Brainstem Dz Flashcards
What is the brainstem made up of? What are their alternative names and how can this be remembered?
STY - Midbrain = meSencephalon - Pons = meTencaphalon - Medulla Oblongata = mYelencephalon (together pons and medulla = rhomboencephalon)
Where do the cranial nerves exit the brain?
- 1 and 2: forebrain
- 3 and 4: midbrain
- 5 : PONS
- 6-12: medulla oblongata
What is ARAS? What activities does it affect?
> ascending reticular activating system part of the reticular formation
- collection of neuronal cell bodies - meshwork
- activates cerebral cortex -> awake state and levle of conciousness
affects many activities
- respiration
- CV function
- voluntary excretion
- swallowing
- vomiting
- muscle tone
- voluntary movement
What nuclei are present in the pons?
> pontine nucleus
- integrates visual inputs -> motor
What general functions (motor, sensory etc) do the cranial nerves have?
- motor, sesnory or mixed function
- any autonomic = PARASYMPATHETIC tone (occulomotor, facial, glossopharyngeal and vagus)
- no sympathetic
Which nucleus is responsible for gait generation and where is this found?
> red nucleus
- rostral midbrain (mesencephalon)
- responsibel for the CONTRALATERAL postural reactions
What type of lesion causes decerebrate rigidity?
- diffuse brainstem lesion affecting the mesencephalon (midbrain)
What does decerebrate rigidity look like?
- stuperous
- all 4 limbs stiff
How does decerebellate rigidity occour?
- concious
- flexion of pelvic limbs
- tense forelimbs
Where is the oculomotor nucleus and what is this responsible for?
> midbrain
repsonsible for…
- motor and parasympathetic
- sphincter pupillary muscle constriction
- extraocular muscles (3 recti, not lateral, and the ventral oblique)
- levator palpebrae superioris muscle
Outline the path of the PLR
- optic nerve - chiasm -optic tract
- pretectal nucleus (thalamus)
- oculomotor nucleus (midbrain)
- oculomotor nerve (CN3)
- ciliary ganglion
- short ciliary nerve
How do the short ciliary nerves differ between species? Clinical implications?
(=iridal sphincter muscle)
- dogs: short ciliary fibres (5-8)
- cats: nasal and malar (lateral)
> in cats if one nerve is affected -> D shaped pupil (dyscoria)
What pathologies may affect the short ciliary nerves in cats?
- FeLV associated Lymphoma loves short ciliaries!
Localise the lesion: 5yo FS whippet, 2-3 week hx lethargy and acute onset blindness 4d ago, absent menace OU, fixed dilated pupils OU, normal fundus, depressed mental status
Bilateral optic nerves, optic chiasm
If PLR deficiits and vision loss both present where must the lesion be? potential causes
Where the pathways are shared ie. optic nerves and chiasm
- intramedullary or neoplastic most likely
- optic nerves can be compressed by severe meningitis
How does the eye appear if occulomotor is damaged?
Lateral stabismus and rotation medially d/t unopposed actions of lateral rectus and dorsal oblique
What does trochlear do?
- motor only to dorsal oblique (poor trochlear)
- only CN that crosses over (all others innervate ipsilateral side)
- Only CN that arises dorsally (all others arise medially)
How would the eye appear with a trochlear lesion?
- lateral rotaion of both eyes (only really seen in cats) d/t unoposed ventral oblique (dorsal oblique lost)
- may see BVs off centre looking at fundus
> BUT very rare to jsut have a trochlear lesion! Others probably present.
What is the tectotegmentalspinal tract? Where does it originate? What clinical signs are seen with dysfunction of this pathway?
- sympathetic innervation of the eye
- originates in midbrain, diencephalon has influence over this area
- 3 neuron pathway
- dysfunction = Horner’s syndrome
What are the 1st, 2nd and 3rd order neurons in the tectotegmentalspinal tract?
1 - tectotegmental spinal tract from midbrain through spinal cord
2 - nerves from spine - cranial cervical ganglion [ not in brain]
3 - nerve innervating the eye via tympano occipital fissure and orbital fissure, past trigeminal ganglion
Where do sympathetic and parasympathetic fibres exit the spine?
