Cerebellum (Stephens) Flashcards
- part of the brain that coordinates all somatic motor activity, but does not initiate this activity
- involved w/ unconscious proprioceptive and tactile info to affect gradual alterations of muscle tension necessary for proper maintenance of equilibrium and posture
- assures the smooth and orderly sequence of muscular contraction characteristic of voluntary skilled movements
cerebellum
- central core of white matter in cerebellum
- composed of dense bundles of afferent and efferent fibers interconnecting cerebellar peduncles, cerebellar nuclei, and cerebellar cortex
- four pairs of cerebellar nuclei located here: fastigial nucleus, globose nucleus, emboliform nucleus, and dentate nucleus
corpus medullaris
- most medial nucleus within the CM
- has vestibular connections and functions
fatigial nucleus
- nucleus of the CM that is divided into medial and lateral parts
- medial part: cerebellovestibular efferents from this area to fastigial nuclei project to vestibular system
- lateral part: efferents from this area w/ fibers from emboliform and dentate nuclei
globose nucleus
- small, worm-shaped nucleus of the CM
- sends efferents through superior cerebellar peduncle along w/ fibers from dentate nucleus
emboliform nucleus
- large, convoluted cup-shaped nucleus of the CM
- gives rise to vast majority of efferents from neocerebellum
- these efferents along w/ those from globose and emboliform, project to red nucleus, ventral lateral nucleus of thalamus, brainstem tegmentum, and RF
- most of the efferents in the superior cerebellar peduncle originate in this nucleus
- mostly reponsible for planning and execution of fine movement
dentate nucleus
What are the different afferent fiber courses of the inferior cerebellar peduncle?
cerebellar afferent fibers, use the mnemonic: DDT Always Ruins Olives
- Dorsal spinocerebellar tract (DSCT)
- Direct arcuate fibers (or cuneocerebellar tract)
- Trigeminocerebellar tract
- Arcuocerebellar fibers
- Reticulocerebellar fibers
- Olivocerebellar fibers
- afferent fibers tract of the inferior cerebellar peduncle
- conveys unconscious, precise, proprioceptive info from lower 1/2 of the body and lower extremities to cerebellum
- originates in the nucleus dorsalis (C8-L1), courses through ipsilateral inferior cerebellar peduncle, and terms in the anterior vermis of cerebellum
dorsal spinocerebellar tract (DSCT)
- afferent fibers tract of the inferior cerebellar peduncle
- conveys unconscious, precise proprioceptive info from upper 1/2 of the body and upper extremities to the cerebellum
- fibers originate in the accessory cuneate nucleus and term in the vermis
direct arcuate fibers (or cuneocerebellar tract)
- fiber tract that originates in main sensory trigeminal nucleus and project to anterior vermis via inferior and superior cerebellar peduncles
- one of the two unconscious sensory tracts from face
- conveys general unconscious, precise tactile, and proprioceptive info from head to cerebellum
trigeminocerebellar tract
- afferent fibers tract of the inferior cerebellar peduncle
- form important cerebro-cerebellar motor feedback loop
- originate in arcuate nuclei of upper medulla and are displaced pontine nuclei
- arcuate nuclei receive fibers from ipsilateral cerebral cortex and project to contralateral cerebellar hemisphere via external arcuate fibers
arcuocerebellar fibers
- afferent fibers tract of the inferior cerebellar peduncle
- convey general sensory modalities to the cerebellum
- originate in the lateral reticular nuclei and project bilat to cerebellar hemispheres
reticulocerebellar fibers
- afferent fibers tract of the inferior cerebellar peduncle
- originate in inferior olivary nucleus (ION) and term as climbing fibers in contralateral cerebellar hemisphere
- ION: important processing and relay center for sensory info from SC and motor info from RF and pyramidal system; receives direct input from central tegmental fasciculus and spino-olivary tract
olivocerebellar fibers
- consists of ascending and descending fibers from medial group (motor) of reticular nuclei
- located in center of tegmental RF
- originates in red nucleus, central (periaqueductal) gray matter and midbrain tegmentum
- critical link between extrapyramidal system and cerebellum
central tegmental fasciculus (CTF)
- comprised of pontocerebellar fibers, which form an important feedback loop between motor cortex and cerebellum
- originates in pontine nuclei
- in cross-section, this structure forms islands of neurons separated by coarse fascicles of descending corticospinal corticopontine fibers and transversely oriented pontocerebellar fibers
- corticopontine fibers term in ipsilateral pontine nuclei which project to cortex of contralateral cerebellar hemispheres
middle cerebellar peduncle
What are the fiber tracts present through the superior cerebellar peduncle?
