Module 2 Flashcards
- is situated in the posterior cranial fossa and is covered superiorly by the tentorium cerebelli
- largest part of the hindbrain and lies posterior to the 4th ventricle, pons and medulla oblongata
- somewhat ovoid in shape and constricted in its median part
Cerebellum
Cerebellum consists of two cerebellar hemispheres joined by a narrow median __
vermis
The cerebellum is connected to the posterior aspect of the brainstem by three symmetrical bundles of nerve fibers called the ___
superior, middle, and inferior cerebellar peduncles
The cerebellum is divided into three main lobes:
- Anterior lobe
- Middle lobe
- Flocculonodular lobe
– superior surface of the cerebellum and is separated from the middle lobe by a wide V-shaped fissure called the primary fissure
Anterior lobe
– sometimes called the posterior lobe
– is the largest part of the cerebellum, is situated
between the primary and uvulonodular fissures.
Middle lobe
– is situated posterior to the uvulonodular fissure
Flocculonodular lobe
– found along the margin of the cerebellum separates the superior from the inferior surfaces
Horizontal fissure
The cerebellum is composed of an outer covering of gray matter called ____
cortex and inner white matter.
Embedded in the white matter of each hemisphere are three masses of gray matter forming the ____
intracerebellar nuclei
3 Functional Divisions of the Cerebellum
- Paleocerebellum
- Neocerebellum
- Archicerebellum
- Consists of the vermis of the anterior lobe, the pyramids, the uvula, and the paraflocculus
- Also known as the spinocerebellum
- Plays a role in the control of muscle tone and the axial and limb movements.
Paleocerebellum
- Corticocerebellum or cerebrocerebellum
- Consists of the middle portion of the vermis and most of the cerebellar hemispheres
- Also known as pontocerebellum
- Projects fibers to the cerebral cortex through the thalamus
- Plays a role in the planning and initiation of movements, as well as regulation of fine limb movements.
Neocerebellum
- Corresponds to the flocculonodular lobe
- Also called the vestibulocerebellum
- Receives input from areas of the brain concerned with eye movements
- Plays a role in the control of body equilibrium and eye movements.
Archicerebellum
A section made through the cerebellum parallel with the median plane divides the folia at right angles, and the cut surface has a branched appearance, called the ____
arbor vitae
The gray matter of the cortex throughout its extent has a uniform structure. It may be divided into three layers:
- an external layer, the molecular layer
- a middle layer, the Purkinje cell layer
- an internal layer, the granular layer
Cerebellar Output
Spinocerebellum fastigial>>medial descending systems>> motor execution interposed>>lateral descending systems>> motor execution Cerebrocerebellum dentate>>areas 4 and 6>>motor planning Vestibulocerebellum vestibular nuclei>>balance and eye movements
Internal Structure of the Cerebellum
Gray matter – outside and inside (Small aggregations of gray matter in the interior, called cerebellar nuclei)
White matter – inside
Gray matter of the Cerebellum: 3 Layers
Molecular layer – stellate cells, basket cells
Purkinje cell layer – Purkinje cells, which are large Golgi type 1 neurons
Granular layer – granule cells (fibers of which form parallel fibers), neuroglial cells, Golgi cells
Gray matter of the Cerebellum
- Purkinje cell – output
- Mainly inhibitory except granule cells (utilizes glutamate)
- Main neurotransmitter: γ-ABA
- Output of the cerebellar nuclei is excitatory but is modulated by an inhibitory cortical loop, effected by Purkinje Cell output
White matter of the Cerebellum
- Intrinsic fibers
- Afferent fibers
- Efferent fibers
– connect different regions WITHIN the cerebellum (folium-folium; hemisphere-hemisphere)
Intrinsic fibers
– form the greater part of the white matter, PROCEED to the cerebellar cortex; enter though the INFERIOR and MIDDLE cerebellar peduncles
– 3 types: mossy (predominantly), climbing (olivocerebellar tracts), multilayered
Afferent fibers
– constitute the OUTPUT of the cerebellum; commence as the axons of the Purkinje cells, which synapse with the neurons of the cerebellar nuclei; exit mainly through the SUPERIOR and INFERIOR cerebellar peduncle
Efferent fibers
Cerebellar Peduncles
Inferior Cerebellar Peduncle – connects to the medulla oblongata; restiform body
Middle Cerebellar Peduncle – connects to the pons; brachium pontis
Superior Cerebellar Peduncle – connects to the midbrain; brachium conjunctivum
Inferior Cerebellar Peduncle: Afferent tracts
- The dorsal spinocerebellar tract
- The cuneocerebellar tract
- The olivocerebellar tract
- The vestibulocerebellar tract
- The reticulocerebellar tract
- The arcuatocerebellar tract
Inferior Cerebellar Peduncle: Efferent tracts