- craniosacral: parasymp
- thoracolumbar: symp
What are the 3 forms of Horner’s syndrome? Clinical signs associated with each?
> 1st order - intracranial signs - spinal cord dysfunction > 2nd order - brachial plexus - cervical trauma > 3rd order - middle/inner ear dz - facial paralysis - vestibular dysfunction
What nucleus is in the pons? Functions?
Trigeminal
- 3 braches (opthalmic, maxillary, mandibular)
- all 3 sensory
- mandibular only mm. of mastication
Where are the regions innervatedby each branch of trigem?
- opthalmic does around the orbit, globe (cornea) AND THE NARES
- maxillary dorsal face
- mandibular obvs mandible
Ddx for a specific nerve branch targetted pathology?
- granulomatous neuritis
- neoplasia
What are the muscles of mastication innervated by trigem?
- temporalis
- masseter
- pterygoid (lateal and medial)
- digastricus rostral
How would a unilateral trigem neuropathy manifest?
- severe masticatory muscle atrophy
- no sensation to one side of face
- may have ulcer in affected eye d/t lack of sensation
What sings wouldb e expected if midbrain affected?
- altered mental status
- ipsilateral posture deficits
What is dropped jaw and what signs may be seen alongside it?
- in ability to close mouth d/t dysfunction of mandibular trigem branch
- hypersalivation
- difficulty eating and drinking
- abnormal facial sensation
- some presetn with Horner’s 2* as nerves pass next to each other
Ddx dropped jaw?
> non neuro - bilateral luxation of TMJ - mandibular fx - oral FB with inability to cloe the mouth > neuro - inflam/infectious - trauma (carrying heavy objects) - toxic (botulism) - idiopathic (trigem neuropathy or cranial polyneuropathy) - neoplasia (lymphoma)
Diagnostics for dropped jaw?
- haem and biochem
- rads of thorax
- abdo ultrasound
- MRI brain
- CSF
r/o other causes > idiopathic trigeminal neuritis and Horner’s syndrome
Tx dropped jaw? ( idiopathic trigeminal neuritis and Horner’s syndrome )
- put elastic band around face to allow them to close mouth and eat
- physioltherapy
Which CN nuclei are found in the medulla oblongata (myelencephalon?) What else is present here?
6-12 and respiratory centres
What does CN 6 innervate?
> abducent
- motor to extraocular mm. lateral rectus only
- motor to retractor bulbi m.
What would a CN6 lesion cause the eyes to do?
Medial strabismus d/t unopposed medial rectus and no globe retraction
Causes of facial n. paralysis
- otitis media/interna (as leaves medulla oblongata v. close to base of the ear)
- trauma
- neoplasia
- polyneuropathy (hypothyroid dogs)
- 75% idiopathic dgos, 25% cats
What does the facial n. innervate?
- motor to the face
- parasympathetic to salivary and lacrimal glands
So what would a facial n. lesion likely cause?
- KCS
- facial paralysis
Which nerve is very closely assocaited with the facial n?
vestibulocochlear nerve exits via same foramina (so head tilt may also be seen with facial n. problems)
Is vision necessary for vestibulocochlear pathway?
no
What would vestibulocochlear lesions cause?
See vestibular lecture
- head tilt
- hearing loss
What makes up the nucleus ambiguous?
CN IX, X, XI
- motor, sensory and parasympathetic
What are CN IX and X responsible for?
- Gag reflex
- Motor, sensory and autonomic
> IX - motor pharynx and palatine structures
- sensory (caudal 1/3 tongue and pharyngeal mucosa)
- parasympathetic (parotid and zygomatic glands)
- gag and swallow
> X - motor larynx (RLN) pharynx and oesophagus
- sensory (larynx, pharynx, thoracic and abdominal viscera)
- parasympathetic (thoracic and abdo viscera)
What is CN XII responsible for? When may theis be damaged?
- hypoglossal canal
- motor mm. of tongue
> damage w/ very cranial cervical lesions - dalmation, hemiparesis, mild cervical discomfort
