Brainstem and forebrain disease (1 and 2) Flashcards
What is the forebrain?
area of brain rostral to tentorium cerebelli:
- telencephalon or cerebrum
- thalamus (part of diencephalon)
Name 3 lobes of cerebrum
- olfactory bulbs/tracts
- frontal lobes
- parietal lobes
- temporal lobes
- occipital lobes
Function - olfactory bulb
- Perception of smell
- limbic system
Function - temporal lobe of cerebrum
- auditory area
- vestibular conscious perception
- pyriform lobe: olfactory and limbic systems
Function - frontal lobes
- mainly motor area - corticospinal and corticonuclear tracts (gives motor info to contralateral limbs)
Function - parietal lobes of cerebrum
- mainly sensory-motor areas (sensory info of contralateral limbs)
Function - occipital lobes of cerebrum
visual conscious perception
Outline the visual pathway
retina –> optic nerve –> optic chiasm –> optic tract –> lateral geniculate nucleus (LGN) –> optic radiation to occipital lobe (visual conscious perception)
What is a sign of optic neuritis when looking at an eye using ophthalmoscopy?
where the fundus looks like there is something pushing outwards from behind it
T/F: a cat with slow onset vision loss adapts to home very well and doesn’t seem blind to owner until introduced into an unfamiliar environment.
True
Which tests can you use to assess vision?
- in dim and bright light
- observing the animal moving in an unfamiliar environment
- negotiating obstacle course
- visual placing
- menace response
Outline pathway of menace response
Visual pathway to occipital lobe –> association fibres –> motor cortex of frontal lobe –> projection fibres –> pontine nucleus –> transverse fibres of pons –> cerebellar cortex –> efferent cerebellar fibres –> facial nuclei –> increased firing in facial nn –> blinking
Describe how menace response is learned
- absent in first 10-12 weeks (dogs and cats)
- absent if stressed, lethargic or disorientated
CS - forebrain dysfunction
- altered mental status (depression, delerium, confusion, stupor, coma)
- behavioural changes (thalamic)
- seizures
- abnormal behaviour (hemi-neglect syndrome)
- gait - normal, head-pressing, pacing (to side of lesion), circling
- posture - head turn usually associated with body turn (pleurothotonus) and circling, postural reaction deficits (contralateral to lesion)
- decreased facial sensation (contralateral to lesion, all 3 branches of trigeminal are sensory, only mandibular is motor)
- spinal reflexes NORMAL unless multifocal
What is mesencephalon?
midbrain
What is metencephalon?
the pons, a part of rhombencephalon
What is the myelencephalon?
the MO, a part of the rhombencephalon
Which CNs have got parasympathetic components?
- occulomotor (3)
- facial (7)
- glossopharyngeal (9)
- vagus (10)
What is ARAS?
Ascending reticular activating system, part of the reticular formation. Found in brainstem. Reduced ARAS activity –> reduced sleep. It activates the cerebral cortex - keeps in an awake state with a certain level of consciousness.
What is the reticular formation?
a collection/ meshwork of neuronal cell bodies in the brainstem
Function - reticular formation meshwork
- respiration
- CV function
- voluntary excretion
- swallowing
- vomiting
- mm tone
- voluntary movement
What does the red nucleus in the midbrain/ mesencephalon control?
gait generation
What does a lesion in rostral midbrain cause?
contralateral postural deficits
What is decerebrate rigidity?
- extension of all limbs
- mentally v stuporous
- contrasts with decerebellate
What is decerebellate rigidity?
- increased mm tone
- mental status ok not stuporous (eyes open looking around) as brainstem not affected
What is the oculomotor nucleus?
- found in midbrain
- motor (to extraocular mm: dorsal, ventral, medial adn ventro-medial oblique) and parasympathetic parts (assess PLR for sphincter pupillary mm contraction)
Describe PLR pathway
optic nerve –> optic chiasm –> pretectal nucleus (thalamus) –> occulomotor nucleus (midbrain) –> occulomotor nn (CN3) –> ciliary ganglion –> short ciliary nerve
(remember an animal doesn’t need to see to have a PLR, there is a double crossover of fibres to reach occulomotor nucleus)
How are the short ciliary nerves to the iridal sphincter mm different?
- DOGS: short ciliary fibres (5-8)
- CATS: nasal and malar fibres (2)
What is dyscoria?
abnormal pupil size
What causes a reverse D-shaped pupil dyscoria?