- Fastigiobulbar tract
- - Cerebelloreticular tracts
Middle Cerebellar Peduncle: Afferent tracts
Fibers from the pontocerebellar tract (corticopontocerebellar tract)
Superior Cerebellar Peduncle: Afferent tracts
The ventral spinocerebellar tract
The tectocerebellar tract
The trigeminocerebellar tract
The cerulocerebellar tract
Four Masses of Gray matter
- Dentate Nucleus – largest of the cerebellar nuclei; has a shape of a crumpled bag with the opening medially
- Emboliform Nucleus – ovoid and is situated to the dentate nucleus, partially covering its hilus
- Globose Nucleus - consists of one or more rounded cell groups that lie medial to the emboli form nucleus
- Fastigial nucleus - lies near the midline in the vermis and close to the roof of the fourth ventricle; it is larger than the globose nucleus
Clinical Features of Cerebellar Dysfunction
- Incoordination (ataxia) of volitional movement
- A characteristic tremor (“intention” or ataxic tremor)
- Disorders of equilibrium and gait
- Diminished muscle tone
- “Cerebellar sign par excellence”
- May affect the limbs, trunk or gait
- Asynergia ; Dysmetria Adiodochokinesis; Dysdiadochokinesis
Ataxia or dystaxia
– lack of synergy of the various muscle components in performing more complex movements so that movements are disjointed and clumsy and broken up into isolated successive parts
Asynergia
- Abnormalities in the rate, range and force of movement
Dysmetria
– abnormality in the rhythm of rapid alternating movements
Adiodochokinesis; Dysdiadochokinesis
- It is related to a depression of gamma and alpha motor neuron activity
- The least evident of the cerebellar abnormalities
- More apparent with acute than with chronic lesions
- Failure to check a movement - a closely related phenomenon (impairment of the check reflex)
Hypotonia
- Hypermetria – overshooting the target
- When the finger approaches the target, there is a side-to-side movement of the finger before reaching the target.
- Titubation - A rhythmic tremor of the head or upper trunk (three to four per second)
Intention or ataxic tremor
- Scanning dysarthria – variable intonation (prosody) and abnormalities in articulation; described also as staccato, explosive, hesitant, slow altered accent, and garbled speech.
- Speech production is often labored with excessive facial grimacing.
- Thought to be a result of generalized hypotonia.
Cerebellar Dysarthria
Disturbances of Ocular Movement (Cerebellum)
- Inability to hold eccentric gaze
- Slower smooth pursuit movements with “catch-up” saccades
- Nystagmus
- Other “cerebellar” eye signs – ocular flutter, opsoclonus, ocular bobbing, square wave jerks at rest, skew deviation, failure to suppress the vestibulo-ocular reflex
– usually gaze-evoked, upbeat, rebound with abnormal kinetic nystagmus if with midline cerebellar lesions; periodic alternating nystagmus with lesions of the uvula, nodulus; downbeat nystagmus with posterior midline lesions
Nystagmus
Disorders of Equilibrium and Gait
- Standing with feet together may be impossible
- In walking, the patient’s steps may be uneven and placement of the foot may be misaligned
- Wide-based stance with increased trunk sway, irregular stepping with a tendency to stagger as if intoxicated
- Impaired tandem walking
The 4 Cerebellar Syndromes
- Hemispheric syndrome
- Rostral vermis syndrome
- Caudal vermis syndrome
- Pancerebellar syndrome
- Incoordination of ipsilateral appendicular movements
- -* Usual etiologies: Infarcts, neoplasms, abscesses
Hemispheric syndrome
- A wide-based stance and titubating gait
- Ataxia of gait, with proportionally little ataxia on the heel-to-shin maneuver with the patient lying down
- Normal or only slightly impaired arm coordination
- Infrequent presence of hypotonia, nystagmus, and dysarthria
Rostral vermis syndrome
- Axial disequilibrium (truncal ataxia) and staggering gait
- Little or no limb ataxia
- Sometimes spontaneous nystagmus and rotated postures of the head
Caudal vermis syndrome
– Bilateral signs of cerebellar dysfunction affecting the trunk, limbs, and cranial musculature
– Some etiologies: infectious and parainfectious processes; hypoglycemia; hyperthermia; paraneoplastic cerebellar; degeneration associated with small cell lung cancer
Toxic processes
Pancerebellar syndrome
Disorders of the Cerebellum
V – Vascular – strokes, hemorrhage, vasculitis
I – Infectious – cerebellitis, post-infectious, abscesses
T – Traumatic, Toxic – gross trauma, intoxication with drugs
A – Autoimmune
M – Metabolic
I – Inflammatory
N – Neoplastic, Nutritional – alcoholism, paraneoplastic
D – Degenerative, Developmental (including Congenital), Demyelinating – Multiple sclerosis, spinocerebellar degeneration, Chiari malformations
- Around 20% of metastases occur in the posterior fossa.
