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MCB163 #6

Spinocerebellar pathways

QuestionAnswer
Cerebellum 1.the function of the cerebellum is not known2.not essential for movement3.not critical for survival
Cerebellum Connects to 1.it has no direct, descending projections to the spinal cord2.its output is directed mainly towards the subcortical midbrain and forebrain motor centers and to descending motor systems
cerebello-rubro-thalamic pathway ultimately influences motor planning via thalamic input to premotor cortex
cerebello-vestibulo-spinal pathway has a crucial role in the maintenance of postural reflexes and antigravity adjustments
Cerebellum Input Sources from receives sensory input from all modalities
Level of Cerebellum Functions the functions of the cerebellum take place below consciousness
The Prime Role of The Cerebellum 1.is to inhibit neurons postsynaptic to it
Damage to the Cerebellum 1.Diminishes this disinhibition(neurons postsynaptic to it)2.Resulting in increased facilitation of the postsynaptic neurons3.clinically, this is manifest as positive signs
Positive Signs of Cerebellum Damage a. tremor at rest due to pathological motoneuronal dischargeb. increased rigidity of limbs due to loss of facilitation to reduce output to extensor musclec. inaccuracy of target pursuit due to loss of afferent feedback to smoothly adjust pursuit
Cerebellum Evolution subdivisions of the cerebellum reflect function and the evolutionary specializations of the organism1. The Vermin 2.flocculonodular lobe 3.the cerebrocerebellum
the vermis the target of input from the spinocerebellar system
the flocculonodular lobe receives vestibular projections
the cerebrocerebellum dominated by cortico-ponto-cerebellar influences
parallel pathways for the sensory evaluation of muscle length and tension1. conscious pathway2. subconscious pathway
parallel conscious pathway dorsal column system
parallel subconscious pathway spinocerebellar system
spinocerebellar system receptors 1. cutaneous touch and deep pressure 2. neuromuscular spindles (Ia system)3. Golgi tendon organs (Ib system)4. joint receptors include both static and dynamic5. mossy fibers organized somatotopically
neuromuscular spindles (Ia system): length detectors arranged in parallel within muscle
Golgi tendon organs (Ib system): tension detectors arranged in series in tendons
joint receptors include both 1.static (for maintained position)2.dynamic (for rapid, active joints) inputs
spinal input to the cerebellar cortex 1.made up of mossy fibers 2.and is organized somatotopically
the spinocerebellar tracts spinocerebellar input from the lower body
cuneocerebellar tracts input from the upper body and head
output of cerebellar cortex 1. corticonuclear projection to deep cerebellar 2. cerebellofugal projections a. dentato-rubro-thalamic b. fastigio-reticular pathways
1. corticonuclear projection to deep cerebellar nuclei 1.are entirely inhibitory2.damage to them thus results indisinhibition postsynaptically, that is, facilitation
cerebellofugal projections influence forebrain and spinal centers
dentato-rubro-thalamic inputs ultimately reach the premotor cortex and are integral for motor planning
fastigio-reticular pathways pass limb-joint data to reticulospinal fibers that control tone in proximal extensors
Circuitry of spinocerebellar system-first synapse dorsal nucleus of Clarke and adjacent parts of spinal laminae V-VIII of Rexed
second synapse reaches cerebellar cortex as mossy fiber input17 Spinocerebellar Pathways
Cerebellar control of Posture and Balance cerebellar output reaches the thalamus and extrapyramidal motor system for the subconscious control of posture and movement
Spinoreticular tracts-a multisensory input to the pontine reticular formation and serving an alerting/attentional function
Spinoreticular tracts-afferent input is to spinal laminae V-VIII, and the second order neurons decussate en route to the reticular formation
reticular formation a poorly-differentiated area of the brain stem, centered roughly in the pons.
Created by: scottsorge
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