- ventral spinocerebellar tract (VSCT)
- trigeminocerebellar tract
- tectocerebellar fibers
- fiber tract that passes through superior cebellar peduncle and terms in anterior vermis
- conveys general proprioceptive info from lumbosacral levels to cerebellum
- originates from scattered neurons in base of dorsal horn and intermediate gray matter, decussates in anterior white commissure, ascends in lateral funiculus
ventral spinocerebellar tract (VSCT)
- fibers that originate in superior and inferior colliculi, course in either superior or middle cerebellar peduncles, and term in cerebellar hemispheres
- convey visual and auditory info
tectocerebellar fibers
What type of fibers are sent from the fastigial and medial portion of globose?
these structures bilaterally send fastigiobulbar efferent fibers to vestibular nuclei and RF
What type of fibers are sent from lateral globose, emboliform, and dentate nuclei?
- these structures project efferent fibers through superior cerebellar peduncle
- path: fibers decussate in upper pons and lower midbrain, and bifurcate into descending and ascending limbs; descending limb terms in lateral reticular nuclei and ION (feedback loop); ascending limb decussate in upper pons and lower midbrain either synapsing in RN and/or coursing through RN to term in ventral anterior nucleus of thalamus (dentato-rubro-thalamic pathway)
*Hannah, when you read this know that I love you and you WILL get through this. Your grade on this test does not determine your worth. The way you care about educating yourself to best care for your patients is what will define you!*
Describe the structure and associated functions of the cerebellar cortex:
- 3 layers, 5 types of intrinsic neurons, all inhibitory neurons except granule cell
- molecular layer: outermost, primarily synaptic zone, outer stellate and basket cells of this layer and inhibitory upon Purkinje cells (disinhibition)
- Purkinje cell layer: middle, cells are inhibitory w/ dendritic trees extending into molecular layer, ~100,000 synapses on a single cell, all info entering cortex eventually converges upon Purkinje cells, these axons are only efferent from cortex, most of them term in deep cerebellar nuclei
- granular layer: innermost, granule cells and Golgi cells, granule are excitatory w/ axons extending to molecular layer (parallel fibers) which synapse of Purkinje, outer stellate, basket, and Golgi cells; most cerebellar afferents term on dendrites of granule cells (cerebellar glomerulus)
What signs and symptoms would result from a unilateral cerebellar lesion?
- ipsilateral deficits b/c extensive crossing/recrossing of tracts entering/leaving cerebellum
- midline lesions of vermis affect axial musculature
- signs/symptoms: ataxia, dysmetria, dysdiadochokinesia, intention tremor, decomposition of movement, slurred or scanning speach, rebound phenomenon, hypotonia and hyporeflexia, asthenia, nystagmus
- slurred speech, stumbling, falling, and incoordination
- broad-based, staggering gait
ataxia
- lack of coordination of movement typified by the undershoot or overshoot of intended position with the hand, arm, leg, or eye
- missing the mark during tests such as touching fingertip to nose w/ eyes closed
dysmetria
impaired ability to perform rapid, alternating movements such as pronation and supination
dysdiadochokinesia
- tremor is usually characteristic of lesions involving the superior cerebellar peduncle or dentate nucleus
- present during voluntary movements such as reaching for a pencil on a table, and absent during rest
- as the patient reaches for the object, the tremor (actually an escalating series of gross over compensations) progressively worsens
intention tremor
- some patients with cerebellar dysfunction may exhibit a breakdown of the fluid, multi-joint patterns of movement
- movements tend to be performed one joint at a time, and take on a “robotic” appearance
decomposition of movement
- it is not unusual to witness this speech pattern in alcohol intoxicated individuals
- alcohol, as well as cerebellar disorders, affects an individual’s ability to coordinate the complex motor speech patterns involved in vocalization
slurred or scanning speech
inability of opposing muscles to stop an action when resistance is suddenly removed, e.g. biceps curl
rebound phenomenon
decreased muscle tone and weakness of muscles in response to stimuli
hypotonia and hyporeflexia
decreased muscle strength, abnormal physical weakness, or decreased energy
asthenia
- eyes make repetitive, uncontrolled movements
- these movements often result in reduced vision and depth perception and can affect balance and coordination
- may result from lesions of the vestibulocerebellum
nystagmus
What is the relationship between alcohol consumption and cerebellar damage?