- - Usual neoplasms that metastasize to the brain parenchyma: lung, breast, melanoma, GI, kidney
Cerebellar Neoplasms
- a primary cerebellar neoplasm that arises in the posterior part of the vermis and neuroepithelial roof of the fourth ventricle
- ~20% of childhood brain tumors
- Occur in children around 4-8 years of age
- Males> females
Medulloblastoma
- Arises from the lining in the walls of the ventricles
- ~70% originate from the 4th ventricle
- Tumor of childhood
Ependymoma and Papilloma of the 4th ventricle
- May occur anywhere in the neuraxis
- - ___ in the posterior fossa and optic nerves are more frequent in children and adolescents
Astrocytoma
- Occur most often in association with von Hippel-Lindau disease
- May have an associated retinal angioma, or hepatic and pancreatic cysts
- Tendency to develop malignant renal or adrenal tumors
- Pxs may have polycythemia due to elaboration of erythropoietic factor
Hemangioblastoma
- Congenital anomalies at the base of the brain, consisting of:
1. Extension of a tongue of cerebellar tissue into the cervical canal
2. Displacement of the medulla into the cervical canal
- Congenital anomalies at the base of the brain, consisting of:
- Chiari II- associated with a meningomyelocoele
- Hydomyelia, syringomyelia are common associated findings
Arnold-Chiari Syndrome
- Almost always secondary to a purulent focus elsewhere in the body
- ~40% are related to diseases of the paranasal sinuses, middle ear, mastoid cells
- From otogenic sources, around 1/3 lie in the anterolateral part of the cerebellar hemisphere; the remainder occur in the middle and inferior parts of the temporal lobe
Brain Abscesses
- Result from thrombotic or embolic occlusion of a cerebellar vessel
- Symptoms: vertigo, dizziness, nausea, vomiting, gait unsteadiness, limb clumsiness, headache, dysarthria, diplopia and decreased level of alertness
- Prominent signs: limb and gait ataxia, dysarthria, nystagmus, altered mental status
Cerebellar Strokes
Cerebellar Strokes (Artery affected and Percentage)
PICA 40%
AICA 5%
SCA 35%
Cortical watershed and deep cerebellar whitematter borderzone infarcts 20%
Clinical tests for arm dystaxia
- Ask the patient to extend the arms straight out front
- Do the finger to nose test
- Rapid pronation-supination test, thigh-slapping test
Clinical tests for leg dystaxia
- Heel-to-shin test
- - Heel-tapping test
Clinical tests for dystaxia of station and gait
- Observe the patient’s stance
- Ask the patient to walk
- Tandem-walk
Clinical demonstration of hypotonia
- Inspect for hypotonia – rag doll posture
- Checking for hypotonia
- Pendulous or hypotonic muscle stretch reflexes
Overshooting and checking tests of arms
- Wrist-slapping test
- - Arm-pulling test
Eye movements, speech
- Check smooth pursuit
- - Listen to patient’s speech
Types Of Circulation
Anterior circulation – is supplied by the internal carotid Posterior circulation – is supplied by the anterior vertebral artery
Two most important arteries are the
Internal Carotid
Vertebral Artery
Arterial Supply Of The Brain
- Consumes 15% of the cardiac output
- 20% of oxygen in the body goes to the brain
- Normal blood flow 50-100ml/g of the brain per
minute - Consists of two pairs of major vessels, Internal carotid
arteries and Vertebral arteries.
– Found within the subarachnoid space
– Enters skull through foramen magnum
At the junction between the medulla and the pons the two vertebral arteries fuse to form the ___
Basilar Artery
Branches Of The Internal Carotid Are:
- Caroticotympanic artery (inconsistent)
- Pterygoid (30%)
- Meningohypophyseal trunk
- Anterior meningeal
- Artery to inferior portion of cavernous sinus
- Capsular artery
- Ophtalmic artery
- Superior hypophyseal artery
- Posterior communicating
- Anterior Choroidal
There are three most important branches of the
carotid artery that we must know; these are:
ophthalmic artery
posterior communicating
anterior choroidal
• It enters orbit via the orbit canal and lateral to the
optic nerve
• Supplies eyes and orbital contents
• Terminal branch supply the frontal area of the scalp,
the ethmoid and frontal sinuses and the
ophthalmic artery
- is a branch of the ophthalmic artery
- provides the only blood supply to the five layers of the retina
- is an end artery; its occlusion results in blindness
Central artery of the retina
– Arises from the carotid siphon, runs posteriorly
above the oculomotor nerve and joins the posterior
cerebral artery; part of the circle of Willis
– Connection between internal carotid system and vertebral artery system through the posterior
cerebral artery
– Stroke of this area results in bitemporal hemianopsia
(Loss of vision on the outer half of each eye) as it
supplies the optic chiasm)
– is a common site for berry aneurysms
Posterior communicating artery (PCoA)
- it is formed because the two anterior cerebral arteries usually meet over short distance of midplane. At the medial aspect of the brain.