Parasympathetic fibres (nsasl and molar fibres in cats). In cats, FeLV-associated lymphosarcoma infiltration can cause this (lymphoma likes short ciliary nn)
What is idiopathic hypertrophic pachymeningitis?
an immune-mediated type of meningitis
How can you differentiate an infectious and immune-mediated meningitis?
CSF sample -> no bacteria/ neutrophils etc suggests immune-mediated and vice versa
Function - trochlear nn (CN4)
Motor (from trochlear nucleus) to extraocular mm (dorsal oblique only). This is the only CN to arise in dorsal midbrain. It is also the only CN to innvervate the contralateral mm (all other CNs innervate the ipsilateral mm)
What is the tectotegmental spinal tract?
- tract originates in midbrain
- SNS innervation to eye
- diencephalon has influence over this part of midbrain
- 3-neuron pathway
- dysfunction –> Horner’s syndrome
What are the 3 parts of sympathetic innervation to the eye?
- 1st order neuron: tectotegmental spinal tract
- 2nd order neuron: cranial cervical ganglion
- 3rd order neuron: tympano-occipital fissure
* lesion in any part of this pathway –> Horner’s
CS - 1st order Horner’s syndrome
- intracranial signs
- spinal cord dysfunction
Causes - 2nd order Horner’s syndrome
- brachial plexus problem –> lame
- cervical trauma
Causes and CS - 3rd order Horner’s syndrome
- CAUSES: middle/inner ear disease
CS: facial paralysis, vestibular dysfunction
What does the pons (metencephalon) contain?
- trigeminal nucleus (trigeminal nerve)
- UMN (ipsilateral)
Classic CS of lesions to ophthalmic branch of trigeminal nn
- no corneal sensation
- no sensation inside ipsilateral nare
Which mm does the trigeminal nn (CN5 innervate)?
- temporalis
- masseter
- pterygoid (lateral and medial)
- digastricus rostral
What is a dropped jaw? Cause? Other CS?
inability to close mouth
- dysfunction of motor part of trigeminal nn (mandibular branch)
- hypersalivation with difficulty drinking and eating
- some dogs can also have abnormal facial sensation
- some dogs present with Horner’s syndrome
Ddx - dropped jaw - 2 main categories and examples
NON-NEURO CASES:
- bilateral luxation of TMJ
- mandibular fracture
- oral FB inability to close mouth (due to overstretching)
NEURO CASES:
- inflammatory/ infectious
- trauma (carrying large heavy objects with mouth)
- toxic (botulism)
- idiopathic (trigeminal neuropathy or cranial polyneuropathy_
- neoplasia (lymphoma)
Diagnostic tests - dropped jaw
- CBC and comprehensvie biochem
- radiograph thorax
- abdominal ultrasound
- MRI brain
- CSF
What is found in MO?
- CN nuclei (6-12)
- UMN (ipsilateral)
- respiratory centre (thus may need ventilator if dysfunction with this)
Function - abducent nn (CN 6)
- motor (abducent nucleus)
- extraocular mm (retractor bulbi mm and lateral rectus mm. Thus dysfunction –> strabismus (medial) and won’t be able to retract eyeball.
Function - facial nn
- motor
- parasympathetic (lacrimal and salivary glands)
Function - vestibulocranial nn
Unique sensory CN for balance
Dysfunction –> imbalance and heariing loss
Which CNs control eye movement?
- occulomotor
- abducens
- trochlear from vestibulocochlear?
What is the nucleus ambiguus?
contains motor, sensory and P/S nn all at the same level in the MO
What controls the gag reflex?
Stems from nucleus ambiguus - the important CNs are 9 and 10
Function - glossopharyngeal nn (CN9)
- motor to pharynx and palatine structures
- sensory (caudal 1/3 tongue and pharyngeal mucosa)
- P/S (parotid and zygomatic glands)
Function - vagus nn (CN10)
- motor larynx (recurrent laryngeal nn), pharynx and oesophagus
- sensory (larynx, pharynx, thoracic and abdominal viscera)
- P/S (thoracic and abdominal viscera)
Describe hypoglossal nn (CN12)
- exits from hypoglossal canal
- motor (mm of tongue)
- cranial cervical lesions
- dalmation, hemiparesis, mild cervical dysfunction
ddx- facial neuropathy
- infxn middle/inner ear
- trauma
- neoplasia
- polyneuropathy (canine hypothyroid)
- idiopathic (–> 75% dogs, –> 25% cats)
Facial P/S neuropathy - CS
- KCS
- dry nose
- head tilt