- chronic alcohol ingestion may cause cortical atrophy of anterior lobe of cerebellum and in advanced cases neocerebellum and dentate nucleus
- later stage symptoms: severe ataxia of lower extremities and trunk, minor involvement of upper limbs
- may be seen in conjunction w/ Korsakoff’s syndrome (vit B1 deficiency)
- damage may due to alcohol’s toxic effect to cerebellum, consequences of vit B1 deficiency, and toxic effect on Purkinje cells
Cerebellar cortical influences converge on which of the following?
a) Deep cerebellar nuclei
b) Granule cells
c) Parallel fibers
d) Stellate cells
e) Purkinje cells
e) Purkinje cells
A unilateral lesion of the right cerebellar lobe would result in which of the following?
a) Bilateral cerebellar deficits
b) Contralateral cerebellar deficits
c) Ipsilateral cerebellar deficits
d) No neurological deficits
c) Ipsilateral cerebellar deficits
Olivocerebellar fibers have a strong influence on which of the following?
a) Cerebellar glomerulus
b) Deep cerebellar nuclei
c) Granule cells
d) Parallel fibers
e) Purkinje cells
e) Purkinje cells
Unconscious precise proprioceptive information from the upper extremity is conveyed by which of the following?
a) Dorsal spinocerebellar
b) Central tegmental fasciculus
c) Ventral spinocerebellar tract
d) Cuneocerebellar tract
e) Trigeminocerebellar tract
d) Cuneocerebellar tract
The efferent fibers in the superior cerebellar peduncle project to which of the following?
a) Ventral posterior lateral nucleus
b) Ventral posterior medial nucleus
c) Ventral anterior nucleus
d) Intralaminar nuclei
c) Ventral anterior nucleus
The cerebral cortex influences the cerebellum via which of the following?
a) Pontocerebellar fibers
b) Corticopontine fibers
c) Olivocerebellar fibers
d) Corticobulbar fibers
e) Central tegmental fasciculus
b) Corticopontine fibers
The heel to shin test assesses coordination and may be abnormal if there is loss of motor strength, proprioception or a cerebellar lesion. If motor and sensory systems are intact, an abnormal, asymmetric heel to shin test is highly suggestive of an:
ipsilateral cerebellar lesion
- an autosomal recessive degenerative disease of adolescence and early adulthood
- involves a progressive neuronal necrosis and resultant demyelination of the proprioceptive neurons in the dorsal roots, posterior columns, medial lemniscus, spinocerebellar tracts, and corticospinal tracts, in addition to the degeneration of the Purkinje cells, dentate nucleus and superior cerebellar peduncles; cardiac hypertrophy and diffuse myocardial fibrosis are also present
- initially develops in the lower limbs and progresses to the upper limbs over the course of a few years
- dysdiadochokinesia, dysmetria, nystagmus, and intention tremor are all present bilaterally
- patient exhibits a wide-based gait w/ severe ataxia and some degree of spasticity
- optic atrophy, hearing loss, dysarthric speech (slow, staccato and explosive) as well as dementia may eventually develop
- death occurs 10 to 20 years after onset from cardiac or pulmonary complications
Friedreich’s ataxia