- is the most common site of berry aneurysms
Anterior communicating artery (ACA)
– arises from the internal carotid artery
–supplies the choroid plexus of the temporal horn of the lateral ventricle, hippocampus, amygdala, optic tract, lateral geniculate body, globus pallidus, and ventral part of the posterior limb of the internal capsule
– supplies the proximal portion of optic radiations as they leave the lateral geniculate
body to form Meyer loop
Anterior choroidal artery
– originates at the terminal bifurcation of the internal carotid artery.
– gives direct branches to the optic chiasm.
– supplies the medial surface of the frontal and parietal lobes and corpus callosum.
– supplies part of the caudate nucleus and putamen and anterior limb of the internal
capsule via the medial striate artery of Heubner
– supplies the leg and foot area of the motor and sensory cortices (paracentral lobule)
Anterior cerebral artery
– largest branch of the ICA; supplies many deep structures as much as the lateral aspect of the cerebrum, it breaks up into several branches that course in the depth of the lateral fissure , over the insula before reaching the convexity of the hemisphere.
– Supplies the lateral convexity of the hemisphere and underlying insula
– Supplies the trunk, arm, and face areas of the motor
and sensory cortices
– Supplies the Broca and Wernicke speech areas
– Supplies the caudate nucleus, putamen, globus
pallidus and the anterior and posterior limbs of the
internal capsule via lateral striate arteries
Middle cerebral artery (MCA)
– it is the largest medial artery.
– It is also the most important since it supplies blood to the
Caudate Nucleus, Putamen, Outer Globus Pallidus, and
Anterior Limb of the internal capsule
– Branch of the anterior cerebral artery
– Once there’s an injury it’ll show collateral face and
arm weakness
– Expressive aphasia in the dominant hemisphere
Recurrent Artery of Heubner
- It is the branch of the 1st part of the subclavian
artery - Joins its opposite partner to form basilar artery at
the level of pons (vertebrobasilar system)
Gives rise to the following: Anterior Spinal Artery, Posterior Spinal Artery and Posterior Inferior Cerebellar Artery
Vertebral Artery
- supplies the anterior two-thirds of the spinal cord, including the anterior and lateral horns.
- supplies the pyramids, medial lemniscus, and intra-axial fibers of the hypoglossal nerve (cranial nerve [CN] XII) in the medulla.
Anterior spinal artery
- supply the posterior third of the spinal cord, including the posterior horns and columns.
- supply the gracile and cuneate fasciculi and nuclei in the medulla.
Posterior spinal arteries
– gives rise to the posterior spinal artery.
– Largest branch
– Supplies the dorsolateral zone of the medulla
– Supplies the inferior surface of the cerebellum and the choroid plexus of the fourth ventricle.
– Supplies the medial and inferior vestibular nuclei, inferior
cerebellar peduncle, nucleus ambiguus, intra-axial fibers of the glossopharyngeal nerve (CN IX) and the vagal nerve (CN X), spinothalamic tract, and spinal trigeminal nucleus and tract.
– Supplies the hypothalamospinal tract to the ciliospinal center of Budge at T1–T2 (Homer Syndrome)
Posterior Inferior Cerebellar Artery
- is formed by two vertebral arteries
- gives rise to: Pontine arteries; Labyrinthine artery, Anterior inferior cerebellar artery, Superior Cerebellar Artery and Posterior Cerebellar Artery
Basilar Artery
– include penetrating and short circumferential branches.
– Supplies corticospinal tracts and the intraaxial
exiting fibers of the abducent nerve
(CN VI).
Pontine arteries
– also called the auditory artery or internal auditory artery
– arises from the basilar artery in 15% of the population.
– Perfuses the cochlea and the vestibular
apparatus.
Labyrinthine artery
– Supplies the inferior surface of the cerebellum.
– Supplies the facial nucleus and intra-axial fibers, spinal trigeminal nucleus and tract, vestibular nuclei, cochlear nuclei, intraaxial fibers of the vestibulocochlear nerve,
spinothalamic tract, and inferior and middle cerebellar peduncles.
– Gives rise to the labyrinthine artery in 85% of the population.
– Supplies the hypothalamospinal tract (Horner syndrome)
Anterior inferior cerebellar artery