Describe the motor functions of the accessory nerve (11)
LMN’s are in the nucleus ambiguus and in the anterior horn of the upper cervical cord. They innervate trapezius and sternomastoid.
Shrug shoulders
What nerves does swallowing involve?
9 and 10
Parasympathetic fibres through vagus nerve
What nerves foes sneezing involve?
9 10 11 and 5
Spinal reflexes in lower spinal cord
What is the jugular foreamen?
The lower cranial nerves (IX, X, XI) may all be affected at the base of the skull (jugular foramen) by tumour, trauma or an inflammatory process. XII leaves the skull via the hypoglossal foramen and is only affected by large tumours
Describe the motor functions of the hypoglossal nerve
This innervates both the extrinsic and intrinsic muscles of the tongue. LMN’s are in the hypoglossal nucleus.
Unilateral lesions result in weakness and atrophy of the tongue on the affected side. When protruded the tongue deviates towards the affected side.
Describe Bulbar and pseudobulbar palsy
Bulbar refers to the motor nuclei of the brainstem (strictly the medulla[“bulb”]). Corticobulbar fibres pass from the cortex to brainstem nuclei. As with elsewhere in the motor system there are UMN (pseudobulbar) and LMN (bulbar) lesions.
=Bulbar (LMN); atrophy and fasciculation of the innervated muscles.
=Pseudobulbar (UMN); usually have to be bilateral lesions due to bilateral innervation. Exaggerated reflexes (jaw) and spastic paresis of the tongue.
=Dysphonia, dysphagia and dysarthria are seen in both.
Bulbar palsies are most commonly seen in MND (chronic) and Guillain-Barre (acute).
Pseudobulbar palsies are most commonly seen in vascular disease and demyelination.
What are the other components of the brainstem?
-Reticular formation
=Periaqueductal grey matter (midbrain) has ascending arousal pathways, and descending pain suppression pathways
-Autonomic control centres
=Cardiovascular
=respiratory
-Ascending and descending white matter pathways
What is the Reticular activating system?
-Thalamus (cortical activation, sleep spindle)
-Input from hypothalamus (sleep/wake switch)
=Deactivation= coma
