Neurolocalisation 2 - Cranial Flashcards
(36 cards)
Which are the different neurolocalisations we re aiming to differentiate?
Forebrain.
Cerebellum.
Brainstem.
Cranial nerves.
What does the brainstem do?
Reticular activating system.
- passes vital info to the brain.
- regulates arousal and response to environment.
- obtundation seen if detective.
Cranial nerve reflex arcs.
- all housed in brainstem.
Vestibular nuclei.
- large part of brainstem.
- regulate balance.
- communication w/ cerebellum.
Motor and sensory tracts.
- carry info for proprioception and movement to and from brain.
What does the cerebellum do?
Regulates movement.
Vestibular connections:
- vital for balance and coordination.
What do cranial nerves generally do?
Provide specific sensory info or motor output.
What does the forebrain do?
Sensory, association and motor areas:
- integrate input to provide a learned output (response).
First step of cranial localisation process.
Assess forebrain function.
- are the responses to the environment appropriate?
- are our tested responses normal?
3 important tests of forebrain function?
Behavioural responses (mentation).
Proprioceptive responses (hopping, paw placement).
Menace response.
*less reliable, so less important:
- response to nasal mucosal stimulation.
- visual fixation response.
Assessing behavioural responses…
1. Mentation definition.
- Mental activity; can be inappropriate w/ poor forebrain function (usually dysregulated) or w/ abnormalities in the reticular activation system of brainstem (usually obtunded to comatose).
Can be:
- manic = inappropriately over responsive (only from forebrain, not brainstem).
- obtunded = reduced response to external stimuli.
- stuporous = only responsive to noxious stimuli.
- comatose = unresponsive to any stimuli.
Assessing mentation.
Ask the owner if the behaviour seems appropriate to them.
Judge behaviour from a combination of what is seen as appropriate to the owner and what is appropriate to you.
What are seizures always a sign of?
Forebrain disease.
Key concepts in proprioceptive responses and forebrain function.
Proprioceptive responses on one side of the body are regulated by the CONTRALATERAL forebrain.
Some forebrain diseases can only have mild gait disturbances, but dramatic proprioceptive deficits.
What does the menace response screen the function of?
Eye.
Optic tract.
Forebrain.
Cerebellum.
Brainstem.
Facial nerve.
Broad groups of cranial nerve test types.
Tests involved in distant exam of head and face.
Tests assessing eyes (symmetry, movement, vision).
Tests assessing swallowing and barking.
What cranial nerve are difficult to test / cannot be tested?
Olfactory (I).
Trochlear (IV).
Accessory spinal (XI).
Cranial nerve examination process.
Efficient and systematic:
- distant exam of head and face.
- assess eyes.
- assess swallowing/barking.
Cranial nerve exam interpretation.
Re-ordering of the info.
- go through each nerve and decide if there is dysfunction or not.
- then decide if that indicates a nerve problem (peripheral) or a cell body problem (brainstem) by combing all signs together.
Assessing cranial nerves - observation of the head and face.
Is there a head tilt.
- tests vestibular nuclei in brainstem; VII and cerebellum).
- need to look at horizontal axis of eyes when distracted e.g. walking.
- persistent head tilt indicates cerebellar, brainstem (or possibly thalamic) dysfunction.
Masticatory muscle mass and tone normal.
- tests trigeminal, mandibular branch; Vmd).
- should not be able to palpate inner edge of zygomatic arch.
- LMN lesion of V (mandibular) if unilateral; LMN lesion or myopathy if bilateral.
- animals should be able to hold mouth closed AND open them fully.
– dropped jaw (inability to close) = bilateral trigeminal paresis.
– trismus (inability to open) almost always as masticatory muscle disease.
Is the face moving on both sides.
- watch eyebrows, ears, lips, nares and muzzle for movement.
- if no spontaneous movement at appropriate times, likely facial nerve lesion.
Assessing cranial nerve - examining the eyes.
Are palpebral fissures and 3rd eyelids symmetrical?
Are the pupils the same size?
Can they blink?
Can they see?
Do the pupils respond to light?
Can the globes move?
Is there abnormal/pathological nystagmus?
Palpebral fissure and 3EL position.
Look face-on at the animal.
Palpebral fissure narrowing can be oculomotor (III) or facial (VII) but almost always sympathetic denervation (Horner’s syndrome).
3EL protrusion (dogs):
- sympathetic denervation (Horner’s; has other signs too).
- retrobulbar mass (pushes eye and 3EL forward; cannot retro pulse).
- masticatory muscle atrophy (enophthalmus).
3EL protrusion (cats):
- as above.
- also illness as under active control.
Pupil size.
Parasympathetic (III) and sympathetic.
Examine in light and also use reflective tapetum to highlight pupil in dark.
Mydriasis (inappropriate dilation)
= large pupil will not constrict in light.
Miosis (inappropriate constriction)
= small pupil will not dilate in dark.
Horner’s syndrome = loss of sympathetic innervation to one of the eyes.
- unable to dilate pupil.
- unable to constrict vessels in the sclera/conjunctiva.
- narrowed palpebral fissure.
- 3EL protrudes.
Miosis differentials:
- Horner’s syndrome.
- uveitis.
- reflex constriction w/ corneal pain.
Can they blink?
Palpebral reflex.
Tests trigeminal (V - mx, md), brainstem, facial (VII).
Tap skin beside eye; medial canthus (tests maxillary branch) more reliable than lateral.
Ca also stimulate cornea (tests ophthalmic branch) w/ clean material e.g. tissue, cotton bud.
No blink = facial, brainstem or trigeminal lesion.
A brainstem lesion could give BOTH facial and trigeminal dysfunction (but would need to affect other brainstem function too).
If no blink, how can you differentiate between a trigeminal vs a facial lesion?
Trigeminal - sensory absent, motor intact.
– observe no response to touching face, but will blink/move spontaneously, may have masticatory atrophy or paresis.
Facial - sensory intact, motor to palpebral muscles absent.
– observe reduced spontaneous movement, other motor reflexes (head movement, globe retraction) intact and unaffected.
Cam they see? - menace.
Menace response.
Move hand towards eye.
Tests optic tract for sensory.
- signal from optic tract at front of brain to visual cortex at back of brain, to motor cortex, down to brainstem, cerebellum vital here, then to facial nerve for motor.
Get blink if they can see.
Testing eye tests CONTRALATERAL forebrain and IPSILATERAL cerebellum.
Hold head to cover contralateral eye.
Make sure they can blink by tapping face.
Make sure they are looking at you!
Then make small movement from far away.
Absent menace can be due to lesion in:
- retina, optic tract, contralateral forebrain, ipsilateral cerebellum, brainstem, facial nerve.
Can they see? - visual fixation.
Ask an animal to watch an object e.g. cotton wool, laser pointer, light.
Should see eye or head movement.
Retinal and optic tract or forebrain lesions cause loss of visual fixation.
Requires attention so false negatives often seen in difficult to restrain patients.
Useful in ruling out blindness following an absent menace response.
