Principles of Forebrain and Brainstem Disease Flashcards
What structures compose the forebrain and are involved in forebrain disease?
Cerebrum and Thalamus
- Area of the brain rostral to the tentorium cerebelli
- does NOT include the brainstem and CN’s
- Thalamus (part of diencephalon)
Anosmia
- the loss of the sense of smell, either total or partial. It may be caused by head injury, infection, or blockage of the nose
- can be in reference to loss of smell unilaterally due to a lesion on one olfactory bulb (ex: tumor growth) - would be rare to pick up on these clinical signs
The Limbic System
- The structures and interacting areas of the limbic system are involved in motivation, emotion, learning, and memory.
- The limbic system is where the subcortical structures meet the cerebral cortex.
- The limbic system operates by influencing the endocrinesystem and the autonomic nervous system
Optic Chiasm
- The optic chiasm is an X-shaped structure formed by the crossing of the optic nerves in the brain. The optic nerve connects the brain to the eye. To biologists, the optic chiasm is thought to be a turning point in evolution
Main parts of the motor sensory cortex of the brain
(or sensory motor cortex)
- Frontal Lobe
- Parietal Lobe
Pure sensory cortex of the brain
(cannot initiate any motor activity)
- OCCIPITAL LOBES
- only does visual conscious perception
Pineal Gland
- located in the Thalamus
- important in circadian and seasonal reproductive activity
- The pineal gland, conarium, or epiphysis cerebri, is a small endocrine gland in the brain of most vertebrates. The pineal gland produces melatonin, a serotonin-derived hormone which modulates sleep patterns in both circadian and seasonal cycles
Tetraparesis
Tetraparesis, or quadraparesis, is a condition in which all four limbs are weak
Ventriculoperitoneal shunting
Ventriculoperitoneal shunting is surgery to treat excess cerebrospinal fluid (CSF) in the cavities (ventricles) of the brain (hydrocephalus)
- -put in a valve and you have to make sure the direction of the valve is AWAY from the brain!!
- want that fluid to drain into the abdomen
Dorsal Metencephalon becomes…
the cerebellum
the mesencephalon becomes…
- the midbrain
the ventral metencephalon becomes…
- the pons
The myelencephalon becomes..
the medulla oblongata
the rhomboencephalon is made up of which parts?
(2)
- pons (ventral metencephalon)
- medulla oblongata (myelencephalon)
Autonomic fibers will always be….
PARASYMPATHETIC
CN that is in charge of the lacrimal glands
- CN VII - Facial n.
Which CN has parasympathetic fxn?
- CN X - Vagus n.
which CN is in charge of making the pupil smaller? (contract)
- CN III - Oculomotor n.
- which is a parasympathetic fxn of this nerve
the 4 Autonomic CN’s
- Oculomotor n. (CN III)
- Facial n. (CN VII)
- Glossopharyngeal n. (CN IX)
- Vagus n. (CN X)
- means they are always parasympathetic!
The only CN coming from the pons
CN V - Trigeminal n.
CN’s from the midbrain
(2)
CN III and IV
CN’s coming from the medulla oblongata
- CN VI to XII
Severe dysfunction in the Ascending Reticular Activating System will result in what presentation?
- Unconscious Mental Status
Important in gait generation…
- red nucleus
- in the midbrain (most rostral part of the brainstem)
proprioceptive pathways and postural reactions
- contralateral forebrain
- ipsilateral brainstem
What does it mean when a patient has Decerebrate Rigidity posture?
- means that there is a lesion in the midbrain (brainstem)
- is so severe that they are always unconscious
- different to other postures in that they will always be unconscious with this
Opisthotonos
recognize the 3 rigidity postural reactions
- Schiff Sherrington
- Decerebellate rigidity
- Decerebrate rigidity
Decerebellate Rigidity posture
Lesion in rostral part of the cerebellum
-they will be conscious!
- can be increased tone on all 4
- sometime the pelvic limbs will are flexed because you have increased tone on the iliopsoas muscle, but sometimes they cannot be flexed –> don’t rely on the pelvic limbs being flexed or not
Oculomotor n - CN III is….
- motor and parasympathetic
- motor to the majority of the extraocular muscles - does everything except for the dorsal oblique and lateral rectus m.’s
- does the dorsal, the ventral, medial rectus and the ventral oblique
- also the motor to the levator palpebrae superioris muscle
- also responsible for constricting hte iris muscle when we conduct the PLR - sphincter pupillary muscle constriction
what happens when there is a dysfunction of the oculomotor n. ?
- pupil is dilated
- may have ptosis of the upper eyelid
Is the forebrain involved in the PLR?
NO.
- PLR is a REFLEX and therefore the forebrain is not involved
Dyscoria
An abnormality in the shape of the pupil of the eye
If you see this presentation, what should you immediately test for?
(2)
- Lymphoma
- FeLV
attack the short ciliary nerves
What does the Trochlear Nerve do?
- Innervates the Dorsal Oblique -extraocular muscle
- motor fibers
- if it is not working, then you don’t really see anything in terms of clinical signs
- BUT, it is the only cranial nerve that arises from the dorsal part of the brainstem and is the only cranial nerve that crosses over and does the contralateral muscle
Which Branch of the trigeminal nerve is Motor?
MANDIBULAR BRANCH
Only one of these branches is MOTOR –> Mandibular!
Innervates the muscles of mastication
- Masseter
- Rostral digastricus
- Temporalis
- Pterygoids (medial and lateral)
- Very tiny tympanic muscle (ex: for popping ears under pressure)
Functions of the Abducens nerve (CV VI)
- Motor
- Extraocular muscle: lateral rectus
- retractor bulbi m.
- job is to abduct the eye
What presentation could you get if you had an issue with the inner ear?
(2 together)
- vestibular signs
- facial drooping (issues with the facial n. CN VII)
both run closely together by the inner ear
xeromycteria
- pathological dryness of the nose
- would see if parasympathetic fibers of the facial nerve are affected along with dry eye (KCS)
- if you see this all together with a normal mental status, this can only happen in the inner ear
Keratoconjunctivitis Sicca
- Keratoconjunctivitis sicca (KCS), commonly referred to as “Dry Eye”, is one of the most common dog eye problems.Dry Eye affects 1 in 22 of all dogs in the UK. Dry Eye is caused by destruction of the tear glands by your dog’s own immune system. This means that too few natural tears are produced
Vestibulocochlear Reflex
- way of testing CN VIII - vestibulocochlear n.
- -move head side to side
-gives bilateral and symmetrical connections to the CN 6,3, 4 to control the extraocular muscles
Nucleus Ambiguus
(3 components)
- Glossopharyngeal (CN IX)
- Vagus (CN X) - all parasympathetic remember!
- Accessory n (CN XI)
- extremely important in the gag reflex!
- gag reflex could be affected if there is a lesion here and then there is a risk of aspiration pneumonia for these patients
- so check this!! - especially is you expect a lesion on the caudal part of the medulla oblongata
Most commonly encountered brain tumor in cats?
other honorable mentions - 5
- meningioma
- other common ones:*
- CNS lymphoma
- gliomas (astrocytomas and oligodendrogliomas)
- Choroid plexus tumors
- Ependymomas
- Pituitary Tumors
stroke
- result of an infarction of the CNS
- generally a vascular disorder
Predominating clinical sign in cats with a Thiamine Deficiency
- signs of brainstem dysfunction (particularly vestibular dysfunction) usually predominate
- Thiamine deficiency will cause an encephalopathy and is occassionally encountered even in cats that are fed a commercial diet
Exception to toxins regarding symmetrical neuropathies
anticoagulant rodenticide toxicity
- may cause focal hemorrhage into the CNS and therefore deficits referable to a focal lesion
Bacteria commonly found in abscesses formed by cat bite trauma
- Actinomyces viscosus
- generally sensitive to Amoxycillin/Clavulanate
the 8 parts of a neurological examination
- Mentation
- Posture
- Gait
- Postural Reactions
- Spinal Reflexes
- Cranial Nerves
- Palpation
- Nociception
